Somatosensory Perception

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Somatosensory Perception
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What does Somatosensory System do?

• Tells us what body is up to
• Sensations internal, touch, temp, pain, position
  in space, movement of joints etc

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Somatosensory Receptors

• All over the body
• More sensitive areas more receptors
• Different receptors for different kinds of
  stimuli
• Tell 2 things
• when stimulus starts
• whether stimulus is still occurring

Fig 10.23
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3 Types of Somatosensory Perception

• Nociception
• Pain temp
• Hapsis
• Fine touch pressure
• Proprioception
• Location movement of body

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The Case of Christina

• Massive proprioceptive loss from head to toes

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• 2 pathways
• Dorsal-Column medial-lemniscus - fine touch
• pressure, proprioception
• Axons big, myelinated
• Anterolateral - pain temp
• Axons small,
• unmyelinated

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Cortical Areas
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Stimulation of somatosensory cortex allowed
mapping of function
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Somatosensory Cortex
Somatotopic map
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There are 4 parallel strips

• Each most sensitive to a particular kind of
  stimulus

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Secondary Somatosensory Cortex

• primary to secondary ctx
• more complex processing
• Shape, weight, texture etc combined to form
  perception of whole e.g. Pencil, coin
• Calculates where visual objects are w/ respect to
  body position
• confirms which movements have taken place and
  which ones come next

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Damage to Somatosensory CTX

• 2 types
• Astereognosia -cant recognize objects placed in
  hand contralateral to lesion (can recognize
  visually)
• Asomatognosia - failure to recognize parts of
  own body, usually right sided lesion (thus left
  neglect)

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The Case of the Man Who Fell out of Bed
Damage to right posterior parietal lobe
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PAIN!!!!!
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The Case of the Woman Who Felt No Pain
Read case study (Miss C.) on page 175 in book
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Congenital Insensitivity to Pain

• Rare, recessive disorder
• Development of small fibers carrying sensations
  of pain, heat cold disrupted
• Other somatosensory input intact

Gabby
Ashlyn
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Cortical Representation of Pain is VERY Complex

• Not organized in same way as other senses (ex.
  Areas active during chronic versus brief differ)
• Anterior cingulate ctx - important in emotional
  reaction to pain (lobotomy pts)

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Descending Pain-control Circuit
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Rubbing a Stubbed Toe Makes it Feel BetterWHY?
Dorsal column
Anterolateral
Fine touch pressure pathway inhibits pain
pathway We need pain to survive!