12/8/2023 0 Comments Free nerve endings signal![]() This receptor adapts readily and, like Meissner’s corpuscles, detects mainly (a) movement of objects on the surface of the body or (b) initial contact with the body.įifth, located in the deeper layers of the skin and also in still deeper internal tissues are many Ruffini’send-organs, which are multibranched, encapsulatedendings, as shown in Figure 46–1. Thus, each hair and its basal nerve fiber, called the hair end-organ, are also a touch receptor. These receptors, along with the Meissner’s corpuscles discussed earlier, play extremely important roles in localizing touch sensations to specific surface areas of the body and in determining the texture of what is felt.įourth, slight movement of any hair on the body stimulates a nerve fiber entwining its base. Also note that the entire group of Merkel’s discs is innervated by a single large myelinated nerve fiber (type Aβ). This causes the epithelium at this point to protrude outward, thus creating a dome and constituting an extremely sensitive receptor. Merkel’s discs are often grouped together in a receptor organ called the Iggo dome receptor, which projects upward against the underside of the epithe-lium of the skin, as also shown in Figure 47–1. Therefore, they are responsible for giving steady-state signals that allow one to determine continuous touch of objects against the skin. These receptors differ from Meissner’s corpuscles in that they transmit an initially strong but partially adapting signal and then a continuing weaker signal that adapts only slowly. The hairy parts of the skin also contain moder-ate numbers of expanded tip receptors, even though they have almost no Meissner’s corpuscles. Third, the fingertips and other areas that contain large numbers of Meissner’s corpuscles usually also contain large numbers of expanded tip tactile receptors, one type of which is Merkel’s discs, shown in Figure 47–1. Meissner’s corpuscles adapt in a fraction of a second after they are stimulated, which means that they are particularly sensitive to movement of objects over the surface of the skin as well as to low-frequency vibration. These corpuscles are present in the nonhairy parts of the skin and are particularly abundant in the finger-tips, lips, and other areas of the skin where one’s ability to discern spatial locations of touch sensations is highly developed. Inside the capsu-lation are many branching terminal nerve filaments. Second, a touch receptor with great sensitivity is the Meissner’s corpuscle (illustrated in Figure 46–1), anelongated encapsulated nerve ending of a large (type A β ) myelinated sensory nerve fiber. For instance, even light contact with the cornea of the eye, which contains no other type of nerve ending besides free nerve endings, can nevertheless elicit touch and pressure sensations. their special characteristics are the following.įirst, some free nerve endings, which are found everywhere in the skin and in many other tissues, can detect touch and pressure. There are at least six entirely different types of tactile recep-tors, but many more similar to these also exist. There are three principal differences among them: (1) touch sensation generally results from stimulation of tactile receptors in the skin or in tissues immediately beneath the skin (2) pressure sensation generally results from deformation of deeper tissues and (3) vibration sensation results from rapidly repetitive sensory signals, but some of the same types of receptors as those for touch and pressure are used. Althoughtouch, pressure, and vibration are frequently classified as separate sensations, they are all detected by the same types of receptors. Interrelations Among the Tactile Sensations of Touch, Pressure, and Vibration. Mechano-thermal: Mechano-thermal nociceptors respond to both mechanical and thermal stimuli.Detection and Transmission of Tactile Sensations.Polymodal: Polymodal nociceptors respond to mechanical, thermal, and chemical stimuli.Most visceral nociceptors (those located on organs inside the body) are silent nociceptors. Silent: Silent nociceptors must be first activated or "awakened" by tissue inflammation before responding to a mechanical, thermal, or chemical stimulus. ![]()
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