- Primary motor cortex
Name = PAGENAME
GraySubject = 189
GrayPage = 821
Brodmann area 4of human brain.
Caption2 = Primary motor cortex labeled as somatomotor cortex.
Artery = Anterior cerebral Middle cerebral
BrainInfoType = ancil
BrainInfoNumber = 421
MeshName = Motor+Cortex
MeshNumber = A08.186.211.730.885.213.270.548
The primary motor cortex (or M1) works in association with pre-motor areas to plan and execute movements. M1 contains large neurons known as
Betz cells which send long axons down the spinal cordto synapse onto alpha motor neurons which connect to the muscles. Pre-motor areas are involved in planning actions (in concert with the basal ganglia) and refining movements based upon sensory input (this requires the cerebellum).
Scientists have long considered arrangement of the primary motor area to be similar in all mammals.
The human primary motor cortex is located in the dorsal part of the precentral gyrus and the anterior bank of the
central sulcus. The precentral gyrus is in front of the postcentral gyrusfrom which it is separated by the central sulcus. Its anterior border is the precentral sulcus, while inferiorly it borders to the lateral fissure("Sylvian fissure"). Medially, it is contiguous with the paracentral lobule.
The "internal pyramidal layer (layer V)" of the precentral cortex contains giant (70-100 micrometers) " pyramidal neurons" (a.k.a. "Betz cells"), which send long
axons to the contralateral motor nuclei of the cranial nerves and to the lower motor neurons in the ventral horn of the spinal cord. These axons form the corticospinal tract. The " Betz cells"' along with their long axons are referred to as the upper motor neuron(UMN).
"Homunculus" or "Little Man"
There is a precise somatotopic representation of the different body parts in the primary motor cortex, with the leg area located close to the midline, and the head and face area located laterally on the convex side of the cerebral hemisphere ("motor
homunculus"). The arm and hand motor area is the largest, and occupies the part of precentral gyrus, between the leg and face area.
In humans, the lateral area of the primary motor cortex is arranged from top to bottom in areas that correspond to the buttocks, torso, shoulder, elbow, wrist, fingers, thumb, eyelids, lips and jaw. Interior sections of the motor area folding into the
medial longitudinal fissurecorrespond with the legs.
This arrangement, elucidated by
Wilder Penfieldand others, is called a motor homunculus(Latin: "little man"). [http://nawrot.psych.ndsu.nodak.edu/Courses/Psych465.S.02/Movement/Fig.%208-4.jpgHere's] a picture of it.
Not all body parts are equally represented by cell density in the motor area in proportion to their size in the body. Lips, parts of the face and hands enjoy especially large areas of cells in the motor area. Evidence suggests motor cells not used can be recruited by other cells to account for deficiencies arising from trauma such as amputation or paralysis.
As the motor
axons travel down through the cerebral white matter, they move closer together and form part of the "posterior limb" of the internal capsule.
They continue down into the
brainstem, where some of them, after crossing over to the contralateral side, distribute to the cranial nervemotor nuclei. (Note: a few motor fibers synapsewith lower motor neurons on the same side of the brainstem).
After crossing over to the contralateral side in the
medulla oblongata( pyramidal decussation), the axons travel down the spinal cordas the " lateral corticospinal tract".
Fibers that do not cross over in the
brainstemtravel down the separate ventral corticospinal tract and most of them cross over to the contralateral side in the spinal cord, shortly before reaching the lower motor neurons.
Branches of the
middle cerebral arteryprovide most of the arterial blood supply for the primary motor cortex.
The medial aspect (leg areas) is supplied by branches of the
anterior cerebral artery.
Lesions of the precentral gyrus result in
paralysisof the contralateral side of the body ( facial palsy, arm-/leg monoparesis, hemiparesis) - see upper motor neuron.
Upper motor neuron
List of regions in the human brain
* [http://www.thebrain.mcgill.ca/flash/a/a_06/a_06_cr/a_06_cr_mou/a_06_cr_mou.html Overview at mcgill.ca]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Motor cortex — Topography of human motor cortex. Different body parts are represented by distinct areas, lined up along a fold called the central sulcus. Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and … Wikipedia
Memory cells (motor cortex) — Memory cells are found in the primary motor cortex (M1), a region located in the posterior portion of the frontal lobe of the brain. Their behavior is described by Bizzi et al. as: In a baseline epoch (no force field on the end effector), they… … Wikipedia
Motor Skill Consolidation — represents the process by which motor skills are transformed from an initial fragile state, in which they are especially prone to being disrupted or lost, to a more solid or permanent state. Any newly formed motor skill, such as learning to… … Wikipedia
Motor imagery — is a mental process by which an individual rehearses or simulates a given action. It is widely used in sport training (AKA, Mental Practice of Action), neurological rehabilitation, and has also been employed as a research paradigm in cognitive… … Wikipedia
Motor coordination — is shown in this animated sequence by Eadweard Muybridge of himself throwing a disk Motor coordination is the combination of body movements created with the kinematic (such as spatial direction) and kinetic (force) parameters that result in… … Wikipedia
Primary sensory areas — The primary sensory areas are the main cerebral areas that receive sensory information from thalamic nerve projections. Though some areas of the human brain that receive primary sensory information remain poorly defined, each of the five sensory… … Wikipedia
Motor strip — The motor strip is a band running down the side of the frontal lobe of the brain that controls all bodily and bowel movements. It is another term for the Primary Motor Cortex. It is located anterior to the central sulcus. Categories: BrainBiology … Wikipedia
Motor neurone disease — Classification and external resources spinal diagram ICD 10 G12.2 … Wikipedia
Cortex — (Latin: bark , rind , shell or husk ) may refer to: Contents 1 Sciences 2 Anatomy 2.1 Organs 2.1.1 The brain 3 … Wikipedia
Motor skill — A motor skill is a learned sequence of movements that combine to produce a smooth, efficient action in order to master a particular task. The development of motor skill occurs in the motor cortex, the region of the cerebral cortex that controls… … Wikipedia