Muscle Physiology

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 Z line

H Band

Sarcomere Relaxed

Sarcomere Partially Contracted

Sarcomere Completely Contracted

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 UnitAll 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 + ATP Creatine phosphate + ADP

Creatine Phosphate

• Molecule with stored ATP energy

Creatine + ATPCreatine phosphate + ADP

Muscle Fatigue

• 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 Muscle Cardiac 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

THE END