Physiology week 15 Flashcards
What are skeletal muscles innervated by
- Large myelinated nerve fibers from motoneurons
On average how many neuromuscular junctions does each muscle fiber have
- 1
Explain the motor end plate region
A region where a large myelinated nerve fiber connects with a skeletal muscle fiber
Where do the nerve terminals branch and invaginae
- In the muscle fiber surfave but remain outside the plasma membrane
Explain the function of Schwann cells
- Cover the motor end plate, insulating it
Name the 3 synaptic components
- Synaptic gutter
- Synaptic cleft
-Subneural clefts
Explain the structure of the Synaptic gutter(synaptic trough)
The invaginated portion of the muscle membrane
Explain the location of the synaptic cleft
- Between the axon terminal and muscle fiber membrane
Explain the structure of the subneural clefts
- Small membrane folds that increase the surface are for neurotransmitter action
What degenerates ACh
- Acetylcholinesterase
Explain what happens in the Acetycholine release process starting from a nerve impulse
- A nerve impulse at the neuromuscular junction triggers the release of 125 Ach vesicles into the synaptic space
-Voltage-gated calcium channels in the neural membrane open, allowing Ca²⁺ influx, which activates Ca²⁺-calmodulin kinase.
What is the function of the enzyme phosphorylates synapsin protein
Frees the ACh vesicles to move them to the release sites to undergo excocytosis
Explain what hapens from the binding of Ach to receptors
-ACh binds to receptors near the subneural clefts, opening ACh-gated ion channels.
-These channels permit the movement of Na⁺, K⁺, and Ca²⁺, but Na⁺ influx is dominant, leading to depolarization.
-This depolarization creates the end plate potential, which triggers an action potential, causing muscle contraction.
Where is Acetycholinesterase released
Synaptic space
Weak action potentials may be due to
- Curare which blocks the ACh receptors or botulinm toxin
Where is the Ach receptors and voltage gated sodium channels located
- Near the subneural cleft
Explain the structure of the Fetal ACh receptor
- A protein complex with 5 subunits
- Fetal form: 2 alpha, 1 beta, 1 delta , 1 gamma
Explain the structure of the Adult form of ACh receptors
2 alpha, 1 beta, 1 delta ,1 Epsilon( replaces gamma)
Why does sodium influx dominates
- High extracellular Na+ and intracellular K+ concentrations
- Muscle membrane negative potential
Explain ACh breakdown
- How is is signal termination ensured
- Acetylcholinesterase in the synaptic cleft degrades ACh preventing continous muscle activation
- A small portion of ACH diffuses away ensuring signal termination
