Summary

Summary

The human brain controls movements, sensations, consciousness, and cognitive abilities. The adult brain is divided into the cerebrum (with cerebral hemispheres), diencephalon, brain stem, and cere-bellum. The cerebral hemispheres and cerebellum contain the nuclei of gray matter surrounded by white matter and an outer gray matter cortex. Each cerebral hemisphere consists of the cerebral cortex, cerebral white matter, and basal nuclei (ganglia). The cerebral hemispheres each receive sensations from and dispatch motor impulses to the opposite side of the body. The brain contains four ventricles filled with CSF. It is covered by convolutions, gyri, sulci, and fissures.

The diencephalon includes the thalamus, hypo-thalamus, and epithalamus. The hypothalamus con-trols the ANS and part of the limbic system as well as gastrointestinal activity, body temperature, and ante-rior pituitary gland activity. The brain stem includes the midbrain, pons, and medulla oblongata. The cerebellum also has two hemispheres and interprets impulses from the motor cortex and sensory path-ways. It coordinates motor activity in the body. The limbic system is the emotional–visceral part of the brain, and also plays a role in memory.

Patterns of electrical activity in the brain are called brain waves, which can be recorded by an EEG. Brain waves include alpha, beta, theta, and delta waves. Consciousness has four basic components: alertness, drowsiness, stupor, and coma. Sleep is a state of partial consciousness from which a person can be aroused by stimuli. The two major types of sleep are NREM and REM sleep. There are four stages of NREM sleep, leading to restorative slow-wave sleep. Then, as alpha waves return, REM sleep begins, and most dreaming will occur in this phase. Sleep and wakefulness occur in natural 24-hour circadian rhythms. Deprivation of REM sleep can result in various personality disorders.

In most people, the left brain hemisphere controls language, whereas the right brain hemisphere controls the emotional content of language. Memory storage includes short-term and long-term memory. Mem-ories transferred to long-term memory become per-manent, but this takes time. The brain is protected by the meninges, CSF, and the blood–brain barrier. The meninges include the dura, arachnoid, and pia mater, which enclose the brain, spinal cord, and related blood vessels. The brain’s blood supply brings continuous oxygen and nutrients through the internal carotid and vertebral arteries. The blood–brain barrier blocks cer-tain molecules from entering the brain, maintaining a needed stability to the brain environment. Com-mon brain injuries include trauma, cerebrovascular accidents (strokes), and degenerative brain disorders (Alzheimer’s, Parkinson’s, and Huntington’s diseases).

The spinal cord is a two-way impulse conduction pathway and reflex center inside the vertebral column. Each spinal cord segment is designated by its paired spinal nerves. The central gray matter of the spinal cord is H-shaped, and each side of its white matter has dorsal, lateral, and ventral columns known as funiculi, each containing ascending and descending tracts. Ascending tracts are sensory, whereas descending tracts are motor. Spinal cord trauma often results in various degrees of paralysis. As we age, the CNS (pri-marily the brain) decreases in the amount of neurons, size, and weight. Cognitive abilities may decline in specific areas or overall.