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Explain the different structures and functions of the two main types of cells in the nervous system.
The neurons and neuroglia are the two main types of cells found in the nervous system. The neuron is responsible for the transmission of impulses of the nervous system. The neuron, which is the active nerve cell, is made up of 3 main parts: the cell body, axon, and dendrites. The cell body holds the nucleus and the cytoplasm. The axon sends impulses away from the cell body. The axon is a slender projection that is sometimes covered in a myelin sheath for protection and to increase the rate of impulse transmissions. Dendrites extend from the cell body. They are responsible for sending impulses toward the cell body.
Neuroglia is a type of connective tissue found in the nervous system that provides support for the neurons. Unlike neurons neuroglia do not spend impulses. Through the use of phagocytosis, which engulfs and digests unwanted substances, neuroglia serves as protection for the nervous system. Astrocytes, microglia, and oligodendrocytes are the three types of neuroglia cells. Astrocytes are only found in the central nervous system. They are the greatest quantity and largest of the neuroglia cells. Astrocytes join with the brain's blood capillaries to form the blood-brain barrier that prevents harmful substances from entering the brain tissue and cerebrospinal fluid. The microglial cells work within the nervous tissue to eliminate cellular debris, waste products and pathogens. Oligodendrocytes are found in interstitial nervous tissue. They join with axons to form the myelin sheath which helps to insulate and speed nerve impulses.
Describe the structures and functions of the peripheral nervous system (PNS). Be sure to include the nerves associated with the PNS, and contrast the functions of the somatic and autonomic nervous systems.
The peripheral nervous system is responsible for sending sensory and motor impulses between the central nervous system and the rest of the body. It is made up of nerves and ganglion and consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The nerves send impulses to and from the brain and spinal cord to other parts of the body. Ganglia are masses of nerve cell bodies located outside the central nervous system. The peripheral nervous system contains afferent nerves and efferent nerves. The afferent nerves send impulses toward the central nervous system from the body where as the efferent nerves send impulses from the central nervous system to the body.
The peripheral nervous system is broken down into the somatic and autonomic nervous systems. The somatic nervous system is responsible for voluntary control over skeletal muscle contractions. The autonomic nervous system is responsible for the involuntary control over smooth muscle, cardiac muscle, and glandular activity when commanded by the central nervous system. The autonomic nervous system has two types of nerves, they are sympathetic and parasympathetic, each of which is responsible for its own set of involuntary body functions. The response to immediate threats to the internal body environment (increasing heart rate, constricting blood vessels, and raising the blood pressure) is controlled by the sympathetic nerves. The parasympathetic nerves are responsible for returning the body to its more relaxed state (slowing the heart rate, increasing peristalsis of the intestines and increasing glandular secretions).
Name the two primary components of the central nervous system (CNS). Describe the protective membranes associated with the CNS. Differentiate between afferent and efferent nerve structure and function.
The two primary components of the central nervous system are the brain and spinal cord. Both the brain and spinal cord are surrounded by bone, connective tissue (known as meninges), and cerebrospinal fluid for protection.
The meninges are composed of three layers. The outer layer is a tough white connective tissue called dura mater. Under the dura mater is a space containing serous fluid known as the subdural space. The space just outside the dura mater is a cushion of fat and connective tissue called the epidural space. The second or middle layer of the meninges is the arachnoid membrane. This layer attaches to the inner later of the meninges. The subarachnoid space lies just below the arachnoid membrane and contains the cerebrospinal fluid that acts as a shock absorber and gives protection to the spinal cord and brain. The last layer of the meninges is tightly affixed to the surface of the brain and spinal cord and is called the pia mater.
The central nervous system communicates to the rest of the body through the use of afferent and efferent nerves. The sensory or afferent nerves transmit impulses from the body to the central nervous system. The central nervous system uses motor or efferent nerves to send impulses to the muscles and gland of the body causing responses to these commands.
Name and give a brief description of the structures of the brain. Include the functions of these structures.
The four major division of the brain include the cerebrum, cerebellum, diencephalon and the brain stem.
The cerebrum is the uppermost and largest of these four divisions. It is responsible for consciousness, memory, sensation, emotion, and voluntary movement. It contains the cerebral cortex which gives the brain its distinctive wrinkled look.
The cerebellum is attached to the brain stem and is responsible for maintaining muscle tone and coordination movement and balance.
Located between the cerebrum and midbrain is the diencephalon. It is made up of the thalamus, hypothalamus and the pineal body. The thalamus receives sensory stimuli and relays them to the cerebral cortex. The hypothalamus activates, controls, and integrates the peripheral autonomic nervous system, endocrine system processes and sensory functions of the body. The pineal body produces melatonin and is believed to be involved in regulating the body's biological clock.
The brain stem is located between the diencephalon and the spinal cord. It is made up of the midbrain, pons, and medulla oblongata. The brain stem is a pathway for impulses between the brain and spinal cord. It is responsible for the control of vital functions including respiration, blood pressure, and heart rate.
Choose 10 pathological conditions affecting the nervous system; describe each including diagnosis and treatment, if applicable.
Anencephaly- The absence of the brain and spinal cord. Life cannot continue with this defect. It can be detected in early pregnancy through the use of amniocentesis or ultrasonography.
Encephalitis- Mostly caused by a virus that enters the central nervous system it is the inflammation of the brain or spinal cord tissue. Symptoms include restlessness, seizure, headache, fever, stiff neck, altered mental state, and decreased consciousness. Outcome depends on degree of inflammation, age, and the cause. Treatment includes medication, treatment of symptoms and prevention of complications.
Petit mal seizure- Small seizures in which there is sudden temporary loss of consciousness lasting only a few seconds. The individual may experience blank facial expressions and repeated blinking during the episode. There is no loss of consciousness. The seizure may last 5-10 seconds and may go unnoticed by the individual.
Migraine headache- Recurring, pulsating, vascular headache usually developing on one side of the head. Pain slowly intensifies and may be accompanied by nausea, vomiting, irritability, fatigue, sweating and chills. Treatment for migraines includes medication to prevent occurrences and medication to reduce the symptoms.
Shingles- Also called herpes zoster is an acute viral infection. It is characterized by the inflammation of the underlying spinal or cranial nerve pathway which produces vesicular eruptions of the skin along these pathways. Symptoms may include pain before and during eruption, fever, itching, GI disturbances, headache, tiredness, and sensitivity in the skin of the surrounding area. Treatment for shingles includes administering antiviral medications, analgesics, and corticosteroids to decrease the severity of the symptoms.
Meningocele- A sac covered with skin or a thin membrane protruding from the bony defect in the vertebrae which contains meninges and cerebrospinal fluid. Spinal nerve roots may be moved out of place but still function properly. Surgery is used to close the meningocele.
Spina bifida occulta- Congenital defect of the central nervous system in which a portion of one or more vertebrae is not closed. Symptoms include hair growth over the areas, port wine nevus, and lipoma in the area. There are usually few neurological symptoms present therefore no treatment is required.
Carpal tunnel syndrome- Pinching or compressing of the median nerve within the carpal tunnel due to inflammation and swelling of the tendons usually do to repetitive use of the hand, fingers, or wrists. This pinching causes continuous or occasional pain. Treatment for carpal tunnel may include anti-inflammatory medication, splints, physical therapy or surgery.
Cerebral contusion-A small, scattered venous hemorrhage in the brain, also called a brain bruise, which occurs when the brain strikes the inner skull. Symptoms sometimes include swelling in the brain, increased intracranial pressure, combativeness and altered consciousness. Treatment may include observation, maintaining cerebral perfusion and administration of corticosteroids and osmotic diuretics.
Tension headache- Occurs from long, endured contraction of the skeletal muscles around the face, scalp, upper back, and neck. Acetaminophen or aspirin may be used to relieve a tension headache. Tranquilizers maybe taken to reduce muscle tension.