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Anatomy and Physiology of Domestic Animals
Veterinary Science 135

MUSCULAR SYSTEM

The general function of the muscular system is to move the body both internally and externally.

The nervous system gives the orders; the muscular system carries them out.

I. General terminology

II. Skeletal muscle -- moves the skeleton

A. Microscopic anatomy

1. Skeletal muscle cells -- "fibers"

a. Shape

b. Nuclei

c. Striations

d. Myofibrils

e. Protein filaments

i. Actin

ii. Myosin

2. Neuromuscular junction

a. Each nerve fiber innervates >1 muscle fiber

b. Motor unit

3. Connective tissue

a. Endomysium

b. Perimysium

c. Epimysium

B. Physiology

1. Muscle contractions are initiated by nerve impulses

          a. Nerve impulse reaches neuromuscular junction

          b. Neurotransmitter (acetylcholine) binds to receptors on cell membrane

c. Impulse travels to sarcoplasmic reticulum

d. Calcium ions (Ca⁺⁺) released into sarcoplasm from sarcoplasmic reticulum

e. Ca⁺⁺ "turns on" contraction process

f. Muscle fiber contracts (shortens)

g. Ca⁺⁺ pumped back into sarcoplasmic reticulum "turns off" contraction

h. Elasticity of muscle cell returns it to original length (lengthens)

2. Contraction is all or nothing

3. Mechanics of muscle contraction

a. "Sliding" of actin filaments over myosin filaments

4. Chemistry of muscle contraction

a. Calcium

b. Adenosine triphosphate (ATP)

c. Creatine phosphate (CP)

d. Importance of oxygen & glucose

i. Glycogen

ii. Myoglobin

e. Aerobic vs anaerobic metabolism

i. Aerobic metabolism

ii. Anaerobic metabolism

5. Heat production

6. Refractory period

C. Gross anatomy

1. Muscle attachments

a. Tendon

b. Aponeurosis

c. Origin

d. Insertion

2. Muscle actions

a. Agonist (prime mover)

b. Antagonist

c. Synergist

d. Fixator

3. Muscle naming

a. Action

b. Shape

c. Location

d. Direction of fibers

e. Number of heads

f. Attachment sites

III. Cardiac Muscle -- Heart

A. Microscopic anatomy

1. Shape

2. Intercalated disks

3. Striations

4. Nuclei

B. Physiology

1. Specialized to contract rhythmically

2. Autonomic nerve supply

a. Sympathetic stimulation

b. Parasympathetic stimulation

IV. Smooth Muscle -- Internal Organs

A. Microscopic anatomy

1. Shape

2. Striations

3. Nuclei

B. Physiology

1. Visceral smooth muscle

a. Cells "linked"

b. Found primarily in walls of hollow organs

c. Continuous irregular contractions

d. Autonomic nerve supply

i. Sympathetic stimulation

ii. Parasympathetic stimulation

2. Multi-Unit smooth muscle

a. Individual units

b. Found where fine contractions needed

c. Contractions localized and discrete

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