On This Page:ToggleStructure and LocationFunctionsMotor HomunculusDysfunction
On This Page:Toggle
On This Page:
It can be divided into two main regions:the primary motor cortex, which initiates movements, and thenonprimary motor cortex, which handles movement planning and selection. Each hemisphere controls muscles on the opposite side of the body.
Structure and Location
The motor cortex is situated within the frontal lobe, adjacent to a groove called thecentralsulcus.
Specifically, the primary motor cortex occupies theprecentral gyrus,a ridge just in front of the central sulcus, while the nonprimary motor cortex lies anterior to this.
It maintains direct communication pathways with other motor control structures including thethalamus, basal ganglia, brain stem, andspinal cord, making it the only motor control center above the spinal cord with this capability.
Motor cortex functions
Some of the main functions of the motor cortex include:
Primary Motor Cortex Functions
The primary motor cortex initiates motor movements throughpyramidalneurons– large triangular-shaped nerve cells that serve as the main output cells. These neurons transmit movement information through two key pathways:
Rather than controlling individual muscles, the primary motor cortex orchestrates movement sequences requiring multiple muscle groups.
Nonprimary Motor Cortex
The nonprimary motor cortex consists of two specialized areas:the premotor cortex and the supplementary motor cortex.
The premotor cortexplans and executes movementswhile working with thecerebellumto select appropriate actions.
One of its most fascinating features is the presence of mirror neurons – specialized cells that activate both when performing an action and when observing others perform the same action.
This unique characteristic makes the premotor cortex essential for learning through imitation.
The supplementary motor cortexmanages more complex aspects of movement control.It executes learned motor skills and orchestrates sequences of movements, while continuously adapting actions based on sensory input.
This region is particularly important for making real-time adjustments during ongoing movements, ensuring smooth and coordinated motor actions.
Motor Homunculus
The motor homunculus isa representation of the body partsalong the primary motor cortex, or precentral gyrus.
Each movable body part is represented contralaterally, meaning the primary cortex in the right cerebral hemisphere controls motor movements on the left side of the body and vice-versa.
The body parts areorganized systematically along the gyrus– the lowest parts of the body are arranged near the top, while the head and face are arranged near the bottom.
Near the bottom of the gyrus, movements of the face, eyes, tongue, and jaw would result from activity in this area.
Body parts that perform more precise movements, such as the hands and face, have disproportionately large representations compared to those that perform simpler movements, like the trunk and legs.
Motor Vs. Sensory Homunculus
The motor homunculus is not to be confused withsensory homunculus, which is a sensory representation in thesomatosensory cortexin the postcentral gyrus.
This homunculus represents how body parts feel, whereas the motor homunculus represents how body parts move.
The regions of the body representations on the sensory homunculus differ slightly from that of the motor counterpart as some areas of the body are more sensitive to sensations rather than movements, such as the head.
Motor Cortex Dysfunction
Common causes of motor cortex damage include stroke or traumatic brain injury. When the motor cortex is damaged, it can lead toupper motor neuron syndrome, which produces several characteristic symptoms:
Recovery is possible throughneuroplasticity– the brain’s ability to reorganize and compensate for damaged areas.
Through physical and occupational therapy, healthy parts of the brain can learn to take over some motor functions, particularly when reinforced through repetitive exercise and activities.
References
Neuroscientifically Challenged (2015, October 23). Know Your Brain: Motor Cortex. https://www.neuroscientificallychallenged.com/blog/know-your-brain-motor-cortex
Knierim, J. (2020, October 20). Chapter 3: Motor Cortex. Neuroscience Online. https://nba.uth.tmc.edu/neuroscience/m/s3/chapter03.html
Flint Rehab (2020, November 19). Primary Motor Cortex Damage: Definition, Symptoms, and Treatment. https://www.flintrehab.com/primary-motor-cortex-damage/
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
