The billions of neurons that make up the nervous system of the human body can be categorized into two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). Each has subdivisions that function in specialized ways.
The Central Nervous System. The central nervous system is composed of two major subdivisions: the brain and the spinal cord. These two parts are joined at the base of the brain so that there is constant passage of signals to and from the brain and body.
The CNS is encased in protective bone, with the skull surrounding the brain and the backbone (or spinal column) surrounding the spinal cord. Both parts receive sensory messages from the afferent
In general, the spinal cord serves two major functions: (1) carrying impulses back and forth from body to brain or brain to body and (2) controlling many reflexes. The brain controls many more sophisticated functions, including perception, memory, and voluntary movements as well as basic functions such as breathing and swallowing. (Brain signals even may modify actions that occur at the spinal cord level.)
Structure and Function of the Brain. The brain has three major anatomic regions or layers. The first layer forms the hindbrain, a well-protected central core that controls basic, rudimentary behaviors. The hindbrain of a human is very similar to that of other vertebrate animals. Above the hindbrain, the second layer, or midbrain, is the area through which all sensory and motor information going to and from the forebrain and the spinal cord must pass. The third layer is called the forebrain, which contains the cerebral cortex and the limbic system and controls higher mental processes.
EXAMPLE 3.6. Rather than thinking of a person standing, it is easier to envision the construction of the brain if one imagines a person "on hands and knees." The part of the brain pointing ahead is the forebrain, while the hindbrain is farthest toward the back, connecting with the spinal cord, which stretches toward the "tail."
Hindbrain. The hindbrain, or central core, includes the medulla, pons, and cerebellum; it has as its center the reticular formation (or reticular activating system). The behaviors controlled by the hindbrain include heartbeat and circulation, breathing, chewing, and salivating in the medulla; sleep and movement information in the pons; and movement and balance in the cerebellum. The reticular formation controls attention and arousal both for activity and when a person wants to sleep. The hindbrain is thought to be involved with basic survival and varies little among different species (see
EXAMPLE 3.7. Damage to the cerebellum can cause ataxia, a condition of uncoordinated movement, loss of balance, and muscle tremors. Lack of control can be so bad that, for example, an ataxic person may reach for a cup of coffee only to knock it off the table and into a companion's lap.
Was this article helpful?
This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.