Central Nervous System | Cannabis Wiki
The Central Nervous System Explained
The central nervous system (CNS) is one of two main divisions of the nervous system, consisting of the brain and the spinal cord.
Think of a computer and all of its many wires throughout the system that enable it to perform its many functions. This massive system of wires and networks send and receives messages. There are numerous wires that are twisted together into a braid, call the power cable, which connects the computer to the electricity that gives it the necessary power to operate.
Now, think of the nervous system with all its many nerves throughout the body that enable the body to carry on its many functions. This system of nerves sends and receives messages. There are many nerve fibers that are twisted together into bundles, called nerves, that connect the brain and the spinal cord with various parts of the body, relaying messages back and forth. Sound complicated? You bet!
The nervous system is perhaps the most intricate of all body systems. Consisting of the brain, spinal cord, and nerves, the nervous system functions to regulate and coordinate all body activities and to detect changes in the internal and external environment, evaluate the information, and respond to the stimuli by bringing about bodily responses. It is the center of all mental activity including thought, learning, and memory.
Anatomy and Physiology of the Central Nervous System
The nervous system is divided into two subdivisions: the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of twelve pairs of cranial nerves and thirty-one pairs of spinal nerves. The central nervous system is responsible for processing and storing sensory and motor information, and for controlling consciousness. The peripheral nervous system is responsible for transmitting sensory and motor impulses back and forth between the central nervous system and the rest of the body.
Cells of the Nervous System
There are two main types of cells found in the nervous tissue: neurons and neuroglia. The neuron, known as the functional unit, is the actual nerve cell; it transmits the impulses of the nervous system. A neuron consists of three basic parts: a cell body, one axon, and one or more dendrites.
The cell body is the structure that contains the nucleus and cytoplasm, as do other cells. The axon is a single, slender projection that extends from the cell body. Axons conduct impulses away from the cell body. Some axons are covered with a myelin sheath, which protects the axon and speeds the transmission of the impulses. Axons that are covered with this myelin sheath appear white, making up the white matter of the nervous system. Axons that not covered with the myelin sheath appear gray, making up the gray matter of the nervous system. The dendrites branch extensively from the cell body, somewhat like tiny trees. The dendrites conduct impulses toward the cell body. Neurons are not continuous with one another throughout the body; instead, a small space exists between the axon of one neuron and the dendrite of another neuron. This space between the two nerves which the impulse must cross is known as a synapse. Chemical substances are released into the synapse to activate or inhibit the transmission of nerve impulses across the synapses; these substances are known as neurotransmitters.
Nerves are classified according to the direction in which they transmit impulses. Afferent nerves transmit impulses towards the brain and spinal cord; they are also known as sensory nerves. Efferent nerves transmit impulses away from the brain and spinal cord; they are also known as motor nerves. The central nervous system also contains connecting neurons that conduct impulses from afferent nerves to (or toward) motor nerves; these are known as interneurons.
The neuroglia, a special type of connective tissue for the nervous system, provide a support system for the neurons. Neuroglia do not conduct impulses; they protect the nervous system through phagocytosis by engulfing and digesting any unwanted substances. There are three types of neuroglia cells: astrocytes, microglia, and oligodendrocytes.
Astrocytes are star-shaped cells with numerous radiating processes for attachment. they are the largest and most numerous of the neuroglial cells and are found only in the central nervous system. The astrocytes wrap themselves around the brain’s blood capillaries, forming a tight sheath. This sheath, plus the wall of the capillary, forms the blood-brain barrier that prevents the passage of harmful substances from the bloodstream into the brain tissue or cerebrospinal fluid.
Microglia are small interstitial cells that have slender branched processes stemming from their bodies. Microglial cells are phagocytic in nature and engulf cellular debris, waste products, and pathogens with the nerve tissue. During times of injury or infection of the nerve tissue, the number of microglial cells dramatically increase, and the cells migrate to the damaged or infected area.
Ogligodendrocytes are found in the interstitial nervous tissue. They are smaller than astrocytes and have fewer processes. The processes of the ogligodendrocytes fan out from the cell body and coil around the axons of many neurons to form the protective myelin sheath that covers the axons of many nerves in the body. The myelin sheath acts as an electrical insulator and helps to speed the conduction of nerve impulses.