The alpha motoneuron stimulates the extrafusal muscle fibers to contract, thus relieving the stretch. The activity of gamma motoneurons tightens the spindles, thus making them more sensitive to stretch and better able to monitor the length of the muscle, even during muscle shortening. This is a disynaptic reflex, because the sensory neurons synapse with interneurons, which in turn make inhibitory synapses with motoneurons. The sensory input also crosses the spinal cord to cause stimulation of extensor and inhibition of flexor muscles in the contralateral leg. Damage to the cerebellum produces intention tremor and degeneration of dopaminergic neurons in the basal nuclei produces Parkinson's disease.
Intermediate fibers are fast-twitch but adapted for aerobic respiration.
Also unlike the situation in skeletal muscles, action potentials can cross from one myocardial cell to another. Depending upon their neural regulation, smooth muscles can be classified as single-unit or multiunit. The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy .