Week 3 - Development of the limbs, back, shoulder joint and arm Flashcards
1
Q
Where/when do limb buds appear
A
Limb buds appear on the ventro-lateral body wall
- Lower limb bud appears after the upper limb bud
- First appear during the fourth week of development
2
Q
What do limb buds consist of?
A
A core of proliferating mesenchymal cells with an ectoderm covering
3
Q
How do limb buds develop?
A
- Begins with the activation of mesenchyme within lateral mesoderm (derived from the somatic layer of lateral plate mesoderm)
- Elongation is through proliferation of mesenchyme core
- There is thickened ectoderm at the apex of the limb bud (these ectodermal cells divide to form an apical ectodermal ridge)
- Somites form the limb musculature
4
Q
What are the degrees of symmetry within the embryo at this point?
A
- Top and bottom (proximal-distal)
- Front and back (dorsal-ventral)
- Side to side (anterior-posterior)
5
Q
What happens to the notochord?
A
The remnants of it become marooned by the axial skeleton formation
- This is called the nucleus pulpous
- It is able to herniate (causing a slipped disk)
6
Q
What does the apical ectodermal ridge (AER) do?
A
- Critical for limb development
- Orchestrates limb development
- Induces development of the digits within the hand/foot plates
- It marks the boundary between dorsal and ventral limb ectoderm
- Regresses after the appearance of paddles
7
Q
How does the apical ectodermal ridge orchestrate limb development?
A
- Exerts an inductive influence on the immediately underlying mesenchyme
- This tells it to remain undifferentiated, so the limb bund can continue to elongate
- Mesenchyme begins to differentiate as it gets further away from the AER, since the signals can no longer have an effect
8
Q
What is the ‘zone of polarising activity’?
A
A signalling centre located at the posterior base of the limb bud
- It controls patterning and maintains the AER
- It generates asymmetry in the limbs
9
Q
How do the hand and foot plates develop?
A
- Digital rays form:
- – Mesenchyme organises itself into condensations within plates
- – This forms cartilaginous models of the digital bones
- AER breaks up and is maintained only over the tips of the digital rays
- Interdigital spaces are progressively sculpted by programmed cell death
- AER causes the digits to elongate
10
Q
What controls axis specification?
A
- Anterior-posterior: zone of polarising activity
- Proximal-distal: AER
- Dorsal-ventral: ectoderm
11
Q
How do bones form?
A
- Signals from the AER to remain undifferentiated stop
- Lateral plate mesoderm condenses and differentiates
- Cartilage model forms
- Endochondral ossification
- Primary and secondary ossification centres appear in the epiphyses and maintain bone growth
12
Q
How do muscles develop from limbs buds?
A
- Myogenic precursors migrate into limbs from somites
- They coalesce into 2 common muscle masses around the newly formed skeletal elements
- – Ventral = flexor, dorsal = extensor
- Individual muscles then split from common masses
13
Q
How do limbs rotate during development?
A
They extend ventrally at first As they elongate they rotate - Upper limb = laterally - Lower limb = medially Before rotation: - Thumbs up, elbows out - Soles facing in and knees out After rotation: - Thumbs out and elbows down - Soles down and knees up
14
Q
How is the limb bud innervated?
A
- Upper limb bud appears opposite the caudal cervical spinal segments
- Lower limb bud appears opposite lumbar and sacral spinal segments
- Spinal nerves enter the limb bud early in its development
15
Q
What are some common limb developmental defects?
A
- Syndactyly: fusion of digits, may involve just connective tissue or bones may be fused
- Polydactyly: extra digits, genetic recessive trait
- Amelia: complete absence of a limb
- Meromelia: partial absence of 1 or more limb structures
Upper limb affected more often than lower limb
Rare and usually hereditary but teratogen-induced defects have been described
16
Q
What are the 2 groups of muscles in the back?
A
- Intrinsic: hold the spine erect, used for posture
- Extrinsic: superficial group and the intermediates (used in respiration)
17
Q
What are the posterior axio-appendicular muscles?
A
Muscles that attach the upper limb to the trunk
There are 3 groups:
- Superficial: trapezius, latissimus dorsi
- Deep: levator scapulae, rhomboids (major + minor)
- Scapulo-humeral: deltoid, trees major, 4 rotator cuff muscles
18
Q
What is the trapezius innervated by?
A
Accessory nerve
- And proprioreceptor fibres from C3 and C4
19
Q
What does the trapezius do?
A
- Directly attaches the pectoral girdle to the trunk
- Acts on scapulothoracic joint
- Divided into 3 parts:
- – Superior: elevates scapula and rotates it during abduction of arm
- – Middle: retracts scapula
- – Inferior: depresses scapula (pulls inferiorly)
20
Q
How does the scapula rotate?
A
Superior and inferior parts of trapezius act together
- They rotate the scapula upwards and outwards on chest wall, elevating the glenoid cavity
- Serratus anterior also aids upward rotation
- This rotation is responsible for abduction of the arm above horizontal
21
Q
What does the latissimus dorsi do?
A
Extends, adducts and medially rotates upper limn
22
Q
How is the latissimus dorsi innervated?
A
By the thoracodorsal nerve
23
Q
Where is the levator scapulae muscle found?
A
- Originates from the transverse processes of the C1-C4 vertebrae
- Attaches to the medial border of the scapula
24
Q
How is the levator scapulae muscle innervated?
A
By the dorsal scapular nerve and cervical nerves
25
What are the actions of the levator scapulae muscle?
- Elevates scapula
| - Rotates scapula, depressing glenoid cavity
26
Where is the rhomboid major found?
- Originates from the spinous processes of T2-T5 vertebrae
| - Attaches to the medial border of the scapula, below the rhomboid minor
27
Where is the rhomboid minor found?
- Originates from the spinous processes of C7-T1 vertebrae
| - Attaches to the medial border of the scapula, above the rhomboid major
28
What innervates the rhomboids?
Dorsal scapula nerve
29
What are the actions of the rhomboids?
Retract and rotate the scapula, depressing the gleaned cavity
30
What innervates the deltoid?
Axillary nerve
31
Where is the deltoid found?
- Originates from the scapula and clavicle
- Attaches to the deltoid tuberosity on the lateral surface of the humerus
- Forms rounded part of the shoulder; regimental patch
32
What are the actions of the deltoid?
- Anterior fibres (clavicular): flexion of arm
- Middle fibres (acromial): abducts arm from 15-90 degrees
- Posterior fibres (spinal): extends arm (along with lat. dorsi)
33
Where is the teres major found?
- Originates from the posterior surface of the scapula
| - Attaches to the intertubecular groove of the humerus
34
What innervates the teres major?
Lower subscapular nerve
35
What are the actions of the teres major?
Adducts at the shoulder and medially rotates the arm
36
What is the rotator cuff?
A collective name given to 4 short muscles that originate from the scapula and attach to the humeral head
- They act to 'pull' the humeral head into the glenoid fossa,
which gives the glenohumeral joint a lot of additional stability
- Muscles: supraprinatus, infraspinatus, subscapularis, teres minor
- The muscles all insert into the greater tubercle of humerus
- The tendons blend with each other to form a cuff
- This cuff also fuses with the capsule, strengthening it
37
What are the actions of the supraspinatus?
- Initiation and first 15 degrees of abduction
| - Assists deltoid for 15-90 degrees
38
What are the actions of the infraspinatus?
Lateral rotation of the arm
39
What are the actions of the teres minor?
Lateral rotation of the arm
40
What are the actions of the subscapularis?
Medially rotates the arm
41
What innervates the supraspinatus?
Suprascapular nerve (C5, C6)
42
What innervates the infraspinatus?
Suprascapular nerve (C5, C6)
43
What innervates the teres minor?
Axillary nerve
44
What innervates the subscapularis?
Upper and lower sub scapular nerve
45
What is the shoulder joint?
Also called the glenohumeral joint
- A synovial joint of the ball and socket type
- Formed between the articular surfaces of the scapula and the humerus head (both are lined by hyaline cartilage)
- Allows a wide range of movements in multiple planes
- One of the most mobile joints in the human body, but at the cost of joint stability
46
How is stability achieved in the shoulder joint?
- Muscles of the rotator cuff
- Other muscles
- Ligaments
- Capsule
47
How and why is the glenoid fossa deepened?
By a fibrocartilage rim, called the glenoid labrum
| - This reduces the disproportion in the surfaces (humeral heads much larger than the glenoid fossa)
48
What is the capsule in the shoulder joint?
A fibrous sheath which encloses the structure of the joint
| - It is lax, allowing greater mobility, but tough
49
What is the capsule of the shoulder joint attached to?
- Glenoid labrum and margins of glenoid cavity of scapula
| - Anatomical neck of humerus
50
Where is synovial membrane found in the shoulder joint?
Lines capsule and bone up to edge of articulating surfaces
51
What are the synovial bursa?
- Synovial fluid sacs which act as a cushion between tendons and other joint structures
- They reduce friction in the joint
- Clinically important bursa = subacromial and subscapular
52
What does the subacromial bursa do?
Facilitates movement of:
- Supraspinatus tendon over the coraco-acromial arch
- The deltoid muscle over the shoulder joint capsule and greater tubercle of humerus
53
What does the subscapular bursa do?
- Facilitates movement of the tendon of subscapularis muscle over the scapula
- Communicates with the joint cavity
54
What ligaments are found in the shoulder joint?
Intracapsular:
- 3 gleno-humeral ligaments: superior, middle, inferior
Extracapsular:
- Coracoacromial (between acromion and coracoid process)
- Coracohumeral (from base of coracoid process to anterior part of greater tubercle)
- Transverse humeral (holds the tendon of the long head of biceps in place during shoulder movement)
55
Which of the ligaments in the shoulder joint is the most important?
Coracoacromial
56
Describe the gleno-humeral ligaments
They are 3 fibrous bands extending between glenoid labrum and humerus
- Play a key role in stabilising the bony structures
- Most are thickenings of the joint capsule
- Can only be seen from inside the capsule
57
What is the coraco-acromial arch?
The coracoacromial ligament, acromion and the coracoid process
- A strong osseoligamentous structure
58
What does the coraco-acromial arch do?
Prevents the humeral head's upper displacement
59
What factors contribute to the mobility of a joint?
- Type of joint
- Bony surfaces
- Laxity of the joint capsule
60
What factors contribute to the stability of the shoulder joint?
- Rotator cuff muscles
- Glenoid labrum
- Ligaments
61
What is the blood supply to the shoulder joint?
- Anterior and posterior circumflex humeral arteries
| - Suprascapular artery
62
What is the nerve supply to the shoulder joint?
- Suprascapular
- Axillary
- Lateral pectoral
63
How does dislocation of the glenohumeral joint occur?
Usually caused by trauma on a fully abducted arm
Anterior dislocations are the most prevalent, but posterior dislocations can sometimes occur
Anterior:
- The humeral head dislocates anteriorly due to pull of powerful adductors
- Humeral head comes to lies below the coracoid process (forced anteriorly and inferiorly)
- Usually caused by excessive extension and lateral rotation of the humerus
64
What are some complications of a dislocation to the glenohumeral joint?
The axillary nerve runs in close proximity to the shoulder joint
- It can be damaged in dislocation
- Injury to it causes paralysis of the deltoid and loss of sensation over the regimental badge area
The radial nerve can be stretched
Tearing of the joint capsule is associated with an increased risk of future dislocations
65
What is tendonitis?
Inflammation of the muscle tendons, usually due to overuse
66
What is a characteristic sign of rotator cuff tendonitis?
Painful arc:
| - Pain in the middle of abduction, where the affected area comes into contact with the acromion
67
What is rotator cuff tendonitis?
Tendonitis in the rotator cuff muscles
- The humeral head and rotator cuff impinge on the coraco-acromial arch, producing irritation the arch and inflammation of the rotator cuff
- Over time, this causes degenerative changes in the subacromial bursa and the supraspinatus tendon
- This increases friction between the structures of the joint
- Relatively common, because these muscles are often under heavy strain
68
Which muscles cause flexion of the glenohumeral joint?
- Pectoralis major
- Anterior deltoid
- Biceps brachii
- Coracobrachialis
69
Which muscles cause extension of the glenohumeral joint?
- Posterior deltoid
- Latissimus dorsi
- Teres major
70
Which muscles cause abduction of the glenohumeral joint?
- 0-20: supraspinatus
- 20-90: central deltoid
- above 90: rotation of scapula (trapezius, serratus anterior)
71
Which muscles cause medial rotation of the glenohumeral joint?
- Subscapularis
- Teres major
- Pectoralis major
- Latissimus dorsi
72
Which muscles cause lateral rotation of the glenohumeral joint?
- Infraspinatus
| - Teres minor
73
Where is the biceps brachii found?
2 headed muscle
- Long head originates from the supraglenoid tubercle of the scapula
- Short head originates from the coracoid process of the scapula
- Distally, the biceps attaches to the radial tuberosity on the radius
74
Describe the biceps brachii
- 2 headed muscle
- Not attached to the humerus
- The tendon of then long head passes through the shoulder joint and intertubecular groove of the humerus to meet the short head
- The 2 heads combine at the humeral shaft to form the muscle belly
75
What is the main action of the biceps brachii?
Supination of the forearm
| - Also flexes the arm at the elbow and at the shoulder
76
What innervates the biceps brachii?
Musculocutaneous nerve
77
What is the bicipital aponeurosis?
A connective tissue sheet
- Given off by the biceps tendon
- Forms the roof of the cubital fossa
- Blends with the deep fascia of the anterior forearm
78
What is the main action of the coracobrachialis?
Flexor of the arm
79
What innervates the coracobrachialis?
Musculocutaneous nerve
80
Where is the coracobrachialis found?
- Originates from the coracoid process of the scapula
- Passes through the axilla
- Attaches to the medial side of the humeral shaft, at the level of the deltoid tubercle
81
What is the main action of the brachialis?
The main flexor at the elbow
82
Where is the brachialis found?
- Originates from the medial and lateral surfaces of the humeral shaft
- Forms the base of the cubital fossa
- Inserts into the tuberosity of the ulna
83
What innervates the brachialis?
Musculocutaneous nerve
| - Small lateral portion is innervated by the radial nerve
84
Where is the triceps brachii found?
Found on the posterior arm
- Lateral head: originates from the humerus, superior to the radial groove
- Long head: originates from the infraglenoid tubercle
- Medial head: originates from the humerus, inferior to the radial groove
- The tendon attaches to the olecranon of the ulna
85
Describe the triceps brachii
- 3 headed muscle
- The 3 heads combine to make 1 muscle
- This converges to a tendon
86
What is the main action of the triceps brachii?
Extension of the arm at the elbow
87
What innervates the triceps brachii?
Radial nerve
88
How does the subclavian artery change name?
- Begins as the left and right subclavian artery
- Become the axillary artery when it enters the axilla
- Becomes the brachial artery after the posterior and anterior circumflex humeral arteries break off
- The brachial artery bifurcates into the radial and ulnar arteries
89
Which arteries are found in the arm?
- Axillary artery
- Brachial artery
- Deep artery (profound brachia) is found in the radial groove
90
What are the motor functions of the musculocutaneous nerve?
Innervates the muscles in the anterior compartment of the arm (biceps brachia, brachialis, coracobrachialis)
91
What are the sensory functions of the musculocutaneous nerve?
Gives rise to the lateral cutaneous nerve of the forearm
| - This innervates the skin of the lateral aspect of the forearm
92
What are the motor functions of the radial nerve?
- Directly innervates the 3 heads of the triceps brachia
| - Innervates the muscles in the posterior compartment of the forearm
93
What are the sensory functions of the radial nerve?
Divides into 4 branches which provide cutaneous innervation to the skin of the upper limb:
- Lower lateral cutaneous nerve of arm
- Posterior cutaneous nerve of arm
- Posterior cutaneous nerve of forearm
- Superficial branch of the radial artery (innervates the dorsal surface of the lateral 3.5 digits and their associated palm area)
94
What are the motor functions of the ulnar nerve?
Innervates:
- Flexor carpi ulnaris
- Flexor digitorum profundus
- Hypothenar muscles
- Medial 2 lumbricals
- Adductor policis
- Interossei of the hand
95
What are the sensory functions of the ulnar nerve?
- Palmar cutaneous branch (innervates the skin of the medial half of the palm)
- Dorsal cutaneous branch (innervates the skin of the medial 1.5 fingers and associated palm area)
- Superficial branch (innervates the palmar surface of the medial 1.5 fingers)
96
What are the major superficial veins of the upper limb?
- Cephalic
| - Basilic
97
Where does the cephalic vein travel?
- Arises from the dorsal venous network of the hand
- Ascends the antero-lateral aspect of the upper limb, passing anteriorly at the elbow
- Travels between the deltoid and the pectoralis major muscles at the shoulder
- Enters the axilla
- Terminates within the axilla by joining the axillary vein
98
Where does the basilic vein travel?
- Originates from the dorsal venous network of the hand
- Ascends the medial aspect of the upper limb
- At the border of the teres major, it moves deep into the arm
- Here, it combines with the brachial veins to form the axillary vein
99
Describe the cubital fossa
An area of transition between the anatomical arm and the forearm
- Located as a depression on the anterior surface of the elbow joint
- From lateral to medial, it contains:
- -- Biceps tendon, brachial artery, median nerve
100
What are the borders of the cubital fossa?
- Lateral = medial border of the brachioradialis
- Medial = lateral border of the pronator teres
- Superior = imaginary line between the medial and lateral epicondyle
101
What can cause damage to the musculocutaneous nerve?
A stab wound to the axilla region
102
What are the consequences of damage to the musculocutaneous nerve?
- Loss of sensation over the lateral side of the forearm
- Coracobrachialis, biceps brachii and brachialis muscles are paralysed
- Flexion at the shoulder and elbow is weaker but can still occur die to the pec. major and brachioradialis muscles respectively
- Supination of affected limb is greatly weakened
103
What can cause damage to the radial nerve in the axilla?
- Dislocation of the humerus at the glenohumeral joint
- Fractures of proximal humerus
- Excessive pressure on the axilla
104
What are the consequences of damage to the radial nerve in the axilla?
- Triceps brachii and muscles in the posterior compartment of the arm are paralysed
- Loss of extension of wrist, forearm and fingers
- Unopposed flexion of wrist
- All 4 cutaneous branches of the radial nerve are affected
- Loss of sensation over the lateral and posterior upper arm, posterior forearm and dorsal surface of the lateral 3.5 digits
105
How can you test the biceps reflex?
- Support patient's arm, with it flexed at roughly 60 degrees
- Place your thumb over the biceps tendon
- Hit your thumb with the tendon hammer
106
How can you test the triceps reflex?
- Rest the patient's arm across their chest
| - Hit the triceps tendon just proximal to the elbow
107
How can you test the supinator reflex?
- Place 3 fingers on the supinator tendon as it crosses the radius
- Hit the fingers
108
What may be the cause of a humeral fracture?
Usually falls or direct trauma
109
What are the different types of humeral fracture?
- Proximal humeral
- Humeral shaft
- Distal humeral
110
Where is the most common place for a humeral fracture?
The surgical neck
111
What are the consequences of a humeral fracture?
Sharp, intense pain at time of injury
Pain may increase when:
- Attempting to perform movements of the upper limb
- Lying on the affected side
- Applying pressure to the shoulder
- Firmly touching the humerus at the site of injury
112
What may be damaged in a fracture of the surgical neck of the humerus?
- Axillary nerve
| - Posterior circumflex artery
113
What may be damaged in a mid-shaft fracture of the humerus?
Since they are both tightly bound in the radial groove:
- The radial nerve
- Profunda brachii artery
114
Where are the most common places for a distal humeral fracture?
- Supracondylar ridge
| - Medial epicondyle
115
What may be damaged in a distal humeral fracture?
- Brachial artery
- Ulnar nerve
- Radial nerve
- Medial nerve
116
What is winged scapula?
- Damage to the long thoracic nerve, paralysing the serratus anterior
- This moves the medial border and inferior angle of the scapula markedly away from the posterior thoracic wall (making the scapula look like a wing)
- The upper limb may not be able to be abducted above the horizontal position, because the serratus anterior is unable to rotate the glenoid cavity superiorly to allow complete abduction of the limb
117
Why is venepuncture possible in the cubital fossa?
- The median cubital vein is located superficially within the roof of the cubital fossa
- It connects the basilic and cephalic veins
- It can be easily accessed
118
How can rotator cuff injuries occur?
- Trauma may tear or rupture 1 or more of the tendons of the muscles
- Repetitive use of the rotator cuff, resulting in tears of the musculotendinous rotator cuff
119
What is the consequence of rotator cuff injuries?
Instability of the glenohumeral joint
120
What is subacromial bursitis?
- An inflammatory reaction due to irritation of the subacromial bursa
- Pain occurs during 50-130 degree of abduction
- The supraspinatus tendon is in intimate contact with the inferior surface of the acromion during this arc
121
What are the consequences of axillary nerve injury?
- Deltoid atrophies
| - Loss of sensation may occur over the lateral side of the proximal arm (regimental badge area)
122
How can axillary nerve injury occur?
- Usually during fracture of the surgical neck of the humerus
- During dislocation of the glenohumeral joint
- Compression due to incorrect use of crutches
123
How can dislocations of the glenohumeral joint occur?
Commonly by direct or indirect injury
124
Where do most dislocations of the glenohumeral joint occur?
Inferiorly:
| - Due to presence of the coraco-acromial arch and support of the rotator cuff (upward dislocation is prevented)
125
How do you describe dislocations of the glenohumeral joint?
As anterior or posterior dislocations
- Indicates whether the humeral head has descended anterior or posterior to the infraglenoid tubercle and long head of the triceps
- The head ends up lying anterior or posterior to the glenoid cavity
