Muscle Physiology

Human Anatomy and Physiology I

Oklahoma City Community College

Dennis Anderson

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Characteristics of Muscle Tissue

• Excitability (Irritability)

• Contractility

• Extensibility

• Elasticity

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Muscle Tissue

• Skeletal Muscle

• Cardiac Muscle

• Smooth Muscle

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Skeletal Muscle

• Long cylindrical cells• Many nuclei per cell• Striated• Voluntary• Rapid contractions

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Cardiac Muscle

• Branching cells

• One or two nuclei per cell

• Striated

• Involuntary

• Medium speed contractions

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Smooth Muscle

• Fusiform cells

• One nucleus per cell

• Nonstriated

• Involuntary

• Slow, wave-like contractions

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MuscleMotor Neuron

Muscle Stimulation

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Motor Neuron

vesicle

acetylcholine

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Myoneural Junction

muscle

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Acetylcholine Receptors

Muscle membrane

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Acetylcholine Stimulates Muscle to Contract

AcetylcholinesteraseBreaks Down Acetylcholine

muscle

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MuscleMotor Neuron

Damaged Neuron

Acetylcholine not released

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Skeletal Muscle

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Microanatomy of Skeletal Muscle

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Z line Z line

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H Band

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Sarcomere Relaxed

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Sarcomere Partially Contracted

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Sarcomere Completely Contracted

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AI IH

Sarcomere

Z Z

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Binding Site Tropomyosin

Troponin

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Myosin

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Neuromuscular Junction

Action Potential

Voltage change in a neuron or muscle cell

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Acetylcholine Opens Na+ Channel

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Muscle Contraction Summary

• Nerve impulse reaches myoneural junction

• Acetylcholine is released from motor neuron

• Ach binds with receptors in the muscle membrane to allow sodium to enter

• Sodium influx will generate an action potential in the sarcolemma

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Muscle Contraction Continued

• Action potential travels down T tubule

• Sarcoplamic reticulum releases calcium

• Calcium binds with troponin to move the troponin, tropomyosin complex

• Binding sites in the actin filament are exposed

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Muscle Contraction Continued

• Myosin head attach to binding sites and create a power stroke

• ATP detaches myosin heads and energizes them for another contraction

• When action potentials cease the muscle stop contracting

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Motor UnitAll the muscle cells controlled by one

nerve cell

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Motor Unit Ratios

• Back muscles– 1:100

• Finger muscles– 1:10

• Eye muscles– 1:1

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ATP

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Creatine

• Molecule capable of storing ATP energy

Creatine + ATP Creatine phosphate + ADP

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Creatine Phosphate

• Molecule with stored ATP energy

Creatine + ATPCreatine phosphate + ADP

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Myoglobin

• Stores oxygen in muscle cells

• Similar to hemoglobin in blood

• Has higher affinity for oxygen than hemoglobin

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Hemoglobin

Myoglobin

Oxygen

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Muscle Fatigue

• Lack of oxygen causes ATP deficit

• Lactic acid builds up from anaerobic respiration

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Muscle Atrophy

• Weakening and shrinking of a muscle

• May be caused– Immobilization

– Loss of neural stimulation

– Lack of exercise

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Muscle Hypertrophy

• Enlargement of a muscle

• More capillaries• More mitochondria• Caused by

– Strenuous exercise

– Steroid hormones

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Steroid Hormones

• Stimulate muscle growth and hypertrophy

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Anabolic Steroids

• Decrease testosterone production– Testicular shrinkage

– Infertility

• Liver tumors• Prostate cancer• Heart disease• Stroke

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Muscle Tonus

• Tightness of a muscle

• Some fibers always contracted

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Tetany

• Sustained contraction of a muscle

• Result of a rapid succession of nerve impulses

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Tetanus

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Refractory Period

• Brief period of time in which muscle cells will not respond to a stimulus

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Skeletal Muscle Cardiac Muscle

Refractory Periods

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Isometric Contraction

• Produces no movement

• Used in– Standing– Sitting– Posture

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Isotonic Contraction

• Produces movement

• Used in– Walking– Moving any part of the body

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Myasthenia Gravis

• Receptors on muscle membrane for acetylcholine are destroyed

Normal receptor

Defective receptors

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Muscular Dystrophy

• Degeneration of muscle tissue

• May be inherited– 30 different genetic diseases

• Body does not produce the protein dystrophin– Muscle cell membrane distorted

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Muscular Dystrophy

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Shin Splints

• Pain in the anterior region of the tibia

• Inflammed tibialis anterior muscle– Muscle tear– Unusual exercise

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Muscle Strain or Pull

• Excessive stretching of a muscle

• Muscle tissue may tear

• Muscle becomes inflammed and sore

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THE END