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Encyclopedia > Upper motor neuron

Upper motor neurons are any neurons that carry motor information down to the final common pathway, that is, any neurons that are not directly responsible for stimulating the target muscle. The main effector neurons for voluntary movement lie within layer V of the primary motor cortex and are called Betz cells. The cell bodies of these neurons are some of the largest in the brain, approaching nearly 100μm in diameter. These neurons connect the brain to the spinal cord, from which point nerve signals continue to the muscles by means of the lower motor neurons Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse[1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... The primary motor area is a group of networked cells in mammalian brains that controls movements of specific body parts associated with cell groups in that area of the brain. ... Betz cells are pyramidal cell neurons located within the fifth layer of the grey matter in the primary motor cortex. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... In geometry, a diameter (Greek words diairo = divide and metro = measure) of a circle is any straight line segment that passes through the center and whose endpoints are on the circular boundary, or, in more modern usage, the length of such a line segment. ... A sketch of the human brain by artist Priyan Weerappuli, imposed upon his sketch of the profile of Michaelangelos David In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... The Spinal cord nested in the vertebral column. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... 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. ...


Pathways

Upper motor neurons travel in several pathways through the CNS:

  • tectospinal tract/colliculospinal tract: pathway from the superior colliculus to lower motor neurons, involved in involuntary adjustment of head position in response to visual information.
  • rubrospinal tract: pathway from red nucleus to lower motor neurons, involved in involuntary adjustment of arm position in response to balance information.
  • reticulospinal tract: pathway from reticular formation, regulates various involuntary motor activities and assists in balance.

The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... 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. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ... The corticobulbar (or corticonuclear) tract is a white matter pathway connecting the cerebral cortex to the brainstem (the term bulbar referring to the brainstem). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Position of the pons in the human brain The pons (sometimes pons Varolii after Costanzo Varolio) is a knob on the brain stem. ... Medulla in general means the inner part, and derives from the Latin word for marrow. In medicine it is contrasted to the cortex. ... The tectospinal tract is part of the indirect extrapyramidal tract and is responsible for coordinating head and eye movements, It is responsible for impulses that are motor. ... The superior colliculus is part of the brain that sits below the thalamus and surrounds the pineal gland in the mesencephalon of vertebrate brains. ... The rubrospinal tract is part of the indirect extra-pyramidal tract and is responsible for large muscle movement such as the arms and the legs. ... The red nucleus is a structure in the rostral midbrain involved in motor coordination. ... The vestibulospinal tract is one of the descending spinal tracts of the ventromedial pathway. ... See also Labyrinth, an article treating the mythical maze that imprisoned the Minotaur. ... The reticular formation is a part of the brain which is involved in stereotypical actions, such as walking, sleeping, and lying down. ...

Lesions

Upper motor neurone lesions are indicated by spasticity, exaggerated reflexes, loss of voluntary motor control and the Babinski sign. An upper motor neurone lesion is a lesion of the neural pathway above the anterior horn cell or motor nuclei of the cranial nerves. ... Spasticity is a disorder of the bodys motor system in which certain muscles are continuously contracted. ... A reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. ... In medicine (neurology), the Babinski reflex or Babinski sign is a reflex that can identify disease of the spinal cord and brain. ...


External links


  Results from FactBites:
 
Upper Motor Neuron System Hypotonia (269 words)
The term refers to all the neurons in the brain (Figure 103.1[1]), cerebellum (Figure 103.1[2]), and brainstem (Figure 103.1[3]) that directly or indirectly convey information to the motor neurons in the brainstem and in the anterior horns of the spinal cord (lower motor neurons).
Neurons from the cerebral cortex and the brainstem (red nucleus, reticular formation, and lateral vestibular nucleus) connect directly with the lower motor neurons.
Neurons from the basal ganglia and the cerebellum also influence the lower motor neurons but they do so indirectly by connecting with cortical or brainstem neurons that make direct contact with the motor neurons.
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