Cortex and Brain Structure

Introduction
- Discussion centers on the structure and functions of the cortex within the forebrain.

General Features
- The cortex, the outer surface of the brain, is highly folded and convoluted.
- Important Terminology:
- Gyrus / Gyri: The raised areas of the cortex.
- Sulcus / Sulci: The grooves or indentations on the surface of the cortex.
Hemispheric Structure
- The forebrain consists of two hemispheres: left and right.
- Both hemispheres share the same color.
- The hemispheres have lateral surfaces (exposed outer parts) and medial surfaces (facing each other).
- Corpus Callosum: A thick band of white matter (axons) connecting the two hemispheres, facilitating communication.
- Appears in coronal and sagittal views of the brain on MRI scans; has a horseshoe shape.
- Anatomically revealed in a post-mortem examination of a brain.
Lobes of the Cortex
- Each hemisphere has four distinct lobes:
- Frontal Lobe:
  - Anterior to the central sulcus.
  - Notably larger in humans compared to other mammals.
  - The frontmost point is known as the frontal pole.
- Parietal Lobe:
  - Located posterior to the central sulcus.
- Temporal Lobe:
  - Positioned inferiorly, divided from the frontal and parietal lobes by the lateral fissure.
  - The frontmost part is called the temporal pole; the back part leads to the preoccipital notch.
- Occipital Lobe:
  - Situated at the rear of the brain.
  - Bound by the parieto-occipital sulcus and the previously mentioned structures.
  - The most posterior point is the occipital pole.

Cerebrospinal Fluid (CSF)
- Surrounds the brain, providing protection and shock absorption during movement.
- Illustrations show the positioning of the skull and cortical surface, with CSF depicted in blue.
Meninges
- Three protective layers surrounding the brain:
- Dura Mater:
  - The tough outer layer, adhered to the skull (light pink representation).
- Pia Mater:
  - A thin layer that conforms to the surface contours of the brain, covering gyri and sulci.
- Arachnoid Mater:
  - Intermediate layer; includes a spongy region where CSF circulates, resembling spider legs.
Ventricles of the Brain
- Comprise spaces filled with cerebrospinal fluid (CSF).
- Types of Ventricle:
- Lateral Ventricles (2): One on each side of the brain, connected to the third ventricle via the intraventricular foramen.
- Third Ventricle: Centrally located, feeds into the fourth ventricle through the aqueduct of the midbrain.
- Fourth Ventricle: Located at the hindbrain, it transitions into the central canal of the spinal cord.
- Visual aids depict the complex shapes and arrangement of the ventricles across various brain scans.

Precentral and Postcentral Gyri
- Postcentral Gyrus: Primary somatosensory cortex; responsible for processing tactile sensory information from the body.
- Precentral Gyrus: Primary motor cortex; involved in initiating motor movements.
Brain Mapping through Stimulation
- Developed by neurosurgeon Wilder Penfield in the 1950s.
- Methodology:
- Uses electrical stimulation of exposed cortical surface during awake neurosurgery to determine functional areas.
- Patients are awake to provide real-time feedback on sensations or movements.
- Use-case: Identifying critical areas (e.g., speech centers) to avoid during surgical procedures.
- Case study: Demonstrates the brain mapping process in identifying areas related to speech and movement.
Distribution of Functions
- Each cortical region is associated with specific functions:
- Occipital Lobe:
  - Primary visual cortex processes initial input from the eyes, leading to perception of vision.
- Temporal Lobe:
  - Handles semantic knowledge (meaning of words), object identification, and auditory processing (via primary auditory cortex).
- Parietal Lobe:
  - Responsible for spatial attention, integrating sensory information, object localization, and numerical cognition (associated with the perception of quantity).
- Frontal Lobe:
  - Engaged in higher-order functions including planning, self-control, and abstract thinking; the largest lobe in humans relative to other animals.

Important Reminder:
- No brain region functions in isolation; complex behaviors arise from the interaction between various cortical regions and the nervous system as a whole.
- Final note encapsulates the dynamic and collaborative nature of brain functions, emphasizing the complexity of behavior from a neurobiological standpoint.