CNS (Central Nervous System) Functions, Parts, and Locations
What Is the CNS (Central Nervous System)?
- The central nervous system consists of the brain and spinal cord (see Multimedia File 1).
- The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures.
- The spinal cord is connected to a section of the brain called the brainstem and runs through the spinal canal. Cranial nerves exit the brainstem. Nerve roots exit the spinal cord to both sides of the body. The spinal cord carries signals (messages) back and forth between the brain and the peripheral nerves.
- Cerebrospinal fluid surrounds the brain and the spinal cord and also circulates within the cavities (called ventricles) of the central nervous system.
- The leptomeninges surround the brain and the spinal cord. The cerebrospinal fluid circulates between 2 meningeal layers called the pia matter and the arachnoid (or pia-arachnoid membranes).
- The outer, thicker layer serves the role of a protective shield and is called the dura matter.
- The basic unit of the central nervous system is the neuron (nerve cell).
- Billions of neurons allow the different parts of the body to communicate with each other via the brain and the spinal cord. A fatty material called myelin coats nerve cells to insulate them and to allow nerves to communicate quickly.
What are the different parts of the CNS (diagram)
Picture of the central nervous system (CNS). Click to view larger image.
The Brain and Cerebrum
The cerebrum is the largest part of the brain and controls voluntary actions, speech, senses, thought, and memory.
The surface of the cerebral cortex has grooves or infoldings (called sulci), the largest of which are termed fissures. Some fissures separate lobes.
The convolutions of the cortex give it a wormy appearance. Each convolution is delimited by two sulci and is also called a gyrus (gyri in plural). The cerebrum is divided into two halves, known as the right and left hemispheres. A mass of fibers called the corpus callosum links the hemispheres. The right hemisphere controls voluntary limb movements on the left side of the body, and the left hemisphere controls voluntary limb movements on the right side of the body. Almost every person has one dominant hemisphere. Each hemisphere is divided into four lobes, or areas, which are interconnected.
- The frontal lobes are located in the front of the brain and are responsible for voluntary movement and, via their connections with other lobes, participate in the execution of sequential tasks; speech output; organizational skills; and certain aspects of behavior, mood, and memory.
- The parietal lobes are located behind the frontal lobes and in front of the occipital lobes. They process sensory information such as temperature, pain, taste, and touch. In addition, the processing includes information about numbers, attentiveness to the position of one's body parts, the space around one's body, and one's relationship to this space.
- The temporal lobes are located on each side of the brain. They process memory and auditory (hearing) information and speech and language functions.
- The occipital lobes are located at the back of the brain. They receive and process visual information.
Anatomy of the brain. Click to view larger image.
The cortex, also called gray matter, is the most external layer of the brain and predominantly contains neuronal bodies (the part of the neurons where the DNA-containing cell nucleus is located). The gray matter participates actively in the storage and processing of information. An isolated clump of nerve cell bodies in the gray matter is termed a nucleus (to be differentiated from a cell nucleus). The cells in the gray matter extend their projections, called axons, to other areas of the brain.
Fibers that leave the cortex to conduct impulses toward other areas are termed efferent fibers, and fibers that approach the cortex from other areas of the nervous system are termed afferent (nerves or pathways). Fibers that go from the motor cortex to the brainstem (for example, the pons) or the spinal cord receive a name that generally reflects the connections (that is, corticopontine tract for the former and corticospinal tract for the latter). Axons are surrounded in their course outside the gray matter by myelin, which has a glistening whitish appearance and thus gives rise to the term white matter.
Cortical areas receive their names according to their general function or lobe name. If in charge of motor function, the area is called the motor cortex. If in charge of sensory function, the area is called a sensory or somesthetic cortex. The calcarine or visual cortex is located in the occipital lobe (also termed occipital cortex) and receives visual input. The auditory cortex, localized in the temporal lobe, processes sounds or verbal input. Knowledge of the anatomical projection of fibers of the different tracts and the relative representation of body regions in the cortex often enables doctors to correctly locate an injury and its relative size, sometimes with great precision.
Medically Reviewed by a Doctor on 3/9/2017