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Alpha motor neuron lesions also result in abnormal EMG potentials (e.g., fibrillation potentials) and fasciculations, the latter being spontaneous, involuntary muscle contractions. Diseases that impair signaling between α-MNs and extrafusal muscle fibers, namely diseases of the neuromuscular junction have similar signs to those that occur with ...
An axon (from Greek ἄξων áxōn, axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body.
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]
They send an inhibitory axon to synapse with the cell body of the initial alpha neuron and/or an alpha motor neuron of the same motor pool. In this way, the Renshaw cell action represents a negative feedback mechanism. A Renshaw cell may be supplied by more than one alpha motor neuron collateral and it may synapse on multiple motor neurons.
The axon leaves the soma at a swelling called the axon hillock and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. Neurons may lack ...
There are four subdivisions of group A nerve fibers: alpha (α) Aα; beta (β) Aβ; , gamma (γ) Aγ, and delta (δ) Aδ. These subdivisions have different amounts of myelination and axon thickness and therefore transmit signals at different speeds. Larger diameter axons and more myelin insulation lead to faster signal propagation.
At the time of Henneman’s initial study of motor neuron recruitment, [1] it was known that neurons varied greatly in size, that is in the diameter and extent of the dendritic arbor, size of the soma, and diameter of axon. However, the functional significance of neuron size was not yet known.
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.