Your Body’s Central Processing Unit
BRAIN
The major component of the central nervous system (CNS), the brain comprises the cerebrum, cerebellum, and the brain stem. All activities of the body are controlled from the brain, whether that is sensing the internal and external world, reflexively or consciously responding to stimuli, coordinating all body movements, or simply dreaming of a better world.
The spinal cord is the extension of the CNS throughout the axial core of the body. The spinal cord receives and sends information and transmits that information to and from the brain.
Cerebrum
The cerebrum, or the forebrain, is the organ used for conscious thought, for receiving and perceiving sensory information, and for initiating motor responses. On its surface are numerous folds (gyri) and grooves (sulci) that allow for the outer cortex, a layer of neural tissue, to be packed into a smaller space.
Each hemisphere of the cerebrum is functionally divided into regions. These regions of the brain, called lobes, are responsible for specific functions:
· The frontal lobe is involved in decision-making, overriding instinctual urges that may not be appropriate socially, and planning for future events. Long-term memories are also formed in this region of the brain. This lobe makes up the front half of the cerebrum.
· The parietal lobe connects to the frontal lobe at the midpoint of the brain. It is the location of the somatosensory center of the brain that processes sensory information such as touch and is a major integrating center for incoming information.
· On the side of the cerebrum is the temporal lobe. This region is responsible for the processing of vast amounts of information related to incoming sound and vision. New memories as well as understanding spoken language occur here.
· The final lobe, the occipital lobe, is the very back portion of the brain and functions as the primary visual center of the brain to interpret, integrate, and perceive visual information.
Cerebellum
Positioned beneath the occipital lobes of the cerebrum, the cerebellum functions principally for the coordination of motor activity. It consists of two major lobes, called cerebral hemispheres, with a smaller interconnecting region, the vermis. New research is shedding light on the other activities that the cerebellum may be involved in, such as learning, mood, and behavior.
Brain Stem
The posterior portion of the brain, which is connected to the spinal cord, is termed the brain stem and is composed of the pons and the medulla oblongata. The pons is the enlarged beginning of the brainstem, and is located where nerve tracts that enter and exit the cerebrum are organized. Additionally, the pons has regulatory centers for breathing and heart rate. Extending downward and comprising the nerve tracts to and from the spinal cord is the medulla oblongata. This region also serves as a critical regulator of basic body functions such as respiration and heart rate. The brain stem continues to function in individuals who have clinically been determined to be “brain dead.”
Spinal Cord Gray Matter
White matter makes up the outer layers of the spinal cord, while the gray matter (neural cell bodies) is in the center of the cord. The spinal cord has a gray matter connection called the commissure. In each half of the cord, the remainder of the gray matter is present as the dorsal horn and the ventral horn. The dorsal horn contains synapses between sensory neurons (bringing in information from the periphery) and interconnecting neurons that transmit the signal elsewhere. The bodies of the interneurons are located here. Cell bodies of the motor neurons (sending information out to the periphery) are located in the ventral horn of the gray matter.
Anatomy of a Word
interneuron
An interneuron is a type of neuron that links sensory neurons with motor neurons. They exist only within the central nervous system.
Spinal Cord White Matter
The white matter surrounding the gray matter of the spinal cord consists of the myelinated axons of nerves that carry sensory information to the brain (ascending or afferent fibers) or motor information from the brain (descending or efferent fibers), down the cord to go out to targets in the body. These nerves form synapses with nerve cell bodies in the gray matter of the spinal cord before proceeding either up or out of the cord.