Somatosensory System Flashcards
Three seperate systems :
Exteroceptive: external stimuli
Proprioceptive: body position
Interoceptive: body conditions (temp blood pressure)
Pacinian corpuscle
Sensitive to sudden or vibrating stimulus
1 type of touch receptor
Free nerve endings
Temperature and pain
Pacinian corpuscles
Adapt rapidly. Large and deep. Onion like.
Respond to sudden displacements of skin
Merkels disks
Gradual skin indentation
Ruffini endings
Gradual skin stretch
Dermatome
Area of body innervated by the left and right dorsal roots of a given segment of spinal cord
Skin area connected to a single sensory spinal nerve
Info from touch receptors in head
Enters CNS through cranial nerves
Info from receptors below head
Enters spinal cord and passes toward the brain (31 segments)
Dorsal column medial-lemnisucs system
1 pathway do somatosensation
Mainly touch a proprioception
First synapse in dorsal column nuclei of medulla
Anterolateral system
2 somatosensory pathway
Mainly pain and temperature
Synapse upon entering spinal cord
Three tracts: spinothalamic, spinoreticular, spinotectal
Primary somatosensory cortex (S1)
Postcentral gyrus
Somatotopic organization (somatosensory homonculus) ^More sensitive more cortex
Input Largely from contralateral
S||
Mainly input from S1
Somatotopic
Input from both sides of body
Much output from both S1 and S2 goes to association cortex in posterior parietal lobe
Somatotopy of 1
Map of body surface sensation onto specific areas of brain
Evidence:
Electrical stimulation of S1
Record activity of a single neuron and determine site of receptive field on body
Not scaled like human body
Astereognosia
Inability to recognize objects by touch
Pure cases rare
Asomatognosia
Failure to recognize parts of ones own body
Phantom limb
Intact cortex but damage in periphery experience a continuing sensation of an amputated body part.
2 possible explanations of phantom limb
- area of somatosensory cortex reorganizes it’s connections and becomes responsive to other parts
- Irritation of nerves in the stump which sends signals to S1 areas that represent amputated part
Relieve phantom pain
Mirror study:
Combo of visual and tactile experience of the “good” hand had altered the activity in opposite S1 area
Circuitry identified by these studies:
- Electircal stimulation of periaqueductal gray had analgesic effects
- PAG and other brain areas have opiate receptors
- Excistence of endogenous opiates (natural analgesics) -endorphins
Events that limit pain ( Melzack and Wall) Gate theory
Certain areas of spinal cord receive messages from other receptors in the skin and from brain - if active they close the “gates” fro the lib messages
Through opiod mechanisms
PAG activated by painful stimuli
Stimuli that induce analgesia
Long distance running
Sexual activity
Certain kinds of music
Certain kinds of lingual stimuli = release endorphins and enkephalins. Brakes on further pain
Intermittent or low intensity continuous shock = releases endorphins and enkephalins
High intensity shock decrease pain sensitivity without inducing endorphins and enkephalins release
2 non pharmaceutical treatments for controlling pain
- Acupuncture
2. Transcutaneous electrical nerve stimulation
