Sensory structures — A/L Biology

What must I remember about Sensory structures?

• Sensory receptors are specialized cells or modified dendritic endings that convert environmental stimuli into electrical receptor potentials (sensory transduction).
• Mechanoreceptors respond to mechanical energy: Meissner's corpuscles (light touch and low-frequency vibration in fingertips), Pacinian corpuscles (deep pressure and high-frequency vibration in dermis/subcutis), Merkel discs (sustained touch/texture), and Ruffini endings (skin stretch).
• Thermoreceptors are free nerve endings responding to temperature: Cold receptors (activated from 10°C to 35°C) and Warm receptors (activated from 30°C to 45°C); temperatures above 45°C or below 10°C activate nociceptors (pain).
• Nociceptors (pain receptors) are unmyelinated or lightly myelinated free nerve endings that respond to damaging mechanical, thermal, or chemical stimuli (e.g., bradykinin, prostaglandins, ATP released from injured tissues).
• Chemoreceptors transduce chemical molecules: Olfactory receptor neurons in nasal epithelium detect volatile odorants; Gustatory receptor cells housed in taste buds across tongue papillae detect dissolved tastants (sweet, sour, salty, bitter, umami).

Test yourself (1 minute)

1. Receptor adaptation

   Phasic receptors (e.g., Pacinian corpuscles) adapt rapidly, ceasing firing during sustained stimuli; Tonic receptors (e.g., pain receptors, Merkel discs) adapt slowly or not at all, signaling continuous threat.

2. Two-point discrimination threshold

   Distance required to perceive two distinct tactile points is smallest on fingertips (high receptor density, small receptive fields) and largest on back/thigh (low receptor density).

3. Sensory cortex somatotopic map (Sensory Homunculus)

   Body areas with highest tactile acuity (hands, lips, tongue) occupy disproportionately large areas of the primary somatosensory cortex.

Practise Sensory structures questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 5

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Where does Sensory structures fit in the syllabus?

Year 2 · Term 1