Introduction
Accessory sensory system includes:
- smell / nose
- taste / tongue
- sight / eye
- hearing and balance / ear
The nervous system directs immediate responses to stimuli, usually by coordinating the activities of other organ systems. There are two major nervous systems: central nervous system (CNS) and peripheral nervous system (PNS).
- The central nervous system consists of:
- the brain, which performs complex integrative functions and controls voluntary activities
- the spinal cord, which relays information to and from the brain, performs less complex integrative functions, and directs many simple involuntary activities
The central nervous system:
- is the control center for the nervous system
- processes information
- provides short-term control over activities of other systems
- integrates and coordinates sensory data and motor commands
- is the seat of higher functions such as intelligence, memory, and emotion
- has an elaborate system to protect its vital non-repairable tissues
There are four parts to this protective system:
- Bone: The brain is encased in the skull, and the spinal cord is encased in the vertebral column.
- Meninges: There are three layers:
- outer is dura mater
- middle is arachnoid
- innermost is pia mater
- Cerebrospinal fluid: Similar to plasma, but composed of water, glucose, protein, and several ions. Its function is for cushioning.
- Blood-brain barrier: An arrangement of cells that supplies the brain and spinal cord and allows selected substances to cross. Not all harmful substances are prevented from crossing the barrier, however.
- The peripheral nervous system links CNS with other systems and sensory organs. It includes all the neural tissue outside the CNS.
The PNS framework is divided into several divisions:
- Afferent division brings sensory information to the CNS.
- Efferent division carries motor commands to muscles and glands. The efferent division is comprised of two nervous systems:
- Somatic nervous system (SNS), which provides voluntary control over skeletal muscles
- Autonomic nervous system (ANS), which provides automatic, involuntary regulation of smooth muscle, cardiac muscle, and glandular activity or secretions. Within the ANS are two more divisions:
- sympathetic: consists of:
- preganglionic neurons located between segments T1 and L2 of the spinal cord
- ganglionic neurons located in two types of ganglia near the vertebral column (paired sympathetic chain ganglia and unpaired collateral ganglia)
- specialized neurons in a modified ganglion in the interior of each adrenal gland (adrenal medulla)
- parasympathetic: consists of:
- preganglionic neurons in the brain stem and in the lateral gray horms of sacral segments S2 to S4
- ganglionic neurons in peripheral ganglia or adjacent to the target organs
- sympathetic: consists of:
- Special nerves of the PNS:
- Cranial Nerves (12 pairs) – connect to the brain rather than to the spinal cord
- Spinal Nerves (31 pairs) – grouped according to the region of the vertebral column from which they originate
This page was updated in December 2005.
