Somatosensory Cortex

Question 1

Post Central Gyrus

Answer 1

of Parietal Lobe, just posterior to Central Sulcus that separates Parietal/ Frontal Lobes

Penfield Map

• Multiple parallel maps for touch, proprioception, temperature, and pain

Question 2

Penfield Map

Answer 2

Topological maps of body surface: Feet, legs, body, arms, hands, face

(“homunculus”,“little man”)

Question 3

Magnification Facter

Answer 3

Any area with small Receptive Field and a high density of high acuity (1:1) receptors takes up a disproportionately large area of the cortical map (i.e. that body area is magnified in cortex – like Fovea of retina)

• Thus bizarre Penfield Map has large hands (object ID, manipulate, gesture) & mouth (speak, eat, kiss) vs. small torso

Question 4

Gate Theory

nociceptors release….

Answer 4

of endogenous Analgesia (pain reduction) via negative feedback from brain or body

• Nociceptors release Substance P in Spinal cord, stimulating “T Cells” to send message up to brain, except when…

Question 5

Periaqueductal Gret Area (PAG in Midbrain)

inhibits?

stimulate?

Answer 5

releases inhibitory Endorphins (“endogenous morphine”)

=> Inhibits Inhibitory cells in Raphe System in hindbrain, allowing Raphe to send Excitatory NT to Spinal Cord

=> Stimulate inhibitory inter-neurons in Grey Matter of Cord, prevent T Cells from reacting to Substance P (“Close Gate”)

Question 6

Touch Receptors

Answer 6

near source of pain are stimulated (e.g. scratch around mosquito bite!)
- Collateral that synapses in Spinal Cord stimulates inhibitory inter-neurons, prevent T Cells from reacting to Substance P

Question 7

Within brain

Answer 7

some cells that release Substance P have NT receptor sites on their Terminals that respond to inhibiting Endorphins

• e.g. On cue from Hypothalamus when sexual activity begins (anticipatory pain prevention)
• e.g. During strenuous exercise (producing “Runner’s high”)

Question 8

• So, via Axo-Axonal connections,

Answer 8

Endorphins directly inhibit Presynaptic release of Substance P in brain

Question 9

Acupuncture

Naloxone?

Answer 9

may work by stimulating PAG Endorphin release, by directly stimulating inhibitory inter-neurons in cord, or both

• Naloxone – an Endorphin Antagonist – blocks effects of Acupuncture