The Brain & Spine
The brain can be divided into 3 main structures: the cerebrum made up of the left and right hemispheres, the cerebellum, and the brain stem.
The cerebrum, a large wrinkled structure, lies over the brain stem and hides most of its structure. The cerebrum is responsible for many functions, including speech, memory, consciousness, and logical and emotional thought. It also interprets our senses and movement. These functions can all be mapped to specific areas on the surface of the cerebrum, showing a direct correlation between location and function.
The cerebellum is responsible for fine tuning our movement by monitoring how we use our muscles and our balance systems. If this part of the brain becomes damaged in any way, for example following a stroke, the sufferer often has serious problems controlling their movements.
The third region of the brain is called the brain stem. It is responsible for regulating many of our life support mechanisms, such as our heart rate, blood pressure and breathing. It also regulates when we sleep or wake.
As the brain is arguably our most important organ, the body goes to great lengths to protect it. Firstly it is surrounded by the meninges that is a tough membrane covering the brain, then there’s a fluid cushion to absorb impacts, and finally the whole assembly is surrounded by the bony skull. The brain remains one of the few organs in the human body that cannot yet be transplanted from one person to another.
The spinal cord is a bundle of nerve cells that connects the brain to the rest of the body, and is encased by the bony spinal column <../skeleton/s_backbone.shtml>. The spinal cord doesn’t fill the length of the spinal column, but extends from the bottom of the skull down through the first 19 vertebrae of the back. The nerves that extend beyond the end of the spinal cord into the lowest part of the spine are called the cauda equina, because they look like a horses tail.
If you took a cross section through the spinal cord, you’d see that it has three distinct layers. In the middle, there’s a tiny channel that carries cerebrospinal fluid throughout the spinal cord. The next layer, around the central channel is greyish, and carries neurones with specialised functions. The third layer is white and carries fibres that take signals to and from the brain.
Nerves divide off from the spinal cord and form massive branching networks that spread throughout the body. The nerves carry signals from the body to give us sensation and return the signals that control our reactions. 31 pairs of nerves branch from the spinal cord, and each pair of nerves links to the part of the body that is closest to the branch point.