Pathophysiology Nervous system
At a healthy myoneural junction, acetylcholine is responsible for stimulating muscle activity. What mechanisms are in place to prevent the continuous stimulation of a muscle fiber after the neurotransmitter is released from the presynaptic membrane? Explain in details
Sample Answer
Mechanisms preventing continuous stimulation of muscle fiber
The mechanisms involve diffusion, degradation and reuptake. Continuous stimulation of the muscle fiber is prevented through diffusion of the neurotransmitter in neighboring cells, reuptake through the cleft and degradation by enzymes like acetylcholine esterase (AChE). Once action potentials reach the terminal of nerves, further propagation of ACh occurs in the cell where channels with gated calcium are opened. These are associated with various events in the nerve terminal and result in synaptic vesicles fusing with the plasma membranes and release of the quanta of acetylcholine (ACh) present in the synaptic cleft (Blottner and Salanova, 2015). The nerve depolarization duration determines the release levels of calcium influx in the nerve terminal. After release of ACh from presynaptic vesicles, it is diffused quickly in the synaptic cleft in microseconds to arrive at the post synaptic membrane receptors known as the acetylcholine esterase (AChE). The AChE enzyme is mainly found at the neuromuscular junctions postsynaptic and it immediately hydrolyzes or breaks down acetylcholine (ACh) into choline and acetic acid (Trang and Khandhar, 2019).
Its main role is terminating neuronal signaling and transmission between synapses therefore preventing dispersal of ACh and activation of nearby receptors. After it is broken down, instant reuptake occurs by the presynaptic nerve terminal for de novo transmitter synthesis (Blottner and Salanova, 2015). The interaction of AChE with the ACh substrate leads to the hydrolysis, breakdown and inactivation of ACh as well as subsequent controlling of ACh amounts in the synapse. Such degradations ensure that acetylcholine will not rebind to receptors or reopen its channels, which would cause unwanted and extended contraction and excitation of muscles or continuous stimulation.
References
- Blottner, D., & Salanova, M. (2015). Neuromuscular System. In The NeuroMuscular System: From Earth to Space Life Science (pp. 63-87). Springer, Cham.
- Trang, A., & Khandhar, P. B. (2019). Physiology, Acetylcholinesterase. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK539735/
