IQ City Medical College - Anatomy Exam Answers

MBBS Phase One - Third Internal Assessment

QUESTION 2 (15 marks) - Otitis Media with Effusion in a 7-year-old

a) Which anatomical area is affected? (1 mark)

b) Boundaries and Contents of the Middle Ear (6 marks)

Walls / Boundaries:

Contents:

1. Ossicles - Three interconnected bones:
   • Malleus (handle attached to tympanic membrane, head in epitympanic recess)
   • Incus (connected to malleus by synovial joint)
   • Stapes (footplate in oval window, connected to incus by synovial joint)
2. Muscles:
   • Tensor tympani (supplied by CN V3; attaches to handle of malleus; dampens vibration)
   • Stapedius (supplied by CN VII; attaches to neck of stapes; protective reflex against loud sounds)
3. Chorda tympani (branch of CN VII) - crosses the cavity between the handle of malleus and long process of incus
4. Tympanic plexus - on the promontory, formed by tympanic branch of CN IX (Jacobson's nerve) + sympathetic fibers; provides sensory supply to middle ear mucosa and preganglionic parasympathetic fibers (via lesser petrosal nerve) to parotid gland
5. Air and mucous membrane lining

c) Where will the ENT surgeon make an incision to drain the effusion and why? (3 marks)

Why antero-inferior?

• Anterosuperior - avoided: contains the anterior malleal fold, chorda tympani runs nearby
• Posterosuperior - most dangerous: overlies the ossicular chain (incus, stapes), chorda tympani, and the facial nerve canal
• Posteroinferior - acceptable but less preferred: risk of damaging ossicular reflections
• Antero-inferior - SAFEST: farthest from the ossicular chain, chorda tympani, facial nerve, and major blood vessels; allows gravity-assisted drainage of effusion

d) Course and Branches of the Facial Nerve in This Region (3 marks)

Course through the temporal bone:

1. CN VII enters the internal acoustic meatus (with CN VIII and labyrinthine artery)
2. Enters the facial canal (Canal of Fallopius) in the petrous temporal bone
3. Labyrinthine segment - passes to the geniculate ganglion (first genu); gives off:
   • Greater petrosal nerve (preganglionic parasympathetic to lacrimal, nasal, palatal glands via pterygopalatine ganglion)
4. Tympanic (horizontal) segment - runs across the medial wall of the middle ear, superior to the oval window, deep to the lateral semicircular canal (second genu); gives off:
   • Nerve to stapedius
5. Mastoid (vertical) segment - descends in posterior wall; gives off:
   • Chorda tympani (carries taste from anterior 2/3 tongue + secretomotor to submandibular/sublingual glands)
6. Exits skull via the stylomastoid foramen

Extracranial branches in the region:

• Posterior auricular nerve (to occipitofrontalis, auricular muscles)
• Branches to stylohyoid and posterior belly of digastric
• Then enters the parotid gland and divides into 5 terminal branches:
  • Temporal
  • Zygomatic
  • Buccal
  • Marginal mandibular
  • Cervical (Mnemonic: "To Zanzibar By Motor Car")

e) What is Ramsay Hunt Syndrome? (2 marks)

1. Facial nerve palsy (ipsilateral LMN type - forehead involved, Bell's palsy-like)
2. Painful vesicular eruption in the ear (auricle, external auditory canal, tympanic membrane) and sometimes soft palate/anterior tongue
3. Sensorineural hearing loss and vertigo (if CN VIII is also affected, due to proximity at the internal acoustic meatus)

QUESTION 3 (15 marks) - Explain the Following

a) Why fracture of the skull in the region of pterion may cause extra-dural hemorrhage

• Frontal, Parietal, Temporal (squamous part), and Greater wing of Sphenoid

• Is a branch of the maxillary artery (from external carotid)
• Enters the skull via the foramen spinosum
• Runs in grooves (and sometimes tunnels) on the inner surface of the temporal and parietal bones
• Its anterior branch passes directly under the pterion

• A blow to the temporoparietal region (e.g., a cricket bat, punch) fractures the thin pterion
• The bone fragment lacerates the anterior branch of the middle meningeal artery
• Arterial blood accumulates in the potential space between the inner table of the skull and the outer (endosteal) layer of the dura mater
• Creates a biconvex (lens-shaped) hematoma on CT
• Classic presentation: brief loss of consciousness → lucid interval → rapid deterioration (as expanding hematoma compresses the temporal lobe and uncus, causing uncal herniation and CN III palsy)
• Management: Emergency temporal craniotomy / burr hole decompression

b) Why after thyroidectomy, patients may complain of hoarseness of voice

• Right RLN: loops under the right subclavian artery and ascends in the right tracheo-oesophageal groove
• Left RLN: loops under the arch of the aorta (ligamentum arteriosum) and ascends in the left tracheo-oesophageal groove

• During ligation of the inferior thyroid artery (the RLN may be caught in the ligature if anatomy is not carefully identified)
• The RLN lies in the "danger triangle" between the inferior thyroid artery branches
• Excessive traction, diathermy, or inadvertent division
• Unilateral injury: hoarseness (the affected vocal cord lies in the paramedian or cadaveric position)
• Bilateral injury: stridor, respiratory distress (emergency tracheotomy needed)

c) Why abducent nerve palsy is a common feature of increased intracranial pressure

1. Arises from the abducent nucleus in the pons (floor of 4th ventricle)
2. Exits at the pontomedullary junction (between pons and pyramid of medulla)
3. Travels upward through the subarachnoid space
4. Passes over the apex of the petrous temporal bone (Dorello's canal)
5. Bends sharply over the petrous ridge (pierces the dura and crosses under the petroclinoid ligament/Gruber's ligament)
6. Enters the cavernous sinus
7. Enters the orbit via the superior orbital fissure to supply lateral rectus

• Raised ICP causes downward displacement (tonsillar herniation) and generalized brain shift
• The nerve is stretched over the sharp petrous ridge (Gruber's ligament acts as a fulcrum)
• This produces stretching/compression of the nerve even without a lesion at the base of the pons
• Results in ipsilateral lateral rectus palsy → convergent squint (esotropia) + failure of abduction
• Called a "false localizing sign" because the palsy does not indicate the actual site of the lesion

d) Sensory and Motor Speech Areas of the Brain

Motor Speech Area:

• Located in the posterior part of the inferior frontal gyrus (F3) of the dominant hemisphere
• Controls the motor planning and articulation of speech (coordinates movements of lips, tongue, larynx)
• Damage: Broca's (expressive/non-fluent) aphasia - patient understands but cannot produce fluent speech; speaks in short, telegraphic phrases with effort; writing also affected

Sensory Speech Area:

• Located in the posterior superior temporal gyrus of the dominant hemisphere
• Involved in comprehension and interpretation of spoken and written language
• Connected to Broca's area via the arcuate fasciculus
• Damage: Wernicke's (receptive/fluent) aphasia - fluent but nonsensical speech (word salad, neologisms); poor comprehension; reading also impaired

Additional Areas:

• Angular gyrus (Area 39) and supramarginal gyrus (Area 40) in the inferior parietal lobe - involved in reading, writing, and integration of language
• Primary auditory cortex (Areas 41 and 42) - Heschl's gyrus, superior temporal plane - receives auditory input that feeds into Wernicke's area
• Arcuate fasciculus - white matter tract connecting Wernicke's and Broca's areas; damage causes conduction aphasia (fluent speech, good comprehension, poor repetition)

e) A Gradually Increasing Lateral Cystic Swelling in the Neck, Not Present at Birth

• Appears in late childhood or early adulthood (not at birth - hence it is not a cystic hygroma or dermoid, which are present at birth)
• Gradually enlarging after URTI (infection causes expansion of the cyst)
• Located along the anterior border of the sternocleidomastoid (SCM), at the junction of upper 1/3 and lower 2/3 of SCM
• Soft, fluctuant, transilluminable
• Not fixed to skin but may be attached deeply

• Lies deep to platysma and investing layer of deep cervical fascia
• Anterior to SCM
• Contains cholesterol crystals in straw-colored fluid
• The branchial sinus/fistula (if present) opens at the anterior border of SCM and passes between the internal and external carotid arteries, lateral to CN IX, and opens into the tonsillar fossa

QUESTION 4 (20 marks) - Short Notes (Applied Based)

a) Wallenberg's Syndrome (Lateral Medullary Syndrome)

b) Hydrocephalus

1. Non-communicating (Obstructive) Hydrocephalus: Obstruction within the ventricular system
   • Aqueductal stenosis (commonest cause in children)
   • Arnold-Chiari malformation
   • Dandy-Walker malformation
   • Tumor (ependymoma, colloid cyst of 3rd ventricle)
2. Communicating Hydrocephalus: Obstruction outside the ventricles or impaired reabsorption
   • Meningitis (post-inflammatory scarring of arachnoid granulations)
   • Subarachnoid hemorrhage
   • Normal pressure hydrocephalus (NPH): classic triad = Wet (incontinence) + Wobbly (gait apraxia) + Wacky (dementia)

c) Horner's Syndrome and Frey's Syndrome

Horner's Syndrome

1. Ptosis (partial, 1-2 mm) - superior tarsal muscle (Muller's muscle) paralysis
2. Miosis - pupillary constrictor is unopposed (dilator paralysis)
3. Anhidrosis - loss of sweating (ipsilateral face/body depending on level)
4. Enophthalmos (apparent) - inferior tarsal muscle paralysis + ptosis gives illusion of sunken eye

• 1st order (central): Hypothalamus → descends ipsilaterally through brainstem → intermediolateral cell column of C8-T2 (ciliospinal center of Budge). Causes: stroke, syringomyelia, tumor
• 2nd order (preganglionic): T1 → over lung apex and subclavian artery → superior cervical ganglion. Causes: Pancoast tumor (lung apex), cervical rib, subclavian artery aneurysm
• 3rd order (postganglionic): From superior cervical ganglion → along internal carotid artery through cavernous sinus → long ciliary nerves to dilator pupillae. Causes: internal carotid artery dissection, cavernous sinus thrombosis, cluster headache

Frey's Syndrome (Auriculotemporal Syndrome / Gustatory Sweating)

• Parasympathetic secretomotor fibers (from the auriculotemporal nerve branch, originally running to parotid gland) are severed during parotidectomy
• These fibers regenerate and aberrantly innervate the sweat glands and cutaneous blood vessels of the overlying skin
• Eating stimulates these fibers (which now supply sweat glands instead of parotid) → gustatory sweating and flushing

d) Syringomyelia and Brown-Séquard Syndrome

Syringomyelia

1. Bilateral loss of pain and temperature in a "cape" distribution (neck, shoulders, upper limbs) - with preserved light touch and proprioception (posterior columns intact) = dissociated sensory loss
2. LMN weakness and wasting of hands/upper limbs (anterior horn cells involvement)
3. Later: UMN signs in lower limbs (corticospinal tract compression)
4. Charcot joints (neuropathic arthropathy of shoulder/elbow due to lost pain)
5. Horner's syndrome (if ciliospinal center of Budge at C8-T1 is affected)

Brown-Séquard Syndrome

QUESTION 5 (18 marks) - Short Notes (Recall Type)

a) Cartilages of the Larynx and Their Nerve Supply

Cartilages of the Larynx:

1. Thyroid cartilage - largest; two quadrilateral laminae fused anteriorly at the "Adam's apple" (laryngeal prominence); angle is 90° in males (prominent) vs. 120° in females; has superior and inferior cornu
2. Cricoid cartilage - only complete ring in the airway; signet ring shape (narrow anteriorly, broad posteriorly = lamina); forms the base of the larynx; articulates with thyroid (cricothyroid joint) and arytenoids (cricoarytenoid joint)
3. Epiglottis - leaf/spoon-shaped fibroelastic cartilage; attached to inner angle of thyroid cartilage by thyroepiglottic ligament; covers laryngeal inlet during swallowing

Nerve Supply of the Larynx:

• Arises from the inferior (nodose) ganglion of vagus
• Divides into:
  • Internal laryngeal nerve (sensory): Pierces the thyrohyoid membrane; supplies sensation to laryngeal mucosa ABOVE the vocal cords (epiglottis, aryepiglottic folds, vestibule). Also carries taste from epiglottis.
  • External laryngeal nerve (motor): Runs with the superior thyroid artery; supplies cricothyroid muscle (the only intrinsic laryngeal muscle supplied by SLN; tenses vocal cords to produce high-pitched sounds)

• Right RLN: loops under right subclavian artery
• Left RLN: loops under arch of aorta (at ligamentum arteriosum)
• Both ascend in the tracheo-oesophageal groove
• Supplies: ALL other intrinsic laryngeal muscles (posterior cricoarytenoid - only abductor; lateral cricoarytenoid; transverse and oblique arytenoids; thyroarytenoid; vocalis)
• Also provides sensory supply below the vocal cords

b) Cavernous Sinus

Boundaries:

• Medially: Pituitary gland and body of sphenoid (pituitary tumors may invade sinus)
• Laterally: Temporal lobe
• Anteriorly: Superior orbital fissure and optic canal
• Posteriorly: Petrous apex (connects to superior and inferior petrosal sinuses)

Contents (important):

1. CN III (Oculomotor) - uppermost
2. CN IV (Trochlear)
3. CN V1 (Ophthalmic division of trigeminal)
4. CN V2 (Maxillary division of trigeminal) - lowermost in lateral wall

Connections/Tributaries:

• Receives blood from: Superior and inferior ophthalmic veins, superficial middle cerebral vein, sphenoparietal sinus
• Drains via: Superior petrosal sinus (to transverse sinus), inferior petrosal sinus (to internal jugular vein)
• The two cavernous sinuses communicate via anterior and posterior intercavernous sinuses (forming the "circular sinus")

Clinical Significance:

• Cavernous sinus thrombosis (CST): Most commonly from facial infections (danger zone of face), spreading via valveless emissary veins → presents with proptosis, chemosis, ophthalmoplegia, fever, and signs of CN III, IV, V1, V2, VI palsies
• Carotid-cavernous fistula: Pulsatile exophthalmos, bruit
• Pituitary tumors, meningiomas, and nasopharyngeal carcinoma can invade the sinus

c) Vagus Nerve - Nuclear Origin, Functional Components, Course and Branches in the Neck

Nuclear Origin (Functional Components):

Course in the Neck:

1. CN X exits the skull through the jugular foramen (with CN IX and XI)
2. Two ganglia lie in the foramen/just below:
   • Superior (jugular) ganglion - contains cell bodies of GSA fibers
   • Inferior (nodose) ganglion - contains cell bodies of GVA/SVA fibers
3. Descends in the neck within the carotid sheath (between the common carotid artery medially and the internal jugular vein laterally), posterior to both
4. Passes into the thorax by entering the superior mediastinum

Branches in the Neck:

1. Pharyngeal branches - join with CN IX and sympathetic fibers to form the pharyngeal plexus (supplies pharyngeal muscles and soft palate, except stylopharyngeus - CN IX, and tensor veli palatini - CN V3)
2. Superior laryngeal nerve - arises from inferior ganglion; divides into:
   • Internal branch (sensory to larynx above vocal cords, pierces thyrohyoid membrane)
   • External branch (motor to cricothyroid muscle)
3. Recurrent laryngeal nerve - arises in the chest (loops under subclavian artery on right, under aortic arch on left), ascends in tracheo-oesophageal groove; gives off tracheal, oesophageal, and inferior cardiac branches in the neck
4. Cardiac branches in the neck:
   • Superior cervical cardiac branch (from superior ganglion)
   • Inferior cervical cardiac branch (from below inferior ganglion)
   • Both carry preganglionic parasympathetic (cardio-inhibitory) and afferent (pain) fibers from heart
5. Carotid body branches - to carotid body and sinus (chemoreceptors and baroreceptors)

QUESTION 6 (20 marks) - Short Notes

a) Histology of the Cerebellum

Three Layers (from outside to inside):

• Sparse in neurons
• Contains: Stellate cells (inhibitory, in outer part) and Basket cells (inhibitory, in inner part; their axons wrap around Purkinje cell somata like "baskets")
• Contains: Axons of granule cells (parallel fibers - run parallel to long axis of folia) and dendrites of Purkinje cells
• Parallel fibers synapse on Purkinje cell dendrites (excitatory, glutamate)
• Climbing fibers from inferior olive also synapse here on Purkinje cells (powerful excitatory, 1:1 ratio)

• A single row of large, flask-shaped neurons = the most distinctive feature
• Purkinje cells are the ONLY OUTPUT neurons of the cerebellar cortex
• Their dendrites fan out extensively into the molecular layer (like a tree in one plane - "dendritic tree")
• Their axons project to the deep cerebellar nuclei (dentate, emboliform, globose, fastigial) and vestibular nuclei
• Inhibitory neurons (GABA-ergic)
• Large, pale vesicular nucleus with prominent nucleolus

• The deepest layer, closest to the white matter
• Packed with small granule cells - most numerous neurons in the entire brain (~50 billion)
• Granule cells are EXCITATORY (glutamate); receive mossy fiber input and send axons to molecular layer as parallel fibers
• Also contains Golgi cells (inhibitory interneurons, large, feedback inhibition of granule cells)
• Contains "Rosettes of mossy fibers" = mossy fiber boutons synapsing with granule cell dendrites (glomeruli)

Deep Cerebellar Nuclei (receive Purkinje cell output):

• Dentate (largest, for coordination of limb movements)
• Emboliform and Globose (= Interposed nuclei; for limb synergy)
• Fastigial (medial, for balance and trunk)

b) Neuroglia

Types and Functions:

• MS = demyelination of CNS (oligodendrocytes affected)
• Guillain-Barré syndrome = demyelination of PNS (Schwann cells affected)
• Glioblastoma multiforme = malignant astrocytoma
• Microglia = HIV encephalitis, Alzheimer's (amyloid plaques trigger microglial activation)

c) Derivatives of the First Branchial Arch

Skeletal/Cartilaginous Derivatives (from Meckel's cartilage):

1. Malleus (head and neck) - ossicle of middle ear
2. Incus (body and short process) - ossicle of middle ear
3. Anterior ligament of malleus
4. Sphenomandibular ligament
5. Mandible - formed by intramembranous ossification around Meckel's cartilage (the cartilage itself mostly regresses)
6. Contributions to the zygomatic bone and squamous temporal bone (debated)

Muscular Derivatives (all supplied by CN V3 - mandibular nerve):

• Muscles of mastication: Masseter, temporalis, medial pterygoid, lateral pterygoid
• Tensor tympani (in middle ear - damping of tympanic membrane vibration)
• Tensor veli palatini (in soft palate - opens Eustachian tube during swallowing)
• Mylohyoid (floor of mouth)
• Anterior belly of digastric (posterior belly = 2nd arch, supplied by CN VII)

Nerve:

• Mandibular nerve (CN V3) - nerve of the 1st branchial arch

Vascular:

• Maxillary artery (terminal branch of external carotid) supplies 1st arch derivatives

d) Proper Handling of Cadavers

Legal Basis:

• Donated voluntarily and documented with legal consent
• Obtained through proper channels (body donation programs, unclaimed bodies with legal authority)
• Not mishandled or used outside institutional premises

Safety Precautions:

1. Personal Protection:
   • Wear nitrile/latex gloves at all times (double gloving preferred)
   • Wear lab coat/apron and safety goggles
   • Closed-toed shoes - no sandals in the dissection hall
   • Wash hands thoroughly before and after
2. Infection Control:
   • Cadavers are preserved in formalin (formaldehyde 10% in water) which kills most pathogens but prions are resistant
   • Blood-borne pathogens (HIV, Hepatitis B/C) can survive in preserved tissues
   • Report any needle stick or cut immediately
   • No eating, drinking, or touching face in the dissection hall
3. Chemical Safety:
   • Formalin is a carcinogen and severe irritant
   • Work in well-ventilated dissection halls
   • Avoid prolonged inhalation (use activated charcoal masks if available, or N95)
   • Formaldehyde vapors can cause conjunctivitis, respiratory irritation, and with chronic exposure, nasopharyngeal cancer
4. Dissection Technique:
   • Use sharp, clean instruments (scalpels, forceps, scissors)
   • Dissect carefully and systematically following the dissection manual
   • Blunt dissect where nerve/vessel identification is required
   • Never discard tissue outside designated biological waste bins

Ethical Considerations:

1. Respect and Dignity: The cadaver is a "first teacher" - treat with utmost respect; no photography, jokes, or inappropriate behavior
2. Confidentiality: Do not reveal identity of donor if known
3. Waste Disposal: Tissue waste in red biohazard bags; sharps in puncture-proof containers
4. Post-dissection: Remains must be properly stored (covered, refrigerated) and ultimately given a dignified burial/cremation after the academic session

Storage:

• Embalmed bodies kept in tanks or trays with formol-saline or in cold storage
• Must be kept moist with wet sheets/formalin-soaked gauze to prevent drying and distortion