A. Introduction:
1.
As you can imagine, the sensory part of the brain is the system that ‘senses’ all kind of sensory experience from the outside world and transmits that info to several regions in the brain.
2.
In the previous chapters, we already discussed several types of receptors involved in the detection of several senses.
3.
This sensory information can cause many different reactions; from immediate action to long term storage in our memories.
4.
Also be aware that all this info does not need to go all the way to our ‘upper’ brain. Much of this info will also excite other levels of our brain, even in our spinal cord (as we shall see later).
5.
The diagram shows the major pathways of our sensory system. As you can see, the sensory nerves first go to and trough the spinal cord before reaching the brain. There it becomes very complicated as it travels through various parts of the brain such as the cerebellum, the pons, medulla to finally end in the sensory cortex.
1.
When the sensory nerves enter the spinal cord through the dorsal root, it immediately splits into several branches.
When the sensory nerves enter the spinal cord through the dorsal root, it immediately splits into several branches.
2.
Some of these branches move to the dorsal side of the spinal column and then upward in a dorsal column all the way to the brain.
Some of these branches move to the dorsal side of the spinal column and then upward in a dorsal column all the way to the brain.
3.
Another branch enters the dorsal horn and there divides into several (many!) branches that connect to local neurons. Hey thereby form all kinds of local neuronal circuits.
Another branch enters the dorsal horn and there divides into several (many!) branches that connect to local neurons. Hey thereby form all kinds of local neuronal circuits.
4.
Some of these fibres induce local spinal cord reflexes. Other fibres move up the spinal cord to end in the cerebellum.
Some of these fibres induce local spinal cord reflexes. Other fibres move up the spinal cord to end in the cerebellum.
1.
But the most “important” fibres go straight to the cortex of the large brain; the cerebral cortex.
But the most “important” fibres go straight to the cortex of the large brain; the cerebral cortex.
2.
And, they end up in a special ordained region, depending upon from which area of the body they came from.
And, they end up in a special ordained region, depending upon from which area of the body they came from.
3.
As shown in the diagram, specific regions, show which areas receive impulses from the thigh region, or from the thorax, of, more specifically, from the fingers, the tongue or the face, etc.
As shown in the diagram, specific regions, show which areas receive impulses from the thigh region, or from the thorax, of, more specifically, from the fingers, the tongue or the face, etc.
4.
In other words, although all these action potentials are similar on the way to the brain, they, depending where they came from, all go to specific areas.
In other words, although all these action potentials are similar on the way to the brain, they, depending where they came from, all go to specific areas.
1.
There is another interesting concept which is very popular in physiology and medicine in general; the dermatomes; see diagram. (dermis = skin)
There is another interesting concept which is very popular in physiology and medicine in general; the dermatomes; see diagram. (dermis = skin)
2.
It is actually not that important but probably popular because of this beautiful picture of a human with all these coloured stripes, as seen from the front and the back.
It is actually not that important but probably popular because of this beautiful picture of a human with all these coloured stripes, as seen from the front and the back.
3.
This actually refers to the fact that the sensory endings in the skin, especially the taste sensors, are connected, through a long list of afferent nerves, to the spinal cord and finally to the brain cortex.
This actually refers to the fact that the sensory endings in the skin, especially the taste sensors, are connected, through a long list of afferent nerves, to the spinal cord and finally to the brain cortex.
4.
Depending on the location of the skin sensors, the efferent nerves will enter the spinal cord through the space between adjacent spinal vertebrae.
Depending on the location of the skin sensors, the efferent nerves will enter the spinal cord through the space between adjacent spinal vertebrae.
5.
If something happens in a particular region (cancer, trauma, whatever) or in the nerve bundle that runs to the spinal cord, then this could disrupt the transport of signals from that particular area of the skin to the brain.
If something happens in a particular region (cancer, trauma, whatever) or in the nerve bundle that runs to the spinal cord, then this could disrupt the transport of signals from that particular area of the skin to the brain.
6.
This disruption can cause local pain, rash, or other sensory problems.
This disruption can cause local pain, rash, or other sensory problems.
7.
You may notice that some areas, such as the face, are not coloured in this diagram. That’s because their innervation is quite complicated.
You may notice that some areas, such as the face, are not coloured in this diagram. That’s because their innervation is quite complicated.
8.
In reality, the boundaries of the dermatomes are not as ‘sharp’ as suggested by the diagram but nevertheless, nice to know and to visualize.
In reality, the boundaries of the dermatomes are not as ‘sharp’ as suggested by the diagram but nevertheless, nice to know and to visualize.
