MUSCULAR SYSTEM

Muscle comes from the Latin word musculus which means little mouse. It is a body tissue consisting of long cells that contract when stimulated and produces motion. It is also the driving force and the power behind movement in most invertebrates and vertebrates.

1.0 General Functions

Functions:1. Movement - cause movement at joints.2. Posture adjust the position of the body with respect to gravity; holds us upright.3. Joint Stability exerts tension around the joint; allows movement.4. Heat production cellular metabolic process; causes blood to flow to the area heat.

2.0 Types of Movement

LOCOMOTION AND MUSCULAR SYSTEM: Invertebrates

Invertebrate Muscles Striated muscle appears in invertebrate groups as cnidarians and arthropods Periodic bands that pass across the widths of muscle cells Smooth muscles are capable of slow, long-lasting contractions. Fibrillar muscle contracts at frequencies; limited extensibility.

A. Phylum Porifera Ciliary and flagellary movement; They depend on the flagellar beat of their choanocytes to circulate through their bodies for food gathering and respiratory gas exchange.

*Choanocytes a continuous inner lining of flagellated collar cells in loose contact with one another.

B. Phylum Coelenterata Epitheliomuscular type of an outer layer of longitudinal fibers at base of gastroderms; modifications of this is in more complex cnidarians, such as separate bundles of independent fibers in the mesoglea Unlike colonial polyps, which are permanently attached, hydras can move about freely by gliding on a basal disc, aided by mucous secretions. Using an inchworm movement, they can bend over and attach tentacles to the substratum. They may even turn end over end or detach themselves and, by forming a gas bubble on the basal disc, float to the surface.

C. Phylum Platyhelminthes They adhere to the objects or surfaces by sticky mucus secreted by the epidermal glands and do not swim independently in water. Locomotion is usually by gliding, with the anterior end forward and slightly raised. This is accomplished by backward strokes of the cilia on the ventral surface, over a slime track produced by the glands. Less often worm travels by crawling. This results from muscular movements; contraction of the circular muscles elongates the body, the anterior end is then affixed by mucus, and the posterior part is drawn up by contraction of the longitudinal muscles. Differential action of local muscle groups produces turning or twisting movements. A moving worm tests its environment by turning the head region from side to side.

D. Phylum Nematoda Body wall muscles of nematodes are very unusual. They lie beneath the hypodermis and contract longitudinally only. There are no circular muscles in the body wall. The muscles are arranged in four bands, or quadrants. Each muscle cell has a contractile fibrillar portion (or spindle) and a noncontractile sarcoplasmic portion (cell body). The spindle is distal and abuts the hypodermis, and the cell body projects into the pseudocoel. From each cell body a process or muscle arm extends either to the ventral or the dorsal nerve. Though not unique to the nematodes, the arrangement is very curious; in most animals nerve processes extend to the muscle, rather than the other way around. Their fluid-filled pseudocoel, in which the internal organs lie, constitutes a hydrostatic skeleton. Nematodes do not have circular body wall muscles to antagonize the longitudinal muscles; therefore the cuticle must serve that function. As muscles on one side of the body contract, they compress the cuticle on that side, and the force of the contraction is transmitted (by the fluid in the pseudocoel) to the other side of the nematode, stretching the cuticle on that side. This compression and stretching of the cuticle serve to antagonize the muscle and are the forces that return to the body to resting position when the muscles relax; this action produces the characteristic thrashing motion seen in nematode movement.

E. Phylum Annelida The body wall has strong circular and longitudinal muscles adapted for swimming, crawling, and is covered with epidermis and a thin, outer layer of nonchitinous cuticle. Setae tiny chitinous bristles that helps in locomotion Thin layer of circular muscles and a thicker layer of longitudinal muscles; there is no skeleton. The form of the animal is maintained by the elasticity and contraction of the body wall on the coelomic fluid within. Contraction of the circular muscles elongates the body, contraction of the longitudinal muscles shortens it, and local or differential action of these same muscles produces the bending movements.

F. Phylum Arthropods Arthropods move by using muscles directly to move adjacent rigid skeletal units. The exoskeleton provides a solid place for muscles attachment. Muscles are attached across an articulating membrane to two rigid limit or body pieces in antagonistic pairs (extensor and flexor). Contraction of the flexor muscle draws the distal unit of the limb inward, and contraction of the extensor moves the limb outward. Contraction of these muscles acting across many such joints in limbs leads to extremely precise and accurate movement when coordinated by the more highly evolved nervous system.

G. Phylum Mollusca Locomotion is via the large flat foot, a characteristic mollusk feature. The foot is muscular and has numerous mucous glands and cilia on its sole. Locomotion is either by ciliary-mucus movement or by muscular action. A mucus trail is laid down and the cilia act upon it to propel the animal slowly forward. Muscular movement is accomplished via one or more continuous waves of muscular contraction and expansion moving over the sole of the foot, each wave serving to move the animal forward a small-distance. Bivalve Molluscs adductor muscles; smooth muscles that gives ability to clam up against the predators

H. Phylum Echinodermata Locomotion by tube feet, which project from ambulacral areas, by movement of spines, or by movement of arms which project from central disc of body Water vascular system composed of water-filled canals provides means in locomotion; contraction of the muscles comprising the ampullae drives water into the tube feet, whereas contraction of the tube feet moves water into the ampullae.

LOCOMOTION AND MUSCULAR SYSTEM: Vertebrates

Vertebrates Muscles Broadly classified on the basis of the appearance of muscle cells when viewed with light microscope.Types: Skeletal muscle-appears transversely striped (striated) with alternating dark and light bands. Cardiac muscle-possesses striations like skeletal muscle but is uninucleate and with branching cells. Smooth muscle-lacks the characteristic alternating bands of the striated type.

Fishes The propulsive mechanism of a fish is its trunk and tail musculature. The axial, locomotory musculature is composed of zigzag bands, called myomeres. Muscle fibers in each myomere are relatively short and connect the though connective tissue partitions (myosepta) that separate each myomere from the next.

Amphibians Muscles of the limbs are presumably homologous to radial muscles that move the fins and fishes, but the muscular arrangement has become so complex in tetrapod limbs that its exact correspondence with fin musculature is unclear. Long hindlimbs and powerful muscles form an efficient lever system for jumping. Elastic connective tissues and muscles attach the pectoral girdle to the skull and vertebral column, and function as shock absorbers for landing on the forelimbs.Reptiles The body is slung low between paired, stocky appendages, which extend laterally and move in the horizontal plane Limbs of other reptiles are more elongate and slender, and are held closer to the body In Crocodilians, larger and stronger jaw muscles permits powerful jaw closure and tail is muscularly elongated and compressed In snakes, loss of appendages is accompanied by greater use of body wall in locomotion; ribs have muscular connections to large belly scales to aid movement

Mammals Appendages are directly beneath the body of most mammals; the skeleton bears the weight of the body. Muscle mass is concentrated in the upper appendages and have little muscle in their lower leg.

Birds The locomotor muscles of wings are relatively massive to meet demands of flight. Largest of these is the pectoralis, which depresses the wings in flight. Its antagonist is the supracoracoideus muscle, which raises the wing. Both pectoralis and supracoracoideus are anchored to the keel. Positioning the main muscle mass low in the body improved aerodynamic stability.

3.0 MUSCLE STRUCTURE

Embryonic OriginMesoderm- this is the embroyonic layer where muscle tissues are developed.Skeletal muscles are derived from mesenchymal myoblasts. It stems from the dermatomyotomes of the paraxial mesodermMyoblast - fused parallel bundles to form multinucleated cells; myofibrils are seen in the cytoplasm.

Myotome migrates to form non-segmented muscles > Epaxial (epimere) extensor muscles of the neck, vertebral column and lumbar region. > Hypaxial (hypomere) muscles of the pelvic diaphragm, anus and sex organs.

Smooth Muscles forms splanchnic mesenchyme surrounding the gutCardiac Muscle forms from splanchnic mesenchyme around the embryonic heart

Types of Muscles:

Cardiac Muscles

Location: in heart and roofs of large blood vessels onlyShape: elongated; cylindrical that branchNuclei: uninucleate; and centralFunction: pumping of blood in the circulatory system

Skeletal Muscles

Location: attached to skeletonsShape: elongated; cylindricalNuclei: multinucleated (syncitium); peripheralFunction: contraction for voluntary movements

Smooth Muscles Location: lining the alimentary, respiratory, unorgential; blood vessels; cilliary muscles of the eye; arrector pill; in hollow organsShape: spindle-shaped; elongatedNuclei: uninucleate; centralFunction: propulsion of substances along internal passageways

Functional Characteristics of Muscle Tissue

Excitability - ability to receive and respond to stimulusContractility - ability to shorten (forcibly)Extensibility - ability to be stretched when relaxedElasticity - ability to resume to its resting length

I. SKELETAL MUSCLE- A collection of striated voluntary muscle fibers connected at either or both extremities with the bony framework of the body; may be appendicular or axial; histologically, a muscle consisting of elongated, multinucleated, transversely striated skeletal muscle fibers together with connective tissues, blood vessels, and nervesORIGIN, INSERTION, AND BELLYOrigin (head) fixed or immovable point of attachment.Insertion- attachment on the movable bone.- Some muscle have thicker middle region called the Belly.

Orientation of Fascicles- All skeletal muscle is made up of Fascicles (bundles of fiber). Its arrangements vary considerably, resulting in muscles with different shapes and functional capabilities.

Fusiform muscle- thick in the middle and tapered at each end.Parallel muscle- long, strap-like muscles of uniform width and parallel.Convergent muscles- fan-shapedPennate muscle- feather-shapedCircular muscle (spincters)- form rings around body openings

CONNECTIVE TISSUES ASSOCIATED WITH MUSCLES(1) Connective Tissue SheathsPerimysium-surrounds individual fascicles. It contains lots of blood vessels and nerves that provide nutrients and regulate contraction.Endomysium-surrounds individual muscle fibers. Contains tiny capillaries and individual neurons providing nutrients and innervation of the muscle fiber.Epimysium-surrounds the entire muscle.

(2) Connective Tissue FasciaDeep fascia- connective tissue sheets between adjacent muscleSuperficial fascia- connective tissue sheets between muscles and skin.

(3) MUSCLE ATTACHMENT TO BONEDirect (fleshy) attachment- collagen fibers of the epimysium are continuous with the periosteum of bones.Indirect attachment- collagen fibers of the epimysium continue as a tendon that merges into the periosteum of nearby bone.

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Gross Organization of Skeletal Muscles

Structure and Organizational LevelDescription

MusclesIt consists of hundreds and thousands of muscles cells, connective tissue wrappings, blood vessels and nerve fibers.

Muscle FasciculusBundle of muscle cells covered by a connective tissue sheath

Muscle fibersExtremely long, cylindrical, multinucleate cells that reach from one end of the muscle to the other

MyofibrilsContain contractile units called sarcomeres; is packed together and invested by the cell membrane; are rod-like.

SarcomeresFunctional unit of the myofibrils.

Myosin filamentComposed of many myosin molecules packed together in an elongate bundle. It is of two types- Thin and thick filaments.

Ultrastructure of Muscle Fiber

Thick filament - myosin (found in the center along the M-line) It has a head joined by a flexible hinge region.

Thin filament - actin (found outlined to the z-lines) It is composed of f-actin which is composed of g-actin subunits.

> Tropomyosin - lie near the grooves between the actin strands. > Troponin - complex of three globular proteins is located at intervals along the actin filament.

The sarcoplasmic reticulum is a smooth endoplasmic reticulum surrounding each myofibril.

T-Tubules are infoldings of sarcolemma that conducts electrical impulses. (Starting from the surface to the terminal cisterns)

Sarcomere- Contractile unit of muscle A bandsDark bands where in thick myofilaments are positioned.

I bandLight bands where in only thin myofilaments are positioned.

Z lineActin is anchored in the Z-lines which are the outer edges of the sarcomere. Darker are that extends along the thick filaments.

M lineThe center of the sarcomere and A band where proteins hold thick filaments in position. Attaches myosin filaments.

H zoneThe region in the middle of the sarcomere where thick filaments are not overlapped by thin filaments. There are only thick filaments.

NAMING SKELETAL MUSCLESAccording to Body parts or regionPectoral- muscle in the chestFemoris -muscle in the thighBrachii- muscle in the armAbdominis- muscle in the abdomenGluteus- muscle in the buttock region

According to Relative LocationInter: between (intercostals)Lateralis: located to the side or laterally (vastuslateralis)Medialis: located toward the middle or midline (vastusmedialis)Anterior: toward the front or anterior surface (tibialisanterioror serratusanterior)Posterior: toward the rear or posterior surface (tibialisposterior)

According to Direction of fibersRectus- straightTransverse- acrossOblique- slanted or diagonalOrbicularis- ringlike

According to type of action performedAbductors- muscle which move a limb away from the midline of the body.Flexors- muscle which bend a limb at a joint.Levators- muscle which lift a part.Extensors- muscle which straighten a limb at joint.Adductors- muscle which move a limb towards the midline.

According to number of heads of originBiceps- muscle with 2 headsTriceps- muscle with 3 headsQuadriceps- muscle with 4 heads

According to points of attachmentSternocleidomastoid- Sternoandcleidofor its origin, the sternum and clavicle; andmastoidfor its insertion, the mastoid processStyloglossus- points of attachment are styloid processes and tongue

According to shape and sizeDelloid- triangularTrapezius- four-sidedLongus- longestMaximus- largestMinimus- smallestBrevis- shortFusiform- spindled-shapedRhomboid- quadrilateral

According to movementPrime mover or agonist muscle- execute actual movementAntagonist muscle- acts against the prime mover to perform the action efficiently and smoothlyFixator muscle- steadies the bone giving origin to the prime mover so that the insertion will move.

CARDIAC MUSCLECardiac muscle is involuntaryThe cells are Y shaped and are shorter and wider than skeletal muscle cells. They are predominatly mononucleated. The arrangement of actin and myosin is similar to skeletal striated muscleCardiac muscle cells have a branched shape so that each cell is in contact with three of four other cardiac muscle cells. Together all of the cardiac muscle cells in the heart form a giant network connected end to end. At the ends of each cell is a region of overlapping, finger-like extensions of the cell membrane known as intercalated disks.These intercalated disks allow for communication between the cardiomyocytes. Three types ofcell junctionmake up an intercalated disc: fascia adherens,desmosomesandgap junctions.Fascia adherensare anchoring sites foractin, and connect to the closest sarcomere.Desmosomesstop separation during contraction by bindingintermediate filaments, joining the cells together. Desmosomes are also known asmacula adherens.Gap junctionsallowaction potentialsto spread between cardiac cells by permitting the passage of ions between cells.The myocardium is considered as one single functioning unit, the most muscular part of the heart and mainly responsible for its contractions.The passage of signals from cell to cell allows cardiac muscle tissue to contract very quickly in a wave-like pattern to effectively pump blood throughout the body.Another feature that is unique to cardiac muscle tissue isautorhythmicity.Cardiac muscle tissue is able to set its own contraction rhythm due to the presence of pacemaker cells that stimulate the other cardiac muscle cells. The pacemaker cells normally receive inputs from the nervous system to increase or decrease the heart rate depending on the bodys needs. However, in the absence of nervous system stimulation, the pacemaker cells can produce a regular heart rhythm.

SMOOTH MUSCLEAlso calledinvoluntary muscle.It consists of narrow spindle-shaped cells with a single, centrally located nucleus. Smooth muscle lacks neuromuscular junctions, but have varicosities instead, numerous bulbous swellings that release neurotransmitters to a wide synaptic cleft.They have a less developed sarcoplasmic reticulumIt has no striations, no sarcomeres, and a lower ratio of thick to thin filaments when compared to skeletal muscle.Has tropomyosin but no troponinIn smooth muscle thick and thin filaments are arranged diagonally, spiral down the length of the cell, and contract in a twisting fashion.Muscle fibers contain longitudinal bundles of noncontractile intermediate filaments anchored to the sarcolemma and surounding tissues via dense bodies.Contracts slowly and automatically. It constitutes much of the musculature of internal organs and the digestive system.

Two types of smooth muscles:Multi-unit smooth muscle- fibers are independent of each other. Innervate individual cells therefore they allow for fine control and gradual responses. Found in the large elastic arteries, trachea, and iris of the eye.Single unit smooth muscle- muscle fibers are arranged in sheet; cells are joined by tight junction. Muscle fibers transmit impulses from cell to cell, so it contracts as a unit. Found in the organs of the digestive and reproductive system that require peristalsis to move its content.

4.0 Muscle Physiology

Muscle Contraction- Muscles contract when the muscle fibers generate tension through actin and myosin cross-bridge cycling with the help of motor neurons. Although the term Contraction implies shortening, muscle contraction does not shorten muscles because tension in the muscles can be produced without changes in muscle length.I. Sliding Filament Theory of Muscle Contraction The Sliding Filament Theory of Muscle Contraction is the binding of myosin to actin, forming cross-bridges that generate filament movement. Muscles contract when sarcomeres shorten. The thick and thin filaments that compose sarcomeres do not shorten; instead they slide past one another, causing the sarcomere to shorten while the filaments remain the same length.

Structures involved:Myofibril - cylindrical organelle running the length of the muscle fiber, containing Actin and Myosin filamentsSarcomere - the functional unit of the Myofibril, divided into I, A and H bands.Actin - a thin, contractile protein filament, containing Active or binding sitesMyosin - a thick, contractile protein filament, with protrusions known as Myosin HeadsTropomyosin - actin-binding protein which regulates muscle contractionTroponin - a complex of the three proteins, attached to Tropomyosin

Process of MovementMyosin is a molecular motor that acts like an active ratchet. Chains of actin proteins form high tensile passive thin filaments that transmit the force generated by myosin to the ends of the muscle. Myosin also forms thick filaments. Each myosin paddles along an actin filament repeatedly, binding, ratcheting, and letting go, sliding the thick filament over the thin filament.ATP binds to myosin and is hydrolyzed by ATPase into ADP and phosphate. The energy released by this process activates the myosin head and cocks it into a high-energy, extended position.The cocked myosin head binds to a newly-exposed active site on the thin filament, generating a cross-bridge between the actin and myosin.Myosin releases the ADP and phosphate, returning to a low-energy position, pulling the thin filament along; this movement is called a power stroke. Shortening occurs when the extensible region pulls the filaments across each other (like the shortening of a spring). Myosin remains attached to the actin.The binding of ATP destabilizes the myosin-actin bond, allowing myosin to detach from actin. While detached, ATP hydrolysis occurs, recharging the myosin head. If the actin-binding sites are still available, myosin can bind with actin again.The collective bending of numerous myosin heads (all in the same direction), combine to move the actin filament relative to the myosin filament. This results in muscle contraction.

Although smooth muscle contraction is similar to skeletal muscle contraction, there are a few differences. The cross-bridges in smooth muscle contraction remain in the attached state longer, so it uses less ATP to maintain a high level of force in smooth muscle than in skeletal muscle. Smooth muscle does not contain troponin. Instead, it contains thin filament protein tropomyosin and other notable proteins - caldesmon (calmodulin binding protein) and calponin (calcium binding protein). The phosphorylation of caldesmon and calponin by various kinases, which is dependent upon calcium binding to calmodulin, plays a role in smooth muscle contraction. When calcium binds to calmodulin, it activates a signalling cascade (myosin light-chain kinase) that results in myosin phosphorylation, which then initiate contraction.In invertebrate smooth muscle, contraction is initiated with calcium directly binding to myosin and then rapidly cycling cross-bridges generating forces.

Sliding Filament ModelA model proposed to explain the Sliding Filament TheoryWhen a sarcomere contracts, the Z-lines move closer together and the I band gets smaller. The A-band stays the same width and, at full contraction, the thin filament overlaps.

II. Biochemistry of Muscle Contraction- Muscle contraction is initiated when all the cells in the bundle (simultaneously) receive a signal from their motor nerve in the form of an action potential. Action Potential - a transient electrical polarization of the cell membrane that is propagated to a region of the cell membrane where there is a special connection (T tubule) to the sarcoplasmic reticulum. Sarcoplasmic Reticulum - an organelle in the interior of the muscle cell that sequesters (accumulates) calcium ions.1. Action Potential is propagated through the Sarcolemma, then to the T tubule. At the T tubule, the action potential is then spread out to the T tubule membrane and into the interior of the muscle cell near the ends of Sarcoplasmic Reticulum.2. T tubules depolarize, thus opening up calcium ion channels on the sarcoplasmic reticulum, which in turn increases the permeability of calcium ions on the sarcoplasmic reticulum.3. Calcium ions are diffused into the Sarcoplasm4. Tropomyosin connects to two sides of actin, covering up sites where myosin can bind to actin myofilament, and troponin are attached to the tropomyosin. Calcium ion binds to tropomyosin, changing the conformation of troponin and move the tropomyosin. This opens up the myosin binding sites on the actin, allowing the myosin heads to bind and create cross-bridges used for muscle contraction5. As soon as the sarcoplasmic reticulum has released its calcium contents, and the action potential has dissipated, the sarcoplasmic reticulum begins pumping calcium ions back into its interior from the cytoplasm. It consumes ATP for this pumping processalthough not anywhere near as much ATP as is used by myosin for muscle cell contraction. 6. When the muscle cell has completed contraction, the cytoplasmic calcium concentration has dropped to normal levels, and troponin and tropomyosin have converted back to their normal conformation. This prevents binding of thick filaments to thin filaments and allows the muscle cell to relax back to its normal length (i.e., to elongate).

- Muscle cells require large amounts of ATP. Mitochondria are cellular organelles, which specialize in the production of ATP under aerobic conditions. Ideally, muscle cells have large quantities of carbohydrate, typically in the form of glycogen. As needed, glycogen is converted into three-carbon sugars in the cytoplasm by way of the citric acid cycle, which produces small amounts of ATP. The three-carbon sugars are then consumed by the mitochondria to produce much larger quantities of ATP. Since, the muscle cell uses so much ATP for each contraction cycle, it stores some of the ATP energy in its cytoplasm in the form of creatine phosphate, which can be easily and quickly converted back into ATPIII. Motor Unit- The motor unit is the functional unit of muscle contraction and includes the motor nerve fiber and the muscle fibers it innervates- A motor unit consists of the motor neuron (one somatic efferent) and the grouping of muscle fibers (cells) innervated through the connection. After an efferent axon enters the muscle, it branches and forms synapses with a number of muscle fibers. However there is no overlap in the innervation of the muscle fibers by different efferent neurons. Each individual muscle fiber is connected to only one efferent neuron.- All fibers of the motor unit are of the same type and all fibers contract upon activation of a motor unit.- The number of muscle fibers within a motor unit varies, and is a function of the muscle's ability for accurate and refined motion.- Precision is inversely proportional to the size of the motor unit.- Groups of motor units are innervated to coordinate contraction of a whole muscle and generate appropriate movement.-The number of muscle fibers within each unit can vary within a particular muscle and still more widely from muscle to muscle.- The muscles that act on the largest body masses have motor units that contain most of the muscle fibers.- Smaller muscles consist of less muscle fibers in each unit.

Types:a. Type I- very resistant to fatigue because they are nourished with an extensive blood supply to maintain aerobic metabolism- slow-twitch oxidative- the first motor units recruited by the central nervous system when a muscle is actuvated, and continue to be recruited as long as the muscle remain active- well-adapted for low intensity workb. Type II- fast-twitch motor units- recruited after Type I motor units to provide short bursts, or phases, of higher muscle tension as required (phasic motor unit)- have two subcategories:> Type IIb - they are very prone to fatigue, but produce the most force when stimulated. These are the last motor unit recruited when a muscle gets activated, and the first to stop being recruited when the force from a muscle is no longer needed> Type IIa - The immediate motor units. Their peak force and their resistance to fatigue fall between Type I and Type IIb. They are also recruited after Type I but before Type IIb, and stop being activated after Type IIb but before Type I.

- An individual muscle contains all three types of motor units. This provides each muscle with the ability to produce an increased force output from a low level to a high level, and it also provides each muscle with a certain degree of muscular endurance.- Greater percentage of Type I fibers means the muscle has better endurance capability.- Greater percentage of Type IIb fibers means the muscle has better power capability.

Recruitment of Motor Units:Motor unit recruitment depends on the force/resistance of the exercise. With light intensity exercise, the Type I motor units are recruited. Increase in load permits Type IIa (fast twitch) to be recruited. When the load becomes even greater, the Type IIa will be recruited with the help of the two motor units recruited earlier. Therefore Type I motor units are always firing no matter what the intensity.Henneman's Size Principle- States hat under load, motor units are recruited from smallest to largest. This means that slow-twitch, low-force, fatigue-resistant muscle fibers are activated before fast-twitch, hih-force, less fatigue-resistant muscle fibers.- With this, the amount of fatigue an organism experienxe will be minimize by using fatigue-resistant muscle fibers first and only using fatigable fibers when high forces are needed.

IV. All-Or-None Response - The all-or-none law is a principle that states that the activation of individual muscle or nerve cells, where the response to stimuli (depolarisation) only occurs above a certain threshold. If the stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response. Essentially, there will either be a full response or there will be no response at all.- Each time a neuron fires, it does so with the same level of intensity, and that the action potential will stay the same size all the way down the axon.- It applies to a single muscle fiber and not to the entire muscle

V. Types of Muscle Contraction:Tension - force exerted by the muscle on an objectLoad - force exerted by object on a muscleA. Isometric Contraction- Contraction which generate force without changing the length of the muscle. This is typical of muscles found in the hands and forearms: muscles do not change length, and joints are not moved, so force for grip is sufficient.

B. Isotonic Contraction- Maintain constant tension in the muscle as muscle changes length. This only occurs when a muscle's maximal force of contraction exceeds the total load on the muscle.> Concentric Contraction- In this type, the muscles shorten while generating force. It also alters the angle of the joints to which the muscles are attached. This contraction is due to the sliding filament mechanism.> Eccentric Contraction- The muscle elongates while under tension due to opposing force (external load) which is greater than the force generated by the muscle. This contraction can either be voluntary or involuntary.

Graded Muscle Responses:

(1) Simple Muscle Twitch- Muscle contracts and relaxes in response to a stimulus that causes an action potential on the muscle fibers. - Stages of Muscle Twitch:1. The Latent Period- Defined as the time it takes the muscle to react to the stimulus- It begins at stimulation and typically lasts about 0.02 seconds.- The action potential sweeps across the sarcolemma and the sarcoplasmic reticulum releases calcium ions. The muscle fiber does not produce tension during the latent period, because the contraction cycle has yet to begin. 2. The Contraction Phase- It is the time where the muscle is actually contracting.- Tension rises to a peak. As tension rises, calcium ions are binding to troponin, active sites on thin filaments are being exposed, and cross-bridge interactions are occurring. - The contraction phase ends roughly 0.04 seconds after stimulation- This is responsible for the sliding of actin and myosin past each other which results to contraction of sarcomere.3. The Relaxation Phase- The last period from when the muscle length returns back to normal.- It continues for about another 0.05 seconds.- Calcium levels are falling, active sites are being covered by tropomyosin, and the number of active cross-bridges is declining.- This results in the relaxation.

(2) Wave Summation- Stimuli are delivered more frequently, so the muscle does not have time to completely relax. This increases the muscle contraction. With rapid stimulation, a muscle fiber is re-stimulated while there is still some contractile activity. As a result, there is a summation of the contractile force. In addition, with rapid stimulation, there isn't enough time between successive stimulations to remove all the calcium from the sarcoplasm. So, with several stimulations in rapid succession, calcium levels in the sarcoplasm increase. More calcium means more active cross-bridges and, therefore, a stronger contraction.

(3) Tetanus (Lockjaw)- Occurs when the muscle fiber is stimulated so rapidly it does not have time to relax at all between stimuli. It has the highest force of muscle contraction.Unfused / Incomplete Tetanus - the peaks of individual twitches can still be determineFused / Complete Tetanus - the stimuli are spaced sufficiently close; smooth continuous contraction without any evidence of relaxation

(4) Staircase (Treppe) Effect- A gradual step-like increase in the strength of contraction that can be observed in a series of twitch contractions that occur about 1 second apart- When muscle cells are initially stimulated when cold, they will exhibit gradually increasing responses until they have warmed up.- It is due to the increasing availability of Ca2+ in the sarcoplasm - more Ca 2+ ions exposed, more active sites on the thin filaments for cross bridges attachment.- As the muscle begins to work and liberates heat, its enzymes become more efficient and the muscle becomes more pliable.

VI. Neuromuscular Junction- The site of communication between motor neurons and skeletal muscle fibres. This is where the synaptic bulb of an axon terminal and muscle fiber connect. It connects the nervous system to the muscular junction via synapses. This results in muscle contraction.Axon- these are the long processes of neurons. - When the axon of motor neuron travels and enters the muscle it forms a lot of branches called axon terminals.Synaptic end bulb it is found at the end of each axon terminal.Synaptic vesicles- contain chemical neurotransmitters called Acetylcholine (or abbreviated as Ach)Motor end plate- it is the part closest to the synaptic end bulb.Synaptic cleft it is the area between the axon terminal and the sarcolemma.Synapse- the tiny gap where in nerve impulses passes from one neuron to another.

- Specialisations of the neuromuscular junction mean that activity in and release of transmitter from motor neurons produces contraction of skeletal muscle fibres rapidly and reliably.

- The neuromuscular junction comprises four cell types: the motor neuron, terminal Schwann cell, skeletal muscle fibre and kranocyte, with the motor neuron and muscle fibre separated by a gap called the synaptic cleft.

- The motor nerve terminal contains synaptic vesicles, filled with neurotransmitter, which release their transmitter into the synaptic cleft at multiple specialised sites called active zones, in response to action potential firing.

- Released transmitter acts at receptors on the muscle membrane, which occur in highdensity clusters at the peaks of muscle membrane infoldings called junctional folds.

- Junctional folds are unique to the neuromuscular junction, increasing the reliability of transmission by localisation of acetylcholine receptors to the crests of the folds and enhancing the effect of depolarisation by localisation of sodium channels in the troughs.

- Schwann cells are essential for the development and maintenance of the neuromuscular junction and play important roles in the remodelling and regeneration of damaged neuromuscular junctions.

- Acetylcholinesterase in the synaptic cleft hydrolyses acetylcholine and limits the temporal and spatial effects of released of acetylcholine, ensuring precision of muscle control.

- Transmitter binding causes two types of electrical signals in skeletal muscle, miniature endplate potentials caused by the spontaneous release of a single vesicle of acetylcholine and larger endplate potentials. Endplate potentials are caused by activitydependent release of multiple transmitterfilled vesicles and trigger action potential firing in, and thus contraction of, the muscle fibre.

VII. Excitation-Contraction Coupling- Excitation-Contraction Coupling is a term used to describe the connection between the electrical action potential and the mechanical muscle contraction. It is the physiological process of converting an electrical stimulus from neurons into a mechanical response, in which the electrical stimulus is an action potential and the desired mechanical response is contraction.

1. Acetylcholine is released by the axonal ending, diffuses to the muscle cell, and attaches to the ACh receptors on the sarcolemma.2. An action potential is generated along the sarcolemma and travels down the T tubule3. Calcium ions are released in the sarcoplasmic reticulum due to the chabge in voltage4. Calcium ions bind troponin; cross bridges form between actin and myosin5. Acetylcholinesterase removes ACh from the synaptic cleft6. Calcium ions are transported back into the sarcoplasmic reticulum7. Tropomyosin binds active sites on actin causing the cross bridge to detach

The Invertebrate Nervous SystemFUNCTIONS: To receive information from internal and external environment. To encode and transmit and process impulses for appropriate action. To coordinate and integrate the function of cells, tissues and organ systems so that they act harmoniously as a unit.NEURON/ NERVE CELL the structural and functional unit of the nervous system. produce signals that can be communicated from one part of animal's body to another.THREE PRINCIPAL PARTS Cell Body/ Soma - central part of the neuron. Dendrite - conducts signal toward the cell body. Axons - conducts signal away from the cell body. THREE FUNCTIONAL TYPES OF NEURON Afferent Neuron (Sensory) - transmit information from the environment to central nervous system. Interneuron -integrating centers and receives signals from sensory neuron to transmit them to motor neuron. Efferent Neuron (Motor) - send processed information from central nervous system to effectors and gland. Myelin Sheath- laminated lipid sheath. Hydras and sea anemones do not have myelinated sheath. Neurolemmocyte (Schwann Cells)- wraps the myelin sheath in layers. Neurofibril nodes (Nodes of Ranvier)- segment the myelin sheath at regular intervals. Glial Cells- supporting cells of nervous system. Astrocytes- provide nourishment to neurons. Oligodendrocytes- provide support to axons and to produce the Myelin sheath. Microglia- protect the brain from invading microorganisms.

NATURE OF NERVE IMPULSESNerve Impulse/Nerve Signals/Action Potential- A language (signal) and an electro-chemical message of neurons. - An impulse is an "all-or-none" phenomenon: either the fiber is conducting an impulse or not. Impulses are alike; the only way a nerve fiber can vary it signals is by changing the frequency of impulse conduction. The higher the frequency the greater is the level of excitation. RESTING MEMBRANE POTENTIAL- A resting neuron is not conducting a nerve impulse.- A membrane of neurons have selective permeability that creates ionic imbalance across membrane. This is the basis of resting membrane potential and change in imbalance generates signal.- The interstitial fluid surrounding neurons contain high concentration of NaCl but low concentration of potassium ion and large impermeable anions with negative charge such as proteins. Inside, the neuron is reversed. These differences are pronounced; approximately 10 times more Na outside than inside and 25-30 times more K inside than outside.- Resting membrane is usually -70mv with inside membrane negative.ACRTION POTENTIAL- Rapidly moving change in electrical membrane potential.- The most significant property of nerve action potential is, it is self propagating.- resting membrane potential depends on the high permeability to K+, 50 to 70 times greater than permeability to Na+.- Upon depolarization, the membrane potential suddenly changes from about -70 to +30mv, and then rapidly returns to resting level.-Increased potassium permeability causes the action potential to drop rapidly toward the resting membrane potential during the repolarization phase.

SYNAPSES: JUNCTION BETWEEN NERVESSynapse - a gap separating neuron to another neuron.TWO DISTINCT TYPES OF SYNAPSES:Electrical Synapses- Much less common than chemical synapse.-demonstrated in both invertebrate and vertebrate groups.-points at which ionic currents flow directly across a narrow gap junction from one neuron to another.-important for escape reactions.- observed in other excitable types and form an important method of communication between cardiac muscle cells of the heart and smooth muscle cells.Chemical Impulses- contain packets of specialized chemicals called "neurotransmitters".- Presynaptic neurons- neurons bringing impulses toward chemical synapses.- Postsynaptic neurons- those carrying impulses away.-At a synapse, membranes are separated by a narrow gap called synaptic cleft, having a width of approxiamately 20nm.- synaptic vesicles- a small secretory vesicle that contains a neurotransmitter. It can be found inside an axon near the presynaptic membrane and releases its contents into synaptic cleft after fusing with the membrane.- excitory synapse - a place where depolarized postsynaptic membranes are released.- inhibitory synapes - where moved resting membrane potential is stabilized against depolarization is released.INVERTEBRATES: DEVELOPMENT OF CENTRALIZED NERVOUS SYSTEMGENERAL EVOLUTIONARY TRENDS IN NERVOUS SYSTEM1. More complex animals possess more detailed nervous systems. Phylum Cnidaria- simplest form of nervous organization, these invertebrate animals have nerve net.Examples: hydras, sea anemones and jellyfishes.Phylum Echinodermata- has nerve nets but increasing complexity.Examples: sea stars, sea urchins and sea anemones.2. In Cephalization, the concentration of receptors and nervous tissue in the animal's anterior end.Platyhelminthes- contains ganglia and distinct lateral nerve cords.Example: flatworms

3. Bilateral Symmetry- a body plan with roughly equivalent right and left halves.Platyhelminthes- bilobed mass of ganglion cells.Phylum Annelida- example: earthwormPhylum Arthropoda- examples: crustacean, insects, spider and centipedes.Phylum Mollusca- examples: squid, snails, clams and octopus.4. The more complex an animal, the more interneuron it has. The more interneuron, the more complex behavior patterns an animal can perform.Phylum Echinodermata- nervous system is divided into several parts.Example: starfish5. Consequence of increasing number of interneuron.

NERVOUS SYSTEM OF INVERTEBRATESINVERTEBRATENERVOUS SYSTEM STRUCTUREEXAMPLES

Phylum CnidariaSimple nerve nets Jellyfishes, Hydras, Sea Anemones

Phylum CtenophoraSimple nerve nets/plexusComb jellies

PlatyhelminthesLongitudinal nerve cords; Bilobed mass of ganglion cellsFlatworms

Phylum NematodaNerve ring around pharynx; longitudinal nerve cordsRoundworms

Phylum AnnelidaDorsal anterior cerebral ganglia; double ventral nerve cord; nerve ringEarthworms

Phylum ArthropodaDorsal cerebral ganglia; ventral nerve cordsCrustacean, Insects, Centipedes

Phylum EchinodermataNerve net; Nerve ring; Radial nervesStarfish, Sea Urchin

Phylum MolluscaVisceral Nerve Cords; Pedal Nerve Cords, Squid, Octopus

The Vertebrate Nervous System

The basic organization of the nervous system is similar in all vertebrates. A notochord and a tubular nerve cord characterize the evolution of the vertebrate nervous system. A notochord is a rod of mesodermally derived tissue encased in a firm sheath that lies ventral to the neural tube. It is first appeared in marine chordates and is present in all vertebrate embryos but absent in adults. During embryological development, vertebrae serially arranged into vertebral column replaced the notochord. A related character in the vertebrate evolution was the development of a single tubular nerve cord above the notochord. During early evolution, the nerve cord underwent expansion, regional modification, and specialization into a spinal cord and brain. Over time, the anterior end thickened variably with nervous tissue and functionally divided into the hindbrain, midbrain and forebrain.

Division of the Nervous System1. Central Nervous System composed of brain and spinal cord2. Peripheral Nervous System composed of all nerves of the body outside the brain and spinal cord.2 Group of nerves1. Afferent Nerves (sensory) transmit information to the central nervous system2. Efferent Nerves (motor) carry commands away from the central nervous systemThe motor nerves are divided into the:1. Somatic Nervous System (voluntary) relays command to the skeletal muscles2. Autonomic Nervous System (involuntary) stimulates other muscles such as smooth and cardiac muscle and glands of the bodyThe Nerves of the Autonomic Nervous System is divided into:1. Sympathetic Nervous System responsible or the fight-or-flight response2. Parasympathetic Nervous System functions during relaxationThe Spinal Cord It is the connecting link between the brain and most of the body and it is involve in spinal reflex actions Reflex involuntary response to a stimulus The Gray Matter Consists of cells and dendrites and is concerned mainly with reflex connections at various levels of the spinal cordThe White Matter Consists of myelinated axons of motor and sensory neuronsProtection of the Spinal Cord1. Meninges three layers of protective membrane that surrounds the spinal cord2. Dura Mater outer layer, tough fibrous membrane3. Arachnoid middle layer, delicate and connects to the innermost layer4. Pia Mater innermost layer, contains small blood vessels that nourish the spinal cordSpinal Nerves Directly related to the number of segments in the trunk and tail of a vertebrateThe Brain Develops at the anterior end of the spinal cord and controls everything in the body During embryonic development, the brain undergoes regional expansion as a hollow tube of nervous tissue that forms and developed into the hindbrain, midbrain and forebrain.The Hindbrain It is continuous with the spinal cord and includes the medulla oblongata, cerebellum and pons Medulla Oblongata contains reflex center for breathing, swallowing, cardiovascular function and gastric secretion Cerebellum coordinates motor activity associated with limb movement maintaining posture and spatial orientation

PhylumCerebellum

FishesLarge In active swimmers and small in inactive swimmers

AmphibiansHave rudimentary cerebellum because of their simple locomotor movement

Mammals and BirdsLarger because of complex locomotor patterns

Pons a bridge of transvers nerve tracts from the cerebrum of the forebrain to both sides of cerebellumThe Midbrain A center for coordination reflex responses to visual input. As the brain evolved it took an added functions relating to the tactile (touch) and auditory The Forebrain Just anterior to the midbrain lie the thalamus and hypothalamus Thalamus is the major relay station that analyze and passes sensory information to higher brain centers Hypothalamus housekeeping centers that regulate body temperature, water balance, appetite and thirst2 Hemisphere of the Brain1. Left hemisphere - for language development, mathematics and learning2. Right Hemisphere spatial, musical etc

Paired of Cranial NervesCranial NerveFunction

Olfactor (I)Sense: smell

Optic (II)Sense: vision

Oculomotor (III)Motor: nerve to extrinsic eye muscle

Trachlear (IV)Motor: extrinsic eye muscle

Trigeminal (V)Mixed nerve: sensory from skin, head and mouth

Abducens (VI)Motor: extrinsic eyeball muscles

Facial (VII)Mixed nerve: sensory to lateral line of head

Auditory (VIII)Sensory: from the inner ear

Glossopharyngeal (IX)Sensory: taste, touch and movements of the pharynx

Vagus (X)Mixed nerve: lungs, heart, digestive system and gills

Spinal Accessory (XI)Motor: muscles of pharynx, larynx and neck

Hypoglossal (XII)Motor: movements of toungue

#s XI and XII are lacking in amphibians, fishes and cyclostomes

Types of ResponseResponse

Taxisresponse by which and animal orients itself toward or away from a given stimulus

Positive Rheotaxisa fish that heads into a current so that the 2 sides of its body are stimulated equally by flowing water

Negative Geotaxisan insect that climbs upward in position to gravity

Photopositivea moth that flies directly to a light

Photonegativea cockroach that scuttles for cover when spotted by a light at night

Monosynaptic Reflexit involves only an afferent and efferent neuron and a single synapse. Ex. Knee jerk

Polysynaptic Reflexhaving one or more interneurons between the sensory and motor pathways. Ex. Winking of eyelids, sudden secretion of tears

Allied Reflexescombined to produce a harmonious effect such as walking in mammals, crawling of earthworms and caterpillars

Chain ReflexesIt acts in sequence, the response of one becoming the stimulus of the next.

SENSORY RECEPTORS Specialized receptors designed for detecting environmental status and change Help maintain homeostasis A stimulus is any form of energy (electrical, chemical, mechanical, etc.) an animal can detect with its receptors Receptors are biological transducers (to change over); they convert one form of energy into another

CLASSIFICATION OF RECEPTORS BASED ON LOCATION

ExteroceptorsAny receptor that detects external stimuli

InteroceptorsAny receptor that detects stimuli from the internal environment of an organism

ProprioceptorsSensitive to changes in tension of muscles and provides sense of body position

CLASSIFICATION OF RECEPTORS BASED ON THE FORM OF ENERGY TO WHICH IT RESPONDS

RECEPTORFUNCTION

BaroreceptorsSense changes in pressure

ChemoreceptorsRespond to chemicals

GeoreceptorsRespond to force of gravity; Gives information about its orientation relative to up and down

HygroreceptorsDetect the water content of air

PhonoreceptorsRespond to sound

PhotoreceptorsSensitive respond to light

Proprioceptorsstretch receptor; respond to mechanically induced changes caused by stretching, compression, bending, or tension

Tactile receptorsTouch receptors

ThermoreceptorsRespond to temperature changes

NOTE: Tactile receptors, Proprioceptors, Phonoreceptors, and Georeceptors may be classified under Mechanoreceptionin that these receptors, in short, respond to motion.

SENSORY RECEPTORS IN THE INVERTEBRATE PHYLA1. Phylum Porifera Sponges have no nervous system or organs like most animals do. This means they dont have eyes, ears or the ability to physically feel anything. However, they do have specialized cells that carry out different functions within their bodies for movement, or for filtrating small organisms.2. Phylum Cnidaria Sensory structures of cnidarians are distributed throughout the body and include receptors for perceiving touch and certain chemicals Specialized receptors are located at the tentacles of polyp (coral) or medusa (jellyfish) Specialized sense organs for monitoring gravity and low-frequency vibrations often appear as statocysts. A statocyst is a simple sac lined with hair cells and containing a solid granule called a statolith. The delicate, hairlike filaments of sensory cells are activated by the shifting position of the statolith when the animal changes position.3. Phylum Platyhelminthes Cephalization a trait related to a flatworms sense organ. Organisms with cephalization have a defined head area. This adaptation allows organisms to concentrate their sensory organs towards the front of their bodies, allowing them to preferentially sense the area in front of them rather than the area behind them Eyespots flatworms have prominent eyespots. Consist of a single layer of photosensitive cells. The photosensitive cells contain a pigment that reacts to light, and signal nerve cells when they do so. Have no lenses to focus images; cannot produce images. Instead, the eyespots can only tell light from dark4. Phylum Nematoda Sensory papillae are concentrated around the head and tail. Amphids one of a pair of anterior sense organs in certain nematodes. Modified cilia serve as the sensory endings. Amphids are thought to be chemoreceptors. Phasmids similar to amphids, but have fewer nerve endings.5. Phylum Annelida Photoreceptors sensitive to light are present in earthworm. The earthworm Lumbricus, have simple unicellular photoreceptor cells scattered over the epidermis or concentrated in particular areas of the body. Most polychaetes react negatively to increased light intensities. However, fanworms react negatively to decreasing light intensities. If shadows cross them, fanworms retreat into their tube. Tactile receptors are sensitive to mechanically induced vibrations propagated through water or solid substrate. Statocysts are in the head region of polychaetes, ciliated tubercles, ridges, and bands, all of which contain receptors for tactile senses, cover the body wall A heat-sensing mechanism draws leeches and ticks to warm-blooded hosts.6. Phylum Mollusca Sensual information that is acquired by sense cells dispersed over the snails outer skin. Those sense cells are especially concentrated on the head, the tentacles, and the lips. Cephalopod mollusks have eyes much like those of vertebrates. The complex camera eyes of squids and octopuses are the best image-forming eyes among the invertebrates. Cephalopod and Vertebrate eyes compared:CEPHALOPODVERTEBRATE EYE

Both eyes contain a thin transparent cornea and a lens that focuses light on the retina and is suspended by, and controlled by, ciliary muscles.

The receptor sites on the retinal layer face in one direction of light entering the eye. The retinal layer is inverted, and the receptors are the deepest cells in the retina.

Both eyes are focusing and image-forming, although the process differs in detail

Light is focused by muscles that move the lens toward or away from the retina , and by altering the shape of the eyeball. Muscle that alter the shape (thickness) of the lens focus light.

7. Phylum Arthropoda Responses to pressure changes have been identified in crustaceans, ctenophores, jellyfish medusa, and squids. Some crustaceans coordinate migratory activity with daily tidal movements, possibly response to pressure changes accompanying water depth changes. Insect chemoreceptors are located in sensory hairs called sensilla. Taste sensilla occur on the mouthparts, legs, wing margins, and ovipositor in females. Olfactory sensilla occur on the head on two pairs of olfactory organs: the antennae and the maxillary palps. Some insects produce species-specific compounds, called pheromones. Pheromones are diverse group of organic compounds that an animal releases to affect the behavior of another individual of the same species. Information regarding territory, societal hierarchy, sex, and reproductive state are transmitted via this system. Ants, for example, produce releaser pheromones, such as alarm and trail pheromones, and primer pheromones, which alter endocrine and reproductive systems of different castes in a colony. Some insects have hygroreceptors that can detect small changes in the ambient relative humidity. This sense enables them to seek environments with a specific humidity or to modify their behavior with respect to the ambient humidity (e.g., to control the opening or closing of spiracles). Variety of hygrosensory structures have identified on the antennae, palps, underside of the body, and near the spiracles of insects. Crickets, grasshoppers, and cicadas possess phonoreceptors called tympanic or tympanal organs. This organ consists of a tough, flexible tympanum that covers an internal sac that allows the tympanum to vibrate when sound waves strike it. Most arachnids possess phonoreceptors in their cuticle called slit sense organs that can sense sound-induced vibrations. Centipedes have organs of Tomsvary, which is believed to be sensitive to sound. Among arthropods there are both simple and compound eyes. Arthropod compound eyes are composed of many independent visual units called ommatidia. Eyes of bees, for example. Many insects have color vision; honeybees can use ultraviolet light to see nectar guides in flowers. Honeybees learn to recognize particular flowers by color, scent, and shape. Many flying insects also detect polarized light and use it to navigate through their environments. Resolution (the ability to see objects sharply) is poor compared with that of a vertebrate eye. A fruit fly, for example, must be closer than 3 cm to see another fruit fly as anything but a single spot. Proprioceptors have been most thoroughly studied in arthropods, where they are associated with appendage joints and body extensor muscles Crayfish stretch receptors are neurons attached to muscles. When the crayfish arches its abdomen while swimming, the stretch receptor detects the change in muscle length. When the muscle is stretched, so is the receptor.8. Phylum Echinodermata Because many echinoderms of this group have only simple nervous system without a controlling brain, they are limited in their actions and responses to stimuli. They have nerves running from mouth into each arm or along the body. They have tiny eyespots at the end of each arm which only detect light or dark Some of their tube feet, are also sensitive to chemicals and this allows them to find the source of smells, such as food. The statocyst is useful for telling the animal whether it is upside down or not. An upside-down echinoderm is in danger since its belly is not protected by its spiny skin.Taste Chemoreceptor: Gustation (L, gustus, taste)The tongue is covered with many papillae, which give the tongue its bumpy appearance. In the crevices between the papillae are thousands of specialized receptors called taste buds.

Taste buds are short-lived because they are usually subjected to wear and tear by abrasive foods. For some mammals, they usually lasted 5 to 10 days only, so its a good thing that they are continually being replaced. Bitter Taste is the most sensitive, because it provides early warning against potentially dangerous substances, many of which are bitter.

The four generally recognized taste sensations are sweet, sour, bitter, and salty. Each is attributable to different kind of taste bud.

Vertebrates, other than mammals, may have taste buds on other parts of the body. For example, reptiles and birds do not usually have taste buds on the tongue; instead, most taste buds are in the pharynx.

TOUCHTactile (touch) receptors are generally derived from modifications of epithelial cells associated with sensory neurons. Most tactile receptors are sensitive to mechanically induced vibrations transmitted through water or a solid substrate. Web-building spiders have tactile receptors that can sense struggling prey in webs through vibrations of the web threads. Progressively stronger stimuli will lead to stronger receptor potentials until a threshold current is produced; this current will initiate an action potential in the sensory nerve fiber. Stronger stimuli will produce a burst of action potentials. However, if the pressure is sustained, response slowly diminishes. This response is called adaptation (not to be confused with the evolutionary meaning of this term). Pain is a distress call from the body signaling some noxious stimulus or internal disorder. Pain receptors are present throughout the body of mammals, except for the brain and intestines. These nerve endings are also called nociceptors (L. no-cere, to injure _ receptor). Severe heat, cold, irritating chemicals, and strong mechanical stimuli (e.g., penetration) may elicit a response from nociceptors that the brain interprets as pain or itching.

Thermoreceptors, sensors for temperature, may be present in either the epidermis or dermis. Mammals have different areas sensitive to warm or coldwarm or cold spots. The ability to detect changes in temperature has become well developed in a number of animals. Snakes use these pit organs to locate warm-blooded prey

Lateral-line System of Fish and Amphibian

A lateral line is a distant touch receptor system for detecting: wave vibrations and currents in water or a predator or a prey that may be causing water movements, in the vicinity of the fish. The lateral-line system consists of sensory pits in the epidermis of the skin that connects to canals that run just below the epidermis.

SmellThe sense of smell or olfaction (L. olere, to smell _ facere, to make), is due to olfactory neurons (receptor cells) in the roof of the vertebrate nasal cavity. Functions: identification of: food, sexual mates and predators. Receptor cells are densely packed; for example, a dog has up to 40 million olfactory receptor cells per square centimeter. In most fishes, openings (external nares) in the snout lead to the olfactory receptors.

For amphibians, it is usually used for mate recognition and locating food. Vultures locate the dead and dying prey largely by smell.

Olfaction is most highly developed in mammals. Mammals use this sense to locate food, recognize members of the same species, and avoid predators. A human nose is said to be able to discriminate around 20 000 different smells, but it is still trivial compare to those who rely hugely in their sense of smell for survival. Dogs, for example, scan and observe their surroundings using their nose as much as humans use their eyes for it.

Olfaction has minor roles for most birds. With the exception of the vultureswho locates the dead and dying prey largely by smell. Many reptiles possess blind ending pouches that open through the secondary palate into the mouth cavityJacobsons (vomeronasal) organs

Vision

Photoreceptors (Gr. photos, light _ receptor) are light-sensitive. A camera is modeled somewhat after vertebrate eyes. The acuity of an animals eyes depends on the density of cones in the fovea, the region of keenest vision, is located in the center of the retina. The human fovea and that of a lion contain approximately 150,000 cones per square millimeter. But many water and field birds have up to 1 million cones per square millimeter. Their eyes are as good as our eyes would be if aided by eight-power binoculars. The retina is composed of several cell layers. 3 layers of the spherical eyeball1. Sclera provides support and protection2. A choroid coat in the middle layer3. The light sensitive Retina that contains many light-sensitive receptor cells.

Rods and cones are found in the retina layer. Cones are primarily concerned with color vision in ample light; rods, with colorless vision in dim light. Fovea Centralis located at the center of the retina, in direct line with the center of the lens and cornea, center of the eye's sharpest vision. It is densely packed with cones. Blind Spot is a region where there are no cones or rods.Unlike humans, who have both day and night vision, some vertebrates specialize for one or the other. Strictly nocturnal animals, such as bats and owls, have pure rod retinas. Purely diurnal forms, such as the common gray squirrel and some birds, have only cones; they are virtually blind at night. Color vision occurs in some members of all vertebrate groups with the possible exception of amphibians. Bony fishes and birds have particularly good color vision. Surprisingly, most mammals are color blind; exceptions are primates and a few other species such as squirrels.

To focus on images the lens changes shape, depending on the distance of the object. When the object is near to the viewer the lens is usually rounder. This is called accommodation.

Three main types of eye refraction Emmetropia (normal-sightedness) myopia (nearsightedness) hyperopia (farsightedness)

Emmetropia is the normal condition of perfect vision, in which parallel light rays are focused on the retina without the need for accommodation. The bird's eye resembles that of the vertebrate in structure but is relatively larger and almost immobile. However, birds can turn their head with their long and flexible necks to scan the visual field. Some birds have two fovea per eye. Center "search" fovea gives wide angle of monocular visionobserves the landscape below during flight. Posterior "pursuit" fovea gives binocular vision that produce depth perceptionto capture prey and landing in a tree branch.Vision is one of the most important senses in the amphibians because they are primarily sight feeders. Contain 4 types of photoreceptors and they are therefore capable of color vision with a broader sensitivity to color than humans. Accommodation for amphibians and fishes is performed through a forward movement of the lens by the protractor lentis muscle, which moves the lens along the optic axis of the eye toward or from the retina. Some reptiles possess a median (parietal) eye that develops from outgrowths of the roof of the forebrain

Hearing Importance: mechanism to alert them to either nearby or faraway potentially dangerous activity. It also became important in the search for food and mates communication. Adaptation to hearing in air resulted from the evolution of an acoustic transformer that incorporates a thin, stretched membrane, called either an eardrum, tympanic membrane, or tympanum, that is exposed to the air. Vestibular apparatus is concerned with posture and equilibrium. When the body is still, the otoliths in the semicircular canals rest on hair cells. When the head or body moves horizontally, or vertically, the granules are displaced, causing the gelatinous material to sag. This displacement bends the hairs slightly so that hair cells initiate a generator potential and then an action potential.Auditory apparatus is concerned with hearing. The human ear has three divisions: the outer, middle, and inner ear. The outer ear consists of the pinna, ear canal and eardrum. The middle ear consists of the ossicles and ear drum. The inner ear consists of the cochlea, the auditory (hearing) nerve Hearing in most mammals have an external sound-collecting appendage, or pinna . Sounds travel through the air as sound waves. In normal hearing the external part of the ear helps to direct these sound waves down the ear canal (external auditory canal) to the ear drum. This causes the ear drum (tympanic membrane) to move and vibrate.

3 smallest bones in the human ear/body (Auditory Ossicles) 1. The Malleus (hammer) adheres to the tympanic membrane and connects to the incus.2. The Incus (anvil) connects to the stapes, which adheres to the oval window3. Stapes (stirrup) conducts sounds into the inner ear The ears of anurans (frogs) consist of a tympanum, a middle ear, and an inner ear. Tympanum vibrates in response to sounds and transmits these movements to the middle ear, a chamber behind the tympanum. The sense of equilibrium and balance in amphibians involves the semicircular canals. These canals help detect rotational movements and gravity. Fishes lack the outer and/or middle ear, which conducts sound waves to the inner ear in other vertebrates. Vibrations pass from the water through the bones of the skull to the inner ear. For fishes with bony ossicles, vibrations are amplified by the swim bladder and sent through the ossicles to the skull.

EXCRETIONEtymology:Excretory comes from the latin word excretio which means to eliminateDefinition: It can be broadly defined broadly as the elimination of metabolic waste products from an animals body.Functions:Collect water and filter body fluidsEliminate excretory products from the bodyExcretion Process:Filtration, pressure-filtering of body fluids producing a filtrateReabsorption, reclaiming valuable solutes from the filtrateSecretion, addition of toxins and other solutes from the body fluids to the filtrateExcretion, the filtrate leaves the systemParts:Kidney:The kidneys are located in the back of the abdominal cavity that is found in the retroperitoneum and they get blood from paired renal arteries. The kidneys excrete urine into one of the ureters. The kidneys serve a variety of functions including regulating blood pressure, maintaining the bodys acid-base balance and regulating electrolytes. They also naturally filter the blood, diverting the waste towards the urinary bladder. When the kidneys produce urine, they excrete wastes including ammonium and urea. Other functions include producing hormones and reabsorbing amino acids, glucose and water.

Ureters:Each ureter is a muscular tube that brings the urine between the kidneys and the urinary bladder. They usually have a diameter of between 3 and 4 mm and a length of between 25 and 30 cm. They cross over the pelvic brim close to the bifurcation of iliac arteries, which is where kidney stones are commonly found. They then run along the pelviss lateral walls before curving towards the bladder in the back.Bladder:The urinary bladder is responsible for collecting any urine that the kidneys excrete. The urine is stored here before urination occurs. In order to fulfil this function, the bladder is an elastic, hollow, and muscular organ that rests on a persons pelvic floor. Urine enters the urinary bladder using the ureters and the urethra carry it out.

Urethra:The urethra is a tube which connects a persons urinary bladder to their genitals so that urine can be removed from the body. In females, the urethra exits on top of the vaginal opening. The urethra in males is longer and it carries urine (as well as sperm) through the penis. There is also an external urethral sphincter which allows us to voluntarily control urination.

Other parts:Lungs: Cellular respiration is necessary to provide our bodies with energy as without it, the bodys cells will die. However, cellular respiration produces the waste product of carbon dioxide which then needs to be eliminated from the system. This carbon dioxide diffuses out from the cells in the body, entering the bloodstream and eventually going to the lungs. The lungs contain alveoli which diffuse the carbon dioxide from the blood so it can enter the lung tissue and eventually leave the body during exhalation.

Skin: Sweat is a crucial part of the excretory system as it is responsible for eliminating sweat from the body. Salt contains several metabolic wastes including urea, salts and water. In addition to excreting metabolic wastes, sweat also cools down the body. The sweat glands are able to receive the various wastes because they are mixed in with capillaries, which are tiny blood vessels. This means that the wastes can diffuse out of the blood and enter the sweat glands before passing out of the skin in the form of sweat.

Large Intestine: The large intestine is around 5 feet in length and is responsible for transporting waste so it can be excreted. In general, it collects waste from all over the body and then extracts usable water, allowing for the removal of solid waste. It does so because any waste products or food that the small intestine doesnt absorb will enter the large intestine. Once it is there, bacteria, water and undigested food are combined to create feces. Sometimes it will take food 24 hours to complete its journey through a persons large intestine.

Liver: The liver is responsible for detoxifying and breaking down any toxins such as chemicals and poisons that enter our bodies. One of the ways in which the liver fulfils this function is by taking ammonia in its poisonous form and converting it into urea which the kidney will eventually filter, creating urine. In addition, the liver produces bile which the body then uses to help break fats down into unusable waste and usable fats. Bile is stored in a persons gall bladder after the liver produces it. The small intestine uses it to break down acidic wastes such as ammonia as well as fats and ethanol, converting them into harmless substances. The liver also serves several functions within the circulatory system. It is also responsible for maintaining the bodys proper levels of glucose based on cues from insulin (which increases the amount of glucose stored) and glucagon (which decreases the amount of glucose stored). The liver also helps detoxify the blood by removing any chemicals that are potentially hazardous.

Nitrogenous Wastes:Nitrogen wastes are, a by product ofproteinmetabolism. Amino groups are removed fromamino acidsprior to energy conversion. The NH2(amino group) combines with a hydrogen ion (proton) to form ammonia (NH3).

Deamination > Ammonia > Urea > Uric acidDuring Deamination, enzymes remove the amino group asammonia(NH3). Ammonia is toxic, even at low concentrations, and requires large amounts of water to flush it out of the body. Many animals, including humans, create a less poisonous substance, urea, by combining ammonia with carbon dioxide. Ananimalcan retain urea for some time before excreting it, but it requires water to remove it from the body as urine.Birds,insects, landsnails, and mostreptilesconvert ammonia into an insoluble substance, uric acid. This way, water is not required water to remove urea from the body. Ammonia: One nitrogen per molecule; highly toxic; requires lots of water to flush Urea: two nitrogens; less toxic; less water to flush Uric Acid: Four nitrogens; non-toxic; requires very little water to flush

Osmoregulation: refers to the state aquatic animals are in: they are surrounded by freshwater and must constantly deal with the influx of water. Necessary for animals in all habitats. If the osmotic concentration of the body fluids of an animal equals that of the medium the animal is osmoconformers there is little water transport between the inside of the animal and theisotonicoutside environment. Animal that maintains its body fluids at a different osmotic concentration from that of its surrounding environment is as osmoregulation Osmoregulators face two problems: prevention of water loss from the body and prevention of salts diffusing into the body.

Reported by: Cruz, Frances Gabrielle A.EXCRETION IN INVERTEBRATES

By Excretory Organs:A. Contractile Vacuoles Occur in Protozoans (Paramecium) Tiny, spherical, intracellular vacuole of unicellular eukaryotes Accumulate excess water from within the cytoplasm and periodically discharge to the exterior so as to maintain the normal fluid balance within the cell As water enters the cell, a vacuole grows and finally contracts and empties its contents through a pore on the surface. Vacuoles have many proton pumps located within their membrane. Proton pumps create H+ and HCO- gradients that draw water into the vacuole, forming an isosmotic solution. These ions are excreted when the vacuole empties. The chief excretory product is Ammonia Examples: Paramecium Small and have a large surface area in proportion to their volume High surface area to volume ratio facilitates excretion Excretion occur by diffusion across the plasma membrane Water enters because of osmosis. The excess water enters the contractile vacuole. The contractile vacuole will swell. Then, it will move to the edge of the cell. It will eventually, bursts and expels water. The cycle is repeated.

In addition, Echinodermata, Cnidarians and Porifera have no excretory organs but their excretion is by DIFFUSION. For examples: Sea Stars Metabolic wastes are transported in the coelom by diffusion and by the action of ciliated cells lining the body cavity Excretion occur by diffusion across dermal branchiae, tube feet and other membranous structures Hydra - Excretion by diffusion through the cell walls into gastrovascular cavity. Then, to the mouth into surrounding water Sponges- excretion by diffusion through the poresB. Nephridium It came the Greek word NEPHROS meaning KIDNEY Most common type of invertebrate excretory organ A tubular structure designed to maintain appropriate osmotic balance It has TWO TYPES:1. Protonephridium It came from the Greek word PROTOS meaning FIRST Earliest type of nephridium With inner ends closed Its simplest system is Flame Cell Systems occur in Platyhelminthes and Rotifers Flame Cells Scattered among the body cells from which wastes are drawn to pass out in a branched system of ducts Bulblike Located along the excretory canals Fluid filters into the flame cells from the surrounding interstitial fluid. Cilia propel the fluid through the excretory canals and out the body through excretory pores Function primarily in eliminating excess water Nitrogenous waste simply diffuses across the body surface into the surrounding water Ex: Flatworm Body fluids collected by flame cells (protonephridia) are passed down a system of ducts to excretory pores on the body surface2. Metanephridium It came from the Greek word META meaning BEYOND More advanced type of nephridium With inner ends open Occurs in Mollusks and Annelids Ex: Earthworm Its body is divided into segments and that each segment has a pair of metanephridia Each metanephridium begins with the nephrostome (a ciliated funnel) that opens from the body cavity of a segment into a coiled tubule As cilia move the fluid through the tubule, a network of capillaries surrounding the tubules reabsorbs and carries away ions Each tubule leads to an enlarged bladder that empties to the outside of the body through nephridiopore (an opening) Metanepridium differs in Protonephridium in:1. The tubule is open at both ends, allowing fluid to be swept into the tubule through a nephrostome (a ciliated funnel-like opening)

2. Metanephridium is surrounded by a network of blood vessels that assists in reabsorption from the tubular fluid of water and valuable materials (salts, sugars and amino acids)

But both have the same basic process of urine formationC. Antennal (Green) Glands The excretory organs of some crustaceans (Crayfish) because of their location near the antennae and their green color It is located at the ventral part of the head Fluid filters into the antennal gland from the hemocoel Occur in most Crustaceans Ex: Crayfish Antennal glands are located in front of and to both sides of the esophagus, and divided into an endsac Fluid where collects by filtration and a labyrinth Labyrinth Labyrinth walls are greatly folded and glandular Important site for reabsorption It leads through a nephridial canal into a bladder From the bladder, a short duct leads to an excretory poreD. Malpighian Tubules The excretory organs of insects It is attached to the interior end of the hind gut and closed at their free ends Operate in conjunction with specialized glands in the wall of rectum These are thin, elastic, closed and lack arterial supply. These collect wastes from the body fluids and discharge them into the hindgut Excretion involves the active transport of potassium ions into the tubules from the surrounding hemolymph and the osmotic movement of water that follows The nitrogenous waste is uric acid that enters the tubules: it passes into the gut and out of the body Ex: Grasshopper Uric acid and ions (Na+ & K+) are actively transported into the malpighian tubules followed by water that comes through osmosis Some water, ions and organic compounds are reabsorbed in the basal portion of the Malpighian tubules and the hindgut. The rest are reabsorbed in the rectum Then, the uric acid moves into the hindgut and is excreted

Additional Information: Coxal Glands These are common among Arachnids (spiders, scorpions, ticks, mites) A spherical sacs that resemble the For collecting and excreting urine Consisting of an end sac Ex: Spider It has Malpighian Tubules and Coxal Glands An excretory pore at the base (coxa) of one of the legs for urine Coxal gland muscles are attached to the thin saccular filtration membrane.

SUMMARY OF EXCRETION IN INVERTEBRATESInvertebratesExcretory OrganNitrogenous Wastes

PROTOZOA (Paramecium)

Contractile Vacuoles

-remove excess water from organism (DIFFUSION)

Ammonia

PHYLUM ECHINODERMATA(Sea Stars)No excretory organ

-excretion is by wastes passing out the tube feet (DIFFUSION)Ammonia

PHYLUM CNIDARIA (Hydra)No excretory organ

-excretion is by DIFFUSION through cell walls into gastrovascular cavity. Then, to mouth into surrounding waterAmmonia

PHYLUM PORIFERA (Sponges)No excretory organ

-excretion is also by DIFFUSION through the poresAmmonia

PHYLUM PLATYHELMINTHES (Flatworms)Protonephridia (Flame cells)

Ammonia and Urea

PHYLUM NEMATODA Roundworms

RotifersConsist of one/more large gland cells opening to an excretory pore/canal system

Protonephridia

Ammonia and Urea

PHYLUM ANNELIDA (Earthworm)MetanephridiaAmmonia and Urea

PHYLUM ARTHROPODA Insects

Crustaceans (Crayfish)

Arachnids (Spiders)Malpighian Tubules

Antennal (Green) Glands or Maxillary Glands

Malpighian Tubules and Coxal GlandsUric acid

Ammonia

Uric Acid

PHYLUM MOLLUSCAMetanephridiaAmmonia and Urea

Vertebrates Kidney Variation1. Vertebrate Kidney Function and Structure The organization of kidneys differs in somewhat different groups of vertebrates, but in all, the basic functional unit is the Nephron Nephron is made up of: Renal CorpuscleBowmans capsule-expanded chamberGlomerulus -tuft capillaries that can be found in the Bowmans capsule Renal tubuleProximal convoluted tubule-convoluted portion of the vertebrate nephron that lies between Bowman's capsule and the loop of Henle and functions especially in the resorption of sugar, sodium and chloride ions, and water from the glomerular filtrateLoop of Henle-The part of the renal tubule that loops around into a U turnDistal convoluted tubule-nephron segment that lies immediately downstream of the macula densa. Although short in length, the distal convoluted tubule plays a critical role in sodium, potassium, and divalent cation homeostasis. Glomerular Filtration The glomerulus acts as a specialized mechanical filter, which produces an almost protein-free filtrate of the plasma in the fluid-filled space of the Bowmans capsule as a result of high blood pressure across glomerular capillary walls The diameter of the afferent arteriole entering the glomerulus is greater than that of the exiting efferent arterioleTubular Reabsorption Active transport in which cellular energy is used to transport materials from tubular fluid to the surrounding capillary network and thus into the blood circulation For most substances there is an upper limit to the amount of substance that can be reabsorbed, this is termed the Transport Maximum (renal threshold) for that substance Aldosterone, a steroid hormone secreted by the adrenal gland that increases both active reabsorption of sodium and secretion of potassium by distal tubules The secretion of aldosterone is regulated by the enzyme renin, produced by the juxtaglomerular apparatus, a complex of cells located at the junction of the afferent arteriole with the glomerulus and by elevated blood potassium levels. Angiotensin, a blood-borne hormone that has several related effects Stimulates the release of aldosterone Increases the secretion of antidiuretic hormone Increases blood pressure Stimulates thirst, which also is stimulated by decreased blood volume or increased blood osmolarity.Tubular Secretion Tubular secretion enables a kidney to increase the urine concentrations of materials to be excreted Tubular epithelium has both cationic and anionic transporters in their membrane The distal convoluted tubule is the site of most tubular excretion

2.The three types of kidneysArchinephros or Holonephros, a pair of kidneys extending the entire length of the coelom and composed of segmentally arranged tubules , each opening into the coelom by a peritoneal funnel, provided near the funnel with a glomerulus, and opening laterally into a duct connecting with the cloaca. Its duct is called archinephric duct.

Pronephros the anterior pronephros is usually only a transient embryonic developmental stage in all vertebrates. Tubules that appear within the anterior part of the nephric ridge are called pronephric tubules. These tubules join to form a common pronephric duct. This duct grows posteriorly in the nephric ridge, eventually reaching and opening into cloaca. In most vertebrates, the embryonic pronephros regresses, and it is replaced by a second type of embryonic kidney, the mesonephros.

Mesonephros tubules of the mesonephric kidney arise in the middle of the nephric ridge. Mesonephric tubules do not produce a new duct but instead tap into the preexisting presonephric duct. The pronephric duct is now properly renamed as the mesonephric duct. The extended mesonephric kidney with additional posterior tubules is termed the opisthinephros. It is found in most adult fishes and amphibians.

Metanephros the formation of the metanephric duct that appears as a ureteric diverticulum arising at the base of the preexisting mesonephric duct is the first embryonic hint of a metanephros. The ureteric diverticulum grows dorsally into the posterior region of the nephric ridge. Here it enlarges and stimulates the growth of metanephric tubules that come to make up the metanephric kidney. The metanephric duct is usually called the ureter.

Opisthonephros Tubules arising from the middle and posterior nephric ridge form an extended kidney, the opisthonephros, that may develop into the adutl kidney of fishes and amphibians.

Comparative table of the three types of kidneys

Kidney typeEmbryonic history and adult structurein fishes and amphibians in reptiles, birds, and mammals

Pranephros of head kidney First to apprear in embryo; develops segmentally, for forward in body cavity; each unit with a nephrostome opening from the coelam; no glomeruliFunctions in lava; disappears in adultAppears transiently in embryo and soon disappears

Mesonephros, or midkidneyDevelops segmentally in middle part of body cavity; some nephrostomes open to coelom, but excretion chiefly by glomeruliBecomes functional kidney of adult Appears after pronephros; functions during embryonic life, disappearing before hatching or birth; duct persists as ducts deferens in male

Metanephros, or hind kidneyLast to develop; not segmental; posterior in body cavity; no nephrostomes; many glameruli; all excretion from bloodstreamNot developed Last to appear; becomes functional kidney after hatching a birth

OSMOREGULATION IN VERTEBRATES

I. Osmoregulation Over time, the rates of water uptake and loss must balance. Animal cellswhich lack cell wallsswell and burst if there is a continuous net uptake of water, or shrivel and die if there is a substantial net loss of water.Two Types of Solution1. Osmoregulators an osmoregulator is an animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment. An osmoregulator must discharge excess water if it lives in a hypoosmotic environment or take in water to offset osmotic loss if it inhabits a hyperosmotic environment. Osmoregulation enables animals to live in environments that are uninhabitable to osmoconformers, such as freshwater and terrestrial habitats. It also enables many marine animals to maintain internal osmolarities different from that of seawater. Because diffusion tends to equalize concentrations in a system, osmoregulators must expend energy to maintain the osmotic gradients via active transport. The energy costs depend mainly on how different an animals osmolarity is from its surroundings, how easily water and solutes can move across the animals surface, and how much membrane-transport work is required to pump solutes.2. Osmoconformers Oneavailable only to marine animalsis to be isoosmotic to the surroundings as an osmoconformer. Although they do not compensate for changes in external osmolarity, osmoconformers often live in water that has a very stable composition and, hence, they have a very constant internal osmolarity.

II. Osmoregulation in VertebratesOrganismsEnvironmental Concentration Relative to Body FluidsMajor Nitrogenous Waste

Key Adaptation

FISHES

Freshwater FishesHypoosmotic

Ammonia

Absorb ions through gills

Saltwater FishesHyperosmoticAmmoniaAbsorb ions through gills

SharksIsoosmoticAmmoniaSecrete ions