The document discusses the microscopic anatomy and physiology of the muscular system. It identifies key structures in skeletal muscle such as myocytes, sarcoplasm, myofibers and myofibrils. The process of muscle contraction is described in four stages: nerve stimulus and acetylcholine release, generation of an action potential, muscle fiber contraction, and relaxation. Contraction occurs when calcium ions stimulate the binding of myosin to actin, pulling the sarcomere shorter. Relaxation requires ATP and the return of ions to their original positions.

1. Muscular System: Microanatomy
and Physiology
EHS Unit 3 Day 1

2. Goals
• Identify key structures in the microscopic
anatomy of skeletal muscles.
• Discuss the process of muscle contraction.

3. Muscular System Overview
• This is the term for the collective skeletal
(voluntary) muscles. There have three
functions.
– Allow movement (works with???)
– Give shape to the body, posture and compresses
the vital organs.
– Generates heat to regular temperature (what
other system regulates temp??)

4. Characteristics of Muscle Tissue
• Excitability
– Able to respond to impulse from nerve cell
• Contractility
– Able to shorten in length to produce movement.
• Extensibility
– Ability to stretch beyond resting length.
• Elasticity
– Ability to return to resting length after contracting
or stretching.

5. Structure of a Skeletal Muscle
• Made of of Myocytes
– Myocytes are long, cylindrical cells with multiple
nuclei.
– Sarcoplasm is the special cytoplasm of muscle
cells that contains myoglobin (carries oxygen) and
glycosomes (stores energy).
– These cells are also filled with fibers called
myofibers.

6. Myofibrils
• These contain the contracting units of the muscle.
– They are banded.
– The space from one Z band to the next is a sarcomere.
– Bands are created by the pattern of Myosin (thick) and
Actin (filaments)
– During muscle contraction, the sarcomere shortens from
both ends:

8. The Process of Muscle Contraction
• Occurs in Stages:
1. Nerve Stimulus and Release of ACh at
Neuromuscular Junction
2. Generation of Action Potential Across
Sarcolemma (muscle cell membrane)
3. Muscle Fiber Contraction
4. Relaxation

9. Nerve Stimulus
• An impulse originating in the central nervous
system travels through the peripheral nervous
pathway to the neuromuscular junction.
– At the synapse, the nerve releases ACh
(acetylcholine), a neurotransmitter.
– ACh receptors in the muscle bind with the ACh
molecules.
– ACh cases Ion channels to open, allowing for
generation of action potential.

10. Action Potential
• This is the term for the electrical impulse that
travels along the muscle unit.
– It is generated by the movement of ions across the
sarcolemma.
– The movement of K+ and Na+ ions create this. (A
wave of depolarization followed by repolarization)
• When stimulated, ACh opens ion gates which allow Na+
to move in rapidly. (Depolarization)
• Once ACh is broken down, Na+ gates close and K+ gates
open, allowing potassium to move out of the cell.

11. Fiber Contraction
• The action potential stimulates the release of
calcium ions in the cell.
– Calcium allows the myosin heads to bind to the
actin strands.
– ATP and phosphate are then used to produce the
contractions (the myosin pulls in a rowing motion
towards the middle of the sarcomere)

12. Relaxation
• Following contraction, the cell must return to
it’s original shape.
– ATP is used, broken into ADP and phosphate.
– Ca+ ions are returns to their location.
– Actin and Myosin return to original location.
– Relaxation is a necessary break in the contraction
cycle, because ions need to return to original
location, ATP and Oxygen need to be replenished.

13. Aerobic Vs. Anaerobic Contraction
Aerobic
• Requires oxygen
• Uses stored ATP
• Then, used direct
phosphorylation of ADP
when exertion increases.
Anaerobic
• When oxygen is depleted
and ATP or ADP production
cannot keep up with
demands (prolonged or
extremely intense exercise)
.
• Generates energy via
glycolysis.
• Produces lactic and
pyruvate acids as waste
products.

14. Muscle Fatigue
• This occurs when the muscle can no longer
respond to nerve stimulus.
– With prolonged exercise, acids (waste products)
build up in the cell and prevent the contraction
mechanism from working.
– This can also be caused by severe electrolyte
imbalance that prevents generation of action
potential. (What do we say we need if we have
cramps?)