Somatic Motor Neurons

Somatic Motor Neurons

Neurons conduct nerve impulses. Motor neurons control effectors, which include the skeletal muscle. Each skeletal muscle fiber is connected in a functional manner to the axon of a motor neuron. These pass outward from the brain or spinal cord. Each func-tional connection is called a synapse. At the synapses, neurons­ communicate with other cells by releasing neurotransmitters (chemicals that enable commu-nication). Skeletal muscle fibers usually ­contract when stimulated by motor neurons.

A neuromuscular junction is the connec-tion between a motor neuron and a muscle fiber (­FIGURE 9-7). A motor end plate is formed by special-ized muscle fiber membranes and has abundant mito-chondria and nuclei, with greatly folded sarcolemmas.

Motor neurons branch out and project into muscle fiber membrane recesses. Cytoplasm at these distal ends have many mitochondria and tiny ­synaptic vesicles that contain neurotransmitters. Upon receiving impulses, the vesicles release neu-rotransmitters into the synaptic cleft between the neuron and motor end plate, stimulating muscle contraction.