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Acetylcholine binds to nicotinic acetylcholine receptors of alpha-motor neurons. [3] The somatic nervous system controls all voluntary muscular systems within the body, and the process of voluntary reflex arcs. [10] The basic route of nerve signals within the efferent somatic nervous system involves a sequence that begins in the upper cell ...
The general (spinal) somatic efferent neurons (GSE, somatomotor, or somatic motor fibers) arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord. They exit the spinal cord through the ventral roots , carrying motor impulses to skeletal muscle through a neuromuscular junction .
A motor neuron (or motoneuron or efferent neuron [1]) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. [2]
Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles to contract or relax. UMNs represent the major origin point for voluntary somatic movement.
The central nervous system is responsible for the orderly recruitment of motor neurons, beginning with the smallest motor units. [4] Henneman's size principle indicates that motor units are recruited from smallest to largest based on the size of the load. For smaller loads requiring less force, slow twitch, low-force, fatigue-resistant muscle ...
This is an activity-dependent event. Partial blockage of the receptor leads to retraction of corresponding presynaptic terminals. Later they used a connectomic approach, i.e., tracing out all the connections between motor neurons and muscle fibers, to characterize developmental synapse elimination on the level of a full circuit.
In the direct pathway, the motor cortices send activating signals to the caudate and putamen (which together form the dorsal striatum). The cells of the direct pathway in the caudate and putamen that receive these signals are inhibitory and, once they become activated, send inhibitory signals to the GPi and SNpr and stop activity there.
Unlike the topographic maps of the senses, the neurons of the motor cortex are efferent neurons that exit the brain instead of bringing information to the brain through afferent connections. The motor system is responsible for initiating voluntary or planned movements ( reflexes are mediated at the spinal cord level, so movements that ...