Central Nervous System Function

Brain and Spinal Cord
The central nervous system is composed of the brain, spinal cord, and neurons. Sciepro/Science Photo Library/Getty Images

The nervous system includes the brainspinal cord, and a complex network of neurons. This system is responsible for sending, receiving, and interpreting information from all parts of the body. The nervous system monitors and coordinates internal organ function and responds to changes in the external environment. This system can be divided into two parts: the central nervous system and the peripheral nervous system.

The central nervous system (CNS) is the processing center for the nervous system. It receives information from and sends information to the peripheral nervous system. The two main organs of the CNS are the brain and spinal cord. The brain processes and interprets sensory information sent from the spinal cord. Both the brain and spinal cord are protected by a three-layered covering of connective tissue called the meninges.

Within the central nervous system is a system of hollow cavities called ventricles. The network of linked cavities in the brain (cerebral ventricles) is continuous with the central canal of the spinal cord. The ventricles are filled with cerebrospinal fluid, which is produced by specialized epithelium located within the ventricles called the choroid plexus. Cerebrospinal fluid surrounds, cushions, and protects the brain and spinal cord from trauma. It also assists in the circulation of nutrients to the brain. 


Colored scanning electron micrograph (SEM) of a Purkinje nerve cell from the cerebellum of the brain. The cell comprises a flask-shaped cell body, from which branch numerous thread-like dendrites. DAVID MCCARTHY/Science Photo Library/Getty Images

Neurons are the basic unit of the nervous system. All cells of the nervous system are comprised of neurons. Neurons contain nerve processes which are "finger-like" projections that extend from the nerve cell body. The nerve processes consist of axons and dendrites which are able to conduct and transmit signals. Axons typically carry signals away from the cell body. They are long nerve processes that may branch out to convey signals to various areas. Dendrites typically carry signals toward the cell body. They are usually more numerous, shorter and more branched than axons.

Axons and dendrites are bundled together into what are called nerves. These nerves send signals between the brain, spinal cord, and other body organs via nerve impulses. Neurons are classified as either motor, sensory, or interneurons. Motor neurons carry information from the central nervous system to organs, glands, and muscles. Sensory neurons send information to the central nervous system from internal organs or from external stimuli. Interneurons relay signals between motor and sensory neurons.


Human Brain Lateral View
Human Brain Lateral View. Credit: Alan Gesek/Stocktrek Images/Getty Images

The brain is the control center of the body. It has a wrinkled appearance due to bulges and depressions known as gyri and sulci. One of these furrows, the medial longitudinal fissure, divides the brain into left and right hemispheres. Covering the brain is a protective layer of connective tissue known as the meninges.

There are three main brain divisions: the forebrain, the brainstem, and the hindbrain. The forebrain is responsible for a variety of functions including receiving and processing sensory information, thinking, perceiving, producing and understanding language, and controlling motor function. The forebrain contains structures, such as the thalamus and hypothalamus, which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions. It also contains the largest part of the brain, the cerebrum. Most of the actual information processing in the brain takes place in the cerebral cortex. The cerebral cortex is the thin layer of gray matter that covers the brain. It lies just beneath the meninges and is divided into four cortex lobes: frontal lobes, parietal lobes, occipital lobes, and temporal lobes. These lobes are responsible for various functions in the body that include everything from sensory perception to decision-making and problem solving. Below the cortex is the brain's white matter, which is composed of nerve cell axons that extend from the neuron cell bodies of gray matter. White matter nerve fiber tracts connect the cerebrum with different areas of the brain and spinal cord.

The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

The hindbrain extends from the spinal cord and contains structures such as the pons and cerebellum. These regions assist in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The hindbrain also contains the medulla oblongata which is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.

Spinal Cord

Spinal Cord Cross-section
Light micrograph and computer illustration of a spinal cord. At right it is seen inside the vertebrae (bones). The section at left shows the white and grey matter with dorsal and ventral horns. KATERYNA KON/Science Photo Library/Getty Images

The spinal cord is a cylindrical shaped bundle of nerve fibers that is connected to the brain. The spinal cord runs down the center of the protective spinal column extending from the neck to the lower back. Spinal cord nerves transmit information from body organs and external stimuli to the brain and send information from the brain to other areas of the body. The nerves of the spinal cord are grouped into bundles of nerve fibers that travel in two pathways. Ascending nerve tracts carry sensory information from the body to the brain. Descending nerve tracts send information pertaining to motor function from the brain to the rest of the body.

Like the brain, the spinal cord is covered by the meninges and contains both gray matter and white matter. The interior of the spinal cord consists of neurons contained within an H-shaped region of the spinal cord. This region is composed of gray matter. The gray matter region is surrounded by white matter containing axons insulated with a special covering called myelin. Myelin functions as an electrical insulator that helps axons to conduct nerve impulses more efficiently. Axons of the spinal cord carry signals both away from and toward the brain along descending and ascending tracts.

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Bailey, Regina. "Central Nervous System Function." ThoughtCo, Oct. 13, 2017, thoughtco.com/central-nervous-system-373578. Bailey, Regina. (2017, October 13). Central Nervous System Function. Retrieved from https://www.thoughtco.com/central-nervous-system-373578 Bailey, Regina. "Central Nervous System Function." ThoughtCo. https://www.thoughtco.com/central-nervous-system-373578 (accessed October 22, 2017).