it clarify the general and sensory nerve ending related receptors way of activation and function.

2. Main classification of the receptor
Receptor
Receptor of the- Receptor of the-
Ligand sensory nerve
ending

3. Receptor of the ligand

4. Definition
• Receptor is the regulatory protein ,located on
the surface or inside the target cell that serves
to recognize the appropriate ligand and
initiate the response to it, but itself has no
other function.

5. Ligand
• It is signal triggering ion or molecule binding
to a site on a target protein.
• Ligand binding to a receptor protein alter its
chemical conformation.
• The conformational change determines the
functional state of a receptor protein .

6. Some terms for the ligand-receptor
interaction description.
1) Agonist: A ligand that can bind to a receptor and
trigger a physiological response is called agonist
for that receptor.
2) Partial agonist: ligand that binds to activate a
given receptor, but has only partial efficacy at
the receptor relative to a full agonist. They may
also considered ligands which display both
agonistic and antagonist effects when both a full
agonist and partial agonist are present.

7. • The partial agonist actually act as a
competitive antagonist competiting with the
full agonist for receptor occupancy and
producing the net decrease in the receptor
activation observed with the full agonist
alone.
• Ex- dichloroisoproterenol on beta adrenergic
receptor, pentazocine on µ opiod receptor.

8. 3) Inverse agonist: An agent that produces a
response after activating the receptor in the
opposite direction to that of the agonist.
Ex-DMCM on benzodiazepin receptor.
4) Antagonist: An agent which prevents the
action of an agonist on a receptor or
subsequent response, but does not have any
effect of its own.

10. Regulation
• Up regulation:
suppose for a target cell , no
ligand is available. In this case , no receptor,
specific for the chemical signal is occupied by the
chemical signal. Therefore all the receptor in the
cell are free to combine with the specific
chemical signal and the receptors are in the state
of maximum up regulation. If only a few of the
receptors are occupied, then still, the receptors
will be in a state of up regulation, though not
maximum up regulation.

11. • Down regulation:
When all the receptors are
occupied by the chemical signal molecules,
the receptors are in a state of down
regulation. When only some are occupied but
others are free, the state is one of down
regulation.

12. Specificity of receptor
• Post-ganglionic parasympathetic nerve secrete
the ACh as NT. Cholinoreceptors can combine
with ACh but not with NA.
• However, the some receptors can combine with
ligand molecules which have minor differences
between their chemical structure. Thus Ad and
NA have only minor chemical difference between
their structure,α-adreno receptor can combine
with Ad and NA, that is both Ad and NA are
agonist of α-adreno receptor.

13. • This phenomenon, however is not always
true. Thus, there is no great difference
between Ach and choline. However
cholinoreceptor can readily bind with ACh but
the affinity of choline for cholinoreceptor is
negligible.

14. Classification

15. Ionotropic receptor

18. Metabotropic receptor

20. 3 major pathway through which GPCRs
function.
• Adenylyl cyclase- cAMP pathway
• Phospholipase C- IP3-DAG pathway
• Channel regulation.

21. cAMP pathway

22. • The PK-A phosphorylates and and alters the
function of many enzymes, ion channels,
transporters and structural protein to manifest as
increased contractility in heart, relaxation in
smooth muscle, glycogenolysis, lipolysis, inhibition
of secretion/mediator release, hormone synthesis
etc. In addition, cAMP directly opens a specific
type of membrane Ca ion channels called CNG in
the heart, brain and kidney. Responses opposite to
the above are produced when AC is inhibited by
inhibitory Gi protein, for ex- Ad and NA on α2
receptor.

23. IP3-DAG pathway

24. • The IP3 mobilises Ca ion from intracellular
organellar depots and DAG enhances PKc
activation by Ca ion. Cytosolic Ca ion act as a
third messenger and is a highly versatile
regulator acting through calmodulin, PKc and
effectors-mediates/modulates contraction,
secretion, eicosanoid synthesis, neuronal
excitability, intracellular movements,
membrane function, metabolism, cell
proliferation etc.

26. Gene regulating receptors

27. Gene regulating receptors

28. Enzyme linked receptor
a)intrinsic enzyme receptor
• The intracellular domain either a protein kinase or
guanylyl cyclase.
• In most case the protein kinase phosphorylates
tyrosine residues on substrate proteins, e.g. insulin,
EGF, NGF, but in few it is a serine or threonine protein
kinase. In the monomeric state, the kinase remains
inactive. Agonist binding induces dimerization of
receptor molecules and activates the kinase to
autophosphorylate tyrosine residues on each other,
increasing their affinity for binding substrate proteins
and carrying forward cascade of tyrosine
phosphorylations.

29. • The enzyme can also be guanylyl cyclase as in
the case of ANP. Agonist activation of the
receptor generates cGMP in the cytosol as a
second messenger which in turn activates
cGMP- dependent protein kinase and
modulates cellular activity.

31. 2) JAK-STATE-kinase binding receptor
• Agonist binding induced dimerization alters the
intracellular domain conformation to increase its
affinity for a cytosolic tyrosine protein kinase
JAK(JANUS-KINASE). On binding, JAK gets activated and
phosphorylates tyrosine residue of the receptor, which
now binds another free moving protein STAT(signal
transducer and activator of transcription) which is also
phosphorylated by JAK. Pairs of phosphorylated STAT
dimerize and translocate to the nucleus to gene
transcription resulting in biological response. Many
cytokines, growth hormone ,interferon etc act
through this type of receptor.

32. Functions
• To propagate regulatory signals from outside to
within the effecter cell when the molecular
species carrying the signal cannot itself penetrate
the cell membrane.
• To amplify the signal.
• To integrate various extracellular and
intracellular regulatory signals.
• To adapt to short term and long term changes in
the regulatory melieu and maintain homeostasis.

33. Receptor of sensory nerve ending

34. Definition
• Receptors are the sensory nerve ending
terminating in the periphery as the bare
unmyelinated ending or specialized
capsulated structure.

35. Classification
Receptor
Exteroceptor Interoceptor

36. Exteroceptor
1)cutaneus

38. 2) chemoreceptors
a) Taste buds
b) olfactory cells

39. Taste buds

40. Olfactory receptor

41. Teloreceptor
• Rods and cones
• Hair cells

42. Rods and cones

43. Hair cells

44. Interoceptor
1) viscero-receptor
a) Stretch receptor
b) Baro receptor
c) Chemo receptor
d) Osmo receptor

45. Stretch receptor

46. Baroreceptor and regulation of
visceral function

47. Chemoreceptor

48. Osmo receptor

49. 2)Proprioceptor
Receptor
• Muscle spindle.
• Golgi tendon.
• Pacinian corpuscle.
• Free nerve ending.
• Hair cells
Location
• Muscle
• Tendon
• Ligament.
• Fascia, joints.
• Vestibular apparatus

50. Somatic Receptor: Muscle Spindle
• are stretch receptors in
the muscle
• – a type of
proprioceptorsense
• organs that monitor
the position and
movements of body parts
• more abundant in
muscles that require fine
control

51. • Two types of intrafusal
muscle fibers based
anatomically on the
location of their nuclei
• Nuclear bag: the
nuclei
are located in the center
of the fiber, which bulges
out into a bag.
• • Nuclear chain:the
nuclei
spread out along the fiber
like a chain.
• Only the ends of the
intrafusal fibers contain
sarcomeres and are able
to contract

52. • Muscle Spindle
• consist of modified muscle fibers
(intrafusal fibers to distinguish them from
extrafusal fibers, i.e. the rest of the
muscle)
• only the two ends of an intrafusal fiber
have sarcomeres and are able to contract
• middle portion acts as a stretch receptor

53. • Have three types of nerve fibers
• Both contain primary afferent nerve fibers (Ia) which end in
annulospiral fibers that coil around middle that respond
mainly to
muscle stretch
• secondary afferent nerve fibers wrap primarily around the
ends of
nuclear chain fibers that respond mainly to prolonged strecth
• gamma motor neurons fibers which innervate the ends of
the
intrafusal fibers (constitutes about 1/3 of fibers in a spinal
nerve)

55. Adjustment of length of intrafusal
fiber by gamma motor neuron.

56. Golgi tendon organ

57. • Golgi tendon organ stretch receptors are located within
the tendons, detecting the amount of
stretch exerted by the muscles on the bones to
which they are attached; encode degree of
stretch by the rate of firing; don’t respond to
length, but to how hard it is pulling
• synapse onto an interneuron in the spinal cord
gray matter which then synapse onto the
relevant alpha motor neuron, producing
inhibitory (glycine) potentials
• – decreases muscular contraction, prevents injury