Neurology glossary

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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.

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

To move toward the sagittal midline

Proceeding from the periphery toward the central nervous system

A condition in which the patient experiences pain to a stimulus that would normally be non-painful

Loss of pain sensation

CNS malformation with absence of the forebrain, resulting from failure of closure of the cephalic end of the neural tube during development

Absence of sweating

Inequality in pupil diameter

Loss of sense of smell

Complete loss of voice

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

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

Incoordination; typically a sensory phenomenon. There are three types of ataxia: general proprioceptive, vestibular, and cerebellar.

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

A disorder characterized by degeneration of the axon


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.

Repetitive involuntary blinking of the eyelids

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

Point on dorsal midline where the left and right frontoparietal sutures (junction between frontal and parietal bones) intersect the sagittal suture

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


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

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”

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

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

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

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”)

Involuntary, rhythmic muscular contractions and relaxations that are often elicited by a reflex

Mental status characterized by being unresponsive to noxious stimuli

Complex partial seizure
Partial seizure with impaired consciousness or awareness

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

A contusion resulting from the brain hitting the skull on the side opposite the impact

Permanent shortening of muscles and tendons

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

Axons projecting from the cerebrum to lower motor neurons in the brainstem

Traumatic brain injury (contusion) occurring at the site of impact with an object

Surgical removal of a bone flap to access the brain; bone flap not replaced at the end of surgery

Surgical repair of a defect or deformity of the skull, for example following removal of multilobular tumor of bone

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

A condition in which a distinct lesion or pathogenesis is presumed, but has not been proven

Rotation of the eye around an dorsal-ventral axis; see also excyclotorsion, incyclotorsio


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

To cross over

Abnormal mental status characterized by confusion, disorientation, fear, irritability, inattention and varying degree of consciousness

Sustained, acquired loss of memory and other intellectual capacities that impairs daily functioning

Loss or destruction of the myelin sheath surrounding the axon; results in slowed nerve conduction

Receiving portion of the neuron

Loss of nerve supply

Cutaneous distribution of sensory innervation on the skin

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

Rare malformation characterized by longitudinal splitting of the spinal cord by a septum

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

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

Pain or discomfort from a stimulus (e.g., touch) that is normally non-painful

Distorted perception of taste

Broad category of movement disorders characterized by excessive motor activity

Impaired rate and range of motion; tendency to overshoot or undershoot the target

Decreased myelination due to biochemically abnormal myelin

Difficulty swallowing

Abnormal voice, often due to laryngeal muscle weakness such as that due to laryngeal paralysis, hypothryoidism, myasthenia gravis, etc.

Incomplete closure of a raphe; in neurology it is due to to neural tube closure defect

Involuntary muscle spasms causing abnormal posture or body movements


Edinger-Westphal nucleus
A nucleus of the oculomotor nerve (III) supplying pre-ganglionic parasympathetic fibers for pupillary constriction and lens accommodation

Motor pathways extending from the CNS to the periphery

Recording of electrical potentials arising from the cerebral cortex at the skin of the head

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.

Inflammation or infection of the brain

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

Any disorder of the brain

Innermost layer of connective tissue around each individual muscle fiber

Retraction of the eyeball back into the orbit

Epithelial lining of the ventricles of the brain and central canal of the spinal cord

Primary CNS tumor arising from the ependymal cells of the ventricles or central canal

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

Rotation the eyeball such that the dorsal pole rotates outward (laterally)

Protrusion of the eyeball

Lesion external to the brain (i.e., not in the brain parenchyma)

Lesion outside the tissue of interest (i.e., outside the brain or spinal cord)

Motor fibers from the brain that do not pass through the pyramids


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

Bundle of muscle (muscle fascicle) or nerve (nerve fascicle) surrounded by a layer of connective tissue (perimysium or perineurium)

Spontaneous axonal firing resulting in visible twitching of the muscle innervated; usually indicative of of deneration

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

Small lobe of the cerebellum; involved in vestibular function

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

Portion of the CNS arising from the prosencephalon containing the cerebral hemispheres and diencephalon

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

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


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

Collection of nerve cell bodies

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.)

Knee-like bend in the rostral end of the corpus callosum

Supporting cells of the nervous system, including astrocytes, oligodendrocytes, microglia and ependymal cells

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.

A convoluted ridge on the outer surface of the cerebrum caused by infolding of the cerebral cortex and surrounded by sulci


Loss of sensation on one half of the body

Decreased attention or awareness of one side of space, usually contralateral to a forebrain lesion

Weakness on one side of the body

Paralysis on one side of the body

Hippocampal commissure
Transverse fibers connecting the right and left hippocampus to each other

A C-shaped structure on the medial edge of the cerebral hemisphere; part of the limbic systemic involved in long-term memory and emotion

Spasmodic or rhythmic dilation and constriction of the pupil

Congenital defect in which most of the cerebral hemispheres are replaced by sacs filled with cerebrospinal fluid

Increased size of ventricles and amount of cerebrospinal fluid in the brain

Abnormally increased sensitivity to sound

Hypertrophy of bone

Excessive response to a painful stimulus

Increased muscle tone

Hypnagogic myoclonus
Shock-like muscle twitch that occurs when falling asleep or drowsy

Underdevelopment of an organ or tissue due to an abnormal deficiency of cells or structural elements

Reduced muscle tone


Sudden attack, stroke, or seizure; in epileptology, it is the actual seizure in which chaotic electrical activity is present

Disorder without a known cause

Cyclotorsion (rotation) of the eye such that the dorsal pole rotates inward (medially)

Tissue damage or cellular death due to prolonged or severe ischemia or hemorrhage

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

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

Space between the pia and arachnoid mater that contains cerebrospinal fluid

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)

Located on the same side of the body


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

Measure of variability of potentials recorded from individual muscle fibers as by single fiber electromyography; increased variability occurs with myasthenia gravis


Ketogenic diet
Diet that is high fat and low carbohydrate that is sometimes used to control seizures in specific types of epilepsy in humans

Process in which repeated subconvulsive stimulation, either electrically or chemically, permanently lowers the seizure threshold


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

Combination of the pia and arachnoid mater

Group of white matter disorders characterized by white matter degeneration or abnormal growth/development of myelin

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

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


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)

Primitive neuroepithelial tumor that often arises from the cerebellum

Three connective tissue membranes surrounding the brain and spina cord, including the pia, arachnoid and dura mater

Tumor arising from the meninges

Inflammation or infection of the meninges

A form of spina bifida characterized by herniation of meninges through a defect in the dorsal arches

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


Bone marrow-derived phagocytic glial cell involved in the immune response in the CNS

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)

Pupillary dilation

Medulla oblongata

Insulating sheath surrounding axons that speed nerve conduction velocity; made by oligodendrocytes in the CNS and Schwann cells in the PNS

Inflammation or infection of the spinal cord

Radiographic procedure in which contrast agent is injected into the subarachnoid space, thereby highlighting the edges of the spinal cord on post-injection radiographs

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

A disorder of the spinal cord

Sudden, shock-like contraction of muscle groups

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

A disorder of the muscles

A muscle disorder characterized by abnormally prolonged muscle contraction due to delayed relaxation

Literally means “mucus swelling;” a disorder characterized by swelling of the dermis from excessive deposition of mucopolysaccharides, most often with severe hypothyroidism


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.

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

A disease of nerves

Chemical released from a nerve terminal that passes across the synapse to stimulate another neuron, muscle or effector organ

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

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.

A collection of neuronal cell bodies

Nucleus pulposus
Central core of the intervertebral disc with a gelatinous consistency; a remnant of the embryonic notochord

Involuntary, rhythmic oscillation of the eyeballs


Mild to moderate reduction in alertness

A type of glial cell that is responsible for synthesis and maintenance of CNS myelin

Primary CNS tumor originating from oligodendrocytes

Opening pressure
Pressure obtained upon entering the subarachnoid space when performing a CSF tap

Paralysis of one or more extraocular muscles responsible for eyeball movement

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

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


Pacinian corpuscle
The largest skin receptor located in the dermis that is responsive for the sensation of vibration and deep pressure

Paralysis of a muscle group

Absence of motor function in a body part

Weakness in the pelvic limbs

Complete absence of voluntary movement in the hind limbs

Sagittal section that is lateral of midline

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

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

Connective tissue sheath surrounding muscle fascicles

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

Abnormal intolerance to sound

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

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

Gas (air) within the vertebral canal

Disorder characterized by inflammation or infection of multiple muscles

Inflammation of multiple nerve roots

The portion of the brainstem located between the midbrain and medulla

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

Physical act of grasping, seizing, or picking up food

An infectious protein agent responsible for spongiform encephalopathies (e.g., feline spongiform encephalopathy, bovine spongiform encephalopathy, Scrapie)

The most rostral portion of the brain consisting of the cerebrum and diencephalon

An exaggerated reflex due to decreased tone in the antagonistic muscles

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

A subdivision of the motor system consisting of the descending tracts that pass through the pyramids, such as the corticospinal tract


Quadrigeminal bodies
Two pairs of elevations on the dorsal surface of the midbrain, consisting of the rostral and caudal colliculi


Inflammation or infection of spinal nerve roots

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

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

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


Vertical plane passing through the midline of a standing patient

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

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

Repetitive stereotyped movements

Misalignment of the eyes

Condition of unresponsiveness in which the patient can only be aroused by a noxious stimulus

Developing over days to weeks

Subarachnoid space
Space between the pia and arachnoid mater that contains cerebrospinal fluid

Structures located immediately below the cerebral cortex, including the corona radiata, internal capsule, basal ganglia and thalamus

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

Groove between two gyri

Structures located above the sella turcica

Junction between two bones of the skull

Symptomatic epilepsy
Epilepsy due to an identifiable cause, such as a brain tumor or encephalitis

Transient loss of consciousness due to lack of blood flow to the brain, often the result of a cardiac arrhythmia

Fluid-filled cavity within the brainstem; may occur as an extension of syringomyelia

Central cavitation / fluid-filled structure within the spinal cord parenchyma


Dorsal aspect of the midbrain containing the rostral and caudal colliculi

Ventral aspect of the midbrain

Rostral portion of the prosencephalon consisting of the cerebral hemispheres

Tentorium cerebelli
Fold of dura mater separating the occipital lobes and cerebellum

Sustained muscular contraction

Weakness in all four limbs

Paralysis of all four limbs

Large gray matter structure of the diencephalon that functions as a major relay station between the cerebrum and the brainstem and spinal cord

Tremor of the head and neck

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

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

Involuntary, rhythmic, alternating contraction of agonist and antagonist muscles

Reduced opening of the jaw due to tonic spasm of the masticatory muscles; most often the result of tetanus


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


Toward the bottom surface of a standing patient

Ventral horn
Ventral portion of spinal cord gray matter containing motor neurons

Four cerebrospinal fluid-filled cavities within the brain; consists of paired lateral ventricles, third ventricle, and fourth ventricle

Inflammation of the ventricles in the brain

Median region of the cerebellum

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


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


Yellowish discoloration of the cerebrospinal fluid resulting from lysis of red blood cells following subacute to chronic subarachnoid hemorrhage

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.

Dry mouth due to decreased salivary secretion