PY11.1-7 | Special Senses — Summary & Reflection

REFLECT

Kolb Reflection — Special Senses

Take 5 minutes before the Practice Quiz. Write your answers briefly in your notebook.

1. Concrete Experience — Which of the 7 competencies did you find most challenging today? (PY11.1–11.7)

1. Reflective Observation — Did anything surprise you? For example: rods hyperpolarise in light (opposite to most receptors); olfactory signals bypass the thalamus; K⁺ is what depolarises cochlear hair cells because endolymph has high K⁺.

3. Abstract Conceptualisation — Complete these two sentences:
a. "Vitamin A deficiency causes night blindness because __ which connects to what I learned in Biochemistry about ___."
b. "The visual pathway crosses at the chiasma so that each hemisphere processes the __ visual field from both eyes."

4. Active Experimentation — In your next clinical posting or anatomy practical:
a. Examine a patient's direct and consensual pupillary light reflexes
b. Use a tuning fork to perform a Rinne's test on yourself (apply to mastoid, then in front of ear)
c. Cover one eye and note your visual field with the other

KEY TAKEAWAYS

What You Have Learned — Special Senses

PY11.1 — Smell (Olfaction)
• Olfactory receptor cells: bipolar neurons in olfactory epithelium (cribriform plate area); unique regeneration
• Transduction: odorant → GPCR → cAMP → CNG channels → depolarisation
• Pathway: Olfactory nerve (CN I) → olfactory bulb → olfactory cortex (no thalamic relay — unique)
• Applied: Anosmia (head injury → cribriform plate); COVID-19; Zinc deficiency; Foster Kennedy syndrome

PY11.2 — Taste (Gustation)
• Five basic tastes: Sweet, Sour, Salty, Bitter, Umami
• Taste buds in fungiform, circumvallate, foliate papillae; taste receptor cells (modified epithelium)
• Pathway: Anterior 2/3 tongue → CN VII (chorda tympani); Posterior 1/3 → CN IX; Epiglottis → CN X → NTS → Thalamus → Gustatory cortex
• Applied: Bell's palsy → anterior tongue taste loss; Zinc deficiency → hypogeusia; bitter = lowest threshold

PY11.3 — Ear Anatomy and Vestibular
• Outer ear: pinna, EAC, tympanic membrane
• Middle ear: ossicles (malleus-incus-stapes), Eustachian tube, acoustic reflex (stapedius/tensor tympani)
• Inner ear: cochlea (scala vestibuli, media, tympani; organ of Corti; IHC/OHC); vestibular (semicircular canals → angular; saccule/utricle → linear)

PY11.4 — Hearing and Deafness
• Tonotopy: HIGH frequency → BASE; LOW frequency → APEX (Bekesy)
• Pathway: Cochlea → CN VIII → Cochlear nuclei → Superior olivary complex → Inferior colliculus → MGB → Auditory cortex (Heschl's gyrus)
• Conductive vs Sensorineural: Rinne (Positive=normal/SNHL; Negative=conductive); Weber (Lateralises to deaf ear in conductive; to better ear in SNHL)
• Ototoxins: Aminoglycosides, furosemide, cisplatin → OHC damage

PY11.5 — Eye Anatomy and Visual Pathway
• Refractive media: Cornea (43 D, 70%) > Lens (15-17 D); Aqueous → IOP → Glaucoma
• Retina: Rods (120M, rhodopsin, scotopic); Cones (6M, fovea, photopic)
• Visual pathway: Optic nerve → Chiasma (nasal fibres cross) → Optic tract → LGN → Optic radiations → V1
• Visual field defects: Chiasma → bitemporal hemianopia; Optic tract/cortex → homonymous hemianopia
• Light reflex: Pretectal nucleus → Edinger-Westphal → both pupils (consensual)

PY11.6 — Image Formation and Refractive Errors
• Accommodation: Ciliary muscle contracts → Zonules relax → Lens more convex
• Myopia (short-sighted): image in front of retina → concave lens
• Hypermetropia: image behind retina → convex lens
• Astigmatism: unequal corneal curvature → cylindrical lens
• Presbyopia: lost lens elasticity, age >40 → convex reading glasses

PY11.7 — Colour Vision
• Trichromatic theory: 3 cone types (L/M/S = Red/Green/Blue)
• Opponent theory: Red-Green, Blue-Yellow pairs at ganglion cell level
• Photopigment: Opsin + 11-cis retinal; light → all-trans retinal → hyperpolarisation (cGMP decreases)
• Colour blindness: X-linked recessive; Red-Green most common; Ishihara plates for screening
• Dark adaptation: Rod adaptation up to 30–45 min; requires Vitamin A (link to Biochemistry)

Estimated reading time: 60–70 minutes | NMC CBME 2024 Competencies: PY11.1–PY11.7