Forelimb Anatomy Demonstration
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What is the sequence of events that happens in the forelimb in order for the animal to propel itself forwards and when during this sequence does weight bearing occur?
- Extension - limb becomes weight bearing
How is the forelimb attached to the trunk in the common domestic species and what is the functional significance of this?
There is no physical joint between the trunk and forelimb, it is attached only by muscle. This increases stride length during locomotion for increased speed.
How do the roles of extrinsic and intrinsic muscles in the process of locomotion differ and why is this the case?
Extrinsic muscles perform protraction, retraction, abduction and adduction as their origin is on the axial skeleton and insertion on the appendicular skeleton. Intrinsic muscles perform flexion and extension as their origin and insertion is on the appendicular skeleton.
How would you classify each of the following bones and what is the function of each type of bone? a) Scapula b) Humerus c) Radius and ulna d) Carpal e) Proximal sesamoids
- a) Flat - large surface area of attachment for muscles and protection of underlying structures
- b) Long - support and leverage within the limb
- c) Long - support and leverage within the limb
- d) Short - large range of movement and shock absorption
- e) Sesamoid - redirect tendons over angled surfaces and protect them from friction
What covers the rough areas of the bone surface and the smooth articular surfaces? Why is this the case?
- Rough - periosteum
- Smooth - hyaline cartilage - provides smooth friction free surface are for movement of the joint. Also no nerve endings in cartilage so no bleeding or pain when the joint moves
Why does the scapula have a flat medial surface?
To allow a smooth gliding action of the shoulder joint during locomotion - scapular glide
Where in the canine humerus are fractures most likely to occur and why?
At the supratrochlear foramen as the hole represents a weakness in the bone
How important is it to stabilise fractures of the ulna?
Midshaft fractures are not important as the radius is the main weight bearing bone. Distal fractures of the styloid process need stabilised due to attachment of collateral ligaments of carpus and resulting carpal instability. Proximal fractures through the olecranon process need stabilised due to involvement with elbow joint.
Which palpable features are the landmarks for locating the shoulder joint and which bone is each located on?
- Scapula - acromion process
- Humerus - greater tubercle
Which palpable feature is the site of insertion of the muscles that extend the elbow joint and which bone is it located on?
Olecranon process - ulna
Which palpable features are the site of attachment of the collateral ligaments of the elbow joint and which bone is each located on?
Medial and lateral epicondyles - humerus
Which palpable features are the sites of attachment for the collateral ligaments of the carpal joint and which bone is each located on?
- Medial styloid process - radius
- Lateral styloid proces - ulna
Which aspect of the limb is the accessory carpal bone located on and what is the function of the muscles that insert onto it?
Palmar aspect. Carpal flexors, they also provide stability to the ACB.
What is the function of the pre scapular lymph nodes and why is it important to palpate them?
They drain the lymph from the forelimb. If they are enlarged it can be an indication of infection.
Name the 5 components that are present in a typical synovial joint and give at least one function for each
- Synovial fluid - nourishes and lubricates the joint
- Synovial membrane - produces synovial fluid
- Joint capsule - supports synovial membrane and encases joint
- Hyaline cartilage - prevents friction
- Collateral ligaments - fibrous condensation of joint capsule medially and laterally to support joint and restrict movement to flexion and extension
In cases of degenerative joint disease, where specifically does the new bone form and why is this knowledge useful clinically?
New bone forms around the osteochondral junction. We can look at these areas on radiographs.
How does the shoulder compensate for having poor collateral ligaments?
It has extra medial and lateral muscular support. The supraspinatous and infraspinatous muscles cross the lateral aspect of the joint and suprascapularis crosses the medial aspect.
Why are fractures of the elbow joint more likely to occur than dislocations? Give anatomical reasons for your answer
A dislocation can only occur when the joint is in extreme flexion. The anconeal process also provides great support to this joint, making dislocation very hard.
What is the function of the muscles that insert onto the accessory carpal bone and which joint within the carpus is responsible for most movement?
Function = carpal flexion. Radio-carpal joint
What do all the extrinsic muscles of the forelimb all have in common with each other and what is their function?
They all have their origin on the axial skeleton and insert onto the appendicular skeleton. They all move the limb relative to the trunk.
What effect will each of the extrinsic muscles have on the forelimb when it contracts and why?
- Brachiocephalicus - limb protraction, shoulder extensor
- Latissimus dorsi - limb retraction, shoulder flexor
- Serratus ventralis - limb protraction (cranial) and retraction (caudal)
- Pectorals - limb adduction
- Trapezius - limb abduction
Which of the extrinsic muscles of the forelimb get their nerve supply from the brachial plexus and which don't?
- Do - latissimus dorsi, pectorals, serratus ventralis
- Don't - brachiocephalicus, trapezius
What do all the intrinsic muscles of the forelimb have in common with each other and what is their function?
They all have their origin and insertion on the appendicular skeleton. They produce flexion and extension of the joints in the forelimb.
What effect will each of the intrinsic muscles have on the shoulder and/or elbow joint when it contracts and why? Biceps brachii, deltoideus, teres major and triceps brachii
- Biceps brachii - shoulder extensor, elbow flexor
- Deltoideus - shoulder flexor
- Teres major - shoulder flexor
- Triceps brachii - shoulder flexor, elbow extensor
What is the common function of the muscles supplied by the a) axillary nerve b) musculocutaneous nerve?
- a) Shoulder flexor
- b) Elbow flexor
Which extrinsic muscles have an effect on the shoulder joint and why?
- Brachiocephalicus - shoulder extensor
- Latissimus dorsi - shoulder flexor
- As both run over the shoulder joint, from origin to insertion
What effect will each of these intrinsic muscles have on the carpus and/or digits when it contracts? Extensor carpi radials, extensor carpi ulnaris, common digital extensor, flexor carpi ulnaris, superficial digital flexor, deep digital flexor
- Extensor carpi radialis - carpal extensor
- Extensor carpi ulnaris - carpal extensor and flexor
- Common digital extensor - carpal and digital extensor
- Flexor carpi ulnaris - carpal flexor
- Superficial digital flexor - carpal and digital flexor
- Deep digital flexor - carpal and digital flexor
Which muscles are supplied by the median and ulnar nerves and what is their common function?
Superficial digital extensor, deep digital extensor, flexor carpi ulnaris - all are carpal flexors
Which muscles are supplied by the radial nerve and what is their common function?
Extensor carpi radialis, extensor carpi ulnaris, common digital extensor - all are carpal extensors
Where in a long bone are the articular surfaces usually located?
At the epiphysis
How do joint spaces appear in radiographs and why?
As a black.dark grey space because they are filled with fluid and soft tissue
What are the functions of the radius and ulna?
- Radius - weight bearing
- Ulna - provides leverage
What are the articular surfaces of the shoulder joint?
Glenoid cavity of scapula and head of humerus
What are the articular surfaces of the elbow joint?
Trochlear notch of ulna, trochlea of humerus, head of radius
What is/are the functions of the biceps brachii muscle and what is its nerve supply? Which muscle antagonises its actions?
- Functions = shoulder extensor, elbow flexor. Nerve supply = Musculocutaneous nerve
- Antagonistic muscle = triceps brachii
Which aspect of the limb joints do the major blood vessels cross and why?
The flexor aspect, so they are not constricted when the limb flexes or stretched during limb movement.
If a dog was to suffer damage to its brachial plexus, which movements within the limb would remain and which would be lost?
- Lost - extension/flexion, retraction, and abduction. Limb would not be able to weight bear. Loss of cutaneous sensation to entire limb.
- Remain - limb protraction/shoulder extension and abduction as brachiocephalicus and trapezius would still be functional
If a dog was to suffer from radial nerve damage what would be the effect within the forelimb in terms of function and sensation?
- Function - Loss of ability to extend elbow, carpus, distal limb and to weight bear.
- Sensation - Loss of sensation down cranial antebrachium and dorsal aspect distal limb.
What is the function of muscles that receive their motor supply from the median and ulnar nerves?
Carpal and digital flexors
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