Central Nervous System Help

By — McGraw-Hill Professional
Updated on Aug 18, 2011

Central Nervous System

The central nervous system (CNS) consists of the brain and spinal cord. The functions of the CNS include body orientation and coordination, assimilation of experiences (learning), and programming of instinctual behavior. The CNS contains gray and white matter. The gray matter consists of either nerve cell bodies and dendrites, or of unmyelinated axons and neuroglia. It forms the outer convoluted cerebral cortex and cerebellar cortex in the brain and forms the inner portion of the spinal cord. The white matter consists of aggregations of myelinated axons and forms nerve tracts, within the CNS.


There are five regions of the brain, some with multiple structures:

Brain region Structures
Telencephalon Cerebrum
Diencephalon Thalamus, Hypothalamus, and Pituitary gland
Mesencephalon Superior colliculus, Inferior colliculus, and Cerebral peduncles
Metencepahlon Cerebellum and Pons
Myelencephalon Medulla oblongata


The cerebrum consists of five paired lobes within two convoluted cerebral hemispheres. The hemispheres are connected by the corpus callosum. The cerebrum is responsible for higher functions, including perception of sensory impulses, instigation of voluntary movement, memory, thought, and reasoning. The outer convoluted surface, the cerebral cortex, is composed of gray matter. Elevated folds of the convolutions are the gyri (gyrus, singular) and the depressed grooves are the sulci (sulcus, singular). The convolutions greatly increase the surface area of the gray matter. Beneath the cerebral cortex is the thick white matter, the cerebral medulla.


The diencephalon, a major autonomic region of the forebrain, is almost completely surrounded by the cerebral hemispheres. It contains the:

  • Thalamus. The thalamus is a paired organ immediately below the lateral ventricle. It is a relay center for all sensory impulses, except smell, to the cerebral cortex.
  • Hypothalamus. The hypothalamus consists of several nuclei interconnected to other parts of the brain. Most of its functions relate to regulation of visceral activities including: cardiovascular regulation, body-temperature regulation, water and electrolyte balance, gastrointestinal activity and hunger, sleeping and wakefulness, sexual response, emotions, and control of endocrine functions through stimulation of the anterior pituitary.
  • Epithalamus. The pineal gland extends from the epithalamus. It secretes the hormone melatonin, which may play a role in the onset of puberty.
  • Pituitary Gland. The pituitary is divided into the anterior pituitary, the adenohypophysis, and the posterior pituitary, the neurohypophysis. This gland has endocrine functions.
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