At the neuromuscular junction: To terminate contraction, acetylcholine is broken down by acetylcholinesterase at the muscle cell membrane. Opening of muscarinic acetylcholine receptors increases the sodium permeability of the skeletal muscle membrane. Action potential propagation to the lower motor neuron triggers the opening of voltage gated Ca2+ channels allowing Ca2+ to flow into the cell and bind to muscle proteins triggering contraction. Action potential propagation to the lower motor neuron terminal opens voltage-gated Ca2+ channels triggering exocytosis of vesicles containing glutamate. Acetylcholine binding to acetylcholinesterase results in muscle contraction.
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In the neuromuscular junction, the stimulation of the motor neuron ultimately results in the release of the neurotransmitter acetylcholine from the presynaptic neuron into the synapse. The release of acetylcholine into the synapse is dependent on the activation of synaptotagmin, which is required for the fusion of acetylcholine-containing vesicles to the plasma membrane. Next, acetylcholine enters the synapse and binds to and activates the transmitter-gated ion channel on the muscle cell, initiating membrane depolarization and muscle contraction.
Adi S.
After acetylcholine crosses the synaptic cleft and binds to the acetylcholine receptor, the very next step that occurs at the neuromuscular junction is the opening of calcium channels in the sarcolemma. This allows calcium to rush into the muscle cell, causing the interior of the sarcolemma to go from negative to positive. Calcium is then released by the sarcoplasmic reticulum and binds to troponin, resulting in muscle contraction. Additionally, sodium pumps in the sarcolemma are activated, causing sodium to rush into the muscle cell and further changing the interior of the sarcolemma from positive to negative. Finally, sodium channels in the sarcolemma open, allowing sodium to rush into the muscle cell and causing the interior of the sarcolemma to go from negative to positive.
Supreeta N.
Muscle Contraction Worksheet Muscles will contract in response to a "message" from a motor neuron (nerve cell). Label the drawing with the correct parts of the neuron. Soma, axon, dendrite, terminal boutons (buttons), node of Ranvier, myelin sheath. Use this word list to fill in all the blanks below. Actin Action potential Acetylcholine Troponin Calcium channels Myosin Sarcoplasmic reticulum Tropomyosin Synaptic vesicles Transverse tubules Sarcolemma 1. An ______ travels down the length of the neuron's axon. 2. The Action Potential will cause ______ at the end of the axon to open. 3. Ca++ is in high concentration outside the cell & in low concentration inside the cell. Therefore, Ca++ diffuses into the axon. (Define diffusion. Does it require the input of energy?) 4. Ca++ influx causes ______ containing ______ (the neurotransmitter released at ALL skeletal muscles) to move to the axonal terminus, fuse onto the membrane, and release ACh from the neuron (exocytosis). 5. The binding of ACh to the ACh receptors on the motor end-plate initiates the formation of an action potential along the ______ of the muscle fiber!
Madhur L.
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