Central Nervous System (Cns)

Central Nervous System (Cns)

The central nervous system is comprised of the brain and the spinal cord. The brain receives sensory information from the nerves that pass through the spinal cord and from other nerves as well, such as those from sensory organs involved in sight and smell. Once received, the brain processes the sensory signals and initiates responses.

The spinal cord is a principle conduit of sensory information to and from the brain. Information flows to the central nervous system from the peripheral nervous system, which senses signals from the environment outside the body (sensory-somatic nervous system) and from the internal environment (autonomic nervous system). The brain's responses to incoming information flow through the spinal cord nerve network to the various effector organs and tissue regions where the target responsive action will take place.

Both the spinal cord and the brain are made up of structures of nerve cells called neurons. The long main body extension of a neuron is termed an axon. Depending on the type of nerve, the axons may be coated with a material called myelin. Both the brain and spinal cord components of the central nervous system contain bundles of cell bodies (out of which axons grow) and branched regions of nerve cells that are called dendrites. Between the axon of one cell body and the dendrite of another nerve cell is an intervening region called the synapse. In the spinal cord of humans, the myelin-coated axons are on the surface and the axon-dendrite network is on the inside. In the brain this arrangement is reversed.

Another important component of the central nervous system are the meninges. The meninges are three sheets or layers of connective tissue that cover all of the spinal cord and the brain. Going from the outside in the layers are called the dura matter, arachnoid and the pia matter. Infections of the meninges are called meningitis. Bacterial, viral, and protozoan meningitis is serious and requires prompt medical attention. Between the arachnoid and the pia matter is a fluid called the cerebrospinal fluid. Bacterial infections of the cerebrospinal fluid can occur and are life-threatening.

Along the length of the spinal cord are positioned thirty-one pairs of nerves. These are known as mixed spinal nerves, as they convey sensory information to the brain and response information back from the brain. Spinal nerve roots emerge from the spinal cord that lies within the spinal canal. Both doral and ventral roots fuse in the intervertebral foramen to create a spinal nerve. Although there are only seven cervical vertebra , there are eight cervical nerves. Cervical nerves one through seven (C1-C7) emerge above (superior to) the corresponding cervical vertebrae. The last vervical nerve (C8) emerges below (inferior to) the last cervical vertebrae from that point downward the spinal nerves exit below the corresponding vertebrae for which they are named.

The brain itself is an enlargement of one end of the spinal cord. There are three regions that comprise the brain: the forebrain (also known as the prosencephalon), the midbrain (mesencephalon), and the hindbrain (rhombencephalon). The hindbrain consists of the medulla oblongata, pons and cerebellum. Functions associated with this region include breathing and coordinated body movements. The midbrain is involved in body movement. The so-called pleasure center is located here, which has been implicated in the development of addictive behaviors. The forebrain contains the intellectual centers. Regions of the forebrain control attributes of personality, vision, speech, and hearing.

Diseases that affect the nerves of the central nervous system include rabies, polio, and sub-acute sclerosing pan-encephalitis. Such diseases affect movement and can lead to mental incapacitation. The brain is also susceptible to disease, including toxoplasmosis and the development of empty region due to prions. Such diseases cause a wasting away of body function and mental ability. Brian damage can be so compromised as to be lethal.