HES 319 Lecture Notes - Alpha Motor Neuron, Motor Unit, Myocyte
Document Summary
An alpha motor neuron and all the muscle fibers it innervates. A pool of motor neurons lie in an elongated cluster (motor nucleus) over 1-4 spinal segments. Motor neurons for one muscle are clustered together. The dendritic trees of alpha motor neurons receive synaptic inputs from sensory neurons, spinal interneurons, and descending motor neurons. A typical muscle consists of many thousands of muscle fibers working in parallel, and organized into a smaller number of motor units. When an axon reaches the muscle, it branches and innervates from a few fibers up to several thousand muscle fibers. The muscle fibers that belong to a motor unit reside in a portion of the muscle. A motor unit has a certain territory where the muscle fibers from that motor unit are. In cross section we see muscle fibers from different motor units are intermingled. Motor units vary in their response properties (speed, force)