The Nervous System
- Pp. 436-480 (45)Robert E. Smith
The first year of life is critical in brain development, for the total brain volume doubles, as measured by MRI. This is when the brain is most susceptible to damage by genetic defects and environmental insults. It is also the time in which therapeutic intervention can have its maximum effect. A principal component of the nervous system is the neuron. Neurons are arranged in networks and circuits. The normal human brain has many local regions, or centers, and many pathways between them. The autonomic nervous system is organized into three divisions: the sympathetic, parasympathetic and enteric. Their maintenance activities are primarily performed without conscious control or sensation. The sympathetic and parasympathetic nervous systems work to maintain a type of balance. They have opposite effects on the body. The sympathetic division is used in actions requiring quick responses. The parasympathetic division is used in actions that do not require immediate reaction. Messages are sent to and from neurons in the form of primary messengers, called neurotransmitters. L-DOPA is used to treat Parkinson’s disease, which affects about 1% of the population over 65. Alzheimer’s disease (AD) is the most common neurodegenerative disease. Phenobarbital, carbamazepine, valproic acid and its sodium salt, gabapentin, ethosuximide, lamotigrine, and tiagabine are anti-epileptics. Diazepam, buspirone, &#946;-blockers, tricyclic antidepressants and monoamine oxidase inhibitors treat anxiety disorders. Currently the first-line treatment is either SSRIs or SNRIs. The four main classes of antidepressant drugs are MAOIs, TCAs, SSRIs and SNRIs.