Question

Excitation contraction coupling in skeletal muscle

Answer 1

Excitation - contraction coupling in the skeletal muscle is the sequence of events through which the nerve fiber stimulates the skeletal muscle fiber causing its contraction. The cholinergic nerve fibers innervate the skeletal muscle fibers through the neuromuscular junctions, they release their neurotransmitters that cause activation of the muscle cell plasma membrane ligand gated ion channel-coupled receptors causing ion transport that in turn will activate the contractile mechanism of the muscle fiber.

Answer 2

The neuromuscular junction is the site where the neuronal axon terminals (synaptic terminal) of a motor neuron come in contact with the plasma membrane of the skeletal muscle fiber (motor end plate). In reality there is no physical contact between the two membranes, but rather a small gap exists, being similarly functional to the synaptic cleft of a chemical synapse. The synaptic terminal of the neuron is of a sausage-like shape being embedded within the muscle fiber rather than lying over the the cell. The area of the muscle plasma membrane comes in relative contact with the synaptic neuronal terminal, presents a highly folded membrane forming a wavy pattern when it is cut perpendicularly to the longitudinal axis of the neuromuscular junction indicating many features of the excitation-contraction coupling of the skeletal muscle fibers.

increase of the muscle fiber postsynaptic terminal surface area indicates increased number of ligand-gated ion-channel-coupled receptors on which the neurotransmitter released by the neuron can act on.

since the folds extend inside the muscle fiber it is presumed that it promotes contraction of the deeper sarcomeres when stimulation of the motor end plate occurs.

The neuromuscular junction usually refers to the interaction of an α motor neuron with a skeletal muscle fiber. The neuronal synaptic terminal are cholinergic and secrete acetylcholine (ACh) a neurotransmitter that promotes contraction of the skeletal muscle fibers. ACh introduces different effects over smooth muscle and striated muscle acting through different types of receptors. Skeletal muscle fibers contain nicotinic cholinergic receptors whereas the smooth muscle cells consist of muscarinic cholinergic receptors that are both excitatory and inhibitory.

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