January 21, 2010

The more axons used the lesser time in the reaction period. Handy to know right? That's why it's more easier for you to spell something or txt your buddy without much thought because there's more axon's for that being used than when you are trying to remember AP and where to find the basal ganglia.

Somatosensory cortex: caudal (in front of) to the central sulcus.

Homunculus (lit. "little person") indicates which parts of the motor cortex are used for certain parts of the body.

Plasticity --> change The brain is very plastic in the sense that parts of the brain, if not used (like in amputation), can be taken over by the neighboring section of the brain and be used by that specific body part. Consider the experimentation on the chimp where the scientist sewed together his fingers one at a time to prove this thesis. The neighboring areas of the brain used by the index finger would slowly start merging with the middle finger area and when one area was prodded, both fingers were affected. This process was continued until the whole area was taken over by the felxing of the hand. The plasticity surely shows in the reversal of this experimentation where the chimpanzee was able to use his index finger area only for his index finger and not both index and middle finger. Plasticity is a relatively new concept brought more into the light by Dr. Ramachandran who discovered the intricacies of 'blindsight' and helps amputated patients move past their phantom pains.

Lat. Spinothalamic Pathway- Fibers that carry pain and temperature information from the substantia gelatinosa to the thalamus. Pain and temperature information carried by Aδ and C fibers and carried mostly with in the Lateral Spinothalamic pathway. --> information enters spinal column through Dorsal horn of the synapse in layer II and III of the dorsal horn (grey matter) [crosses in the medulla] --> These 2° (secondary) order neurons cross with in the spinal comumn and proceed rostraly up the cord to the ventral posterior (VP) and intralaminar nuclei of the thalamus --> 3° (thirdly) neuron project to the somatosensory cortex and anterior cingulate cortex= emotional response.

Something you should know: White matter is faster than the grey matter. That's why pain information crosses over into the white matter and the temperature travels up through the grey matter.

Aδ and C fibers in dorsal ganglion cells-Pain

capsacin= chemical in hot peppers. Why is it soooo hot?! Because it keeps the channels open in an AP, there is no refraction period. It activates receptors in dorsal root ganglion (DRG) cells. Substance P => NT

Substance P: a neuropeptide: an undecapeptide that functions as a NT and as a neuromodulator. Substance P and its closely related neuropeptide neurokinin A (NKA) are produced from a polyprotein precursor after differential splicing of the preprotachykinin A gene. It is released from the terminals of specific sensory nerves, it is found in the brain and spinal cord, and is associated with inflammatory processes and pain.

opioids = morphine, blocks the 2° neuron (in red) from getting pain signal.

Decending pathway modulating incoming info. by opioids. Periaqueductal Grey (PAG), aqueductal-> around the fluid. Grey-> lots of cells/Mμ receptors