equine anatomy exam 1

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Dorsal

Towards back or withers

Ventral

Towards belly or underside

Cranial

Towards the head

Caudal

Towards the tail

Anterior

Towards the head

Posterior

Towards the tail

Medial

Towards the inside of the body

Lateral

Towards the outside of the body

Ipsilateral

Referring to structures on the same side of the body

Contralateral

Referring to structures on opposite sides of the body

Superficial

Referring to structures closer to the surface of the body

Deep

Referring to structures farther from the surface of the body

External

Referring to structures located on the outer side of the body or away from center

Internal

Referring to structures located within the body or closer to the center

Adaxial

Referring to structures that are closer to the midline or axis of the body

Abaxial

Referring to structures that are farther from the midline or axis of the body

Palmar

Towards the back of the front leg

Plantar

Towards the back if the hind leg

What is anatomy?

Structure of the horse

What does anatomy determine?

• how the horse looks

• how the horse will move

• what the horse will be able to do

• how the horse will be throughout its life

How many bones in a horse?

206

Purpose of the skeleton

• to protect vital organs of the horse

• to provide structural framework for muscles, tendons, etc.

Purpose of bones

• serve as levers

• store minerals

• sites of red blood cell formation

• should NOT be in contact

long bones

• found in horses’ limbs

• aid in locomotion, mineral storage

• act as levels

short bones

• found in the joints

• absorb concussion, allow joints to bend upon impact

flat bones

protect vital organs by enclosing body cavities

irregular bones

vertebrae of horse, protect CNS

example of long bones

cannon bone, femur, etc.

example of short bones

knee (carpus)

example of flat bones

ribs

example of irregular bones

spinal column

How do bones change?

they are constantly remodeling due to stress, based on concussion

Structure of bone

Not hollow, yet not solid

Articular cartilage

located at the ends of bones where they meet to form joints

Cancellous (spongy) bone

Found in the broad ends of long bones

Cortical bone

Dense part of the bone, able to withstand impact

Periosteum

Touch outer cover around bone

Epiphysis

Ends of bones

What are joints?

The connection between bones

Arthritis

Narrowing of joint space with a decrease in synovial fluid; damage to cartilage as it comes into contact as the joint moves

Developmental orthopedic disease

Joint issue, common in young horses and occurs when bone does not form properly at birth

What types of activities predispose horses to joint disease?

high impact + repetitive motions such as jumping (extends joints)

Hyaluronic Acid joint injections

Down regulates inflammation can improve joint structure

Why is arthritis hard to treat?

Cartilage takes a while to turn over, some medicines can speed this process up but not by much

What is soft tissue in the horse?

Primarily ligaments and tendons, some muscle

Tendons

Bind muscle to bone; NO contractile properties

Ligaments

Bind bone to bone; NO contractile properties

Why are soft tissue injuries so hard to rehab in horses?

Tendons are ligament injuries frequently recur even if initial injury heals because they typically grow back not as elastic

How is collagen typically laid down to repair soft tissue injuries?

Type-3 (weaker) fills void much quicker than type-1 collagen which is much stronger due to crosslinks

What is elastic modulus in regards to soft tissue?

Amount you can deform soft tissue and have it still return to shape

How do muscles create movement?

Contractile proteins stacked in the muscle slide + shorten

In what way do muscles resist movement?

They counteract the body weight of the horse

How did leg structure of horses change with evolution?

Leg structure changed from splay foot for support to harder single toe

What is the splint bone?

Remnant toe

Unguligrade

Hoof walking; example: deer, horse

Digitgrade

Toe walking; Example: Dog

Plantigrade

Sole walking; Example: Human, rabbit

What makes the horse a fast runner?

• much longer limbs

• from wrist/hock down, NO muscle, only tendons + ligaments to provide elastic motion (snap forward)

• large muscles housed higher in horse

• limited transverse movement (removal of ulna + fibula)

How is transverse movement limited in horses?

No ulna or fibula

How do differences in relative bone lengths affect speed and power?

Greater ground contact relative to size (plantigrade) = more POWER

Smaller ground contact relative to size (unguligrade) = more SPEED

How many cervical vertebrae?

7

How many thoracic vertebrae?

18

How many lumbar vertebrae?

6

How many sacrum vertebrae?

5

Cervical vertebrae characteristics

Larger vertebral arch, small dorsal and transverse spinous processes, larger articular processes

Thoracic vertebrae characteristics

Very tall dorsal spinous process, small transverse and articular spinous process

Lumbar vertebrae characteristics

Very long transverse spinous processes, midsized dorsal and articular spinous processes

Function of Atlas

Joints with skull, nodding motion

Function of axis

rotation of head, has a raised dorsal spinous process in order to attach to Nuchal ligament

Purpose of Nuchal ligament

Energy conservation; holds onto heavy head as a “strap” while the horse is grazing as opposed to using muscles

Most flexible portion of vertebrae

Cervical, chain allows movement of head + neck, “S” shaped

Articular surface for ribs (attachment points)

Thoracic vertebrae; capitulum (head) and tuberculum of rib

How many ribs?

18

How are the thoracic vertebrae oriented?

First 15 point backwards, middle straighteWhy ns out, last two incline forward

Why do horses have flat backs?

Grazing animals, GI track is HEAVY w/ a large volume; rigid spine stabilizes

Lumbar + sacrum; allows for hindlegs to move together

Lumbosacral joint

Spine + pelvis; allows for hindlegs to move individually and link hindquarters with rest of body; series of small synovial joints rather than 1 large joint

Sacroiliac joint

What types of horses are horses are more predisposed to sacroiliac arthritis?

Standardbred horses; trotters, shear SI joint

most lateral part of pelvis

Tuber coxae

“hunter bump”, over sacrum

Tuber Sacrale

Seat bone

Ischium (Tuber Ischii)

Ilium

Connects to femur, hip socket

Acetabulum

Pubis

~18 tail bones

Coccygeal Vertebrae

Difference in front vs hind articulation with spine

Hind: Sacroiliac joint

Front: NO joint

Site of glutes attachment

Major trochanter of femur

Connects w/ acetabulum

Head of femur

Uses patellar ligament to lock stifle

Trochlea of femur

Articulate w/ next bone (tibia)

Condyle of femur

Epicondyle of femur

Joins femur + tibia

Stifle joint

What locks the stifle?

Patellar ligaments

Why does the horse lock its stifle?

To conserve energy

What moves the patella to lock and unlock the stifle?

Quadriceps pull patellar ligaments up and around trochlea

Meniscus

What causes locking stifles?

Poor confirmation or weak musculature around stifle (specifically quadriceps)

Protracting muscles of hind quarters

Psoas, tensor facia latae, quadriceps (vastus muscles), peroneus tertius

Retracting muscles of hind quarters

Gluteal muscles, hamstrings (biceps femoris, semitendinosus, semimembranosus), gastrocnemius

Protracting, attaches to pelvis + femur

Psoas