Chapter 14 – The Brain and Cranial Nerves (Vocabulary)

Principal Parts of the Brain

• Four macroscopic regions

  • Brainstem

  • Cerebellum

  • Diencephalon

  • Cerebrum

• Anatomical relationships & continuity

  • Medulla continuous with spinal cord

  • Midbrain continuous with diencephalon

Protection of the Brain

• Bony shield: cranial bones (neurocranium)

• Meninges (superficial → deep)

  • Dura mater (periosteal & meningeal layers)

  • Arachnoid mater (spider-web trabeculae, subarachnoid space)

  • Pia mater (vascular membrane adherent to cortex)

• Cerebrospinal fluid (CSF) cushions & chemically stabilises

Blood Supply & Blood–Brain Barrier (BBB)

• Arterial inflow

  • Vertebral arteries

  • Internal carotid arteries

• Venous return via internal jugular veins

• Brain metabolic statistics

  • \text{O}_2\,\text{utilisation} \approx 20\% of total body demand

  • Interruption → neuronal weakening, permanent damage or death in minutes

  • Glucose deficiency → mental confusion, dizziness, convulsions, unconsciousness

• BBB characteristics

  • Tight junctions of endothelial cells + astrocyte end-feet + thick basement membrane

  • Selective permeability prevents toxins & many drugs; lipid-soluble molecules pass more readily

  • Trauma, inflammation or toxins may disrupt barrier → uncontrolled entry of substances

Ventricular System & Cerebrospinal Fluid

• Four ventricles

  • Two lateral ventricles (cerebral hemispheres)

  • Third ventricle (diencephalon)

  • Fourth ventricle (between pons/medulla & cerebellum)

• Choroid plexus: fenestrated capillaries + ependymal cells → produces CSF (~\text{500 mL day}^{-1})

• CSF functions

  • Mechanical protection (buoyancy ↓ brain weight by ~97 %)

  • Homeostatic pH & ionic balance for neuronal signalling

  • Circulation of nutrients ((\text{O}_2), glucose) & removal of wastes

• Flow pathway (lateral → third → cerebral aqueduct → fourth → subarachnoid space via median & lateral apertures → arachnoid granulations → dural venous sinuses → heart)

Brainstem

• Conduit for ascending/descending tracts; houses nuclei for 10 of 12 cranial nerves

Medulla Oblongata

• Gray-matter nuclei

  • Cardiovascular centre: heart rate & vessel diameter

  • Respiratory centre (with pons): rhythm of breathing

  • Reflex centres: swallowing, vomiting, coughing, sneezing, hiccupping

  • Inferior olivary nucleus: proprioceptive relay to cerebellum (motor learning)

  • Gracile & cuneate nuclei: somatosensory relay

  • Gustatory, cochlear & vestibular nuclei: taste, hearing, equilibrium

• Contains parts of CN VIII, IX, X, XI, XII

• Pyramids: decussation of \sim90\% corticospinal fibres → contralateral control

Pons

• Bridge between cerebellum & cerebrum; transverse & longitudinal tracts

• Pontine nuclei: motor relay cortex → cerebellum (voluntary movement coordination)

• Pontine (pneumotaxic & apneustic) respiratory group: modifies medullary rhythm

• Vestibular nuclei (shared w/ medulla) for balance

• CN nuclei: V, VI, VII, VIII

Midbrain (Mesencephalon)

• Cerebral peduncles: major motor tracts from cortex

• Tectum

  • Superior colliculi: visual reflexes, tracking, head/eye movements

  • Inferior colliculi: auditory reflexes, startle response

• Substantia nigra: dopaminergic neurons modulate basal nuclei; degeneration → Parkinson’s

• Red nucleus: rubrospinal coordination of distal limb movements

• CN nuclei: III & IV

Reticular Formation (RF)

• Diffuse network through medulla ↔ diencephalon

• Functions

  • Reticular activating system (RAS): cortical arousal, consciousness, sleep-wake transitions

  • Muscle tone regulation & posture

  • Filters $>99\%$ of sensory input to prevent overload

Cerebellum

• Anatomy

  • Two hemispheres + central vermis; surface folia, deep arbor vitae (white matter)

  • Anchored by superior, middle, inferior cerebellar peduncles

• Functions

  • Comparator: receives intended motor commands & sensory feedback, outputs corrective signals

  • Coordinates timing & force of skeletal muscle contraction

  • Maintains posture, equilibrium & muscle tone

  • Cognitive roles: language, pattern recognition, emotional regulation (evidence-based)

Diencephalon

Thalamus

• Bilateral egg-shaped nuclei, majority of diencephalon mass

• Relay station for all sensory input except olfaction

• Motor relay cerebellum ↔ cortex; role in consciousness & pain perception

Hypothalamus

• Visceral control centre; links nervous & endocrine systems

• Key nuclei & functions

  • Autonomic regulation (HR, BP, GI motility, pupil size)

  • Hormone production: releasing/inhibiting hormones → anterior pituitary; syntheses of oxytocin & ADH

  • Emotional behaviour (with limbic system)

  • Feeding (hunger) & satiety centres; thirst centre

  • Thermostat: monitors T_{body} and triggers shivering/sweating

  • Suprachiasmatic nucleus: circadian rhythms

Epithalamus

• Pineal gland → melatonin (sleep–wake cycle, antioxidant)

• Habenular nuclei: emotional responses to odours

Cerebrum

Lobes & Surface Anatomy

• Frontal, Parietal, Temporal, Occipital, Insula (deep within lateral sulcus)

• Surface features: gyri (ridges), sulci (shallow grooves), fissures (deep grooves)

• Corpus callosum: major commissural tract joining hemispheres

Cortex Organisation

• Gray-matter cortex \approx 2\text{–}4\,\text{mm} thick; billions of neurons

• White matter tracts

  • Association fibres (within a hemisphere)

  • Commissural fibres (between hemispheres)

  • Projection fibres (cortex ↔ lower CNS)

Functional Areas

• Sensory areas: primary somatosensory, visual, auditory, gustatory, olfactory cortices

• Motor areas: primary motor cortex (precentral gyrus), premotor, Broca’s (speech production)

• Association areas: Wernicke’s (language comprehension), prefrontal cortex (executive), somatosensory association, visual & auditory association, etc.

Limbic System

• Structures: hippocampus, amygdala, cingulate gyrus, mamillary bodies, olfactory bulbs, etc.

• Functions: emotion (pleasure, fear, anger), motivation, memory consolidation → directs appropriate autonomic & motor responses

Hemispheric Lateralization

• Left hemisphere (dominant in \sim90\% right-handed)

  • Language, logic, math, science, sign language, reasoning

• Right hemisphere

  • Spatial, musical, artistic, face recognition, emotional prosody, olfactory discrimination

• Lateralization is relative, not absolute; corpus callosum enables integration

Brain Waves (EEG)

• Alpha (8–13 Hz): awake, relaxed, eyes closed – disappear in sleep

• Beta (14–30 Hz): active cortex – sensory input, problem solving

• Theta (4–7 Hz): children & stressed adults – emotional stress, some disorders

• Delta (0.5–4 Hz): deep sleep in adults, awake infants – presence in awake adult = brain damage

Cranial Nerves

Overview

• 12 pairs (I–XII); motor, sensory, or mixed; all except I & II arise from brainstem

• Emerge in anatomical clusters:

  • Cerebrum: I (Olfactory), II (Optic)

  • Midbrain: III (Oculomotor), IV (Trochlear)

  • Pons: V (Trigeminal), VI (Abducens), VII (Facial), VIII (Vestibulocochlear)

  • Medulla: IX (Glossopharyngeal), X (Vagus), XI (Accessory), XII (Hypoglossal)

Individual Nerves & Core Functions

• I Olfactory – smell (special sensory)

• II Optic – vision

• III Oculomotor – eye & eyelid movement; pupil constriction; lens accommodation

• IV Trochlear – eye movement via superior oblique

• V Trigeminal – facial somatic sensation; mastication muscles; middle ear muscle

• VI Abducens – eye abduction via lateral rectus

• VII Facial – taste (anterior 2/3 tongue); facial expression; lacrimal & salivary glands

• VIII Vestibulocochlear – hearing (cochlear) & equilibrium (vestibular)

• IX Glossopharyngeal – taste (posterior 1/3); baro/chemoreception; swallowing; parotid secretion

• X Vagus – visceral sensation (thoraco-abdominal); parasympathetic to heart, lungs, GI; voice & swallow

• XI Accessory – sternocleidomastoid & trapezius movement

• XII Hypoglossal – tongue movement for speech & swallowing

Development of the Nervous System

• Week 3: ectoderm → neural plate → neural groove & folds → neural tube closure (primary neurulation)

• Neural crest → peripheral ganglia, Schwann cells, meninges

• Primary brain vesicles: prosencephalon, mesencephalon, rhombencephalon (3–4 weeks)

• Secondary vesicles (7 weeks): telencephalon & diencephalon; mesencephalon; metencephalon & myelencephalon

• Cerebral hemispheres overgrow diencephalon by week 11; cerebellum, brainstem differentiate

Aging & the Nervous System

• Neuronal loss & synaptic decline

• ↓ Conduction velocity, processing speed, reflexes, voluntary motor response

• Sensory degeneration: vision, hearing, taste, smell, balance, touch

Neurological Disorders

• Cerebrovascular accident (CVA / stroke)

  • 85\% ischaemic (embolus/thrombus), 15\% haemorrhagic

  • Neuronal death from hypoxia → deficits dependent on area (speech, paralysis, etc.)

• Transient ischaemic attack (TIA)

  • Temporary arterial insufficiency; symptoms < 24 h (typically 5–10 min)

  • Warning of impending stroke

• Alzheimer’s disease

  • Progressive dementia; β-amyloid plaques & neurofibrillary tangles; cerebral atrophy

• Brain tumours

  • Benign or malignant; symptoms due to mass effect & location (headache, seizures)

• Attention-Deficit Hyperactivity Disorder (ADHD)

  • Persistent inattention, hyperactivity, impulsivity; multifactorial (genetic + environment)

High-Yield Review Tables (from backup slides)

• Brainstem summary (medulla, pons, midbrain) – nuclei, tracts, reflexes

• Diencephalon summary – thalamus, hypothalamus, epithalamus functions

• Cerebrum summary – sensory, motor, association, basal nuclei, limbic system roles

These bullet-point notes encompass every major & minor concept, structural detail, functional role, physiological statistic, clinical correlation, and developmental/aging consideration presented in the transcript, allowing thorough exam preparation without referring back to the original slides.