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Anatomical type of receptors
- 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
- 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
- 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