I. This document discusses sensory receptors and their classification.
II. Sensory receptors are specialized nerve endings that convert stimuli into receptor potentials. There are three main types of receptors structurally: bare nerve endings, capsulated nerve endings, and sense organs.
III. Receptors can be classified in several ways, including by the source of the stimulus (exteroceptors, enteroceptors, telereceptors), the type of stimulus (mechanoreceptors, thermoreceptors, chemoreceptors, nociceptors), or their anatomical location (superficial, deep, visceral).
2. 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
3. INTRODUCTION
•Receptors are the biological transducers which
convert various forms of energy into action potential
in nerve fibers
4. 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
5. 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.
6. 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.
7. • 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.
11. A. DEPENDING ON THE SOURCE OF STIMULUS
(SHERRINGTON’S CLASSIFICATION)
1. EXTEROCEPTORS,
2. ENTEROCEPTORS,
3. TELERECEPTORS,
12. 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.
13. 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
14. • 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.
15. 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.
16. 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.
17. • 5. Nociceptors, i.e. The receptors which respond to
Extremes of mechanical, thermal and chemical stimuli
Producing pain.
18. 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.
19.
20.
21.
22. 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.
23.
24.
25. • APPLICATION OF STIMULUS TO
RECEPTORS
• CHANGES IN PERMEABILITY OF MEMBRANE
• GRADED DEPOLARIZATION /
HYPERPOLARIZATION
• GENERATOR OR RECEPTOR POTENTIALS
• LOCAL CURRENTS - ELECTROTONIC
MECHANISM OF RECEPTOR
FUNCTION
26.
27.
28.
29. 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
33. • 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.
34. 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.
35. • 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.
36. 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 -
37. Intensity discrimination :
• Intensity discrimination is basis on logarithmic
• 10 fold increase in strength of stimulus doubles
the intensity of sensation.
38. 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.
39. 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
40. 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
41. 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
42. 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.
43. 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.
44. 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).
45. REFERENCES
•TEXT BOOK OF MEDICAL PHYSIOLOGY
• GUYTON & HALL
•HUMAN PHYSIOLOGY
• VANDER
•TEXT BOOK OF MEDICAL PHYSIOLOGY
• INDUKURANA & SEMBULINGAM
•NET SOURCE
Sherrington’s law = whenever an agonist muscle receives an excitatory signals to contract, inhibitory signals in sent to antagonist Muscle
Stimulation of an afferent neuron with a receptor
ending. Electrodes measure graded potentials and action
potentials at various points in response to different
stimulus intensities. Action potentials arise at the first node of Ranvier in response to a suprathreshold stimulus,
and the action potential frequency and neurotransmitter release increase as the stimulus and receptor potential
become larger. (vander book pg 193)
Action potentials from an afferent fi ber leading from the pressure receptors of a single sensory unit increase in frequency as branches of the
afferent neuron are stimulated by pressures of increasing magnitude.
The influence of sensory unit size and density on acuity. (a) The information from neuron A indicates the stimulus location more precisely
than does that from neuron B because A’s receptive fi eld is smaller. (b) Two-point discrimination is fi ner on the lips than on the back, due to
the lips’ numerous sensory units with small receptive fi elds.
Recording of receptor potential from the pacinian corpuscle: A, placement of recording electrodes; B, record of
receptor potential and action potential produced by graded pressure to the pacinian corpuscle; C, same response as in B after
removal of connective tissue capsule indicates that receptor potential originates from the unmyelinated nerve endings and not the
capsule; D, blockage of first node of Ranvier abolishes conduction of receptor potentials produced and E, no response is produced
when the sensory nerve is cut.