Sense of Touch Touch and Pressure Often called

Sense of Touch

Touch and Pressure • Often called cutaneous sensations because most of their receptors are in the skin • Governed by mechanoreceptors of different types which are widely distributed

Meissner’s Corpuscles • Primary receptors for touch are Meissner’s corpuscles; small oval capsules of connective tissue containing the dendrites of two or more neurons • If connective tissue is moved, even slightly, by a mechanical disturbance, it contacts the dendrites which respond by generating a nerve impulse

Meissner’s Corpuscle

Meissner’s Corpuscles • Most abundant in the skin of the fingers, palms, soles, lips, and external genitals • The Sensory Homunculus represents the density of touch receptors in different areas of the body

Merkel’s discs • Merkel’s discs are another type of touch receptor that are found only in thin skin. • Widespread and sensitive to sustained pressure • Often associated with hair follicles

Pacinian Corpuscles • The receptors responsible for the sensation of pressure are known as Pacinian corpusles • They consist of a knoblike ending of a single sensory neuron surrounded by layers of connective tissue that resemble the layers of an onion

Pacinian Corpuscles

Temperature • The sensation of temperature is detected by free nerve endings in the skin • These are simply the exposed ends of dendrites and it is not well understood how they generate nerve impulses • Extreme temperatures will also trigger pain receptors (below 10 and above 45 degrees Celsius)

Pain • Pain is a necessary evil that warns the brain when a homeostatic imbalance needs attention • Pain is detected by branching dendrites of sensory neurons that end freely throughout the skin, muscles, and most visceral organs • It is thought that these dendrites are sensitive to chemicals produced as cells are damaged; the greater the cellular damage, the greater the sensation of pain

Pain • Pain may also be caused by the overstimulation of any receptor • Visceral pain receptors tend to respond only to widespread disturbances giving sensations such as heartburn, intestinal cramps, headaches, etc. • Visceral pain is also harder to trace to its source because major nerve pathways are shared with other parts of the body

Referred Pain

Pain • The intensity of pain can be controlled by use of drugs: • Analgesics, which interfere with the transmission of impulses, • Anesthetics, which produce an absence of sensation, • Surgery, accupuncture, hypnosis, massage, and controlled breathing are also effective for certain cases

Body Position • Receptors that make you aware of body position are known as proprioceptors • These provide information on the degree of muscle contraction, the amount of tension in tendons, position of a joint, and the position of the head relative to the ground • Muscle spindles monitor the length of a muscle during contraction

Body Position • Your brain keeps track of movements and combines these with information from the middle ear to determine the position of the body and it’s various parts in space