Medical Terminology: The Nervous System

1. What is The Nervous System?
The nervous system is divided into the central and peripheral nervous systems. The central nervous system (CNS) is composed of the brain and spinal cord. The peripheral nervous system (PNS) contains the spinal nerves and peripheral nerves. The basic component of the nervous system is the nerve cell or neuron.
A neuron is composed of the nucleus within the cell body, a dendrite (that receives the signal), an axon (the extension of the cell that can pass on an impulse to the next nerve cell), and the axon terminals (that can transmit the signals to other cells). The messages are sent from one nerve cell to another, crossing a synapse (or gap) between cells.
Neurotransmitters are chemicals released by the presynaptic neuron to enhance the communication between nerve cells. There are specific receptor sites for the different neurotransmitters on the postsynaptic neuron. Electrically charged ions transmit signals along the cell membranes of the nerve cells. A myelin coating on the outer surface of the nerve cells helps to speed the transmission along the nerve cells. This myelin coating also gives a white color to the nerve cells.
Some neurons are afferent neurons. They carry sensory information from the peripheral areas of the body to the CNS. These neurons do not have dendrites. Motor neurons that transmit information from the CNS to the muscles or glands are efferent neurons.
The brain is protected within the skull. The outermost layer of the brain is the cerebral cortex, made up primarily of neural cell bodies, giving a gray appearance. The cerebral cortex is divided into right and left hemispheres and into frontal, parietal, occipital, and temporal lobes. The frontal lobe has motor and premotor areas, as well as Broca’s area, which controls speech articulation, behavior, moral decision making, and emotional outbursts. The parietal area interprets sensory stimuli, pain, and touch. The temporal lobe is where language is interpreted (Wernicke’s area). It also processes auditory information, and controls memory formation and storage.
The occipital lobe houses the visual cortex. The diencephalon includes the thalamus, hypothalamus, and basal ganglia. The thalamus relays the sensory information from the body to the appropriate part of the cerebral cortex. Descending messages from the cerebral cortex are passed through the thalamus to the body.
The hypothalamus controls neuroendocrine function and maintains homeostasis, or constancy, within the body. The basal ganglia control highly skilled movements that require precision without intentional thought. The brain stem is comprised of the pons, medulla oblongata, and midbrain. The spinal column is protected within the vertebral column. Both motor and sensory fibers are found within the spinal column. Motor nerves are located along the anterior horns and sensory nerves are located along the posterior horns of the spinal column. The motor nerve fibers are more protected from traumatic injury this way.
If a patient sustains an external injury to the back that damages the spinal column, the first area to be impacted will be the sensory nerves, hopefully maintaining motor function. If enough damage has occurred, then both sensory and motor function will be lost. Peripheral nerve fibers leave the spinal column to travel to the rest of the body. Impulses travel from the CNS to muscle fibers to control voluntary motion and involuntary function of organs. Impulses are also sent from the body to the CNS for input.

2. Head Injury
The patient experiences a trauma to the head. The resulting injury may be a minor scalp laceration or a major internal injury with or without a skull fracture. There may be internal hemorrhage or cerebral edema, resulting in hypoxia and a decrease in cognitive and functional capabilities.
There are a variety of injuries that may be sustained. Open head injuries are typical of projectile wounds from gunshots or knives. Closed head injuries are typical of trauma from falls, motor vehicle accidents, sports, or fights.
Concussion involves a blow to the head in which there is a bruising-type injury as the brain is thrust against the inside of the skull. The point of injury where the brain makes impact against the skull is referred to as a coup injury.
There is also a contrecoup injury that occurs on the side opposite of the area that was impacted as the head recoils away from the point of impact and the brain is thrust against the inside of the skull at the opposite point of the head, resulting in injury there as well.
Patients with concussion may experience a transient loss of consciousness associated with bradycardia, or slowing of the heart rate; low blood pressure; slow, shallow breathing; amnesia of the injury and the events immediately following the injury; headache; and temporary loss of mental focus.
Cerebral contusion is a more serious injury than concussion. Greater damage is done to the brain, cerebral edema or hemorrhage may occur and lead to necrosis. Patients typically have longer loss of consciousness with a cerebral contusion. Hemorrhages can occur at a variety of levels: between the skull and the outer coverings (dura) of the brain, within the layers covering the brain, or within the brain tissue. The bleeding may occur acutely, at the time of injury, or hours to weeks later.
An epidural hematoma happens at the time of injury from an arterial site. The blood accumulates between the skull and the dura mater, or the outermost layer covering the brain. The site is often in the temporal area. The patient is typically awake and talking immediately after the blow to the head. Within a short time, the patient becomes unstable and then unconscious.
Emergency neurosurgery is necessary to relieve the pressure and stop the bleeding. Subdural hematoma is typically bleeding from a venous source into the area below the dura mater and above the arachnoid mater. This may occur acutely in some patients, but can also occur as a slow, chronic bleed, especially in the elderly patient. The elderly patient with a chronic bleed may have a significant amount of blood accumulate before symptoms occur because of age-related changes in the volume of brain tissue.
A subarachnoid hemorrhage causes blood to accumulate within the area below the arachnoid mater and above the pia mater. The cerebrospinal fluid is found in this area. An intracerebral bleed is an accumulation of blood within the tissues of the brain. This may be the result of a shearing force on the brain tissue from a twisting motion between the upper part of the brain (cerebrum) and the brainstem or tearing of small vessels within the brain. There will be associated edema and elevation of intracranial pressure.
Simple skull fractures are displaced and do not require specific intervention. Depressed skull fractures have bone fragments that have been broken off from the skull and pressed down toward the brain tissue. These fractures need to be corrected surgically. A basilar skull fracture has classic signs that include periorbital bruising (raccoon sign), blood behind the ear drum (Battle’s sign), and leaking of cerebrospinal fluid from the nose or ear (check for glucose content to distinguish from a runny nose).

3. Amyotrophic Lateral Sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS) is commonly called Lou Gehrig’s disease and is a progressive, degenerative disorder that involves both the upper and lower motor neurons. There is no change in mental status or sensory function with the disease, although the disease does result in paralysis of the motor system, except the eyes. As the disease progresses, families often can communicate with the patient through eye movements. Males are affected more commonly than females. The disorder may present at any age, but onset is usually between age 40. and the late sixties. There is a familial form of the disease that has been linked to an abnormality in chromosome 21.

4. Bell’s Palsy
This is an acute idiopathic facial paralysis of the seventh cranial nerve that affects one side of the face. Often caused by inflammation, the disorder is more common in diabetic patients. One side of the face is paralyzed, making the patient unable to close the eyelid, raise the eyebrow, or smile on the affected side of the face. Some patients experience pain around the ear on the affected side. The patient may have an associated change in taste.

5. Brain Abscess
Collection of pus creates a space-occupying area within the brain. Symptoms are similar to any other space-occupying lesion. The infection may be a primary site within the brain or may have traveled from nearby sites such as the ear or sinuses through bone erosion. It may also enter the brain via the systemic circulation from any infected site in the body, such as the lungs in bronchiectasis.
The organism causes a local inflammatory reaction; there is pus and liquefaction of the affected tissue. Cerebral edema of the surrounding tissue occurs. The area becomes encapsulated within 10. to 14. days from the onset of the infection. Infections are typically streptococci, staphylococci, anaerobes, or mixed organism. Immunocompromised patients may have fungal or yeast present in the abscess. Up to 20% of patients may have more than one abscess.

6. Brain Tumor
A brain tumor is a growth of abnormal cells within the brain tissue. The tumor may be a primary site that originated in the brain or a secondary site that has metastasized from a cancer site elsewhere in the body. Because the tumor is growing within the confined space of the skull, the patient eventually develops signs of increased intracranial pressure. Some cell types grow faster than others; patients with more aggressive, fast-growing cancers develop symptoms more quickly.

7. Cerebral Aneurysm
A cerebral aneurysm is a balloon-like outpouching caused by a congenital or developed weakness in a cerebral artery. Trauma, infection, or vessel wall lesions caused by atherosclerosis can all lead to the development of an aneurysm. Increased pressure within the vessel lumen may cause the aneurysm to rupture, causing significant intracranial bleeding.

8. Encephalitis
Encephalitis is an inflammation of the brain tissue, most often caused by a virus, although it can also result from bacteria, fungus, or protozoa. In the case of viral encephalitis, the patient typically had viral symptoms before the current illness. The virus enters the CNS via the bloodstream and begins to reproduce. Inflammation in the area follows, causing damage to the neurons.
Demyelination of the nerve fibers in the affected area and hemorrhage, edema, and necrosis occur, which create small cavities within the brain tissue. Herpes simplex virus 1, cytomegalovirus, echovirus, coxsackievirus, and herpes zoster can all cause encephalitis. Some forms of encephalitis can be transmitted by insects such as mosquitoes or ticks to humans, and can cause diseases such as West Nile virus, St. Louis encephalitis, or equine encephalitis.

9. Guillain-Barré Syndrome
Guillain-Barré syndrome is an acute, progressive autoimmune condition that affects the peripheral nerves. Symptoms occur as the myelin surrounding the axon on the peripheral nerves is damaged from the autoimmune effect. The disease typically follows a viral infection, surgery, other acute illness, or immunization by a couple of weeks.
Ascending Guillain-Barré exhibits muscle weakness and/or paralysis begins in the distal lower extremities and travels upward. Patient may also experience altered sensory perception in the same areas, such as the sensation of crawling, tingling, burning, or pain. The progression of symptoms may take hours or days.
Descending Guillain-Barré begins with muscles in the face, jaw, or throat and travels downward. Respiratory compromise is a concern as the paralysis reaches the level of the intercostal muscles and diaphragm. Breathing can become compromised more quickly in patients with descending disease. Level of consciousness, mental status, personality, and pupil size are not affected.

10. Huntington’s Disease (Chorea)
Huntington’s disease is a degenerative disease that presents with a gradual onset of involuntary, jerking movements (chorea) and a progressive decline in mental ability, resulting in behavioral changes and dementia. The disease is transmitted genetically, as an autosomal dominant trait located on chromosome 4. Family members of patients can have genetic testing done to identify the presence of the gene. The symptoms typically appear between the ages of 30. and 50. years.

11. Meningitis
Meningitis is the inflammation of the meningeal coverings of the brain and spinal cord, most commonly caused by bacteria or viral origin, although it can also be caused by fungus, protozoa, or toxic exposure. Bacterial meningitis is the most common and is typically a result of Streptococcus pneumoniae (pneumococcal), Neisseria meningitides (meningococcal), or Haemophilus influenzae.
The incidence of H. influenzae meningitis infections has decreased since the vaccine against H. influenzae began to be used routinely in infants in the early 1990s. Other organisms that can cause bacterial meningitis include Staphylococcus aureus, Escherichia coli, and Pseudomonas.
Organisms typically travel either through the bloodstream to the CNS or enter by direct contamination (skull fracture or extension from sinus infections). Bacterial meningitis is more common in colder months when upper respiratory tract infections are more common.
People in close living conditions, such as prisons, military barracks, or college dorms are at greater risk for outbreaks of bacterial meningitis due to the likelihood of transmission. Viral meningitis may follow other viral infections, such as mumps, herpes simplex or zoster, enterovirus, and measles.
Viral meningitis is often a self-limiting illness. Patients who are immunocompromised have an increased risk for contracting fungal meningitis. This may travel from the bloodstream to the CNS or by direct contamination. Cryptococcus neoformans may be the causative organism in these patients.

12. Multiple Sclerosis (MS)
Multiple sclerosis (MS) is an autoimmune disease that results in demyelination of the white matter of the nervous system. Nerve impulses travel along the myelin coating on the outside of the nerve cells. With the disruption in the myelin on the outside of the nerve cells, the transmission of information from cell to cell within the nervous system is altered.
The patient’s sensations, movements, or mental function may be affected. A patient with relapsing-remitting disease will have episodes of exacerbation when symptoms occur and then months or years of symptom-free episodes.
A portion of these patients progress to enter a disease state that has a steady pattern of deterioration without relation to periodic exacerbations; this is referred to as secondary progressive disease. Other patients have primary progressive disease and develop steady deterioration from the onset of the disease.

13. Myasthenia Gravis
Myasthenia gravis is a disorder of the PNS involving antibodies that have been produced by the body; they bind to receptor sites that normally bind acetylcholine. This prevents the acetylcholine from binding to the receptor sites on the skeletal muscle, causing abnormal muscle contraction in the affected area.
The areas of the body most commonly affected by the autoimmune disease include the muscles in the eyes, face, lips, tongue, throat, and neck, resulting in weakness and fatigue of these areas. The disease does not seem to be hereditary, but does have a family tendency toward autoimmune disorders.
The majority of patients have a hyperplasia (excessive growth of normal cells) of the thymus gland. Myasthenia gravis is more likely to develop in young adults and is more common in women.

14. Parkinson’s Disease
There is a gradual degeneration of the midbrain area known as the substantia nigra. The neurons use the neuro-transmitter dopamine to send their signals from cell to cell. The loss of neurons within the substantia nigra continues and results in diminished voluntary fine motor skills owing to dopamine loss. There is also development of sympathetic noradrenergic lesions, causing norepinephrine loss within the sympathetic nervous system.
There is excess effect of the excitatory neurotransmitter acetylcholine on the neurons; this causes increased muscle tone, leading to rigidity and tremors. There seems to be a genetic tendency toward development of Parkinson’s disease. Environmental factors such as exposure to airborne contaminants, occupational chemicals, toxins, or a virus have been implicated in the development of the disease. The typical age of onset is after the fifth decade of life.

15. Spinal Cord Injury
Injury to the spinal cord results in compression, twisting, severing, or pulling on the spinal cord. The damage to the cord may involve the entire thickness of the cord (complete), or only a partial area of the spinal cord (incomplete). The most common cause of spinal cord injury is trauma.
Any level of the spinal cord may have been affected by the injury. Loss of sensation, motor control, or reflexes may occur below the level of injury or within one to two vertebrae or spinal nerves above the level of injury. The loss may be unilateral or bilateral. Damage to the vertebrae may have occurred at the same time as the spinal cord injury.
Swelling because of the initial trauma may make the injury seem more severe than it actually is. When the initial swelling resolves, the actual degree of permanent injury can be more accurately assessed.

16. Stroke
A stroke is also known as a cerebrovascular accident (CVA) or a brain attack. Blood supply is interrupted to part of the brain, causing brain cells to die. This results in the patient losing brain function in the affected area.
Interruption is usually caused by an obstruction of arterial blood flow (ischemic stroke), such as formation of a blood clot, but can also be caused by a leaking or ruptured blood vessel (hemorrhagic stroke). A blood clot may develop from a piece of unstable plaque lining a vessel wall that breaks free, or an embolus that travels from elsewhere in the body and lodges within the vessel.
The bleeding may occur as a result of trauma or spontaneously, as in the setting of uncontrolled hypertension. Ischemia occurs when insufficient blood is getting to the brain tissue. This leads to lack of available oxygen (hypoxia) hypoxia glucose (hypoglycemia) for the brain. When these nutrients are not available for a sustained period, the brain cells die, causing an area of infarction.
Permanent deficits result from infarction. There is increased risk for stroke in patients with a history of hyper-tension, diabetes mellitus, high cholesterol, atrial fibrillation, obesity, smoking, or oral contraceptive use. Patients may also experience a transient ischemic attack (TIA) in which the symptoms result from a temporary problem with blood flow to a specific area of the brain. The symptoms have a duration between a few minutes and 24. hours.

17. Seizure Disorder
This is a disorder that involves a sudden episode of abnormal, uncontrolled discharge of the electrical activity of the neurons within the brain. The patient may experience a variety of symptoms depending on the type of seizure and the cause.
Seizures may be a symptom of another condition—such as a tumor or stroke that has increased the intracranial pressure, a metabolic disorder, withdrawal from alcohol or drugs—or may result from a chronic seizure disorder such as epilepsy.
Before the seizure, the patient may experience an aura, a sensory alteration involving sight, sound, or smell. After the seizure, the patient enters a postictal stage in which there may be confusion and the patient is often fatigued. The patient may not recall any of the seizure or the time immediately surrounding the seizure.

18. Computed Tomography (CT) With or Without Contrast
The practitioner may do an initial test without contrast for first images and then give contrast and repeat images to compare. This is done to check for bleeding, tumor, abscess, infarction, and hydrocephalus.

19. Computed Tomography Angiography (CTA)
Computed tomography angiography (CTA) creates a three-dimensional reconstruction of the vasculature within the area imaged.

20. Cerebral Angiography
Contrast material is injected to visualize the cerebral circulation, carotid, and vertebral arteries. This test is done to identify aneurysms, arteriovenous malformations, traumatic injuries, strictures, occlusions, and tumors. The head is immobilized during the test.
Wire is inserted via the femoral arterial site and passed to the carotid or vertebral vessel under fluoroscopic guidance. Contrast dye is injected so that three-dimensional images can be obtained. After the test, the practitioner needs to monitor vital signs and perform neurologic checks and neurovascular checks of the extremity (capillary refill, peripheral pulses, skin color, and temperature). The practitioner must also check for bleeding at the site.

21. Electroencephalography (EEG)
The EEG records the electrical activity from the cerebral hemispheres of the brain and creates a graphic recording. It determines general brain activity as well as the site of origin of seizure activity. It is also used to diagnose sleep disorders and determine brain death.

22. Lumbar Puncture
A spinal needle is inserted into the subarachnoid space at levels of L3–L4. or L4–L5. with the patient lying on the side with knees drawn up to his or her chest. This test is performed under local anesthesia. It is done to obtain pressure readings, obtain cerebrospinal fluid for analysis, inject contrast material or air for diagnostictests, inject medications, or reduce increased intracranial pressure. The patient must lie flat for several hours after the procedure to reduce the risk of spinal headache caused by leakage of spinal fluid. The practitioner should encourage oral fluid intake.

23. Magnetic Resonance Imaging (MRI) With Gadolinium
The MRI is done to detect differences in tissue integrity, tumors, and disk disease. Because of the use of a magnetic field to create images, an MRI is not for patients with implanted hardware (e.g., pacemakers, etc.) or pregnant women.

24. Single Photon Emission Computed Tomography (SPECT)
Single photon emission computed tomography (SPECT) involves an intravenous injection of a radiopharmaceutical to enhance the image. It is done to detect cerebral blood flow, stroke, dementia, amnesia, neoplasm, head trauma, seizures, persistent vegetative state, brain death, and psychiatric disorders. This test is not for pregnant women.

Basic Questions
Nervous System

1. What is a concussion?
A concussion involves a blow to the head in which there is a bruising-type injury as the brain is thrust against the inside of skull. The point of injury where the brain makes impact against the skull is referred to as a coup injury.

2. What is amyotrophic lateral sclerosis (ALS)?
ALS is commonly called Lou Gehrig’s disease and is a progressive, degenerative disorder that involves both the upper and lower motor neurons.

3. How does ALS affect the sensory function of the patient?
There is no change in mental status or sensory function with the disease. The disease does result in paralysis of the motor system, except the eyes.

4. What is Bell’s palsy?
This is an acute idiopathic facial paralysis of the seventh cranial nerve that affects one side of the face.

5. What is a brain abscess?
A brain abscess is a collection of pus that creates a space-occupying area within the brain.

6. What is a cerebral aneurysm?
A cerebral aneurysm is a balloon-like outpouching caused by a congenital or developed weakness in a cerebral artery.

7. What might cause a cerebral aneurysm?
Trauma, infection, or vessel wall lesions caused by atherosclerosis can all lead to the development of an aneurysm. Increased pressure within the vessel lumen may cause the aneurysm to rupture, causing significant intracranial bleeding.

8. What is encephalitis?
Encephalitis is inflammation of the brain tissue, most often caused by a virus, although it can also be caused by bacteria, fungus, or protozoa.

9. What is viral encephalitis?
In the case of viral encephalitis, the patient typically will have had viral symptoms before the current illness. The virus enters the CNS via the bloodstream and begins to reproduce. Inflammation in the area follows, causing damage to the neurons.

10. What is Guillain-Barré syndrome?
This is an acute, progressive autoimmune condition that affects the peripheral nerves. Symptoms occur as the myelin surrounding the axon on the peripheral nerves is damaged from the autoimmune effect. The disease typically follows a viral infection, surgery, other acute illness or immunization by a couple of weeks.

11. What is ascending Guillain-Barré?
Ascending Guillain-Barré exhibits muscle weakness and/or paralysis that begins in the distal lower extremities and travels upward.

2. What is descending Guillain-Barré?
Descending Guillain-Barré begins with muscles in the face, jaw, or throat and travels downward.

3. What is Huntington’s disease?
This is a degenerative disease that presents with a gradual onset of involuntary, jerking movements (chorea) and a progressive decline in mental ability, resulting in behavioral changes and dementia.

4. What is meningitis?
Meningitis is the inflammation of the meningeal coverings of the brain and spinal cord, most commonly caused by bacteria or virus, although it can also be caused by fungus, protozoa, or toxic exposure.

5. What is multiple sclerosis?
This is an autoimmune disease that results in demyelination of the white matter of the nervous system. Nerve impulses travel along the myelin coating on the outside of the nerve cells. With the disruption in the myelin on the outside of the nerve cells, the transmission of information from cell to cell within the nervous system is altered.

6. What is myasthenia gravis?
This is a disorder of the PNS involving antibodies that have been produced by the body; they bind to receptor sites that normally bind acetylcholine. This prevents the acetylcholine from binding to the receptor sites on the skeletal muscle, causing abnormal muscle contraction in the affected area.

7. What is Parkinson’s disease?
There is a gradual degeneration of the midbrain area known as the substantia nigra. The neurons use the neurotransmitter dopamine to send their signals from cell to cell. The loss of neurons within the substantia nigra continues and results in diminished voluntary fine motor skills due to dopamine loss. There is also development of sympathetic noradrenergic lesions, causing norepinephrine loss within the sympathetic nervous system.

8. When is permanent injury assessed in a spinal cord injury?
Swelling caused by the initial trauma may make the injury seem more severe than it actually is. When the initial swelling resolves, the actual degree of permanent injury can be more accurately assessed.

9. What is a stroke?
A stroke is also known as a cerebrovascular accident (CVA) or brain attack. Blood supply is interrupted to part of the brain, causing brain cells to die. This results in the patient losing brain function in the affected area.

20. What is a seizure disorder?
This is a disorder that involves a sudden episode of abnormal, uncontrolled discharge of the electrical activity of the neurons within the brain. The patient may experience a variety of symptoms depending on the type of seizure and the cause.

21. What causes a seizure?
Seizures may be a symptom of another condition—such as a tumor or stroke that has increased the intracranial pressure, a metabolic disorder, withdrawal from alcohol or drugs—or may be caused by a chronic seizure disorder such as epilepsy.

22. What is the purpose of the SPECT?
SPECT involves an intravenous injection of a radiopharmaceutical to enhance the image. It is done to detect cerebral blood flow, stroke, dementia, amnesia, neoplasm, head trauma, seizures, persistent vegetative state, brain death, and psychiatric disorders

23. What is the purpose of an MRI with gadolinium?
This test is done to detect differences in tissue integrity, tumors, and disc disease.

24. Why is an electronystagmogram administered?
An electronystagmogram assesses the underlying cause of loss of balance and vertigo.

25. What is a lumbar puncture?
A spinal needle is inserted into the subarachnoid space at the levels of L3–L4. or L4–L5. with the patient lying on his or her side with knees drawn up to the chest. This test is performed under local anesthesia. It is done to obtain pressure readings, obtain cerebrospinal fluid for analysis, inject contrast material or air for diagnostic tests, inject medications, or reduce increased intracranial pressure.