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