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What is Somatosensory System?
Sense of Touch
What are the four major components/divisions of the Somatosensory System?
- Discriminative Touch
- Proprioception (Joint Sense)- where limbs are in space
- Nociception (Pain)
- Temperature Sense- detect temp by comparing to body temp
what conveys information to the CNS?
dorsal root ganglion
Sensory receptors can be what two types?
Specialized nerve endings (encapsulated) or bare nerve endings (end of axon)
What are the two classes of sensation?
Epicritic and Protopathic
Epicritic sensation involves what general kind of senses and use what kind of receptors?
- Fine aspects of touch
- mediated by encapsulated receptors.
Epicritic sensations include what four abilities?
- 1. topognosis- detect gentle contact of the skin and localize the position that is touched
- 2. discern vibration and determine its frequency and amplitude
- 3. two-point discrimination- resolve by touch spatial detail, such as the texture of surfaces, and the spacing of two points touched simultaneously
- 4. stereognosis- recognize the shape of objects grasped in the hand.
Protopathic sensations involve what kind of senses and use what kind of receptors?
- pain and temperature senses (itch and tickle)
- mediated by bare nerve ending receptors
What are the four types of mechanoreceptors in the skin?
- Meissner's Corpuscle
- Merkel Disk
- Pacinian Corpuscles
- Ruffini Endings
What two mechanoreceptors in the superficial layers of the skin? (Have relatively small receptive fields)
- Meissner's Corpuscles
- Merkel Disk
What two mechanoreceptors are in the subcutaneous tissue? (Have larger receptive fields)
- Pacinian Corpuscle
- Ruffini Ending
What are the two fast adapting mechanoreceptors?
- Meissner's Corpuscle- small receptive field
- Pacinian Corpuscle- large receptive field
What are the two slow adapting mechanoreceptors?
- Merkel Disk- small receptive field
- Ruffini Ending- large receptive field
Describe Meissner's Corpuscle
- Specialized nerve ending
- Rapidly-adapting: only fire when stimulus changes,
- Small receptive fields
- Detect rapid shape changes (i.e. edges)
Describe Merkel Disk
- Specialized nerve endings
- Slow adapting
- Small receptive field
- Detects compression (pressure)
- Sensitive to contours of objects and spatial patterns
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