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ANATOMY & HISTOLOGY - Complete Answer Sheet

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1. Styloid Apparatus

1. Tympanohyal - fused to temporal bone (petrous part), forms the base
2. Stylohyal - the styloid process proper (~2.5 cm long, projects anteroinferiorly from beneath the ear)
3. Ceratohyal - gives origin to the stylohyoid ligament
4. Hypohyal - lesser cornu of hyoid
5. Basihyal - body of hyoid

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2. Arterial Supply of Anterior Inferior Part of Nasal Septum + Clinical Application

• ~90% of nosebleeds arise from Little's area (anterior epistaxis)
• Most common in children and young adults
• Easily accessible: amenable to direct pressure, cauterization, or anterior nasal packing
• The septal branch of the superior labial artery is most commonly responsible
• Because it lies on thin mucosa overlying cartilage with poor subcutaneous tissue, vessels are poorly supported and easily rupture
• Treatment: Pinch soft part of nose for 10-15 minutes, silver nitrate cautery, or nasal packing

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3. Organ of Corti (with Diagram)

                    TECTORIAL MEMBRANE
                    ___________________
                   /                   \
        IHC (1 row)  |  OHC (3 rows)
         |           |    | | |
    _____|_______Inner_pillar___Outer_pillar_____
   |                 Tunnel of Corti             |
   |_____________BASILAR MEMBRANE________________|
         |                        |
     Habenula          Spaces of Nuel
     perforata         (around OHCs)

• Inner Hair Cells (IHC): 1 row, ~3,500 total - primary sensory cells (95% afferent innervation)
• Outer Hair Cells (OHC): 3 rows, ~12,000 total - cochlear amplifiers (motile; efferent innervation)
• Supporting cells: Pillar cells (form tunnel of Corti), Deiters cells (phalangeal cells), Hensen's cells, Claudius cells, Boettcher cells

• Tunnel of Corti: Between inner and outer pillar cells, filled with perilymph-like fluid (cortilymph)
• Spaces of Nuel: Around outer hair cells

• Base of cochlea: High frequency sounds (high-pitched)
• Apex of cochlea: Low frequency sounds (low-pitched)
• Basilar membrane is narrow and stiff at base, wide and flexible at apex

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4. Scalp: Why Does It Bleed Profusely but Heal Rapidly?

1. The scalp has a very rich blood supply from 5 arteries on each side (supratrochlear, supraorbital, superficial temporal, posterior auricular, occipital)
2. These arteries run within the dense fibrous connective tissue (layer 2), which is firmly adherent to overlying skin and galea below
3. When cut, the fibrous septa hold vessel walls OPEN - they cannot retract and constrict normally
4. Anastomoses between ECA and ICA branches allow rapid blood loss
5. Arteries come from periphery toward center (like spokes of a wheel)

1. Extremely rich blood supply ensures abundant oxygen and nutrients to the wound
2. Immune cells (neutrophils, macrophages) are delivered rapidly
3. Scalp tissue is metabolically active
4. Relatively thin skin with good vascularity
5. Hair follicles act as epithelial stem cell reservoirs for re-epithelialization

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5. Cavernous Sinus Thrombosis - Ophthalmoplegia, Medial Squint, Diplopia

• CN III (Oculomotor) - in lateral wall
• CN IV (Trochlear) - in lateral wall
• CN V₁ (Ophthalmic division of trigeminal) - in lateral wall
• CN V₂ (Maxillary division) - inferior lateral wall

• CN VI (Abducens) - runs directly within the blood
• Internal carotid artery (with sympathetic plexus)

• Bilateral proptosis and chemosis (because both sinuses are interconnected)
• Facial pain/numbness (CN V₁, V₂ involvement)
• Papilledema (raised intracranial pressure)
• Fever, headache, altered consciousness (septic thrombosis)
• Horner's syndrome (sympathetic plexus on ICA compressed)

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6. Thyroidectomy: Precautions Taken and Why

• Why: RLN injury (1-2%) causes hoarseness (unilateral) or stridor/airway obstruction (bilateral)
• Precaution: Nerve is identified in the tracheoesophageal groove before any tissue division; intraoperative nerve monitoring used

• Why: Inadvertent removal or devascularization causes hypoparathyroidism → hypocalcemia (tetany, laryngospasm)
• Precaution: Meticulous dissection on thyroid capsule; autotransplantation to sternomastoid if accidentally removed; postop calcium monitoring

• Why: Injury causes loss of cricothyroid function → inability to raise vocal pitch (affects singers/voice professionals); subtle voice change
• Precaution: Ligate superior thyroid vessels close to the gland capsule

• Why: Thyroid storm (thyrotoxic crisis) can be precipitated by surgical manipulation in hyperthyroid patients (mortality up to 25%)
• Precaution: Antithyroid drugs + beta-blockers + Lugol's iodine for 10-14 days pre-op

• Why: Neck haematoma can cause airway compression - life threatening
• Precaution: Drain placement, close monitoring in recovery room

• Ligate close to thyroid capsule (not trunk) to avoid EBSLN injury

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7. Development of Tongue is Composite (NV Supply)

• Hypoglossal nerve (CN XII) - derived from occipital myotomes
• Palatoglossus - CN X (vagus)

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8. Rotatory Movement of Knee Joint

• Medial (internal) rotation of tibia on femur (or femur laterally on tibia)
• Lateral (external) rotation of tibia on femur

• As the knee reaches full extension, the femur medially rotates on the tibia (or tibia laterally rotates on femur)
• This "screws home" the joint into the close-packed position (fully extended, stable, no muscular effort needed)
• Happens passively due to the shape of the lateral femoral condyle (larger radius of curvature)

• The popliteus muscle medially rotates the tibia on the femur (or laterally rotates the femur on the tibia when foot is fixed)
• This "unlocks" the knee to allow flexion
• Popliteus = "key that unlocks the knee"

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9. Inversion and Eversion - Joints, Muscles, Nerve Supply

• Inversion: Turning the sole of the foot inward (medially), so the sole faces medially
• Eversion: Turning the sole of the foot outward (laterally), so the sole faces laterally

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10. Patella's Tendency to Dislocate Laterally & Factors Preventing It

1. Q-angle (Quadriceps angle): The line of pull of the quadriceps is lateral (ASIS to patella), while the patellar ligament pulls straight down (toward tibial tuberosity). This creates a lateral vector force on the patella.
2. Normal Q-angle is 15° (females) and 10° (males) - increased Q-angle increases lateral tendency
3. The lateral femoral condyle is lower than the medial, partially directing patella laterally

• Increased Q-angle (genu valgum, lateral tibial tuberosity)
• Trochlear dysplasia (shallow groove)
• VMO weakness
• Patella alta (high-riding patella)
• Lateral retinaculum tightness

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11. Case: 50-Year-Old Man - Drooping Mouth, Can't Close Eyes, No Forehead Wrinkles + Taste + Hyperacusis

Q1. Which cranial nerve is affected?

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Q2. Functional Components of CN VII

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Q3. Intracranial Course of CN VII

1. Origin: Motor root from facial nucleus (in pons, lower portion); nervus intermedius (sensory/parasympathetic) from superior salivatory nucleus and nucleus tractus solitarius
2. Loops around abducens nucleus (CN VI) in pons, forming the facial colliculus visible on floor of 4th ventricle
3. Exits pons at the cerebellopontine angle (CPA) between olive and inferior cerebellar peduncle, along with CN VIII and nervus intermedius
4. Enters internal acoustic meatus (IAM) of petrous temporal bone along with CN VIII
5. Travels in the facial canal (Fallopian canal)
6. Geniculate ganglion (sensory ganglion, at genu/bend in facial canal) - gives off greater petrosal nerve
7. Descends vertically in facial canal
8. Gives off nerve to stapedius and chorda tympani (before exiting)
9. Exits skull via stylomastoid foramen

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Q4. Where Does the Nerve Exit the Cranium?

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Q5. Anatomical Basis of Altered Taste and Hyperacusis

• The chorda tympani (branch of CN VII) carries taste fibers from anterior 2/3 of tongue via the lingual nerve
• Chorda tympani leaves the facial nerve in the facial canal (just above stylomastoid foramen), traverses the middle ear, and exits via petrotympanic fissure
• A lesion above the origin of chorda tympani (in the facial canal) will interrupt taste fibers → altered/absent taste (ageusia) on anterior 2/3 tongue

• The nerve to stapedius (branch of CN VII in the vertical part of facial canal) supplies the stapedius muscle
• Stapedius normally dampens the movement of the stapes to protect against loud sounds (acoustic reflex)
• When paralyzed, the stapes moves too freely → hyperacusis (ordinary sounds perceived as abnormally loud/unpleasant)
• Lesion must be above the origin of the nerve to stapedius (proximal to it in the canal)

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Q6. Other Clinical Signs That May Be Observed

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12. Histology

A. Spinal Cord

• Posterior horn (dorsal): Receives afferent (sensory) input; contains substantia gelatinosa (laminae I-II), nucleus proprius (III-IV)
• Anterior horn (ventral): Contains large multipolar motor neurons (lamina IX) - α and γ motor neurons
• Lateral horn (only T1-L2 & S2-4): Preganglionic autonomic neurons (lamina VII)
• Central canal: Lined by ependymal cells

• Posterior funiculus: Fasciculus gracilis (medial) + fasciculus cuneatus (lateral) - proprioception, fine touch
• Lateral funiculus: Lateral corticospinal tract (descending), spinothalamic tract (ascending), spinocerebellar tracts
• Anterior funiculus: Anterior corticospinal tract, vestibulospinal, reticulospinal tracts

• Large multipolar neurons in anterior horn (Nissl substance visible)
• Ependymal cells lining central canal
• Neuroglia (astrocytes, oligodendrocytes, microglia)
• Blood vessels (anterior spinal artery territory in grey matter)

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B. Trachea

• Respiratory epithelium: Ciliated cells, goblet cells, basal cells, serous cells, brush cells, neuroendocrine (Kulchitsky) cells
• Cilia beat upward (mucociliary escalator)
• C-shaped cartilage distinguishes trachea from bronchi (complete rings in trachea)
• No smooth muscle in walls EXCEPT trachealis posteriorly (unlike bronchioles which have smooth muscle all round)

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C. Thyroid Gland

• Follicles: Round or ovoid structures of varying sizes; lined by follicular epithelium (simple squamous to cuboidal to columnar depending on activity)
• Colloid: Homogeneous, eosinophilic material filling follicle lumen (stored thyroglobulin); shows "scalloping" (resorption vacuoles) when active
• Follicular cells: Flat (inactive/involuted), cuboidal (normal), tall columnar (overactive/stimulated by TSH)
• Parafollicular C-cells: Between follicles (not inside); larger, pale cells; produce calcitonin; derived from neural crest (ultimobranchial body)
• Stroma: Thin fibrous capsule with septa; rich capillary network (fenestrated)

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13. Muscles of Mastication - Nerve Supply and Movements

• Mouth opening (Depression): Mainly lateral pterygoid + gravity + suprahyoid muscles (digastric, mylohyoid, geniohyoid - not muscles of mastication)
• Mouth closing (Elevation): Temporalis + masseter + medial pterygoid
• Protrusion (jaw forward): Lateral + medial pterygoid (bilateral)
• Retraction: Posterior fibers of temporalis
• Side-to-side (chewing/grinding): Alternating contraction of pterygoids of each side

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14. Arterial Supply of Brain and Spinal Cord

A. Brain

1. Internal Carotid Arteries (ICA) - anterior circulation (80%)
2. Vertebral Arteries - posterior circulation (20%)

• Anterior communicating artery (ACoA)
• Anterior cerebral arteries (ACA) × 2 - from ICA
• Internal carotid arteries
• Middle cerebral arteries (MCA) × 2 - from ICA (largest branch)
• Posterior communicating arteries (PCoA) × 2 - connect ICA to PCA
• Posterior cerebral arteries (PCA) × 2 - from basilar artery

• Ophthalmic artery
• Posterior communicating artery
• Anterior choroidal artery
• Internal, then bifurcates into ACA + MCA

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B. Spinal Cord

• Formed by union of branches from both vertebral arteries (at the level of the medulla)
• Runs in the anterior median fissure throughout spinal cord length
• Supplies anterior 2/3 of cord: anterior and lateral grey horns, anterior funiculi, lateral funiculi
• Reinforced by radicular arteries at various levels (most important: Artery of Adamkiewicz / Arteria radicularis magna at T9-L2, predominantly left side)

• Arise from vertebral arteries or posterior inferior cerebellar arteries (PICA)
• Run along posterior lateral surface (beside posterior nerve roots)
• Supply posterior 1/3: posterior grey horns, posterior funiculi

• Radicular arteries from: vertebral, ascending cervical, intercostal, lumbar, sacral arteries
• Enter via intervertebral foramina and reinforce anterior and posterior spinal arteries

• Infarction of anterior 2/3 of cord
• Features: bilateral UMN paralysis below lesion, loss of pain/temperature (spinothalamic) below, BUT preserved proprioception and vibration (dorsal columns = posterior spinal artery territory)

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