Deck 3 Flashcards
1
Q
What is the anatomic spatial relationship between the origin of CN VII and VIII as they emerge from the medulla?
A
CN VII is ventral to CN VIII
2
Q
Where does the facial nerve emerge from the skull? What is the name for the part of the facial nerve that wraps around the nucleus abducens?
A
Stylomastoid foramen
Genu of the facial nerve
3
Q
How can you tell that this horse only has facial paralysis affecting the buccal branches and not anything more proximal?
A
The normal ear position and normal eyelash position
4
Q
If you have concurrent facial paralysis and neurogenic dry eye, where along the facial nerve is the lesion?
A
Needs to be at or proximal to the emergence of the major petrosal nerve in the middle ear. It canNOT be distal to the stylomastoid foramen.
5
Q
What is this equine radiograph illustrating?
A
Temporohyoid osteopathy
6
Q
What is the most common cause of facial tetany? How can you distinguish it from facial contracture?
A
Otitis media
If it resolves under anesthesia, then it is probably facial tetanus. Additionally if you perform a facial nerve block and it resolves, then it is also facial tetanus.
7
Q
What is the only intrinsic thyroid muscle NOT supplied by the recurrent laryngeal nerve?
What nerve innervates this muscle?
What cranial nerve forms the neurons going into the recurrent laryngeal nerve?
A
Cricothyroid — innervated by the cranial laryngeal nerve, a branch of vagus
Internal branch of the accessory nerve, which joins the vagus nerve as it runs through the jugular foramen
8
Q
What are the two most common clinical signs associated with guttural pouch mycosis?
A
Dysphagia (involvement of CNN IX and X) and epistaxis (involvement of internal carotid artery)
9
Q
What is the presumed cause of equine laryngeal hemiplegia? Which side is more affected and why?
A
Presumably related to a “dying-back” neuropathy. It affects the left side more because the recurrent laryngeal nerve is longer on the left as it has to travel around the aorta / ligamentum arteriosum.
10
Q
If the space on the right is the guttural pouch, what are the other structures in this picture?
A
Left - internal carotid artery
Middle - CNN IX and X
11
Q
What is the most common way to cause iatrogenic laryngeal paralysis?
A
Aggressive jugular venipuncture and damage to the vagus nerve (containing the CN XI GSE fibers going to the larynx) — this is only recognized clinically if it is damaged bilaterally.
12
Q
Where does the hypoglossal nerve emerge from the brainstem?
A
Just lateral to the pyramids as a series of rootlets
13
Q
What are the two most common causes of unilateral tongue atrophy in large animals?
A
Listeriosis in cattle, and sarcocystis neurona in horses
14
Q
Disruption of these tracts can cause CNN deficits with acute prosencephalic disease? What is the most frequent CN deficit seen when this occurs?
A
Corticonuclear (supplying the brainstem GSE motor nuclei)
Dysphagia, particularly in LA
15
Q
Describe the pathogenesis of equine herpesvirus-1
A
Results in a vasculitis of small blood vessels within the CNS, causing either ischemic or hemorrhagic infarction, resulting in signs typically reflective of a TL myelopathy in horses. Signs are usually acute and non-progressive, as would be expected with a vascular disease.
16
Q
Where is the “primary integrating center” of the autonomic nervous system?
What part of it primarily influences parasympathetic and sympathetic, respectively?
What are the three sources of afferents going to this center?
A
Hypothalamus
Rostral portion — parasympathetic
Caudal portion — sympathetic
Cerebrum, thalamic nuclei, and ascending GVA pathways
17
Q
Broadly speaking, what two things control pupillary size?
A
Amount of light entering pupil (parasympathetic) and patient emotional status (sympathetic)
18
Q
What anatomic location are germ cell neoplasms located in? Breed predilection?
A
Middle cranial fossa
Dobermans
19
Q
What two structures enter the tympano-occipital fissure but NOT the jugular foramen?
A
Internal carotid artery and the (post)ganglion sympathetic fibers from the cranial cervical ganglion
20
Q
What muscles are being innervated by the sympathetics that result in ptosis, enophthalmos and third eyelid elevation when there is Horner syndrome?
A
There is periorbital smooth muscle located in the orbit, that has the functions of keeping the eye more forward and holding the upper lower and third eyelids back.
21
Q
Does this dog have parasympathetic or sympathetic dysfunction to the left side? What would the opposite look like?
A
Sympathetic — results in vasodilation to the nasal mucosa, which in turn results in poor airflow AND increased nasal secretions. Result = nasal crusts
If it was parasympathetic dysfunction, you would get nasal plenum hyperkeratosis due to loss of lateral nasal gland function.
22
Q
What is an additional, tell-tale sign of Horner syndrome / sympathetic dysfunction in horses?
A
Sweating in the distribution of the sympathetic dysfunction
23
Q
Decreased eyelash angle in horses can be caused by what three different neuroanatomic localizations
A
- CN VII
- CN III
- Horner
24
Q
What is the main location where the sympathetics to the head can be affected, resulting in Horner without any other apparent neurologic deficits?
What sinister disease process can cause such signs?
A
Within the carotid sheath as a part of the vagosympathetic trunk.
Thyroid mass
25
What supplies the sympathetic innervation to the neck? What is the ganglion in which these ganglionic fibers originate?
The vertebral nerve (running with vertebral artery) (1)
Cervicothoracic ganglion (4)
26
Describe the PLR pathway
27
List 7 causes for mydriasis
List 3 causes for miosis
Mydriasis:
1. GVE oculomotor palsy
2. Optic nerve/ retinal disease
3. Iris atrophy
4. Application of atropine
5. Ingestion of belladonna alkaloids
6. Glaucoma
7. Unilateral cerebellar lesions (can be ipsilateral or contralateral)
Miosis:
1. Horner
2. Iritis
3. Keratitis / uveitis (any cause of ocular pain) and activation of the oculopupillary reflex
28
Offer a reason why benzodiazepines may result in bilateral miosis.
Benzodiazepines cause CNS inhibition, particularly of cerebral neurons. If we inhibit cerebral UMNs, maybe this will cause UMN disinhibition to the GSE oculomotor nuclei, resulting in miosis.
29
Why do we see miosis prior to mydriasis in head trauma cases?
Studies have shown that miosis occurs when mild compression / damage occurs to the midbrain, but as this progresses (ie continued hemorrhage / herniation), the GSE motor nuclei / nerves themselves become too damaged and then you get bilateral LMN signs (aka mydriasis).
30
Where are the cell bodies located for the:
- sympathetic neurons supplying the bladder
- parasympathetic neurons supplying the bladder
Sympathetic: lateral grey horn of L1-5
Parasympathetic: lateral grey horn of S1-3
31
What two branches of CN VII involve parasympathetic function, what ganglia to synapse on, and what do they innervate?
- Major petrosal nerve: joins with the deep petrosal nerve (symp) to form nerve of petrosal canal; then synapses in pterygopalatine ganglion. From here, ganglionic fibers travel with the trigeminal nerve to innervate lacrimal gland, palatine gland, nasal glands, and third eyelid gland
- Chorda tympani: runs through the tympanic cavity and joins lingual nerve (branch of mandibular). Synapses after this in sublingual and mandibular ganglia, immediately adjacent to respective salivary glands.
32
Describe the innervation of the salivary glands
What is the clinical significance of these pathways?
Mandibular / sublingual — parasympathetic pre-ganglionics travel from facial nerve into chorda tympani, then into lingual nerve, and then synapse into mandibular and sublingual ganglia, and then ganglionics go into the salivary glands
Zygomatic / parotid — parasympathetic pre-ganglionics travel from glossopharyngeal nerve into tympanic nerve (in the tympanic cavity), then into minor petrosal nerve into the otic ganglion (near oval foramen); from here, ganglionics travel with mandibular nerve and innervate their glands
Idiopathic trigeminal neuritis often results in the accumulation of thick, ropey saliva in the oral cavity. Tartar can also build up due to challenge in saliva characteristics.
33
What is this dog’s diagnosis? How can you tell? What are some classic clinical signs?
Dysautonomia
Pupillary dilation, nasal crusting
Dysphagia, vomiting, regurgitation, poor anal tone, bradycardia, dry eye etc…
34
Fill in the blanks
35
What two gyri are involved in / possess the motor cortex in dogs? What is the name of the motor system originating here?
Rostral suprasylvian (2) and post-cruciate (1)
Pyramidal motor system
36
What percentage of pyramidal neurons cross in the decussation? Where does this decussation occur?
What do these decussed axons form in the SC? Non-decussed?
~75%
- caudal medulla
- Lateral corticospinal tract
- Ventral corticospinal tract
37
What are the name of the axons of pyramidal neurons that terminate on cranial nerve nuclei?
Corticonuclear
38
What cortical lamina is the pyramidal layer? What is the clinical significance of this?
The third layer; the pyramidal neurons are often affected first in cases of hypoxia / metabolic stress, and thus, this layer is the one frequently affected in laminar cortical necrosis.
39
True or false: there are extra-pyramidal neurons in the cerebral cortex
True - they project to basal nuclei or brainstem nuclei
40
What two structures form the lentiform nuclei? What is medial and what is lateral to this nuclei?
Pallidum (medial) and putamen (lateral)
The internal capsule is medial and the external capsule is lateral
41
Where is the claustrum located?
Between the external capsule medially and the extreme capsule laterally
42
What type of neurotransmitter does the substantia nigra produce? Where does the substantia nigra project to?
Dopamine
Projects to caudate nucleus
43
What are the two extrapyramidal nuclei located in the midbrain?
Which one of these produces a tract that goes into the spinal cord? Where in the spinal cord is this tract located?
Red nucleus
Substantia nigra
The red nucleus produces the rubrospinal tract, which is located in the lateral funiculus, immediately adjacent to the lateral corticospinal tract.
44
45
Where do the neurons in the rubrospinal tract decussate? What is the function of the rubrospinal tract?
Almost immediately within the midbrain near the red nucleus
Synapses on the LMN cell bodies in the ventral grey horn, and facilitates the limb flexor muscles (which helps with gait initiation).
46
What are the two reticular formation extrapyramidal tracts? What are their functions and locations? Who controls them?
Pontine and medullary reticulospinal tracts
Pontine — facilitates limb extensors, ipsilateral ventral funiculus
Medullary — inhibits limb extensors, ipsilateral lateral funiculus
Neurons in the contralateral cerebral cortex form a corticoreticular tract to control these UMNs
47
From where does the olivary nuclei receive input?
To where does the olivary nuclei primarily project?
Various telencephalic, diencephalic and mesencephalic nuclei (specifically, lentiform nuclei, zona incerta and red nuclei)
Contralateral cerebellum
48
Describe the gamma loop. What are the two correlates that are independent of the gamma motor neurons?
Neuromuscular spindles are within the muscle. They are dually innervated with gamma motor neurons and 1a afferent neurons (also termed annulospiral).
Activation of the gamma motor neuron by UMN systems causes the neuromuscular spindle to stretch and activate the 1a afferent neurons.
These afferent neurons directly synapse on alpha motor neurons in the ventral horn, stimulating their activity.
This then causes those muscles to contract, creating muscle tone.
Independent of the gamma motor neurons, the stretch of gravity can cause activation of this pathway via passive stretching of the neuromuscular spindle. Passive stretching of the neuromuscular spindle also occurs when eliciting a patellar reflex in a similar manner.
49
Why is alpha-gamma co-activation important?
Co-activation allows the neuromuscular spindles to maintain enough tension to detect change in the muscle length, and in doing so, having the neuromuscular spindle be able to constantly send information regarding such changes upstream to higher processing centers so that movement / motion can be coordinated effectively.
50
Explain the golgi tendon reflex. What is a clinical situation in which this reflex is recognized?
Golgi tendon organs are located in tendons and are supplied by 1b sensory neurons. They detect the amount of tension in the tendons. Once this tension exceeds a certain level, the 1b neurons send inhibitory signals to the alpha motor neurons of the contracting muscle AND facilitatory signals to the antagonist muscles.
Clinical apparent in the “clasp knife reflex” when a hypertonic limb abruptly flexes after pressure is applied to it.
51
Spinal walking is dependent on this group of interneurons?
Central pattern generators
52
What are the two divisions of locomotion?
What groups of muscles are active during each phase?
Postural and protraction (swing) phases
Extensor muscles are active during the postural phase, and flexors are active during the first part of the protraction phase while extensors become active near the end.
53
What extra-pyramidal UMN tracts are active during the postural phase? During the protraction phase?
Postural phase — pontine reticulospinal and vestibulospinal
Protraction phase — medullary reticulospinal and rubrospinal
54
UMN paresis is the result of ________.
LMN paresis is the result of ________.
Difficulty initiating gait
Difficulty supporting weight
55
Decerebrate rigidity is due to a lesion within the ________. What is the mechanism of this rigidity?
Midbrain
The facilitatory centers in the pontomedullary reticular formation can function independent of telencephalic influence, while the inhibitory ones cannot. Additionally, the vestibulospinal tracts also are still functioning, providing more excitatory extensor input.
56
Which axons cross at the optic chiasm and which don’t?
The axons originating from the medial retina (which see the lateral visual fields) cross, and the ones from the lateral retina do not cross.
57
What is the name of the white matter immediately surrounding the spinal cord grey matter? What does this white matter do?
Fasciculus proprius - also called the propriospinal system
Helps integrate reflex arcs that extend over multiple spinal cord segments.
58
Define dermatome, cutaneous zone and autonomous zone.
Dermatome — sensory area supplied by a single spinal nerve
Cutaneous zone — sensory area supplied by a named nerve
Autonomous zone — an area of sensation that is supplied by only one named nerve
59
What reflex is abnormal in sensory ganglioradiculoneuritis?
Patellar reflex
Withdrawal reflex is preserved
60
Interruption of this tract can result in vestibular signs with cranial cervical spinal cord disease
Spinovestibular
61
How many vestibular receptors are present in each inner ear? What are their names?
Five — 3 are cristae ampullares (one in each semi-circular duct) and 2 are maculae (one each in the utricle and saccule)
62
Dysfunction of these axons located in this part of the spinal cord is the reason for Schiff-Sherrington posture?
Axons from the border cells located in the L1-5 spinal cord segments
63
Describe the arterial blood supply to the spinal cord.
There are paired dorsal spinal arteries and a single ventral spinal artery. The dorsal spinal arteries are supplied by the dorsal radicular arteries, and the ventral spinal artery is supplied by the ventral ones. The ventral spinal artery gives off a branch called the central branch that travels dorsally in the ventral fissure to supply the ventral grey horns.
64
What is the pattern of degeneration in degenerative myelopathy?
Primarily the lateral and ventral funiculi
65
What disease is this? Where do clinical signs usually start? What is the name of the white matter tract that is spared?
Afghan hound myelinolysis - primary demyelination
Mid-thoracic causing a T3-L3 myelopathy
Fasciculus proprious / propriospinal tract
66
What is Brown-Séquard syndrome?
This refers to a spinal cord lesion causing contralateral hypalgesia due to crossing over of the pain pathways (spinothalamic tract) immediately in the spinal cord.
67
What are the classic clinical signs associated with globoid cell leukodystrophy?
What is the pathophysiology?
What are two breeds of dog this is common in?
UMN quality ataxia / paresis in either PL or all limbs + cerebellar signs
Deficiency in the lysosomal enzyme galactosylceramidase 1 — allows accumulation of a substrate that is toxic to oligodendrocytes/Schwann cells, resulting in a primary demyelination. The globoid cells are actually macrophages (gitter cells?) that come eat up the myelin.
Westies and Cairn terriers
68
What is the diagnosis? What breed of horse is this most common in?
Cervical vertebral stenosis at C3-4 as demonstrated by the dorsal tipping of the cranial aspect of C4 vertebra and the extension of the lamina of C3.
Thoroughbreds
69
What is a sagittal ratio? What is considered abnormal?
It is a (semi)-objective means of assessing for vertebral foraminal (canal) stenosis in horses via measurements made on a lateral cervical radiograph.
Anything less than <0.5 is indicative of stenosis
70
What three equine neurologic diseases are associated with Vitamin E deficiency? Which ones affect young versus older horses?
Equine degenerative encephalomyelopathy - young horses
Equine neuroaxonal dystrophy - young horses
Equine motor neuron disease - old horses
71
What are the classic clinical features of equine herpesvirus-1?
T3-L3 myelopathy
Urinary incontinence
Mild tail / anal hypotonia
72
What type of fluid is present within the bony labyrinth of the inner ear? Membranous labyrinth? What is each fluid derived from?
Bony labyrinth contains perilymph, a derivative of CSF.
Membranous labyrinth contains endolymph, a derivative of serum.
73
Explain how the crista ampullaris functions.
The crista ampullaris is within the lumen of semicircular duct, filled with endolymph. It bulges into the lumen due to connective tissue underneath it, and is lined by neuroepithelial (hair cells) cells. These hair cells are embedded in a protein-polysaccharide matrix called the cupula. Movement of the endolymph (ie when the head moves) causes cupula to move, which then bends the hair cells. Depending on the direction of the endolymph (and thus the head) movement, inhibitory or excitatory signals get sent to the vestibular nuclei in the brainstem. Recall that these nuclei are constantly active. Each crista ampullaris is paired with a mirror one in the opposite ear that is experiencing the opposite motion so that opposite signals get sent to the corresponding vestibular nuclei, helping coordinate conjugate eye movement (ie adduction of one and abduction of the other).
74
How do the maculae work?
Similar to the cristae ampullares, these are lined by neuroepithelial hair cells. They are then covered by a membrane of gelatinous material, called the statoconiorum membrane. On the surface of this membrane are statoconia (little rocks). As these statoconia are moved (by gravity, acceleration, deceleration), they weigh on the membrane which weighs on the hair cells, causing them to signal (or not signal). Important for static equilibrium given that they are affected by gravity (due to the weight of the rocks).
75
Where are the three possible locations a vestibular neuron can synapse after leaving CN VIII?
1. Vestibular nuclei
2. Fastigial nucleus in cerebellum
3. Flocculonodular lobe of cerebellum (termed direct vestibulocerebellar tract)
76
Broadly speaking, where are the vestibular nuclei located?
They are adjacent to the lateral wall of the fourth ventricle within the pons and medulla.
A - rostral
B - medial
C - lateral
D - caudal
77
What are the names of the 2 spinal cord tracts originating from the vestibular nuclei? What do they do? What specific vestibular nuclei do they arise from?
Lateral and medial vestibulospinal tracts (part of the extrapyramidal UMN system).
They travels ipsilateral in the ventral funiculus and facilitates extensors, and inhibits flexors. It also inhibits contralateral extensors. The lateral one runs the whole length of the spinal cord while the medial one just goes to the cranial thoracic region.
Lateral: lateral vestibular nuclei
Medial: rostral, medial and caudal
78
What are the three brainstem places that vestibular nuclei project to?
1. Medial longitudinal fasciculus, which goes to the motor nuclei of CNN III, IV, and VI
2. Into the reticular formation
3. To the thalamus for eventual cerebral cortical projection for conscious perception
79
In traditional (non-paradoxical) vestibular disease, which side of the body may have more tone?
Hypertonia may be appreciated contralateral to the vestibular lesion. Loss of vestibular tone on the affected side results in dysfunction of the vestibulospinal tracts, which translates to less tone on the affected side and release of inhibition of the extensors on the contralateral side.
80
Explain why “brow-stag” occurs.
There are likely connections between between the vestibular nuclei and facial motor nucleus. Activation of the facial motor nucleus triggers movement of the levator anguli oculi medialis muscle.
81
Which cerebellar peduncle is commonly implicated in paradoxical vestibular dysfunction? Why?
Caudal cerebellar peduncle
This peduncle contains inhibitory neurons running from the flocculonodular lobe to the ipsilateral vestibular nuclei.
82
What are two possible explanations for why cranial cervical spinal cord disease can cause vestibular signs?
Damage to the descending veestibulospinal tracts or interruption of the GSA/GP afferent from the cranial neck to the vestibular nuclei coordinating head and neck positioning.
83
What are the major clinical signs associated with thiamin deficiency in cats?
Vestibular ataxia
Pupillary dilation / blindness
Seizures
Cervical ventroflexion
84
What are the classic MRI features of thiamin deficiency in small animals?
Symmetric T2W hyper-intensity within the vestibular nuclei, caudal colliculi, oculomotor nuclei, and lateral geniculate nuclei
One cat had it in facial nerve nuclei too
85
Why do CNN VII and VIII deficits occur in cases of THO?
Immobility of the joint between the tympanic portion of the temporal bone and the stylohyoid bone predisposes to fracture of the temporal bone.
86
What is the presumed pathogenesis of cerebellar cortical abiotrophy seen in Kerry Blue terriers? What other nuclei / spots are affected besides the cerebellum?
Disruption in the processing of glutamate — either too much being released as a neurotransmitter or it not being broken down appropriately.
Olivary nuclei, caudate nuclei, substantia nigra
87
A mutation in this gene is responsible for the abiotrophy of Kerry Blue Terriers?
What is the other breed of dog to have this same disease / genetic mutation?
SERACI
Chinese crested
88
What percentage of axons cross at the optic chiasm in the following species?
Man
Cat
Dog
Horse
Cow
Man - 50%
Cat - 65%
Dog - 75%
Horse - 80%
Cow - 90%
Has to do with how the eyes are positioned within the head. The more frontal they are, the more crossing occurs at the chiasm.
89
What percentage of axons within the post-chiasmatic optic tract synapse in the lateral geniculate nucleus, and what percentage continue to reflex visual pathways?
80% synapse
20% continue on to reflex pathways
90
In what species is the optic canal extra-long? What are the clinical implications of this?
The horse.
They can be damaged within this canal secondary to external trauma. If the head suddenly stops moving after hitting something, the eyes continue to move, but the nerve can’t within the canal and it gets stretched / kinked at the rostral opening of the canal.
91
What muscle helps maintain the size of the palpebral fissure in large animals? What is its innervation?
Levator anguli oculi medialis m
Facial nerve
92
List five breeds of dogs with a late onset cerebellar cortical abiotrophy.
What neurolocalization is often suspected in these dogs when their clinical signs are mild?
Gordon setters
Old English sheepdogs
Scottish terriers
American Staffordshire terriers
Brittany spaniels
Cervical myelopathy
93
What is the name of the axis of the bony portion of the cochlea?
What runs through this structure?
What is the name of the thin shelf of bone protruding from this structure?
Where is this shelf of bone missing?
Modiolus
The pre-ganglionic axons of the bipolar CN VIII cochlear neurons
Spiral lamina
At the apex of the cochlea, called the helicotrema
94
Explain why the scali vestibuli and scala tympani are named accordingly? How are they oriented in relationship to the cochlear duct?
It is based off of what they communicate with at their proximal most aspects. The scala vestibuli communicates with the vestibule, while the scala tympani would communicate with the tympanic cavity, but instead meets the cochlear window.
The scala vestibuli is located dorsal to the cochlear duct, while the scala tympani is ventral to it.
95
Which scala (vestibuli or tympani) has a connection to the subarachnoid space? What is the name of this connection?
The scala tympani communicates with the SAS via the cochlear canaliculus.
96
Which layer of the cochlear duct contain the stria vascularis, and which contains the organ of Corti? Which layer contains nothing?
Lateral layer — stria vascularis
Bottom / basilar membrane — organ of Corti
Top / vestibular membrane — nothing
97
Which window in the medial aspect of the tympanic cavity is associated with the ossicles? Which is not? What are their alternate names?
Vestibular window is associated with the stapes, and the cochlear window is not.
The vestibular window is also called the oval window. The cochlear window is also called the round window.
98
What is the name of the proteinaceous layer in which the hair cells of the spiral organ are embedded in? What is on the opposite side (base) of these hair cells?
Tectorial membrane
Dendritic zones of the cochlear portion of CN VIII
99
Which portions of the cochlear respond to low frequency sound and which respond to high frequency sounds? What explains the difference?
The base of the cochlea responds to high frequency sounds, while the apex responds to low frequency sounds.
This is likely related to the length of the basilar membrane (which possesses the organ of Corti), which is shorter at the base and longer at the apex.
100
Where does the cochlear portion of CN VIII enter the brainstem? What nuclei are present here?
Laterally at the junction of the pons and medulla. The axons enter into the dorsal & ventral cochlear nuclei that are so far lateral that they almost appear to be with the nerve.
