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Range of motion (ROM): 

The extent of a joint’s free movement. The normal ROM of the elbow, for instance, carries the forearm through a half-circle. Passive ROM is tested while the limb is relaxed. Active ROM is movement controlled by the patient.

A molecule on a neuron that receives a neurotransmitter. Reception of the neurotransmitter causes changes in the neuron which increases or decreases its likelihood of “firing,” or sending its own signal to other neurons. Dopamine receptors are located on corpus striatum neurons, and on nigral cells.


Reduced penetrance:

Reduced expression of a genetic disorder. The term penetrance refers to the frequency with which a specific genetic mutation produces its typical effect in those with the genetic abnormality. For example, if fewer than 100 percent of individuals who inherit a gene mutation for an autosomal dominant disorder develop the disease, the specific trait is said to have “reduced penetrance.”


Involuntary, predictable response to a particular stimulus.


Resistant to or not readily yielding to treatment.


In reference to the heart, regurgitation is the backward flow of blood through a defective valve.

REM sleep:

The period of sleep that is associated with dreaming, rapid eye movements (REM), and certain involuntary muscle movements.

Restless legs syndrome (RLS):

A neurologic movement disorder characterized by unusual, uncomfortable sensations (paresthesias/dysesthesias) deep within the calves and/or thighs, resulting in an irresistible urge to move the legs, and motor restlessness in response to or in an effort to alleviate discomfort. In some patients, the arms may also be affected. Symptoms become obvious or worse during periods of relaxation or inactivity; occur most frequently during the evening or the early part of the night; and may be temporarily relieved by voluntary movements of the affected area. Most patients experience associated sleep disturbances, including difficulties drifting off to and remaining asleep. RLS is also often associated with periodic limb movements of sleep (PLMS) or repeated, stereotypic, upward extension of the great toe and foot, potentially followed by flexion of the knee, hip, or ankle. Episodes of PLMS typically occur during periods of lighter (i.e., non-REM) sleep.

Restorative sleep: 

A refreshing sleep, i.e., receiving a sufficient amount of rest to feel refreshed and to engage in the activities of daily living without experiencing excessive daytime sleepiness (EDS).


The nerve-rich membrane that forms the innermost region of the eye. As light passes through other areas of the eye (including the cornea, pupil, and lens), it is bent or refracted to focus on the retina, which contains nerve cells that respond to light (photoreceptors). Images formed on the retina are converted into nerve impulses that are transmitted to the brain via the optic nerve (second cranial nerve).


Referring to the retina.


 spasmodic torticollis in which the head is drawn directly backward.


Peptides are short chains of amino acids.


The retroperitoneal area is the area behind the peritoneum, the covering of the intestines. The kidneys and the adrenal glands lie in the retroperitoneal area.

Reye syndrome:

A potentially life-threatening disease characterized by sudden inflammation and swelling of the brain (acute encephalopathy) and rapid fat accumulation within certain internal organs (viscera), particularly the liver, occurring subsequent to certain viral infections, such as chickenpox or upper respiratory tract infections (e.g., influenza B). Reye syndrome primarily occurs in children and adolescents, although it has sometimes been reported during infancy or young adulthood. About a week after the onset of a viral infection, patients may develop uncontrollable vomiting, followed by a rapid onset of listlessness, confusion, and memory loss, a state of unconsciousness (coma), seizures, and/or other findings, potentially leading to life-threatening complications. Evidence suggests that the use of aspirin-containing preparations (salicylates) as a treatment for particular viral infections plays a role in the development of Reye syndrome. Therefore, experts advise that such medications be avoided for the treatment of viral infections during infancy, childhood, adolescence, and young adulthood.

Rhythmical myoclonus:

Involuntary, shock-like contractions or spasms of a muscle or muscle group that occur in a rhythmical pattern. This usually occurs as a result of a lesion in the central nervous system.

Ribonucleic acid (RNA):

RNA is a chemical that is found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.


Ribosomes are small structures within a cell that are the site of protein synthesis.


Stiffness and resistance to movement. May be a symptom of a neurologic movement disorder such as Parkinson’s disease.

Rush Hallucination Inventory: 

This standardized clinician-administered questionnaire assesses the presence or absence of false visual (see), auditory (hear), tactile (touch), or gustatory (taste) experiences in the setting of a clear sensorium.


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