SENSORY RECEPTORSSENSORY RECEPTORSNeurophysiological AspectNeurophysiological Aspect

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Updated September, Updated September, 20072007

Prof. Dr. Muhammad Abdul AzeemProf. Dr. Muhammad Abdul AzeemUmmal Qura University, MeccahUmmal Qura University, Meccah

Receptor TypesReceptor Types1.1. MechanoreceptorsMechanoreceptors

–– Tactile (Skin)Tactile (Skin)–– Free Nerve Endings (Skin)Free Nerve Endings (Skin)–– Expanded tip endings (MerkelExpanded tip endings (Merkel’’s Disc; Skin)s Disc; Skin)–– Spray Endings (RuffiniSpray Endings (Ruffini’’s Endings; Skin)s Endings; Skin)–– Encapsulated Endings (Paccinian Corpuscle; Skin)Encapsulated Endings (Paccinian Corpuscle; Skin)–– Encapsulated Endings (Paccinian Corpuscle; Skin)Encapsulated Endings (Paccinian Corpuscle; Skin)–– Muscle Endings (Muscle Spindle, Golgi Tendon Muscle Endings (Muscle Spindle, Golgi Tendon

organ)organ)–– Hearing (Chochlea)Hearing (Chochlea)–– Equilibrium (Vestibular apparatus)Equilibrium (Vestibular apparatus)–– Baroreceptors (Carotid & Aortic Bodies)Baroreceptors (Carotid & Aortic Bodies)

ContinuedContinued……………………………………Receptor TypesReceptor Types

2. 2. ThermoreceptorsThermoreceptors (Warmth & Cold)(Warmth & Cold)

3. 3. NociceptorNociceptor (Pain)(Pain)

4. 4. Electromagnetic ReceptorsElectromagnetic Receptors (Vision; Rods & Cones)(Vision; Rods & Cones)

5. 5. ChemoreceptorsChemoreceptorsTaste (Tongue), Smell (Nose), Carotid & Aortic bodies Taste (Tongue), Smell (Nose), Carotid & Aortic bodies

(CO2 & O2), Hypothalamic (blood glucose), Supraoptic (CO2 & O2), Hypothalamic (blood glucose), Supraoptic Nuclei in hypothalamus (osmolality)Nuclei in hypothalamus (osmolality)

Various SkinSkin

Receptors

•• Definition of a ReceptorDefinition of a ReceptorThe biological transducers that detect The biological transducers that detect sensations like touch, warmth, cold, light, sensations like touch, warmth, cold, light, pressure, chemical etc.pressure, chemical etc.

•••• Differential Sensitivity of ReceptorsDifferential Sensitivity of Receptors––Modality of Sensation Modality of Sensation –– The The ““Labeled Labeled

LineLine”” Principle, i.e., every type of Principle, i.e., every type of sensation is a single modality.sensation is a single modality.

–– specific sensation, a single one is specific sensation, a single one is detected by specific receptor. detected by specific receptor.

•• It respond to specific & single stimuli.It respond to specific & single stimuli.•• It posses a specific morphological It posses a specific morphological

structure.structure.•• It also adapts to stimuli that may be It also adapts to stimuli that may be

Characteristics of ReceptorCharacteristics of Receptor

•• It also adapts to stimuli that may be It also adapts to stimuli that may be either,either,–– Fast adaptingFast adapting–– Slow adaptingSlow adapting

–– MechanismsMechanisms–– Slowly adapting receptors detect Slowly adapting receptors detect

continuous stimulus of same strength and continuous stimulus of same strength and called called ““tonictonic”” receptorsreceptors

–– Rapidly adapting receptors detect change Rapidly adapting receptors detect change

••Adaptation of ReceptorsAdaptation of Receptors

–– Rapidly adapting receptors detect change Rapidly adapting receptors detect change in stimulus strength and thus termed as in stimulus strength and thus termed as dynamic, rate, movement or commonly as dynamic, rate, movement or commonly as phasic receptors.phasic receptors.

Transduction by ReceptorsTransduction by Receptors

•• Local currents at nerve endings Local currents at nerve endings –– receptor receptor potentialspotentials–– Mechanisms of receptor potentialsMechanisms of receptor potentials–– Mechanisms of receptor potentialsMechanisms of receptor potentials–– Receptor potential amplitude.Receptor potential amplitude.–– Relation of the receptor potential to action Relation of the receptor potential to action

potentialspotentials

Conversion of Receptor Potentialinto Action Potential Through Threshold

Conversion of Receptor Potential intoAction Potential

in Paccinian Corpuscle

Relation Between Amplitude of Receptor Potential & Stimulus Strength

Rapid & Slow Adaptation in Various Receptors

Classification & Function of NervesClassification & Function of Nerves

Types ofNerve Fibers

Diameter(u)

NCVMeters/se

c

Types ofMotor Nerves

Types ofSensory Nerves

Sensory Functions

MotorFunctions

Mye

lina

ted

20120AαI, IA, IBMuscle

spindle & GTO

Skeletal Muscle Type

Aα

1590Aα, AβI, IA, IBMuscle

spindle & GTO

Skeletal Muscle Type

Aα

1060Aβ, AγII

Muscle Spindle,

Hair Receptors,

Skeletal Muscle &

Mye

lina

ted

1060Aβ, AγIIReceptors, vibration,

high discriminati

on

Muscle & Spindle Type Aα

530AδIII

Hair Receptor,

Deep Pressure,

touch, Pricking

Pain, Cold & Warmth

Muscle Spindle Type Aγ

Unmyelinated12 to 0.562 to 0.5CIV

Crude touch & Pressure,

Tickle & Itching

Pain, Cold & Warmth

Sympathetic Type C fibers

Spatial SummationSpatial Summation

Temporal SummationTemporal Summation

Neuronal Pool

•• Relaying of signals through Relaying of signals through neuronal poolsneuronal pools

–– Organization of neurons Organization of neurons –– Threshold and subThreshold and sub--threshold stimulithreshold stimuli–– excitation and facilitationexcitation and facilitation–– excitation and facilitationexcitation and facilitation–– Inhibition of a neuronal poolInhibition of a neuronal pool

Discharge & Facilitated Zones of Neuronal Pool

DIRVERGENCE OF SIGNALS THROUGH NEURONAL POOLS

CONVERGENCE OF SIGNALS

Conversion of Excitatory impulse into Inhibitory in Neuronal Pool

AFTER AFTER DISCHARGE DISCHARGE

FROM FROM NEURONAL NEURONAL

POOLPOOL–– Synaptic after dischargeSynaptic after discharge–– Synaptic after dischargeSynaptic after discharge–– Reverberatory (Oscillatory) Reverberatory (Oscillatory)

circuit, a cause of signal circuit, a cause of signal prolongationprolongation

–– Characteristics of signal Characteristics of signal prolongation from a prolongation from a reverberatoty circuitreverberatoty circuit

Facilitation and Inhibitionin Neuronal Pool

Continuous Output through Reverberation in Neuronal Pool

INSTABILITY AND STABILITY OF NEURONAL CIRCUITS

•• Inhibitory circuits as a mechanism for stabilizing nervous Inhibitory circuits as a mechanism for stabilizing nervous system functionsystem function

•• Synaptic fatigue as a means of stabilizing the nervous Synaptic fatigue as a means of stabilizing the nervous systemsystem

–– Automatic shortAutomatic short--term adjustment of pathway term adjustment of pathway sensitivity by the fatigue mechanismsensitivity by the fatigue mechanism

STABILITY IN NERVOUS SYSTEM

sensitivity by the fatigue mechanismsensitivity by the fatigue mechanism–– LongLong--term changes in synaptic sensitivity term changes in synaptic sensitivity

caused by automatic downgrading or caused by automatic downgrading or upgrading of synaptic receptorsupgrading of synaptic receptors

Neural Fatigue