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