PHARMACOLOGY AND THE EFFECTS OF DRUG ABUSE
In this module you will learn about the structures and functions of the brain and the central and peripheral nervous systems. You will also know the immediate and longterm
effects of each drug on the brain and other tissues, organs and systems of the human body.
THE BRAIN AND THE NERVOUS SYSTEM
Neurons
The human body is made up of trillions of cells. Cells of the nervous system, called nerve cells or neurons, are specialized to carry "messages" through an electrochemical process. The human brain has about 100 billion neurons. The neurons carry messages electrochemically through what is called action potential.
Neurons come in many different shapes and sizes. Some of the smallest neurons have cell bodies that are only 4 microns wide. Some of the biggest neurons have cell bodies that are 100 microns wide. (1 micron is equal to one thousandth of a millimeter).
Neurons are the oldest and longest cells in the body. You have many of the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. In fact, you have fewer neurons when you are old compared to when you are young. Neurons can be quite large - in some neurons, such as corticospinal neurons (from motor cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the spinal cord and up to the brain stem), can be several feet long.
BRAIN STRUCTURES AND FUNCTIONS
The Cerebral Cortex
The functions of the cerebral cortex part of the brain consist of thought, voluntary movement, language, reasoning, and perception. The word "cortex" comes from the Latin word for "bark" (of a tree). This is because the cortex is a sheet of tissue
that makes up the outer layer of the brain. The thickness of the cerebral cortex varies from 2 to 6 mm. The right and left sides of the cerebral cortex are connected by a thick band of nerve fibers called the "corpus callosum." In higher mammals such as humans, the cerebral cortex looks like it has many bumps and grooves. A bump or bulge on the cortex is called a gyrus (the plural of the word gyrus is "gyri") and a groove is called a sulcus (the plural of the word sulcus is "sulci").
The Cerebellum
The cerebellum governs the functions of movement, balance, and posture.The word "cerebellum" comes from the Latin word for "little brain." The cerebellum is located behind the brain stem and is similar to the cerebral cortex as it too is divided into hemispheres and has a cortex that surrounds these hemispheres.
Brain stem
The brain stem governs the functions of breathing, heart rate, and blood pressure. The brain stem is a general term for the area of the brain between the thalamus and spinal cord. Structures within the brain stem include the medulla, pons, tectum, reticular formation and tegmentum. Some of these areas are responsible for the most basic functions of life such as breathing, heart rate and blood pressure.
Hypothalamus
The hypothalamus governs the functions of body temperature, emotions, hunger, thirst, and daily biological rhythms. The hypothalamus is composed of several different areas and is located at the base of the brain. Although it is the size of only a pea (about 1/300 of the total brain weight), the hypothalamus is responsible for some very important functions. One important function of the hypothalamus is the control of body temperature. The hypothalamus acts like a "thermostat" by sensing changes in body temperature and then sending signals to adjust the temperature. For example, if you are too hot, the hypothalamus detects this and then sends a signal to
expand the capillaries in your skin. This causes blood to be cooled faster. The hypothalamus also controls the pituitary.
Thalamus
The thalamus governs the functions of sensory processing andmovement.
The thalamus receives sensory information and relays this information to the cerebral cortex. The cerebral cortex also sends information to the thalamus, which then transmits this information to other areas of the brain and spinal cord.
Limbic System
The limbic system governs our emotions. The limbic system (or the limbic areas) is a group of structures that includes the amygdala, the hippocampus, mammillary bodies and cingulate gyrus. These areas are important for controlling the emotional response to a given situation. The hippocampus is also important for memory.
Hippocampus
The Hippocampus is the part of the limbic areas of the brai that governs the functions of learning and memory.
Basal Ganglia
The basal ganglia are a group of structures, including the globus pallidus, caudate nucleus, subthalamic nucleus, putamen and substantia nigra, that are important in
coordinating movement.
Midbrain
The midbrain governs the functions of vision, auditory response, eye movement, and body movement. The midbrain includes structures such as the superior and inferior colliculi and red nucleus. There are several other areas also in the midbrain.
Congratulations! You have finished Module 3 Lesson1
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