chromefert.blogg.se - Nerve endings

#Nerve endings skin
#Nerve endings free

Mechanoreceptors sense stimuli due to physical deformation of their plasma membranes. There are three classes of mechanoreceptors: tactile, proprioceptors, and baroreceptors. They are slow to adjust to a stimulus and so are less sensitive to abrupt changes in stimulation. Free nerve endings are sensitive to painful stimuli, to hot and cold, and to light touch. Free nerve endings are the most common nerve endings in skin, and they extend into the middle of the epidermis.

#Nerve endings free

A free nerve ending, as its name implies, is an unencapsulated dendrite of a sensory neuron.

#Nerve endings skin

Mechanoreceptors in the skin are described as encapsulated (that is, surrounded by a capsule) or unencapsulated (a group that includes free nerve endings). What is commonly referred to as “touch” involves more than one kind of stimulus and more than one kind of receptor. These categories are based on the nature of stimuli each receptor class transduces. Sensory receptors are classified into five categories: mechanoreceptors, thermoreceptors, proprioceptors, pain receptors, and chemoreceptors. (credit: modification of work by Don Bliss, National Cancer Institute) Mammalian skin has three layers: an epidermis, a dermis, and a hypodermis. The hypodermis, which holds about 50 percent of the body’s fat, attaches the dermis to the bone and muscle, and supplies nerves and blood vessels to the dermis. Below the epidermis and dermis is the subcutaneous tissue, or hypodermis, the fatty layer that contains blood vessels, connective tissue, and the axons of sensory neurons. Below this, the much thicker dermis contains blood vessels, sweat glands, hair follicles, lymph vessels, and lipid-secreting sebaceous glands ( Figure 17.4). The epidermis serves as a barrier to water and to invasion by pathogens. It is relatively thin, is composed of keratin-filled cells, and has no blood supply. Recall that the epidermis is the outermost layer of skin in mammals. A variety of receptor types-embedded in the skin, mucous membranes, muscles, joints, internal organs, and cardiovascular system-play a role. Somatosensation occurs all over the exterior of the body and at some interior locations as well. Somatosensation is also known as tactile sense, or more familiarly, as the sense of touch. Somatosensation is a mixed sensory category and includes all sensation received from the skin and mucous membranes, as well from as the limbs and joints.

Explain why the perception of pain is subjective.

Describe the topographical distribution of somatosensory receptors between glabrous and hairy skin.

Describe four important mechanoreceptors in human skin.

Nerve fibers usually considered to be pain sensitive were found in the loose areolar tissue and periphery of the annulus fibrosus but none was seen within the body of the disc or in the nucleus pulposus. No significant increase in nerve elements was observed in several degenerated lumbar dises studied with the cholinesterase technique. Encapsulated nerve terminations were found only in the region of the fibrous facet capsules in the adult tissues. Complex, unencapsulated endings were concentrated primarily in the periosteum of the lumbar vertebrae and within the synovial intervertebral facet-joint capsules. In the adult specimens, fine free nerve fibers were observed in practically all anatomical locations studied. The cartilaginous end plates of the vertebrae had a nerve supply closely associated with the vascular sinusoids in the developing tissues of the fetuses and infants. No nerve elements were found in the deeper zones of the annulus or in the nucleus pulposus. Many free nerve fibers and nerve networks were found in the anterior and posterior longitudinal ligaments and in the peripheral layers of the annulus fibrosus. In the fetuses and newborn infants, encapsulated (Vater-Pacini) endings were primarily concentrated around the facet-joint capsules and on the ventrolateral surface of the annulus fibrosus. Nerve endings of three morphological types were found: (1) free fiber endings, (2) complex unencapsulated endings which sometimes had expanded tips, and (3) encapsulated endings. The nerve terminals of the human lumbar vertebral column and its related structures were studied with cholinesterase and silver-impregnation techniques in specimens from twenty-one autopsies (including two fetuses and two newborn infants) and fifteen surgical procedures.