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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]
There are three types of efferent fibers: general somatic efferent fibers (GSE), general visceral efferent fibers (GVE) and special visceral efferent fibers (SVE). Subtypes of general somatic efferent fibers include: alpha motor neurons (α) – these target extrafusal muscle fibers, and gamma motor neurons (γ) that target intrafusal muscle fibers.
A motor nerve, or efferent nerve, is a nerve that contains exclusively efferent nerve fibers and transmits motor signals from the central nervous system (CNS) to the muscles of the body. This is different from the motor neuron , which includes a cell body and branching of dendrites, while the nerve is made up of a bundle of axons.
Afferent neurons convey information from tissues and organs into the central nervous system and are also called sensory neurons. Efferent neurons (motor neurons) transmit signals from the central nervous system to the effector cells. Interneurons connect neurons within specific regions of the central nervous system.
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 .
The pyramidal tracts include both the corticobulbar tract and the corticospinal tract.These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body.
General visceral efferent fibers (GVE), visceral efferents or autonomic efferents are the efferent nerve fibers of the autonomic nervous system (also known as the visceral efferent nervous system) that provide motor innervation to smooth muscle, cardiac muscle, and glands (contrast with special visceral efferent (SVE) fibers) through postganglionic varicosities.
The lateral vestibulospinal tract is a group of descending extrapyramidal motor neurons, or efferent nerve fibers. [2] This tract is found in the lateral funiculus, a bundle of nerve roots in the spinal cord. The lateral vestibulospinal tract originates in the lateral vestibular nucleus (Deiters’ nucleus) in the pons. [2]