![]() ![]() The somatosensory systems also monitor the temperature of the body, external objects and environment, and provide information about painful, itchy and tickling stimuli. Once again, lateral inhibition and spatial opponency exist and form detectors that allow people to estimate sharp pressure features along the surface of the skin.The somatosensory systems inform us about objects in our external environment through touch (i.e., physical contact with skin) and about the position and movement of our body parts (proprioception) through the stimulation of muscle and joints. ![]() Some neurons also have receptive fields that correspond to local patches on the skin, much in the same way as receptive fields works for vision (recall Figure 5.8 from Section 5.2). Inside of the primary somatosensory cortex, neurons fire in a spatial arrangement that corresponds to their location on the body (topographic mapping ). This enables rapid motor response, for the purpose of withdrawing from painful stimuli quickly, and for the knee-jerk reflex. Long before the thalamus, some of the signals are also routed through the spinal cord to motor neurons that control muscles. The signals are routed through the thalamus, with relevant information eventually arriving at the primary somatosensory cortex in the brain, where the higher-level processing occurs. The neural pathways for the somatosensory system work in a way that is similar to the visual pathways of Section 5.2. Through these receptors, the body is aware of the relative positions, orientations, and velocities of its various moving parts. Joint receptors: These lie at the joints between bones and help coordinate muscle movement while also providing information to the central nervous system regarding relative bone positions. ![]() The organs report changes in muscle tension. Golgi tendon organs: These are embedded in tendons, which are each a tough band of fibrous tissue that usually connects a muscle to bone.Muscle spindles: As the name suggests, these are embedded inside of each muscle so that changes in their length can be reported to the central nervous system (which includes the brain).Regarding proprioception (and kinesthesis), there are three kinds of receptors: The temporal resolution is not the same as for hearing, which extends up to 20,000 Hz the Pacinian corpuscles allow vibrations up to a few hundred Hertz to be distinguished from a static pressure. This has implications on touch perception, which will be covered shortly. The density is high at the fingertips, and very low on the back. The spatial resolution or acuity corresponds to the density, or receptors per square area, which varies over the body. Touch has both spatial and temporal resolutions. Yet another class is nocireceptors, which appear in joint tissues and cause a pain sensation from overstretching, injury, or inflammation. In some critical places, such as eyelids, lips, and tongue, thermoreceptors called the end-bulbs of Krause also appear in the skin. Meissner's corpuscles are only in parts where there are no hair follicles ( glabrous skin ), and the hair follicle receptors obviously appear only where there is hair. The first four of these receptors appear in skin all over the body. Hair follicle receptors: These correspond to nerve endings that wrap closely around the hair root they contribute to light touch sensation, and also pain if the hair is removed.Their response is faster than Merkel's discs and Ruffini's corpuscles, allowing vibrations up to 30 to 50 Hz to be sensed this is not as high as is possible as the Pacinian corpuscles. Meissner's corpuscles: These are also just below the epidermis, and respond to lighter touch.Merkel's disks: These structures appear just below the epidermis and respond to static pressure (little or no variation over time), with a slow temporal response.Their response is fast, allowing them to sense vibrations (pressure variations) of up to 250 to 350 Hz. Pacinian corpuscles: These are small bodies filled with fluid and respond to pressure.Ruffini's endings or corpuscles: These are embedded deeply in the skin and signal the amount of stretching that is occurring at any moment.These neurons are special (called pseudounipolar ) in that axons perform the role of both dendrites and axons in a typical neural cell. They have axons that extend up into the outer skin ( epidermis ), with the primary function of sensing temperature extremes (hot and cold), and pain from tissue damage. Free nerve endings: These are neurons with no specialized structure.Their names, structures, and functions are: Figure 13.1 depicts the six main touch receptors, which are embedded in the skin ( dermis ). The somatosensory system has at least nine major kinds of receptors, six of which are devoted to touch, and the remaining three are devoted to proprioception and kinesthesis. Six major kinds of receptors in human skin. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |