Encapsulated Nerve Endings
Author: Dr. R. Menaka
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These cells are all characterized by a capsule or more or less flattened connective tissue cells, which enclose the terminations of the axons.
They include,
End Bulbs- also known as receptors for cold. They are spherical or oval in shape and consist of a thick lamellated capsule of connective tissue cells and fibers, surrounding a central cavity or inner bulb. Within this end bulb, the naked axons of one or more myelinated fibers are present.
Occurrence: lips, m.m.of tongue, connective tissue of nerve trunks, cheeks, synovial membrane of certain joints, soft palate, glans penis, clitoris, epiglottis, nasal cavities, lower end of rectum, peritoneum and other serous membranes, tendons and ligaments.
2. Meissner�s Corpuscles - (for tactile corpuscles)
These corpuscles are concerned with the sense of discriminative touch.
They are oval in shape and composed of flattened horizontally arranged connective tissue cells and lamella surrounded by connective tissue capsule. After losing the myelin sheath, the naked axons pass in to the corpuscle, branch and pursue a spiral course among the connective tissue elements.
One myelinated fiber is distributed to each corpuscles.
Occurrence: In hairless portion of the skin, most numerous in fingertips, palms of hands and soles of feet.
3. Pacinian Corpuscles
They are stimulated by deep or heavy pressure. They are laminated elliptical structures.
Each corpuscles is formed of a layer of connective tissue lamellae of connective tissue fibers, lined by a single layer of connective tissue cells. Each capsule is supplied with a single myelinated fiber. As it enters the base of the corpuscle the fiber loses its myelin and the naked axon extends through the center of the inner bulb and ends in a knob like expansion. Fine capillary networks are seen within the lamellae but they don�t enter the inner bulb.
Occurrence: Found in deeper subcutaneous tissue of hand, foot, peritoneum, pancreas, mesentry, penis, clitoris, urethra, nipple, mammary gland, and in connective tissue in vicinity of tendons, ligaments etc.
4. Muscle Spindle (Neuromuscular spindles) - In voluntary muscle, sensory nerves end in end bulb and muscle spindles. The muscle spindle is a cylindrical elongated structure with in which are one or several muscle fibers, connective tissue , blood vessels and myelinated nerve fibers. The whole is enclosed in a connective tissue capsule, which is pierced at various points by one or more nerve fibers. The thicker myelianted sensory fibers lose their myelin, as they branch repeatedly with in the spindle. The axon terminate in close opposition to the sarcolemma of the enclosed muscle fibers. The muscle fibers of the muscle spindle are thinner, richer in sarcoplasm and have more nuclei.
5. Muscle Tendon Spindle - also known as organ of Golgi - Found at the junction of muscle and tendon. Spindle shaped composed of tendon bundles, covered by a connective tissue capsule. Into this there enter one or several afferent nerve fibers which terminate in arborization around bundle.