DeLahunta Chapter 5 - GSE - LMN, spinal nerves 1st (p.102-130)

Question 1

What is a LMN, and which systems are involved?

Answer 1

The lower motor neuron (LMN) is the efferent neuron of the peripheral nervous system (PNS) that connects the central nervous system (CNS) with the muscle to be innervated. The entire function of the CNS is manifested through the LMN. The LMN includes two components: (1) the general somatic efferent (GSE) system and (2) the general visceral efferent (GVE) system.

Question 2

Where are the cell bodies of the LMN in the spinal cord?

Answer 2

Ventral grey horns

Question 3

What is the synaptic cleft - what is its width? What neurotransmitter is released in the synapse in LMN-GSE system?

Answer 3

The synaptic clef is the space between the presynaptic membrane (axolemma) and the postsynaptic membrane (sarcolemma) and is about 2 nm wide.

Acetylocholine
Postsynaptic membrane has nicotinic AChR.

Question 4

Why an animal with complete sciatic dysfunction may have a hip which can flex?

Answer 4

1) ilopsoas muscle ->innervated by all lumbar spinal nerve ventral. branches with contribution caudally to femoral n.
2) femoral nerve–>rectus femoris muscle

Question 5

What is the contribution of femoral nerve in the withdrawal reflex?

Answer 5

Complete sciatic n. dysfunction can give absent withdrawal if stimulate D5.
But if stimulate D1–>innervated cutaneously by saphenous n <– branch of femoral nerve
Therefore –> hip flexion/pull away the limb wihtout flexion of the other joints

Question 6

What branches of which nerve do the following reflexes test?
- Gastrocnemius reflex
- Cranial crural (cranial tibial) reflex

Answer 6

cranial crural –> fibular nerve (L6-7)
gastrocnemius –>tibial (L7-S1)

Question 7

Pathway of cutaneous trunci reflex

Answer 7

Polysynaptic reflex:

Skin –> spinal nerves –> dorsal root –> ganglion (GSA NEURON)

–> dorsal grey matter (LONG INTERNEURON) [also projects contralateraly]–> fasciulus proprius travelling to C8-T1 SCS and synapses with…

… the GSE NEURON of the ventral grey horn –>lateral thoracic nerve –> cutanus trunci muscle

Question 8

What are the terms below:
-Wallerian degeneration
-ellipsoid
-digestion chamber
-axonal buds
-central chromatolysis?

Answer 8

-Wallerian degeneration is a trophic degeneration that occurs in the neuron at the site of the lesion and travels in a distal direction from the cell body
-This is a secondary demyelination. In this process of Wallerian degeneration, this secondary demyelination includes the formation of swellings along the internodes, called ellipsoids, and the fragmentation of myelin into droplets.
-Digestion chamber is a term used for a myelin ellipsoid containing axonal granules.
-Each axon puts out a number of processes called axonal buds, which grow into the existing cords of proliferating Schwann cells.
-The rate of growth is about 1 to 4 mm per day.
-If an impediment such as hemorrhage or fibrosis prevents the axonal buds from reaching the nearest bands of Schwann cells, the axonal buds will continue to grow in a haphazard manner and form an observable swelling known as a neuroma. These neuromas may be a source of considerable discomfort. They are often a sequel to the neurectomies that are performed in the distal extremities of the horse to eliminate a source of discomfort, such as a degeneration of the distal sesamoid bone, referred to as navicular disease.
-A reaction occurs in the cell body in the spinal cord, called the axonal reaction, in which a slight swelling of the cell body, a displacement of the nucleus to one side of the cytoplasm (an eccentric nucleus), and a disbursement of the granular endoplasmic reticulum of the Nissl substance within the cytoplasm occur. The last event is referred to as central chromatolysis and represents the efforts of the cell body to produce more products for the axoplasmic flow necessary for the regeneration to progress.

Question 9

What are the 3 means of infection/intoxicaion with botulism?

Answer 9

1) ingestion of neurotoxin from feed (e.g. corpses)
2) ingested contamnated soil - diffuse absorspion of spores in the GI (young foals)– > clinically: diffuse tremors
3) rare: through wound

Question 10

Two cat breeds more commonly diagnosed with acquired myasthenia gravis? Is the
outcome for cats diagnosed with acquired myasthenia gravis without cranial
mediastinal mass favourable or guarded?

Answer 10

-Somali
-Abysinian

-Favourable - All cats (8) had an excellent long-term outcome, achieving immune remission within 6 months of diagnosis, including 4 cats that did not receive any treatment and whose natural course of disease involved spontaneous remission

(hOps://onlinelibrary.wiley.com/doi/full/10.1111/jvim.15655 )

Question 11

Name a single cat breed and its genetic mutation for congenital myasthenic syndrome?

Answer 11

Sphynx
C0LQ gene missense mutation

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0137019

Question 12

What is the responsible gene for Centronuclear (Type II Defciency) Autosomal
Recessive Polymyopathy in Labrador Retrievers? What is the prognosis for this
condition?

Answer 12

PTPLA gene

good prognosis for life because it is self-limiting. It rarely progresses be- yond more than 9 or 10 months and rarely causes recumbency. Owners learn to limit the amount of exercise to avoid having to carry the dog home.

Question 13

What is a motor unit?

Answer 13

“The GSE and its muscles cells”
The number of muscle cells innervated by a single GSE neuron – which varies from 100-150 muscle cells in proximal limb muscles to 3-4 in the extraocular muscles.

Question 14

Excluding the hip, flexion of all of the joints of the pelvic limb is a function of the GSE components of which nerve?

Answer 14

sciati nerve

Question 15

Which cell myelinates the axons in the spinal cord?

Answer 15

Within spinal cord parenchyma - oligodendrocytes
As soon as PNS –> Schwann cells

Question 16

Which nerve is responsible for flexion of the elbow?

Answer 16

musculocutaneous nerve

Question 17

What is a nerve?

Answer 17

Collection of axons in the pNS myelinated by schwan cells encased in various layers: epineurium, perineurium, endoneurium

Question 18

What is motor endplate?

Answer 18

1 axonal branch innervating 1 muscle cell at a motor endplate.

specialized region of a muscle cell that acts as a functional and structural interface between motor neurons and muscle fibers

Question 19

What is special about the Schwann cell at the level of synapse?

Answer 19

It does not form myelin.

Question 20

How does the action potential travels from the nerve to the muscle?

Answer 20

1)axon –> presynaptic membrane –> Ca channels OPEN
2) this open icreases Ca a in the axollemma –> triggers the realease of Ach in synaptic cleft from synaptic vesicles
3) Ach binds the nicAchR of the postsynaptic membrane
4) Then, opening of Na channels –> influx of Na –> depolarisation of postsynaptic membrane –> spreads along –>if enough spreading, muscle contraction

Question 21

How is the Ach eliminated from the synaptic cleft normally?

Answer 21

1) hydrolysed by Ach-esterase which released by the muscle cell membrane
2) diffusion away from the cleft

Question 22

Patellar reflex pathway and nerve assesed

Answer 22

Tendon myotatic reflex
Monosynaptic reflex

Sensory part: receptor in skin or neuromuscular spindle –> spinal nerve–> dorsal root –> ganglion (GSA neuron)

Motor part: from GSA neuron to ventral grey horn (GSE neuron) –> ventral root–> muscle to contract

NERVE: femoral nerve (L4-5-6 SCS)

Question 23

Withdrawal reflex on pelvic limb and nerve assessed

Answer 23

Polysynpatic reflex

Sensory part: skin –> dorsal root –> ganglion (GSA neuron) –> INTERNEURON (dorsal grey horn)

Motor part: ventral grey horn (GSE neuron) –> ventral root –>muscle

Sciatic nerve (L6-7-S1)
-cranial: fibular nerve (L6-7)
-caudal: tibial nerve (L7-S1)

Question 24

What is assessed by withdrawal, biceps, triceps and extensor carpi radialis reflexes in the thoracic limb?

Answer 24

withdrawal r –> all nerves (C6-T2 SCS)
biceps r–> musculocutaneous n. (C6-7 SCS)
triceps r–>radial n. (C7-T2)
extensor carpi radialis r.–> radial n. (C7-T2)

Question 25

Which nerves are responsible for:
-shoulder flexion
-elbow flexion
-carpal and digital flexion

Answer 25

shoulder flexion:
–acillary n (C7-8) (C6)
–radial n. (C7-T1) (T2)
–thoracodorsal n.

elbow extension: musculocutaneous n. (C6-8)

carpal/digital flexion:
–medial n. (C8-T1) (T2)
–ulnar n. (C8-T1) (T2)

Question 26

What is neurogenic atrophy and when is it clinically evident?

Answer 26

7 days after denervation

muscle looses protein –> death of muscle cell and replacement by fat or fibrous tissue

Question 27

What is the general findings of EMG/MNCV in axonopathy or myopathy vs myelinopathy?

Answer 27

axonopathy/myopathy: EMG fibrilation ptentials & positive sharp waves

myelinopathy: MNCV decreased

Question 28

What is a normal MNCV in general?

Answer 28

50-60m/s

Question 29

What is myotonia and what is pseudomyotonia? What is myotonic discharge?

Answer 29

Myotonia is the continuous muscle contraction that persists reagardless of the stimulation (E.G. percussion or needle insertion) of discontinuation of voluntary effort (hyperexcitable muscle membrane)

-muscular disase (vs tetanus which is PNH)

-usually associated with inherited channelopathies

EMG feature: dive bomber sound - myotonic dishcarge. it is a high frequency and amplitude discharge which lasts over 4-5 seconds

Pseudomyotonia: similar EMG with complex repetitive discharges
-in Cushings
In hyperadrenocorticism, pseudomyotonia is not due to a primary defect in the muscle membrane or ion channels, as in true myotonia. Instead, it results from the muscle weakness, neuromuscular dysfunction, and CNS effects caused by chronic glucocorticoid exposure, muscle atrophy, and, in some cases, electrolyte imbalances such as hypokalemia. These factors lead to delayed muscle relaxation, mimicking the appearance of myotonia.

Question 30

Which condition can recover quicker, an axonopathy or myelinopathy?

Answer 30

Myelinpathy because Schwann cells have a faster recover rate and they remyelinate

Question 31

Which is a special stain for myelin in histopath?

Answer 31

Luxol fast blue

Question 32

Which are the most resistant and which the most sensitive species to botulism?

Answer 32

Resistant: dogs, cats, pigs
Sensitive: horses, rumminants

Question 33

Which types of botulism neurotoxin affect which species?

Answer 33

Dogs: Type C
Cattles: Type C-D
Horses: Type B-C

Question 34

Which 5 junctionopathies you know and which of them are pre or postsynaptic?

Answer 34

PRESYNAPTIC
1) Botulism - presynaptic (interferes with release of Ach)

2) Tick paralysis - presynpatic (interference with Ca –> decrease release of AcH)

POSTSYNPATIC
1) Acquired myasthenia gravis - postynaptic (abs for nicAcHR of postsynaptic membrane)

2) organophosphate intoxication - poststynaptic (blockage of AchR)

3) Snake envenomation - postsynaptic

Question 35

What is the DDx for a cow in sternal recumbency with neck flexed to the one side and neck rested on the thorax?

Answer 35

1) botulism
2) hypokalemic myopathy
3) milk fever (metabolic myopathy due to hypocalcemia)

=Inability to bear weight of neck/head due to weakness

Question 36

Which dog breeds have genetic predisposition and which are overrepresented in acquired M. gravis? Also overerpresented cats?

Answer 36

genetic predisposition:
-Great dane
-Newfoundland

overrepresentation:
-G.Retriever
-GSD
-Akita
-German shorthair pointer
but other also

Cats:
-Somali
-Abyssinian

Question 37

Why does megaosophagus occurs in acquired myasthenia gravis?

Answer 37

Cause 2/3 of oesophagus in dogs has striated muscles (innvervated by GSE neurons) and having Ach receptors.

Cats do have mainly smmooth muscle (only proximal oesophagus has some striated)

Question 38

Which breeds of dogs and which of CATTLE do you know with genetic proof of congenital myasthenia gravis?
Do you remember the gene for the cattle?

Answer 38

dogs:
1) Smooth Fox Terrier
2) Parson/Jack Russel Terrier
3) Gammel Dansk Horsehund
+Springel spaniel
+Miniature smooth daxy
(https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.15855)

Cattle:
BRAHMAN calves - CHRNE gene (https://pubmed.ncbi.nlm.nih.gov/17121978/)

Question 39

Which ticks cause tick paralysis?

Answer 39

-salive from female ticks
-USA: Dermacentro variabilis or D.andersoni
-Australia: Ixodes holocyclus

Question 40

Which snake Delahunta reports to cause snake envenomation junctionopathy? What are 2 classic characteristics of this disease?

Answer 40

In USA
-coral snake
-rattlesnake

Very rapid progression from 30min-24h

+/-haemolysis/haemoglobinuria
+/- paniculitis around bite wound

Question 41

Most common breed for MMM?

Answer 41

GSD

Question 42

What are the histopath features of MMM?

Answer 42

Necrotizing myositis & oedema, haemorrhage –> macrophage, plasma, lympho&raquo_space;> neutro, eos

Question 43

What is the DDx of trismust?

Answer 43

1) tetanus
2) MMM (mechanical due to fibrosis)
3) pontine lesions

Question 44

What is the histopath features of immunemediated polymyositis?

Answer 44

myonecrosis & macrophages & lymphoplasmacytic interstitial inflammation

Question 45

Which infectious causes may cause polymyositis in dogs?

Answer 45

Hepatozoon americanum&raquo_space; Toxo, Neo, lepto icterohaemorrhagic.

Question 46

Name 2 common breeds with dermatomyositis?

Answer 46

1) collies
2) shetland sheepland

Question 47

Causes of hypokalemic myopathy in which species?

Answer 47

1) old cats : CKD, excessive kaliodiurisis due to hyperaldostenorism due to neoplasm of adrenal cortex

2) inherited hypokalemic myopathy of Burmese cats (WNK4 gene mutation on chromosome E1) autosomal recessive - 2-6mo and episodic

3) Iatrogenic hypokalemic myopathy in cattle due to administration of mineralocorticosteroid (isoflupredone) for ketosis or clostridial mastitis [prognosis guarded] - classic lateral flexion of the neck

Question 48

Which inherited myopathies do you know for Labradors?

Answer 48

1) centronuclear myopathy
2) muscular dystrophy
3) episodic induced collapse (although more diffure neuromuscular)

Question 49

Centronuclear myopathy of labradors:
1) which genetic mutation and trait
2) which is the muslce deficiency?
3) common clinical sign
4) histopath findings - why called centronuclear?
5) prognosis
6)

Answer 49

1) PTPLA gene (autosomal recessive)
2) no dystrophy, but deficiency of Type II muscles
3) patellar reflex deficit (due to involvement of the small striated intrafusal muscle cells in neuromuscular spndles that form the sensory component of the patellar reflex)
4) depletion of type II m. fibers, lack of myonecrosis, variation of muscle fiber size, few cells with centrally positioned nuclei (where the name comes from)
5)good - self limiting
6) very young - mo

Question 50

Muscular dystrophy - dystrophinopathy of Labradors:
1) trait of inheritance
2) typical signs
3)histopath feature and in IHC
4) onset

Answer 50

1) sex-linked recessive (generally only males); females can have it but usually carriers
2)
-hyperslivation and decrease in range of mouth opening
-muscle hypertrophy of tongue, pharynx, or caudal thight, but otherwise m. atrophy
-exercise intolerance
3) myonecrosis (refleceted also in bloods) - in IHC lack of dystrophin

4)young

Question 51

Exercise-induced collapse in Labradors:
1) genetic mutation and trait:
2) progressive or nonprogressive?
3) age of onset?
4) why this gene is responsible for this sign?

Answer 51

1) DNM1 (dynamin1) and autosomal recessive
2) nonprogressive
3) 7mo-2yo (adult version as well)
4) it is a protein which is responsible for repackaging neurotramsnitters into synpatic vesicles for releas in brain and SC