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A. Introduction
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The Central Nervous System consists of the brain and the spinal cord. The brain is contained (and protected) in the skull while the spinal cord is located in and protected by the vertebral column.
The brain itself consists of the following components:
- The cerebrum (large brain)
- The cerebellum (small brain)
- The truncus cerebri (brain stem)
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Let’s start with the major regions. As you can see in the picture, the front (anterior) part of the brain consists of the frontal region (also called frontal lobe). This is our cognitive region (memory, emotions, social interaction, motor control, etc).
Behind the frontal lobe is the parietal lobe. This centre collects information from several sensors such as touch and the position and movements of our body such as our arms, legs etc.
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In the adjoining diagram, you can now see the brain from above (= cranial). This shows that we have actually two brains; one right and one left! So, we actually have two frontal lobes, two temporal lobes etc!
Below the brain (cerebrum) there are three additional structures:
- the brain stem
- the cerebellum
- the spinal cord
The brain stem is the structure that connects the brain (cerebrum) with the cerebellum and the spinal cord.
The cerebellum plays a major role in the regulation of our movements (= motor control) together with balance control (you don’t want to lose your balance!).
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In addition, we also have the entry or exit points of quite a number of cranial nerves. On the diagram are shown:
- the olfactory (nose) tract
- the optical chiasm (the start of the optical nerve)
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After having seen the brain from the side, from above and from below, now is the time to cut the brain in half and see how it looks inside!
Most of the structures seen from above or outside are also visible in this cross-section.
But at the ‘bottom’ of most lobes, there is a structure called ‘corpus callosum’, which, in turn, surrounds an internal area, in the middle of the brain.
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The brain must be kept alive at all costs! There are several systems that provide the brain and the brain cells with oxygen, nutrients etc. The most important one is of course the blood circulation (which will be discussed later).
- Two lateral ventricles in the cerebrum (left and right)
- A third ventricle located in the upper brainstem
- A fourth ventricle located in the lower brainstem
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These ventricles are connected through several canals. Below the fourth ventricle, starts the central canal that runs all the way down the spinal cord.
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The liquor itself is produced by special cells located mostly in the wall of the fourth ventricle. From there it flows through the other cavities and through the arachnoidal space into the sinus sagittal, located in the dura matter which surrounds the brain.
The main function of the cerebrospinal liquor is to provide a fluid ‘shell’ around the cerebrum in which the brain can ‘float’. This is important as it protects the brain tissue from internal damage when the skull is being hit by an object.
The second purpose of the liquor is to drain metabolic products from the brain tissue to the lymph circulation. Approximately 0,5 l liquor is being produced every day.
In this cross-section of the spinal cord, you may notice two different shades of ‘grey’ on its surface; the ‘white matter’ and the ‘grey matter’.
The grey matter, in the centre of the cord, consists mainly of the soma of the nerves; the cell bodies. Surrounding this grey matter, is the white matter, which is mainly caused by the myelin-sheath surrounding the nerve cables.
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Since there are a lot of these ‘cables’ (= axons) running up or down the spinal cord, this are mostly located surrounding the central zone which makes this area more ‘whitish’.
On the other side of the roots are the posterior roots, which is the entry point for the sensory nerves, that conduct sensory information from various parts of the body to the brain.