Neurology glossary
a
Abduct
To move away from the sagittal midline
Absence seizure
Generalized seizure characterized by suddenly freezing in position, staring off into space, and impaired consciousness. Unclear if these occur in dogs & cats.
Accommodation
Adjustment of the focal length of the lens of the eye to focus on objects at varying distances
Action potential
A rapid, transient, all-or-none electrical impulse generated by a neuron at the axon hillock propagated toward the synapse.
Action tremor
A tremor that occurs only during movement of an affected body part
Adduct
To move toward the sagittal midline
Afferent
Proceeding from the periphery toward the central nervous system
Allodynia
A condition in which the patient experiences pain to a stimulus that would normally be non-painful
Analgesia
Loss of pain sensation
Anencephaly
CNS malformation with absence of the forebrain, resulting from failure of closure of the cephalic end of the neural tube during development
Anhidrosis
Absence of sweating
Anisocoria
Inequality in pupil diameter
Anosmia
Loss of sense of smell
Aphonia
Complete loss of voice
Arachnoid
Middle layer of meninges (arachnoid mater) surrounding the brain and spinal cord. CSF is located between the pia mater and arachnoid mater
Arachnoid villi
Tufts of arachnoid mater that extend through the dura mater into the veins or venous sinuses; one of the major routes of CSF reabsorption
Arbor vitae
White matter tracts of the cerebellum, which on cross-section (see image above) have the appearance of a tree trunk with its many branches into the cerebellar folia
Arteriovenous malformation
Vascular anomaly characterized by abnormal connection between arteries and veins that bypass the capillary system
Arteritis
Inflammation of arteries
Ascending reticular activating system
A collection of neurons in the central core through the entire length of the brainstem that is responsible for arousal and consciousness
Ataxia
Incoordination; typically a sensory phenomenon. There are three types of ataxia: general proprioceptive, vestibular, and cerebellar.
Athetosis
Involuntary, slow, writhing movements
Autonomic nervous system
A subdivision of the peripheral nervous system that regulates homeostasis and visceral function; there is no voluntary control over this system
Axonopathy
A disorder characterized by degeneration of the axon
b
Basal ganglia
Deep cerebral nuclei, including the caudate nucleus, putamen, globus pallidus, subthalamus, and substantia nigra
Basilar artery
Large artery ventral to the brainstem formed by fusion of the two vertebral arteries; one of the main sources of blood supply to the brain
Bell’s palsy
An inflammatory disorder of the facial nerve in man resulting in lower motor neuron facial muscle weakness, hyperacusis, impaired taste and impaired lacrimation. It is thought to be due to reactivation of Herpes simplex virus. Clinically similar to Idiopathic Facial Paralysis in dogs.
Blepharospasm
Repetitive involuntary blinking of the eyelids
Brachium
An anatomical structure consisting of a collection of axons that resemble an arm
Brainstem auditory evoked response
Series of electrical responses arising from various structures in the auditory pathway recorded at the skin following repetitive stimulation of the ears via a clicking sound; used as a screening test for deafness; can be used as one tool to determine brain death
Bregma
Point on dorsal midline where the left and right frontoparietal sutures (junction between frontal and parietal bones) intersect the sagittal suture
Bulbar
Relating to lower cranial nerve nuclei
Butterfly glioma
A glioma that crosses midline via a white matter commissure leading to a bihemispheric mass lesion with the appearance of wing-like extensions
c
Catamenial
Refers to menses; in neurology, the term is used most often to in catamenial epilepsy in which seizures are occur or are worse during specific times of the estrus cycle
Cataplexy
Sudden loss of postural tone resulting in collapse, often occurring with excitement or stress; frequently occurs with narcolepsy
Cauda equina
Collection of nerve roots within the vertebral canal after termination of the spinal cord that supply the pelvic limbs and pelvic structures; cauda equina literally means “horse’s tail”
Caudal
Toward the tail
Caudal commissure
A site of decussation in the midbrain conveying axons between the pretectal regions and most of the axons are involved in the PLR, but some connect tegmental nuclei
Caudal fossa
Caudal portion of the cranial vault between the tentorium cerebelli and the foramen magnum containing the cerebellum, pons, and medulla oblongata
Caudate nucleus
One of the basal ganglia (deep cerebral nuclei) that is located on the ventral to the floor of the lateral ventricles
Caudotentorial
Lesion caudal to the tentorium cerebelli in the pons, medulla, or cerebellum
Cavernous sinus
Paired venous structures on either side of the sella turcica surrounding the pituitary gland
Central cord syndrome
Spinal cord injury in which the central region (gray matter) is more severely affected, resulting in thoracic limb weakness that is more severe than pelvic limb weakness
Central nervous system
Part of the nervous system comprising the brain and spinal cord
Centrum semiovale
Large region of white matter dorsolateral to the lateral ventricle between the internal capsule and corona radiata
Cerebellar herniation
Displacement of cerebellar tissue caudally into or through the foramen magnum (caudal cerebellar herniation) or rostrally under the tentorium cerebelli (rostral cerebellar herniation)
Cerebellar peduncle
Three major white matter structures containing efferent and afferent axons of the cerebellum; they are the rostral, middle, and caudal cerebellar peduncles
Cerebellopontine angle
Space located at the junction of the cerebellum, pons, and medulla containing cranial nerves V-XI, blood vessels, the flocculus of the cerebellum, and choroid plexus
Cerebellum
Structure in the caudal fossa dorsal to the pons and medulla; responsible for rate and range of motion; receives input and sends output to and from the cerebrum, brainstem, and spinal cord
Cerebral cortex
Outermost layer of the cerebral hemisphere consisting of a convoluted layer of gray matter
Cerebral hemisphere
One half of the cerebrum which contains the cerebral cortex, basal ganglia, hippocampus, amygdala and other structures
Cerebrospinal fluid
Clear, colorless fluid surrounding the brain and spinal cord; functions to provide nutrition to the brain, immunologic protection, and acts as a shock absorber; also an important determinant in cerebral autoregulation of cerebral blood flow
Cheyne-Stokes respiration
Respiratory pattern characterized by alternating periods of increasing rate/depth of breathing followed by decreasing rate/depth of breathing, often with periods of apnea
Chorea
Involuntary, irregular, rapid jerking movements
Choroid plexus
Tufts of modified ependymal cells and capillaries extending into the ventricles; secretes cerebrospinal fluid
Choroid plexus tumor
A benign (papilloma) or malignant (carcinoma) tumor arising from the choroid plexus
Cingulate gyrus
A gyrus located dorsal to the corpus callosum on midline; a cortical component of the limbic system involved in emotional and cognitive processing
Cisterna magna
Cerebrospinal fluid space between the cerebellum and dorsal medulla; CSF is collected from this location during atlanto-occipital tap (A/O tap, “high tap”)
Clonus
Involuntary, rhythmic muscular contractions and relaxations that are often elicited by a reflex
Coma
Mental status characterized by being unresponsive to noxious stimuli
Complex partial seizure
Partial seizure with impaired consciousness or awareness
Concussion
Traumatic closed brain injury resulting in temporary neurologic impairment and often a transient loss of consciousness
Conduction block
Failure of action potential conduction along an anatomically-intact axon
Contracoup
A contusion resulting from the brain hitting the skull on the side opposite the impact
Contracture
Permanent shortening of muscles and tendons
Contralateral
Occurring on the opposite side of the body
Conus medullaris
Tapered, caudal-most portion of the spinal cord
Corona radiata
Fan-like white matter projections into and out of the cerebral cortex
Corpus callosum
Largest of the cerebral commissures; primarily connects neopallium (cerebral cortex) on each side
Cortical blindness
Blindness due to bilateral cerebral disease, especially the primary visual cortex in the occipital lobes
Corticobulbar
Axons projecting from the cerebrum to lower motor neurons in the brainstem
Coup
Traumatic brain injury (contusion) occurring at the site of impact with an object
Craniectomy
Surgical removal of a bone flap to access the brain; bone flap not replaced at the end of surgery
Cranioplasty
Surgical repair of a defect or deformity of the skull, for example following removal of multilobular tumor of bone
Craniotomy
Surgical procedure in which a bone flap that is removed for access to the brain is replaced at the end of surgery
Creatine kinase
Muscle enzyme that is released from muscle cells in some forms of myopathy
Cryptogenic
A condition in which a distinct lesion or pathogenesis is presumed, but has not been proven
Cyclotorsion
Rotation of the eye around an dorsal-ventral axis; see also excyclotorsion, incyclotorsio
d
Decerebellate rigidity
Body posture characterized by rigid extension of the thoracic limbs, flexion of the pelvic limbs, and extension of the neck (opisthotonus); due to severe rostral cerebellar dysfunction
Decerebrate rigidity
Body posture characterized by rigid extension of all four limbs and the neck (opisthotonus); due to severe midbrain dysfunction
Decussate
To cross over
Delirium
Abnormal mental status characterized by confusion, disorientation, fear, irritability, inattention and varying degree of consciousness
Dementia
Sustained, acquired loss of memory and other intellectual capacities that impairs daily functioning
Demyelination
Loss or destruction of the myelin sheath surrounding the axon; results in slowed nerve conduction
Dendrite
Receiving portion of the neuron
Denervation
Loss of nerve supply
Dermatome
Cutaneous distribution of sensory innervation on the skin
Diaschisis
Reduced metabolism or function of one region due to disease in an anatomically-distant, but connected, region due to disruption of afferent or efferent fibers
Diastematomyelia
Rare malformation characterized by longitudinal splitting of the spinal cord by a septum
Diencephalon
Rostral end of the brainstem consisting of the thalamus, hypothalamus, subthalamus, and epithalmus; anatomically a portion of the brainstem, but functionally more similar to the cerebrum
Diffuse axonal injury
Widespread damage to white matter of the brain due to rotational shearing forces that occur with traumatic brain injury
Dorsal
Of, on, or relating to the upper side or back of an animal, plant, or organ
Dorsal column
Ascending tracts in the dorsal funiculus of the spinal cord carrying proprioceptive and tactile information to the brain
Dorsal horn
Gray matter in the dorsal aspect of the spinal cord that receives sensory input from the body through the dorsal roots
Dorsal rhizotomy
Surgical procedure in which the dorsal spinal nerve roots are transected to reduce spasticity or chronic pain
Dorsal root ganglion
Collection of sensory nerve cell bodies located that transduce sensory information into neural signals and transmit these signals to the CNS
Drop metastases
Metastatic tumors that spread from the primary tumor via the ventricular system to distant sites
Dura mater
Thick, fibrous, outermost layer of meninges surrounding the brain and spinal cord
Dural tail sign
Tail of contrast enhancement extending along the meninges away from the primary lesion; most commonly observed with meningioma, but can also be seen with lymphoma and other intradural tumors, as well as non-neoplastic inflammatory lesions
Dysesthesia
Pain or discomfort from a stimulus (e.g., touch) that is normally non-painful
Dysgeusia
Distorted perception of taste
Dyskinesia
Broad category of movement disorders characterized by excessive motor activity
Dysmetria
Impaired rate and range of motion; tendency to overshoot or undershoot the target
Dysmyelination
Decreased myelination due to biochemically abnormal myelin
Dysphagia
Difficulty swallowing
Dysphonia
Abnormal voice, often due to laryngeal muscle weakness such as that due to laryngeal paralysis, hypothryoidism, myasthenia gravis, etc.
Dysraphism
Incomplete closure of a raphe; in neurology it is due to to neural tube closure defect
Dystonia
Involuntary muscle spasms causing abnormal posture or body movements
e
Edinger-Westphal nucleus
A nucleus of the oculomotor nerve (III) supplying pre-ganglionic parasympathetic fibers for pupillary constriction and lens accommodation
Efferent
Motor pathways extending from the CNS to the periphery
Electroencephalogram
Recording of electrical potentials arising from the cerebral cortex at the skin of the head
Electromyography
Diagnostic tool in which spontaneous electrical potentials are recorded in sedated or anesthetized patients; there should be essentially no recordable activity in non-moving muscles, but spontaneous discharges may be detected in myopathic and neuropathic disorders. In human medicine, EMG is performed in awake patients and muscle activity can be recorded during voluntary movement.
Encephalitis
Inflammation or infection of the brain
Encephalocele
Broad term to describe failure of bone fusion in the skull resulting in protrusion of meninges and/or brain parenchyma; strictly speaking, encephalocele is protrusion of the brain, while meningocele is protrusion of the meninges and meningoencephalocele is protrusion of both structures
Encephalopathy
Any disorder of the brain
Endomysium
Innermost layer of connective tissue around each individual muscle fiber
Enophthalmos
Retraction of the eyeball back into the orbit
Ependyma
Epithelial lining of the ventricles of the brain and central canal of the spinal cord
Ependymoma
Primary CNS tumor arising from the ependymal cells of the ventricles or central canal
Epilepsy
Any disorder characterized by chronic, repetitive, unprovoked seizures
Evoked potentials
Recordings of the electrical response to stimulation of specific sensory pathways; examples include sensory nerve conduction velocity, somatosensory evoked potentials, brainstem auditory evoked potentials, and electroretinogram
Excyclotorsion
Rotation the eyeball such that the dorsal pole rotates outward (laterally)
Exophthalmos
Protrusion of the eyeball
Extra-axial
Lesion external to the brain (i.e., not in the brain parenchyma)
Extraparenchymal
Lesion outside the tissue of interest (i.e., outside the brain or spinal cord)
Extrapyramidal
Motor fibers from the brain that do not pass through the pyramids
f
F-Wave
A long-latency compound muscle action potential observed after supramaximal stimulation of a nerve
Falcine herniation
Displacement of the cingulate gyrus under the falx cerebri to the contralateral side, often secondary to increased intracranial pressure from a space-occupying mass
Falx cerebri
Fold of dura mater between the two cerebral hemispheres
Fascicle
Bundle of muscle (muscle fascicle) or nerve (nerve fascicle) surrounded by a layer of connective tissue (perimysium or perineurium)
Fasciculation
Spontaneous axonal firing resulting in visible twitching of the muscle innervated; usually indicative of of deneration
Fibrillation
Spontaneous electrical activity from a single muscle fiber not visible to the naked eye externally; observed during electromyography; indicative of a neuropathy or myopathy
Flaccid paralysis
Severe form of hypotonia
Flocculus
Small lobe of the cerebellum; involved in vestibular function
Fontanel
Soft, membranous gap in the skull due to incomplete closure of cranial bone plates during development
Foramen magnum
Large opening in the of the skull through which the spinal cord and vertebral arteries pass into the calavaria
Foramen of Luschka
Lateral exits of CSF from the fourth ventricle to the subarachnoid space. Also known as the lateral apertures.
Foramen of Magendie
Midline exit of CSF from the fourth ventricle to the subarachnoid space of the cerebellomedullary cistern. Also known as the median aperture. This structure is present in primates, but not dogs and cats.
Foramen of Monro
Connection between the lateral ventricles and third ventricle; also called the interventricular foramen
Forebrain
Portion of the CNS arising from the prosencephalon containing the cerebral hemispheres and diencephalon
Fornix
White matter structure that connects the hippocampus to the hypothalamus and septal nuclei
Fried egg artifact
Perinuclear halo in oligodendrocytes that are characteristic of oligodendrogliomas
Frontal lobe
One of four major lobes of the cerebrum located rostral to the cruciate sulcus
Funiculus
Any of the 3 major divisions of white matter in the spinal cord; A slender cord-like strand, especially a bundle of nerve fibers in a nerve trunk
g
Gamma motor neurons
A type of motor neuron that is involved in muscle contraction; unlike alpha motor neurons that contract the muscle, gamma motor neurons keep muscles spindles taut, adjusting the sensitivity of the muscle spindles and allowing continued firing of alpha motor neurons
Ganglion
Collection of nerve cell bodies
Gemistocyte
A reactive astrocyte with increased glial filaments and glassy eosinophilic cytoplasm
Generalized seizure
Seizure activity in both cerebral hemispheres simultaneously; clinically appears as bilateral motor activity and loss of consciousness; ANS signs may also be present (urination, salivation, etc.)
Genu
Knee-like bend in the rostral end of the corpus callosum
Glia
Supporting cells of the nervous system, including astrocytes, oligodendrocytes, microglia and ependymal cells
Gliosis
A dense collection of glial processes in an area of CNS injury
Gray matter
Portion of the central nervous system containing neuronal cell bodies and dendrites
Guillain-Barre Syndrome
An acute, inflammatory demyelinating polyneuropathy in man characterized by generalized lower motor neuron weakness, paresthesias, hyporeflexia, and labeled autonomic nervous system dysfunction. Thought to be due to autoimmune response triggered by a previous illness or recent vaccination. Clinically similar to Coonhound Parlysis and Acute Idiopathic Polyradiculoneuritis in dogs.
Gyrus
A convoluted ridge on the outer surface of the cerebrum caused by infolding of the cerebral cortex and surrounded by sulci
h
Hemianesthesia
Loss of sensation on one half of the body
Hemineglect
Decreased attention or awareness of one side of space, usually contralateral to a forebrain lesion
Hemiparesis
Weakness on one side of the body
Hemiplegia
Paralysis on one side of the body
Hippocampal commissure
Transverse fibers connecting the right and left hippocampus to each other
Hippocampus
A C-shaped structure on the medial edge of the cerebral hemisphere; part of the limbic systemic involved in long-term memory and emotion
Hippus
Spasmodic or rhythmic dilation and constriction of the pupil
Hydranencephaly
Congenital defect in which most of the cerebral hemispheres are replaced by sacs filled with cerebrospinal fluid
Hydrocephalus
Increased size of ventricles and amount of cerebrospinal fluid in the brain
Hyperacusis
Abnormally increased sensitivity to sound
Hyperostosis
Hypertrophy of bone
Hyperpathia
Excessive response to a painful stimulus
Hypertonicity
Increased muscle tone
Hypnagogic myoclonus
Shock-like muscle twitch that occurs when falling asleep or drowsy
Hypoplasia
Underdevelopment of an organ or tissue due to an abnormal deficiency of cells or structural elements
Hypotonicity
Reduced muscle tone
i
Ictus
Sudden attack, stroke, or seizure; in epileptology, it is the actual seizure in which chaotic electrical activity is present
Idiopathic
Disorder without a known cause
Incyclotorsion
Cyclotorsion (rotation) of the eye such that the dorsal pole rotates inward (medially)
Infarction
Tissue damage or cellular death due to prolonged or severe ischemia or hemorrhage
Infundibulum
Connection between the hypothalamus and pituitary gland containing the axons of hypothalamic neurons projecting to the posterior pituitary gland
Intention tremor
A type of tremor whose severity worsens as the affected body part approaches the intended target, which may be missed; typically the result of cerebellar dysfunction
Internal capsule
Broad band of white matter with afferent and efferent fibers to and from the cerebral cortex
Interneuron
A neuron that receives input from one neuron and projects to another neuron, most commonly within the spinal cord
Intracranial pressure
Pressure exerted by the brain, cerebrospinal fluid and cerebral blood within the calvaria
Intrathecal
Space between the pia and arachnoid mater that contains cerebrospinal fluid
Intumescence
A swollen or enlarged part of a plant or animal; a swollen mass; in clinical neurology it describes two enlargements of the spinal cord (C6-T2 and L4-S3)
Ipsilateral
Located on the same side of the body
j
Jacksonian seizure
Seizure characterized by contiguous spread of electrical discharge through the cerebral cortex with corresponding spread of motor activity to contiguous anatomical areas; a.k.a., Jacksonian march
Jitter
Measure of variability of potentials recorded from individual muscle fibers as by single fiber electromyography; increased variability occurs with myasthenia gravis
k
Ketogenic diet
Diet that is high fat and low carbohydrate that is sometimes used to control seizures in specific types of epilepsy in humans
Kindling
Process in which repeated subconvulsive stimulation, either electrically or chemically, permanently lowers the seizure threshold
l
Lacunar infarct
Small infarction caused by occlusion of a single penetrating branch of a cerebral artery; most commonly observed in the thalamus in dogs and cats
Lambert-Eaton myasthenic syndrome
Autoimmune disorder in which antibodies are directed against voltage-gated calcium channels in the presynaptic motor nerve that causes impaired release of acetylcholine and subsequent muscular weakness
Leptomeninges
Combination of the pia and arachnoid mater
Leukodystrophy
Group of white matter disorders characterized by white matter degeneration or abnormal growth/development of myelin
Limbic
Subdivision of the nervous system that is important in emotion and memory; consists of the hippocampus, parahippocampal gyrus, cingulate gyrus, fornix, and multiple subcortical structures including portions of hypothalamus and thalamus
Lissencephaly
A condition in which there is an absence of secondary sulci due to abnormal migration of cortical cells during development causing a smooth appearance to the surface of the cerebrum
Locus ceruleus
Nucleus in the dorsal wall of the pons containing a large amount of melatonin; it is one of the main sources of norepinephrine in the brain and projects to many other regions of the nervous system and mediates arousal
Long tract signs
Clinical signs referable to dysfunction of the corticospinal tract, spinothalamic tract, and dorsal columns/medial lemniscus
Lower motor neuron
Neurons located in the brainstem or spinal cord that connect to muscle; dysfunction lesions to hypotonicity, loss of reflexes, and muscle atrophy
m
Marcus Gunn pupil
A syndrome in which the affected pupil appears to dilate, rather than constrict, when light is shone into the affected eye while performing a swinging-flashlight test; indicative of a pre-chiasmic lesion (retina, optic nerve)
Medulloblastoma
Primitive neuroepithelial tumor that often arises from the cerebellum
Meninges
Three connective tissue membranes surrounding the brain and spina cord, including the pia, arachnoid and dura mater
Meningioma
Tumor arising from the meninges
Meningitis
Inflammation or infection of the meninges
Meningocele
A form of spina bifida characterized by herniation of meninges through a defect in the dorsal arches
Meningomyelocele
Congenital defect in which there is protrusion of the meninges and spinal cord tissue through an opening in the vertebrae due to incomplete fusion of the dorsal arches
Mesencephalon
Midbrain
Microglia
Bone marrow-derived phagocytic glial cell involved in the immune response in the CNS
Miosis
Pupillary constriction
Motor neurons
Nerve cells that innervate and direct movement of muscles
Motor unit
Motor neuron axon and the individual muscle fibers it innervates
Myasthenia gravis
Literally “serious muscle weakness.” A disease of the neuromuscular junction due to autoantibodies directed against the nicotinic acetylcholine receptor (acquired myasthenia) or developmental lack of receptors (congenital myasthenia)
Mydriasis
Pupillary dilation
Myelencephalon
Medulla oblongata
Myelin
Insulating sheath surrounding axons that speed nerve conduction velocity; made by oligodendrocytes in the CNS and Schwann cells in the PNS
Myelitis
Inflammation or infection of the spinal cord
Myelogram
Radiographic procedure in which contrast agent is injected into the subarachnoid space, thereby highlighting the edges of the spinal cord on post-injection radiographs
Myelomalacia
Literally means “soft spinal cord;” ascending-descending myelomalacia (a.k.a., hemorrhagic myelomalacia) is a process that occurs in some patients following severe spinal cord injury
Myelopathy
A disorder of the spinal cord
Myoclonus
Sudden, shock-like contraction of muscle groups
Myokymia
An involuntary, spontaneous, localized quivering of a few bundles within a muscle or a few muscle groups, but without sufficient force to move a joint
Myopathy
A disorder of the muscles
Myotonia
A muscle disorder characterized by abnormally prolonged muscle contraction due to delayed relaxation
Myxedema
Literally means “mucus swelling;” a disorder characterized by swelling of the dermis from excessive deposition of mucopolysaccharides, most often with severe hypothyroidism
n
Narcolepsy
A disorder characterized by sudden sleep attacks; may also manifest as excessive daytime sleepiness and abnormal REM sleep
Neurogenic KCS
A form of keratoconjunctivitis sicca (“dry eye”) due to denervation of the lacrimal gland with disease or injury of the parasympathetic nucleus of the facial nerve, pterygopalatine ganglion, or the pre- or postglanglionic parasympathetic fibers that course with the facial nerve and then the zygomatic branch of the trigeminal nerve.
Neuroleptanalgesia
Form of analgesia achieved by concurrent administration of an analgesic and a sedative
Neuromuscular junction
The synapse between a motor neuron and a muscle fiber
Neuropathy
A disease of nerves
Neurotransmitter
Chemical released from a nerve terminal that passes across the synapse to stimulate another neuron, muscle or effector organ
Nociception
A sensory process in which nociceptors convert (transduce) a noxious stimulus (e.g., heat, cold, pressure, chemicals) causing tissue damage into an electrical signal carried by sensory neurons to the spinal cord and up to the brain. Nociception is necessary, but not sufficient for, a patient to experience pain.
Non-communicating hydrocephalus
Ventricular enlargement due to blockage of CSF flow from one ventricular system region to another, most commonly at the mesencephalic aqueduct
Notochord
A flexible rod-like structure that helps organize nervous system development and around which the vertebral column form. The nucleus pulposus of the intervertebral disks arises from the notochord.
Nucleus
A collection of neuronal cell bodies
Nucleus pulposus
Central core of the intervertebral disc with a gelatinous consistency; a remnant of the embryonic notochord
Nystagmus
Involuntary, rhythmic oscillation of the eyeballs
o
Obtunded
Mild to moderate reduction in alertness
Oligodendrocytes
A type of glial cell that is responsible for synthesis and maintenance of CNS myelin
Oligodendroglioma
Primary CNS tumor originating from oligodendrocytes
Opening pressure
Pressure obtained upon entering the subarachnoid space when performing a CSF tap
Ophthalmoplegia
Paralysis of one or more extraocular muscles responsible for eyeball movement
Opisthotonus
Extension of the head and neck, often the result of cerebellar dysfunction
Optic chiasm
An X-shaped structure where axons of the optic nerves converge, partially cross over (65% cats, 75% dogs), and then diverge to become the optic tracts
Optic nerve
Portion of the visual pathway containing axons of retinal ganglion cells passing from the retinas to the optic chiasm
Optic neuritis
Inflammatory disease of the optic nerves
Optic radiations
Portion of the visual pathway from the lateral genticulate nucleus in the thalamus to the primary visual cortex in the occipital lobe
Optic tract
Portion of the visual pathway extended from the optic chiasm to the lateral geniculate nucleus of the thalamus
Orthotic
Mechanical device, such as a brace or splint, that is designed to correct or compensate for abnormal limb movement
Otoacoustic emission
Auditory tones that can be heard or recorded emanating from the ears
Otogenic meningoencephalitis
Infection/inflammation of the meninges (otogenic meningitis) and the brain (meningoencephalitis) due to extension of otitis media-interna into the calvaria
p
Pacinian corpuscle
The largest skin receptor located in the dermis that is responsive for the sensation of vibration and deep pressure
Palsy
Paralysis of a muscle group
Paralysis
Absence of motor function in a body part
Paraparesis
Weakness in the pelvic limbs
Paraplegia
Complete absence of voluntary movement in the hind limbs
Parasagittal
Sagittal section that is lateral of midline
Paresthesia
Skin sensation, such as burning, prickling, itching, or tingling, with no apparent physical cause
Partial seizure
Seizure that occurs within a focal area of the forebrain; a.k.a., focal seizure
Penumbra
The area surrounding the core of irreversibly damaged cells that has reduced electrical activity, but has preserved ionic homeostasis and is capable of recovery
Periaqueductal gray
Gray matter surrounding the mesencephalic aqueduct in the midbrain
Permysium
Connective tissue sheath surrounding muscle fascicles
Perineurium
Connective tissue sheath surrounding nerve fiber bundles
Peripheral nervous system
Portion of the nervous system outside the brain and spinal cord consisting of the spinal nerve root, plexus, peripheral nerve, neuromuscular junction, and muscle
Phonophobia
Abnormal intolerance to sound
Photophobia
Abnormal intolerance to light
Pia mater
Innermost layer of meninges that is attached to the external surface of the brain and spinal cord
Pineal gland
A body attached to the caudal third ventricle on midline; a major site of melatonin synthesis
Pneumocephalus
Presence of gas (usually air) in the cranial cavity; majority of cases in the vet med have occurred recent transfrontal craniotomy, but also following rhinotomy, trauma, or secondary to gas-producing organisms
Pneumorrhachis
Gas (air) within the vertebral canal
Polymyositis
Disorder characterized by inflammation or infection of multiple muscles
Polyradiculoneuritis
Inflammation of multiple nerve roots
Pons
The portion of the brainstem located between the midbrain and medulla
Porencephaly
Cyst-like structure in the brain that is usually due to a destructive lesion or congenital malformation
Positive sharp wave
Abnormal spontaneous muscle activity that may be observed during electromyography; characterized by an initial positive (downward) wave followed by a negative (upward) wave; can occur with myopathies and neuropathies
Prehension
Physical act of grasping, seizing, or picking up food
Prion
An infectious protein agent responsible for spongiform encephalopathies (e.g., feline spongiform encephalopathy, bovine spongiform encephalopathy, Scrapie)
Prosencephalon
The most rostral portion of the brain consisting of the cerebrum and diencephalon
Pseudo-hyperreflexia
An exaggerated reflex due to decreased tone in the antagonistic muscles
Ptosis
Drooping of the superior eyelid leading to a narrowed palpebral fissure
Pupillary light response
Constriction of the pupils in response to a bright light source
Pyramidal
A subdivision of the motor system consisting of the descending tracts that pass through the pyramids, such as the corticospinal tract
q
Quadrigeminal bodies
Two pairs of elevations on the dorsal surface of the midbrain, consisting of the rostral and caudal colliculi
r
Radiculoneuritis
Inflammation or infection of spinal nerve roots
Radiculopathy
Clinical signs associated with spinal nerve root compression
REM sleep behavior disorder
A disorder in which there is incomplete or failure of muscle atonia that normally occurs in REM sleep causing abnormal movements during REM sleep; movements can be misinterpreted as seizure activity
Repetitive nerve stimulation
An electrodiagnostic test in which the compound muscle action potential is recorded from a muscle during a brief series of electrical stimulations of the motor nerve that innervates the muscle
Rhombencephalon
Hindbrain (brainstem); includes the pons, cerebellum, and medulla
Ring enhancement
Peripheral contrast enhancement of a lesion, such as a glioma, metastatic tumor, or abscess
Rooting reflex
Normal neonatal reflex consisting of turning the head towards a stimulus presented to the side of the mouth, latching on, and sucking
Rostral
Toward the front of the brain
Rostral commissure
One of three commissures connecting the cerebral hemispheres to each other; primarily connects the paleopallium on each side (olfactory bulbs, olfactory peduncles, piriform lobes and amygdaloid bodies)
Ruffini corpuscles
Thermoreceptors located in the skin
s
Sagittal
Vertical plane passing through the midline of a standing patient
Schizencephaly
Congenital defect characterized by abnormal clefts extending from the cerebral cortex to the underlying ventricle
Schmorl node
A defect in the vertebral endplate thought to be due to protrusion or extrusion of cartilaginous disc material into the adjacent vertebral body
Schwann cell
Glial cell that forms the myelin in the peripheral nervous system
Sella turcica
Saddle-like prominence on the dorsal surface of the sphenoid bone that contains the pituitary gland
Sharp wave
Transient EEG wave that appears as a positive deflection with a pointed peak lasting 70-200 milliseconds
Single fiber electromyography
An electrodiagnostic test in which the action potentials are recorded from a single muscle fiber following stimulation of the motor nerve; normal muscle fibers have action potentials with little variability in latency; patients with myasthenia gravis have increased variability in onset of action potential leading to jitter
Somatosensory evoked potentials
An electrodiagnostic test in which a series of electrical waves generated by neural structures along the somatosensory pathways are recorded following electrical stimulation of a peripheral nerve
Spike
EEG pattern consisting of a pointed peak lasting less than 70 milliseconds; correlated with epilepsy
Spina bifida
Congenital malformation in which the vertebral arches fail to close; can allow herniation of the meninges and/or spinal cord through the incompletely closed vertebral arches
Spinal shock
Temporary loss or reduction of spinal reflex activity caudal to a physiological or anatomical transection of the spinal cord
Spongiform encephalopathy
Neurodegenerative disorders characterized by vacuolation (spongy appearance); e.g., feline spongiform encephalopathy
Status epilepticus
Continuous seizure activity longer than 30 minutes or two or more seizures without full recovery of consciousness between seizures
Stereotypy
Repetitive stereotyped movements
Strabismus
Misalignment of the eyes
Stupor
Condition of unresponsiveness in which the patient can only be aroused by a noxious stimulus
Subacute
Developing over days to weeks
Subarachnoid space
Space between the pia and arachnoid mater that contains cerebrospinal fluid
Subcortical
Structures located immediately below the cerebral cortex, including the corona radiata, internal capsule, basal ganglia and thalamus
Subdural
A potential space between the dura and arachnoid mater; in health, the arachnoid mater is held against the dura by cerebrospinal fluid in the subarachnoid space
Subdural hematoma
Hemorrhage into the subdural space between the dura and arachnoid mater
Substantia gelatinosa
Region of grey matter that caps the apex of the dorsal horn throughout the length of the spinal cord
Sulcus
Groove between two gyri
Suprasellar
Structures located above the sella turcica
Suture
Junction between two bones of the skull
Symptomatic epilepsy
Epilepsy due to an identifiable cause, such as a brain tumor or encephalitis
Syncope
Transient loss of consciousness due to lack of blood flow to the brain, often the result of a cardiac arrhythmia
Syringobulbia
Fluid-filled cavity within the brainstem; may occur as an extension of syringomyelia
Syringomyelia
Central cavitation / fluid-filled structure within the spinal cord parenchyma
t
Tectum
Dorsal aspect of the midbrain containing the rostral and caudal colliculi
Tegmentum
Ventral aspect of the midbrain
Telencephalon
Rostral portion of the prosencephalon consisting of the cerebral hemispheres
Tentorium cerebelli
Fold of dura mater separating the occipital lobes and cerebellum
Tetany
Sustained muscular contraction
Tetraparesis
Weakness in all four limbs
Tetraplegia
Paralysis of all four limbs
Thalamus
Large gray matter structure of the diencephalon that functions as a major relay station between the cerebrum and the brainstem and spinal cord
Titubation
Tremor of the head and neck
Tolerance
Gradual loss of response to a drug (e.g., oral diazepam) with chronic use
Tonic-clonic seizure
Generalized seizure characterized by initial extension of the limbs (tonic phase) followed by rhythmic muscle contractions (clonic phase); a.k.a., grand mal seizure
Tonic seizure
Generalized seizure characterized by stiffening of the entire body
Tonsillar herniation
Herniation of the cerebellar tonsils into the foramen magnum
Torticollis
A form of dystonia characterized by head turn due to involuntary neck muscle contraction
Transient ischemic attack
Transient neurological signs associated with a sudden reduction of blood flow to a particular region of the brain; signs last < 24 hrs; a.k.a., “mini stroke”
Transtentorial herniation
Displacement of cerebral tissue (usually temporal or occipital lobe) under the tentorium cerebelli with compression of the brainstem (midbrain
Transverse myelitis
Inflammatory disorder affecting both sides of the spinal cord causing both motor and sensory deficits
Tremor
Involuntary, rhythmic, alternating contraction of agonist and antagonist muscles
Trismus
Reduced opening of the jaw due to tonic spasm of the masticatory muscles; most often the result of tetanus
u
Upper motor neurons
First order neurons that originate in the brain and synapse on interneurons or lower motor neurons of the brainstem and spinal cord
v
Ventral
Toward the bottom surface of a standing patient
Ventral horn
Ventral portion of spinal cord gray matter containing motor neurons
Ventricles
Four cerebrospinal fluid-filled cavities within the brain; consists of paired lateral ventricles, third ventricle, and fourth ventricle
Ventriculitis
Inflammation of the ventricles in the brain
Vermis
Median region of the cerebellum
Vertigo
A subjective sense that the external world is moving or spinning
Virchow-Robin space
A perivascular space between an artery and vein and the pia mater
w
Wallerian degeneration
Axonal and myelin degeneration that occurs distal to a site of injury
Watershed infarct
An infarct that occurs in “border zones” of the brain that receive blood supply from two major arteries; requires inadequate blood flow from both arteries, most often the result of global hypoperfusion
White matter
The part of the central nervous system containing axons
x
Xanthochromia
Yellowish discoloration of the cerebrospinal fluid resulting from lysis of red blood cells following subacute to chronic subarachnoid hemorrhage
Xeromycteria
Extreme dryness of the nasal passage, usually due to denervation of the lateral nasal gland, which is responsible for most of the moisture in the nose. The gland is innervated by parasympathetic fibers of the facial nerve.
Xerostomia
Dry mouth due to decreased salivary secretion
