HORSE- SPECIES ADAPTATIONS

Question 1

Describe the strategies used to optimise speed

Answer 1

-Increase stride length
-increase stride rate
However these are anatgonistic so a compromise is required - increasing the rate, reduces the length

Question 2

How are horses adapted to increase its stride length

Answer 2

• Mediolaterally flattened thorax with the scapula positioned laterally
• Scapula and shoulder joint free to move- no clavical
• Ulna becomes vestigial- fuses with radius
• Elongation of the distal bones

Question 3

How is the horse adapted to increase its stride rate

Answer 3

• concentration of musculature proximally
• reduction to a single digit (lost other digits as extra unnecessary weight )
• brachium is relatively short and highly muscular- light tendons act as levers

Question 4

Describe the structure, function and adaptations of the equine forelimb

Answer 4

• carry more static body weight (allows hind limbs to minimise wasteful vertical energy)
• shorter ad straighter than hindlimbs (no bone articulation to the skeleton so effectively act as suspension
• broader more rounded hoof
• forelimbs act as suspension and absorb energy (energy storage- tendons)

Question 5

Describe how tendons are able to conserve energy

Answer 5

• tendons are able to store kinetic energy

- potential energy is stored in stretched tendons, which is converted back to kinetic energy

Question 6

Describe the structure, function and adaptations of the equine hindlimb

Answer 6

-forward impulsion of the horse (direct bone articulations- between the femur and pelvis, pelvis and sacral spine)
-reciprocal apparatus allows simultaneous extension of the hip, stifle and hock
-narrower and more pointed hoof (more traction and friction on ground )
No lost energy by extra movement of bones

Question 7

Explain the function of the passive stay apparatus of the equine hindlimb

Answer 7

-minimal energy whilst standing still
On leg straight, other with toe on floor
Stifle and hock positioned at acute angles
Locks in position without muscles

Question 8

Explain the anatomy of the passive stay apparatus of the equine hindlimb

Answer 8

• uses 3 ligaments (medial,middle and lateral
• moves patella over the femur (locks )
• femur cannot move- active process to contract quadriceps to move patella
• medial patella ligament locks-up and medial

Question 9

How does the passive stay apparatus unlock

Answer 9

Quadriceps contract to release, down into gliding position between trochlear ridges

Question 10

What does the suspensory apparatus in horses do

Answer 10

Maintains the fetlock in a position of mild hyper-extension

Question 11

What anatomy is involved in the suspensory apparatus in horses

Answer 11

The suspensory ligament (interosseus muscle ) which originates in the proximal metacarpal/tarsal region.
Runs deep to the DDFT and SDFT to the proximal sesamoid bones and then continues in a series of distal sesamoidean

Question 12

What does it mean when you say stride length is antagonistic to stride rate

Answer 12

It can increase one only by decreasing the other

Question 13

Define inertia in terms of locomotion

Answer 13

inertia is the force needed to move a limb (determined by mass x radial distance^2)

Question 14

How does increasing limb length affect inertia force

Answer 14

Inertia= mass x radial distance^2

If you increase limb length, you increase stride length- so you increase inertia. You limit stride rate

Question 15

Can increased stride length easily be achieved through flexion and extension in back of horses

Answer 15

No, horses are not as flexible as carnivores

Question 16

How does the scapula of the horse allow for speed

Answer 16

Slides forward and back to allow for longer extension of leg and longer strides

Question 17

Explain how the relative lengths of the forelimbs and hindlimbs help the horse to run faster

Answer 17

Forelimbs are shorter and straighter than hind so they can translate horizontal velocity provided by hind limbs whilst minimising wasteful vertical energy. Conserves energy.

Question 18

How does the variation in shape of hoof between fore- and hind-limb of a horse help running?

Answer 18

Broader more rounded hoof to help with landing in forelimb.Narrow hind hoof can grip more to help generate more energy

Question 19

How are the bones arranged in the limbs to conserve energy?

Answer 19

In hindlimb there is direct bone articulations:
•Femur and pelvis
•Pelvis and sacral spine. So fewer space to lose energy.
In forelimb:
No bone articulation to the skeleton so effectively act as suspension

Question 20

What is the main use of the thoracic and hindlimbs?

Answer 20

Thoracic (Forelimb) - Carry static body weight. Needed for converting the kinetic energy of downward movement into the potential energy of stretched muscles & ligaments, which rebound to generate upward movement.
Hindlimb - provide impulsion and passive stay

Question 21

What is the reciprocal apparatus?

Answer 21

Allows simultaneous extension of the hip, stifle and hock, extensor muscle which is proximal can move distal limb

• Cranially the proneus tertius tendon and caudally the superficial digital flexor tendon constitute two fibrous cords that mechanically link stifle and hock joints.

The fibrous cords (reciprocal apparatus) keep the two joints synchronized even during conditions of neuromuscular fatigue. Also allows coordination of limbs.

Question 22

Give another name for the suspensory ligament

Answer 22

Interosseous muscle

Question 23

Where does the interosseous muscle originate and insert?

Answer 23

Proximal metacarpal/tarsal region.Runs to the proximal sesamoid bones and then continues in a series of distal sesamoidean

Question 24

How does the interosseous muscle help with the passive stay apparatus?

Answer 24

Maintains the fetlock in a position of mild hyper-extension

Question 25

What muscles assist with the passive stay of the forelimb?

Answer 25

• Serratus ventralis forms a suspensory sling but must be counter-balanced. Therefore the shoulder is also maintained in extension by
• Supraspinatus muscle
• Co-operative antagonism of the biceps, which has extensive inelastic tendinous components, with reciprocal contraction of the triceps

Question 26

Explain how ligaments in the forelimb assist with the stay apparatus.

Answer 26

• “Superior check ligament” (ALSDFT) is the ligamentous attachment of the radial head•Distal tendonous insertion onto proximal and distal phalanges to the pastern region prevents extension of the carpus and fetlock
• “Inferior check ligament” (ALDDFT) joins the tendon in the mid metacarpus•Distal tendonous insertion of DDFT onto distal phalanx prevents extension of all joints distal to the fetlock

Question 27

What are the superior and inferior check ligaments from?

Answer 27

Accessory ligaments to the superficial and deep digital flexor tendons respectably

Question 28

What prevents the buckling of the stifle in the stay apparatus?

Answer 28

Lacertus fibrosus, running through extensor carpi radialis prevents carpal flexion

Question 29

Can the horse be bred to be faster anymore?

Answer 29

No, reached maximum physiological adaptation.

Question 30

What physiological adaptations does the horse have to help with speed?

Answer 30

•Cardiovascular system-Adaptations are almost more to making it function at sedentary levels (rest)
•Respiratory system - Coupled with stride rate
How does the structure of the hips affect movement.
Hips in large herbivores:
• Much more supportive.
• Asymmetric femoral head.
• Femoral neck is more compact and vertical.
• Limited Rand of Motion.