Action potential

1. AES 6200-10
Module 1 Discussion
Action Potential
Rick Mercadante

2. Key Terms Key Concepts
Key Definitions
● Myoneural junction or neuromuscular junction - where motor neuron and muscle fiber intersect
● Synapse - small gap between motor neuron and muscle fiber
● Sarcolemma - cell membrane of the muscle fiber
● Transverse tubules (t-tubules) - extensions of the sarcolemma that move action potential from
outside of the muscle fiber to inside
● Sarcoplasmic reticulum - muscle cell organelles
● Sarcoplasm - fluid part of muscle fiber
● Troponin - muscle protein molecule found in groove between actin filaments in cardiac and skeletal
muscles only
● Tropomyosin - rod shaped protein molecule on actin filaments essential in creating the binding of
calcium to troponin starting myosin crossbridge binding initiating muscle contraction
● End bulb - end of end of a motor neuron
● Motor end plate - specialized area of muscle fiber membrane
● Axon
● Soma
● Motor unit
● Motor neuron
● Muscle fiber
● Slow oxidative muscle fiber (SO)
● Fast oxidative glycolytic muscle fiber
(FOG)
● Fast glycolytic muscle fiber (FG)
● Fast twitch muscle fiber
● Slow twitch muscle fiber
● Type I muscle fiber
● Type IIa muscle fiber
● Type IIb muscle fiber
● Beta/slow muscle fiber
● Type IIx muscle fiber
● End bulb
● Acetylcholine (ACH)
● Synapse
● Sarcolemma
● Transverse tubules (t-tubules)
● Sliding filament model
● Sarcoplasmic reticulum
● Troponin
● Tropomyosin
● Myosin crossbridge(myosin head)
● Adenosine triphosphate (ATP)
● Adenosine diphosphate (ADP)
● Motor action potential (MAP) or just
Action potential (AP)
● Myoneural junction
● Neuromuscular junction
● Motor end plate
● Electromyography (EMG)
AES 6200-10 Applied Exercise Physiology
Module 1 Study Guide: Action Potential
Housh, T. J., Housh, D. J., & deVries, H. A. (2016). Applied exercise & sport physiology (4th ed.). Holcomb Hathaway Publishers Incorporated.
● An understanding of how the neuromuscular system works is essential to any movement professional,
coach, fitness or exercise educator, or allied exercise based health care professional.
● Action potential (AP) occurs when enough electrical stimulus is sent through the nervous system to the
motor unit of a muscle causing the muscle to contract
● Sliding filament model
○ Most widely accepted model for muscle contraction but there is still debate
○ Requires neural stimulation
● Steps leading to muscle contraction
○ Electrical impulse travels through a motor neuron to the end bulb of the neuron
○ Acetylcholine (ACH) is released
○ ACH binds to motor end plate starting AP
○ AP spreads along sarcolemma into interior of muscle fiber through t-tubules
○ AP travels to sarcoplasmic reticulum through t-tubules
○ AP causes sarcoplasmic reticulum to release calcium into sarcoplasm
○ Calcium binds to troponin
○ Troponin and calcium binding cause tropomyosin molecules to change shape
○ Changing shape of tropomyosin uncovers binding sites on actin molecule starting
myosin cross bridge to bind with actin
○ Electrical impulse ceases muscle relaxation occurs
● AP can be measured by electromyography (EMG)
○ Qualitative EMG - used to diagnose abnormal neuromuscular function
○ Quantitative EMG - used to measure amount of electrical impulse being transmitted to a
muscle and how muscle reacts under different circumstances

3. AES 6200-10 Applied Exercise Physiology
Module 1 Study Guide: Action Potential
Questions
1. What causes calcium to be released into the muscle fiber sarcoplasm?
2. What neurotransmitter is involved in AP?
3. What gap is the stimulatory neurotransmitter released into before binding the the receptor site on the
muscle fiber membrane?
4. What causes tropomyosin molecules to change shape?
5. Where does the electrical impulse pass through to get to the muscle fiber?
6. How does the AP get from the sarcolemma into the interior of the muscle fiber?
7. The intersection of the motor unit and muscle fiber is called the myoneural junction. (T/F)
8. What happens when ACH spreads along the muscle fiber cell membrane?
9. How do researchers determine how much AP is required to cause muscle contraction?
10. The sliding filament model of muscle contraction is one of many widely accepted models that explain the
mechanism of muscle contraction. (T/F)