The nervous system involves a complex interaction between special elements designed to originate or carry unique electrochemical charges to and from the various organs within the body.
Like its endocrine counterpart, the nervous system initiates and regulates bodily functions and ensures its owner of an awareness to the surrounding environment.
Anatomy and Physiology
The smallest component of the nervous system is the neuron. There are over 10 billion of these dynamic cells in the body, and they have the ability to originate and propagate nerve impulses.
These result from changes in electrolyte ratios, namely, those of sodium and potassium, occurring across the cell membrane of the neuron.
For this reason, abnormalities in the amounts of sodium and potassium within the body can have devastating effects on nervous system function.
Generated impulses are transmitted to their respective targets along special cellular projections, originating from the cell body, called nerve fibers.
Speeds of transmission along these nerve fibers can reach over 110 meters per second. Groups or bundles of fibers coursing together are what are referred to as nerves.
Within the nervous system, neurons can link together to form a continuous chain to allow for the uninterrupted passage of a nerve impulse to its desired destination. A synapse is described as this connection between two nerve cells.
Special chemical transmitters located at synapses (neurotransmitters) transfer the impulses from the end of one neuron to the receptive end of another, allowing the impulse to continue in its travels.
Neurotransmitters are also found at the junctions between nerve fibers and their target muscles or organs. In cats, organophosphate insecticide poisoning exerts its deadly effects by interfering with the normal breakdown of acetyl- choline, one of these neurotransmitters.
The brain is the control center for the entire nervous system. Internally, it is composed of gray matter, which is a collection of neuron cell bodies and synapses between nerve cells, and white matter, made up of nerve fibers originating from the neuron cell bodies.
The mammalian brain is divided into three divisions: the cerebrum, the cerebellum, and the brainstem. The largest of the three, the cerebrum, is responsible for memory, sensory awareness, learning, and muscular movement.
The cerebellum, located in back of and just beneath the cerebrum, functions to coordinate muscular activity and movement, and control body posture. The final division of the brain, the brainstem, serves a variety of functions.
It acts as an important intermediary by relaying messages between the cerebrum, cerebellum, and the spinal cord, and influencing activities such as heartbeat, breathing, vision, and hearing.
A special portion of the brainstem, called the hypothalamus, provides an important link between the nervous system and the endocrine system.
The spinal cord is the major highway of activity for the transmission of nerve impulses between the brain and the rest of the body. It runs along the course of the back within the spinal canal formed by the vertebral column.
Like the brain, the spinal cord also contains gray matter and white matter. Large spinal nerves containing numerous smaller nerve fibers branch off from the main cord along its course and travel to respective target muscles and organs.
The spinal cord can also serve as coordinating center for certain reflex activities involving the muscles of the limbs without first requiring a nerve impulse to be sent.
to the brain. Clinicians can often assess the extent of damage to a spinal cord by evaluating these spinal reflex arcs.
Spinal nerves branching off from the spinal cord contain two main types of nerve fibers: somatic nerve fibers, which carry information to and from skeletal muscle, skin, joints, and appendages (effects such as muscle contraction, produced by somatic fibers, are said to be under conscious or voluntary control from the brain), and autonomic nerve fibers, which innervate glands and internal organs throughout the body.
Unlike somatic nerves, autonomic nerves act mainly on reflex, with little voluntary control. Blood pressure, cardiac output, breath- ing, gastrointestinal motility, body temperature, and hormone secretion are only some of the many vital life functions under the influence of this unique system.
Three thin layers of tissue called meninges cover both the brain and the spinal cord. Between these layers is found a special type of fluid, called cerebrospinal fluid. Meninges with their accompanying cerebrospinal fluid serve to protect, support, and nourish the underlying nervous tissue.
Abnormal increases in the amount of cerebrospinal fluid can cause serious damage to the spinal cord and brain. Hydrocephalus is the term used to describe such a condition affecting the brain.