American Medical Association Family Medical Guide - American Medical Association [411]
All the biochemical processes inside your body and the actions of your internal organs are involuntary—that is, you are not aware of them and you have no control over them. A system of nerves called the autonomic system regulates vital functions such as heartbeat, blood pressure, and body temperature.
Disorders of Blood Vessels in the Brain
Four major arteries deliver blood to the brain: two carotid arteries in the front of the neck and two vertebral arteries in the back of the neck. At the base of the brain, the four arteries join together to form a circle of connections from which smaller arteries branch out to supply blood to all parts of the brain.
Vascular disorders such as a stroke occur when an artery ruptures or becomes blocked, cutting off the blood supply to part of the brain. Areas of the brain that receive blood from a single artery are especially vulnerable to damage from an obstruction of blood flow.
The Nervous System and the Brain
The Nervous System
The central nervous system, which includes the brain and spinal cord, is an intricate communications network that controls the inner workings of our body and allows us to respond to our environment. The peripheral nervous system is made up of the peripheral nerves, which run from the spinal cord to all other parts of the body. The central nervous system and the peripheral nervous system work together as a unit: the peripheral nerves gather information from the environment through the senses (such as touch and smell), transmit the sensory information to the central nervous system, and carry signals from the central nervous system to the skin, muscles, bones, joints, and internal organs (including the heart).
The Brain
The brain lies well protected within the rigid, bony case of the skull. The cerebrum, the largest part of the brain, is responsible for the processes involved in movement and thinking. The cerebellum, located under the cerebrum at the top of the spinal cord, controls functions such as balance and coordination. The brain stem, which merges into the top of the spinal cord, contains nerve centers for the cranial nerves and fibers that connect the brain to the rest of the body. The brain stem controls vital functions such as breathing, heart rate, and circulation.
The Cerebral Cortex
The cerebral cortex processes and interprets information coming in from the environment and is responsible for voluntary movement, sensations (such as hearing, vision, taste, and smell), and such higher functions as speech, memory, and intelligence. Some of these functions are localized in specific areas—for example, the primary auditory cortex detects qualities of sounds such as degrees of loudness. Adjacent to the areas of known function, called primary areas, are sections called association areas, which process and interpret the various types of sensory information (such as sound) received by the primary areas and relay the sensory information to other regions for voluntary and involuntary motor responses. For example, while the primary auditory cortex detects simple qualities of sound such as volume, the auditory association cortex analyzes the information to allow us to recognize whole sounds such as spoken words or musical melodies. These association areas—the auditory association cortex, the visual association cortex, and the somatic sensory association cortex—make up more than three fourths of the cortex.
Major arteries of the brain
The carotid arteries run up each side of the neck to supply the brain with blood. The vertebral arteries run up the back of the neck through the spinal cord. At the bottom of the brain, these arteries branch into