NERVOUS SYSTEM (part 1.5) Sensory areas of the cortex

Sensory Areas of the Cortex

Primary sensory areas :: Sensory pathways project to specific regions of the cerebral cortex. These areas are where sensations are perceived.
Primary somatosensory cortex :: also known as general sensory area, receives general sensory input such as pain, pressure, and temperature, from the thalamus.
Taste area :: it is an area where taste sensations are consciously perceived in the cortex, and is located i_n the insula, deep to the inferior end of the postcentral gyrus.
Olfactory cortex :: is on the inferior surface of the temporal lobe and is where both conscious and unconscious responses to odor are perceived and processed.
Primary auditory cortex :: where auditory stimuli are processed by the brain, is located in the superior part of the temporal lobe.
Visual cortex :: where portions of visual images are processed, is located in the occipital lobe. In the visual cortex, color, shape, and movement are processed separately rather than as a complete “color motion picture”.
The Homunculus :: an upside-down half of this represents the pattern of the primary somatosensory cortex in each hemisphere representing the opposite side of the body, with the feet located superiorly and the head inferiorly. Each region has a homunculus.
Projection :: allows the brain to refer a stimulus to the appropriate location on the surface of the body. Example is when you feel the touch of a mosquito landing on your arm and you know exactly where to slap.

Sensory Processing

Association areas :: cortical areas that are immediately adjacent to the primary sensory areas. These areas function in the process of recognition as they receive and integrate information from the primary somatosensory area and other brain regions.

Occipital Lobe: Primary Visual Cortex

Primary visual cortex (light, vision) :: receives sensory input from the retina (light receptors in eye) which has a function of perception and processing of light.
Visual association area :: area that has complex processing of visual information (“cat “grandma”).
Visual neglect :: failure to attend to objects in affected hemispace. Its location of lesion is at the right parietal lobe.
Visual agnosia :: inability to recognize visually presented objects. Its location of lesion is at the bilateral occipitotemporal lobes.
Prosopagnosia :: inability to recognize familiar faces. Its location of lesion is at the bilateral occipitotemporal lobes.

Temporal Lobe: Primary Auditory Cortex

Primary auditory (sound, hearing) :: receives sensory input from the ear which has a function of perception and processing of sound.
Auditory association area :: area that interprets sound into context.
Cortical hearing loss :: inadequate transmission of the neural impulses from the inner ear to the temporal lobes. It is associated with diseases of the White Matter.
Cortical deafness :: affects perception of all sounds
Cortical agnosia :: affects perception of environmental sounds
Verbal auditory agnosia :: affects perception of language and results in severe receptive dysphasia
Olfactory association :: Association area of smell
Gustatory association :: Association area of taste

Parietal Lobe: Primary Somatosensory Cortex

Primary somatosensory cortex (body sensations) :: receives impulses involved in touch, pain, pressure, stretch from contralateral side of the body which has a function to process, the perception of body sensations, proprioceptive input from skin, joint, and muscles.
Somatosensory association :: complex processing of body sensations stimuli. It has the perception of complex patterns such as texture and shape of something you are holding.

Voluntary Movement

Voluntary movements :: are consciously activated to achieve a specific goal, such as walking, or typing.

  1. Cerebral cortex communicates with the basal nuclei and cerebellum to plan, coordinate and execute movements.
  2. Upper motor neurons in the premotor areas of the cerebral cortex are stimulated and send action potentials down the descending tracts to the lower motor neurons.
  3. Lower motor neurons are stimulated and they then stimulate skeletal muscles to contract.

Motor areas of the Cerebral Cortex

Motor pathways :: from the primary motor cortex, or primary motor area, and controls many voluntary movements, especially the fine motor movements of the hands.
Primary motor cortex :: occupies the precentral gyrus. Its cortical functions are spatially arranged according to the general body plan similar to the spatial arrangement of the primary somatosensory cortex.
Upper motor neurons :: these are located in three areas of the cortex. About 30% in the primary motor cortex, 30% in the premotor area, and the rest in the primary somatosensory cortex.

Frontal Lobe: Primary Motor Cortex

Primary motor cortex :: its function is for the voluntary control of skeletal muscles. Contralateral control.
Supplementary motor area :: movement sequences.
Pre-motor cortex :: it is located anterior to the primary motor cortex and is the staging area where motor functions are organized before they are initiated in the primary motor cortex.

The Prefrontal Cortex helps in Planned Movement in Man

Prefrontal area :: controls the motivation and foresight to plan and initiate movements. This association area is well developed only in primates and especially in humans.

Modifying and Refining Motor Activities: The Basal Nuclei

Basal nuclei :: important in planning, organizing and coordinating motor movements and posture.
Complex neural circuits :: these connect the basal nuclei with each other, with the thalamus, and with the cerebral cortex. These connections form several feedback loops, some of them stimulatory and others inhibitory.