Sensory receptors & coding of sensory information

🖇 IntroductionReceptor = specialized structure detects stimulus & converts it to electrical signal.Types: modified neurons / specialized cells.Nervous system parts: sensory – motor – integrative.Function: detect internal & external changes → send to CNS.---📌 Functions of ReceptorsDetector: senses environmental change.Transducer: converts energy → electrical potential.Sensitizer: detects minimal stimuli.Meter/Gauge: measures intensity of stimulus.---🟠 Properties of Receptors1️⃣ Specificity & Adequate StimulusEach receptor has specific form of energy.Adequate stimulus = minimal energy needed.Example: rods & cones → light.Can respond to other energies but need high threshold.2️⃣ Excitability & Generator Potential (GP)GP = graded, local depolarization (except photoreceptors → hyperpolarization).Not all-or-none, can summate, long duration (>5 ms).If GP reaches threshold (≈10 mV) → action potential.Stronger stimulus → higher GP → more APs.Mechanism: opening Na⁺ channels (mechanical/chemical/thermal).Pacinian corpuscle: model receptor, adequate stimulus = pressure.3️⃣ Compression Function (Weber–Fechner law)Impulse frequency ∝ log of stimulus intensity.Large change in intensity → small change in frequency.Allows detection of wide range of intensities.Example: 1000× stimulus ↑ → only 3× frequency ↑.4️⃣ AdaptationDefinition: ↓ receptor discharge with continuous constant stimulus.Types:Rapidly adapting (phasic): Pacinian, Meissner → touch/clothing.Slowly adapting (tonic): pain, baroreceptors, muscle spindles, Golgi tendon.Moderately adapting: thermoreceptors (20–40 °C).Mechanisms:Structural readjustment.Accommodation of Na⁺ channels.Energy dissipation.Photopigment reduction (in eye).---🟣 Clinical ImportanceRapid adaptation prevents overload of unimportant stimuli (e.g. clothes).Slow adaptation ensures protection (pain) & homeostasis (BP control, posture).Compression function allows receptors to work over huge ranges (light, sound).

الأسئلة اللي ركز عليها الدكتور:Function of receptorsDefinition of adequate stimuliDefinition of generator potentialProperties of generator potential( خلي بالك برده مش هيجيلك تعريفات في الامتحان ولكن زي ما الدكتور قال يحييها mcq عادي أو أي طريقة تانية)