Chapter 4: Cranial Nerves - Answers

Q1 (LA) [June 22] - A 40-year-old male with weakness of facial muscles following right parotid gland operation [4+5+3+3]

(a) Functional Components of the Affected Cranial Nerve (CN VII - Facial Nerve) [4 marks]

(b) Intracranial Course of the Facial Nerve [5 marks]

1. Nucleus of origin: The facial nerve arises from the facial nucleus in the tegmentum of the lower pons. The motor root fibres first loop around the abducens (VI) nucleus, forming the facial colliculus, before emerging anterolaterally.
2. Emergence: The facial nerve emerges from the lateral aspect of the lower border of the pons at the cerebellopontine angle (CPA), along with the nervus intermedius (nerve of Wrisberg) and CN VIII (vestibulocochlear nerve).
3. Course in the posterior cranial fossa: The nerve passes laterally across the posterior cranial fossa toward the internal acoustic meatus (IAM), in close relationship with CN VIII. It is accompanied by the nervus intermedius (carrying parasympathetic and taste fibres).
4. Internal Acoustic Meatus (IAM): The nerve enters the IAM in the posterior cranial fossa and travels through it within the petrous temporal bone.
5. Facial canal (Fallopian canal): Within the petrous part of the temporal bone, the nerve runs in the facial canal. It first runs laterally (labyrinthine segment), then bends sharply backward at the geniculate ganglion (the genu of the facial nerve - site of taste and parasympathetic cell bodies), then runs posteriorly above the middle ear (tympanic segment), and finally turns downward (mastoid/vertical segment) to exit through the stylomastoid foramen.
6. Stylomastoid foramen: The nerve exits the skull through this foramen, which is located between the styloid and mastoid processes of the temporal bone.

(c) Branches of the Facial Nerve from its Intracranial Part [3 marks]

1. Greater Petrosal Nerve - arises from the geniculate ganglion; carries preganglionic parasympathetic fibres to the pterygopalatine ganglion (secretomotor to lacrimal gland and glands of nose and palate); also carries taste from soft palate.
2. Nerve to Stapedius - arises in the mastoid segment; supplies the stapedius muscle (prevents excessive vibration of the ossicular chain; damage causes hyperacusis).
3. Chorda Tympani - arises just above the stylomastoid foramen; crosses the middle ear, exits through the petrotympanic fissure, and joins the lingual nerve; carries taste from anterior 2/3 of tongue and preganglionic parasympathetic fibres to the submandibular ganglion (secretomotor to submandibular and sublingual glands).

(d) Relations of the Facial Nerve with the Parotid Gland [3 marks]

1. The nerve enters the posteromedial surface of the parotid gland and passes forward through its substance.
2. Within the parotid gland, the nerve divides into upper (temporofacial) and lower (cervicofacial) trunks. These further divide and anastomose to form the parotid plexus (pes anserinus).
3. The parotid gland is effectively divided into a superficial lobe (lateral/superficial to the nerve) and a deep lobe (medial/deep to the nerve) by the plane of the facial nerve - though there is no true fascial septum between the two lobes.
4. Five terminal branches emerge from the borders of the parotid gland:
   • Temporal (from upper border)
   • Zygomatic (from anterior border)
   • Buccal (from anterior border)
   • Marginal Mandibular (from lower border)
   • Cervical (from lower border)
5. The intimate relationship between the facial nerve and the parotid gland means that surgical removal (parotidectomy) is a difficult dissection if all branches of the nerve are to be preserved. This explains why this patient developed facial muscle weakness following parotid gland surgery.

Q2 (SN) [Nov 21, 2017] - Bell's Palsy [5 marks]

Etiology:

• The most widely accepted cause is reactivation of latent Herpes Simplex Virus type 1 (HSV-1) in the geniculate ganglion, causing inflammation, oedema, and compression of the nerve within the narrow bony facial canal.
• Other proposed causes: microcirculatory failure of vasa nervorum, autoimmune reactions.

Clinical Features (LMN type palsy - all branches affected):

• Inability to close the eye (orbicularis oculi paralysis) - Bell's phenomenon: eyeball rolls up when eye closure is attempted.
• Loss of forehead wrinkling on the affected side (distinguishes LMN from UMN lesion - in UMN, forehead is spared due to bilateral cortical representation).
• Drooping of the angle of the mouth, inability to show teeth, puffing out the cheeks, or whistling.
• Loss of nasolabial fold on the affected side.
• Food and saliva accumulate between the cheek and gums (buccinator paralysis).
• If nerve is affected proximal to the nerve to stapedius: Hyperacusis (abnormal sensitivity to sounds).
• If affected proximal to chorda tympani: Loss of taste from anterior 2/3 of tongue, reduced salivation.
• If affected proximal to greater petrosal nerve: Reduced lacrimation, dry eye.

Distinguishing LMN from UMN (Upper Motor Neuron) Facial Palsy:

Treatment:

• Oral corticosteroids (prednisolone): highly likely to increase probability of nerve function recovery.
• Antiviral agents (acyclovir/valacyclovir) may be added.
• Eye care: artificial tears, eye patching at night (to prevent corneal damage due to inability to close eye).
• Most cases resolve spontaneously within 3-6 months.

Q3 [May 23, 2015, 2019] - Why is Abducent Nerve Palsy a Common Manifestation of Increased Intracranial Pressure?

Reasons for vulnerability of CN VI in raised ICP:

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head & Neck); Vishram Singh Textbook of Anatomy Head, Neck & Brain; Gray's Anatomy for Students (3rd/4th Ed.); Harrison's Principles of Internal Medicine 22E; Bradley and Daroff's Neurology in Clinical Practice.

Chapter 4: Cranial Nerves - Answers (Continued)

Q4 - Features of Hypoglossal Nerve Palsy [2017]

Features of Hypoglossal Nerve Palsy:

• Tongue still deviates toward the paralysed side on protrusion, but there is no wasting, no fasciculations
• UMN lesion of CN XII is usually part of a hemiplegia (e.g., internal capsule lesion)

• Intracranial: tumors of posterior fossa, meningitis, motor neuron disease
• At skull base: fracture of hypoglossal canal, nasopharyngeal carcinoma
• In the neck: surgical injury (carotid endarterectomy, neck dissection), penetrating trauma, tumors of neck

Q5 - Oculomotor Nerve Lesion [2010, 2015]

Muscles supplied by CN III:

• Extraocular muscles: Superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris
• Intraocular muscles (via ciliary ganglion): Sphincter pupillae (pupil constriction), ciliary muscle (accommodation)

Features of Complete CN III Palsy:

Important Clinical Points:

• Surgical CN III palsy (e.g., from posterior communicating artery aneurysm): pupil is involved (dilated) - because parasympathetic fibres run on the outside of the nerve and are compressed first.
• Medical CN III palsy (e.g., due to diabetes - microvascular ischaemia): pupil is usually spared - because ischaemia affects the inner nerve fibres (motor) while the outer parasympathetic fibres survive.

Q6 - Supranuclear Lesion of Facial Nerve Spares the Forehead / Causes Motor Loss Only of Lower Face [2009, 2022]

Anatomical Basis:

1. Upper part (dorsal) - supplies muscles of the upper face (frontalis, orbicularis oculi)
2. Lower part (ventral) - supplies muscles of the lower face (buccinator, orbicularis oris, etc.)

• The upper part of the facial nucleus receives bilateral corticobulbar (supranuclear) innervation - i.e., from BOTH cerebral cortices (ipsilateral AND contralateral).
• The lower part of the facial nucleus receives only contralateral corticobulbar innervation.

Why Supranuclear Lesion Spares the Forehead:

• The lower facial muscles are paralysed on the contralateral side (only contralateral cortical input is lost)
• The forehead (frontalis) and orbicularis oculi are SPARED - because the upper facial nucleus still receives input from the intact ipsilateral cortex (bilateral representation preserves function)

Therefore:

• UMN (supranuclear) facial palsy = Lower face affected only; forehead wrinkles preserved; eye closure intact
• LMN (nuclear/infranuclear) facial palsy = Entire half of face affected, including forehead; cannot wrinkle forehead; cannot close eye (Bell's palsy is an example)

Q7 / (*) - Weber's Syndrome (Crossed Oculomotor Hemiplegia) [2011, 2019, Feb 2023]

Definition:

Anatomical Basis:

• Site of lesion: Base (ventral part/crus cerebri) of the midbrain
• Structures damaged:
  1. CN III nerve fascicles as they pass through the crus cerebri (ipsilateral side)
  2. Corticospinal (pyramidal) tract in the crus cerebri (same side as lesion, but effects are on contralateral body because the tract crosses in the medullary decussation below)

Clinical Features:

Cause:

Why it is called "Crossed" hemiplegia:

Q8 (LQ) - Course and Distribution of Facial Nerve after Stylomastoid Foramen + Bell's Palsy [2021, 2018]

Course and Distribution of Facial Nerve After the Stylomastoid Foramen:

1. Posterior auricular nerve - supplies occipitalis, auricular muscles, and skin of the posterior auricle
2. Branch to the posterior belly of digastric
3. Branch to stylohyoid muscle

• The nerve enters the posteromedial aspect of the parotid gland and divides into:
  • Upper (temporofacial) trunk
  • Lower (cervicofacial) trunk
• These further divide and anastomose to form the parotid plexus (pes anserinus - "goose's foot")

Bell's Palsy:

• Cannot wrinkle forehead (frontalis paralysis) - distinguishes from UMN
• Cannot close the eye - Bell's phenomenon: eyeball rolls upward on attempted closure
• Drooping of angle of mouth, nasolabial fold lost
• Food collection between cheek and teeth (buccinator paralysis)
• Depending on level: hyperacusis (nerve to stapedius affected), loss of taste on anterior 2/3 tongue (chorda tympani affected), dry eye (greater petrosal nerve affected)

• Oral prednisolone (steroids) - mainstay
• Antiviral drugs (acyclovir)
• Eye protection (artificial tears, patching)

Q9 (MCQ) - Nucleus Ambiguus Contributes to Fibers of the Following Cranial Nerves EXCEPT:

Explanation:

• (a) Accessory Nerve (CN XI) - the cranial root of CN XI arises from the caudal part of the nucleus ambiguus and joins the vagus to supply muscles of the larynx and pharynx
• (b) Vagus Nerve (CN X) - supplies muscles of pharynx, larynx, soft palate; the main motor nucleus of the vagus is the nucleus ambiguus
• (c) Glossopharyngeal Nerve (CN IX) - the motor fibres to the stylopharyngeus muscle arise from the rostral part of the nucleus ambiguus

• (d) Facial Nerve (CN VII) - the facial nerve's motor fibres arise from the Facial Motor Nucleus (in the pons), NOT the nucleus ambiguus. The nucleus ambiguus is entirely in the medulla.

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.); Adams and Victor's Principles of Neurology 12th Ed.; Harrison's Principles of Internal Medicine 22E.

Chapter 4: Cranial Nerves - Answers (Page 7)

Q10 (MLQ) [Dec 2024] - Young boy swallowed fishbone → pain in tonsillar region + persistent earache [3+2+1+1+3+2+3 = 15]

Part 1: Explain the Situation [3 marks]

• The fishbone lodged near the tonsillar region irritates branches of CN IX that supply the palatine tonsil and oropharynx → causing local throat pain.
• The persistent earache (otalgia) is referred pain - CN IX also supplies the mucosa of the middle ear, pharyngotympanic (Eustachian) tube, and mastoid air cells via its tympanic branch (Jacobson's nerve). Irritation of the tonsillar branches causes pain referred to the ear via the same nerve.
• This is a classic example of referred otalgia via CN IX.

Part 2: Describe CN IX [2+1+1+3+2 = 9 marks]

• CN IX arises as several rootlets from the anterolateral surface of the upper medulla (behind the inferior olive).
• Rootlets merge and cross the posterior cranial fossa toward the jugular foramen.
• The superior ganglion (GSA) and inferior (petrosal) ganglion (GVA/SA) lie within/just below the jugular foramen.

• CN IX exits the skull through the jugular foramen (together with CN X and CN XI and the internal jugular vein).

1. The nerve passes between the internal carotid artery and internal jugular vein.
2. It then curves forward between the internal and external carotid arteries.
3. It passes deep to the styloid process and the muscles attached to it.
4. It runs between the superior and middle constrictors of the pharynx.
5. It reaches the posterior 1/3 of the tongue (lingual branches) and palatine tonsil (tonsillar branches).

• Tympanic nerve (within foramen → enters middle ear)
• Nerve to stylopharyngeus
• Carotid branch (to carotid sinus and body)
• Pharyngeal branches (join pharyngeal plexus)
• Tonsillar branches
• Lingual branches (taste + sensation from posterior 1/3 tongue)

• Preganglionic parasympathetic fibres arise from the inferior salivatory nucleus → travel in CN IX → exit as the tympanic nerve (Jacobson's nerve) → enter the middle ear → form the tympanic plexus → leave as the lesser petrosal nerve → exit through foramen ovale → synapse in the Otic Ganglion.
• Otic Ganglion: lies just below the foramen ovale, medial to the mandibular nerve (V3).
• Postganglionic fibres travel with the auriculotemporal nerve (branch of V3) to reach the parotid gland (secretomotor).

Part 3: Pathway of Taste Sensation to Gustatory Cortex [3 marks]

• Taste receptors (taste buds) on posterior 1/3 tongue → CN IX (lingual branches) → cell bodies in inferior (petrosal) ganglion of CN IX
• Taste from anterior 2/3 tongue → Chorda tympani (CN VII) → cell bodies in geniculate ganglion
• Both converge → Nucleus Tractus Solitarius (NTS) in the medulla

• NTS → fibres cross to the contralateral side → ascend in the central tegmental tract → synapse in the Ventral Posteromedial (VPM) nucleus of the thalamus

• VPM nucleus → Thalamocortical fibres → Gustatory cortex (primary taste area) in the inferior part of the postcentral gyrus (parietal operculum) and anterior insula

Q11 (LQ) [Dec 2024] - Specialities of CN IV + Pathway Flowchart + Horner's Syndrome [3+5+2 = 10]

Specialities of the Fourth (Trochlear) Nerve [3 marks]

1. Smallest cranial nerve - fewest axons of all cranial nerves
2. Only cranial nerve to arise from the dorsal (posterior) surface of the brainstem (all others arise from the ventral or lateral surface)
3. Only cranial nerve to decussate (cross completely) - fibres from each trochlear nucleus cross to the opposite side before emerging, so each nucleus supplies the contralateral superior oblique muscle
4. Longest intracranial course among the motor cranial nerves (wraps around the midbrain)
5. Supplies only one muscle - the superior oblique (which depresses, intorts and abducts the eye)
6. Passes through the free edge of the tentorium cerebelli and the lateral wall of the cavernous sinus

Flowchart: Pathway of the Trochlear Nerve [5 marks]

Trochlear Nucleus (inferior colliculus level, dorsal midbrain tegmentum)
            ↓
Fibres curve DORSALLY and DECUSSATE in superior medullary velum
            ↓
Emerge from POSTERIOR surface of midbrain (below inferior colliculus)
            ↓
Pass around the midbrain (between posterior cerebral & superior cerebellar arteries)
            ↓
Pierce the FREE EDGE of TENTORIUM CEREBELLI
            ↓
Run in the LATERAL WALL of CAVERNOUS SINUS
(below CN III, above CN V1)
            ↓
Enter the orbit via SUPERIOR ORBITAL FISSURE
(ABOVE the common tendinous ring – outside the ring)
            ↓
Cross above Levator Palpebrae Superioris
            ↓
Enter upper border of SUPERIOR OBLIQUE MUSCLE

Horner's Syndrome [2 marks]

1. Ptosis (partial) - paralysis of Müller's smooth muscle in upper eyelid (not levator palpebrae - so ptosis is partial, unlike CN III)
2. Miosis - small pupil; paralysis of dilator pupillae; pupil still reacts to light
3. Anhidrosis - absent sweating on the ipsilateral face/neck (if lesion is proximal to the superior cervical ganglion)

• 1st neuron: Hypothalamus → ciliospinal centre of Budge (C8-T2) - e.g., Pancoast tumour
• 2nd neuron: Superior cervical ganglion - e.g., neck dissection, cervical rib
• 3rd neuron: Along internal carotid artery / cavernous sinus - e.g., carotid dissection

Q12 (MLQ) [Nov 2025] - 45-year-old woman, left-sided facial palsy + altered taste + hyperacusis [1+2+4+5+3]

1. Which Cranial Nerve is Affected? [1 mark]

2. Functional Components of CN VII [2 marks]

3. Intracranial Course of CN VII [4 marks]

1. Arises from the facial motor nucleus in the pons - fibres loop around the abducens nucleus (forming the facial colliculus) before emerging.
2. Emerges at the cerebellopontine angle (lower border of pons, lateral side), accompanied by the nervus intermedius and CN VIII.
3. Crosses the posterior cranial fossa toward the internal acoustic meatus (IAM).
4. Enters the IAM and passes through the petrous temporal bone in the facial canal (Fallopian canal):
   • Labyrinthine segment → Geniculate ganglion (sharp bend/genu - gives off greater petrosal nerve)
   • Tympanic segment (runs above the middle ear)
   • Mastoid/vertical segment (turns down - gives off nerve to stapedius and chorda tympani)
5. Exits the skull through the stylomastoid foramen.

4. Different Branches of CN VII [5 marks]

• Greater petrosal nerve (from geniculate ganglion) → parasympathetic to lacrimal + nasal/palatal glands; taste from soft palate
• Nerve to Stapedius (from mastoid segment) → stapedius muscle
• Chorda Tympani (just above stylomastoid foramen) → taste from anterior 2/3 tongue + parasympathetic to submandibular and sublingual glands

• Posterior auricular nerve → occipitalis + auricular muscles
• Branch to posterior belly of digastric
• Branch to stylohyoid

• Temporal → frontalis, upper orbicularis oculi
• Zygomatic → lower orbicularis oculi
• Buccal → buccinator, orbicularis oris, upper lip muscles
• Marginal mandibular → lower lip and chin muscles
• Cervical → platysma

5. Brief Anatomical Explanation of the Above Scenario [3 marks]

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 5: Brain Stem - Answers (Page 9)

Q1(i) [Feb 23] - Why is Weber's Syndrome called "Crossed Oculomotor Paralysis"?

• The oculomotor palsy is ipsilateral to the lesion.
• The hemiplegia is contralateral to the lesion (because the corticospinal tract crosses in the medullary decussation below).
• Since they are on opposite sides → "crossed."
• The nerve involved is CN III → "oculomotor paralysis."

Q1(ii) [2009] - Why Does a Lesion in the Pretectal Nucleus Cause Argyll Robertson Pupil?

• Pupil is small (miotic)
• Does NOT react to light (absent light reflex)
• Does react to accommodation/convergence (near reflex is intact)
• Commonly bilateral, irregular, unequal
• Classic sign of neurosyphilis

Light → Retina → Optic nerve → Optic tract → Pretectal nucleus (dorsal midbrain) → Edinger-Westphal nucleus → Ciliary ganglion → Sphincter pupillae → pupil constricts

Blurred near image → Visual cortex → Descends via ventral midbrain → Edinger-Westphal nucleus → Sphincter pupillae → pupil constricts

• A lesion in the pretectal nucleus (dorsal midbrain) interrupts the light reflex pathway before it reaches the Edinger-Westphal nucleus → pupil does NOT react to light.
• The accommodation pathway travels through the ventral midbrain and is spared by the dorsal pretectal lesion → near reflex is preserved.
• Additionally, the lesion also damages sympathetic fibres → causing the miosis (small pupil).

Q2 (SN) [Nov 21] - Bell's Palsy

• Cannot wrinkle forehead, cannot close eye (Bell's phenomenon)
• Drooping of angle of mouth, lost nasolabial fold
• Loss of taste (anterior 2/3 tongue) via chorda tympani
• Hyperacusis (nerve to stapedius affected)
• Dry eye if greater petrosal nerve affected

Q3 (LA) [May 23] - Medulla at Level of Sensory Decussation + Arterial Supply [6+4]

Labelled Diagram: Cross Section of Medulla at Level of Sensory Decussation

                    POSTERIOR
         ┌─────────────────────────────┐
         │   Fasciculus gracilis       │
         │   Fasciculus cuneatus       │
         │   Nucleus gracilis          │
         │   Nucleus cuneatus          │
         │                             │
         │   Internal arcuate fibres   │
         │   (crossing = SENSORY       │
         │    DECUSSATION)             │
         │                             │
         │   Spinal nucleus of CN V    │
         │   Spinal tract of CN V      │
         │                             │
         │   Lateral spinothalamic     │
         │   tract                     │
         │                             │
         │   Corticospinal tract       │
         │   (pyramids, anterior)      │
         └─────────────────────────────┘
                    ANTERIOR

• Posterior: Nuclei gracilis and cuneatus (relay station for fine touch, proprioception from below)
• Internal arcuate fibres: Axons from nuclei gracilis and cuneatus crossing the midline → forming the medial lemniscus = this crossing is the sensory decussation
• Spinal nucleus and tract of CN V (pain/temperature from face)
• Lateral spinothalamic tract (pain/temperature from body, already crossed)
• Anterior corticospinal fibres (in anterior pyramid, cross lower down at motor decussation)
• NO cranial nerve nuclei at this level (below hypoglossal nucleus)

Arterial Supply of Medulla

Q4 (SN) [2025] - Lateral Medullary Syndrome (Wallenberg Syndrome): Anatomical Basis

Clinical Features and Their Anatomical Basis:

Q5 (SN) [2025] - Cross Section of Midbrain at Level of Superior Colliculus + Weber's Syndrome

Cross Section of Midbrain at Level of Superior Colliculus

                      POSTERIOR
         ┌────────────────────────────────┐
         │   SUPERIOR COLLICULUS          │
         │   Periaqueductal grey matter   │
         │   Cerebral aqueduct            │
         │                                │
         │   Medial longitudinal          │
         │   fasciculus (MLF)             │
         │                                │
         │   Oculomotor nucleus (CN III)  │
         │   Edinger-Westphal nucleus     │
         │                                │
         │ TEGMENTUM:                     │
         │   Red nucleus                  │
         │   Medial lemniscus             │
         │   Spinothalamic tract          │
         │                                │
         │ BASE (crus cerebri/peduncle):  │
         │   Corticospinal tract          │
         │   Corticobulbar tract          │
         │   Corticopontine fibres        │
         │   CN III fascicles exiting     │
         └────────────────────────────────┘
                      ANTERIOR

1. Tectum (dorsal): Superior colliculus (visual reflex centre), cerebral aqueduct
2. Tegmentum (middle): CN III nucleus + Edinger-Westphal nucleus, red nucleus, MLF, medial lemniscus, spinothalamic tract, periaqueductal grey matter
3. Base/Crus cerebri (ventral): Corticospinal + corticobulbar + corticopontine tracts; CN III fascicles pass through the medial portion

Weber's Syndrome

1. CN III fascicles (medial peduncle)
2. Corticospinal + corticobulbar tracts (lateral peduncle)

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Part 1 - Transverse Section of Medulla (Closed): Diagram Description

Diagram: Transverse Section of Medulla (Closed) - Key Structures

POSTERIOR (Dorsal Surface):

LATERAL:

ANTERIOR (Ventral Surface):

KEY FEATURE - SENSORY DECUSSATION:

CLINICAL PEARL (from diagram):

• Ipsilateral loss of DCML (fine touch, proprioception) - because nucleus gracilis/cuneatus and medial lemniscus are affected at the same side before they cross
• Contralateral loss of pain and temperature - because lateral spinothalamic tract (already crossed from opposite side) is damaged

Part 2 - Chapter 6: Cerebellum

Q1 (Short Note) [2015] - Cerebellar Ataxia

Definition:

Functions of the Cerebellum (brief):

Features of Cerebellar Ataxia:

• Ataxic (drunken/reeling) gait - wide-based, unsteady, staggering gait; patient staggers toward the side of the lesion
• Truncal ataxia - difficulty sitting or standing without support (lesion of vermis)
• Positive Romberg's test is NOT typically positive in cerebellar ataxia (distinguishes from sensory ataxia where Romberg is positive)

• Scanning (staccato) dysarthria - slurred, explosive, slow, monotonous speech with irregular rhythm; syllables are separated and spoken with equal force

• Nystagmus - most commonly horizontal; fast phase toward the side of the lesion
• Skew deviation of eyes

• Hypotonia - decreased muscle tone on the side of the lesion (pendular knee jerk - leg swings like a pendulum)

• Titubation - rhythmic nodding tremor of the head or trunk

Cerebellar Ataxia vs Sensory Ataxia (important distinction):

Localization within Cerebellum:

• Vermis lesion → Truncal and gait ataxia (midline/axial)
• Cerebellar hemisphere lesion → Ipsilateral limb ataxia (same side as lesion)
• Flocculonodular lobe → Vertigo, nystagmus, vestibular ataxia

Common Causes of Cerebellar Ataxia:

• Acute: Stroke (cerebellar infarction/haemorrhage), alcohol intoxication, drug toxicity (phenytoin), post-viral (chickenpox)
• Chronic/Progressive: Multiple sclerosis, Friedreich's ataxia (hereditary), cerebellar tumour, alcohol-related cerebellar degeneration, hypothyroidism

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 6: Cerebellum

Short Note: Cerebellar Ataxia [2015]

Definition

Functions of Cerebellum (Brief)

Features of Cerebellar Ataxia

• Inability to judge the range/distance of movement
• Overshoots (hypermetria) or undershoots the target
• Test: Finger-nose test, Heel-shin test

• Inability to perform rapid alternating movements (e.g., pronation-supination)
• Test: Ask patient to rapidly pronate and supinate the hand

• Tremor that appears or worsens on purposeful movement, absent at rest
• Coarse tremor that increases as hand approaches the target
• Opposite of resting tremor (Parkinson's)

• Wide-based, staggering, "drunken" gait
• Patient staggers/deviates toward the side of the lesion
• Cannot walk in a straight line (tandem walking impaired)

• Slurred, explosive, monotonous speech
• Syllables are separated and spoken with equal force

• Decreased muscle tone on the ipsilateral side
• Pendular knee jerk - leg swings like a pendulum (due to loss of damping by hypotonic muscles)

• Involuntary rhythmic oscillation of the eyeballs
• Usually horizontal, fast phase toward the side of the lesion

• Patient cannot stop a movement promptly when resistance is suddenly removed
• Positive: forearm rebounds and hits face when resistance released

• Rhythmic tremor/nodding of head or trunk (vermis lesion)

• Complex movements broken into successive parts instead of smooth single action

Important Distinction: Cerebellar vs Sensory Ataxia

Romberg's test: Stand with feet together, eyes closed. Positive = falls with eyes closed only (sensory ataxia). In cerebellar ataxia, patient sways with eyes open also - Romberg is negative.

Localization

Common Causes

• Acute: Cerebellar stroke (infarct/haemorrhage), alcohol intoxication, drug toxicity (phenytoin), post-viral
• Chronic: Multiple sclerosis, Friedreich's ataxia, cerebellar tumour, alcohol-related degeneration

References: B.D. Chaurasia Human Anatomy Vol. 3; Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 7: Fourth Ventricle

Q1 (LA) [Jan 22] - CSF Circulation Pathway + Structures on Floor of Fourth Ventricle [1+3+5+1]

Part A: CSF - Introduction [1 mark]

• Volume: ~150 mL total (35 mL in ventricles, rest in subarachnoid space)
• Pressure: 60-150 mm H₂O
• Production: ~500 mL/day; turned over ~3-4 times daily

Part B: Pathway of CSF Circulation [3 marks]

PRODUCTION
Choroid plexus of LATERAL VENTRICLES (main source)
+ Choroid plexus of 3rd and 4th ventricles
            ↓
LATERAL VENTRICLES (left and right)
            ↓  [via Foramen of Monro (Interventricular foramen)]
THIRD VENTRICLE (midline, diencephalon)
            ↓  [via Cerebral Aqueduct of Sylvius - in midbrain]
FOURTH VENTRICLE (between pons/medulla anteriorly and cerebellum posteriorly)
            ↓
Exits 4th ventricle via THREE openings:
• 1 median aperture = Foramen of Magendie (in roof of 4th ventricle)
• 2 lateral apertures = Foramina of Luschka (bilateral, at lateral recesses)
            ↓
SUBARACHNOID SPACE (around brain and spinal cord)
            ↓  [cisterns: cerebellomedullary/cisterna magna, pontine, interpeduncular cisterns]
Flows upward over cerebral hemispheres
            ↓
REABSORPTION
Arachnoid villi / Arachnoid granulations (Pacchionian bodies)
→ project into SUPERIOR SAGITTAL SINUS
→ CSF drains into venous blood (one-way valve mechanism)

Part C: Structures on the Floor of the Fourth Ventricle [5 marks]

• Upper part: posterior surface of the pons
• Lower part: posterior surface of the medulla oblongata

Boundaries:

• Superolateral: Superior cerebellar peduncles
• Inferolateral: Inferior cerebellar peduncles (medullary striae)
• Apex (superior): Cerebral aqueduct
• Apex (inferior): Obex (small membrane closing the caudal end)

Key Longitudinal Features:

• Medial eminence (medial to sulcus limitans): motor nuclei
• Vestibular area (lateral to sulcus limitans): sensory nuclei

Structures on the Floor (from above downward):

Part D: Clinical Significance [1 mark]

• A tumour (e.g., medulloblastoma, ependymoma) on the floor of the 4th ventricle can compress the cranial nerve nuclei present there, causing:
  • CN VI (abducens palsy) - diplopia, inability to abduct eye
  • CN VII (facial palsy)
  • CN X, XII (vagal/hypoglossal signs - dysphagia, tongue deviation)
• Blockage of the 4th ventricle → obstructive hydrocephalus
• The area postrema (vomiting centre) on the floor explains why posterior fossa lesions commonly cause nausea and vomiting

Q2 (Short Note) [March 2026] - Floor of the Fourth Ventricle

Definition:

Key Longitudinal Landmarks:

1. Median sulcus - midline groove
2. Sulcus limitans - lateral groove on each side; divides floor into medial eminence (motor) and vestibular area (sensory)

Important Structures:

• Facial colliculus - most important landmark; formed by CN VI nucleus + CN VII fibres
• Locus coeruleus - at superior angle; noradrenergic nucleus

• Hypoglossal triangle - overlies CN XII nucleus
• Vagal triangle - overlies dorsal nucleus of CN X
• Area postrema - chemoreceptor trigger zone (vomiting); no BBB
• Stria medullaris - transverse fibres separating pontine and medullary parts
• Obex - at caudal tip

Clinical Pearl:

• Facial colliculus lesion = combined CN VI + CN VII palsy (ipsilateral abducens palsy + ipsilateral facial palsy)
• Area postrema stimulation = intractable vomiting (seen in posterior fossa tumours, MS plaques)
• Obstruction at level of 4th ventricle = non-communicating (obstructive) hydrocephalus

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8: Cerebrum, Diencephalon, Basal Nuclei and White Matter

Q1 - Why Does Hypothalamic Lesion Lead to Diabetes Insipidus? [4 marks]

Normal Physiology:

• Synthesized in the supraoptic nucleus (mainly) and paraventricular nucleus of the hypothalamus
• Transported along axons (hypothalamo-hypophyseal tract) to the posterior pituitary (neurohypophysis) where it is stored and released
• Action: Acts on collecting ducts and DCT of kidney → increases water reabsorption → produces concentrated urine

How Hypothalamic Lesion Causes Diabetes Insipidus:

• Kidney collecting ducts cannot reabsorb water
• Massive production of large volumes of dilute urine (polyuria) - up to 15-20 litres/day
• Compensatory excessive thirst (polydipsia)
• Urine specific gravity very low (<1.005)
• No glucosuria (unlike diabetes mellitus) → hence called insipidus (tasteless/bland)

Types:

• Central (Neurogenic) DI = hypothalamic/pituitary lesion → ADH deficiency → what is described above
• Nephrogenic DI = kidney unresponsive to ADH (hypothalamus is normal)

Causes of hypothalamic lesion causing DI:

Q2 (Case) [June 22] - 65-year-old with Left-sided Paralysis, Internal Capsule Lesion [1+2+2+1+4+4+1]

Clinical Summary:

1. What did he suffer from? [1 mark]

2. Type of Paralysis and Explanation [2 marks]

3. Parts of Internal Capsule + Site of Lesion [2 marks]

• Medially: Thalamus + caudate nucleus
• Laterally: Lentiform nucleus (globus pallidus + putamen)

4. Fibres Passing Through Different Parts [1 mark]

5. Arterial Supply of Internal Capsule [4 marks]

           ACA
            |
    Recurrent artery
    of Heubner
    → Anterior limb

           MCA (proximal)
            |
    Lateral lenticulostriate arteries
    → Anterior limb, Genu, Posterior limb

           ICA
            |
    Anterior choroidal artery
    → Posterior limb (inferior part), Retrolenticular, Sublenticular

6. Most Commonly Ruptured Artery in Cerebral Haemorrhage [1 mark]

• Also called the "Artery of cerebral haemorrhage" or "Artery of stroke" (Charcot's artery of cerebral haemorrhage)
• It is a small end artery with thin walls under constant high pressure in hypertension
• It supplies the internal capsule and basal ganglia
• Rupture → hypertensive intracerebral haemorrhage in the region of the internal capsule → contralateral hemiplegia (capsular hemiplegia)
• This is why hypertension is the most important risk factor for this type of stroke

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8: Cerebrum, Diencephalon, Basal Nuclei and White Matter (Continued)

Note: Q6 (ruptured artery) and the internal capsule case (Q2) were answered in full in the previous response. Below are the new questions from this page.

Q3 (LA) [Nov 21] - Commissural Fibres of Brain + Corpus Callosum + Forceps Major and Minor [3+7+5]

Part A: Commissural Fibres of the Brain [3 marks]

Part B: Parts and Relations of the Corpus Callosum [7 marks]

Parts (from anterior to posterior):

Relations:

• Covered by the cingulate gyrus (separated by the callosal sulcus)
• Covered superiorly by the longitudinal cerebral fissure

• Genu: Related to head of caudate nucleus and anterior horns of lateral ventricles
• Body: Related to body of fornix (attached by septum pellucidum)
• Splenium: Related to tela choroidea and choroid plexus of lateral ventricles; overlies the pineal gland and tectum

• Continues inferiorly as the lamina terminalis

• Overhangs the pineal body, tectum, and superior cerebellar surface

Part C: Forceps Major and Forceps Minor [5 marks]

• Formed by fibres from the genu (and rostrum) of the corpus callosum
• Curves anteriorly into the frontal lobes (frontal horns of lateral ventricles)
• Connects the prefrontal cortices of both hemispheres
• Appears like a pair of forceps pointing anteriorly

• Formed by fibres from the splenium of the corpus callosum
• Curves posteriorly into the occipital lobes
• Connects the occipital cortices (visual areas) of both hemispheres
• Larger than forceps minor

• Fibres from the body and splenium that sweep around the posterior and inferior horns of the lateral ventricles (temporal and occipital horns)
• They form a thin sheet (tapetum) on the lateral wall of the posterior horn

Q4 (LA) [May 23] - Patient with CVA + Hemiplegia + Internal Capsule [2+3+5+5]

1. Functional Components of Facial Nerve (CN VII) [2 marks]

2. UMN vs LMN Lesion of Facial Nerve [3 marks]

3. Branches of Intracranial Part of Facial Nerve [5 marks]

1. Greater Petrosal Nerve (at geniculate ganglion)
   • Carries preganglionic parasympathetic fibres → pterygopalatine ganglion → secretomotor to lacrimal gland and nasal/palatal glands
   • Also carries taste from soft palate
2. Nerve to Stapedius (in mastoid/vertical segment)
   • Supplies stapedius muscle
   • Prevents excessive ossicular vibration; damage → hyperacusis
3. Chorda Tympani (just above stylomastoid foramen)
   • Crosses middle ear → petrotympanic fissure → joins lingual nerve
   • Carries taste from anterior 2/3 tongue
   • Carries preganglionic parasympathetic fibres → submandibular ganglion → secretomotor to submandibular and sublingual glands

4. Bell's Palsy [5 marks]

• Cannot wrinkle forehead; cannot close eye (Bell's phenomenon: eyeball rolls up on attempted closure)
• Drooping of angle of mouth, loss of nasolabial fold
• Food collects between cheek and teeth (buccinator paralysis)
• Hyperacusis (nerve to stapedius affected)
• Loss of taste from anterior 2/3 tongue (chorda tympani affected)
• Dry eye (greater petrosal nerve affected - in high lesions)

• Oral prednisolone (steroids) - within 72 hours of onset
• Acyclovir (antiviral)
• Eye care: artificial tears + eye patch at night

Q5 [2019] - Ischaemic Damage to Anterior Limb of Internal Capsule May Affect Recent Memory Tracing

Answer:

1. Frontopontine fibres (cortex → pons)
2. Anterior thalamic radiation - fibres connecting the anterior nucleus of thalamus ↔ prefrontal cortex (especially cingulate gyrus)

Hippocampus → Fornix → Mammillary bodies (hypothalamus) → Mammillothalamic tract → Anterior nucleus of thalamus → Anterior thalamic radiation (passes through anterior limb of internal capsule) → Cingulate gyrus → Cingulum → Entorhinal cortex → Hippocampus

• The anterior thalamic radiation (which carries signals from the anterior thalamic nucleus to the prefrontal cortex and cingulate gyrus) passes through the anterior limb of the internal capsule.
• This is a critical part of the Papez circuit - the circuit responsible for memory consolidation and recent memory formation.
• An ischaemic lesion of the anterior limb interrupts this thalamo-cortical pathway → disrupts the Papez circuit → impairs recent (short-term) memory tracing.

Q6 [Mar 21] - White Fibres of Brain + Internal Capsule Formation + Parts + Clinical Application + Arterial Supply

Types of White Fibres of the Brain:

How Internal Capsule is Formed:

• Axons from the motor cortex (precentral gyrus) descend, and sensory fibres from the thalamus ascend.
• These projection fibres pass between:
  • Medially: Thalamus + head of caudate nucleus
  • Laterally: Lentiform nucleus (globus pallidus + putamen)
• This compact band of fibres = Internal Capsule
• On horizontal section it appears as a "V" or boomerang shape, with the opening facing laterally.
• Above it, the fibres fan out as the corona radiata; below it they continue as the cerebral peduncle in the midbrain.

Parts of Internal Capsule + Fibres + Clinical Application:

Arterial Supply:

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8 (Continued) - Page 17

Note: Questions 6, 7, and 8 on this page have already been answered in full detail in previous responses:

• Q6 (Commissural fibres + Corpus callosum + Forceps major/minor) → Answered in the previous session
• Q7 (Internal capsule - types, parts, fibres, relations, applied) → Answered fully
• Q8 (Floor of fourth ventricle) → Answered fully

Q9 [Nov 21] - Macular Vision is Spared in Lesion of the Posterior Cerebral Artery

Definition of Terms:

Normal Visual Pathway Recap:

Retina → Optic nerve → Optic chiasma → Optic tract
→ Lateral Geniculate Body (LGB) of thalamus
→ Optic radiation (geniculocalcarine tract)
→ Primary Visual Cortex (Area 17, calcarine sulcus, occipital lobe)

• Macular fibres (central vision) → represented at the occipital pole (most posterior part of visual cortex)
• Peripheral retinal fibres → represented in the anterior/lateral part of the visual cortex (anterior to occipital pole)

Blood Supply of the Visual Cortex:

Why Macular Vision is SPARED in PCA Occlusion:

• The peripheral visual cortex (supplied only by PCA) is infarcted → peripheral visual field is lost
• The occipital pole (macular region) receives collateral blood flow from MCA branches even when PCA is blocked → the occipital pole survives ischaemia
• Therefore, central (macular) vision is preserved

Clinical Manifestation:

LEFT visual field          RIGHT visual field
[intact peripheral]        [peripheral LOST]
[intact central]           [central SPARED] ← macular sparing

Summary Table:

Important Distinction:

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8 Continued (Page from Feb 2022)

Already answered in previous sessions: Q10 (Internal capsule - position/parts/fibres/injury/blood supply), Q11 (Midbrain cross-section at superior colliculus + Weber's syndrome), Q13b (Diabetes Insipidus from hypothalamic lesion).

Q11 (Part) [Feb 2022] - Functional Importance of Substantia Nigra

Two Parts:

1. Pars compacta (compact part) - contains dopaminergic neurons (use dopamine as neurotransmitter)
2. Pars reticulata (reticular part) - uses GABA; functionally similar to globus pallidus interna

Functions / Functional Importance:

Clinical Importance:

• Loss of dopamine → striatum becomes overactive → excessive inhibition of thalamus → reduced motor output
• Features: Resting tremor (pill-rolling), Rigidity (cogwheel/lead-pipe), Bradykinesia (slowness), Postural instability
• Midbrain cross-section shows pale (depigmented) substantia nigra
• Treatment: Levodopa (dopamine precursor) replaces the lost dopamine

Q12 (Short Note) [Feb 2022] - Sensory and Motor Speech Areas of the Brain [5 marks]

Motor Speech Area (Broca's Area):

• Patient understands language but cannot speak fluently
• Speech is slow, effortful, telegraphic ("broken speech")
• Grammar is lost; content words preserved
• Comprehension relatively intact
• Patient is usually frustrated (aware of deficit)

Sensory Speech Area (Wernicke's Area):

• Patient cannot understand spoken or written language
• Speech is fluent but meaningless ("word salad" - paraphasias, neologisms)
• Patient is unaware of their deficit

Other Speech-Related Areas:

Summary Table:

Q13 (Part) [Feb 22] - Anatomical Basis of Hydrocephalus [4 marks]

Definition:

Normal CSF Production and Circulation (brief):

• CSF produced by choroid plexus (~500 mL/day)
• Flows: Lateral ventricles → 3rd ventricle (via Foramen of Monro) → 4th ventricle (via cerebral aqueduct) → Subarachnoid space (via Foramina of Magendie and Luschka) → Absorbed at arachnoid granulations into superior sagittal sinus

Types of Hydrocephalus and Their Anatomical Basis:

• CSF flow is blocked within the ventricular system
• Ventricles upstream of the obstruction enlarge

• CSF CAN communicate freely between ventricles and subarachnoid space
• Problem = impaired absorption at arachnoid granulations
• Causes: Post-meningitis (adhesions block granulations), subarachnoid haemorrhage (blood blocks granulations), venous sinus thrombosis

• Ventricles enlarged but CSF pressure intermittently normal
• Clinical triad: Gait apraxia + Dementia + Urinary incontinence (Wet, Wobbly, Wacky)

Clinical Features (due to raised ICP):

• Infants (sutures not fused): Enlarged head, bulging fontanelle, setting-sun sign (eyes deviate downward), prominent scalp veins
• Adults: Headache (worse in morning), vomiting, papilloedema, CN VI palsy (false localizing sign)

Treatment:

• VP shunt (ventriculoperitoneal shunt) - most common
• Endoscopic third ventriculostomy (ETV) - for obstructive hydrocephalus

Also previously answered: Q13 (Lesion of hypothalamus → Diabetes Insipidus) - see previous session's answer for full details.

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Internal Capsule Case - Jan 2022 [15 marks]

(a) What did he suffer from? [1 mark]

(b) Type of Paralysis + Explanation [3 marks]

(c) Parts of Internal Capsule + Site of Lesion [2 marks]

• Medially: Head of caudate nucleus + thalamus
• Laterally: Lentiform nucleus (putamen + globus pallidus)

Five Parts:

Site of Lesion in this Patient:

• The corticospinal tract (causing hemiplegia) passes through the posterior limb
• The superior thalamic radiation (causing altered sensation) also passes through the posterior limb

(d) Fibres Passing Through Different Parts + Diagram [8 marks]

Fibres in Each Part:

Diagram of Internal Capsule (Horizontal Section):

         MEDIAL
    Caudate nucleus
          |
    ┌─────────────────┐
    │  ANTERIOR LIMB  │← Frontopontine + Anterior thalamic radiation
    │                 │
    │    GENU         │← Corticobulbar (corticonuclear) fibres
    │                 │
    │  POSTERIOR LIMB │← Corticospinal + Superior thalamic radiation
    │                 │
    │  RETROLENTICULAR│← Visual radiation
    │                 │
    │  SUBLENTICULAR  │← Auditory radiation
    └─────────────────┘
          |
    Lentiform nucleus
         LATERAL

• Face → Arm → Trunk → Leg

(e) Most Commonly Ruptured Artery in Cerebral Haemorrhage [1 mark]

• It is a small, thin-walled end artery (no collaterals)
• It is subjected to constant high blood pressure in hypertensive patients
• It arises at a right angle from the MCA → subjected to maximum haemodynamic stress
• It supplies the internal capsule and basal ganglia

• "Artery of cerebral haemorrhage" (Charcot)
• "Artery of stroke"

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8 Continued

Note: Q15 top (internal capsule fibres + most commonly ruptured artery) = already answered in full in previous sessions.

Q15 [Nov 2023] - Tumour of Inferior Parietal Lobule May Lead to Sensory Aphasia [4 marks]

Anatomy of the Inferior Parietal Lobule:

1. Supramarginal gyrus (Brodmann area 40) - curves around the posterior end of the lateral sulcus (Sylvian fissure)
2. Angular gyrus (Brodmann area 39) - curves around the posterior end of the superior temporal sulcus

Why a Tumour Here Causes Sensory Aphasia:

• Wernicke's area (Brodmann area 22 = posterior superior temporal gyrus) is the primary centre for speech comprehension.
• The angular gyrus (area 39) of the inferior parietal lobule is a crucial multimodal association area that:
  • Integrates auditory, visual, and somatosensory information
  • Is intimately connected to Wernicke's area posteriorly
  • Plays a major role in reading, writing, and language comprehension
  • Is considered part of the extended Wernicke's area/language zone
• The supramarginal gyrus (area 40) is involved in phonological processing and repetition.

1. Directly damages the angular gyrus and supramarginal gyrus
2. Compresses or disrupts connections with Wernicke's area
3. Interrupts the arcuate fasciculus and other language association pathways connecting temporal and frontal lobes
4. Results in impaired language comprehension and processing → Sensory (receptive) aphasia

• Fluent but meaningless speech ("word salad")
• Cannot understand spoken words
• Cannot repeat sentences
• Reading and writing also impaired (angular gyrus lesion → alexia + agraphia)
• Patient unaware of their errors (unlike Broca's aphasia)

Q16 (LQ) [March 2024] - 76-year-old Right-handed Hypertensive with Right Hemiplegia + Aphasia [2+3+3+2]

1. Which Artery and Which Hemisphere? [2 marks]

• The patient is right-handed → dominant hemisphere = LEFT
• Right-sided hemiplegia = lesion in the contralateral (LEFT) hemisphere (motor fibres from left motor cortex control right side of body)
• Both Broca's area (speech production) and Wernicke's area (speech comprehension) are in the left (dominant) hemisphere in right-handed people
• The MCA supplies the lateral (outer) surface of the cerebral hemisphere including:
  • Motor cortex (face + arm region)
  • Broca's area (inferior frontal)
  • Wernicke's area (superior temporal)
  • Internal capsule (via lenticulostriate branches)
• Occlusion of the left proximal MCA causes right hemiplegia + global aphasia = exactly what this patient has

2. Anatomical Reason for Difficulty in Speaking and Understanding Speech [3 marks]

Motor Speech Area (Broca's Area):

• Location: Inferior frontal gyrus of left hemisphere, Brodmann areas 44 and 45
• Supplied by: Superior (anterior) division of left MCA
• Function: Motor programming of speech - converts thoughts into spoken words
• Damage → Broca's (Expressive/Non-fluent) Aphasia = cannot speak fluently, but may understand

Sensory Speech Area (Wernicke's Area):

• Location: Posterior superior temporal gyrus of left hemisphere, Brodmann area 22
• Supplied by: Inferior (posterior) division of left MCA
• Function: Comprehension of spoken and written language
• Damage → Wernicke's (Receptive/Fluent) Aphasia = cannot understand language, but produces fluent meaningless speech

In this patient:

• Large left MCA territory infarct has damaged both Broca's and Wernicke's areas (and the arcuate fasciculus connecting them)
• Result: Global Aphasia = total loss of both speech production AND comprehension
• Also: Right-sided cortical areas (face/arm motor strip, sensory strip) damaged → right hemiplegia + sensory loss

3. Which Part of the Brain is Responsible for Right Hemiplegia? [3 marks]

A. Primary Motor Cortex (Precentral Gyrus - Area 4):

• Located in the left precentral gyrus (anterior to central sulcus)
• Upper limb area = upper lateral surface (hand knob area)
• Face area = lower lateral surface
• Leg area = medial surface (paracentral lobule - not in MCA territory)
• Supplied by MCA (face and arm areas); ACA supplies the leg area (paracentral lobule)
• Damage → Right-sided UMN paralysis of face and arm

B. Posterior Limb of the Internal Capsule:

• Corticospinal tract (from motor cortex) passes compactly through the posterior limb of the left internal capsule
• Supplied by lateral lenticulostriate arteries (branches of left MCA)
• Damage here → Dense contralateral UMN hemiplegia (right side) - face, arm, and leg all affected
• This is the most common site causing the hemiplegia in MCA occlusion

Why UMN (not LMN) Paralysis:

• Increased tone, exaggerated reflexes, Babinski positive → all UMN signs
• Fibres cross at medullary decussation → left hemisphere controls right side of body

Somatotopic arrangement in motor cortex (homunculus):

Medial → Leg (ACA territory)
Lateral → Arm → Face (MCA territory)

Summary of Clinical Correlation:

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Chapter 8 Continued - Page 19

Q17 (LQ) [Aug 2024] - Speech Centres in Brain + Types of Aphasia + Artery [5+4+1]

Part A: Different Speech Centres in the Brain [5 marks]

1. Motor Speech Area - Broca's Area

• Location: Inferior frontal gyrus (pars triangularis + pars opercularis), Brodmann areas 44 and 45, left frontal lobe
• Function: Motor programming of speech - coordinates articulation (tongue, lips, larynx, respiration); converts thoughts into spoken words

2. Sensory (Receptive) Speech Area - Wernicke's Area

• Location: Posterior part of superior temporal gyrus, Brodmann area 22, left temporal lobe
• Function: Comprehension of spoken and written language; formulation of meaningful speech

3. Supplementary Motor Area

• Location: Medial aspect of frontal lobe, superior to Broca's area (area 6, medial)
• Function: Initiates speech; involved in the motivation/planning to speak

4. Angular Gyrus (Reading/Writing area)

• Location: Inferior parietal lobule, Brodmann area 39
• Function: Integrates visual (reading), auditory, and somatosensory information for language; essential for reading and writing

5. Arcuate Fasciculus

• A white matter bundle connecting Broca's and Wernicke's areas
• Carries information from the sensory speech area to the motor speech area

Labelled Diagram:

          FRONTAL LOBE       PARIETAL LOBE
    ┌──────────────────────────────────┐
    │  Supplementary                   │
    │  motor area                      │
    │                                  │
    │  [BROCA'S AREA]  Arcuate  [Angular gyrus]
    │  Areas 44, 45  ←fasciculus→  Area 39
    │  Inferior                        │
    │  frontal gyrus                   │
    └───────────────────┬──────────────┘
                        │ Sylvian fissure
    ┌───────────────────┴──────────────┐
    │   TEMPORAL LOBE                  │
    │   [WERNICKE'S AREA]              │
    │   Area 22                        │
    │   Superior temporal gyrus        │
    └──────────────────────────────────┘

Part B: Types of Aphasia with Anatomical Explanation [4 marks]

Part C: Occlusion of Which Artery Causes Which Type of Aphasia [1 mark]

Q18 [Dec 2024] - Calcarine Sulcus Represents Limiting, Axial, and Complete Sulcus

Classification of Sulci (B.D. Chaurasia):

Why the Calcarine Sulcus Represents All Three Types:

1. As a LIMITING Sulcus:

• The cortex within the calcarine sulcus (its floor and walls) = Area 17 (primary visual cortex - striate cortex, with the line of Gennari)
• The cortex above and below the calcarine sulcus = Area 18 and 19 (visual association cortex - peristriate and parastriate)
• The cortex on one wall is architecturally different from the surrounding cortex → it limits the primary visual area
• Therefore it is a limiting sulcus

2. As an AXIAL Sulcus:

• The calcarine sulcus runs along the long axis of the medial occipital lobe (antero-posteriorly)
• The cortex on both banks (upper and lower walls) is the same type (both are striate cortex, area 17)
• It develops within the centre of the visual area and runs along its axis
• Therefore it is an axial sulcus

3. As a COMPLETE Sulcus:

• The calcarine sulcus is so deep that it indents the medial wall of the posterior horn of the lateral ventricle
• This produces a visible elevation (eminence) on the floor of the posterior horn of the lateral ventricle called the "Calcar Avis" (spur of a cock)
• Calcar avis is directly produced by the calcarine sulcus pushing into the ventricular wall
• Therefore it is a complete sulcus

Summary:

• It divides the primary visual cortex into upper bank (receives lower retinal fibres → upper visual field from below the horizontal meridian) and lower bank (receives upper retinal fibres → lower visual field from above the horizontal meridian)

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)

Q19 (LQ) [March 2026] - Contralateral Hemiplegia + Sensory Loss from White Fibre Injury [15 marks]

(I) Name the White Fibre Most Likely Affected [2 marks]

• "White fibres of cerebrum" + contralateral hemiplegia AND sensory loss from a single CVA lesion = classic presentation of internal capsule lesion
• The internal capsule is a compact band of projection fibres (the most important white matter in the cerebrum)
• It contains both the descending corticospinal tract (motor → hemiplegia) and the ascending thalamic sensory radiation (sensory → hemisensory loss) in its posterior limb
• The internal capsule is the site most commonly affected in hypertensive CVA (rupture of lenticulostriate artery)

(II) Different Parts of the Internal Capsule [2 marks]

(III) Relations of the Internal Capsule with Diagram [3 marks]

Relations:

• Anterior limb: Head of caudate nucleus (medially), separated from thalamus by a groove
• Posterior limb: Thalamus (medially)
• The thalamostriate vein and stria terminalis lie in the groove between the caudate nucleus and thalamus (just medial to the internal capsule)

• Anterior limb: Lentiform nucleus (putamen + globus pallidus) laterally
• Posterior limb: Lentiform nucleus (globus pallidus and putamen) laterally

Diagram (Horizontal Section):

         LATERAL VENTRICLE
              ↑
    Head of caudate nucleus  ←— MEDIAL
         |
    ┌────────────────────────────────┐
    │    [ANTERIOR LIMB]             │
    │         |                      │
    │       [GENU]                   │
    │         |                      │
    │    [POSTERIOR LIMB]            │
    │         |                      │
    │  [RETROLENTICULAR PART]        │
    │         |                      │
    │  [SUBLENTICULAR PART]          │
    └────────────────────────────────┘
         |                      |
    Thalamus (medial)    Lentiform nucleus (lateral)

    Above: Corona radiata → Cerebral cortex
    Below: Cerebral peduncle → Brainstem

(IV) Table of Fibres Passing Through Different Parts [4 marks]

(V) Arterial Supply of the Internal Capsule [4 marks]

Blood Supply Diagram:

         ICA (Internal Carotid Artery)
         /              \
       ACA              MCA
        |            (proximal)
  Recurrent          Lateral lenticulostriate
  artery of Heubner  arteries
        ↓                   ↓
  Anterior limb    Anterior limb + Genu +
                   Posterior limb (superior)

         ICA
          |
  Anterior choroidal artery
          ↓
  Posterior limb (inferior) +
  Retrolenticular + Sublenticular

Most Important Clinical Point:

References: B.D. Chaurasia Human Anatomy Vol. 3 (Head, Neck & Brain); Vishram Singh Textbook of Anatomy - Head, Neck & Brain; Gray's Anatomy for Students (4th Ed.)