Unencapsulated nerve endings
Found as receptors for the general senses--Dendrites not wrapped in connective tissue
Free nerve endings
Most basic, bare dendrites found in the epithelial tissues. Receptors for hot and cold
Tactile (Merkel) discs
unencapsulated dendritic endings, lies in the deeper layers of the epidermis functioning as light touch receptors
phasic dendrites wrapped around the base of a hair follicle. Can sense any touch that bends a hair.
Encapsulated nerve endings
dendrites wrapped in glial cells or connective tissue
Tactile (Meissner) corpuscles
small, oval masses of flattened connective tissue cells within connective tissue sheaths. Two or more sensory nerve fibers branch into each corpuscle and end within it as tiny knobs. Abundant in hairless portions of skin. Respond to the motion of objects that barely contact the skin. Associated with the sensation of light touch.
Krause end bulbs
Same as Meissner/Tactile but found in mucous membranes, not skin
Lamellated (pacinian) corpuscles
sensory bodies that are relatively large structures composed of connective tissue fibers and cells. Common in the deeper dermal and subcutaneous tissues and in muscle tendons and joint ligaments. Respond to heavy pressure and are associated with the sensation of deep pressure.
heavy touch, pressure, joint movements & skin stretching
A first-order neuron refers to the afferent neuron in a sensory pathway.
2. In the medulla, they synapse with second-order neurons that decussate to the opposite side of the brain to the thalamus.
3. At the thalamus, second-order neurons synapse with third-order neurons that project to the somesthetic cortex of the postcentral gyrus.
4. Pathways for heat and cold perception travel first to the spinal cord where they synapse with second-order neurons on the way to the brain.
CNS modulation of pain
A 'specific' pathway, probably the spinothalamic tracts, which projects to the somatosensory cortex
A 'non-specific' pathway, probably involving the spinoreticulothalamic tracts, which makes widespread and diffuse connections with many areas of the forebrain
something that reduces pain
An opioid neuromodulator. Widespread throughout the brain and dorsal horn of the spinal cord, are considered less potent then endorphins.
natural, opiatelike neurotransmitters linked to pain control and to pleasure
chemicals produced naturally within the body that decreases or eliminate pain they closely resemble the actions of morphine