primary motor cortex

Examples of primary motor cortex in the following topics:

• Motor Areas

  • The motor areas of the brain are located in both hemispheres of the cortex.
  • Primary motor cortex: Main contributor to the generation of neural impulses that control the execution of movement.
  • Premotor cortex: Located anterior to the primary motor cortex and responsible for some aspects of motor control.
  • It is located on the midline surface of the hemisphere anterior to the primary motor cortex.
  • $$Topography of the human motor cortex, including the premotor cortex, SMA, primary motor cortex, primary somatosensory cortex, and posterior parietal cortex.

• Neural Mechanisms (Cortex)

  • The primary motor cortex is the neural center for voluntary respiratory control.
  • The center for diaphragm control is posterior to the location of thoracic control (within the superior portion of the primary motor cortex).
  • The inferior portion of the primary motor cortex may be involved in controlled exhalation.
  • Topography of the primary motor cortex, on an outline drawing of the human brain.
  • Each part of the primary motor cortex controls a different part of the body.

• Mapping the Primary Somatosensory Area

  • A cortical homunculus is a pictorial representation of the anatomical divisions of the primary motor cortex and the primary somatosensory cortex, i.e., the portion of the human brain directly responsible for the movement and exchange of sensory and motor information of the body.
  • The primary somesthetic cortex (sensory) pertains to the signals within the postcentral gyrus coming from the thalamus, and the primary motor cortex pertains to signals within the precentral gyrus coming from the premotor area of the frontal lobes.
  • Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).
  • The idea of the cortical homunculus was created by Wilder Penfield and serves as a rough map of the receptive fields for regions of primary somatosensory cortex.
  • The postcentral gyrus is located in the parietal lobe of the human cortex and is the primary somatosensory region of the human brain.

• Overview of the Cerebrum

  • The frontal lobe also contains the motor cortex, which is important for planning and implementing movement.
  • These functions originate within the primary motor cortex and other frontal lobe motor areas where actions are planned.
  • Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons, which innervate the muscles.
  • Damage to motor areas of cortex can lead to certain types of motor neuron disease.
  • Notice the folded structure of the cortex: the "valleys" of the cortex are known as sulci.

• Sensory Areas

  • The cortex is commonly described as composed of three parts: sensory, motor, and association areas.
  • Parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas.
  • The primary somatosensory cortex, located across the central sulcus and behind the primary motor cortex, is configured to generally correspond with the arrangement of nearby motor cells related to specific body parts.
  • Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina.
  • Similarly, there is a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex.

• The Brain

  • The cortex of a rat or mouse is almost completely smooth.
  • The cortex of a dolphin or whale, on the other hand, is more convoluted than the cortex of a human.
  • This deep fold marks the line where the primary somatosensory cortex (main sensory receptive area for the sense of touch) and primary motor cortex (one of the principal areas of the brain involved in motor function) come together.
  • Functionally, the cortex is commonly described as comprising three parts: sensory, motor, and association areas.
  • Its functions includes relaying sensory and motor signals to the cerebral cortex and regulating consciousness, sleep, and alertness.

• Parts of the Cerebellum

  • The cerebellum, which looks like a separate structure attached to the bottom of the brain, plays an important role in motor control.
  • Based on surface appearance, three lobes can be distinguished in the cerebellum: the flocculonodular lobe, anterior lobe (above the primary fissure), and the posterior lobe (below the primary fissure).
  • Its primary connections are with the vestibular nuclei, although it also receives visual and other sensory input.
  • It sends fibers to deep cerebellar nuclei that in turn project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.
  • It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming corticopontocerebellar pathways), and sends output mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus.

• Sensory and Motor Tracts

  • The spinothalamic tract is a somatosensory tract while the corticospinal tract conducts motor impulses from the brain.
  • Both sensory pathways use three different neurons to get information from sensory receptors at the periphery to the cerebral cortex.
  • These neurons are designated primary, secondary, and tertiary sensory neurons.
  • It contains mostly motor axons.
  • The primary purpose of the corticospinal tract is voluntary motor control of the body and limbs.

• Thalamus

  • The thalamus is a small structure in the center of the brain that acts as a relay center for sensory and motor information.
  • Its functions include relaying sensory and motor signals to the cerebral cortex and regulating consciousness, sleep, and alertness.
  • Each of the primary sensory relay areas receives strong back projections from the cerebral cortex.
  • Similarly, the medial geniculate nucleus acts as a key auditory relay between the inferior colliculus of the midbrain and the primary auditory cortex.
  • The ventral posterior nucleus is a key somatosensory relay, which sends touch and proprioceptive information to the primary somatosensory cortex.

• Organization of Motor Neuron Pathways

  • The motor pathway, also called the pyramidal tract or the corticospinal tract, serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei.
  • The motor impulses originate in the giant pyramidal cells (Betz cells) of the motor area, i.e., precentral gyrus of the cerebral cortex.
  • The axons of these cells pass in the depth of the cerebral cortex to the midbrain and the medulla oblongata.
  • The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons.
  • This drawing shows the regions of the human cerebral cortex as delineated by Korvinian Brodmann on the basis of cytoarchitecture.