primary visual cortex

Examples of primary visual cortex in the following topics:

• Visual Processing

  • Visual signals are processed in the brain through several different pathways.
  • Within the nerves, different axons carry different parts of the visual signal.
  • Once in the brain, visual information is processed in several places.
  • When visual signals leave the thalamus, they travel to the primary visual cortex at the rear of the brain.
  • From the visual cortex, the visual signals travel in two directions.

• Sensory 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.
  • For example, the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left eye.
  • 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.

• Thalamus

  • It is generally believed to act as a relay between a variety of subcortical areas and the cerebral cortex.
  • For the visual system, for example, inputs from the retina are sent to the lateral geniculate nucleus of the thalamus, which in turn projects to the primary visual cortex in the occipital lobe.
  • 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.

• Cerebral Hemispheres and Lobes of the Brain

  • The left temporal lobe holds the primary auditory cortex, which is important for processing the semantics of speech.
  • The occipital lobe contains most of the visual cortex and is the visual processing center of the brain.
  • The visual cortex receives raw sensory information through sensors in the retina of the eyes, which is then conveyed through the optic tracts to the visual cortex.
  • Damage to the primary visual cortex (located on the surface of the posterior occipital lobe) can cause blindness, due to the holes in the visual map on the surface of the cortex caused by the lesions.
  • The parietal lobe is comprised of the somatosensory cortex and part of the visual system.

• Cerebral Lobes

  • The precentral gyrus, forming the posterior border of the frontal lobe, contains the primary motor cortex, which controls voluntary movements of specific body parts.
  • For example, it comprises the somatosensory cortex and the dorsal stream of the visual system.
  • This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions.
  • The temporal lobe is involved in primary auditory perception such as hearing and holds the primary auditory cortex.
  • The superior temporal gyrus includes an area where auditory signals from the ear first reach the cerebral cortex and are processed by the primary auditory cortex in the left temporal lobe.

• Overview of the Cerebrum

  • It is primarily involved in vision: seeing, recognizing, and identifying the visual world.
  • 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.
  • The cerebral cortex is the outer layer depicted in dark violet.
  • Notice the folded structure of the cortex: the "valleys" of the cortex are known as sulci.

• 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.

• 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; it is 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.

• Parts of the Cerebellum

  • Like the cerebral cortex, the cerebellum is divided into two hemispheres.
  • 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 receives proprioception input from the dorsal columns of the spinal cord (including the spinocerebellar tract) and from the trigeminal nerve, as well as from visual and auditory 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.

• 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.