Post on 27-Dec-2015
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 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
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
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