anatomical type of receptors
DESCRIPTION
Skin, muscle and other receptors of the human body.TRANSCRIPT
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ANATOMICAL TYPE OF RECEPTORS
Dr. Abdul QadeerMBBS;FCPS;FICS
Assistant Prof. of SurgeryLCMD, Karachi.
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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
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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, haversiansystem of bone, tympanic membrane and dental pulp and muscle
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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
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Free nerve endings
• Free nerve endings detect:
1. Pain (most common)
2. Crude touch
3. Pressure
4. Tickle sensation
5. Cold & heat may be
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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
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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
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Hair follicle receptors
• Nerve fibers wind around the follicle below sebaceous gland
• Bending and release of hair will stimulate the follicle receptor
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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
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Meissner’s corpuscle
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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
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Ruffini corpuscles
• Located in the dermis of hairy skin
• They are stretch receptors of skin
• They are slowly adapting mechanoreceptors
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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
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Joint receptors
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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
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Neuromuscular spindles
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Neuromuscular spindle
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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
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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
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Neurotendinous spindle(Golgi tendon organ)
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Neurotendinous spindle(Golgi tendon organ)
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The end