Receptor by Pandian M, Tutor, Dept of Physiology, DYPMCKOP, MH. This PPT for MBBS and tutorial topic

RECEPTOR
PANDIAN M
DEPT OF PHYSIOLOGY
DYPMCKOP

SLO
• INTRODUCTION
• SENSORY RECEPTORS
• STRUCTURALLY 3 TYPES OF RECEPTORS
• TRANSDUCERS
• CLASSIFICATION OF RECEPTORS
• A. DEPENDING ON THE SOURCE OF STIMULUS
(SHERRINGTON’S CLASSIFICATION)
• B. DEPENDING UPON TYPE OF STIMULUS
• C. CLINICAL OR ANATOMICAL CLASSIFICATION OF RECEPTORS
• PRODUCTION OF RECEPTOR POTENTIAL
• PROPERTIES OF RECEPTORS
• Properties of receptor potential

INTRODUCTION
•Receptors are the biological transducers which
convert various forms of energy into action potential
in nerve fibers

SENSORY RECEPTORS
Definition:
-Specialized nerve endings or specialized cells
-More sensitive to specific type of stimulus
-Are able to convert stimulus energy into
electrical energy which is called as
RECEPTOR POTENTIAL
-Can generate A.P. in the nerve connected

STRUCTURALLY 3 TYPES OF
RECEPTORS
1. BARE NERVE ENDINGS - nerve endings that
terminate in periphery as bare unmyelinated endings.
2. CAPSULATED NERVE ENDINGS - In the form of
specialized capsulated structures i.e. Connective tissue
lamellae
3. SENSE ORGANS – Specialized cells located at the end of
afferent nerve.

TRANSDUCERS
• Receptors function like a transducer.
• Transducer is a device, which converts one form of energy
into another.
• So, receptors are often defined as the Biological transducers,
which convert (transducer) Various forms of energy
(stimuli) in the environment into Action potentials in nerve
fiber.

• The stimulus arriving at the given sensory receptor may be in the
form of:
• Mechanical force causing depression of the skin, which Stimulates
mechanoreceptors,
• Light or electromagnetic wave, which stimulates photoreceptors of
the retina,
• Chemical, e.g. A molecule of NaCl on the tongue which stimulates
chemoreceptors,
• Cold or warm temperature stimulating thermoreceptors and
• Sound energy stimulating auditory receptors, and so on and so forth.

Classifications
I.Depending upon source of stimulus
II. Depending upon type of stimulus
III. Clinical or anatomical classification of
receptors

A. DEPENDING ON THE SOURCE OF STIMULUS
(SHERRINGTON’S CLASSIFICATION)
1. EXTEROCEPTORS,
2. ENTEROCEPTORS,
3. TELERECEPTORS,

1. Exteroceptors, i.e. The receptors which receive stimuli from immediate
surrounding outside the body, e.g. Cutaneous receptors for pain, touch and
temperature.
2. Enteroceptors, i.e. The receptors which receive stimuli from within the body, e.g.
Chemoreceptors, baroreceptors, Proprioceptors, osmoreceptors and glucoreceptors
3. Telereceptors, i.e. The receptors that receive stimuli from the distance, e.g. Visual
receptors, cochlear receptors and olfactory receptors.

II. Depending upon type of stimulus
1. Mechanoreceptors- special sense, muscle,
skin, visceral, vascular
2. Thermoreceptors- skin, hypothal.
3. Chemoreceptors- olfactory, gustatory.,
4. Nociceptors
5. Electromagnetic receptors - retina

• 1. Mechanoreceptors, i.e. Those receptors which respond to mechanical stimuli.
These include:
(i) cutaneous receptors (in epidermis and dermis) for Cutaneous tactile
sensibility.
(ii) cutaneous receptors for deep tissue sensibility.
(iii) muscle and joint receptors
(iv) hair cells, e.G. Hair cells in organ of corti (cochlear) or Auditory
receptors, and hair cells in vestibular apparatus or vestibuloreceptors for
equilibrium.
(v) baroreceptors of carotid sinus and aortic arch for Detecting level of
arterial blood pressure.

2. Thermoreceptors, which detect environmental
temperature,
•e.g. Cold receptors and warm receptors.
3. Photoreceptors or electromagnetic receptors,
i.e. rods and cones of the retina, which respond to light
stimuli.

4. Chemoreceptors, which detect change in the chemical composition of the
environment in which they are located,
• e.g. Taste receptors,
• Olfactory receptors,
• Osmoreceptors in supraoptic nuclei of hypothalamus,
• Aortic and carotid bodies receptors, which detect level of arterial pO2, pCO2
and pH,
• Glucoreceptors,
• Chemoreceptors on the surface of medulla for detecting level of blood pCO2 and
• Chemoreceptors in hypothalamus detecting levels of blood glucose, fatty acids
and amino acids.

• 5. Nociceptors, i.e. The receptors which respond to
Extremes of mechanical, thermal and chemical stimuli
Producing pain.

C. CLINICAL OR ANATOMICAL
CLASSIFICATION OF RECEPTORS
1. Superficial receptors, i.e. Those present in skin and
mucous membrane.
2. Deep receptors, i.e. Those present in muscles, tendons,
joints and subcutaneous tissue.
3. Visceral receptors, which are present in the visceral organs.

PRODUCTION OF RECEPTOR POTENTIAL
• When a stimulus excites the receptor, it changes the potential across
the membrane of the receptors.
• This change in the potential is called receptor or generator potential.

• APPLICATION OF STIMULUS TO
RECEPTORS
• CHANGES IN PERMEABILITY OF MEMBRANE
• GRADED DEPOLARIZATION /
HYPERPOLARIZATION
• GENERATOR OR RECEPTOR POTENTIALS
• LOCAL CURRENTS - ELECTROTONIC
MECHANISM OF RECEPTOR
FUNCTION

Properties of receptors
1. Produces Generator potential ( not A.P.)
2. Specificity
3. Graded response
4. Perception and discrimination of intensity
5. Muller’s law of specific nerve energy
6. Law of projection
7. Adaptation
8. Spatial and temporal summation

EXPT. TO DEMONSTRATE
MECHANISM
Structure Diagram Response
AP GP
Intact
AP
GP
Removal of capsule
”
Block at first node
No A.P. GP
Cutting of nerve No AP & GP

• When a mild pressure is applied on the corpuscle, a mild Non-propagated
depolarizing potential, called the generator or receptor potential, can be recorded.
• When the pressure is increased in steps, the magnitude of receptor potential is
increased (Fig -B).
• The depolarized segment of the unmyelinated nerve Ending produces
electrotonic depolarization (current Sink action) in the first node of ranvier.
• When the magnitude of receptor potential is sufficient (Above 10 mv), an action
potential is generated in first Node of ranvier, which is propagated in the nerve
fibre (Fig. b).
• If still greater pressure is applied on the receptor, the frequency of discharge is
proportionately increased.

1. SPECIFICITY OF RESPONSE – MÜLLER LAW
• Specificity of response or müller law refers to the response given by a
particular type of receptor to a Specific sensation.
• For example, pain receptors give response only to pain sensation.
• Similarly, temperature receptors give response only to temperature
sensation. (Ruffini’s receptors)
• In addition, each type of sensation depends upon the Part of the brain
in which its fibers terminate.
• Specificity of response is also called müller’s doctrine of specific
nerve energies.

• Adaptation: when a receptor is continuously stimulated
with the same strength of stimulus, after some time the
receptor stop sending impulse through the afferent nerve.
• This property called adaptation.
• Depending upon this property the receptor has 2 types
• 1. Phasic receptors – which adapt rapidly touch and
pressure receptors
• 2. Tonic receptors- which adapt slowly pain and temp
recep.

On off
Adaptation :
decline in responsiveness on prolonged stimulation
a. fast adapting – phasic –
e.g. tactile receptors,
olfactory receptors
On off
Stim.
Stim.
b. slow adapting – Tonic –
e.g. proprioceptive
receptors
c. non adapting -

Intensity discrimination :
• Intensity discrimination is basis on logarithmic
• 10 fold increase in strength of stimulus doubles
the intensity of sensation.

Law of projection :
Sensation is localized at the site where receptor is located
even when the stimulus is applied at any point on the
sensory pathway.

Spatial and temporal summation
Summation of stimuli applied simultaneously on the
receptor or of stimuli applied repeatedly at the same site.
stim. 1(small)
Stim.2(large)
Repeated stim.
Stim.1 Stim.2 Stim.1+2
Temporal summation
Spatial summation
Recording
graded response

COMPARISON BETWEEN
• GENERATOR
POTENTIAL
• LOCALIZED
• MAGNITUDE DECREASES
WITH TIME AND SPACE
• GRADED RESPONSE
• LASTS FOR 1-2 MSEC.
• NO REFRACTORY PERIOD
• SUMMATION POSSIBLE
• ACTION POTENTIAL
• PROPOGATED
• MAGNITUDE REMAINS
SAME
• ALL OR NONE
PHENOMENON
• LASTS FOR 0.1-0.2
MSEC.
• REFRACTORY PERIOD
PRESENT
• NO SUMMATION

FUNCTIONS OF INPUT TO CNS
1. CONTROL OF OUTPUT :- FOR
HOMEOSTASIS
• MOTOR ACTIVITY
• VISCERAL
2. STIMULATION OF RAS
3. UNDERSTANDING THE WORLD
4. STORAGE IN MEMORY
5. IMPACT ON EMOTIONS

Properties of receptor potential
• The receptor potential is not action potential. It is similar to
excitatory post-synaptic potential in synapse, end plate Potential in a
neuromuscular junction and electrotonic potential in a nerve fibre.
The important properties of receptor potential are:
1. Graded response. Receptor potential is a graded response, .i.e. Its
amplitude increases with increasing velocity of stimulus
application, and increasing strength of stimulus.
Thus, Unlike action potential it does not obey all or none law.

2. Summation, i.e. Receptor potential from two stimuli can be
added if the second stimulus arrives before the receptor
Potential developed due to first stimulus is over. Thus,
receptor potential unlike action potential (which cannot be
added) can be added together.
3.Refractory period is not there in the development of
receptor potential while the action potential has a refractory
period of 1 ms.

4. Local response, i.E. Receptor potential cannot be
Propagated.
5.Duration of receptor potential is greater
(approximately 5–10 ms) than action potential
(approximately 1–2 ms).

REFERENCES
•TEXT BOOK OF MEDICAL PHYSIOLOGY
• GUYTON & HALL
•HUMAN PHYSIOLOGY
• VANDER
•TEXT BOOK OF MEDICAL PHYSIOLOGY
• INDUKURANA & SEMBULINGAM
•NET SOURCE

Receptor by Pandian M, Tutor, Dept of Physiology, DYPMCKOP, MH. This PPT for MBBS and tutorial topic

In this document