ner692



1. Olfactory Bulb 2. Optic Nerve 3. Oculomotor Nerve 4. Trochlear Nerve 5. Trigeminal Nerve 6. Abducens Nerve 7. Facial Nerve 8. Vestibulocochlear Nerve 9. Glossopharyngeal Nerve 10. Vagus Nerve 11. Accessory Nerve 12. Hypoglossal Nerve


	The peripheral nervous system (PNS) is composed of two systems: the afferent nervous system and the efferent nervous system. The afferent nervous system brings information into the brain from the sensory receptors. The efferent nervous system is the part of the PNS that deals with carrying the signals from the central nervous system to the body. There are 12 pair cranial nerves and 31 pairs of spinal nerves in humans. These nerves connect the PNS to the CNS. Most contain both afferent and efferent neurons; however, the olfactory (smell) and optic (sight) contain only afferent neurons.

		Voluntary contractions of the skeletal muscles are controlled by the somatic nervous system. These motor neurons mainly respond to external stimuli and a conscious decision is made to move the muscles. Reflexes are automatic reactions to a stimulus. In most cases reflexes are controlled by the spinal cord and the brain stem. The nervous system that controls smooth and cardiac muscle is the autonomic nervous system. This system regulates the internal environment and it is involuntary. The autonomic nervous system contains two subdivisions: the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system and the parasympathetic nervous system have opposite effects when they act upon the same organ. The parasympathetic nervous system enhances activities and is able to conserve energy. Conversely the sympathetic nervous system increases energy expenditures and prepares the individual for action.

The nervous system is comprised of two main parts: the brain and the spinal cord. The spinal cord is a long bundle of white nerve matter that resides in the middle of the spinal column. This serves as the link between the brain and the body. It also serves as the center from which reflexes stem from.

The brain is much more complex than the spinal cord. It has many divisions within it. These are the brain stem, the cerebellum, the cerebrum.

The brain stem is the core for most of the life systems commands such as breathing and heartbeat. It is the most primitive of the brain divisions and the process that are contained within it cannot be consciously controlled.

The cerebellum is the next most advanced of the brain divisions. It controls balance and the coordination of muscles to obtain movement.

The cerebral cortex is by far the most advanced part of the brain. This is where conscious though takes place. The cerebellum itself can be divided into the left and right hemispheres. It can also be divided into the parts that control specific functions such as hearing and sight. The right hemisphere, generally, is the artistic side of the brain. People who are right brained (their right hemisphere is dominate over the left) are into art, music, and abstract thinking. Left brained people are very logical. They excel in math and physics and other logical thought processes. The two hemispheres are connected by the corpus callosum which is the means for the two hemisphere to communicate with each other. However, it has been proved by scientific experiment that both hemispheres with function normally if the corpus callosum is severed.


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