Primary motor cortex

Jump to: navigation, search
Brain: Primary motor cortex
Ba4.png
Brodmann area 4 of human brain.
Illu cerebrum lobes.jpg
Primary motor cortex labeled as somatomotor cortex.
Gray's subject #189 821
Part of Precentral gyrus
Artery Anterior cerebral
Middle cerebral
NeuroNames ancil-421
MeSH Motor+Cortex

WikiDoc Resources for Primary motor cortex

Articles

Most recent articles on Primary motor cortex

Most cited articles on Primary motor cortex

Review articles on Primary motor cortex

Articles on Primary motor cortex in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Primary motor cortex

Images of Primary motor cortex

Photos of Primary motor cortex

Podcasts & MP3s on Primary motor cortex

Videos on Primary motor cortex

Evidence Based Medicine

Cochrane Collaboration on Primary motor cortex

Bandolier on Primary motor cortex

TRIP on Primary motor cortex

Clinical Trials

Ongoing Trials on Primary motor cortex at Clinical Trials.gov

Trial results on Primary motor cortex

Clinical Trials on Primary motor cortex at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Primary motor cortex

NICE Guidance on Primary motor cortex

NHS PRODIGY Guidance

FDA on Primary motor cortex

CDC on Primary motor cortex

Books

Books on Primary motor cortex

News

Primary motor cortex in the news

Be alerted to news on Primary motor cortex

News trends on Primary motor cortex

Commentary

Blogs on Primary motor cortex

Definitions

Definitions of Primary motor cortex

Patient Resources / Community

Patient resources on Primary motor cortex

Discussion groups on Primary motor cortex

Patient Handouts on Primary motor cortex

Directions to Hospitals Treating Primary motor cortex

Risk calculators and risk factors for Primary motor cortex

Healthcare Provider Resources

Symptoms of Primary motor cortex

Causes & Risk Factors for Primary motor cortex

Diagnostic studies for Primary motor cortex

Treatment of Primary motor cortex

Continuing Medical Education (CME)

CME Programs on Primary motor cortex

International

Primary motor cortex en Espanol

Primary motor cortex en Francais

Business

Primary motor cortex in the Marketplace

Patents on Primary motor cortex

Experimental / Informatics

List of terms related to Primary motor cortex

Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [1] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.

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 cord to 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.

Location

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 gyrus from 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.

Layers

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 fissure correspond with the legs.

This arrangement, elucidated by Wilder Penfield and others, is called a motor homunculus (Latin: little man).

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.

Pathway

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 nerve motor nuclei. (Note: a few motor fibers synapse with 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 cord as the lateral corticospinal tract.

Fibers that do not cross over in the brainstem travel 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.

Blood supply

Branches of the middle cerebral artery provide 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.

Pathology

Lesions of the precentral gyrus result in paralysis of the contralateral side of the body (facial palsy, arm-/leg monoparesis, hemiparesis) - see upper motor neuron.

Additional images

See also

External links

de:Gyrus praecentralis fi:Motorinen aivokuori


Linked-in.jpg