Chapter 1 Principles of neuromuscular transmission

Abstract

Motor neurons are the efferent neural pathways that innervate the muscles of the body and are thus involved in all voluntary and involuntary movements. It is the motor neurons that actually conduct the impulses to the muscles. The motor neuron nuclei and cell bodies are located in the anterior horn of the gray matter of the spinal cord, while the metabolic and chemical processes primarily take place in the cell bodies. Axons exiting the vertebral canal from every spinal cord segment travel along the spinal nerve to the motor endplates of the muscle fibers in the target supply area where they divide off into several branches. For better insulation and more rapid conduction of impulses, the axons of motor neurons are encased in a myelin sheath. The myelin sheath is interrupted by regularly spaced nodes of Ranvier. In the vicinity of the nodes of Ranvier, the axon is in direct contact with the extracellular space. While each individual motor neuron innervates several muscle fibers, an individual muscle cell is innervated by a single axon only.