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Upper motor neuron
The motor tract
Anatomical terminology
[edit on Wikidata]
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 in the cerebral cortex are the main source of voluntary movement.
They are the larger pyramidal cells in the cerebral cortex. There is a type of giant pyramidal cell called Betz cells and are found just below the surface of the cerebral cortex within layer V of the primary motor cortex. The cell bodies of Betz cell neurons are the largest in the brain, approaching nearly 0.1mm in diameter.
The primary motor cortex, or precentral gyrus, is one of the most important areas in the frontal lobe. The precentral gyrus is the most posterior gyrus of the frontal lobe and it lies anterior to the central sulcus. The pyramidal cells of the precentral gyrus are also called upper motor neurons. The fibers of the upper motor neurons project out of the precentral gyrus ending in the brainstem, where they will decussate (intersect) within the lower medulla oblongata to form the lateral corticospinal tract on each side of the spinal cord. The fibers that do not decussate will pass through the medulla and continue on to form the anterior corticospinal tracts. The upper motor neuron descends in the spinal cord to the level of the appropriate spinal nerve root. At this point, the upper motor neuron synapses with the lower motor neuron, each of whose axons innervate a fiber of skeletal muscle.[1][2]
These neurons connect the brain to the appropriate level in the spinal cord, from which point nerve signals continue to the muscles by means of the lower motor neurons. The neurotransmitter glutamate transmits the nerve impulses from upper to lower motor neurons, where it is detected by glutamatergic receptors.
Contents
1Pathways
2Lesions
3See also
4References
5External links
Pathways
Upper motor neurons travel in several neural pathways through the central nervous system (CNS):
Tract
Pathway
Function
corticospinal tract
from the motor cortex to lower motor neurons in the ventral horn of the spinal cord
The major function of this pathway is fine voluntary motor control of the limbs. The pathway also controls voluntary body posture adjustments.
corticobulbar tract
from the motor cortex to several nuclei in the pons and medulla oblongata
Involved in control of facial and jaw musculature, swallowing and tongue movements.
colliculospinal tract (tectospinal tract)
from the superior colliculus to lower motor neurons
Involved in involuntary adjustment of head position in response to visual information.
rubrospinal tract
from red nucleus to lower motor neurons
Involved in involuntary adjustment of arm position in response to balance information; support of the body.
vestibulospinal tract
from vestibular nuclei, which processes stimuli from semicircular canals
It is responsible for adjusting posture to maintain balance.
reticulospinal tract
from reticular formation
Regulates various involuntary motor activities and assists in balance.
Lesions
Any upper motor neuron lesion, also known as pyramidal insufficiency, occurs in the neural pathway above the anterior horn of the spinal cord. Such lesions can arise as a result of stroke, multiple sclerosis, spinal cord injury or other acquired brain injury. The resulting changes in muscle performance that can be wide and varied are described overall as upper motor neuron syndrome. Symptoms can include muscle weakness, decreased motor control including a loss of the ability to perform fine movements, increased vigor (and decreased threshold) of spinal reflexes including spasticity, clonus (involuntary, successive cycles of contraction/relaxation of a muscle), and an extensor plantar response known as the Babinski sign.[3]
See also
Lower motor neuron
Upper motor neuron lesion
Lower motor neuron lesion
References
^Saladin, Kenneth S. Anatomy & Physiology: the Unity of Form and Function. Dubuque: McGraw-Hill, 2010. Print.1
^"Frontal Lobe." Rice University Web Calendar. 26 June 2000. Web. 06 Dec. 2010. <"Archived copy". Archived from the original on 2010-07-26. Retrieved 2010-12-07.CS1 maint: Archived copy as title (link)>.
^Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark (9 May 2018). "Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome". Archived from the original on 3 May 2018. Retrieved 9 May 2018 – via www.ncbi.nlm.nih.gov.
External links
"motoneuron" at Dorland's Medical Dictionary
v
t
e
Nervous tissue
CNS
Tissue Types
Grey matter
White matter
Projection fibers
Association fiber
Commissural fiber
Lemniscus
Nerve tract
Decussation
Neuropil
Meninges
Cell Types
Neuronal
Pyramidal
Purkinje
Granule
Spindle
Interneuron
Glial
insulating:
Myelination: Oligodendrocyte
other
Astrocyte
Ependymal cells
Tanycyte
Microglia
PNS
General
Dorsal
Root
Ganglion
Ramus
Ventral
Root
Ramus
Ramus communicans
Gray
White
Autonomic ganglion (Preganglionic nerve fibers
Postganglionic nerve fibers)
Nerve fascicle
Funiculus
Connective tissues
Epineurium
Perineurium
Endoneurium
Neuroglia
Myelination: Schwann cell
Neurilemma
Myelin incisure
Node of Ranvier
Internodal segment
Satellite glial cell
Neurons/ nerve fibers
Parts
Soma
Axon hillock
Axon
Telodendron
Axon terminals
Axoplasm
Axolemma
Neurofibril/neurofilament
Dendrite
Nissl body
Dendritic spine
Apical dendrite/Basal dendrite
Types
Bipolar
Unipolar
Pseudounipolar
Multipolar
Interneuron
Renshaw
Afferent nerve fiber/ Sensory neuron
GSA
GVA
SSA
SVA
fibers
Ia or Aα
Ib or Golgi or Aα
II or Aβ and Aγ
III or Aδ or fast pain
IV or C or slow pain
Efferent nerve fiber/ Motor neuron
GSE
GVE
SVE
Upper motor neuron
Lower motor neuron
α motorneuron
β motorneuron
γ motorneuron
Termination
Synapse
Electrical synapse/Gap junction
Chemical synapse
Synaptic vesicle
Active zone
Postsynaptic density
Autapse
Ribbon synapse
Neuromuscular junction
Sensory receptors
Meissner's corpuscle
Merkel nerve ending
Pacinian corpuscle
Ruffini ending
Muscle spindle
Free nerve ending
Nociceptor
Olfactory receptor neuron
Photoreceptor cell
Hair cell
Taste bud
UpToDate Contents
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… combination of upper and lower motor neuron signs and symptoms. The upper motor neuron findings of weakness with slowness, hyperreflexia, and spasticity result from degeneration of frontal motor neurons located …
…and drift downward. A unilateral pronator drift in one arm suggests an upper motor neuron lesion affecting that arm. In the upper extremities, test shoulder abduction, elbow extension, elbow flexion, wrist …
…genetic, inflammatory/immunologic, infectious, neoplastic, toxic, or metabolic in origin Upper motor neuron impairment can occur with the common acute stroke syndromes, space occupying lesions of the …
… involvement of upper and/or lower motor neurons. ALS is the most common form of motor neuron disease. The diagnosis of ALS is based upon clinical criteria that include the presence of upper motor neuron and lower …
… spectrum, with potentially different etiologies that share a final common pathway leading to upper and lower motor neuron degeneration. It is therefore appropriate to place ALS among the neurodegenerative diseases …
English Journal
Predicting centre of mass horizontal speed in low to severe swimming intensities with linear and non-linear models.
de Jesus K, de Jesus K, Ayala HVH, Dos Santos Coelho L, Vilas-Boas JP, Fernandes RJP.
Journal of sports sciences. 2019 Jul;37(13)1512-1520.
We aimed to compare multilayer perceptron (MLP) neural networks, radial basis function neural networks (RBF) and linear models (LM) accuracy to predict the centre of mass (CM) horizontal speed at low-moderate, heavy and severe swimming intensities using physiological and biomechanical dataset. Ten t
Exploring the frequency and clinical background of the "zebra sign" in amyotrophic lateral sclerosis and multiple system atrophy.
Sugiyama A, Sato N, Kimura Y, Shigemoto Y, Suzuki F, Morimoto E, Takahashi Y, Matsuda H, Kuwabara S.
Journal of the neurological sciences. 2019 Jun;401()90-94.
In amyotrophic lateral sclerosis (ALS), the "zebra sign" in the precentral gyrus on phase difference enhanced magnetic resonance imaging (PADRE) recently has been reported as a possible imaging biomarker for upper motor neuron (UMN) involvement. A previous study has shown that the "zebra sign" allow
Grapperon AM, Ridley B, Verschueren A, Maarouf A, Confort-Gouny S, Fortanier E, Schad L, Guye M, Ranjeva JP, Attarian S, Zaaraoui W.
Radiology. 2019 Jun;()182276.
Background Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that mainly affects the upper and lower motor neurons. Recent sodium (Na) MRI studies have shown that abnormal sodium concentration is related to neuronal suffering in neurodegenerative conditions. Purpose To use Na
… We herein report the first case of Klinefelter syndrome with a rare mosaic form of 47, XXY and 48, XXXY, combined with both spastic paraplegia and peripheral motor neuropathy. … A motor nerve conduction study and the magnetic motor evoked potential suggested motor axonal neuropathy and corticospinal tract disorders. …
… We herein report the first case of Klinefelter syndrome with a rare mosaic form of 47, XXY and 48, XXXY, combined with both spastic paraplegia and peripheral motor neuropathy. … A motor nerve conduction study and the magnetic motor evoked potential suggested motor axonal neuropathy and corticospinal tract disorders. …
The central nervous system provides the activity of skeletal muscles through two sets of neurons- the upper and the lower motor neuron. Upper motor neuron is a neuron that starts at the cerebral cortex or brainstem and creates a ...
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The function of the UMN can be thought of as similar to that of the corticospinal tract i.e. to facilitate voluntary movement. To be more specific, one cortical motor neuron is responsible for activating a group of muscles at different times ...