Chapter 9Chapter 9Muscular SystemMuscular System

Functions of a Muscle Tissue

1.1. Movement: Movement: 1.1. SkeletalSkeletal - locomotion , vision, facial expression.2.2. CardiacCardiac – blood pumping3.3. SmoothSmooth – food digestion

2.2. PosturePosture - (skeletal)3.3. Joint StabilityJoint Stability - (skeletal)4.4. Heat GenerationHeat Generation - (skeletal)

Chapter 9Muscular System

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Three Types of Muscle Tissues

Skeletal Muscle• usually attached to bones• voluntary- under conscious control• striated

Smooth Muscle• walls of most viscera, blood vessels, skin• involuntary - not under conscious control• not striated

Cardiac Muscle• wall of heart• involuntary - not under conscious control• striated

Structure of a Skeletal Muscle

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Skeletal Muscle• organs of the muscular system• skeletal muscle tissue• nervous tissue• blood

Connective tissues and muscle tissue:

1.fascia – covers the muscle2.tendon – attaches the muscle3.aponeuroses – muscle to

muscle

Functional Characteristics of Muscle

• ExcitabilityExcitability – receive and respond to stimuli

• ContractilityContractility – shorten forcibly and when stimulated

• ExtensibilityExtensibility – stretched or extended

• ElasticityElasticity – bounce back to original length

Structure of a Skeletal Muscle

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Coverings of a muscle1. EpimysiumEpimysium - outter2. PerimysiumPerimysium - middle3. Endomysium. Endomysium - inner

Organization of MuscleOrganization of Muscle• muscle• fascicles• muscle fibers• myofibrils • thick and thin filaments

Structure of a Skeletal Muscle

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Coverings of a muscle1. EpimysiumEpimysium – connective tissue surrounding the entire muscle2. PerimysiumPerimysium – connective tissue surrounding a fascicle3. Endomysium. Endomysium – thin connective tissue surrounding each muscle cellOrganization of MuscleOrganization of Muscle• musclemuscle• fasciclesfascicles – bundle of muscle cells• muscle fibers muscle fibers – a muscle cell• myofibrilsmyofibrils – a long, filamentous organelle found within muscle cells that has a banded appearance• thick and thin filaments (myofilament)- thick and thin filaments (myofilament)- actin &myosin filaments• sarcomeresarcomere – contractile unit of muscle

Skeletal Muscle Fiber

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• sarcolemma -• sacroplasm• sarcoplasmic reticulum• transverse tubule• triad

• cisterna of sarcoplasmic reticulum• transverse tubule

• myofibril• actin filaments• myosin filaments• sarcomere

Skeletal Muscle Fiber

• sarcolemma – Plasma membrane surrounding each muscle fiber

• sarcoplasm – specialized cytoplasm• sarcoplasmic reticulum – network of tubes and sacs• transverse tubule – tubular organelles that run across

fibers, right angles• triad

• cisternae of sarcoplasmic reticulum• transverse tubule

• myofibril – consists of the many, bundled myofilaments • actin filaments – thin filaments• myosin filaments – thick filaments• sarcomere – basic contractile unit of muscle

Acting and Myosin Filaments Actin and Myosin

Sarcomere

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• I band• A band• H zone• Z line• M line

Sarcomere Structure

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A sarcomere is defined as the segment between two neighboring Z- lines .  

•Z-line- the disc in between the I bands. Appears as a series of dark lines. •I-band is the zone of thin filaments that is not superimposed by thick filaments. •A-band contains the entire length of a single thick filament. •H-band is the zone of the thick filaments that is not superimposed by the thin filaments.

•Finally, inside the H-zone is a thin M-line formed of cross-connecting elements of the cytoskeleton.

Sliding Filament Theory

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When sarcomeres shorten, actin and myosin filaments slide past one anotherVIDEO#1VIDEO #2

Skeletal Muscle Contraction

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How does a muscle contract?

Sequence of a Muscle ContractionBrain

Spinal Cord

Nerve(Action potential)

Motor Unit

Neuromuscular Junction(Calcium is released)

Acetylcholine(Neurotransmitter)

Contraction

Motor Unit

• single motor neuron (a single nerve)• one motor neuron and many skeletal muscle fibers

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Neuromuscular Junction

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• site where a motor nerve fiber and a skeletal muscle fiber meet

Muscle Contraction

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• Action potential causes the release of Ca at the NMJ.•a neurotransmitter releases a chemical substance from the motor end fiber, causing stimulation of the muscle fiber•That substance is called acetylcholine (ACh)•ACh causes the muscle fibers to become stimulated and contract (shorten).

Relaxation of a Muscle

• acetylcholinesterase – an enzyme that breaks down acetylcholine. NMJ

• muscle impulse stops• calcium moves back into sarcoplasmic

reticulum• myosin and actin action prevented• muscle fiber relaxes• Cd

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Sequence of a Muscle ContractionBrain

Spinal Cord

Nerve(Action potential)

Motor Unit

Neuromuscular Junction(Calcium is released)

Acetylcholine(Neurotransmitter)

Contraction

Recruitment of Motor Units

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Recruitment - increase in the number of motor units activated

• whole muscle composed of many motor units

• as intensity of stimulation or contraction increases, recruitment of motor units continues until all motor units are activated = all or none principle all or none principle

Question ????

We now know how a muscle contracts and relaxes, so We now know how a muscle contracts and relaxes, so is energy needed for that to happen?is energy needed for that to happen?

NO NO or or YESYES

??

How is energy that is stored in carbohydrates released?

Cellular Respiration Oxygen

Glucose

Useable Energy is Useable Energy is Adenosine triphosphate Adenosine triphosphate (ATP)(ATP)

H2O + CO2

Adenosine triphosphate Adenosine triphosphate (ATP)(ATP)

• It serves as a source of energy for many metabolic processes.

• ATP releases energy when it is broken down into ADP by hydrolysis during cell metabolism.

ENERGY

The energy used to power the interaction between actin and myosin filaments comes from ATP (useable chemical energy) produced by cellular respiration.

ATP stored in skeletal muscle last only about six seconds.

ATP must be regenerated continuously if contraction is to continue

Two Energy Sources for Contraction

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• creatine phosphate – stores energy that quickly converts unusable energy (ADP) to usable energy (ATP) 6 Seconds!!

1) Creatine phosphate (ADP) 2) Cellular respiration

Cellular Respiration (CR)

THREE SERIES OF REACTIONS in CRTHREE SERIES OF REACTIONS in CR1. Glycolysis2. Citric acid cycle3. Electron transport chain

Produces• carbon dioxide• water• ATP (chemical energy)• heat

Two Types of ReactionsTwo Types of Reactions• Anaerobic RespirationAnaerobic Respiration (without O2) - produce little ATP• Aerobic RespirationAerobic Respiration (requires O2) - produce most ATP4-11

Anaerobic Reaction (Glycolysis)

• Recall that glycolysis results in pyruvate acid. If O2 is not present, pyruvate can be fermented into LACTIC ACID.

• Lactic Acid• It is a waste product of pyruvate acid.• Occurs in many muscle cells.• Accumulation causes muscle soreness and fatigue.

Oxygen Supply and Cellular Respiration

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• Anaerobic Phase•Steps are called glycolysis.•occur in the cytoplasm• no oxygen• produces pyruvic acid and produces lactic acid• little ATP

• Aerobic Phase•Steps are called citric acid cycle and electron transport chain.• occur in the mitochondrion•oxygen•produces most ATP / CO2/ H2O

Summary of Cellular Respiration

Total ATP Production

2 ATP – Glycolysis2 ATP – Citrus Acid Cycle34 ATP – Electron Transport Chain

38 ATP – Total energy released from one molecule of glucose.

Oxygen Debt

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• oxygen not available

• glycolysis continues

• pyruvic acid converted to lactic acid

Oxygen debt – amount of oxygen needed by liver to convert lactic acid to glucose

What happens to the lactic acid once it has accumulated?

• The liver filters the blood and rids the body of toxins. Lactic acid is a toxin.

• liver converts lactic acid to glucose

Muscle Fatigue

• Muscle fatigue-Muscle fatigue- is a state of physiological inability to contract

• commonly caused from – decreased blood flow– ion imbalances– accumulation of lactic acid

Cramp – sustained, involuntary contraction

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Muscle Cramp

The exact cause of muscle cramps is still unknown, but the theories most commonly cited include: – Altered neuromuscular control – Dehydration – Electrolyte depletion – Poor conditioning – Muscle fatigue – Doing a new activity

Muscle Cramp

Muscle ToneMuscle Tone

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Muscle tone Muscle tone – continuous state of partial contraction

-Even when a muscle appears to be at rest, a certain amount of sustained contraction is occurring in its fibers.

AtrophyAtrophy – a wasting away or decrease in size of an organ or tissue.

HypertrophyHypertrophy – Enlargement of an organ or tissue.

Types of Contractions

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2. Isotonic – muscle contracts and changes length

2. Concentric – (positive) shortening contraction

1. Eccentric – (negative) lengthening contraction

1. Isometric – muscle contracts but does not change length

Two TypesTwo Types

Two Types of Isotonic ContractionsTwo Types of Isotonic Contractions

Types of Contractions

Smooth and Cardiac Muscle

Smooth Muscle Fibers

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Compared to skeletal muscle fibers• shorter• single nucleus• elongated with tapering ends• myofilaments randomly organized• no striations

Two Types of Smooth Muscle

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Visceral Smooth MuscleVisceral Smooth MuscleLocation - walls of most hollow organs (intestine)• contractions are slow and sustained•exhibit rhythmicityrhythmicity – pattern of repeated contractions• exhibit peristalsisperistalsis – wave-like motion that helps substances through passageways.

Multiunit Smooth MuscleMultiunit Smooth Muscle• irises of eye• walls of blood vessels• contractions are rapid and vigorous• similar to skeletal muscle tissue

Smooth Muscle Contraction

• Resembles skeletal muscle contraction• interaction between actin and myosin• both use calcium and ATP• both depend on impulses

• Different from skeletal muscle contraction• hormones affect smooth muscle• stretching can trigger smooth muscle contraction• smooth muscle slower to contract and relax• smooth muscle more resistant to fatigue

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Cardiac Muscle

AnatomyAnatomy• only in the heart• striated uninuclear cells join end-to-end forming a network• arrangement of actin and myosin are not as organized as

skeletal musclePhysiologyPhysiology• self-exciting tissue (Pacemaker)• rhythmic contractions• involuntary, all or nothing contractionsPumps blood to:Pumps blood to:• 1. lungs for oxygenation• 2. body for distribution of O2 and nutrients

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