The occipital is a region of the scull and the brain located at the lower back portion of the head.
An occlusive cuff is a cuff which closes around the arm or other body part, usually in the location of a major blood vessel for the purposes of measuring blood pressure.
Occult refers to something being obscure, hidden from observation, or difficult to understand.
Ocular counterrolling (CR) is a test based upon the observation that when a normal person is tilted to the right or to the left, the eyes tend to rotate in the opposite direction. If proper technique is used, the amount of counterroll is a specific and valid measure of otolith function. The object of the CR test is to determine whether prolonged physiological deafferentation of the otolith apparatus alters its basic sensitivity.
Ocular torsion is a twisting or turning motion of the eye which results from the combination of gravity and inertial forces during linear acceleration or head tilt.
The term oculogyral refers to rotation of the eyes; oculo = "of the eyes", gyral = "to revolve or rotate"
Oculomotor means relating to or causing movements of the eyeball.
Oculomotor range (EOM)
The oculomotor range (EOM) is defined as the area in which any target can be tracked by eye-movement only. Targets outside of the EOM are defined as targets which require additional head movement to be tracked.
The oculomotor system refers to all body parts which are involved in tracking and gazing at visual targets by eye movements.
OKN (Optokinetic Nystagmus) occurs when the nystagmus of the eye is induced by looking at a moving visual stimuli.
The olfactory complex refers to all body-parts involved in the sense of smell or the process of detecting smells. This is achieved by receptors in olfactory organs, such as the nose, that are sensitive to air-borne or water-borne chemicals. Stimulation of these receptors results in the transmission of information to the brain via the olfactory nerve.
Oligemia (hypovolemia) is a deficiency in the amount of blood in the body.
Omnivorous means eating all kinds of foods indiscriminately, or eating both animal and plant foods.
Ontogenesis refers to the entire development of an individual organism from fertilization to completion of life history.
Ophthalmology is the medical specialty concerned with the eye, its diseases, and refractive errors.
Ophthalmoscopy is the examination of the interior of the eye, especially the retina, with an ophthalmoscope, an instrument with a mirror that is perforated in the center.
Optical means something which pertains or is designed to assist sight; pertaining to or using light.
Optokinetic refers to the occurrence of intermittent rotation of the eye when the subject looks at moving objects. In other words, when the visual scene continually moves before the eyes, such as when a person is riding in a car or turning around, the eyes fix on one highlight after another in the visual field, jumping from one to the next at a rate of two to three jumps per second. The jumps are called saccades and the movements are called optokinetic movements.
Optokinetic nystagmus is a nystagmus evoked by optokinetic stimuli, such as a rotating disk. Nystagmus is a rhythmical oscillation of the eyeball, either pendulum-like or jerky.
The optokinetic reflex is a reflexive eye movement that consists of the intermittent rotation of the eye when a subject looks at moving objects.
An organelle is any part of a cell that has a unique structural, functional or anatomical role. On a smaller scale, organelles are similar to the organs in your body - they are, in effect, the organs of a cell.
Organic means of or originating from carbon compounds.
Orthogonal means pertaining to or composed of right angles.
The term "orthostatic" relates to the upright position of the body; the term is used when describing this position or a condition caused by it. Orthostatic hypotension, for example, is low blood pressure found in some people when they stand upright.
Orthostatic hypotension is a temporary and short-lived condition of low blood pressure sometimes occurring when a person stands or sits upright from a sitting or recumbent position; it can result in light-headedness or fainting.
Orthostatic intolerance is a condition of lightheadedness, possibly leading to fainting, that occurs when an upright position is assumed. It is caused by low blood pressure and an inadequate supply of blood reaching the brain. Astronauts often experience temporary orthostatic intolerance when remaining upright after returning from stays in space, since their blood volume is reduced in weightlessness and the pull of gravity does not allow blood to reach their heads.
The os calcis is the largest bone in the foot. It is commonly referred to as the heel bone. In medical terminology, it is also referred to as the calcaneus.
An oscillation, as it applies to microgravity experiments, is a vibration. However, oscillations can refer to any steady back and forth movements.
An oscillator is any device that produces a to and fro movement; it may also be defined as an electric circuit designed to generate alternating current at a particular frequency.
An oscillometer is a device which measures arterial blood pressure; it consists of a recording apparatus that can register pulsations in a lightly inflated blood pressure cuff around the forearm.
Oscillometry is the measure of arterial blood pressure by recording the pulsation in the lower arm with an oscillometer while a cuff is inflated over the upper arm. An oscillometer consists of a recording apparatus that can register pulsations in a lightly inflated blood pressure cuff around the forearm.
Osmolality is a property of a solution which measures the concentration of the solute per unit of solvent.
An osmoreceptor is any of the group of structures found in the hypothalamus that respond to changes in the osmotic pressure of the blood.
Ossification (osteogenesis) is a three-stage process by which bone is formed. The first step is the formation of a mesh of collagen fibers. Next, the body produces a "cement" substance (polysaccharide). Finally, small crystals of calcium salts are deposited into the cement to form bone.
An osteoblast is a type of cell that is responsible for the formation of bone.
Osteocalcin is a bone matrix protein consisting of 49 amino acids.
An osteoclast is a large cell with multiple nuclei. It resorbs calcified bone. Osteoclasts are only found when bone is being resorbed and can be seen in small depressions on the bone's surface.
Osteogenesis (ossification) is a three-stage process by which bone is formed. The first step is the formation of a mesh of collagen fibers. Next, the body produces a "cement" substance (polysaccharide). Finally, small crystals of calcium salts are deposited into the cement to form bone.
Osteomyelitis is the inflammation of the bone marrow and adjacent bone.
Osteopenia is decreased calcification or density of bone, or can also mean reduced bone mass.
Osteoporosis is the loss of bony tissue, resulting in bones that become brittle and liable to fracture. Infection, injury and synovitis (inflammation of the membrane surrounding a joint), as well as prolonged exposure to microgravity, can cause osteoporosis.
An otolith (or otoconium) is one of the small particles of calcium carbonate in the saccule or utricle of the inner ear. Pressure of the otoliths on the hair cells of the macula provide sensory inputs about acceleration and gravity.
The otolith-spinal reflex is a postural reflex that prepares the body for the jolt associated with landing after a fall. The otolith organs in the inner ear detect a change in acceleration and send signals through a nerve pathway to the spinal cord. Nerve fibers that control the muscles that maintain posture receive the signals in the spinal cord and act on the muscles.
The utricle and the saccule are the otolithic organs of the vestibular system. These organs detect linear accelerations and work in conjunction with the semicircular canals to maintain the body's balance.
Ova are female gametes; eggs.
Oxalate is a salt of oxalic acid, an acid found in many plants and vegetables.
Oxidation is the combination of a substance with oxygen. Oxidation can also describe a type of reaction in which the atoms in an element lose electrons and the valence is correspondingly increased.
Oxidation-reduction refers to any chemical oxidation or reduction reaction, which must comprise both oxidation (to increase the positive charge or valence of an atom by removing electrons) and reduction (to decrease the valence of an atom by adding electrons). In other words, the reactions reverse each other. Oxidation- reduction is often shortened to "redox".
Oxidative relates to oxidation. Oxidation is the combination of a substance with oxygen. Oxidation can also describe a type of reaction in which the atoms in an element lose electrons and the valence is correspondingly increased.
An oxidative enzyme has the power to oxidize an atom, or to cause it to combine with oxygen or to lose electrons.
Oxygen consumption is the amount of oxygen in milliliters per minute required by the body for normal aerobic metabolism; normally about 250 ml/ minute.
Oxygen-18 is a stable isotope of oxygen that occurs naturally. Oxygen-18 is also referred to as heavy oxygen.
Oxyntic cells (parietal cells) are cells of the gastric glands that secrete hydrochloric acid in the lower region of the stomach.