This document summarizes the different types of sensory receptors in the human body. It describes two main categories of receptors - non-capsulated receptors which include free nerve endings, Merkel discs, and hair follicle receptors, and capsulated receptors which include Meissner's corpuscles, Pacinian corpuscles, Ruffini corpuscles, neuromuscular spindles, and neurotendinous spindles. For each type of receptor, it provides details on their anatomical structure, location in the body, and the type of sensation they detect.

1. ANATOMICAL TYPE OF
RECEPTORS
Dr. Abdul Qadeer
MBBS;FCPS;FICS
Assistant Prof. of Surgery
LCMD, Karachi.

3. Types of sensory receptors
Non-capsulated receptors
1. Free nerve endings
2. Merkel discs
3. Hair follicle receptors
Capsulated receptors
1. Meissner’s corpuscles
2. Pacinian corpuscles
3. Ruffini corpuscles
4. Neuromuscular spindles
5. Neurotendinous spindles

5. Free nerve endings
• Widely distributed throughout the body
• They are present in:
1. Epithelial tissue e.g. dermis, cornea, GIT
2. Connective tissues e.g. dermis, fascia,
ligaments, joint capsules, tendons,
periosteum, perichondrium, haversian
system of bone, tympanic membrane and
dental pulp and muscle

6. Free nerve endings
• Afferent nerve fibers may be myelinated or
un-myelinated
• But terminal nerve endings are without myelin
sheath i.e. no Schwann cells covering their tips

7. Free nerve endings
• Free nerve endings
detect:
1. Pain (most common)
2. Crude touch
3. Pressure
4. Tickle sensation
5. Cold & heat may be

8. Merkel discs
• Found in hairless skin e.g. fingertips
• Also found in hair follicles
• Merkel cell: when nerve fiber expands as a
disc in epidermis
• Tactile domes: clusters of Merkel discs in hairy
skin

9. Merkel discs
• Slowly adapting touch
receptors
• Transmit information
about the degree of
pressure exerted on the
skin e.g. when one is
holding a pen

10. Hair follicle receptors
• Nerve fibers wind
around the follicle
below sebaceous gland
• Bending and release of
hair will stimulate the
follicle receptor

11. Meissner’s corpuscles
• Ovoid in shape
• Located in the dermal papillae of the skin
• Especially skin of palm & sole, nipple, external
genitalia
• The corpuscles reduce in number with age
• Very sensitive to touch and able for two-point
discrimination
• They are rapidly adapting mechanoreceptors

12. Meissner’s corpuscle

13. Pacinian corpuscles
• Widely distributed throughout the body
• Abundant in dermis, subcutaneous tissue,
ligaments, joint capsules, pleura, peritoneum,
nipples and external genitalia
• Ovoid in shape, 2 mm long
• Consists numerous concentric lamellae
• It is sensitive to vibration up to 600 stimuli/sec
• They are rapidly adapting mechanoreceptors

15. Ruffini corpuscles
• Located in the
dermis of hairy skin
• They are stretch
receptors of skin
• They are slowly
adapting
mechanoreceptors

16. Joint receptors
• Joints have 4 types of sensory endings
supplying capsule and ligaments of synovial
joints
• Three are encapsulated, resembling pacinian,
Ruffini and tendon stretch receptors
• One non-encapsulated sensitive to excessive
movements and pain

17. Joint receptors

18. Neuromuscular spindles
• Contains:
1. Intrafusal fibers
2. Extrafusal fibers
3. Nuclear bag fibers
4. Nuclear chain fibers
• Stretching & relaxing the spindle causes
impulses to pass along the axons

19. Neuromuscular spindles

21. Neuromuscular spindle

22. Neurotendinous spindle
(Golgi tendon organ)
• Present in tendons
• Located near the junction of tendons with
muscles
• Provide CNS with sensory information
regarding the tension of muscles
• Has intrafusal fibers
• Myelinated nerve fibers pierce the capsule,
loose their myelin sheath, branch & terminate
in club shaped endings

23. Neurotendinous spindle
(Golgi tendon organ)
• Unlike the neuromuscular spindle, which is
sensitive to muscle length, the
neurotendinous organ detects changes in
muscle tension
• Unlike the muscle spindle reflex, this reflex is
inhibitory & inhibits muscle contraction
(hence protective)
• It can influence voluntary muscle activity

24. Neurotendinous spindle
(Golgi tendon organ)

25. Neurotendinous spindle
(Golgi tendon organ)

28. The end