MICROANATOMY

Detailed explanation-1: -Muscle contraction begins when the nervous system generates a signal. The signal, an impulse called an action potential, travels through a type of nerve cell called a motor neuron. The neuromuscular junction is the name of the place where the motor neuron reaches a muscle cell.

Detailed explanation-2: -Skeletal muscle contraction begins first at the neuromuscular junction, which is the synapse between a motoneuron and a muscle fiber. Propagation of action potentials to the motoneuron and subsequent depolarization results in the opening of voltage-gated calcium (Ca2+) channels of the presynaptic membrane.

Detailed explanation-3: -Skeletal muscle fibers are innervated by motor neurons whose cell bodies are located in the ventral horn of the spinal cord. The terminal region of the axon gives rise to very fine processes that run along skeletal muscle cells. Along these processes are specialized structures known as synapses.

Detailed explanation-4: -Skeletal muscle contraction and changes with exercise. (A) Neurotransmitter (acetylcholine, ACh) released from nerve endings binds to receptors (AChRs) on the muscle surface. The ensuing depolarization causes sodium channels to open, which elicits an action potential that propagates along the cell.

Detailed explanation-5: -Skeletal (striated) muscle contraction is initiated by “lower” motor neurons in the spinal cord and brainstem.