Neurological Glossary

Obstructive sleep apnea

Repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure of the throat; characterized by snoring

Obtundation

Mild to moderate reduction in alertness with slow response to stimulation

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/Dolls 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

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

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

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

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

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

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 (Meyers 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

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 doesnt 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

Orthotist

Professional who specialises in the supply and fitting of aids and equipment to help improve mobility

Oscillopsia

Visual disturbance characterized by continuous

Osmophobia

Enhanced sensitivity to odors

Oxycephaly

Premature fusion of all cranial sutures producing an elongated head