Muscular System

Chapter 8

Functional Divisions of Muscle Control

Voluntary –Consciously controlled

Involuntary –Automatically controlled

Structural Types of Muscles

Smooth

CardiacSkeletal

Skeletal Muscle

Move appendages Controls posture Controls GI tract

openings Generates body heat

Attached to skeletonVoluntary movementStriatedLong fibersMany nucleiStrongest contractions

Cardiac Muscle Found in the walls of the heart Involuntary Movement Roughly rectangular with branches that contact

adjacent cells Striated Intercalated Discs = branching fibers that

interconnect Allow cardiac cells to function as a unit

Does not fatigue or develop oxygen debt

Smooth Muscle In walls of hollow organs (GI tract and blood

vessels) Dilates pupils Involuntary movement Spindle-shaped Not striated Slowest and weakest contractions No oxygen debt

Tissue Characteristics Excitability

Can receive and respond to stimuli Contractility

Can shorten and thicken Extensibility

Can stretch Elasticity

Can return to original shape

Gross Anatomy of Muscles

Muscle Belly/Body Medial section

Fascicle Group of muscle

fibers Muscle Fiber

1 individual cell Up to 12 inches

Connective Tissues

Gross Anatomy of Muscles

Fascia Sheet or broad band of dense connective

tissue Surrounds space between skin and muscles

Deep fascia surrounds muscle Supports muscles and hold them together as

single units Serves as route for passage of blood vessels

and nerves

3 Types of Connective Tissue Epimysium

Outermost covering around entire muscle Perimysium

Surrounds fascicles Endomysium

Surrounds each individual fiber Each of these types of connective tissue

transmit blood vessels and nerves to muscle components

Tendons Near bone the three layers of connective

tissues converge to form a thick band of dense connective tissue that extends from muscle to attach to bone.

Aponeurosis

Broad sheet of dense connective tissue

May attach muscle to bone or muscle to another muscle

Naming Muscles

Direction of muscle fibers: Rectus (straight) : parallel to body midline, or

long bone• Rectus abdominis

Oblique: run slanted• External obliques

Naming Muscles

Muscle Size: Maximus: largest

• Gluteus maximus Minimus: smallest

• Gluteus minimus Longus: long

• Adductor longus

Naming Muscles Location:

Bone association• Frontalis, Temporalis

Number of Origins: Biceps:

• 2 Triceps:

• 3 Quadriceps:

• 4

Naming Muscles Location of Origin and Insertion:

Sternocleidomastoid• Origin = sternum and clavicle• Insertion = mastoid process

Shape:Deltoid = triangle

Muscle ActionAdductors, abductors, flexors, extensors

Fiber Organization Parallel: (biceps brachii)

Found in most skeletal muscles Fasicles are parallel to long axis Fxn of muscle is parallel to individual

cells Entire muscle shortens by same %

• Maximum shortening = 30%

Fiber Organization Convergent: (pectoralis

group) Fibers are fanned, come together at a

central point to pull on a tendon, tendonous sheet, or seam of collagen fibers

Versatile contraction direction• Stimulation of one group of fibers can

determine direction of pull

Fiber Organization Pennate:

All fasicles form a common angle with the tendon

Contain more muscle cells than a parallel muscle

Pull at an angle – tendon movement is shorter than parallel

Generates more tension

Fiber Organization Pennate:

Unipennate: • Muscle cells on one side only

Extensor digitorum longus Bipennate:

• Fiber extends on both sides of tendon Rectus femoris

Multipennate: • Tendon brances within the muscle

deltoids

Fiber Organization Circular or Sphincter:(Pyloric Sphincter)

Concentrically arranged cells around an opening

Contraction produces a decrease in the diameter of an opening

Found at entrances and exits in digestive and urinary tracts

Large Small

Muscle Fiber

Myofibrils

Myofilaments(Arranged in Repeating units called

Sarcomeres)

Microscopic Anatomy Sarcolemma

Plasma membrane of each fiber

Sarcoplasm Cytoplasm Contains myoglobin (protein – binds

oxygengenerates ATP; energy source)

Microscopic Anatomy Myofibril

specialized cylindrical organelle made of myofilament bundles 1-2 um diameter up to several thousand in 1 fiber covered by sarcoplasmic reticulum:

specialized smooth ER, stores calcium ions connects to other SR and to sarcolemma by T

tubules

Microscopic Anatomy Myofilament

Structural protein strands in myofibril Made up of mainly actin and myosin

Sarcomere Basic unit of contraction

Sarcomere Anatomy

A Band = area where thick and thin filaments overlap, dark striations

I Band = area where only thin filaments occur, light striations

Z Line = dense protein (connectin) extending perpendicular to length of myofibril

lies in the middle of each I-band connect thin filaments and individual myofibrils to each

other

Sarcomere Anatomy

Sarcomere = area between two Z lines H Zone = area in middle of A bands where there is no

overlap of thin filaments Only visible in relaxed muscles

M Line = fine (desmin) proteins Connects middles of thick filaments Found in middle of H Zone

Thick Myofilaments Myosin

golf club shaped proteins with long tails and "fat" heads

filament consists of staggered myosin macromolecules

have actin binding sites and ATP binding sites with ATPase

Thin Myofilaments Actin

anchored to Z lines kidney bean shaped

monomers; polymerized into long chains

tropomyosin coils around actin

troponin binds to tropomyosin and to actin

Tropomyosin/Troponin Complex blocks active sites on actin chains

6 thin filaments are arranged as a hexagon around each thick filament

Sliding Filament Theory

Thin filaments slide over thick filaments

Z lines pull together

I band and H zone shorten

A band stays same length

Resting Muscle

Calcium ions are stored in SR ATP is bound on thick filaments Troponin is blocking myosin binding site

on actin

Sliding Filament Theory Impulse arrives at neuromuscular junction Ach reaches receptors in muscle cell, signals

ion channels to open Sodium flows into cell Action potential travels down T-tubules Signals SR to release calcium

Sliding Filament Theory Ca2+ binds to troponin molecules in the

thin filaments (actin) Troponin moves laterally to uncover

binding site for myosin Cross bridge attachment

Myosin binds to actin Ca2+ also activates

splitting of ATP Leaves ADP and PO4 hanging on

myosin

Sliding Filament Theory Power stroke

Energy released from splitting ATP is used to tilt myosin head Tilting heads pull actin forward

Much energy is lost as heat ADP and PO4 are released from head

Sliding Filament Theory Rigor Complex

Myosin head remains attached to actin

More ATP binds to myosin causing detachment Cycle repeats, shortening sarcomeres

Sliding Filament Theory

Sliding Filament Theory

SDSU Biology 590 - Actin Myosin Crossbridge 3D Animation

Returning to Rest Cholinesterase inactivates acetylcholine Calcium ions return to sarcoplasmic

reticulum by active transport All cross bridges are broken and thin

filaments are allowed to slide back to original positions

Skeletal Muscle Contraction Physiology

Motor unit Motor neuron and all of the muscle fibers it

stimulates Motor neuron

Nerve cells that carry action potentials to skeletal muscle fibers

Neuromuscular junction Specialized site where neuron and muscle

come together

Muscle Metabolism

Stored ATP is energy source

ATP generated by Phosphorylation of ADP

• Anaerobic Fermentation• Aerobic Respiration (Most ATP generated)

Phosphorylation of ADP

Once contraction begins stored ATP is used up in a matter of seconds

ADP and creatine phosphate stored in muscles High energy molecule

Creatine phosphate is broken down Energy released is used to regenerate

ATP

Anaerobic Cycles

Oxygen is not required Use stored glycogen Lactic acid formed Produces ATP quickly in small amounts Short-term vigorous exercise

Used up within minutes

Aerobic Respiration

Requires oxygen Produces most ATP over long period of

time Mitochondria Energy for hours Prolonged activities where endurance is

important

Muscle Fatigue Physiological inability of muscle to contract

Build up of lactic acid lowers cell’s pH Cell becomes unresponsive to stimulation

Relative deficiency of ATP

Accumulation of lactic acid

Cramps: inability to relax Lack of ATP stops active transport of Ca++ into SR

Oxygen Debt

Temporary lack of oxygen availability Causes accumulation of lactic acid

Muscles feel sore Repaid when additional oxygen is taken in

after exercise (heavy breathing) Lactic acid converted to pyruvic acid Synthesize ATP and creatine phosphate Slow process (hours)

Stimuli

All or none law When muscle fiber is stimulated it will contract

fully or not at all Threshold stimulus = weakest stimulus

that can initiate a contraction Subthreshold stimulus = too weak to

cause a contraction

Motor UnitsMotor Unit:

one motor neuron + muscle fibers it stimulates- avg. = 150

Contraction Strength - how many - how frequently

Recruitment:Stronger stimuli increases # of motor units

activated

Types of Muscle Contraction Twitch

Rapid response to a single stimulus that is slightly over the threshold

1/10th of a second

Myograph

Types of Muscle Contraction

Treppe Produces single twitches that rapidly follow

each other First few progessively increase in force May allow muscle to “warm-up” “Staircase” phenomenon

Types of Muscle Contraction

Wave summation Muscle receives second stimulus before the

first contraction cycle is complete Second contraction will be stronger Increased Force: Contraction may be up to 4

times as great as that achieved by a series of twitches

Types of Muscle Contraction Tetanus

Series of stimuli bombard muscle before each contraction cycle can reach completion• 20 – 30 per second

Wave summation reaches maximum value and is sustained until stimuli stops

Types of Muscle Contraction

Incomplete tetanus Partial relaxation occurs between stimuli

Complete tetanus 30-50 stimuli per second Contraction is maintained without any

relaxation Lockjaw = severe cramping

Types of Muscle Contraction

Isotonic contractions Produces movements as the muscle pulls an

attached structure toward a more stationary structure

Tension held constant until muscle relaxes Produces body movement Provides greater muscle enlargement and

endurance

Types of Muscle Contraction

Isometric Contraction Produces muscle tension Muscle does not shorten

• No body movement• Ex: Push against a wall

Muscles contract and tense but no movement

Group Action

Prime Mover biceps brachii Cause desired action

Antagonist triceps brachii Relax during action

Synergist forearm muscles Steady movement

Fixators chest, back, shoulder Stabilize origin of the prime mover

Example: Elbow

Muscle Development and Coordination

Direction: Cephalic Caudal Gross Motor Fine Motor Lift head….sit up….grab large

objects….Pinch! (9 months)….walk