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CHAPTER 12 - Directly Gated Transmission (Nerve-Muscle Synapse)

Terms in this set (5)

neuromusclar junction
the synapse where motor neurons and skeletal muscle fiber meet
Describe the process of chemical synaptic signaling at the neuromuscular junction
At the muscle, the motor axon ramifies into several fine branches. Each branch forms multiple swellings called synaptic boutons, which are covered by a thin layer of Schwann cells.

The boutons contact a specialized region of the muscle fiber membrane, the end-plate, and are separated from the muscle membrane by a synaptic cleft. Each bouton contains mitochondria and synaptic vesicles clustered around active zones, where the neurotransmitter acetylcholine (ACh) is released. Immediately under each bouton in the end-plate are several junctional folds, the crests of which contain a high density of ACh receptors.

The muscle fiber and nerve terminal are covered by a layer of connective tissue, the basal lamina, consisting of collagen and glycoproteins. Unlike the cell membrane, the basal lamina is freely permeable to ions and small organic compounds, including the ACh transmitter. Both the presynaptic terminal and the muscle fiber secrete proteins into the basal lamina, including the enzyme acetylcholinesterase, which inactivates the ACh released from the presynaptic terminal by breaking it down into acetate and choline. The basal lamina also organizes the synapse by aligning the presynaptic boutons with the postsynaptic junctional folds.
To trigger an action potential,
a synaptic potential must recruit neighboring voltage-gated Na+ channels
The end-plate potential resulting from the opening of acetylcholine receptor-channels opens
Voltage-gated sodium channels.
Describe the process of opening of acetylcholine receptor channels
1. ACh binding to receptor-channel molecule
2. Channel opening
3. Na+ inflow K+ outflow
4. Depolarization (end-plate potential)
5. Opening of voltage-gated Na+ channels
6. Na+ inflow
7. Depolarization
8. Action potential
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