PROPERTIES OF PROPERTIES OF RECEPTORSRECEPTORS::

1. 1. SPECIFICITYSPECIFICITY:: A particular type of receptor responds to A particular type of receptor responds to

a specific stimulus. a specific stimulus. Each type of receptor is sensitive to Each type of receptor is sensitive to a a

particular type of energy.particular type of energy. Stimulus to which a receptor is sensitive Stimulus to which a receptor is sensitive

is called is called ADEQUATE STIMULUSADEQUATE STIMULUS (for (for thermal receptors thermal receptors temp. stimulus). temp. stimulus).

Receptors can respond to stimuli other Receptors can respond to stimuli other than the adequate if than the adequate if stimulus is of high stimulus is of high intensity (normally light is stimulus for intensity (normally light is stimulus for Rods & cones, but firm pressure on eye Rods & cones, but firm pressure on eye ball ball perceive light halos. perceive light halos.

SPECIFICITYSPECIFICITY (continued) (continued) Each type of stimulus / sensation we Each type of stimulus / sensation we

perceive perceive MODALITY OF SENSATIONMODALITY OF SENSATION (pain sensation is one modality & (pain sensation is one modality & thermal sensation is another).thermal sensation is another).

For a specific type of sensation For a specific type of sensation a a specific nervous pathway (for vision specific nervous pathway (for vision visual pathway) & stimulates visual pathway) & stimulates a a particular part of brain.particular part of brain.

Specific nervous pathway for each Specific nervous pathway for each sensation sensation LABELED LINE LABELED LINE PRINCIPLEPRINCIPLE..

2. 2. RECEPTOR / RECEPTOR / GENERATOR POTENTIALGENERATOR POTENTIAL::

When we apply a stimulus to receptor When we apply a stimulus to receptor localized change in membrane potential localized change in membrane potential localized hypo-polarization due to localized hypo-polarization due to sodium influx sodium influx RECEPTOR POTENTIAL. RECEPTOR POTENTIAL.

It resembles EPP (End plate potential) or It resembles EPP (End plate potential) or EPSP (Excitatory post synaptic potential).EPSP (Excitatory post synaptic potential).

When receptor potential reaches When receptor potential reaches threshold threshold action potential along action potential along sensory nerve fiber arising from the sensory nerve fiber arising from the receptor.receptor.

Fig. 46.2, Guyton, 11Fig. 46.2, Guyton, 11thth ed.ed.

Fig. 46.3, Guyton, 11Fig. 46.3, Guyton, 11thth ed.ed.

RECEPTOR / GENERATOR RECEPTOR / GENERATOR POTENTIALPOTENTIAL: (continued): (continued)

Amplitude of receptor potentialAmplitude of receptor potential is directly is directly proportional to proportional to strength of stimulusstrength of stimulus..

Frequency of dischargeFrequency of discharge of impulses from receptor is of impulses from receptor is directly proportional to directly proportional to amplitude of receptor amplitude of receptor potentialpotential..

*Receptor potential is due to sodium influx*Receptor potential is due to sodium influx, so when , so when we apply different types of stimuli we apply different types of stimuli activation of activation of sodium channels sodium channels sodium influx (if we apply sodium influx (if we apply mechanical mechanical stimulus stimulus receptor membrane is receptor membrane is stretched stretched sodium channels are activated, if sodium channels are activated, if electrical /electrical / chemical chemical stimuli stimuli sodium influx). sodium influx).

*Frequency*Frequency of discharge of impulses from receptors of discharge of impulses from receptors one of the one of the sensory input for brainsensory input for brain to assess to assess intensityintensity of stimulus. of stimulus.

Fig.46.4, Guyton, 11Fig.46.4, Guyton, 11thth ed. ed.

3. 3. ADAPTATION OF ADAPTATION OF SENSORY RECEPTORSSENSORY RECEPTORS::

When a stimulus of CONSTANT When a stimulus of CONSTANT INTENSITY is applied CONTINUOUSLY INTENSITY is applied CONTINUOUSLY to receptor to receptor discharge of impulses from discharge of impulses from receptor decreases after sometime. receptor decreases after sometime. (mushkilain itni pareen mujh pay k (mushkilain itni pareen mujh pay k asaan ho gaeen!)asaan ho gaeen!)

Depending upon degree & rate of Depending upon degree & rate of adaptation, 2 types of receptors: PHASIC adaptation, 2 types of receptors: PHASIC & TONIC.& TONIC.

Fig. 46.5, Guyton, 11Fig. 46.5, Guyton, 11thth ed.ed.

Rate & degree of Rate & degree of adaptation:adaptation:

PHASIC PHASIC RECEPTORS:RECEPTORS: Rapid adaptationRapid adaptation.. Tactile / touch Tactile / touch

receptors.receptors. Hair follicle receptors.Hair follicle receptors. Meissner’s corpuscles.Meissner’s corpuscles. Pacinian corpuscles.Pacinian corpuscles. Krause’s corpuscles.Krause’s corpuscles.

TONIC TONIC RECEPTORS:RECEPTORS:

Slow & incomplete Slow & incomplete adaptationadaptation..

Pain receptors.Pain receptors. Cold receptors.Cold receptors. Muscle spindles.Muscle spindles. Proprioceptors.Proprioceptors. Baroreceptors.Baroreceptors.

Fig.5.3, Ganong 22Fig.5.3, Ganong 22ndnd ed. ed.

Physiological significance Physiological significance of of

RapidRapid adaptation: adaptation: TouchTouch receptors receptors rapid adaptation rapid adaptation

perceive new events /stimuli.perceive new events /stimuli. Rapid adaptation Rapid adaptation perceive change in perceive change in

stimulus intensity (we take bath stimulus intensity (we take bath wear wear clothesclothes rapid adaptation of touch rapid adaptation of touch receptors receptors don’t feel their presence after don’t feel their presence after sometimesometime).).

((insect crawlsinsect crawls on skin on skin perceive the new perceive the new stimulusstimulus already adapted to clothes already adapted to clothes if if does not bite does not bite forget its presence forget its presence 22ndnd insectinsect crawls crawls perceive new eventperceive new event due to due to RAPID ADAPTATION).RAPID ADAPTATION).

Physiological significance of Physiological significance of RapidRapid adaptation: (continued) adaptation: (continued)

(if sitting on a chair & bag is (if sitting on a chair & bag is resting resting on backon back of chair of chair skin is adapted to skin is adapted to this intensity of stimulus, if chair is this intensity of stimulus, if chair is pushed from behindpushed from behind can perceive can perceive change in intensity of stimulus).change in intensity of stimulus).

Physiological significance of Physiological significance of SlowSlow adaptation: adaptation:

Pain is protective sensation (protective value Pain is protective sensation (protective value persists due to persists due to incomplete & slow adaptation incomplete & slow adaptation of pain receptorsof pain receptors).).

As long as cause of pain is there As long as cause of pain is there we feel pain. we feel pain. Advantage: we seek the doctor in time.Advantage: we seek the doctor in time. Baroreceptors Baroreceptors in carotid sinus & arch of aorta in carotid sinus & arch of aorta

adapt in 24-48 hrsadapt in 24-48 hrs. If in sec . If in sec could not could not regulate B.P (take part in regulate B.P (take part in short term regulation short term regulation of B.Pof B.P only). only).

Muscle spindlesMuscle spindles maintain maintain muscle tone & muscle tone & postureposture (slowly adapting). If rapidly adapting (slowly adapting). If rapidly adapting useless.useless.

11stst Mechanism of Mechanism of Adaptation:Adaptation:

PACINIAN CORPUSCLEINDENTATION OF

MEMBRANE OF

PACINIAN CORPUSCLE

(UNIFORM

DISTRIBUTION

OF PRESSURE)

1. STRUCTURAL ADAPTATION

(INCREASED

LOCALIZED

PRESSURE)

22ndnd Mechanism of Mechanism of Adaptation:Adaptation:

2. 2. ACCOMMODATIONACCOMMODATION:: Membrane of receptor / nerve ending Membrane of receptor / nerve ending

accommodated to stimulus due to accommodated to stimulus due to * *inactivation of sodium channelsinactivation of sodium channels..

Continuous stimulus to the receptor Continuous stimulus to the receptor continuously continuously receptor becomes receptor becomes inactivated / accommodated (also the inactivated / accommodated (also the basis of fatigue).basis of fatigue).

4. 4. MULLER’S LAW OF SPECIFIC NERVE MULLER’S LAW OF SPECIFIC NERVE ENERGY & LAW OF LOCALIZATION & ENERGY & LAW OF LOCALIZATION &

PROJECTIONPROJECTION::

From a From a particular type of receptorparticular type of receptor specific nerve fibersspecific nerve fibers carry impulses & carry impulses & stimulate stimulate specific part of brainspecific part of brain..

It means that It means that specific nerve fibersspecific nerve fibers carry impulses for carry impulses for a a specific specific stimulus or sensationstimulus or sensation..

If a nerve fiber for a specific sensation If a nerve fiber for a specific sensation are stimulated at are stimulated at any point along the any point along the pathwaypathway sensation perceived is that sensation perceived is that for which the pathway is specific forfor which the pathway is specific for..

MULLER’S LAW OF SPECIFIC NERVE ENERGY MULLER’S LAW OF SPECIFIC NERVE ENERGY & LAW OF LOCALIZATION & PROJECTION& LAW OF LOCALIZATION & PROJECTION: :

(continued)(continued)

If we stimulate a specific nerve fiber for a If we stimulate a specific nerve fiber for a specific sensation at specific sensation at any point in pathwayany point in pathway same sensation is perceived (along the same sensation is perceived (along the pathway pathway of touchof touch, if we stimulate any point , if we stimulate any point sensation sensation perceived will be perceived will be touchtouch, , no matter what is the no matter what is the stimulus.stimulus.

Point to point connection Point to point connection between receptors in between receptors in different parts of body with the sensory cortex.different parts of body with the sensory cortex.

Specific nerve fibers carry impulses fromSpecific nerve fibers carry impulses from receptors of a receptors of a particular part of bodyparticular part of body, e.g., from , e.g., from the the hanhand.d.

Specific nerve fibers Specific nerve fibers carry impulses to sensory carry impulses to sensory cortex & with the help of these specific nerve cortex & with the help of these specific nerve fibers fibers localization of stimuluslocalization of stimulus. .

5. 5. PHANTOM’S LIMBPHANTOM’S LIMB::

A person having amputated leg A person having amputated leg sometimes c/o severe pain & sometimes c/o severe pain & proprioceptive sensations in the proprioceptive sensations in the amputated leg.amputated leg.

MECHANISMMECHANISM:: In stump of amputated leg, are cut ends In stump of amputated leg, are cut ends

of nerve fibers specific for the amputated of nerve fibers specific for the amputated leg.leg.

When stimulated (pressure / infection) When stimulated (pressure / infection) c/o pain in missing leg (Phantom’s limb).c/o pain in missing leg (Phantom’s limb).

6. 6. DETERMINATION OF DETERMINATION OF INTENSITY OF STIMULUSINTENSITY OF STIMULUS::

Brain can determine intensity of Brain can determine intensity of stimulus by 2 types of sensory stimulus by 2 types of sensory inputs:inputs:

FREQUENCYFREQUENCY of discharge of of discharge of impulses from receptors. (directly impulses from receptors. (directly proportional).proportional).

NUMBER OF RECEPTORSNUMBER OF RECEPTORS stimulated. (directly proportional).stimulated. (directly proportional).