Chapter 85 - Biology of muscle disorders Flashcards
1
Q
Which type of muscle makes up about 55% of the body weight in mature Thoroughbred racehorses?
a) Cardiac muscle
b) Smooth muscle
c) Skeletal muscle
d) Striated muscle
A
c) Skeletal muscle
2
Q
What is the primary cause of all movement in the body?
a) Contraction of smooth muscles
b) Contraction of cardiac muscles
c) Contraction of skeletal muscles
d) Relaxation of skeletal muscles
A
c) Contraction of skeletal muscles
3
Q
How are skeletal muscles arranged in the body with respect to bones and joints?
A
They originate on one bone and insert on a different bone while spanning a joint.
4
Q
What type of muscles increase the joint angle?
a) Extensor muscles
b) Flexor muscles
c) Cardiac muscles
d) Smooth muscles
A
a) Extensor muscles
5
Q
What percentage of skeletal muscle consists of muscle cells (myofibers)?
a) 10%
b) 20%
c) 50%
d) 90%
A
d) 90%
6
Q
What surrounds the muscle fibers in skeletal muscle?
a) Fat
b) Connective tissue
c) Nerves
d) Blood vessels
A
b) Connective tissue
7
Q
What is the basic contractile unit of a muscle fiber?
A
d) Sarcomere
8
Q
What proteins are part of the thin filaments in a myofibril?
a) Actin, tropomyosin, and troponin
b) Myosin
c) Creatinine phosphate
d) CPK
A
a) Actin, tropomyosin, and troponin
9
Q
What is the role of calcium ions in muscle contraction?
A
They bind with troponin C, exposing myosin-binding sites.
10
Q
Which enzyme catalyzes the conversion of creatinine phosphate to replenish ATP stores?
A
CPK (Creatine Phosphokinase)
11
Q
What is the efficiency of muscle contraction in converting chemical energy to mechanical energy?
a) 10%
b) 20%
c) 40%
d) 60%
A
c) 40%
12
Q
How is most of the energy lost during muscle contraction?
A
Lost as heat
13
Q
During shivering, which muscle groups are activated to raise core body temperature?
A
Antagonistic muscle groups
14
Q
What is the primary function of creatine phosphokinase (CPK) in muscle cells?
A
Converting ADP to ATP
15
Q
What percentage of the body weight does skeletal muscle make up in nonathletic horse breeds?
a) 10%
b) 25%
c) 42%
d) 90%
A
c) 42%
16
Q
Which type of muscle is responsible for involuntary contractions in the heart?
A
Cardiac muscle
17
Q
What is the name of the repeating unit between the Z-lines in a muscle fiber?
A
Sarcomere
18
Q
What is the function of the neuromuscular junction?
A
To transmit action potentials from nerves to muscle fibers
19
Q
Which part of a muscle fiber contains overlapping thin and thick filaments?
a) I-bands
b) A-bands
c) H-band
d) Z-line
A
b) A-bands
20
Q
A
Figure 85-1. Levels of organization within a typical skeletal muscle.
21
Q
A
Figure 85-2. The sliding of actin along the myosin molecule results in the physical shortening (contraction) of the sarcomere.t.
22
Q
A
Figure 85-3. Typical motion of the hind limb of a horse affected with fibrotic myopathy of the semitendinosus muscle: the limb is jerked backward just before hitting the ground (see also Video 85-1).
23
Q
What happens to the sarcomere during muscle contraction?
A
It contracts and shortens
24
Q
Which specific Myosin Heavy Chain (MyHC) isoforms have been characterized in adult equine skeletal muscles?
a) Type I and IIA
b) Type IIA and IIX
c) Type I and IIX
d) Type I, IIA, and IIX
A
d) Type I, IIA, and IIX
25
What type of muscle fibers are highly efficient and economical for slow repetitive movements and to sustain isometric force?
a) Type I fibers
b) Type IIA fibers
c) Type IIX fibers
d) Type IIAX fibers
a) Type I fibers
26
Which type of muscle fibers create fast crossbridge cycling and develop force rapidly?
a) Type I fibers
b) Type IIA fibers
c) Type IIX fibers
d) Type IIAX fibers
b) Type IIA fibers
27
How does the velocity of contraction of Type IIX fibers compare to Type IIA fibers?
a) Type IIX fibers contract at a slower velocity.
b) Type IIX fibers contract at the same velocity.
c) Type IIX fibers contract at a 3 times higher velocity.
d) Type IIX fibers do not contract.
c) Type IIX fibers contract at a 3 times higher velocity.
28
Which motor units are required for the maintenance of posture?
a) Type IIA motor units
b) Type IIAX motor units
c) Type IIX motor units
d) Type I motor units
d) Type I motor units
29
What subpopulation of adult skeletal muscle stem cells are activated and migrate towards the damaged area to aid in muscle repair?
a) Myofibrils
b) Satellite cells
c) Myotubes
d) Myofibers
b) Satellite cells
30
In practical terms, when are new myofibers typically formed in muscle?
After birth
31
How does muscle enlargement and growth primarily occur?
Through the formation of additional myofibrils
32
What is the main source of fibroblasts for the repair of damaged muscle tissue?
Blood supply
33
What can happen if damaged muscle is replaced with large amounts of scar tissue?
It restricts muscle length and function
34
What is this pathology?
Fibrotic myopathy
35
What is the classic description of fibrotic myopathy?
Abrupt cessation of the cranial phase of the stride in the affected limb
36
Which horse breed(s) were overrepresented in a study on fibrotic myopathy of the semitendinosus muscle?
Quarter Horses
37
What type of injuries are responsible for most cases of fibrotic myopathy in horses?
Traumatic injuries resulting from extreme tension on the hind limbs
38
What causes the characteristic gait of horses with fibrotic myopathy after transportation in a trailer?
Localized myositis of the semitendinosus muscle
39
# [](http://)
How is fibrotic myopathy in the neonate speculated to be caused?
Trauma at or soon after birth
40
What is the likely cause of fibrotic myopathy when the condition progresses to involve both hind limbs
Degenerative neuropathy
41
How is the diagnosis of fibrotic myopathy typically made?
By detecting palpable fibrosis in the affected muscle
42
What is the primary cause of the gait abnormality in horses with fibrotic myopathy?
Mechanical restriction of affected thigh muscles
43
Which diagnostic imaging method is more useful for demonstrating areas of ossification in fibrotic myopathy?
Radiography
44
Fibrotic surgeries are 3, name them
1. Complete resection of abnormal tissue (not recommended)
2. Transection of fibrotic tissue with scalpel or laser
3. Semitendinous tenotomy/tenectomy near medial tibial insertion
45
What is the most commonly applied surgical technique for fibrotic myopathy?
Semitendinosus tenotomy
46
What is the primary goal of early and sufficient postoperative mobilization after surgery for fibrotic myopathy?
To prevent fibrosis at the surgical site
47
What did kinematic analysis show immediately after transection of the insertion tendon or fibrotic area in horses with fibrotic myopathy?
Significant reduction of the gait abnormality
48
Describe semitendinous tenotomy
GA, LR with affected limb down à medial access to the medial aspect of tíbia
Landmarks: i**nsertion of the muscle** on the **caudomedial aspect of the tíbia** just **distal to the medial FT joint** and **caudal to the saphenous vein** overlying **gastrocnemius muscle** **8 cm vertical skin incision** over the palpable tendon + subcut + cruralfáscia until tendon is exposed Large, curve
Kelly or Crile fórceps is passed under the tendon to isolate it from the muscle and the tendon is transected
**Resection of 3-cm segment of the tendon** obviates the recurrence Fascial layers are closed with interrupted or continuous absorb sutures
Skin closed with interrupted or continuous nonabsorb suture
49
How much of the segment you dissect of semitendinous tendon?
3 cm
50
What percentage of horses treated with standing scalpel transection experienced partial recurrence of the gait abnormality after surgery?
d) 33%
51
What is the likely outcome if a degenerative neuropathy is the cause of fibrotic myopathy?
Partial improvement in gait but likely recurrence
52
Which surgical technique for fibrotic myopathy is no longer recommended due to postoperative complications?
) Complete resection of the fibrotic tissue
53
What is another name for stringhalt?
Equine Reflex Hypertonia
54
# [](http://)
How is stringhalt characterized?
Involuntary flexion of one or both hind limbs
55
When does the limb exhibit exaggerated flexion in stringhalt?
During the cranial phase of the stride
56
Which clinical presentation of stringhalt is typically unilateral and of unknown cause?
Classical Stringhalt
57
What is another name for classical stringhalt?
Idiopathic Stringhalt
58
What type of injury has been linked to classical stringhalt in some cases?
Trauma to the dorsoproximal aspect of the metatarsus (MTIII)
59
What is Australian stringhalt primarily associated with?
Plant ingestion
60
Which of the following plants has been associated with Australian stringhalt?
a) Sunflower
b) Dandelion
c) Rose
d) Tulip
b) Dandelion
61
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What causes the onset of Australian stringhalt to be more severe in some cases?
a) Exercise
b) Cold weather
c) Dry season
d) Rainy season
c) Dry season
62
What type of nerve fibers are mainly affected in Australian stringhalt?
Large myelinated nerve fibers
63
What is the common effect of Australian stringhalt on the recurrent laryngeal nerve?
Denervation
64
How do horses with Australian stringhalt typically recover from the condition?
Most recover spontaneously
65
What medical treatment can be used to reduce peripheral nerve activity and excessive muscle contractions in stringhalt?
Phenytoin
66
Which surgical procedure is considered the treatment of choice for idiopathic stringhalt?
Lateral digital extensor tenectomy and partial myectomy
67
What is the goal of lateral digital extensor (LDE) tenectomy and partial myectomy in stringhalt surgery?
To remove the LDE tendon and part of the muscle
68
Which incision is made to access the LDE tendon during tenectomy and partial myectomy?
Distal incision
69
Describe the surgery of tenectomy and myectomy for stringhalt
DR or LR (limb uppermost) or
Standing:
**2 cm line LA** over **LDE tendon proximal** to the junction **with the long digital extensor on the lateral aspect of MTIII**
- proximal local anesth: **LDE about 2 cm above the lateral malleolus of the tíbia**
**Distal transection of tendon** at MtIII junction of LDE and LAT DIG EXT after exposure with kelly forceps
Proximal incision: **lateral aspect of the limb 6 cm above the lateral malleolus of the tíbia skin** -> subcut -> fáscia **directly over the LDE muscle in vertical direction parallel with the muscle fibers** severed the muscle AFTER MAKING SURE IT CORRESPONDS TO DISTAL TENDON, pull through tendon sheath the distal portion and muscle is severed at least **2 cm**
The heavy fascia of the proximad incision is closed with simple interrupted or continuous pattern
Subcut closed USP2-0 absorbable simple continuous pattern
Skin closed with monofilament simple continuous
14 days bandage
70
What is a possible complication of surgical treatment for stringhalt?
Seroma formation
71
What is the prognosis for classical stringhalt following surgery?
Guarded, with unpredictable outcomes
72
peroneus tertius rupture
73
What is another name for the peroneus tertius muscle?
Fibularis tertius
74
Where does the peroneus tertius muscle lie in the horse's leg?
Between the long digital extensor muscle and the tibialis cranialis muscle
75
Figure 85-9. (A) Normal transverse ultrasonographic image of the PT in the proximal aspect of the crus. The PT is visible as the most echogenic structure (arrows). (B) Transverse ultrasonographic image of a midbody rupture of the PT with complete loss of the normal tendon architecture (arrows). (Courtesy K. Vanderperren, Ghent University.)
76
Figure 85-6. LDE tenectomy and partial myectomy. (A) The muscle belly and tendon of the LDE muscle have been isolated through two separate incisions and are elevated with a forceps. (B) The LDE tendon has been transected at the distal incision and has been pulled through the proximal incision. (C) The removed tendon including at least 2 cm of the muscle.
77
Figure 85-9. (A) Normal transverse ultrasonographic image of the PT in the proximal aspect of the crus. The PT is visible as the most echogenic structure (arrows). (B) Transverse ultrasonographic image of a midbody rupture of the PT with complete loss of the normal tendon architecture (arrows).
78
What is the origin of the peroneus tertius muscle?
Distal femur
79
What is the function of the peroneus tertius muscle?
Extension of the tarsus joint
80
In a retrospective study, what was identified as the location of PT rupture in most cases?
Distal aspect of the PT, just proximal to the sleeve formed by the PT
81
What has been speculated as a contributing factor to foals' susceptibility to avulsion injuries?
Inherent weakness in their bones
82
How is the PT tendon typically disrupted in cases of PT rupture due to trauma?
Closed injury with no visible signs
83
What mechanism has been surmised as the cause of PT rupture due to trauma?
Overextension of the hock while the stifle is in flexion
84
What may cause rupture of the PT when a full-limb cast is applied?
Excessive pressure on the tibia
85
How can PT rupture occur when a horse struggles to free a trapped limb?
The PT spontaneously ruptures
86
What is the classic sign of a complete PT rupture?
Inability to extend the hock while the stifle is flexed
87
What is the grade of lameness reported for horses with avulsion injuries of PT?a) Grade 1b) Grade 2c) Grade 3d) Grade 4
c) Grade 3
88
How is the clinical diagnosis of PT rupture confirmed?a) By radiographyb) By blood testsc) By DNA analysisd) By ultrasonography
d) By ultrasonography
89
What is the recommended treatment for horses with avulsion injuries of the PT origin?
Surgical removal of bone fragments by arthro if femur affected
6 W stall rest
12 W pasture
8 w recover gradually
90
How long is the recommended stall rest for horses with PT rupture?
6 weeks
91
Where does the gastrocnemius muscle arise from in horses?a) Caudal and distal aspect of the tibiab) Caudal and distal aspect of the femurc) Cranial aspect of the humerusd) Cranial and proximal aspect of the metatarsus
b) Caudal and distal aspect of the femur
92
What is the gastrocnemius tendon a major part of?
Reciprocal apparatus
93
Figure 85-10. Three-week-old Quarter Horse foal with an avulsion of the gastrocnemius muscle.(A) Weight-bearing results in marked flexion of the tarsus and hyperextension of the stifle. (B) Application of a tube cast over the tarsus allows the foal to bear weight.
94
In which group is the condition of gastrocnemius muscle rupture more common?
Foal, dystocia during birth
95
In mature horses, what can cause rupture of the gastrocnemius muscle?
External trauma or falls with hind limbs extended
96
In partial ruptures of the gastrocnemius muscle, what gait abnormality may be observed?
Lateral rotation of the calcaneus and medial rotation of the toe
97
In total ruptures involving both gastrocnemius and superficial digital flexor muscles, what happens to the affected limb?
It collapses at the tarsus, and the stifle joint becomes hyperextended
98
How is the diagnosis of gastrocnemius muscle rupture confirmed?
d) By ultrasonography and radiographic examination
99
What concurrent diseases were found in 61% of foals with gastrocnemius rupture in a retrospective study?
c) Enterocolitis, flexural limb deformities, encephalopathy, pneumonia, and others
100
What is the main treatment for gastrocnemius muscle rupture in horses?
c) Stall rest alone- Custom-made splints or sleeve casts
101
How long is the splint or cast typically left in place for horses with gastrocnemius muscle rupture?
4 weeks
102
What complication can develop from prolonged casting or splinting?
Pressure sores
103
What is the prognosis for complete ruptures of the gastrocnemius muscle in adult horses?
Poor
104
What is the prognosis for partial ruptures of the gastrocnemius muscle in adult horses?
a) Excellent
b) Good
c) Fair
d) Poor
b) Good
105
What is diagnosis and treatment
Cribbing or crib bitting
Modified Forssel Tx with 2 other modifications tx
106
Describe Modified Forssel tx
1. Remove acessory spinal nerve
2. Remove omohyoideus
3. remove sternothyroid muscle
DR, head 30º angle to horizontal, expose paired bellies of omohoideus and sternothyroid muscles
At cranial aspect of sternomandibularis you search the acessory spinal nerve and inch to see if the sternomandibularis moves and cut 110 cm of nerve BILATERAL
30 cm myectomy is after made in omohyoideus and sternothyroideus
Hemostasis, closure SQ, skin, 2 penrose drains and stent bandage
MODIFICATION is extending to basihyoid and transect muscles at thyroid level
MODIFICATION perform with Nd:YAG laser
