Central Nervous System

Central Nervous System (CNS)

  • Consists of the brain and spinal cord.
  • Cephalization: Evolutionary development of the anterior portion of the CNS, leading to more neurons; highest level in the human brain.

Brain Development

  • Neural tube expands, forming three primary vesicles:
    • Prosencephalon (forebrain)
    • Mesencephalon (midbrain)
    • Rhombencephalon (hindbrain)
  • Posterior end becomes the spinal cord.
  • Primary vesicles develop into five secondary brain vesicles:
    • Forebrain becomes telencephalon and diencephalon.
    • Midbrain remains undivided (mesencephalon).
    • Hindbrain becomes metencephalon and myelencephalon.
  • Telencephalon forms the cerebrum.
  • Diencephalon becomes the epithalamus, thalamus, hypothalamus, and retina.
  • Mesencephalon remains the midbrain.
  • Metencephalon becomes the pons and cerebellum.
  • Myelencephalon becomes the medulla oblongata.
  • The central cavity of the neural tube becomes the ventricles.
  • Brain folds to fit within the skull, increasing surface area.

Brain Regions

  • Four main regions:
    1. Cerebral hemispheres
    2. Diencephalon
    3. Brainstem (midbrain, pons, and medulla)
    4. Cerebellum

Gray and White Matter

  • Gray matter: nonmyelinated neurons and cell bodies.
  • White matter: myelinated and nonmyelinated axons.
  • CNS pattern: central cavity surrounded by gray matter, with white matter external to it.
    • Brainstem contains gray matter nuclei within white matter.
    • Cerebrum and cerebellum have an outer layer of gray matter (cortex) and scattered gray matter nuclei amid white matter.

Ventricles

  • Fluid-filled chambers containing cerebrospinal fluid (CSF), lined by ependymal cells.
  • Lateral ventricles are C-shaped chambers in each hemisphere, separated by the septum pellucidum.
  • Lateral ventricles connect to the third ventricle (in diencephalon) via the interventricular foramen.
  • Third ventricle connects to the fourth ventricle (in hindbrain) via the cerebral aqueduct.
  • Fourth ventricle connects to the central canal of the spinal cord and the subarachnoid space via lateral and median apertures.

Cerebral Hemispheres

  • Form the superior part of the brain; 83% of brain mass.
  • Surface markings:
    • Gyri (ridges)
    • Sulci (shallow grooves)
    • Fissures (deep grooves): longitudinal (separates hemispheres) and transverse cerebral (separates cerebrum and cerebellum).
  • Lobes: frontal, parietal, temporal, occipital, and insula.

Cerebral Cortex

  • "Executive suite" of the brain, responsible for awareness, sensory perception, voluntary motor initiation, communication, memory, and understanding.
  • Thin layer of gray matter (2–4 mm).
  • Contains neuron cell bodies, dendrites, glial cells, and blood vessels.
  • Functional areas:
    • Motor areas: control voluntary movement.
    • Sensory areas: conscious awareness of sensation.
    • Association areas: integrate information.
  • Each hemisphere controls the contralateral side of the body.
  • Lateralization: specialization of cortical function (occurs in one hemisphere).
  • Conscious behavior involves the entire cortex.

Motor Areas

  • Located in the frontal lobe.
  • Primary motor cortex: precentral gyrus; controls precise skeletal muscle movements via pyramidal cells and corticospinal tracts; exhibits somatotopy with motor homunculi.
  • Premotor cortex: plans movements, controls learned motor skills, coordinates actions, and depends on sensory feedback.
  • Broca’s area: motor speech area (usually left hemisphere).
  • Frontal eye field: controls voluntary eye movements.

Sensory Areas

  • Located in parietal, insular, temporal, and occipital lobes.
  • Primary somatosensory cortex: postcentral gyrus; receives sensory information and allows spatial discrimination; exhibits somatosensory homunculus.
  • Somatosensory association cortex: integrates sensory input to understand objects.
  • Visual areas: primary visual cortex (occipital lobe) receives visual information; visual association area interprets visual stimuli.
  • Auditory areas: primary auditory cortex (temporal lobe) interprets pitch, loudness, and location; auditory association area stores sound memories.
  • Vestibular cortex: responsible for balance.
  • Olfactory cortex: involved in the conscious awareness of odors.
  • Gustatory cortex: perception of taste.
  • Visceral sensory area: conscious perception of visceral sensations.

Multimodal Association Areas

  • Receive inputs from multiple sensory areas.
  • Send outputs to multiple areas.
  • Give meaning to information, store it in memory, and tie it to experiences.
  • Parts: anterior association area (prefrontal cortex), posterior association area, and limbic association area.

Anterior Association Area

  • Prefrontal cortex; involved with intellect, cognition, recall, and personality; contains working memory for abstract ideas, judgment, reasoning, persistence, and planning.

Posterior Association Area

  • Temporal, parietal, and occipital lobes; recognizes patterns and faces, localizes us in space, and understands written and spoken language (Wernicke’s area).

Limbic Association Area

  • Part of the limbic system; provides emotional impact and helps establish memories.

Lateralization

  • Division of labor between hemispheres.
  • Cerebral dominance: hemisphere dominant for language (usually left).
  • Left hemisphere: language, math, and logic.
  • Right hemisphere: visual-spatial skills, intuition, emotion, and artistic and musical skills.