Neuro/Sp_senses Flashcards
Damage to which cranial nerve causes MEDIAL strabismus?
CN VI
What are the 4 physiologic compartments of the cranial space?
Blood, CSF, intracellular fluid, extracellular fluid
Where is most CSF formed and where is it drained?
Formed by ultrafiltration from blood vessels of the choroid plexus lining the ventricles
Drains into the subarachnoid space, where it is absorbed
What forms the motor unit?
Lower motor neurons, neuromuscular junction, skeletal muscle fibers
What is the most common cranial nerve to be affected by a nerve sheath tumor?
The trigeminal nerve
What is neuropraxia?
The loss of nerve conduction without structural changes. Can occur from transient loss of blood supply and usually resolves over weeks to months.
What is axonotmesis?
Axonal damage without loss of supporting structures. It requires regeneration of the axons toward its specific muscle target before functional recovery.
How quickly does axonal regeneration occur?
1 mm per day
What is neurotmesis?
The complete severance of the nerve. This is typically seen with severe trauma.
How do patients with toxoplasmosis or neospora typically present?
They initially have flaccid paraparesis that may progress to a chronic state of extreme extensor tone. Once hind limb rigidity has developed, clinical improvement no longer occurs.
List 3 drugs that may result in neuropathies
Vincristine, thallium, organophosphates
How is masticatory myositis confirmed?
Either by muscle biopsy or through serum titers for antibodies against type IIM muscle fibers
Which breeds of dogs are over-represented in cases of acquired myasthenia gravis?
German shepherds, Labs, Akitas
What is the difference between localized, generalized, and fulminant myasthenia gravis?
Localized: Typically show facial, laryngeal, or pharyngeal dysfunction without appendicular muscle involvement
Generalized: Appendicular muscle weakness with out without signs of facial, pharyngeal, or laryngeal dysfunction
Fulminant: Sudden, rapid, progression of severe appendicular muscle weakness resulting in recumbency, frequent regurgitation, and facial, pharyngeal, and laryngeal dysfunction
In what percent of dogs with acquired myasthenia gravis will detectable levels of antibodies to acetylcholine receptors be found?
80-90%
In what percentage of dogs with myasthenia gravis will the disease be related to a thymoma?
15%
How long will it take to see complete resolution of signs in a dog with botulism?
2 to 3 weeks
How long after attachment of a tick will signs of tick paralysis be seen? And how quickly will signs resolve after the tick is removed?
3 to 5 days after attachment, signs will resolve within 24-72 hours after the tick is removed.
What nerves can be safely biopsied to diagnose a neuropathy?
Fascicular biopsies of the ulnar or peroneal nerves
What makes up a lower motor neuron?
Cell bodies found in the brainstem or spinal cord, and their motor axons within the cranial or spinal nerves respectively. They terminate on skeletal muscle fibers at the neuromuscular junction.
Equation for cerebral perfusion pressure?
CPP=MAP-ICP
What types of factors affect the volume of the blood in the brain?
Altered vascular tone or blood viscosity, impaired venous outflow (head-down posture, jugular vein compression, increased intrathoracic pressure)
What is the normal ICP int he dog?
5-12 mm hg
T/F: The upper limit of ICP in which tx for ICH should be instituted has not been defined in dogs, but is 20 mm Hg in humans
True
Name the three primary homeostatic mechanisms responsible for maintaining ICP in normal range
- Volume buffering
- Autoregulation
- Cushing’s response
Describe volume buffering and how it controls ICP
Monro-Kellie Doctrine: Increase in the volume of one component requires a compensatory decrease in one or more of the others if ICP is to remain unchanged
Describe autoregulatory mechanisms that control ICP
Pressure regulation: Prevents underperfusion or overperfusion of the brain; operates at perfusion pressures between 50-150 mm Hg; outside this range the CBF is linear with MAP
Chemical regulation: cerebral vascular resistance is influenced by PaCO2, PaO2, and cerebral metabolic rate of O2 consumption
T/F: Decrease in PaO2 causes vasodilation, causing increased CBF
True
T/F: Increased PaCO2 causes vasoconstriction
False- CO2 combines with water to form hydrogen ions, which stimulates cerebral vasodilation
Two broad categories of causes of ICH?
Vascular (cerebral vasodilation from increased PaCO2, loss of vascular tone, venous outflow obstruction), non-vascular (increased brain water, masses, obstruction of CSF outflow)
Name and describe the states of consciousness
Normal- Normal demeanor and interaction with its environment
Obtunded- Decreased responsiveness or alertness, graded as mild/moderate/severe
Stupor/semicoma- Responds only to vigorous or painful stimuli
Coma- Patient does not respond consciously to any stimuli; cranial nerve reflexes may be present
Abnormalities in mentation indicate dysfunction in one of two which neuroanatomical locations?
Cerebrum
Reticular activating syndrome
What role does the RAS play in mentation?
distinct nuclei in the brainstem that function to activate the cerebral cortex and maintain consciousness; the most important ones are located in the midbrain, rostral pons, and thalamus
What are the main functions of the cerebrum?
Integration of sensory information, planning of motor activity, appropriate responses to information, emotion, memory
Name some common metabolic diseases that may cause altered mentation
hypoxia, ischemia, hypoglycemia, hepatic disease, renal failure, endocrine dysfunction, sepsis, hyperbilirubinemia, hyperthermia/hypothermia, pain, CNS disease, electrolyte or acid-base disturbances
Name some common drugs that may cause altered mentation
anticonvulsants, benzodiazepines, opiates, anesthetic drugs, atropine, abx, steroids, h2 receptor blockers, cardiac glycosides, antihypertensives, illicit drugs
Name structural lesions that cause altered mentation
neoplasia, infection, inflammation, trauma, vascular lesions, hydrocephalus, brain herniation
What are the 5 variables that evaluated in a patient with an altered mentation?
Level of consciousness Motor activity Respiratory patterns Pupil size and reactivity Oculocephalic movements
Name and describe 4 types of breathing patterns and their associated intracranial lesions
- Cheyne-Stokes: hyperpnea alternating with periods of apnea; diffuse cerebral or hypothalamic disease, metabolic encephalopathy
- Central neurogenic hyperventilation: persistent hyperventilation, may result in respiratory alkalosis; midbrain lesions
- Apneusis: paused breathing at full inspiration; pontine lesion
- Irregular/ataxic breathing: Irregular frequency and depth that proceeds apnea; lower pons/medulla lesion
Name and describe the pupillary abnormalities and lesion localizations
- Unilateral mydriatic/unresponsive pupil: ipsilateral midbrain or CN III; increased ICP and unilateral cerebral herniation
- Bilateral miosis: metabolic encephalopathies, diffuse midbrain compression; may precede mydriatic/unresponsive pupils
- Bilateral/mydriatic/unresponsive: bilateral compression of midbrain or CN III; grave prognosis
Loss of oculocephalic reflex may indicate a lesion where?
Pons, midbrain (CN III, IV, VI)
If there is a lesion of CN III, IV, or VI innervating the extraocular eye muscles, you will get a loss of the oculocephalic reflex but should also see what?
persistent, nonpositional strabismus in the affected eye
T/F decerebrate rigidity occurs with lesions of the rostral pons and midbrain
True
T/F decerebellate rigidity may manifest as extensor rigidity of all four limbs?
False- that describes decerebrate rigidity
T/F decerebellate rigidity may manifest as extensor rigidity of the thoracic limbs and extension or flexion of the pelvic limbs
True
What are the three categories of the Modified Glasgow Coma Scale?
- Level of consciousness
- Motor activity
- Brainstem reflexes
True or False: The level of consciousness is the most reliable empiric measure of impaired cerebral function after head injury
True
True or False: Pupils that respond to light, even if miotic, indicate adequate function of the rostral brainstem, optic chiasm, optic nerves, and retinas.
True
Injury to the cervical sympathetic pathway results in what findings in the ipsilateral pupil?
Constricted and fixed or sluggish to direct and contralateral light but normal consensual constriction in contralateral pupil.
May also see ptosis.
Injury to the oculomotor nerve results in what findings in the ipsilateral pupil?
Dilated and fixed to direct light
No consensual constriction from contralateral light but normal consensual constriction in contralateral pupil.
May also see ptosis and ventrolateral strabismus
Injury to the optic nerve results in what findings in the ipsilateral pupil?
Fixed to direct light
Absent consensual constriction in contralateral pupil
Normal consensual constriction from contralateral light
May also see spontaneous fluctuations in pupil size
Injury to the oculomotor and optic nerve results in what findings in the ipsilateral pupil?
Dilated and fixed to direct light
No consensual constriction from contralateral light and no consensual constriction in contralateral pupil
May also see ptosis and ventrolateral strabismus
Injury to the iris or ciliary body results in what findings in the ipsilateral pupil?
Dilated and fixed to direct light
No consensual constriction from contralateral light but normal consensual constriction in contralateral pupil
May also see signs of orbital injury, no strabisumus
What is the oculovestibular reflex?
It is eye movement with irrigation of external auditory ear canal with ice cold water.
When it is absent it is indicative of profound brain-stem failure and is an accepted criterion of brain death in humans.
What is the FOUR score?
It is the Full Outline of Unresponsiveness. It is a new coma scale in human medicine based on the bare minimum of tests necessary for assessing a patient with altered consciousness. It has four components: eye responses, motor responses, brainstem reflexes, and respiratory pattern.
Hepatic encephalopathy occurs most commonly because of what disease in dogs?
PSS
What are less common diseases (other than PSS) that can cause hepatic encephalopathy?
microvascular dysplasia, congenital urea cycle deficiencies, portal hypertension from chronic liver disease, hepatic lipidosis (most common in cats)
Which of the following is associated with HE? A. CSF amino acid alterations B. glutamate neurotoxicity C. generation of reactive oxygen species D. mitochondrial permeability transition E. All of the above
E
Where is ammonia produced?
In the intestines as the end product of amino acid, purine and amine breakdown by bacteria, metabolism of glutamine by enterocytes, and breakdown of urea by bacterial urease
In the normal liver, what is ammonia converted into?
urea or glutamine
T/F: The permeability of the BBB increases during hepatic encephalopathy
T
What are the proposed mechanisms of decreased excitatory neurotransmission in HE?
down-regulation of NMDA receptors, blockage of Cl extrusion from the postsynaptic neuron
T/F the brain has a urea cycle
False- ammonia in the CNS is removed by transamination of glutamate into glutamine in astrocytes
How do glutamate and ammonia potentially cause neurotoxicity and seizures in HE?
Partly because of free radical formation secondary to overstimulation of NMDA receptors by ammonia and glutamate
What is the most important inhibitory neurotransmitter in the CNS?
GABA (gamma-aminobutyric acid)