Cerebral Cortex and Functional Areas - Detailed Notes

Cerebral Cortex and Functional Areas

Learning Objectives

  • Describe the various lobes and external features of the cerebrum.
  • Illustrate the lobes, sulci, and gyri of all the surfaces of the cerebrum.
  • Name the functional areas and their significance.
  • Describe the lesions of the areas and their results.

Brain

  • The brain is like a committee of experts.
  • All parts of the brain work together, but each part has its own special properties.
  • The brain can be divided into three basic units: the forebrain, the midbrain, and the hindbrain.

Cerebrum

  • The cerebrum is divided into 2 hemispheres by a deep fissure.
  • The 2 cerebral hemispheres communicate with each other through a thick tract of nerve fibers (Corpus callosum) that lies at the base of this fissure.
  • Each cerebral hemisphere can be divided into sections, or lobes, each of which specializes in different functions.

Cerebrum - Surfaces

  • Superolateral surface
  • Medial surface
  • Inferior surface
    • Orbital
    • Tentorial

Major Sulci

  • Central: Separates motor and sensory areas.
  • Lateral: Short stem with 3 rami - anterior horizontal, ascending, & posterior.
  • Parieto-occipital: On the medial surface of the hemisphere, begins on the superomedial border 5 cm anterior to the occipital pole; meets the calcarine sulcus on the medial surface.

Frontal Lobe

Sulci
  • Precentral
  • Superior frontal
  • Inferior frontal
Gyri
  • Precentral
  • Superior frontal
  • Middle frontal
  • Inferior Frontal

Parietal Lobe

Sulci
  • Postcentral sulcus
  • Intraparietal sulcus
Gyri
  • Postcentral gyrus
  • Superior parietal lobule
  • Inferior parietal lobule

Temporal Lobe

Sulci
  • Superior temporal
  • Inferior temporal
Gyri
  • Superior temporal
  • Middle temporal
  • Inferior temporal. Inferior temporal gyrus continues on the inferior surface of the cerebrum as the lateral occipito-temporal gyrus.

Occipital Lobe

Sulci
  • Lunate sulcus
  • Transverse occipital sulcus
  • Lateral occipital sulcus

Medial Surface - Sulci and Gyri

  • Includes the paracentral lobule, cingulate gyrus, precuneus, lingual gyrus, hippocampus, and uncus.

Lobes on Medial Surface

  • Lobes are not clearly defined on this surface.
  • The corpus callosum (CC), the largest commissure, is a landmark.
  • Cingulate Gyrus: From the anterior end of the CC, continues above the CC to reach its posterior end, separated by the (supra) callosal sulcus from the CC.
  • Medial Frontal Gyrus: Lies above the cingulate gyrus, separated from the CC by the cingulate sulcus.

Inferior Surface

  • Orbital sulcus - orbital part of the inferior surface
  • Collateral sulcus runs anterior to the calcarine sulcus
  • Occipito-temporal sulcus
  • Occipito-temporal gyrus - medial and lateral
  • Parahippocampal gyrus

The Cerebral Cortex

  • Is the home of our conscious mind.
  • Enables us to:
    • Be aware of ourselves and our sensations.
    • Initiate and control voluntary movements.
    • Communicate, remember, and understand.
  • Three kinds of functional areas:
    • Motor areas
    • Sensory areas
    • Association areas (helping areas that complement the action done by primary areas).

Functional Areas Overview

  • Frontal Lobe:
    • Motor control, problem-solving, concentrating, thinking, behavior, personality, and mood.
    • Broca's Area: Speech control
  • Parietal Lobe:
    • Sensations, language, perception, body awareness, and attention.
  • Temporal Lobe:
    • Hearing, language, and memory.
    • Wernicke's Area: Language comprehension
  • Occipital Lobe:
    • Vision and perception.
  • Cerebellum:
    • Posture, balance, and coordination of movement.
  • Brain Stem:
    • Consciousness, breathing, and heart rate.

Frontal Lobe Areas

The cortex of the frontal lobe is divided into:

  • Precentral area
  • Prefrontal area
Precentral Area

Includes:

  • Primary motor area (area 4)
  • Premotor area (area 6)
  • Area 8
  • Broca's area (area 44, 45)
Primary Motor Area (Area 4)
  • Occupies the whole precentral gyrus and extends into the adjoining part of the paracentral lobule on the medial surface of the cerebral hemisphere.
  • Controls the opposite half of the body through the cortico-spinal tract.
    • Functions:
      • Carries out individual voluntary movements.
    • Lesions:
      • Results in paralysis of the contralateral half of the body (hemiplegia).
      • Fine and more skilled movements are severely affected.
Premotor Area (Area 6)
  • Occupies the posterior parts of the superior, middle, and inferior frontal gyri.
  • Extends also on the medial surface of the cerebral hemisphere in front of area 4 (medial frontal gyrus).
    • Functions:
      • Stores programs of motor activity assembled as a result of past experience.
      • Involved in involuntary movements.
    • Lesion:
      • Results in difficulty in the performance of skilled movements (because every time you perform a movement you begin from scratch).
Area 8
  • An elongated area in front of area 6 in the superior and middle frontal gyri.
  • Extends into the medial surface of the hemisphere in front of area 6 (medial frontal gyrus).
  • Contains a part of the frontal eye field.
Frontal Eye Field I
  • Includes:
    • A large part of area 8.
    • Part of area 6.
    • Area 9.
  • Function:
    • Stimulation of this region causes voluntary conjugate eye movements toward the opposite side.
Motor Speech Area of Broca (Areas 44 and 45)
  • Called anterior speech center.
  • Found in the inferior frontal gyrus.
  • Produces patterns of sequences for word production through its connections with the adjacent primary motor areas (e.g., the muscles of the larynx, mouth, tongue).
    • Lesion in Broca's area:
      • Leads to expressive aphasia (loss of ability to produce speech).
Prefrontal Area

Includes:

  • Remainder of superior, middle, and inferior frontal gyri in the supero-lateral surface of the hemisphere.
  • The remaining part of the medial frontal gyrus.
  • Cingulate gyrus.
  • Gyri in the orbital part of the inferior surface of the hemisphere (orbito-frontal area).
    • Function:
      • Concerned with intellectual functions (choosing between good and bad actions, determining similarities and differences between things).
      • Control of behavior (suppress socially unacceptable responses).
      • Retains long-term memories associated with emotions.

Parietal Lobe Areas

The cortical areas in the parietal lobe include:

  • First Somato-sensory area (SM I)
  • Second Somato-sensory area (SM II)
  • Superior parietal lobule
  • Inferior parietal lobule
First Somato-Sensory Area (Sm I)
  • Corresponds to area (3, 1, 2).
  • Occupies the post-central gyrus and extends into the medial surface of the hemisphere in the paracentral lobule.
    • Anterior part (area 3) concerned with the perception of cutaneous stimuli.
    • Posterior part (area 1, 2) concerned with the perception of proprioceptive impulses.
    • Lesion in (Sm I):
      • Leads to loss of sensations from the opposite half of the body.
      • Elements of fine touch and proprioception are markedly affected, while pain and temperature are slightly affected.
Second Somato-Sensory Area (Sm II)
  • Found above the posterior ramus of the lateral sulcus.
  • Its function is not understood.
Superior Parietal Lobule
  • Includes areas 5, 7.
  • Receives and integrates various sensory information together.
  • Contains stereognosis center.
    • Lesion in this area leads to astereognosis.
Inferior Parietal Lobule
  • Includes:
    • Angular gyrus (area 39).
    • Supra-marginal gyrus (area 40).
  • Both areas (39, 40) are parts of the posterior speech center.
Wernicke's Area
  • Called posterior speech center or sensory speech center.
  • Includes:
    • Area 39 and area 40 in the inferior parietal lobule.
    • Posterior parts of superior and middle temporal gyri in the temporal lobe.
  • Concerned with the comprehension of auditory and visual information received.
    • Lesion in Wernicke's area leads to receptive aphasia (failure to understand spoken or written words).
Primary Gustatory Area
  • Corresponds to area 43.
  • Located in the roof of the lateral sulcus.
  • Receives impulses from the opposite half of the tongue.

Occipital Lobe Areas

Primary Visual Area (Area 17)
  • Situated in the walls of the posterior part of the calcarine sulcus & extends around the occipital pole on the lateral surface of the hemisphere.
Secondary Visual Area (Area 18, 19)
  • Surrounds the primary visual area on the medial and lateral surfaces of the hemisphere.
  • Its function is to relate the visual information received by the primary visual area to past visual experiences, thus enabling the individual to recognize what he is seeing.

Temporal Lobe Areas

Primary Auditory Area (Areas 41 and 42)
  • Situated in the superior temporal gyrus.
  • Receives sounds from both ears.
    • Lesion of the auditory area produces partial deafness in both ears, but more in the contralateral ear.
Secondary Auditory Area (Area 22)
  • Situated posterior to the primary auditory area.
  • Receives impulses from the primary auditory area.
  • Responsible for the interpretation of sounds.
Olfactory Area
  • Called the piriform lobe (uncus).
  • Located on the medial surface of the temporal lobe.
  • Receives impulses from the ipsilateral side of the nose.