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In invertebrates, depending on the neurotransmitter released and the type of receptor it binds, the response in the muscle fiber could either be excitatory or inhibitory. These signals then proceed to the neuromuscular junctions of skeletal muscles.įrom there, acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors ( Nicotinic acetylcholine receptors) of muscles, thereby relaying the stimulus to contract muscle fibers. In turn, alpha motor neurons relay the stimuli received down their axons via the ventral root of the spinal cord. Upper motor neurons release a neurotransmitter, acetylcholine, from their axon terminal knobs, which are received by nicotinic receptors of the alpha motor neurons. These stimuli are conveyed from upper motor neurons through the ventral horn of the spinal cord, and across synapses to be received by the sensory receptors of alpha motor neuron (large lower motor neurons) of the brainstem and spinal cord.
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Stimuli from the precentral gyrus are transmitted from upper motor neurons and down the corticospinal tract, via axons to control skeletal (voluntary) muscles. The basic route of nerve signals within the efferent somatic nervous system involves a sequence that begins in the upper cell bodies of motor neurons (upper motor neurons) within the precentral gyrus (which approximates the primary motor cortex). The somatic nervous system processes sensory information and controls all voluntary muscular systems within the body, with the exception of reflex arcs. 2 Vertebrate and invertebrate differences.