Functions Of The Nervous System
There are also the fiber arm-like processes called dendrites which are neuron processes that convey incoming messages toward the cell body. Then there are the axons that generate and conduct nerve impulses away from the cell body. In a neuron, there are hundreds of dendrites but only one axon; the axon arises from the axon hillock and forms axonal terminals. These axon terminals contain tiny vesicles which have chemicals like neurotransmitters; the neurotransmitters are separated from the neuron by the synaptic cleft. They also have myelin which is whitish, fatty material that protects and insulates fibers. They also increase the transmission rate of the nerve impulses. The cell body carries most of the metabolic functions, but if it is damaged, the cell dies and it is not replaced. Dendrite endings are specialized receptors while the afferent neurons are the neurons carrying impulses from the sensory receptors to CNS (Marieb …show more content…
The nonessential amino acids and potassium ions are prevented from entering the brain which is actively pumped from brain into blood. Only water, glucose, and essential amino acids can pass. The relative impermeability of brain capillaries is responsible for providing protection. There are also the supporting cell like the neuroglia which are lumped together. They support, insulate, and protect delicate neurons. One type of neuroglia is the glia. They are unable to transmit nerve impulses and never lose their ability to divide (Marieb 2003).
Most brain tumors are gliomas formed by glial cells while normal tumors form because of the abnormal and unregulated growth of cells. After the human brain completes its development soon after birth, the vast majority of its cells enter a resting state in which they never divide again; an exception to this rule is when the brain tumor develops. The abnormal brain cells re-enter the cell-cycle because there are large alterations of the number of genes that control cell division and growth (Marieb