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Vets1021: loco > stay apparatus > Flashcards

stay apparatus Flashcards

1
Q

stay apparatus is for

A

for standing for a long time while minimising fatigue, with minimal muscular activity

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2
Q

Horse have 2 mechanisms to reduce fatigue & prolong
ability to monitor for danger (remain alert)

A
  • Nuchal ligament: Enables head to be repeatedly raised without much muscular effort
  • Stay apparatus (so-called passive stay apparatus): Permits standing for a long time while minimising
    fatigue, with minimal muscular activity: involves muscle, ligaments & tendons
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3
Q

3 parts of the stay apparatus

A
  • Stay apparatus of the forelimb (proximal to the carpus)
  • Stay apparatus of hind limb (proximal to the tarsus)
  • Suspensory apparatus (distal to the carpus/tarsus, identical fore & hind)
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4
Q

basic principle of stay apparatus

A

Basic principle is that if the horse relaxes most of its muscles, the legs will remain in a standing position.

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5
Q

sleep in horses; 2 types

A

slow wave sleep (SWS) &
paradoxical sleep (PS - includes REM sleep)

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6
Q

describe muscle tone in slow wave sleep and paradoxical sleep

A

Some muscle tone in SWS but none in PS

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7
Q

what position is horse in slow wave sleep

A

can stand, usually sternal recumbancy

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8
Q

what position is horse in paradoxical sleep

A

lateral recumbency

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9
Q

how long does paradoxical sleep last

A

only a few minutes at a time

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10
Q

total daily sleep required

A

3 or 4hr but large individual variation

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11
Q

the stay apparatus in part is a ____ support mechanism

A

fibrous support mechanism (FSM)

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12
Q

describe the fibrous support mechainsm of the stay apparatus

A

The fibrous support mechanism includes those connective tissue structures found in the thoracic & pelvic limbs of the horse that mechanically FIX the respective joint of the limbs in order to support the weight of the animal in a relatively relaxed, standing position. The same structures are necessary for normal locomotor function.

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13
Q

stay apparatus of forelimb

A

If the muscles of the forelimb relax,
ligaments & tendons should hold the leg
in normal resting position:
* Neutral shoulder & elbow
* Extended carpus
* Over-extended fetlock
* Extended pastern & coffin joints

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14
Q

___% of BW is on thoracic limbs

A

60

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15
Q

If left unsupported by opposing
ligaments & tendons, what
would happen to the jointed
bony column of the thoracic
limb?

A
  • Flexion (elbow joint)
  • marked flexion of shoulder joint
  • Overextension (dorsiflexion) of
    the carpus
    -Marked overextension of the fetlock
  • result; joints would collapse under weight of animal
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16
Q

shoulder stability

A
  • Weight of body tries to flex (collapse) the shoulder
  • Prevented by internal (short) tendon of biceps whose RADIAL insertion effectively
    acts as a fixed point.
  • ALSO via lacertus fibrosus (long tendon of biceps brachii) & the extensor carpi radialis
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17
Q

Elbow stability

A

Body weight (& tension on biceps tendon) tries to flex elbow.
Flexion prevented by:
* Tension of triceps (medial head)
* Collateral ligaments
* Origins of digital flexor muscles (medial humerus)

18
Q

Carpus stability

A
  • Body weight could either flex or hyperextend carpus
  • Flexion prevented by tension on ECR from biceps tendon via lacertus fibrosus
  • Overextension prevented by superior check lig. (Accessory lig. SDFT) (NOT IN HINDLIMBS)
19
Q

Fetlock, pastern, coffin joint
stability

A
  • Suspensory Apparatus: Suspensory ligament, Proximal sesamoid bones (PSB), Ligament from PSB to cannon bone, and phalanxes
  • Accessory ligament (check) DDFT
  • Flexor tendons (DDFT, SDFT)
20
Q

Suspensory Apparatus:

A
  • Suspensory ligament
  • Proximal sesamoid bones (PSB)
  • Ligament from PSB to cannon bone, and phalanxes
21
Q

Hindlimb passive stay apparatus Prevents leg from collapsing by preventing:

A
  • flexion of stifle & hock
  • overextension of fetlock & phalangeal joints
22
Q

important part of hindlimb passive stay apparatus is ____ mechanism

A

reciprocal: links stifle and hock

23
Q

hindlimb reciprocal mechanism links ____ and ____

A

stifle and hock

24
Q

locking of their patellas

A

(stabilising the limb with minimal muscular
effort). However, some muscular effort is needed, which is why horses tire
& alternate their resting hindlimbs

25
Q

check ligaments on hind limb

A

NO superior check ligament, SMALL inferior check ligament

26
Q

Normal locking of the patella; 3 steps

A

1) Stifle extended & patella lifted by quadriceps
2) Patella rotated medially approx 15 degrees by vastus medialis so parapatellar cartilage & medial patellar ligament sit over medial
trochlear ridge
3) Quadriceps relax (?) to lower fibrocartilage onto medial trochlear ridge where it is hooked/locked in place

27
Q

3 steps of unlocking patella

A

1) Lift patella (extend stifle)
2) Rotate patella laterally with gluteofemoris & tensor fascia late
3) Relax quadriceps

28
Q

when unlocking patella; can get stuck, whats this called and why does it occur

A

“INTERMITTENT/PERMANENT UPPER
FIXATION OF THE PATELLA”)
- young horses/off work
- poor conformation
- neuromuscular problem??
***Surgery (desmotomy-transection medial patellar lig.) only on severe permanent cases

29
Q

reciprocal apparatus comprised of 2 cords:

A

peroneus tertius & superficial digital flexor

30
Q

reciprocal apparatus flexes

A

stifle and hock together

31
Q

reciprocal apparatus is mostly

A

tendinous

32
Q

reciprocal apparatus

A

Aids in both (movement & stay apparatus) functions

33
Q

reciprocal apparatus when stifle is locked

A

When stifle is locked, the weight on the limb pressures the hock joint to flex. However, tension in the superficial digital flexor resists
this pressure, and the hock does not flex

34
Q

Horse’s musculoskeletal system evolved to ____ metabolic cost of locomotion

A

reduce

35
Q

at high speed; increase stride length ____ energetic cost of limb protraction (bringing limb forward)

A

decreases

36
Q

how did horse evolve to reduce metabolic cost

A
  • Bulk of muscles proximally in the limb, more distal aspect tendons provide
    energy for locomotion
  • Distal part limb elongated & number bones reduced to single digit
  • Cannon bone longer & lighter
  • Musculotendinous units in the forelimb: support body mass, generate forces used for propulsion, breaking & turning, stabilise joints during stance phase of the stride & flex joints during the swing phase
37
Q

For high speeds achieved at the gallop rapid protraction of the forelimbs is required, how is this achieved

A

special catapult action of biceps muscle

38
Q

describe catapult action in forelimb

A
  • In horses, instead of hight output contraction of muscles, rapid protraction is achieved by the special catapult action of biceps muscle
  • In a catapult system energy is stored slowly with a large force & then released quickly to accelerate a small mass
  • During stance, the elastic biceps muscle is stretched, while carpus is locked in extension
  • Before limb lifts off, the carpus buckles forward, this releases the catapult, bringing
    the leg forward for the next stride
  • The power output of this catapult action of the biceps muscle is about 100 times its
    mass of a non-elastic muscle
39
Q

SDF and DDF have ____ muscle bellies and ___ tendons which is energy efficient

A

small
long

40
Q

describe spring and coil mechanism of flecor tendonds

A
  • During stance phase, flexor tendons are loaded under tension (this stress may be as high as twice of the bodyweight at the gallop)
  • During the first half of stance phase, flexor tendons store great amount of elastic energy, which is released in second half of stance
    phase –> propulsion
  • The muscles bellies of these tendons damp this spring-like action
41
Q

spring and coil mechanism: in thoroughbred horses the SDFT elongates by ___% its original length as response to sustained strength

A

12-16%

Vets1021: loco (25 decks)

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