The Equine Skeleton

Question 1

Define BONE

Answer 1

Bone is a type of connective tissue. Is is the largest part of the skeleton and has a blood supply.
It can be damaged or diseased but can also repair itself, as well as adapt to environmental strength (e.g. training horses on roads improves bone strength).

Question 2

What is the structure of bone?

Answer 2

The outer layer of bone consists of a dense, ivory covered outer shell called compact bone. This is covered by a further layer called the periosteum. Small holes and channels carry blood vessels from the outer coating to the spongy interior, known as cancellous bone. It is filled with red marrow, which is responsible for the production of red and white blood cells, and yellow marrow, which is mainly fat and can be used as a last resort energy source.

Question 3

What are the 5 types of bone?

Answer 3

Long, short, sesamoid, flat, irregular

Question 4

Describe a long bone

Answer 4

They are often limbs e.g. radius, humerus and cannon bones. They are longer than they are wide.

Question 5

Describe a short bone

Answer 5

They are approximately equal in all dimensions. They can absorb concussion and are therefore found in complex joints that have a lot of movement e.g. the carpus (knee) and tarsus (hock).

Question 6

Describe a flat bone

Answer 6

They are made up of a flat sandwich of cancellous bones between layers of cortex. They are usually slightly curved, with no cavity for bone marrow. Main function is the protection of vital organs e.g. the skull protects the brain.

Question 7

Describe an irregular bone

Answer 7

They are unpaired bones on the median plane e.g. vertebrae and hip bones.

Question 8

Describe a sesamoid bone

Answer 8

They occur along the course of tendons to reduce friction, increase leverage or change direction of pull e.g. the patella (kneecap).

Question 9

What are the functions of the skeleton?

Answer 9

• protection of organs
• vertebrates depend on levers made of bone attached to muscle that allow locomotion, defence, offence, grasping etc.
• provides storage for minerals such as calcium and phosphorus

Question 10

What is each section of the equine skeleton called and how many bones in each?

Answer 10

34 bones in the skull
20 bones in each forelimb
20 bones in each hindlimb
37 bones in the ribcage
54 bones in the vetebral column

Question 11

Define DENSE/CORTICAL (COMPACT) BONE

Answer 11

Compact bone is the hard layer that covers most bones and forms almost the entire shaft of long bones.

Question 12

Define CANCELLOUS (SPONGY) BONE

Answer 12

Cancellous bone is composed of spicules (small, needle like structures) arranged to form a porous network. The spaces between are usually filled with bone marrow.

Question 13

Define an OSTEON

Answer 13

An osteon is the basic unit of structure of compact bone, comprising of a Haversian canal and its concentrically arranged lamallae.

Question 14

Define LAMALLAE

Answer 14

Lamallae is a thin layer, membrane, or plate of tissue, especially in bone. It is arrnaged concentrically within the osteon, around the central Haversian canal.

Question 15

Define a HAVERSIAN SYSTEM

Answer 15

Haversian systems are formed when several osteons are put together.

Question 16

Define the MEDULLARY CAVITY

Answer 16

The medullary cavity is the central cavity of bone shafts where red bone marrow/yellow bone barrow is stored.

Question 17

Define PERIOSTEUM

Answer 17

Periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints.

Question 18

Define LACUNAE

Answer 18

Lancunae are small cavities at junctions between lamallae that allow the exchange of nutrients, waste and chemicals.

Question 19

How does bone growth occur?

Answer 19

There are two ways that bone growth can occur:
1. Adding layers on to the surface (increasing girth).
2. Longitudinal growth from the growth plate (made of cartilage) between the diaphysis and epiphysis.
At sexual maturity the growth plate thickens and fuses.

Question 20

What are the 3 types of cells in bone?

Answer 20

Osteoclasts - break down old/damaged bone
Osteocytes - carry nutrients and waste products to and from blood vessels
Osteoblasts - repair damaged and build up new bone.

Question 21

What is endochondral ossification and how does it occur?

Answer 21

It is an essential process during fetal development. #

1. Cartilage model develops
2. Primary ossification centre develops in the midshafts of long bones
3. Secondary ossification centres develop near the end of long bones
4. Osteoclasts remove bone while osteoblasts continue to lay it down
5. Narrow band of cartilage persists

Question 22

What are the 4 classifications of joints based on range of movement?

Answer 22

Synarthrosis joint, synchondrosis joint, amphiarthrosis, disthrosis

Question 23

Describe a synarthrosis joint

Answer 23

These are immovable, fixed joints with bones in very close contact. They are separated by a thin layer of fibrous connective tissue.
Example: the sutures of the skull

Question 24

Describe a synchondrosis joint

Answer 24

These are connected/bound by hyaline cartilage membrane. Most are temporary but some are permanent. They are almost immovable.
Example: the spinal vertebrae

Question 25

Describe an amphiarthrosis joint

Answer 25

These are slightly movable joints that are connecte by a wedge or pad of fibro cartilage. They are compressible and therefore good for shock absorption.
Example: hip bones

Question 26

Describe a disrthrosis joint

Answer 26

These are freely movable joints at the ends of opposing bones. They are covered in hyaline cartilage and separated by a joint cavity.
Example: the elbow

Question 27

What are the 5 types of synovial joint?

Answer 27

1. Hinge joint - folding movement
2. Sliding (plane) joint - sliding movement
3. Ball and socket joint - wide ranging, triaxial, multidirectional
4. Pivot joint - monaxial rotation movement
5. Ellipsoid joint - biaxial movement, knuckle shaped surface

Question 28

What are intervertebral discs?

Answer 28

They are layers of cartilage separating adjacent vertebrae in the spine.

Question 29

What is the structure of the equine rib cage?

Answer 29

First is the cervical section, which contains 7 vertebrae. Next come the 18 thoracic vertebrae which are connected to 18 pairs of ribs. Then, 6 lumbar vertebrae and 5 fused sacral vertebrae which form the sacrum that functions as a single bone. Finally comes the tail vertebrae.

Question 30

Define CARTILAGE

Answer 30

Cartilage is a highly specialised type of connective tissue. It is firm but flexible, with no direc blood and nerve supply. Difficult to repair once damaged.

Question 31

What are the 3 types of cartilage?

Answer 31

Hyaline - the most common. Found in the nose and the trachea. Blue/white in colour and negatively charged. The surface attracts a layer of water to which hyalurinate molecules stick and prevent arthritis.

Elastic - found in the external ear

Fibrous - found in intervertrabral discs.

Question 32

What are the 3 layers within cartilage?

Answer 32

The top layer is the tangetal layer and is flattened chondrocytes.
The middle layer is made up of rnadom collagen fibres and large, round chondrocytes.
The bottom layer is calcified with mineralised chondrocytes with a radial arrangement of collagen fibres.

Question 33

Define SYNOIVAL FLUID

Answer 33

Synovial fluid is a fluid found in the cavities of synovial joints. Its primary function is to reduce friction between the articular cartilage of synovial joints during movement.

Question 34

Define SYNOVIAL JOINTS

Answer 34

Synovial joints are the most common type of joint in the body. A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity.

Question 35

Define LIGAMENTS

Answer 35

A ligament is a short band of tough, flexible fibrous connective tissue which connects two bones or cartilages or holds together a joint.

Question 36

What is the purpose of ligaments?

Answer 36

They exist to support joints. They are tough and unyielding with some degree of resistance and are able to prevent excessive or abnormal joint movement.

Question 37

What are the 3 types of ligament?

Answer 37

Capsular, extracapsular, intracapsular.

Question 38

Define a VOLKMANN CANAL

Answer 38

Volkmann’s canals are inside osteons. They interconnect the haversian canals with each other and the periosteum.