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Physiological Psychology ·
Lower motor neurons (LMNs) are the motoneurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles.
Lower motor neurons are classified based on the type of muscle fiber they block. Alpha motor neurons (α-MNs) innervate extrafusal muscle fibers, the most numerous type of muscle fiber and the one most involved in contracting in a muscle. Gamma motor neurons (γ-MNs) innervate intrafusal muscle fibers, which are involved with muscle spindles and the sense of body position.
At the anterior horn cells within the spinal cord glutamate released from the upper motor neurons triggers depolarization in the lower motor neurons causing an action potential to propagate the length of the axon to the neuromuscular junction where acetylcholine is released to carry the signal across the synaptic cleft to the postsynaptic receptors of the muscle cell membrane, signaling the muscle to contract.
Consequences of lesionsEdit
Damage to lower motor neurons is indicated by abnormal EMG potentials, fasciculations, paralysis, weakening of muscles, and neurogenic atrophy of skeletal muscle.
|Histology: nervous tissue|
|Neurons (gray matter)
soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine, apical dendrite, basal dendrite)
types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
| Afferent nerve/Sensory nerve/Sensory neuron
GSA, GVA, SSA, SVA, fibers (Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain)
| Efferent nerve/Motor nerve/Motor neuron
GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (α motorneuron, γ motorneuron)
neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
| Sensory receptors
Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
| Glial cells
astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
| Myelination (white matter)
Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
| Related connective tissues
epineurium, perineurium, endoneurium, nerve fascicle, meninges