Central Nervous System Lecture Notes

Overview

• The central nervous system (CNS) consists of the brain and spinal cord.
• Focus on the brain first, then the spinal cord.

Characteristics of the Brain

• Described as four fistfuls of pinkish-gray tissue, wrinkled like a walnut.
• Consistency similar to cold oatmeal.
• Weight: approximately 3.5 lbs in males, 3.2 lbs in females.

Brain Development

• Neurolation: Developmental process of the nervous system.
  • Around the third week, the ectoderm thickens to form the neural plate.
  • The neural plate invaginates to form the neural groove and eventually the neural tube.
  • By the fourth week, the neural tube forms and differentiates into the CNS.

Neural Tube Defects

• Spina Bifida: Linked to folic acid deficiency; vertebrae fail to enclose the spinal cord.
  • Occulta: Affects one to few vertebrae; no functional problems.
  • Cystica: Severe form with sac protruding outside the vertebra.
• Microcephaly: Small brain.
• Anencephaly: Absence of brain.

Brain Vesicles Development

• Primary Brain Vesicles (formed by the fourth week):
  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain)
• Secondary Brain Vesicles (fifth week):
  • Telencephalon & Diencephalon from Prosencephalon
  • Mesencephalon continues
  • Metencephalon & Myelencephalon from Rhombencephalon
• These differentiate into adult brain structures.

Adult Brain Structures

• Cerebral Hemispheres: Form the superior part of the brain.
• Diencephalon: Thalamus, hypothalamus, epithalamus.
• Brain Stem: Midbrain, pons, medulla oblongata.
• Spinal Cord: Continuation of the brain stem.

Ventricles of the Brain

• Fluid-filled chambers continuous with each other and the spinal cord's central canal.
• Lateral Ventricles: Paired and C-shaped, separated by septum pellucidum.
• Third Ventricle: Communicates with lateral ventricles via interventricular foramen.
• Cerebral Aqueduct: Connects third and fourth ventricles.
• Fourth Ventricle: Located in the hindbrain, connects to subarachnoid space.

CNS Organization

• Gray Matter: Neuron cell bodies.
• White Matter: Myelinated fiber tracts.
• Gray Matter Nuclei and Cortices: Specific regions like the cerebellum or cerebral hemispheres.

Cerebral Hemispheres

• Divided into lobes: frontal, parietal, occipital, temporal, and insula.
• Sulci: Shallow grooves between gyri (elevated ridges).
• Fissures: Deep grooves; e.g., longitudinal and transverse fissures.

Functional Areas of the Brain

• Motor Areas: Control voluntary movements.
  • Primary Motor Cortex: On pre-central gyrus, controls precise movements.
  • Premotor Cortex: Controls learned motor skills.
  • Broca's Area: Speech production.
  • Frontal Eye Field: Voluntary eye movements.
• Sensory Areas: Conscious awareness of sensation.
  • Primary Somatosensory Cortex: Receives sensory information.
  • Somatosensory Association Cortex: Integrates sensory inputs.
  • Visual and Auditory Cortices: Process visual and auditory info.
  • Olfactory and Gustatory Cortices: Smell and taste.
• Association Areas:
  • Anterior (Prefrontal Cortex): Intellect, learning, personality.
  • Posterior: Patterns, faces, spatial awareness.
• Limbic Association Area: Emotion and memory.

White Matter and Basal Nuclei

• Cerebral White Matter: Myelinated fibers, responsible for communication within the CNS.
  • Commissures: Connect gray areas of hemispheres (e.g., corpus callosum).
  • Association Fibers: Connect parts of the same hemisphere.
  • Projection Fibers: Connect cortex to lower CNS centers.
• Basal Nuclei: Influence muscle movement, regulate attention and cognition.