Somatosensory Cortex Flashcards
Post Central Gyrus
of Parietal Lobe, just posterior to Central Sulcus that separates Parietal/ Frontal Lobes
Penfield Map
- Multiple parallel maps for touch, proprioception, temperature, and pain
Penfield Map
Topological maps of body surface: Feet, legs, body, arms, hands, face
(“homunculus”,“little man”)
Magnification Facter
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
Gate Theory
nociceptors release….
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…
Periaqueductal Gret Area (PAG in Midbrain)
inhibits?
stimulate?
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”)
Touch Receptors
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
Within brain
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”)
- So, via Axo-Axonal connections,
Endorphins directly inhibit Presynaptic release of Substance P in brain
Acupuncture
Naloxone?
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