The main types of cells of the nervous system are: the neurons and the neuroglia. The neuron is the actual nerve cell and consists of the cell body, axon, and one or more dendrites. The cell body is the structure that contains the nucleus and cytoplasm. The axon is a single slender projection that extends from the cell body. An axon conducts impulses away from the cell body. The dendrites branch extensively from the cell body. The dendrites conduct impulses toward the cell body. The function of the neuron is to transmit the impulses of the nervous system. The neuroglia is a special type of connective tissue for the nervous system and provides a support system for the neurons. The function of a neuroglia is to protect the nervous system through phagocytosis by engulfing and digesting any unwanted substances. The three types of neuroglia are: astrocytes, microglia, and oligodendrocytes. The astrocytes are star-shaped cells with numerous radiating processes for attachment. Their functions are to wrap around the brain's blood capillaries forming a sheath. The sheath plus the capillary prevents the passage of harmful substances from the bloodstream into the brain tissue or cerebrospinal fluid. The microglia are small cells that have slender branched processes stemming from their bodies. Microglia engulf cellular debris, waste products, and pathogens within the nerve tissue. The oligodendrocytes are found in the interstitial nervous system. They coil around the axons of many neurons to form the protective myelin sheath. The myelin sheath acts as an electrical insulator and helps to speed the conduction of nerve impulses.
The peripheral nervous system (PNS) consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The PNS contains the afferent (sensory) and efferent (motor) nerves. The afferent nerves carry impulses from the body to the central nervous system. The efferent nerves carry impulses from the central nervous system to the muscles and glands. These cause the target organs to do something in response to the commands received. The PNS is further broken down into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The somatic nervous system provides voluntary control over skeletal muscle contractions. The autonomic nervous system provides involuntary control over smooth muscle, cardiac muscle, and glandular activity and secretions in response to the commands of the CNS. The ANS contains two types of nerves, which are: sympathetic and parasympathetic nerves. Sympathetic nerves regulate essential involuntary body functions such as increasing heart rate, constricting blood vessels, and raising the blood pressure. Parasympathetic nerves regulate essential involuntary body functions such as slowing the heart rate, increasing peristalsis of the intestines, increasing glandular secretions, and relaxing sphincters.
The central nervous system (CNS) consists of the brain and the spinal cord. It is highly complex in structure and function. The two main components of the CNS are: the meninges and the cerebrospinal fluid. The meninges are three layers of protective membranes that surround the brain and spinal cord. These three layers are: the dura mater, arachnoid membrane, and pia mater. The dura mater is the outermost layer of the meninges and is a tough white connective tissue. The arachnoid membrane is the middle layer of the meninges and resembles a spider web in appearance. The pia mater is the innermost layer of the meninges and is tightly bound to the surface of the brain and spinal cord. The cerebrospinal fluid is the fluid flowing through the brain and around the spinal cord that protects them from physical blow or impact. The cerebrospinal fluid flows in and around the organs of the CNS and contains proteins, glucose, urea, salts, and some white blood cells.
The structures of the brain are: the cerebrum, gyri, sulci, longitudinal fissure, cerebellum, thalamus, hypothalamus, brain stem, midbrain, pons, and medulla oblongata. The cerebrum is the largest part of the brain and controls consciousness, memory, sensations, emotions, and voluntary movements. The gyri are elevations on the cerebral cortex. Gyri are separated by grooves called sulci. The longitudinal fissure is a deep groove in the middle of the cerebrum that divides the cerebrum into right and left hemispheres. The cerebellum is attached to the brain stem and has an essential role in maintaining muscle tone and coordinating normal movement and balance. The thalamus receives all sensory stimuli, except those of smell, and relays them to the cervical cortex. The hypothalamus is a small region located just below the thalamus and is responsible for activating, controlling, and integrating the peripheral autonomic nervous system, endocrine system processes, and many sensory functions (i.e. body temperature, sleep, and appetite). The brain stem is the region between the diencephalon and the spinal cord and serves as a pathway for conduction of impulses between the brain and spinal cord. It controls such vital functions as respiration, blood pressure, and heart rate. The midbrain is the upper part of the brain stem. The pons is located between the midbrain and the medulla. The medulla oblongata is the lowest part of the brain stem and is continuous with the spinal cord.
Anencephaly is an absence of the brain and spinal cord at birth, a congenital disorder. It can be detected through an amniocentesis or ultrasonography at birth. Bell's palsy is a temporary or permanent unilateral weakness or paralysis of the muscles in the face following trauma to the face, an unknown infection, or a tumor pressing on the facial nerve rendering it paralyzed. Treatment includes gentle massage, applying warm moist heat, facial exercises, prednisone, and analgesics. Carpal tunnel syndrome is a pinching or compression of the median nerve within the carpal tunnel due to inflammation and swelling of the tendons, causing intermittent or continuous pain that is greatest at night. Treatment involves anti-inflammatory medications, splints, physical therapy, stopping the repetitive overuse, and surgery. Cerebral concussion is a brief interruption of brain function, usually with a loss of consciousness lasting for a few seconds. Cerebral contusion is a small, scattered venous hemorrhage in the brain occurring when the brain strikes the inner skull. Treatment includes close observation for secondary effects. Cerebral palsy is a collective term used to describe congenital brain damage that is permanent but not progressive. Cerebrovascular accident involves death of a specific portion of brain tissue, resulting from a decrease in blood flow to that area of the brain. Treatment depends of the cause and effect of the stroke. Degenerative disk is the deterioration of the intervertebral disk, usually due to constant motion and wear on the disk. Treatment includes bed rest, bracing the back, nonsteroidal anti-inflammatory drugs, analgesics, transcutaneous electrical nerve stimulation, and surgical intervention. Encephalitis is the inflammation of the brain or spinal cord tissue largely caused by a virus that enters the CNS when the person experiences a viral disease. Treatment includes administering medications, treating symptoms, and preventing complications. Epilepsy is a syndrome of recurring episodes of excessive irregular electrical activity of the brain resulting in involuntary muscle movements called seizures. Anticonvulsant medications can reduce or control most seizure activity. Diagnostic testing to confirm a diagnosis of seizures includes the following: complete neurological exam, amulatory electroencephalogram, MRI, and CT scan.
