Neuromuscular Junction

High Yield Facts ⭆ Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage dependent calcium channels to allow calcium ions to enter the neuron. Calcium ions bind to synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. Motor neurons release acetylcholine (ACh) neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine ionotropic receptors (nAChRs) on the cell membrane of the muscle fiber. The binding of ACh to the receptor can depolarize the muscle fiber, results in muscle contraction.

Normally, Acetylcholine (ACh) binds to α-subunit of Acetylcholine Receptor (AChR) at postsynaptic junction. Which ion is responsible for transmission of impulse from postsynaptic junction to nerve fibers?

  1. Chloride (Cl)
  2. Calcium (Ca)
  3. Sodium (Na)
  4. Magnesium (Mg)

Neuromuscular Junction

Presynaptic Fibre (Acetylcholine) ⇒ Synaptic Cleft ⇒ Postsynaptic Fibre (Acetylcholine Receptors)
Neuromuscular junction is a site of transmission of electric impulse between a neuron and a muscle cell. Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage dependent calcium channels to allow calcium ions to enter the neuron. The arrival of a nerve impulse at the presynaptic terminals causes the movement toward the presynaptic membrane of membrane-bound sacs, or synaptic vesicles, which fuse with the membrane and release a chemical substance called a neurotransmitter. This substance transmits the nerve impulse to the postsynaptic fibre by diffusing across the synaptic cleft and binding to receptor molecules on the postsynaptic membrane. The chemical binding action alters the shape of the receptors, initiating a series of reactions that open channel-shaped protein molecules. Electrically charged ions then flow through the channels into or out of the neuron. This sudden shift of electric charge across the postsynaptic membrane changes the electric polarization of the membrane, producing the postsynaptic potential (PSP).
Calcium ions bind to synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. Motor neurons release acetylcholine (ACh) neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine ionotropic receptors (nAChRs) on the cell membrane of the muscle fiber. The binding of ACh to the receptor can depolarize the muscle fiber, results in muscle contraction.

Reference:

Finsterer, Josef, Lea Papic, and Michaela Auer-Grumbach. "Motor neuron, nerve, and neuromuscular junction disease." Current opinion in neurology 24.5 (2011): 469-474.

[Answer is C. Sodium]

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