W5-L2: NMJ

Question 1

What happens when an AP arrives at an axon termonal?

Answer 1

1. AP in a motor neuron arrives to the axon terminal
2. Ca2+ diffuses into the axon terminal through the channels
3. Ach is released from the vesicles to the extracellular cleft to the motor end plate
4. ACh binds to ionotropic receptors (nicotinic), opens an ion channel

Question 2

What happens when Ach opens ion channels?

Answer 2

5.Na+ and K+ pass through these channels following their diffusion gradient (Na+ moves in and K+ moves out)

Question 3

What are the final evenst at the NMJ?

Answer 3

6.Local depolarization of the motor end plate, called end-plate potential (EPP)
7.That AP is then propagated over the surface of the muscle fiber and into the T-tubules

Question 4

What is Acetylonestrase?

Answer 4

• The enzyme acetylecholinesterase breaks down Ach
• Choline of Ach is transported back into the axon terminals
  where it is reused in the synthesis of new Ach
• As more Ach is broken down, more Ach will leave the
  receptors and will be broken down
• What happens when no more Ach is bound?

Question 5

Mechanism of cytosolic increase in Ca2
Where ar the receptors?

Answer 5

DHP Receptor (Dihydropyridine Receptor): Located in the T-tubule membrane, this receptor functions as a voltage sensor. When an action potential travels down the T-tubule, it activates the DHP receptor.

Ryanodine Receptor: Located in the membrane of the sarcoplasmic reticulum (SR), this receptor is a calcium release channel. The activation of the DHP receptor triggers the opening of the ryanodine receptor, allowing calcium ions (Ca2+) to flow from the sarcoplasmic reticulum into the cytosol.

Question 6

What are the Mechanisms of cytosolic decrease Ca2+ ?

Answer 6

Need to remove Ca2+ from troponin by lowering Ca2+ concentration in the cytosol to relax
Calcium ATPase

Question 7

Interaction Between Actin and Myosin
During isometric Tension Development

Answer 7

• Length-tension curve describes relationship between length of sarcomere and amount of tension developed
• Less overlap produces less crossbridge interaction and diminished tension development
• The length-tension relationship in muscle fibers indicates that there is an optimal sarcomere length for maximum force production. Deviations from this optimal length, either by excessive shortening or stretching, result in reduced tension development due to suboptimal overlap of actin and myosin filaments, which impairs cross-bridge formation. This concept is crucial for understanding muscle function and performance, particularly in activities requiring strength and endurance.