Receptors Modified

8/3/2019 Receptors Modified

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FORMS OF ENERGY CONVERTED

BY THE RECEPTORS

1. mechanical (touch, pressure)

2. thermal (degrees of warmth) 3. electromagnetic (light)

4. chemical (odor, taste, oxygen

content of blood)

5. sound



RECEPTORS**The receptors in each of the sense organs are

adapted to respond to one particular form of

energy at a much lower threshold than other receptor respond to this form of energy

** Adequate stimulus the particular form of energy to

which a receptor is most sensitive to



INITIATION OF IMPULSES IN SENSE

ORGANS

Sensory Receptors receptors responsible infeeding the CNS information about the

internal and external environment of the body

*They are called transducers for they convert variousforms of energy in the environment into actionpotentials in the neurons

* They form part of the sense organs



CLASSIFICATION OF SENSE ORGANS

1. SPECI AL SENSES smell, vision, hearing,rotational and linear acceleration, taste

2. CUTA NEOUS SENSES receptors in the skin3. V ISCERAL SENSES those concerned

with perception of the internal environment



OTHER CLASSIFICATIONS:1. Teleceptors receptors concerned with events at

a distance

2. Ex

teroceptors those concerned with the externalenvironment near at hand

3. Interoceptors those concerned with the internalenvironment

4. Proprioceptors those which provideinformation about the position of the body inspace at any given instance



OTHER CLASSIFICATIONS:5. Nociceptors pain receptors

6. Chemoreceptors those receptors which are

stimulated by a change in the chemicalcomposition of the environment in which

they are located

7. Mechanoreceptors those which are

stimulated by mechanical type of stimulus



CUTANEOUS SENSES:Sensory receptors provide input and stimulation thenervous system in the form of the following:

1. touch-pressure2. cold

3. warmth

4. pain



CUTANEOUS SENSE ORGANS:1. naked nerve endings2. expanded tips on sensory nerve

terminalsa. Merkels disksb. Ruffini endings

3. encapsulated endingsa. Pacinian corpuscles

b. Meissners corpusclesc. Krauses end-bulbs

** they respond to tactile stimuli (see p. 584, fig 46.1 of GUY TON for the illustrations)



PR INCIP AL SENSOR Y MOD ALITIES

( first 11 are conscious sensations )

Sensory modality Receptor Sense organ1. vision rods/cones eye

2. hearing hair cells ear

3. smell olfactory neurons olfactory

mucous membrane



Sensory modality Receptor Sense organ

4. taste taste receptor cells taste buds

5. rotational acceleration hair cells earsemicircular canals

6. linear acceleration hair cells ear

utricle and saccule

7. touch/pressure nerve endings nerve endings




8. Warmth nerve endings various

9. cold nerve endings various10. pain naked nerve endings various

11. joint position & movement nerve endings various

12. muscle length nerve endings muscle spindle




13. muscle tension nerve endings Golgi tendon organ

14. arterial BP nerve endings stretch receptors incarotid sinus & aortic arch

15. central venous pressure nerve endings stretch receptors

in the walls of great veins and atria

16. inflation of lungs nerve endings stretch receptors in

lung parenchyma

17. temperature of blood in head neurons hypothalamus




18. arterial ox ygen pressure nerve endings carotid &

aortic bodies19. pH of CSF receptors ventral surface of

medulla oblongata

20. osmotic pressure of plasma nerve cells anterior

hypothalamus

21. A/V blood glucose difference nerve cells hypothalamus



RECEPTOR POTENTIAL

ALL SENSOR Y R ECEPTOR S HAV E ONE FE ATUR E IN COMMON

Regardless of the type of stimulus that excites thereceptor ==== its immediate effect is to CHA NGE theelectrical potential of the receptor

This change of potential is called RECEP TOR P OT EN TIAL



In summationy The basic cause of the change in membrane potential

is change in MEMBRA NE PERME ABILIT Y of the

receptory Allowing Diffusion of IONS readily through and across

the membrane => change in the TRA NSMEMBRA NE POTENTI AL



ADAPTATIONDefinition:Definition: when a maintained stimulus of constant

strength is applied to a receptor, the frequency of the

action potentials in its sensory nerve declines over aperiod of time

** the degree to which adaptation occurs varies with thetype of sense organ:

- touch adapts rapidly

- organs for cold and pain adapt very slowly

and incompletely



By naturey Sensory receptors adaptadapt either partially or completely

to a constant stimulus after a period of time

(C

HARA C

TE

R IS

TIC

or BA SIC

FE

ATU

R E

of receptors)yy W hen a continuous sensory stimulus is applied,W hen a continuous sensory stimulus is applied,

the receptor responds at a high impulse rate atthe receptor responds at a high impulse rate at first, and then at a progressively slower rate until first, and then at a progressively slower rate until

finally, the rate of action potentials decreases to finally, the rate of action potentials decreases to very few, or often to none at all ( EX TI NC TIO N very few, or often to none at all ( EX TI NC TIO N state)state)



Mechanisms by which RECEPTORS

ADAPT:y *basically, adaptive capacity of the receptor potential is

an INDIVIDUAL PROPERTY .INDIVIDUAL PROPERTY .

1.1. Among the Among the mechanomechano receptors, classic is thereceptors, classic is the pacinianpacinian corpusclecorpuscle

FIR ST MECHA NISM: when a distorting force is suddenly applied toFIR ST MECHA NISM: when a distorting force is suddenly applied toone side of the corpuscle (which is V ISCOELA STIC in nature)one side of the corpuscle (which is V ISCOELA STIC in nature) thisthisforce is instantly transmitted to the viscous component of theforce is instantly transmitted to the viscous component of thecorpuscle directly to the same side of the central nerve fiber =>corpuscle directly to the same side of the central nerve fiber =>eliciting a receptor potentialeliciting a receptor potential

However, within few hundredths of a second, the fluid redistributesHowever, within few hundredths of a second, the fluid redistributes nono receptor potential is already elicitedreceptor potential is already elicited

Thus, the receptor potential appears at theThus, the receptor potential appears at the onsetonset of compression, butof compression, butdisappears within a small fraction of a second even though thedisappears within a small fraction of a second even though thecompression continuescompression continues



Pacinian corpuscle adaptation1.1. Among the Among the mechanomechano receptors, classic is thereceptors, classic is the

pacinianpacinian corpusclecorpuscle

SECOND MECHANISMSECOND MECHANISM:: ACC OMMOD ATIO N ACC OMMOD ATIO N this isthis ismuch slower, and occurs in the nerve fiber itself much slower, and occurs in the nerve fiber itself

E ven if by chance the central core fiber continues to beE ven if by chance the central core fiber continues to bedistorted, the tip of the nerve fiber itself gradually becomesdistorted, the tip of the nerve fiber itself gradually becomesaccommodated to the stimulusaccommodated to the stimulus this is a result of thethis is a result of the

progressive inactivation of the sodium channels in the nerve progressive inactivation of the sodium channels in the nerve fiber membrane (the sodium current flow through the channels fiber membrane (the sodium current flow through the channelscauses them gradually to close. This effect is seems to be truecauses them gradually to close. This effect is seems to be true

for all or most cell membrane odium channels) for all or most cell membrane odium channels)



In General principley In the two mechanisms mentioned, the basic

principle is the READJUSTMENTS in the

STRUCTURE of the receptor itself y And partly and in minority, ELECTR ICAL

CHANGES in the terminal nerve fibril itself

Receptors Modified

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