Cerebrum: Sulci, Gyri, and Functional Cortical Areas

External Features of the Cerebrum

• Surfaces of the Cerebrum: The cerebrum is characterized by three distinct surfaces:

  • Superolateral surface: The convex outer surface facing the skull vault.
  • Medial surface: The flat vertical surface facing the longitudinal fissure and the opposite hemisphere; notable for the presence of the corpus callosum.
  • Inferior surface: The "under surface" of the brain, which rests on the floor of the cranial fossae.

• Poles of the Cerebrum: There are three prominent ends or "poles" on each hemisphere:

  • Frontal pole: The anterior-most point of the frontal lobe.
  • Occipital pole: The posterior-most point of the occipital lobe.
  • Temporal pole: The anterior-most point of the temporal lobe.

• Lobes of the Cerebrum: The cerebrum is divided into primary and secondary lobes:

  • Frontal lobe: Located anterior to the central sulcus.
  • Parietal lobe: Located posterior to the central sulcus and superior to the lateral sulcus.
  • Occipital lobe: The posterior-most lobe, separated from the parietal lobe by the parieto-occipital sulcus (on the medial surface).
  • Temporal lobe: Located inferior to the lateral sulcus.
  • Limbic lobe: A functional lobe involved in emotion and memory, often seen on the medial surface surrounding the corpus callosum.
  • Insular lobe: (Also known as the Insula) Deeply situated within the lateral sulcus, hidden by the opercula of the frontal, parietal, and temporal lobes.

• Additional Landmarks and Labels:

  • Pre-occipital Notch: An indentation on the inferolateral border of the hemisphere, approximately $5\,cm$ anterior to the occipital pole.
  • Gurt breves: (As denoted in the source material diagram).

Sulci and Gyri of the Inferior Surface

• Division of the Inferior Surface: The inferior surface is divided into two parts by the stem of the lateral sulcus: the Orbital surface (anterior) and the Tentorial surface (posterior).

• Orbital Surface:

  • Olfactory sulcus: A straight sulcus running anteroposteriorly in the medial part of the orbital surface. It lodges the olfactory bulb and the olfactory tract.
  • Gyrus rectus: The straight gyrus located medially to the olfactory sulcus.
  • Orbital gyri: A complex of gyri (often H-shaped) located lateral to the olfactory sulcus.

• Tentorial Surface:

  • Collateral sulcus: A long sulcus running along the medial part of the tentorial surface. Its anterior end is known as the rhinal sulcus.
  • Parahippocampal gyrus: Located medial to the collateral sulcus. It is continuous anteriorly with the uncus and posteriorly with the lingual gyrus.
  • Occipito-temporal sulcus: Located lateral to the collateral sulcus.
  • Medial and Lateral Occipitotemporal Gyri: The occipito-temporal sulcus separates the Medial occipitotemporal gyrus (MOTG) from the Lateral occipitotemporal gyrus (LOTG).

Functional Cortical Areas of the Superolateral Surface

• Motor Cortical Areas (Frontal Lobe):

  • Primary Motor Cortex (Area $4$): Responsible for the execution of voluntary movements.
  • Pre-motor Cortex (Area $6$): Involved in the planning and sequencing of complex movements.
  • Frontal Eye Field (Area $8$): Controls voluntary scanning movements of the eyes.
  • Prefrontal Cortex (Areas $9, 10, 11, \text{ and } 12$): Involved in executive functions, personality, and decision-making.
  • Broca’s Speech Area (Motor Speech Area): Located in the inferior frontal gyrus (specifically the dominant hemisphere). It comprises:
    • Area $44$: Pars posterior (or pars opercularis).
    • Area $45$: Pars triangularis.

• Sensory Cortical Areas (Parietal, Temporal, and Occipital Lobes):

  • Primary Somatosensory Cortex (Areas $3, 1, 2$): Located in the postcentral gyrus; receives general sensory input (touch, pain, temperature).
  • Association Areas for Somatic Sensation: Includes higher association areas (Areas $5 \text{ and } 7$) for processing and interpreting somatic input.
  • Primary Auditory Cortex (Areas $41, 42$): Located in the superior temporal gyrus.
  • Wernicke’s Area (Auditory Association Area): Critical for the comprehension of written and spoken language.
  • Taste Area: Involved in gustatory perception.
  • Primary Visual Cortex (Area $17$): Located around the calcarine sulcus on the occipital lobe.
  • Visual Association Cortex (Areas $18, 19$): Surrounds the primary visual cortex; essential for interpreting visual stimuli.

Sulci, Gyri, and Functional Areas of the Medial Surface

• Prominent Landmarks:

  • Corpus callosum: The largest commissural bundle connecting the two hemispheres; the most prominent landmark on the medial surface.
  • Septum pellucidum: A thin membrane attached to the under surface of the anterior part of the corpus callosum.
  • Fornix: A bundle of fibers attached to the posterior part of the corpus callosum.
  • Thalamus: An ovoid mass of grey matter located below the fornix.

• Gyri and Functional Areas:

  • Cingulate gyrus: Located immediately superior to the corpus callosum, separated by the callosal sulcus.
  • Medial frontal gyrus: The portion of the frontal lobe seen on the medial surface.
  • Paracentral lobule: The U-shaped gyrus surrounding the end of the central sulcus on the medial surface. It is divided into:
    • Anterior part: Corresponds to Area $4$ (Motor control of lower limb and perineum).
    • Posterior part: Corresponds to Areas $3, 1, 2$ (Sensory perception from lower limb and perineum).
  • Supplementary Motor Cortex (Area $6$): Located on the medial surface anterior to the paracentral lobule.
  • Precuneus: A quadrilateral area located between the marginal part of the cingulate sulcus and the parieto-occipital sulcus.
  • Cuneus: A triangular gyrus bounded by the parieto-occipital sulcus and the calcarine sulcus.
  • Lingual gyrus: Located inferior to the calcarine sulcus.
  • Visual Functional Areas on Medial Surface: Area $17$ is located in the walls of the calcarine sulcus, while Areas $18 \text{ and } 19$ occupy the remaining portions of the cuneus and lingual gyrus.