Cutaneous receptors are classified as exteroreceptors, interoreceptors, and proprioceptors depending on the source of stimulus. Exteroreceptors located in the skin sense touch, temperature, pain and pressure from the external environment. These include mechanoreceptors, thermoreceptors, and nociceptors. Mechanoreceptors like Meissner's corpuscles, Pacinian corpuscles, and Merkel's disks sense different types of touch and vibration. Thermoreceptors detect temperature changes and include free nerve endings and hair follicles. Nociceptors mediate pain through A-delta and C fibers. Signals from cutaneous receptors travel to the somatosensory cortex through the

1. CUTANEOUS RECEPTORS
PRESENTOR: Dr ROHINI
MODERATOR: Dr PASCHAL D’SOUZA

2. SHERRINGTON CLASSIFICATION OF
RECEPTORS
Depending upon the
source of stimulus
• Exteroreceptors
• Interoreceptors
• Proprioreceptors

3. Exteroreceptors
• Receptors responsible for sensing stimulus
coming from external environment.
• Present at or near the surface of the body.
• Includes:
1. Touch
2. Temperature
3. Nociception

4. Interoreceptors
• Respond to stretch ,volume and pressure in
the wall of viscera, excessive muscle
contraction and to overstretching in the
visceral organs.
• Essential in regulating blood flow ,pressure in
the CVS ,maintaining respiration etc.

5. Proprioceptors
• Responds to stimulus arising in muscles ,tendons,
joints etc.
• Essential for coordination of movements and
maintenance of posture.
• Includes
1. Neuromuscular
2. Neurotendinous spindles

6. Depending upon type of stimulus
energy
• Mechanoreceptors
1. Cutaneous receptors
2. Muscle and joint receptors
3. Hair cells
4. Baroreceptors of carotid sinus and aortic arch
• Thermoreceptors
• Nociceptors: receptors responding to pain
• Photorecepetors: rods and cones
• Chemoreceptors

7. Cutaneous receptors
• Sensory receptors
• Located in epidermis as well as dermis of skin
• Exteroreceptors :informs us about touch , temperature
,pain and pressure.
• Densly present over face ,finger tips.
• Includes:
1. Mechanoreceptors
2. Thermoreceptors
3. Nociceptors

8. Mechanoreceptors
• Touch ,pressure , softness, texture of the
stimulus.
• Includes
1. Merkels disc and Meissners corpuscles
2. Pacinian corpuscles
3. Ruffini ‘s end organs
4. Krause end bulbs
5. Free nerve endings

10. Meissner's corpuscles
• Meissner's corpuscles localize in the dermis
between epidermal ridges.
• They contain an unmyelinated nerve ending
surrounded by Schwann cells.
• The center of the capsule contains one or
more afferent nerve fibers that generate rapidly
adapting action potentials following minimal skin
depression.

11. • Present in glabrous (smooth, hairless) skin (the
fingertips)
• Their afferent fibers account for about 40% of
the sensory innervation of the human hand.
• Efficient in transducing information about the
relatively low-frequency vibrations (30–50 Hz)
that occur when textured objects are moved
across the skin.

13. Pacinian corpuscles
• Large encapsulated endings located in the subcutaneous
tissue .
• Has an onion like capsule in which the inner core of
membrane lamellae is separated from an outer lamella by a
fluid-filled space.
• one or more rapidly adapting afferent axons lie at the
center of this structure.
• The capsule again acts as a filter, allowing only transient
disturbances at high frequencies (250–350 Hz) to activate
the nerve endings.

14. • Rapidly adapting
• Involved in the
discrimination of fine
surface textures or high-
frequency vibrations.
• Provide information
primarily about the
dynamic qualities of
mechanical stimuli.

16. Merkel's disks
• Located in the epidermis, where they are
precisely aligned with the papillae that lie
beneath the dermal ridges.
• Account for about 25% of the mechanoreceptors
of the hand and are particularly dense in the
fingertips, lips, and external genitalia.

17. • The slowly adapting nerve fiber associated with
each Merkel's disk enlarges into a saucer-shaped
ending that is closely applied to another
specialized cell containing vesicles that
apparently release peptides that modulate the
nerve terminal.
• Selective stimulation of these receptors in
humans produces a sensation of light pressure.

19. IGGO DOME RECEPTORS
• Merkel's discs are often grouped together in a receptor organ
called the Iggo dome receptor, which projects upward against
the underside of the epithelium of the skin.
• This causes the epithelium at this point to protrude outward,
thus creating a dome and constituting an extremely sensitive
receptor.

20. RUFFINI CORPUSCLES
• These elongated, spindle-shaped capsular
specializations are located deep in the skin, as
well as in ligaments and tendons.
• The long axis of the corpuscle is usually oriented
parallel to the stretch lines in skin.
• Particularly sensitive to the cutaneous stretching
produced by digit or limb movements.

21. Ruffini corpuscle from original slide sent by
Ruffini to Sir Charles Sherrington

22. HAIR FOLLICLE RECEPTOR
• Unencapsulated
• Primary afferent spiral around hair follicle
base.
• Runs parallel to the hair shaft to form a lattice
like pattern.
• Signals the direction and velocity of
movement.
• Rapidly adaptating

24. Krause end bulb
• Type of meissners receptor
• Mainly present in glabrous skin such as skin of
genitalia, papillae of lips,conjunctiva etc
• Afferent fibres belong to A delta
group
• Detects fine touch and pressure

26. Adaptation in cutaneous receptors
• Rapid adaptation means that there is no response to
sustained pressure, only to changes in pressure (either
an increase or a decrease).
• Slow adaptation means that the receptor continues to
respond to pressure for as long as it is sustained, within
some reasonable time frame.
ADAPTATION
RAPIDLY SLOWLY

28. RAPIDLY
ADAPTING
PACINIAN CORPUSCELS
MEISSNER'S CORPUSCLES
High frequency vibration , pressure
Light touch
SLOWLY ADAPTING
MERKELS DISC
RUFFINI
Low frequency vibration and texture
Skin stretching

29. Receptive fields of cutaneous
receptors
• Portion of the skin which, when stimulated,
affects the activity or state of the receptor.

30. • Receptive Fields — the typically oval areas of skin along
which a mechanical stimulus (e.g., touch) leads to a
change in that neurons action potential firing rates.
• In particular, Pacinian corpuscles have fairly large
receptive fields, making them more sensitive (if you
consider the goal of a mechanoreceptor to sense touch
anywhere on the body)
• Meissner’s corpuscles have fairly small receptive
fields, making them more specific

32. The A-beta fibers are large, fast, myelinated afferents. The Meisnner's
corpuscles and Pacinian corpuscles belong to this class. These are
rapidly adapting touch afferents.

33. Pathways from Skin to Cortex
• Two major pathways in the spinal cord: –
• Medial lemniscal pathway consists of large fibers that
carry proprioceptive and touch information .
• Spinothalamic pathway consists of smaller fibers that
carry temperature and pain information .
• These cross over to the opposite side of the body and
synapse in the thalamus, and then on to the
Somatosensory cortex

35. • Signals travel from the thalamus to the somatosensory
receiving area (S1) and the secondary receiving area (S2) in
the parietal lobe .
• Body map (homunculus) on the cortex shows more cortical
space allocated to parts of the body that are responsible for
detail.

36. THERMORECEPTORS
• Thermoreceptors are free dendrite endings in skin, and
thus are primary sensory organs. They have no
specialized epithelial cells or supporting cells.
• The nerves of skin branch from musculocutaneous
nerves that arise segmentally from spinal nerves.
• The pattern of nerve fibers in skin is similar to the
vascular patterns—nerve fibers form a deep plexus,
then ascend to a superficial, subpapillary plexus.

37. • The penicillate fibers are the primary nerve fibers found
subepidermally in haired skin.
• Rapidly adapting receptors that function in the perception
of touch, temperature, pain, and itch.
• Overlapping innervation,leads discrimination to be
generalized.
FREE NERVE ENDING
Penicillate Papillary

38. • Papillary nerve endings are found at the
orifice of a follicle and are thought to be
particularly receptive to cold sensation.
• Hair follicles also contain , slow-adapting
receptors that respond to the bending or
movement of hairs.

40. • A very high concentration of thermosensitive
TRP (Transient Receptor Potential )ion
channels are found in keratinocytes in the
epidermis.
• Each TRP has a unique temperature threshold
of firing.

42. THERMORECEPTIVE NEURONS
C-FIBRES
1.Heat sense neurons
2.Unmyelinated
3.Less velocity of transduction
4.Innervated epidermis
5.Fewer dendrites per neuron
,small receptive fied
A DELTA FIBRES
1.Cold sense neuron
2.Myelinated
3.More velocity of transduction
4.Innervated layers between
epidermis and dermis
5.High receptive field

44. • Cell bodies of the afferent fibers of cutaneous
thermoreceptors reside in the dorsal root
ganglion (DRG) or the trigeminal ganglion on
the dorsal horn of the spinal cord.
• The trigeminal neuron is particularily sensitive
to cold due to its high expression of cold-
activated TRP ion channels.

46. NOCICEPTORS
• Mediate pain
• Terminal branches of thin myelinated A delta and
unmyleniated C fibres
1. Somatic nociceptors: free nerve endings in skin
2. Visceral nociceptors: not well known
• Nociceptors are generally electrically silent and
transmit all-or-none action potentials only when
stimulated.

47. • Nociceptive fibers have been classified on the
basis of their conduction velocity and sensitivity
and threshold to noxious mechanical (M), heat (H),
and cold (C) .
• C fibres:(C-MH, C-MC, C-MHC)
• A-fiber nociceptors are predominately heat- and
or mechanosensitive (A-MH, A-H, A-M)

48. • Excitatory neurons and release glutamate as
their primary neurotransmitter as well as
other components including peptides (e.g.,
substance P, calcitonin gene-related peptide
[CGRP], somatostatin.)