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Complete Neuroanatomy of the Nervous System

For Medical Students — Based on Gray's Anatomy for Students & Neuroanatomy Through Clinical Cases

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PART I: OVERVIEW AND ORGANIZATION OF THE NERVOUS SYSTEM

Structural Division

• Composed of the brain and spinal cord
• Both develop from the neural tube in the embryo
• Enclosed within the cranial cavity and vertebral canal respectively

• All nervous structures outside the CNS that connect the CNS to the body
• Develops from neural crest cells and outgrowths of the CNS
• Consists of:
  • Spinal nerves (31 pairs)
  • Cranial nerves (12 pairs)
  • Visceral nerves and plexuses
  • Enteric nervous system

Functional Division

Development (Embryological)

• Neural plate → neural tube (CNS) by neurulation
• Neural tube gives rise to:
  • Prosencephalon (forebrain) → telencephalon + diencephalon
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain) → metencephalon (pons + cerebellum) + myelencephalon (medulla)
  • Caudal neural tube → spinal cord
• Neural crest cells → PNS ganglia, Schwann cells

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PART II: CELLULAR COMPONENTS

Neurons

• Cell body (soma/perikaryon): Contains the nucleus, Nissl substance (rER for protein synthesis), Golgi apparatus, and mitochondria
• Dendrites: Multiple processes that receive input; contain Nissl substance; highly branched (dendritic tree)
• Axon: Single process for conducting impulses away; arises from the axon hillock (integration zone); no Nissl substance; may be myelinated or unmyelinated
• Axon terminals (boutons): Transmit signals to next neuron or effector organ

• Sensory (afferent): Carry impulses toward CNS
• Motor (efferent): Carry impulses away from CNS
• Interneurons: Within CNS, connect neurons; majority of all neurons

Neuroglia (Glial Cells)

Synapses

• Chemical synapses: Most common; use neurotransmitters
  • Presynaptic terminal → synaptic cleft (~20 nm) → postsynaptic membrane
  • Excitatory: Glutamate (AMPA/NMDA receptors), acetylcholine
  • Inhibitory: GABA, Glycine
• Electrical synapses: Gap junctions; fast, bidirectional; found in cardiac muscle, some CNS neurons
• Neuromuscular junction (NMJ): ACh → nicotinic receptors on motor end plate

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PART III: SPINAL CORD

Extent and Dimensions

• Occupies the superior two-thirds of the vertebral canal
• Extends from foramen magnum (junction with medulla) to approximately the L1–L2 disc in adults
• In neonates, ends at approximately L3
• Terminates as the conus medullaris (cone-shaped)
• A fine pial filament, the filum terminale, continues from the conus inferiorly to the coccyx

Enlargements

External Features

• Anterior median fissure: Along entire anterior surface; deep
• Posterior median sulcus: Along posterior surface
• Posterolateral sulcus: On each side posteriorly; where posterior rootlets enter
• Anterolateral sulcus: Where anterior rootlets emerge

Internal Structure (Cross-Section)

• Anterior (ventral) horn: Motor neurons (alpha, gamma, beta)
• Posterior (dorsal) horn: Sensory relay neurons
• Lateral horn: Present at T1–L2 (sympathetic preganglionic) and S2–S4 (parasympathetic preganglionic)
• Central canal: Ependyma-lined; contains CSF; remnant of neural tube lumen

Rexed's Laminae (Cytoarchitectural)

Ascending (Sensory) Tracts

• Carries: Fine touch, vibration, proprioception, two-point discrimination
• 1st neuron: Dorsal root ganglion → posterior column ipsilaterally
  • Lower body (below T6) → Fasciculus gracilis
  • Upper body (T6 and above) → Fasciculus cuneatus
• 2nd neuron: Nucleus gracilis / Nucleus cuneatus in medulla → decussate as internal arcuate fibers → medial lemniscus → thalamus (VPL)
• 3rd neuron: VPL → primary somatosensory cortex (postcentral gyrus, areas 3,1,2)

• Carries: Pain, temperature, crude touch, pressure
• 1st neuron: Dorsal root ganglion → enters cord → ascends or descends 1–2 levels in Lissauer's tract → synapse in posterior horn (laminae I, IV, V)
• 2nd neuron: Decussates in the anterior white commissure → ascends contralaterally as:
  • Lateral spinothalamic tract: Pain and temperature
  • Anterior spinothalamic tract: Crude touch and pressure
• Terminates in thalamus (VPL) → 3rd neuron to somatosensory cortex

Clinical pearl: Hemisection of the spinal cord (Brown-Séquard syndrome) causes ipsilateral loss of proprioception/vibration AND contralateral loss of pain/temperature below the lesion.

Descending (Motor) Tracts

• Most important motor pathway; controls limb movements
• UMN cell bodies: Primary motor cortex (precentral gyrus, area 4)
• Axons converge → corona radiata → posterior limb of internal capsule → crus cerebri (midbrain) → anterior pons (bundles) → pyramids of medulla → decussate at pyramidal decussation (85–90% cross) → lateral column → synapse on anterior horn (LMN) at all levels

• Origin: Red nucleus (midbrain)
• Decussates immediately in midbrain (ventral tegmental decussation)
• Assists LCST in limb flexion; functionally minor in humans

Spinal Cord Vasculature

• Anterior spinal artery (ASA): Formed by union of branches from both vertebral arteries; runs in anterior median fissure; supplies anterior 2/3 of spinal cord (including anterior horns and lateral columns)
• Posterior spinal arteries (2): Usually from posterior inferior cerebellar arteries (PICA); supply posterior 1/3
• Segmental (radicular) arteries: Reinforce the longitudinal vessels; from vertebral, intercostal, lumbar, and sacral arteries
• Artery of Adamkiewicz (arteria radicularis magna): Largest anterior radicular artery; usually left-sided at T8–L1; critical for thoracolumbar cord

Clinical: ASA infarct → bilateral loss of pain/temperature + motor weakness below lesion; posterior columns spared (vibration/proprioception preserved).

• Three anterior and three posterior longitudinal veins → radicular veins → internal vertebral venous plexus (epidural) → external vertebral plexus → segmental veins

Spinal Nerves

• 31 pairs: 8 cervical (C1–C8), 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
• Each formed by union of anterior (ventral) root (motor) + posterior (dorsal) root (sensory)
• Dorsal root ganglion (DRG): Contains pseudounipolar sensory neurons
• Cauda equina: Nerve roots L2–S5 below the conus medullaris, suspended in CSF within the lumbar cistern (ideal site for lumbar puncture at L3–L4 or L4–L5)

1. General somatic afferent (GSA) — general body sensation
2. General visceral afferent (GVA) — visceral sensation
3. General somatic efferent (GSE) — voluntary muscle
4. General visceral efferent (GVE) — ANS

• Posterior (dorsal) primary ramus: Muscles and skin of back
• Anterior (ventral) primary ramus: Limbs and anterolateral trunk; forms plexuses

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PART IV: BRAINSTEM

Midbrain (Mesencephalon)

• Anterior (ventral): Two cerebral peduncles (crura cerebri) separated by the interpeduncular fossa; CN III emerges from the medial surface of each peduncle
• Posterior (dorsal): Tectum (roof) with four colliculi — superior colliculi (visual reflex) and inferior colliculi (auditory relay); CN IV emerges from the dorsal surface (only cranial nerve to emerge dorsally)
• Periaqueductal gray (PAG): Surrounds cerebral aqueduct; pain modulation, defensive behavior

• Cerebral aqueduct (connecting 3rd and 4th ventricles)
• Tectum (superior colliculus)
• Tegmentum: Contains:
  • Red nucleus (rubrospinal tract origin; iron-rich, reddish)
  • Substantia nigra (dopamine-producing; divided into pars compacta [dopamine] and pars reticulata; degenerated in Parkinson's disease)
  • Oculomotor nucleus (CN III) and Edinger-Westphal nucleus (parasympathetic to pupil)
  • Trochlear nucleus (CN IV)
  • Medial longitudinal fasciculus (MLF) — coordinates eye movements
• Crus cerebri (base): Descending corticospinal, corticobulbar, corticopontine fibers

• Inferior colliculus: Auditory relay to medial geniculate body
• CN IV nucleus

Pons

• Anterior (ventral): Prominent transverse fibers from middle cerebellar peduncle (brachium pontis); CN V (trigeminal) emerges at pons-middle cerebellar peduncle junction; CN VI, VII, VIII at pontomedullary junction
• Posterior (dorsal): Upper floor of 4th ventricle (rhomboid fossa)

• Facial colliculus: Elevation in floor of 4th ventricle caused by CN VII fibers looping around CN VI nucleus
• Medial longitudinal fasciculus (MLF): Below the floor of 4th ventricle throughout pons; coordinates conjugate gaze
• Locus ceruleus: Major noradrenergic nucleus; floor of 4th ventricle

Medulla Oblongata

• Anterior surface: Pyramids (descending corticospinal fibers), olivary eminences, CN VI, VII, VIII (at upper end), CN IX, X, XI
• Posterior surface (open medulla): Forms the lower part of the rhomboid fossa (floor of 4th ventricle); key landmarks include hypoglossal triangle, vagal triangle
• Closed medulla (lower): Resembles spinal cord; central canal present

• Pyramids: Contain the corticospinal tracts; pyramidal decussation at medullospinal junction
• Inferior olives: Relay to cerebellum
• Restiform body (inferior cerebellar peduncle): Connects medulla to cerebellum

• Pyramidal decussation: 85–90% of corticospinal fibers cross
• Nucleus gracilis and nucleus cuneatus: Synapse for posterior column fibers; axons decussate as internal arcuate fibers → medial lemniscus
• Spinal trigeminal nucleus and tract
• CN XII (hypoglossal) nucleus

• Inferior olivary nucleus: Major cerebellar input; receives corticospinal collaterals, spinal cord input
• Nucleus of tractus solitarius: Visceral sensation (taste from CN VII, IX, X)
• Dorsal motor nucleus of vagus (CN X): Parasympathetic preganglionic
• Nucleus ambiguus: Motor neurons for CN IX, X, XI (pharynx, larynx)
• Vestibular nuclei (medial, inferior): Part of the vestibular complex
• Inferior cerebellar peduncle: Afferents to cerebellum (from spinal cord, inferior olive)

• Cardiovascular center (heart rate, blood pressure)
• Respiratory centers (dorsal respiratory group, ventral respiratory group)
• Vomiting center
• Swallowing center

PICA occlusion → Lateral medullary (Wallenberg) syndrome: Ipsilateral facial pain/temperature loss (spinal trigeminal), contralateral body pain/temperature loss (spinothalamic), ipsilateral Horner's syndrome, dysphagia, dysarthria, vertigo, nystagmus.

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PART V: CEREBELLUM

Structure

• Two cerebellar hemispheres + midline vermis
• Anterior lobe (separated from posterior by primary fissure)
• Posterior lobe (largest; separated from flocculonodular by posterolateral fissure)
• Flocculonodular lobe (phylogenetically oldest = archicerebellum)

1. Molecular layer: Dendrites of Purkinje cells, parallel fibers, stellate and basket cells
2. Purkinje cell layer: Large Purkinje neurons (the only output of the cerebellar cortex — GABAergic, inhibitory)
3. Granule cell layer: Granule cells (excitatory, glutamatergic — most numerous neurons in brain), Golgi cells

Cerebellar Peduncles

Afferent Pathways to Cerebellum

1. Mossy fibers: From spinal cord (spinocerebellar tracts), pontine nuclei, vestibular nuclei → synapse on granule cells
2. Climbing fibers: From inferior olivary nucleus → one-to-one contact with Purkinje cell dendrites; powerful excitatory signal; carry error signals

Circuit

Cerebellar Signs (Lesion)

• DANISH: Dysdiadochokinesia, Ataxia, Nystagmus, Intention tremor, Slurred speech (dysarthria/scanning speech), Hypotonia
• Ipsilateral deficits (cerebellum works ipsilaterally — fibers double-cross)

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PART VI: DIENCEPHALON

Thalamus

Hypothalamus

• Suprachiasmatic nucleus: Circadian rhythm; receives direct retinal input
• Preoptic area: Thermoregulation, sleep onset, GnRH secretion
• Supraoptic nucleus: ADH (vasopressin) and oxytocin synthesis
• Paraventricular nucleus: ADH, oxytocin, CRH, TRH synthesis; autonomic outflow
• Ventromedial nucleus: Satiety center (destruction → hyperphagia)
• Lateral hypothalamic area: Hunger center (destruction → starvation)
• Mammillary bodies: Memory (part of Papez circuit); involved in Wernicke's encephalopathy

• Neurohypophyseal tract: PVN and SON axons → posterior pituitary → ADH and oxytocin released into blood
• Hypophyseal portal system: Hypothalamic releasing/inhibiting hormones → anterior pituitary via portal blood (tuberoinfundibular tract)

Epithalamus

• Pineal gland: Melatonin secretion; circadian regulation
• Habenular nuclei: Limbic-to-midbrain relay

Subthalamus

• Subthalamic nucleus (STN): Part of basal ganglia circuit (indirect pathway); lesion → hemiballismus (contralateral)

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PART VII: CEREBRAL HEMISPHERES

Cerebral Cortex

• Two hemispheres separated by the longitudinal cerebral fissure (contains falx cerebri)
• Connected by corpus callosum (largest commissure), anterior commissure, posterior commissure, hippocampal commissure
• Gray matter (cortex) externally; white matter internally with basal ganglia embedded

White Matter Tracts

• Anterior limb: Frontopontine fibers, thalamofrontal (from MD nucleus)
• Genu: Corticobulbar fibers (to CN motor nuclei)
• Posterior limb: Corticospinal tract, somatosensory thalamocortical fibers
• Retrolenticular: Optic radiations (from LGN to V1)
• Sublenticular: Auditory radiations (from MGN to A1)

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PART VIII: BASAL GANGLIA (BASAL NUCLEI)

Components (Corpus Striatum)

• Lenticular (lentiform) nucleus: Putamen + Globus pallidus
• Neostriatum (striatum): Caudate + Putamen

Circuitry

Cortex → Striatum → GPi/SNr (inhibitory) → Thalamus (VA/VL) → Motor cortex

Cortex → Striatum → GPe → STN → GPi/SNr → Thalamus → Motor cortex

• D1 receptors on direct pathway → excitatory (facilitates)
• D2 receptors on indirect pathway → inhibitory (removes suppression)
• Both effects: dopamine facilitates movement

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PART IX: LIMBIC SYSTEM

• Cingulate gyrus (above corpus callosum)
• Hippocampal formation (hippocampus + dentate gyrus + subiculum)
• Amygdala
• Parahippocampal gyrus
• Mammillary bodies
• Anterior thalamic nucleus
• Septal nuclei
• Hypothalamus
• Olfactory cortex

Papez Circuit (Memory/Emotion)

Hippocampus → Fornix → Mammillary bodies → Mammillothalamic tract → Anterior thalamic nucleus → Cingulate cortex → Cingulum → Entorhinal cortex → Hippocampus

Amygdala

• Location: Medial temporal lobe (tip), rostral to hippocampus
• Function: Fear conditioning, emotional memory, threat detection
• Inputs: All sensory cortices, thalamus (direct fast pathway for fear)
• Outputs: Hypothalamus (autonomic fear response), PAG (defensive behavior), prefrontal cortex
• Bilateral lesion: Klüver-Bucy syndrome (hypersexuality, hyperphagia, placidity, visual agnosia)

Hippocampus

• Function: Declarative (explicit) memory — episodic + semantic
• Bilateral damage → anterograde amnesia (cannot form new long-term memories)
• Cell types: Pyramidal cells in CA1–CA4; granule cells in dentate gyrus
• Long-term potentiation (LTP) via NMDA receptors is mechanism of memory formation
• Vulnerable to hypoxia (CA1 — Sommer sector)

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PART X: CRANIAL NERVES

Cranial Nerve Nuclei (Brainstem Location)

Parasympathetic Cranial Ganglia

Reflexes Mediated by Cranial Nerves

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PART XI: MENINGES, VENTRICLES & CSF

Meninges

• Thickest, most external; two layers in cranium:
  • Periosteal layer (adheres to inner skull)
  • Meningeal layer (the true dura)
• Both layers separate at dural venous sinuses
• Dural reflections (septa):
  • Falx cerebri: Vertical partition between cerebral hemispheres in longitudinal fissure; contains superior sagittal sinus (upper free edge), inferior sagittal sinus (lower free edge) → straight sinus
  • Tentorium cerebelli: Horizontal partition between occipital lobes and cerebellum; attached to petrous temporal, occipital bone; tentorial notch (incisura) allows passage of midbrain; contains transverse sinus
  • Falx cerebelli: Small vertical fold between cerebellar hemispheres
  • Diaphragma sellae: Roof over pituitary fossa

• Applied to inner dura
• Arachnoid granulations (Pacchionian granulations): Protrude into dural sinuses (especially superior sagittal sinus); CSF reabsorption sites

• Tightly adherent to brain and spinal cord surface
• Invests blood vessels as they enter brain

• Epidural space (cranial): Potential space between skull and dura (site of epidural hematoma = middle meningeal artery rupture)
• Subdural space: Between dura and arachnoid (bridging veins rupture → subdural hematoma)
• Subarachnoid space: Between arachnoid and pia; contains CSF, cerebral arteries and veins; widened areas = cisterns

Ventricular System

• Within each cerebral hemisphere
• Parts: Anterior horn (frontal lobe), body, posterior horn (occipital), inferior horn (temporal) → trigone at junction
• Communicate with 3rd ventricle via interventricular foramina of Monro

• Narrow slit between thalami; has interthalamic adhesion
• Communicates with 4th ventricle via cerebral aqueduct (of Sylvius) through midbrain
• Recesses: Optic, infundibular, pineal, suprapineal

• Between pons/medulla anteriorly and cerebellum posteriorly
• Floor = rhomboid fossa
• Lateral apertures (foramina of Luschka): Lead to cerebellopontine angle cisterns
• Median aperture (foramen of Magendie): Leads to cisterna magna
• Continues inferiorly as central canal of closed medulla/spinal cord

CSF (Cerebrospinal Fluid)

• ~500 mL/day produced; ~150 mL in circulation at any time
• Produced by choroid plexus (mainly in lateral ventricles; also 3rd and 4th)
• Composition: Ultrafiltrate of plasma; clear, colorless; protein 15–45 mg/dL; glucose 60–80% plasma glucose; few cells (<5 lymphocytes/μL)

Choroid plexus (lateral ventricles) → Foramina of Monro → 3rd ventricle → Cerebral aqueduct → 4th ventricle → Foramina of Luschka (lateral) + Magendie (median) → Subarachnoid space → Arachnoid granulations → Dural venous sinuses → Venous blood

• Buoyancy (reduces effective brain weight from ~1,400g to ~50g)
• Cushioning against trauma
• Chemical homeostasis (removes metabolic waste)
• Nutrient transport

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PART XII: CEREBROVASCULAR ANATOMY

Arterial Supply — Circle of Willis

1. Carotid (anterior) system: Internal carotid arteries
2. Vertebrobasilar (posterior) system: Vertebral arteries → basilar artery

• Lies in the interpeduncular and chiasmatic cisterns
• Components (from anterior):
  • Anterior communicating artery (AComm): Connects two ACAs
  • Anterior cerebral artery (ACA) ×2: Medial surface of hemisphere; frontal & parietal lobes; supplies leg/foot motor and sensory areas
  • Internal carotid artery ×2
  • Middle cerebral artery (MCA) ×2: Lateral cerebral surface; largest; supplies frontal, parietal, temporal lobes (face, arm motor/sensory; Broca's; Wernicke's)
  • Posterior communicating artery (PComm) ×2: Connects ICA to PCA
  • Posterior cerebral artery (PCA) ×2: Occipital lobe (visual cortex); inferior temporal; midbrain

• Vertebral arteries → PICA (posterior inferior cerebellar: lateral medulla + inferior cerebellum)
• Basilar artery → AICA (anterior inferior cerebellar: lower lateral pons + anterior inferior cerebellum) + SCA (superior cerebellar artery: superior cerebellum + dorsal pons) → PCA (posterior cerebral arteries)

Venous Drainage

• Medially: CN VI (abducens) — closest to carotid
• In lateral wall (top to bottom): CN III, CN IV, CN V1, CN V2
• Internal carotid artery (with sympathetic plexus) runs through it

Blood-Brain Barrier (BBB)

• Formed by tight junctions between brain endothelial cells + astrocyte end-feet + pericytes
• Permeable to: O₂, CO₂, lipid-soluble molecules, water (via aquaporins)
• Impermeable to: Large molecules, many drugs, polar substances
• Areas lacking BBB (circumventricular organs): Area postrema, subfornical organ, organum vasculosum, neurohypophysis (allows hypothalamus to sample blood)

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PART XIII: AUTONOMIC NERVOUS SYSTEM (ANS)

Overview

Sympathetic Division (Thoracolumbar)

• Cell bodies in intermediolateral cell column (IML), T1–L2/3
• Exit via anterior roots → white rami communicantes → sympathetic trunk ganglia

1. Synapse in paravertebral ganglion at same level
2. Ascend or descend in sympathetic trunk → synapse at different level
3. Pass through trunk without synapsing → splanchnic nerves → prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric, aortorenal)

• Superior cervical ganglion → superior tarsal muscle (Müller's), pupil dilator, sweat to face
• Disruption → Horner's syndrome: Ptosis (drooping upper lid), miosis (pupil constriction), anhidrosis (no facial sweating), enophthalmos (apparent recession of eye)

• Modified sympathetic ganglion; preganglionic fibers (greater splanchnic nerve) synapse directly on chromaffin cells (modified postganglionic neurons) → release epinephrine (80%) + norepinephrine (20%) directly into blood

Parasympathetic Division (Craniosacral)

• Preganglionic fibers very long; synapse in ganglia near/within target organs
• See cranial nerve parasympathetic ganglia table above

• Provides parasympathetic supply to all thoracic viscera and abdominal viscera down to the left (splenic) colic flexure
• Preganglionic fibers synapse in intramural ganglia of target organs

• Pelvic splanchnic nerves (nervi erigentes)
• Supply: Descending colon, sigmoid, rectum, bladder, genital organs
• Mediate penile/clitoral erection

Enteric Nervous System (ENS)

• "Brain of the gut" — ~500 million neurons; operates semi-independently
• Myenteric (Auerbach's) plexus: Between circular and longitudinal muscle layers; controls peristalsis
• Submucosal (Meissner's) plexus: In submucosa; controls secretion and mucosal function
• Receives sympathetic (inhibitory) and parasympathetic (excitatory) modulation

ANS Neurotransmitters and Receptors

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PART XIV: VISUAL AND AUDITORY PATHWAYS

Visual Pathway

Retina → Optic nerve (CN II) → Optic chiasm → Optic tract → Lateral geniculate nucleus (LGN) → Optic radiations → Primary visual cortex (V1, calcarine sulcus, occipital lobe)

• Nasal retinal fibers (representing temporal visual field) cross to contralateral optic tract
• Temporal retinal fibers (representing nasal visual field) remain ipsilateral

• Afferent: CN II → pretectal nucleus → bilateral EW nuclei (via posterior commissure)
• Efferent: CN III → ciliary ganglion → constrictor pupillae
• Direct reflex (illuminated eye) + consensual reflex (opposite eye)

Auditory Pathway

Hair cells (organ of Corti) → Cochlear nerve (CN VIII) → Cochlear nuclei (dorsal + ventral, pontomedullary junction) → Superior olivary nucleus (bilateral) → Lateral lemniscus → Inferior colliculus (midbrain) → Medial geniculate nucleus (thalamus) → Heschl's gyri (A1) in superior temporal plane

• Bilateral representation at all levels above cochlear nuclei; unilateral cortical lesion does NOT cause deafness
• Tonotopic organization maintained throughout

Vestibular Pathway

Hair cells (semicircular canals + otolith organs) → Vestibular nerve (CN VIII) → Vestibular nuclei (medulla/pons) → Vestibulocerebellum + VL thalamus + Spinal cord (via vestibulospinal tracts) + MLF (eye muscles)

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PART XV: OLFACTORY AND GUSTATORY SYSTEMS

Olfaction (Smell)

• Olfactory receptor neurons: Bipolar neurons in olfactory epithelium (nasal cavity roof)
• Axons → olfactory nerve (CN I) → pass through cribriform plate → olfactory bulb
• Mitral cells in olfactory bulb → olfactory tract → medial olfactory stria (septal area) + lateral olfactory stria (primary olfactory cortex: piriform cortex, entorhinal cortex, amygdala)
• Only sensory system that does NOT relay through thalamus before reaching cortex
• Clinical: Fracture of cribriform plate → anosmia (loss of smell)

Gustation (Taste)

• Taste buds on tongue, epiglottis, soft palate
• Anterior 2/3 tongue: Chorda tympani (CN VII)
• Posterior 1/3 tongue: CN IX (glossopharyngeal)
• Epiglottis and lower pharynx: CN X (vagus)
• All → Nucleus tractus solitarius (NTS) → VPM thalamus → insular cortex

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PART XVI: FUNCTIONAL INTEGRATION — IMPORTANT CLINICAL CORRELATES

Level of Consciousness and Ascending Reticular Activating System (ARAS)

• ARAS: Network of neurons in the reticular formation of brainstem (midbrain and upper pons) → diffuse thalamic projections → widespread cortical arousal
• Neurotransmitters: Norepinephrine (locus ceruleus), serotonin (raphe nuclei), acetylcholine (PPT/LDT nuclei), dopamine, histamine (TMN, hypothalamus), orexin/hypocretin (lateral hypothalamus)
• Bilateral ARAS damage → coma

Sleep

• NREM (Non-REM): Stages 1–3; thalamocortical spindles, delta waves; growth hormone released
• REM sleep: Dreaming; pontine REM generator (PPT nuclei); muscle atonia (via medullary inhibition of motor neurons); eye movements

Pain Modulation (Gate Control and Descending Inhibition)

• Periaqueductal gray (PAG): Primary pain modulation center; receives from cortex, amygdala, hypothalamus
• PAG → Rostral ventromedial medulla (RVM) → Dorsal horn (inhibit nociceptive transmission)
• Endogenous opioids: β-endorphin, enkephalins, dynorphin → μ, δ, κ receptors
• Substantia gelatinosa (lamina II): Integrates inhibitory and facilitatory inputs for pain

Blood-Brain Barrier Clinical Significance

• Protects brain from toxins, pathogens
• Breakdown in meningitis, stroke, tumors (ring-enhancing lesions on MRI)
• Drug delivery challenge: Most chemotherapy agents cannot cross intact BBB

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SUMMARY TABLE: "Which Part Does What"

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