Somatosensory system anatomy

Firstly, some basic anatomy to help you decode Marks' ramblings!

Though it's hard to see the colours, the creamy kind of colour is the parietal lobe. A fissure is a "valley" in the brain that separates the lobes - in this case, the central fissure separates the frontal and parietal lobes. A gyrus is the "hill", that is, the upper bits of the wormy looking things (using proper scientific terminology as always!). So the postcentral gyrus is the hill behind the central fissure. This area is known as the somatosensory centre.

The thalamus is the big yellow blob in roughly the centre of the brain.

The thalamus is basically like a post office - it brings information in, sorts it, and sends it off to the correct place. In this case, it brings in sensory information collected by the spinal cord and sends it off to the somatosensory centre in the parietal lobe.

Now, the spinal cord itself ...

Grey matter is where the cell bodies of the neurones are. White matter is where the myelinated axons from the cell bodies come in and out of the spinal cord. Some sensory information can come into the grey matter through the dorsal horn (dorsal meaning "towards the back"), and then synapses with another neurone cell body in the grey matter.

Within the white matter, there are areas which can be roughly grouped into more specific areas - these are called columns, or funiculi (be aware that your textbook may use this latter term). For example, the lateral columns run on the outer left and right of the spinal cord, whereas the dorsal columns run in the white matter between the dorsal roots.

Now, the diagrams Mark has given you:

Note that the thermoreception pathway is the same as the nociception pathway, except for the first order neurone stimulation input (ie heat/cold or pain).

The main difference to remember (especially in a stressful exam situation!) is that the low threshold mechanoreception pathway crosses sides (left-right or right-left) in the medulla, whereas the thermo- and nociception pathway crosses straight away in the spinal cord.