Histology of Sensory Receptors I. Introduction A ... - Faculty.rmc.edu

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III. Myoneural Receptors A. Golgi tendon organs 1. Golgi tendon organs are small spindle-shaped aggregates containing several bundles of collagen fibers with free nerve endings wrapped around the collagen fibers. The whole complex is surrounded by a thin capsule of flattened fibroblastic cells. 2. Golgi tendon organs occur in the tendons of skeletal muscles and respond to tension in the tendon. B. Neuromuscular spindles (muscle spindles) (Figure 11.12) 1. Neuromuscular spindles contain two types of modified skeletal muscle cells which have organized myofibrils in their distal ends but contain few organized myofibrils in their central regions (where their nuclei are located). a. Nuclear bag fibers contain nuclei clumped in the center of the cell. b. Nuclear chain fibers contain nuclei in a row in the center region of the cell. (1) Primary sensory nerve endings spiral around the central region of both types of modified cells. (2) Secondary sensory nerve endings are attached as highly branched "flower spray" endings on the surface of the nuclear chain fibers on both ends just distal to the central (nuclear) region. (3) Both fiber types have motor synapses (gamma efferent) on both distal regions (where the myofibrils are highly organized) which cause the cell ends to contract, stretching the sensory receptor region in the nuclear region of the cell and stimulating the receptor. (4) The receptor complex is surrounded by a capsule of flattened cells continuous with the Schwann cells of the peripheral nerve supplying the muscle and the perimysium (the part of the connective tissue framework of the muscle which surrounds each bundle of muscle cells and the part which attaches to the tendon at each end of the muscle) of the muscle. The modified muscle cells in the receptor are attached to the capsule at their ends and are therefore attached to the perimysium of the muscle. 2. Neuromuscular spindles monitor tension and stretch in the skeletal muscle since either force pulls on the perimysium which pulls on the muscle cells in the receptor. 2
IV. Encapsulated Receptors A. Pacinian corpuscles (Figure 15.13, Plate 42) 1. Pacinian corpuscles contain a central cylindrical sensory nerve ending surrounded by a capsule "wall" of concentric layers of flattened "fibroblastic" cells interspersed with sparse fine collagen fibers and ground substance. 2. Pacinian corpuscles function as pressure and vibration receptors in subcutaneous and internal connective tissues. B. Meissner's corpuscles (Figure 15.13, Plate 42) 1. Meissner's corpuscles contain highly branched, frequently spirally arranged nerve endings winding among transversely stacked flat fibroblastic cells which form an eliptical aggregate which may be surrounded by a thin capsule of connective tissue (loose to moderately dense, rich in flattened fibroblasts). 2. The function of Meissner's corpuscles is not rigorously defined, but they are presumed to function as light touch receptors since they are most numerous in the dermal papillae of the skin on fingers, lips, and genitalia. C. Ruffinian corpuscles (Figure 15.12) 1. The structure of Ruffinian corpuscles is very similar to Golgi tendon organs. They contain a highly branched nerve ending wound around a spindle-shaped bundle of collagen fibers. The entire complex is wrapped in a connective tissue capsule of fine collagen fibers plus flattened fibroblasts. 2. Ruffinian corpuscles are located in deep connective tissues below skin, in joint capsules, and in the walls of some blood vessels. Their function is unclear, but their location and structure suggests that they may detect vibration or distortion of connective tissues. D. Krause's end bulbs (genital corpuscles) (Figure 15.12) 1. Krause's end bulbs contain a highly branched nerve ending in a fluid-filled cavity surrounded by a spherical capsule of collagen fibers and fibroblasts. 2. Krause's end bulbs are located in dermis of skin and in tendons and ligaments. Their function is unknown, but they are assumed to be mechanoreceptors. V. Baroreceptors A. Baroreceptors are highly branched free nerve endings in the tunica adventitia of all large arteries of the head and neck. B. Baroreceptors apparently detect blood pressure by monitoring the stretch in the wall of the vessel (remember that elastic arteries stretch in response to increased blood pressure). 3
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Histology of Sensory Receptors I. Introduction A ... - Faculty.rmc.edu

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