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Neurological Glossary




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Obstructive sleep apnea
Repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure of the throat; characterized by snoring, excessive daytime sleepiness, and morning headache

Obtundation
Mild to moderate reduction in alertness with slow response to stimulation, decreased interest in environment, and increased number of hours of sleep

Occupational Therapy
Therapy involving evaluation and treatment of physical and psychiatric conditions � Occupational Therapists also advise on equipment needs

Ocular migraine
Form of migraine characterized by monocular visual loss typically followed by an ipsilateral periorbital (or less commonly diffuse) headache

Oculocephalic response (OCR/Doll�s phenomenon)
Reflex eye movements assessed in an uncooperative or unresponsive patient to determine whether brainstem extraocular pathways are intact; performed by quickly turning the head, stimulating proprioceptive afferents from the neck and/or the vestibular system; considered positive (brainstem pathways intact) if head turn produces conjugate eye deviation in the opposite direction; absent response implies that either brainstem pathways are impaired or the patient is too awake to assess

Oculogyric crisis
Acute dystonic reaction to neuroleptic drugs manifested by sudden sustained twisting of the head and upward deviation of the eyes; responsive to anticholinergic or antihistamine medications

Oculomotor nerve (cranial nerve III)
Motor nerve innervating the superior, inferior, and medial recti, inferior oblique, and levator palpebrae superioris muscles and providing preganglionic parasympathetic fibres to the ciliary ganglion to control pupillary constriction; III palsy causes down and out eye deviation, ptosis, and a dilated unreactive pupil (pupillary fibers on the outside so spared with intrinsic lesion); lesions of the nucleus, located in the medial midbrain, typically cause weakness of all muscles innervated by the ipsilateral III nerve, contralateral superior rectus weakness, and bilateral incomplete ptosis;

Oculovestibular response (OVR/cold calorics/vestibulo-ocular response/VOR)
Reflex eye movements that keep vision stable upon head rotation and involve connections between the ipsilateral 8th and 3rd and the contralateral 6th nerve nuclei; horizontal movements are tested by instilling ice water into one ear, stimulating the lateral semicircular canal; in a normal awake patient, the eyes will slowly deviate towards the irrigated ear and then beat quickly away from the irrigated ear as the supratentorial frontal eye fields try to re-fix vision

Odontoid fracture
fracture through the odontoid process of C2 due to horizontal shearing and axial loading; type I usually stable and type II usually unstable Oedema Swelling due to excessive accumulation of fluid in the body tissues.

Olfactory nerve (cranial nerve I)
Sensory nerve mediating smell

Oligemia
Reduction in blood flow associated with an increase in oxygen extraction fraction but maintenance of normal metabolism

Oligoclonal bands
Two to five bands of immunoglobulins on protein electrophoresis of cerebrospinal fluid seen in multiple sclerosis and other central nervous system disorders

Oligodendrocytes
Form of CNS glia responsible for the synthesis and maintenance of myelin and the formation of perineuronal satellites

Oligodendroglioma
WHO grade II primary CNS tumour typically involving the cerebral hemispheres; characterized histologically by uniform round nuclei with a perinuclear halo (fried egg artifact) and perineuronal satellitosis

Olivopontocerebellar atrophy (OPCA)
Older term for a variant of multisystems atrophy characterized by preferential degeneration of the cerebellum and brainstem producing symmetric parkinsonism and ataxia, dysarthria, dysphagia, pyramidal signs, and often ocular motility disorders

Ondine's curse (central alveolar hypoventilation)
Condition in which the respiratory centre in the brain is unable to stimulate breathing in response to an increased amount of carbon dioxide in the blood; typically worsens during sleep

One-and-a-half syndrome
Combination of an abducens nerve nuclear lesion and an ipsilateral medial longitudinal fasciculus lesion resulting in an ipsilateral gaze paralysis and loss of adduction of the ipsilateral eye

On-off phenomenon
Sudden, unpredictable changes in motor performance by patients on levodopa therapy

Onset seizures
Seizures which happen on the day of a stroke.

Opening pressure
Cerebrospinal fluid pressure obtained upon entering the subarachnoid space by spinal puncture

Ophthalmoplegia
Paralysis or weakness of one or more of the muscles that control eye movement

Ophthalmoplegic migraine
Form of migraine characterized by periorbital pain and ocular cranial nerve palsy (usually the third nerve and including ptosis and a dilated pupil)

Opisthotonos
Abnormal posturing of the body with severe arching of the back and the head thrown backwards; may occur with meningeal irritation, especially in infants, or with depressed brain function

Optic atrophy
Wasting of the optic disc that results from partial or complete degeneration of optic nerve fibres and is associated with a loss of visual acuity

Optic chiasm
Partial crossing of about half the axons in each optic nerve to enter the contralateral optic tract; lesion results in loss of vision in the temporal hemifield of both eyes

Optic disc (optic nerve head)
Location where all the ganglion cells exit the retina to form the optic nerve; known as the blind spot since there are no receptors in this part of the retina

Optic nerve
Extent of the visual system pathway from the retina to the optic chiasm; contains axons of ganglion cells in the retina of the ipsilateral eye; lesion results in loss of vision in one eye

Optic neuritis
Inflammation or demyelination of the optic nerve with transient or permanent loss of vision +/- pain

Optic radiations
Extent of the visual system pathway from the lateral geniculate nucleus of the thalamus to primary visual cortex in the occipital lobe; involves temporal (Meyer�s loop) and parietal lobes

Optic tract
Extent of the visual system pathway from the optic chiasm to the lateral geniculate nucleus of the thalamus; contains axons from ganglion cells in the retinas of both the left and right eyes, but information from only one half (either left or right) of each eye's visual field; lesion results in loss of vision in contralateral hemifield of both eyes

Optokinetic nystagmus
Reflexive eye movement that consists of the intermittent rotation of the eye when a subject looks at moving objects; designed to keep an entire moving scene stable on the retina so that it doesn�t blur

Orthoptist
Professional working with people who have visual problems and abnormal eye movements

Orthostatic hypotension
Sudden drop in blood pressure experienced upon standing up

Orthotic
Mechanical appliance such as a leg brace or splint that is designed to control, correct, or compensate for impaired limb function

Orthotist
Professional who specialises in the supply and fitting of aids and equipment to help improve mobility, provide support, etc e.g. wheelchairs, special shoes, splints

Oscillopsia
Visual disturbance characterized by continuous, involuntary, and chaotic eye movements, which make objects appear to be jumping or bouncing

Osmophobia
Enhanced sensitivity to odors

Oxycephaly
Premature fusion of all cranial sutures producing an elongated head


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