The Central Nervous System
- (Harvard University - Harvard Taiwan Student Association)
The Brain
The central nervous system is divided into two major parts: the brain and the spinal cord.
The brain lies within the skull and is shaped like a mushroom. The brain consists of four principal parts: the brain stem, the cerebrum
the cerebellum, and the diencephalon.
The brain weighs approximately 1.3 to 1.4 kg. It has nerve cells called the neurons and supporting cells called the glia.
There are two types of matter in the brain: grey matter and white matter. Grey matter receives and stores impulses. Cell bodies of neurons and neuroglia are in the grey matter. White matter in the brain carries impulses to and from grey matter. It consists of the nerve fibers (axons).
- The Brain Stem
The brain stem is also known as the Medulla oblongata. It is located between the pons and the spinal cord and is only about one inch long.
- The Cerebrum
The cerebrum forms the bulk of the brain and is supported on the brain stem. The cerebrum is divided into two hemispheres. Each hemisphere controls the activities of the side of the body opposite that hemisphere.
The hemispheres are further divided into four lobes: Frontal lobe, Temporal lobes, Parietal lobe, and Occipital lobe.
- The Cerebellum
This is located behind and below the cerebrum.
- The Diencephalon
The diencephalon includes the thalamus and hypothalamus. The thalamus is where sensory and other impulses go and coalesce.
The hypothalamus is a smaller part of the diencephalon.
- Other Parts of The Brain
- the midbrain provides conduction pathways to and from higher and lower centers
- the pons acts as a pathway to higher structures; it contains conduction pathways between the medulla and higher brain centers
- The Spinal Cord
The spinal cord is a long tube-like structure that extends from the brain. The spinal cord is composed of a series of 31 segments. A pair of spinal nerves come out of each segment. The spinal cord region from which a pair of spinal nerves originates is called the spinal segment. Both motor and sensory nerves are located in the spinal cord.
The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. It lies within the vertebral column, the collection of bones (backbone).
