Muscle Physiology
Human Anatomy and Physiology I
Oklahoma City Community College
Dennis Anderson
Characteristics of Muscle Tissue
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Excitability (Irritability)
Contractility
Extensibility
Elasticity
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Muscle Tissue
• Skeletal Muscle
• Cardiac Muscle
• Smooth Muscle
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Skeletal Muscle
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Long cylindrical cells
Many nuclei per cell
Striated
Voluntary
Rapid contractions
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Cardiac Muscle
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Branching cells
One or two nuclei per cell
Striated
Involuntary
Medium speed contractions
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Smooth Muscle
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Fusiform cells
One nucleus per cell
Nonstriated
Involuntary
Slow, wave-like contractions
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Muscle Stimulation
Motor Neuron
Muscle
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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
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Acetylcholinesterase
Breaks Down Acetylcholine
muscle
Damaged Neuron
Acetylcholine not released
Motor Neuron
Muscle
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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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I
Z
Sarcomere
A
H
I
Z
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Binding Site
Tropomyosin
Troponin
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Myosin
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Neuromuscular Junction
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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 Unit
All 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 phosphate + ADP
Creatine + ATP
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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
Oxygen
Myoglobin
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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
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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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Refractory Periods
Skeletal Muscle
Cardiac Muscle
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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
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