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Brain Anatomy & Physiology – Comprehensive Notes

ration or staMacroscopic Anatomy of the Brain

  • Cerebrum

    • Largest brain subdivision; seat of higher cognitive functions.

    • Sub-divided into 4 lobes:

    • Frontal – reasoning, voluntary motor activity, expressive language.

    • Parietal – somatosensory integration, spatial orientation.

    • Occipital – visual processing.

    • Temporal – auditory processing, memory, language comprehension.

    • Key structures

    • Cerebral cortex – thin, highly folded, gray-matter surface; primary site of conscious thought.

    • Corpus callosum – broad commissural tract linking left & right hemispheres, enabling inter-hemispheric communication.

  • Cerebellum

    • Coordinates voluntary movement, maintains posture & balance.

    • Receives proprioceptive input; fine-tunes motor output ("little brain").

  • Diencephalon (superior to brainstem)

    • Thalamus – major sensory relay; contributes to conscious awareness.

    • Hypothalamus – autonomic control center regulating body temperature, hunger, thirst, circadian rhythm & endocrine interactions.

  • Brainstem

    • Midbrain (Mesencephalon) – processes visual & auditory reflexes; maintains consciousness.

    • Pons – Latin “bridge”; connects cerebellum to brainstem, contains respiratory centers.

    • Medulla oblongata – autonomic nuclei controlling heart rate, blood pressure, respiration; houses reflexes (cough, sneeze, vomit).

Surface Features: Gyri, Sulci & Fissures

  • Gyri – elevated ridges that increase cortical surface area.

  • Sulci – shallow grooves between gyri.

  • Fissures – deep grooves

    • Longitudinal fissure – separates left & right cerebral hemispheres.

    • Lateral (Sylvian) fissure – divides temporal lobe from frontal & parietal lobes.

Embryological Development

  • Neural tube – embryonic precursor to CNS

    • Rostral end enlarges into 3 primary vesicles

    1. Prosencephalon (forebrain) → develops into Telencephalon & Diencephalon.

    2. Mesencephalon (midbrain) → persists post-natally as midbrain.

    3. Rhombencephalon (hindbrain) → forms Metencephalon & Myelencephalon.

    • Secondary vesicles total 5 (telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon).

    • Adult derivatives

    • Telencephalon → Cerebrum.

    • Diencephalon → Thalamus & Hypothalamus (remains “diencephalon” after birth).

    • Metencephalon → Cerebellum & Pons.

    • Myelencephalon → Medulla oblongata.

Ventricular System & Cerebrospinal Fluid (CSF)

  • 4 ventricles

    1. Two lateral ventricles – each bears a choroid plexus that secretes CSF.

    2. Third ventricle – midline, in diencephalon.

    3. Fourth ventricle – between pons/medulla & cerebellum.

  • Choroid plexus – capillary/ependymal cell complex that produces CSF.

  • CSF characteristics & physiology

    • Clear, colorless liquid providing nutrition, waste removal & shock absorption.

    • Total volume ≈ 150\,\text{mL}; renewed 3–4× per day.

    • Daily production ≈ 500\,\text{mL}.

    • Ependymal cells (neuroglia) line ventricles & aid CSF formation/flow.

  • Flow pathway: Lateral ventricles → interventricular foramina → 3rd ventricle → cerebral aqueduct → 4th ventricle → median/lateral apertures → subarachnoid space → arachnoid granulations → dural venous sinuses.

Protective Mechanisms

Cranial Meninges (continuous with spinal meninges to & through foramen magnum)
  • Dura mater – outer "tough mother"; dense fibrous CT.

  • Arachnoid mater – middle "spider-like" layer; web of collagen/elastic fibers.

  • Pia mater – inner "gentle mother"; clings to brain surface, highly vascular.

Blood–Brain Barrier (BBB)
  • Formed by tight junctions between capillary endothelial cells + astrocyte end-feet.

  • Selective permeability

    • Freely passes: lipid-solubles (O$2$, CO$2$), small alcohols (ethanol), glucose, some amino acids, anesthetics.

    • Restricts: large molecules, most drugs, pathogens.

  • Function: biochemical isolation of CNS from systemic circulation.

Cerebrovascular Accident (CVA) & Vascular Pathology

  • Aneurysm – arterial wall bulge; rupture precipitates hemorrhagic events.

  • Stroke – sudden loss of cerebral blood flow → neuronal death.

    • Ischemic stroke – vessel occlusion.

    • Hemorrhagic stroke – vessel rupture/bleed.

    • Transient Ischemic Attack (TIA) – "mini-stroke"; temporary deficits, warning sign of future CVA.

Neural Tube Defects & Zika Virus (Clinical Correlation)

  • Failure of proper neural tube closure produces congenital malformations.

  • Zika virus (mosquito-borne flavivirus)

    • ~80\% of adult infections asymptomatic.

    • Maternal infection during pregnancy may cause fetal microcephaly (abnormally small brain & skull).

Cranial Nerves (CN I – XII)

  • There are 12 pairs; all originate in brain/brainstem.

  • Know Roman numeral & name:

    1. I — Olfactory
      II — Optic
      III — Oculomotor
      IV — Trochlear
      V — Trigeminal
      VI — Abducens
      VII — Facial
      VIII — Vestibulocochlear
      IX — Glossopharyngeal
      X — Vagus
      XI — Accessory
      XII — Hypoglossal

    2. These notes collate the anatomical, developmental, physiological and clinical details required for comprehensive understanding of central nervous system structure and function, suitable for exam prepandalone review.