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).
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.
Neural tube – embryonic precursor to CNS
Rostral end enlarges into 3 primary vesicles
Prosencephalon (forebrain) → develops into Telencephalon & Diencephalon.
Mesencephalon (midbrain) → persists post-natally as midbrain.
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.
4 ventricles
Two lateral ventricles – each bears a choroid plexus that secretes CSF.
Third ventricle – midline, in diencephalon.
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.
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.
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.
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.
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).
There are 12 pairs; all originate in brain/brainstem.
Know Roman numeral & name:
I — Olfactory
II — Optic
III — Oculomotor
IV — Trochlear
V — Trigeminal
VI — Abducens
VII — Facial
VIII — Vestibulocochlear
IX — Glossopharyngeal
X — Vagus
XI — Accessory
XII — Hypoglossal
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.