Neuromuscular Junction Quiz

The motor axons are distributed to the appropriate skeletal muscles through peripheral nerves and synapses called neuromuscular junctions or end plates on skeletal muscle fibers.

Each motor fascicle is paired to one motor neuron, forming a motor unit at the NMJ.

A highly specialized region of the sarcolemma of a muscle fiber that is oval in shape and covers an area of about 3000 um².

<p>Release of acetylcholine, binding of acetylcholine, muscle contraction, removal of acetylcholine.</p> Signup and view all the answers

<p>An action potential arrives at the presynaptic terminal, causing depolarization, which opens voltage-gated Ca²⁺ channels, resulting in the release of acetylcholine into the synaptic cleft.</p> Signup and view all the answers

<p>ACh molecules diffuse across the synaptic gap to the motor end plate, bind to receptors, and cause conformational changes.</p> Signup and view all the answers

<p>The conformational changes cause the center pore to open, allowing the influx of Na⁺ and depolarization of the motor end plate, leading to muscle action potential.</p> Signup and view all the answers

<p>From choline and acetyl coenzyme A in the terminal axoplasm of motor neurons, catalyzed by choline acetyltransferase.</p> Signup and view all the answers

<p>It is synthesized from pyruvate in the mitochondria in the axon terminals.</p> Signup and view all the answers

<p>50% is extracted from extracellular fluid by a sodium-dependent active transporter system, and the other 50% is from breakdown at the NMJ.</p> Signup and view all the answers

<p>Inhibited by acetylcholine and activated by nerve stimulation.</p> Signup and view all the answers

<p>Once synthesized, ACh is stored in vesicles within the terminal button, each containing approximately 10,000 molecules.</p> Signup and view all the answers

<p>1% are immediately releasable, 80% are readily releasable, and the remainder form the stationary store.</p> Signup and view all the answers

<p>It may be spontaneous or in response to a nerve impulse.</p> Signup and view all the answers

<p>Occurs randomly and results in miniature end plate potentials.</p> Signup and view all the answers

<p>Nicotinic and muscarinic.</p> Signup and view all the answers

<p>Post-junctional receptors of the motor end plate.</p> Signup and view all the answers

<p>On average, 50 million ACh receptors are found on a normal end plate, situated on the crests of the junctional folds.</p> Signup and view all the answers

<p>Each nicotinic receptor is a protein composed of 5 polypeptide subunits forming a ring structure around a central funnel-shaped pore.</p> Signup and view all the answers

<p>Two ACh molecules bind to the alpha subunit, causing a conformational change that opens the ion channels for about 1 msec.</p> Signup and view all the answers

<p>Acetylcholine receptors found outside the neuromuscular junction.</p> Signup and view all the answers

<p>They can be present anywhere on the muscle membrane but are most concentrated around the end plate in the peri-junctional zone.</p> Signup and view all the answers

<p>These receptors are seven transmembrane G-protein coupled receptors.</p> Signup and view all the answers

<p>M1, M3, and M5: excitatory; M2 and M4: inhibitory.</p> Signup and view all the answers

<p>Instead of being an ion channel, they use a G-protein that activates second messengers when ACh binds.</p> Signup and view all the answers

<p>Muscarinic receptors are in various tissues; nicotinic receptors are mainly in the sympathetic nervous system. One uses ions (nicotinic) and the other uses G-proteins (muscarinic); nicotinic receptors are all excitatory, while muscarinic can be both excitatory and inhibitory.</p> Signup and view all the answers

<p>Extra-junctional receptors located on the pre-terminal bulb that have a positive feedback role.</p> Signup and view all the answers

<p>They increase transmitter production via a second messenger system upon acetylcholine binding.</p> Signup and view all the answers

<p>It rapidly removes ACh from the junctional gap/synaptic cleft by hydrolyzing it to choline and acetate.</p> Signup and view all the answers

<p>An ionic site processing a glutamate residue and an esteratic site containing a serine residue.</p> Signup and view all the answers

<p>Hydrolysis occurs with transfer of the acetyl group to the serine group, resulting in an acetylated enzyme and free choline.</p> Signup and view all the answers

<p>Inhibiting AChE prevents hydrolysis of ACh, resulting in prolonged end plate potentials.</p> Signup and view all the answers