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Glossary

 

A-B-C-D-E-F-G-H-I-J-K-L-M-O-P-Q-R-S-T-U-V-W-X-Y-Z

A

Ablation:

Surgical destruction or removal of tissue, an organ, or a precise region of a particular structure. Ablation may involve surgical cutting (excision); chemical destruction, such as injection of phenol; or the use of high-frequency electrical current or radio waves. For example, pallidotomy is a procedure used in the treatment of Parkinson’s disease or certain other movement disorders. The procedure involves surgical ablation of part of the internal portion of the globus pallidus (GPi)–i.e., a brain region involved in regulating movement–in an attempt to “rebalance” movement and posture control. Once a wire probe is inserted into and precisely positioned within the GPi, it heats and destroys adjacent tissue through the emission of radio waves.

A device used to measure the rate of change in velocity over a specific period of time. Measures the rate or “speed” of the tremor cycle.

Accelerometer: 

Acetylcholine (ACh):

A neurotransmitter present at junctions of nerve and muscle cells and various sites of the central nervous system, including the cerebral cortex and the basal ganglia. Primary functions of acetylcholine include regulating the delivery of messages from neurons to skeletal muscle fibers, smooth (involuntary) muscle fibers, and effector organs as well as between nerve cells in the brain and spinal cord. Acetylcholine also functions as a vasodilator and triggers certain actions within the parasympathetic nervous system, such as lowering blood pressure and slowing heart and breathing rates.

Action tremor:

a tremor that occurs during the performance of voluntary movements. Such tremors include postural, isometric, kinetic, and intention tremors.

Activities of daily living (ADL):

functions that are typically performed as part of a person’s daily routine, such as dressing, bathing, eating, toileting, leisure activities, socialization, and other functions of daily living.

Acute:

Referring to symptoms of abrupt onset, often of marked severity or intensity.

Adenosine triphosphate (ATP):

ATP is the molecule that provides the energy in the cells of all living things.

Agonist:

A muscle whose contraction executes an intended movement.

Akathisia:

a neurologic condition of motor restlessness, manifested by a sensation of muscular quivering, an urge to constantly move about, and an inability to sit still.

Akinesia:

absence of movement or loss of the ability to move such as temporary or prolonged paralysis or “freezing in place.”

Alpha 2-adrenergic agonist:

A drug that reduces the activity of the neurotransmitter norepinephrine by stimulating certain receptors within the central nervous system (central presynaptic alpha 2-adrenergic receptors). The release of norepinephrine triggers action within the sympathetic nervous system. This part of the nervous system regulates certain involuntary activities during stress, such as increasing the heart rate, deepening breathing, and raising blood pressure. Norepinephrine also plays a role in regulating mood and emotion. The administration of alpha 2-adrenergic agonists may result in a reduced heart rate and lowered blood pressure and have depressive or sedative effects.

Alzheimer’s disease: 

A progressive degenerative disease of the brain of unknown cause. Alzheimer’s disease is characterized by widespread loss of nerve cells, particularly in the outer region of the brain (cerebral cortex), with distinctive neurodegenerative changes (including “senile plaques” and “neurofibrillary tangles”) and reduced activity of acetylcholine and other neurotransmitters of the brain. The disease is the most common cause of dementia or progressive deterioration of thought processing and acquired intellectual abilities. Associated symptoms include initial forgetfulness with increasingly severe memory impairment; disorientation and confusion; loss of the ability to recognize familiar people or objects through sensory stimuli (agnosia); and speech disturbances. The disorder may also be characterized by restlessness and agitation; an increasingly impaired ability to conduct purposeful movements; personality disintegration; and symptoms of psychosis, such as the perception of sights, sounds, or other sensations in the absence of external stimuli (hallucinations) and false beliefs of persecution despite evidence to the contrary (paranoid delusions).

Ambulant (ambulatory):

Able to walk; may be used to describe patients who do not require a wheelchair or are not confined to bed.

Ambulation:

The act of walking.

Amino acid:

The chemical “building blocks” or basic structural units of proteins. All proteins in the body are formed from a “pool” of 20 different amino acids. Some are essential amino acids and must be supplied by the diet. The remainder are classified as “nonessential.” These can be made by the body and need not come from the diet.

Amniocentesis:

A screening or diagnostic procedure during which a sample of amniotic fluid surrounding the developing fetus is withdrawn by means of an ultrasound-guided needle. The amniotic sac is a fluid-filled membrane that surrounds and protects the developing fetus within the uterus. Amniotic fluid contains cells that may be used for DNA analysis, chromosomal testing, and enzyme studies. Such testing may detect certain genetic disorders, metabolic diseases, chromosomal abnormalities, or developmental defects. This procedure is typically performed between the 14th and 18th week of pregnancy.

Amino acid:

The chemical “building blocks” or basic structural units of proteins. All proteins in the body are formed from a “pool” of 20 different amino acids. Some are essential amino acids and must be supplied by the diet. The remainder are classified as “nonessential.” These can be made by the body and need not come from the diet.

Amplitude:

the “size” or “height” of a tremor; the extend or breadth of a tremor’s range.

Analog (Analogue):

 (1) A chemical compound or agent that is similar to another in structure yet differs concerning a particular element; it may have a similar or different mode of action. (2) A tissue, organ, or other bodily structure that has the same function or organization as another yet has a different evolutionary origin.

Antagonist:

(1) A drug that blocks a receptor, preventing stimulation. (2) A muscle whose contraction opposes an intended movement.

Antibodies: 

Specialized proteins that function as an essential part of the immune system. Antibodies are produced by certain white blood cells (B cells) in response to the presence of specific, usually foreign proteins (i.e., antigens), helping the body to neutralize and destroy the invading microorganism, foreign tissue cell, or other antigen in question.

Anticholinergics: 

Drugs that block the action of acetylcholine, a neurotransmitter whose effects oppose dopamine. By blocking acetylcholine’s action, these drugs increase dopamine’s ability to control movement.

Anticholinesterase:

An agent that inhibits action of acetylcholinesterase (AChE). AChE is an enzyme that inactivates acetylcholine, a neurotransmitter at the junctions of nerve and muscle cells (neuromuscular junctions) that regulates the delivery of messages from neurons to muscle fibers. By inhibiting the activity of AChE, such medications allow high levels of acetylcholine to accumulate, potentially enabling repeated stimulation of nerves at neuromuscular junctions.

Anticonvulsant medication: 

 An agent that prevents or arrests convulsive seizures.

Antiemetic:

A drug that reduces nausea and vomiting. 

Antigen:

Any substance that may trigger a particular immune response, such as the production of antibodies. Antigens may be foreign proteins of invading microorganisms (e.g., viruses, bacteria), toxins, or foreign tissue cells (e.g., used in transplantation).

Antihistamine: 

a drug that counters the effects of histamine, a compound that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion and that is released during allergic reactions.

Antioxidants:

Agents that inhibit or neutralize potentially harmful compounds known as free radicals. Free radicals are produced during metabolic activity. High levels of free radicals may eventually lead to impaired functioning and destruction of neurons and other bodily cells. Certain antioxidants are thought to neutralize free radicals before cellular damage occurs.

Aorta:

The main artery of the body. The aorta receives oxygen-rich (oxygenated) blood from the lower left chamber (ventricle) of the heart for distribution to most arteries of the body, with the exception of the pulmonary artery, which distributes oxygen-deficient (deoxygenated) blood from the lower right ventricle to the lungs.

Apoptosis:

Cell death due to a programmed pattern of gene expression; a form of cell death in which certain enzymes activate to degrade DNA within the nucleus, resulting in cellular degeneration and loss.

Apraxia:

Loss of the ability to sequence, coordinate, and execute certain purposeful movements and gestures in the absence of motor weakness, paralysis, or sensory impairments. Apraxia is thought to result from damage to the cerebral cortex, such as due to stroke, brain tumors, head injury, or infection. It may also occur as a result of impaired development of the cortex as in certain neurodevelopmental disorders, including Rett syndrome. Apraxia may affect almost any voluntary movements, including those required for proper eye gaze, walking, speaking, or writing.

Archimedes spirals:

a relatively simple test used to evaluate tremor severity. During this test, the patient is asked to draw increasingly wider circles on a piece of paper.

Asterixis:

involuntary, jerking or flapping movements, especially of the hands. Extending the patient’s arm with the wrist bend in a backward position may induce this form of tremor, which may be associated with advanced liver disease.

Astrocyte:

A type of glial cell. Glial cells are the connective tissue cells of the central nervous system (CNS), serving as the supportive structure that holds together and protects neurons. Astrocytes are relatively large glial cells with thread-like projections that connect with neurons and small blood vessels (capillaries). These projections form part of the so-called “blood-brain barrier.” This barrier slows or prevents the passage of unwanted substances, such as harmful chemicals, infectious agents, etc., from the bloodstream into the brain. Astrocytes also accumulate in areas where nerves have been damaged (astrocytosis), sealing off these areas. An excess of astrocytes in damaged areas of the CNS is known as gliosis.

Asterixis:

involuntary, jerking or flapping movements, especially of the hands. Extending the patient’s arm with the wrist bend in a backward position may induce this form of tremor, which may be associated with advanced liver disease.

Astrocyte:

A type of glial cell. Glial cells are the connective tissue cells of the central nervous system (CNS), serving as the supportive structure that holds together and protects neurons. Astrocytes are relatively large glial cells with thread-like projections that connect with neurons and small blood vessels (capillaries). These projections form part of the so-called “blood-brain barrier.” This barrier slows or prevents the passage of unwanted substances, such as harmful chemicals, infectious agents, etc., from the bloodstream into the brain. Astrocytes also accumulate in areas where nerves have been damaged (astrocytosis), sealing off these areas. An excess of astrocytes in damaged areas of the CNS is known as gliosis.

Ataxia: 

A condition characterized by an impaired ability to coordinate voluntary movements. Ataxia may result from damage to the cerebellum, cerebellar pathways, or the spinal cord due to various underlying disorders, conditions, or other factors. These may include infection, head injury, stroke, brain tumors, neurodegenerative disorders, alcohol or drug intoxication, or certain hereditary diseases (e.g., Friedreich’s ataxia, ataxia-telangiectasia). Associated symptoms may vary, depending upon the site of damage within the central nervous system. However, the condition is often characterized by incoordination, postural imbalance, and a lurching, unsteady manner of walking (gait). Additional findings may include slurred speech (dysarthria); rapid, involuntary, rhythmic eye movements (nystagmus); and/or other abnormalities.

Ataxia-telangiectasia (AT): 

A hereditary, progressive disorder that typically becomes apparent in early childhood and is characterized by increasing neurodegenerative changes of the cerebellum, a brain region involved in producing coordinated voluntary movements, sustaining balance, and maintaining proper posture. Associated symptoms typically include delayed motor development; an unsteady, awkward manner of walking; drooling; impaired articulation of speech (dysarthria); dependence on thrusts of the head to achieve proper focusing of the eyes; and involuntary, rapid, jerky eye movements (nystagmus). Affected children may also develop involuntary, “shock-like” muscle spasms (myoclonus); sustained muscle contractions that result in repetitive twisting motions or unusual postures or positions (dystonia); or irregular, jerky, relatively rapid involuntary movements (chorea). AT is also typically associated with permanent widening (dilation) of groups of blood vessels (telangiectasias), particularly in sun-exposed skin regions of the face and the transparent membranes covering the whites of the eyes. In addition, AT is characterized by deficient functioning of the immune system (immunodeficiency), leading to recurrent respiratory and skin infections and an increased risk of certain malignancies (e.g., certain leukemias or lymphomas). The disorder, which is transmitted as an autosomal recessive trait, is thought to result from defective repair of DNA.

Athetosis:

 Involuntary, relatively slow, writhing movements that essentially flow into one another. Athetosis is often associated with chorea, a related condition characterized by involuntary, rapid, irregular, jerky movements. Although athetosis may be most prominent in the face, neck, tongue, and hands, the condition may affect any muscle group. Athetosis may occur in association with certain neurodegenerative diseases, such as Huntington’s or Wilson’s disease, or cerebral palsy (CP). It may also result from infections affecting the brain or the use of particular medications.

Atrophy:

Wasting away or loss of a cell, tissue, or organ due to disease, malnutrition, insufficient blood supply, or other causes, such as loss of skeletal muscle mass due to peripheral nerve damage.

Attention-deficit/hyperactivity disorder:

a diagnosis applied to children and adults who consistently display certain characteristic behaviors over a period of time. The most common behaviors fall into three categories: inattention, hyperactivity, and impulsivity.

Atypical:

Irregular; not standard or characteristic; not conforming to type.

Atypical neuroleptics: 

Antipsychotic drugs that cause less parkinsonian side effects than older treatments for psychosis.

Auditory:

Pertaining to the sense of hearing or the organs involved in hearing.

Augmentation: 

A phenomenon that may occur as a result of the use of certain medications (particularly levodopa). Augmentation is characterized by the emergence of worsening symptoms earlier in the day (e.g., early evening, afternoon, or morning). Many people who take levodopa and some who take other dopamingeric agents develop augmentation, especially those who have severe symptoms or are taking high doses of the drug.

Autoimmune: 

Referring to an immune response against one’s own tissues or organs. Autoimmune diseases result from abnormal immune reactions in which the actions of certain white blood cells (T cells) are directed against “self proteins” (autoantigens) or normal tissue components (i.e., cell-mediated immune response)–or in which specialized proteins (antibodies) produced in response to specific, usually foreign proteins (antigens) improperly act against certain of the body’s own cells (i.e., antibody-mediated immune response). In certain disorders, the autoimmune process may be primarily directed against one organ, such as the thyroid gland in Hashimoto’s thyroiditis or the pancreas in insulin-dependent diabetes mellitus, or may involve multiple organs and bodily systems, such as associated with systemic lupus erythematosus (lupus or SLE).

Autonomic:

The autonomic nervous system controls most of the involuntary reflexive activities of the human body. The system is constantly working to regulate the glands and many of the muscles of the body through the release or uptake of the neurotransmitters acetylcholine and norepinephrine. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body’s “fight or flight” response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body’s functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body’s immune system properly functioning.

Autonomic dysregulation:

This term infers the malfunction of the autonomic nervous system, the portion of the nervous system that conveys impulses between the blood vessels, heart, and all the organs in the chest, abdomen, and pelvis and the brain (mainly the medulla, pons and hypothalamus).

A

Ablation:

Surgical destruction or removal of tissue, an organ, or a precise region of a particular structure. Ablation may involve surgical cutting (excision); chemical destruction, such as injection of phenol; or the use of high-frequency electrical current or radio waves. For example, pallidotomy is a procedure used in the treatment of Parkinson’s disease or certain other movement disorders. The procedure involves surgical ablation of part of the internal portion of the globus pallidus (GPi)–i.e., a brain region involved in regulating movement–in an attempt to “rebalance” movement and posture control. Once a wire probe is inserted into and precisely positioned within the GPi, it heats and destroys adjacent tissue through the emission of radio waves.

A device used to measure the rate of change in velocity over a specific period of time. Measures the rate or “speed” of the tremor cycle.

Accelerometer: 

Acetylcholine (ACh):

A neurotransmitter present at junctions of nerve and muscle cells and various sites of the central nervous system, including the cerebral cortex and the basal ganglia. Primary functions of acetylcholine include regulating the delivery of messages from neurons to skeletal muscle fibers, smooth (involuntary) muscle fibers, and effector organs as well as between nerve cells in the brain and spinal cord. Acetylcholine also functions as a vasodilator and triggers certain actions within the parasympathetic nervous system, such as lowering blood pressure and slowing heart and breathing rates.

Action tremor:

a tremor that occurs during the performance of voluntary movements. Such tremors include postural, isometric, kinetic, and intention tremors.

Activities of daily living (ADL):

functions that are typically performed as part of a person’s daily routine, such as dressing, bathing, eating, toileting, leisure activities, socialization, and other functions of daily living.

Acute:

Referring to symptoms of abrupt onset, often of marked severity or intensity.

Adenosine triphosphate (ATP):

ATP is the molecule that provides the energy in the cells of all living things.

Agonist:

A muscle whose contraction executes an intended movement.

Akathisia:

a neurologic condition of motor restlessness, manifested by a sensation of muscular quivering, an urge to constantly move about, and an inability to sit still.

Akinesia:

absence of movement or loss of the ability to move such as temporary or prolonged paralysis or “freezing in place.”

Alpha 2-adrenergic agonist:

A drug that reduces the activity of the neurotransmitter norepinephrine by stimulating certain receptors within the central nervous system (central presynaptic alpha 2-adrenergic receptors). The release of norepinephrine triggers action within the sympathetic nervous system. This part of the nervous system regulates certain involuntary activities during stress, such as increasing the heart rate, deepening breathing, and raising blood pressure. Norepinephrine also plays a role in regulating mood and emotion. The administration of alpha 2-adrenergic agonists may result in a reduced heart rate and lowered blood pressure and have depressive or sedative effects.

Alzheimer’s disease: 

A progressive degenerative disease of the brain of unknown cause. Alzheimer’s disease is characterized by widespread loss of nerve cells, particularly in the outer region of the brain (cerebral cortex), with distinctive neurodegenerative changes (including “senile plaques” and “neurofibrillary tangles”) and reduced activity of acetylcholine and other neurotransmitters of the brain. The disease is the most common cause of dementia or progressive deterioration of thought processing and acquired intellectual abilities. Associated symptoms include initial forgetfulness with increasingly severe memory impairment; disorientation and confusion; loss of the ability to recognize familiar people or objects through sensory stimuli (agnosia); and speech disturbances. The disorder may also be characterized by restlessness and agitation; an increasingly impaired ability to conduct purposeful movements; personality disintegration; and symptoms of psychosis, such as the perception of sights, sounds, or other sensations in the absence of external stimuli (hallucinations) and false beliefs of persecution despite evidence to the contrary (paranoid delusions).

Ambulant (ambulatory):

Able to walk; may be used to describe patients who do not require a wheelchair or are not confined to bed.

Ambulation:

The act of walking.

Amino acid:

The chemical “building blocks” or basic structural units of proteins. All proteins in the body are formed from a “pool” of 20 different amino acids. Some are essential amino acids and must be supplied by the diet. The remainder are classified as “nonessential.” These can be made by the body and need not come from the diet.

Amniocentesis:

A screening or diagnostic procedure during which a sample of amniotic fluid surrounding the developing fetus is withdrawn by means of an ultrasound-guided needle. The amniotic sac is a fluid-filled membrane that surrounds and protects the developing fetus within the uterus. Amniotic fluid contains cells that may be used for DNA analysis, chromosomal testing, and enzyme studies. Such testing may detect certain genetic disorders, metabolic diseases, chromosomal abnormalities, or developmental defects. This procedure is typically performed between the 14th and 18th week of pregnancy.

Amino acid:

The chemical “building blocks” or basic structural units of proteins. All proteins in the body are formed from a “pool” of 20 different amino acids. Some are essential amino acids and must be supplied by the diet. The remainder are classified as “nonessential.” These can be made by the body and need not come from the diet.

Amplitude:

the “size” or “height” of a tremor; the extend or breadth of a tremor’s range.

Analog (Analogue):

 (1) A chemical compound or agent that is similar to another in structure yet differs concerning a particular element; it may have a similar or different mode of action. (2) A tissue, organ, or other bodily structure that has the same function or organization as another yet has a different evolutionary origin.

Antagonist:

(1) A drug that blocks a receptor, preventing stimulation. (2) A muscle whose contraction opposes an intended movement.

Antibodies: 

Specialized proteins that function as an essential part of the immune system. Antibodies are produced by certain white blood cells (B cells) in response to the presence of specific, usually foreign proteins (i.e., antigens), helping the body to neutralize and destroy the invading microorganism, foreign tissue cell, or other antigen in question.

Anticholinergics: 

Drugs that block the action of acetylcholine, a neurotransmitter whose effects oppose dopamine. By blocking acetylcholine’s action, these drugs increase dopamine’s ability to control movement.

Anticholinesterase:

An agent that inhibits action of acetylcholinesterase (AChE). AChE is an enzyme that inactivates acetylcholine, a neurotransmitter at the junctions of nerve and muscle cells (neuromuscular junctions) that regulates the delivery of messages from neurons to muscle fibers. By inhibiting the activity of AChE, such medications allow high levels of acetylcholine to accumulate, potentially enabling repeated stimulation of nerves at neuromuscular junctions.

Anticonvulsant medication: 

 An agent that prevents or arrests convulsive seizures.

Antiemetic:

A drug that reduces nausea and vomiting. 

Antigen:

Any substance that may trigger a particular immune response, such as the production of antibodies. Antigens may be foreign proteins of invading microorganisms (e.g., viruses, bacteria), toxins, or foreign tissue cells (e.g., used in transplantation).

Antihistamine: 

a drug that counters the effects of histamine, a compound that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion and that is released during allergic reactions.

Antioxidants:

Agents that inhibit or neutralize potentially harmful compounds known as free radicals. Free radicals are produced during metabolic activity. High levels of free radicals may eventually lead to impaired functioning and destruction of neurons and other bodily cells. Certain antioxidants are thought to neutralize free radicals before cellular damage occurs.

Aorta:

The main artery of the body. The aorta receives oxygen-rich (oxygenated) blood from the lower left chamber (ventricle) of the heart for distribution to most arteries of the body, with the exception of the pulmonary artery, which distributes oxygen-deficient (deoxygenated) blood from the lower right ventricle to the lungs.

Apoptosis:

Cell death due to a programmed pattern of gene expression; a form of cell death in which certain enzymes activate to degrade DNA within the nucleus, resulting in cellular degeneration and loss.

Apraxia:

Loss of the ability to sequence, coordinate, and execute certain purposeful movements and gestures in the absence of motor weakness, paralysis, or sensory impairments. Apraxia is thought to result from damage to the cerebral cortex, such as due to stroke, brain tumors, head injury, or infection. It may also occur as a result of impaired development of the cortex as in certain neurodevelopmental disorders, including Rett syndrome. Apraxia may affect almost any voluntary movements, including those required for proper eye gaze, walking, speaking, or writing.

Archimedes spirals:

a relatively simple test used to evaluate tremor severity. During this test, the patient is asked to draw increasingly wider circles on a piece of paper.

Asterixis:

involuntary, jerking or flapping movements, especially of the hands. Extending the patient’s arm with the wrist bend in a backward position may induce this form of tremor, which may be associated with advanced liver disease.

Astrocyte:

A type of glial cell. Glial cells are the connective tissue cells of the central nervous system (CNS), serving as the supportive structure that holds together and protects neurons. Astrocytes are relatively large glial cells with thread-like projections that connect with neurons and small blood vessels (capillaries). These projections form part of the so-called “blood-brain barrier.” This barrier slows or prevents the passage of unwanted substances, such as harmful chemicals, infectious agents, etc., from the bloodstream into the brain. Astrocytes also accumulate in areas where nerves have been damaged (astrocytosis), sealing off these areas. An excess of astrocytes in damaged areas of the CNS is known as gliosis.

Asterixis:

involuntary, jerking or flapping movements, especially of the hands. Extending the patient’s arm with the wrist bend in a backward position may induce this form of tremor, which may be associated with advanced liver disease.

Astrocyte:

A type of glial cell. Glial cells are the connective tissue cells of the central nervous system (CNS), serving as the supportive structure that holds together and protects neurons. Astrocytes are relatively large glial cells with thread-like projections that connect with neurons and small blood vessels (capillaries). These projections form part of the so-called “blood-brain barrier.” This barrier slows or prevents the passage of unwanted substances, such as harmful chemicals, infectious agents, etc., from the bloodstream into the brain. Astrocytes also accumulate in areas where nerves have been damaged (astrocytosis), sealing off these areas. An excess of astrocytes in damaged areas of the CNS is known as gliosis.

Ataxia: 

A condition characterized by an impaired ability to coordinate voluntary movements. Ataxia may result from damage to the cerebellum, cerebellar pathways, or the spinal cord due to various underlying disorders, conditions, or other factors. These may include infection, head injury, stroke, brain tumors, neurodegenerative disorders, alcohol or drug intoxication, or certain hereditary diseases (e.g., Friedreich’s ataxia, ataxia-telangiectasia). Associated symptoms may vary, depending upon the site of damage within the central nervous system. However, the condition is often characterized by incoordination, postural imbalance, and a lurching, unsteady manner of walking (gait). Additional findings may include slurred speech (dysarthria); rapid, involuntary, rhythmic eye movements (nystagmus); and/or other abnormalities.

Ataxia-telangiectasia (AT): 

A hereditary, progressive disorder that typically becomes apparent in early childhood and is characterized by increasing neurodegenerative changes of the cerebellum, a brain region involved in producing coordinated voluntary movements, sustaining balance, and maintaining proper posture. Associated symptoms typically include delayed motor development; an unsteady, awkward manner of walking; drooling; impaired articulation of speech (dysarthria); dependence on thrusts of the head to achieve proper focusing of the eyes; and involuntary, rapid, jerky eye movements (nystagmus). Affected children may also develop involuntary, “shock-like” muscle spasms (myoclonus); sustained muscle contractions that result in repetitive twisting motions or unusual postures or positions (dystonia); or irregular, jerky, relatively rapid involuntary movements (chorea). AT is also typically associated with permanent widening (dilation) of groups of blood vessels (telangiectasias), particularly in sun-exposed skin regions of the face and the transparent membranes covering the whites of the eyes. In addition, AT is characterized by deficient functioning of the immune system (immunodeficiency), leading to recurrent respiratory and skin infections and an increased risk of certain malignancies (e.g., certain leukemias or lymphomas). The disorder, which is transmitted as an autosomal recessive trait, is thought to result from defective repair of DNA.

Athetosis:

 Involuntary, relatively slow, writhing movements that essentially flow into one another. Athetosis is often associated with chorea, a related condition characterized by involuntary, rapid, irregular, jerky movements. Although athetosis may be most prominent in the face, neck, tongue, and hands, the condition may affect any muscle group. Athetosis may occur in association with certain neurodegenerative diseases, such as Huntington’s or Wilson’s disease, or cerebral palsy (CP). It may also result from infections affecting the brain or the use of particular medications.

Atrophy:

Wasting away or loss of a cell, tissue, or organ due to disease, malnutrition, insufficient blood supply, or other causes, such as loss of skeletal muscle mass due to peripheral nerve damage.

Attention-deficit/hyperactivity disorder:

a diagnosis applied to children and adults who consistently display certain characteristic behaviors over a period of time. The most common behaviors fall into three categories: inattention, hyperactivity, and impulsivity.

Atypical:

Irregular; not standard or characteristic; not conforming to type.

Atypical neuroleptics: 

Antipsychotic drugs that cause less parkinsonian side effects than older treatments for psychosis.

Auditory:

Pertaining to the sense of hearing or the organs involved in hearing.

Augmentation: 

A phenomenon that may occur as a result of the use of certain medications (particularly levodopa). Augmentation is characterized by the emergence of worsening symptoms earlier in the day (e.g., early evening, afternoon, or morning). Many people who take levodopa and some who take other dopamingeric agents develop augmentation, especially those who have severe symptoms or are taking high doses of the drug.

Autoimmune: 

Referring to an immune response against one’s own tissues or organs. Autoimmune diseases result from abnormal immune reactions in which the actions of certain white blood cells (T cells) are directed against “self proteins” (autoantigens) or normal tissue components (i.e., cell-mediated immune response)–or in which specialized proteins (antibodies) produced in response to specific, usually foreign proteins (antigens) improperly act against certain of the body’s own cells (i.e., antibody-mediated immune response). In certain disorders, the autoimmune process may be primarily directed against one organ, such as the thyroid gland in Hashimoto’s thyroiditis or the pancreas in insulin-dependent diabetes mellitus, or may involve multiple organs and bodily systems, such as associated with systemic lupus erythematosus (lupus or SLE).

Autonomic:

The autonomic nervous system controls most of the involuntary reflexive activities of the human body. The system is constantly working to regulate the glands and many of the muscles of the body through the release or uptake of the neurotransmitters acetylcholine and norepinephrine. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body’s “fight or flight” response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body’s functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body’s immune system properly functioning.

Autonomic dysregulation:

This term infers the malfunction of the autonomic nervous system, the portion of the nervous system that conveys impulses between the blood vessels, heart, and all the organs in the chest, abdomen, and pelvis and the brain (mainly the medulla, pons and hypothalamus).

Autonomic nervous system: 

The autonomic nervous system (ANS) controls most of the involuntary reflexive activities of the human body. The system is constantly working to regulate the glands and many of the muscles of the body through the release or uptake of the neurotransmitters acetylcholine and norepinephrine. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body’s “fight or flight” response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body’s functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body’s immune system properly functioning.

Autosomal dominant trait:

Human traits, including an individual’s eye color, hair color, or expression of certain diseases, result from the interaction of one gene inherited from the father and one gene from the mother. In autosomal dominant disorders, the presence of a single copy of a mutated gene may result in the disease. In other words, the mutated gene may dominate or “override” the instructions of the normal gene on the other chromosome, potentially leading to disease expression. Individuals with an autosomal dominant disease trait have a 50 percent risk of transmitting the mutated gene to their children.

Autosomal recessive trait:

Human traits, including an individual’s hair color, specific blood group, or expression of certain diseases, result from the interaction of one gene inherited from the mother and one from the father. With autosomal recessive disorders, two copies of the disease gene must be inherited in order for an individual to potentially develop the disease. If both the mother and father carry a copy of the disease gene, each child has a 25 percent risk of inheriting the two genes for the disease. There is a 50 percent risk that their children may inherit one copy of the disease gene and be carriers for the disease trait (heterozygous carriers). In addition, there is a 25 percent chance that the parents’ offspring will inherit two normal copies of the gene and will not develop the disorder nor be carriers for this disease trait.

Axons:

Nerve fibers. Axons are the relatively slender extensions of neurons that transmit nerve impulses away from nerve cell bodies. The ends of the axons or “terminals” release chemical substances known as neurotransmitters, enabling the transmission of nerve impulses to other neurons or effector organs. The whitish, fatty, protein-containing substance called myelin forms an insulating, protective, cylindrical sheath around some axons, serving to increase the speed and efficiency of nerve impulse transmissions.