Muscle Physiology Human Anatomy and Physiology II Oklahoma City Community College Dennis Anderson

Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth Muscle

Skeletal Muscle Long cylindrical cells Many nuclei per cell Striated Voluntary Rapid contractions

Cardiac Muscle Branching cells One or two nuclei per cell Striated Involuntary Medium speed contractions

Smooth Muscle Fusiform cells One nucleus per cell Nonstriated Involuntary Slow, wave-like contractions

Microanatomy of Skeletal Muscle

Z line

H Band

Sarcomere Relaxed

Sarcomere Partially Contracted

Sarcomere Completely Contracted

Binding Site Tropomyosin Troponin

Myosin

Neuromuscular Junction

Acetylcholine Opens Na + Channel

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

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

Muscle Contraction Continued Myosin head attach to binding sites and create a power stroke ATP detaches myosin heads and energizes them for another contaction When action potentials cease the muscle stop contracting

Motor Unit All the muscle cells controlled by one nerve cell

Motor Unit Ratios Back muscles –1:100 Finger muscles –1:10 Eye muscles –1:1

ATP

Creatine Molecule capable of storing ATP energy Creatine + ATPCreatine phosphate + ADP

Creatine Phosphate Molecule with stored ATP energy Creatine + ATPCreatine phosphate + ADP

Muscle Fatique Lack of oxygen causes ATP deficit Lactic acid builds up from anaerobic respiration

Muscle Atrophy Weakening and shrinking of a muscle May be caused –Immobilization –Loss of neural stimulation

Muscle Hypertrophy Enlargement of a muscle More capillaries More mitochondria Caused by –Strenuous exercise –Steroid hormones

Steroid Hormones Stimulate muscle growth and hypertrophy

Muscle Tonus Tightness of a muscle Some fibers always contracted

Tetany Sustained contraction of a muscle Result of a rapid succession of nerve impulses

Tetanus

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

Refractory

Skeletal MuscleCardiac Muscle Refractory Periods

Isometric Contraction Produces no movement Used in –Standing –Sitting –Posture

Isotonic Contraction Produces movement Used in –Walking –Moving any part of the body

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