Neuromuscular junction, also called myoneural junction, site of chemical communication between a nerve fibre and a muscle cell. The neuromuscular junction is analogous to the synapse between two neurons. A nerve fibre divides into many terminal branches; each terminal ends on a region of muscle fibre called the end plate. Synaptic Cleft is the space between the presynaptic terminal and postsynaptic cell. It is roughly the size of 30 nm. The synaptic cleft allows the neurotransmitters to diffuse and reach the other side of the synapse or the neuromuscular junction. It also contains enzymes for the degradation of the excess or extra neurotransmitters. Embedded in the end plate are thousands of receptors, which are long protein molecules that form channels through the membrane. Upon stimulation by a nerve impulse, the terminal releases the chemical neurotransmitter acetylcholine from synaptic vesicles. Acetylcholine then binds to the receptors, the channels open, and sodium ions flow into the end plate. This initiates the end-plate potential, the electrical event that leads to contraction of the muscle fibre. Once the acetylcholine is released into the synaptic cleft, it diffuses across the synaptic cleft and binds to the acetylcholine receptors. This results in the opening of the cation channels. These channels are open to both sodium and potassium ions. As the concentration of sodium ions is higher in the extracellular space, the sodium ions enter through these open cation channels. As a result, depolarization of the skeletal muscle ensues. The depolarization of sarcolemma results in the opening of voltage-gated calcium channels locate on the sarcolemma as well as the membrane of the smooth endoplasmic reticulum

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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Neuromuscular junction, also called myoneural junction, site of chemical communication between a nerve fibre and a muscle cell. The neuromuscular junction is analogous to the synapse between two neurons. A nerve fibre divides into many terminal branches; each terminal ends on a region of muscle fibre called the end plate. Synaptic Cleft is the space between the presynaptic terminal and postsynaptic cell. It is roughly the size of 30 nm. The synaptic cleft allows the neurotransmitters to diffuse and reach the other side of the synapse or the neuromuscular junction. It also contains enzymes for the degradation of the excess or extra neurotransmitters. Embedded in the end plate are thousands of receptors, which are long protein molecules that form channels through the membrane. Upon stimulation by a nerve impulse, the terminal releases the chemical neurotransmitter acetylcholine from synaptic vesicles. Acetylcholine then binds to the receptors, the channels open, and sodium ions flow into the end plate. This initiates the end-plate potential, the electrical event that leads to contraction of the muscle fibre. Once the acetylcholine is released into the synaptic cleft, it diffuses across the synaptic cleft and binds to the acetylcholine receptors. This results in the opening of the cation channels. These channels are open to both sodium and potassium ions. As the concentration of sodium ions is higher in the extracellular space, the sodium ions enter through these open cation channels. As a result, depolarization of the skeletal muscle ensues. The depolarization of sarcolemma results in the opening of voltage-gated calcium channels locate on the sarcolemma as well as the membrane of the smooth endoplasmic reticulum.

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