SPECIAL SENSES- TOUCH (SOMATIC) Nicholas Brazones, Stephanie Hutchinson, Khaled Nada, Wynne Kirchner

Somatic Senses  Somatic senses are associated with receptors in the:  Skin.  Muscles.  Joints.  Viscera.  These include the senses of:  Touch.  Pressure.  Temperature.  Pain.

Touch and Pressure Senses  Touch and pressure are derived from three types of receptors that sense mechanical forces that deform or displace tissues.  Free Nerve Endings  Meissner’s Corpuscles  Pacinian Corpuscles

Free Nerve Endings  These receptors are common in epithelial tissues.  Their free ends extend between epithelial cells.  They are associated with touch and pressure.

Meissner’s Corpuscles  They are small, ovular masses of connective tissue inside of connective tissue sheaths.  These receptors are usually found in hairless parts of the skin (lips, fingertips, palms, soles, nipples, and external genital organs).  They respond to motions that barely touch the skin, interpreting these impulses as the sensation of light touch.

Pacinian Corpuscles  These receptors are relatively large and composed of connective tissue fibers and cells.  They are common in deeper subcutaneous tissues, in muscle tendons, and in joint ligaments.  They respond to heavy pressure, and are associated with the sensation of deep pressure.

Somatic Receptors

Somatic Pathway

Temperature Senses  This sensation depends on two types of free nerve endings:  Warm Receptors.  Cold Receptors.  Both adapt rapidly, so sensations of warmth or coldness fade after about a minute.

Temperature Receptors  They are most sensitive to temperatures above 25˚C (77˚F) and become unresponsive to temperatures above 45˚C (113˚F). Above this temperature, pain receptors are stimulated, causing a burning sensation.  They are most sensitive to temperatures above 10˚C (50˚F) and become unresponsive to temperatures above 20˚C (68˚F). Below this temperature, pain receptors are stimulated, causing a freezing sensation. Warm ReceptorsCold Receptors

Sense of Pain  Other free nerve endings that sense pain are distributed throughout the skin and internal tissues (except for the brain).  Pain receptors protect the body because they are stimulated by tissue damage and perceived as unpleasant.  Pain receptors adapt poorly in that once activated, impulses are sent to the CNS for some time.  Pain receptors are stimulated through certain chemicals or mechanoreceptors.

Visceral Pain  Pain receptors are the only nerves in the viscera that produce sensation.  The viscera tend to respond to stimulation differently.  Localized Pain: May not elicit pain sensations.  Widespread Pain: Strong pain sensations.  Referred Pain: Pain that feels as if it comes from somewhere other than is being stimulated; common in visceral pain.

Pain Nerve Fibers  The two main types of nerves that conduct impulses away from pain receptors are acute pain fibers and chronic pain fibers.  Pain impulses are conducted to the gray matter of the spinal cord and then possibly the brain (unless the pain is stimulated in the head, in which case its goes directly to the brain).

Pain Receptors  They are thin and myelinated.  They conduct nerve impulses rapidly and are cause sharp pain.  This pain is usually sensed from the skin.  They are thin and unmyelinated.  They conduct impulses slowly and produce a dull, widespread, aching pain.  This pain continues after stimulus ceases and is felt in deeper tissues. Acute Pain FibersChronic Pain Fibers

Regulation of Pain Impulses  Pain arises when it reaches the thalamus.  The cerebral cortex determines the intensity and source of the pain and decides the response.  Areas of gray matter in the brain regulate the movement of pain impulses from the spinal cord and trigger the release of pain inhibiting substances.  Enkephalins and endorphins are neuropeptides that suppresses acute and chronic impulses and relieve severe pain.  Serotonin is a monoamine stimulates the release of enkephalins.

Touch Disorders  Diminished tolerance for any tactile sensations. Incoming stimuli are not adequately processed and screened in the brain, causing even a mild sensory input to be extreme, irritating, or even painful.  A person cannot feel, and has never felt, pain. Two types:  Insensitivity: Subject cannot perceive pain.  Indifference: Subject can perceive pain, but lacks appropriate response. Tactile DefensivenessCongenital Analgesia