MSK Session 3 Flashcards
How are somites formed?
Paraxial mesoderm aggregates into pairs of blocks either side of the neural tube
What is the origin of the musculoskeletal system?
Somites and lateral plate mesoderm
How are somites further organised after formation?
Into bone, muscle and skin precursors within the somite
Why does development of the MSK system not take place until relatively late, in the fourth week of development?
It is not necessary for the developing embryo like the CVS or NS
Where do the limb buds appear?
On the ventral-lateral body wall
Why is the UL always more developed than the LL?
It appears ~2 days before
What is the structure of a limb bud?
Core of proliferating mesenchymal cells which are similar to CT cells
Proliferate at a greater rate than the surrounding cells which form the bud
Describe the development of limb buds.
Somatic layer of lateral plate mesoderm
Activation of mesenchyme w/in lateral mesoderm layer
Flexible mesenchyme core proliferates to elongate limb bud
Apical ectodermal ridge regulates elongation
What is the entire embryo covered by?
Endoderm
What does the limb bud need to grow?
Thickening of endoderm at apex
What is the function of the apical ectodermal ridge?
Orchestrate proximal to distal limb development
Ensure limb develops to required length
Regression for proper digit growth
Marks dorsal-ventral limb boundary
What is the final stage of limb development?
Appearance of paddles
What is the function of the dorsal/ventral ectoderm?
Exert dorsalising and ventralising influences over mesenchyme core
What are the corresponding postnatal axes to the embryonic axes of limb development?
Anterior (head) = superior Dorsal = posterior Proximal = proximal Posterior (tail) = inferior Ventral (belly) = anterior Distal = distal
What are the three degrees of symmetry in the embryo?
Side to side
Front and back
Top and bottom
Where is the anrterio-posterio axis of the developing limb?
From the 1st digit to 5th
What makes up the dorsal aspect of the developing limb?
Back of hand and top of foot
What makes up the ventral aspect of the developing limb?
Palm of hand and sole of foot
Where is the proximo-distal axis of the developing limb?
Base of limb to tips of digits
What is the function of the AER as the limb elongates?
Secretes signalling molecules to the underlying mesenchymal cells to prevent their differentiation and continue proliferation
What happens to the proximal mesenchyme as the limb elongates?
Stops receiving signals from AER so it differentiates into constituent tissues
How does the zone of polarising activity generate asymmetry in the limbs?
Determines the anterior-posterior axis
What effect does the ZPA have on the hands and feet?
Ensures they are mirror images of each other
Where is the ZPA located?
Posterior base of the limb bud
What controls patterning as well as maintaining the AER?
ZPA
What are the controllers of axial specification?
Anterio-posterio = ZPA Proximal-distal = AER Dorsal-ventral = ectoderm
How are hands and feet formed?
Limb buds flatten and flare into digital rays
What are digital rays?
Mesenchyme condensations w/in plates
Describe the formation and subsequent sculpture of hand and foot plates.
Flattening and flaring of limb buds –> digital rays form –> AER regresses so only on apexes of digital rays –> interdigital spaces progressively sculpted by programmed cell death
Why is the AER only maintained at the tips of the digital rays?
To allow for their elongation
What can be seen postnatally between the fingers?
Remnants of interdigital spaces
What is amelia?
Complete absence of a limb
What is meromelia?
Partial absence of one or more limb structures
What is phocomelia?
Hands or feet close to trunk due to interference w/AER
What can cause phocomelia?
Thalidomide exposure
What is polydactlyly?
Genetic recessive trait causing extra digits
What is syndactyly?
Error in interdigital space formation causing fusion of digits by CT or bone
Which limb is more affected by limb defects?
UL
What joins the three discrete bones in the hip?
Triadiate cartilage
How do myogenic precursors arrive in the limbs?
Migrate from outside limb buds in somites into limbs
What happens to the myogenic precursors after they have migrated into the limb bud?
Coalesce into 2 common muscle masses either side of newly formed central skeletal elements
What do the two common muscle masses formed by myogenic precursors give rise to?
Ventral = flexor Dorsal = extensor
How do individual muscles email innervated once they have split from the common masses?
Take innervation from somite linked w/spinal cord with them
How do the flexor and extensor compartments compare in the UL and LL?
UL: flexor = anterior, extensor = posterior
LL: flexor = posterior, extensor = anterior
Why do the upper and lower limb have opposite arrangements of flexor and extensor compartments?
Rotation of limbs which affects LL much more
How do the limbs rotate after ventral extension?
UL = laterally LL = medially
How doe the limbs compare before and after rotation?
Before = thumbs up, elbows out, soles facing each other, knees out After = thumbs out, elbows down, soles down, knees up
Why is rotation of the LL not as fixed?
It is more mobile
How do the thumb and big toe rotate?
Thumb = laterally
Big toe = medially
What are maintained during rotation?
Ventral axial lines
What lies on the pre-axial line?
Thumb and big toe
What lies on the post-axial line?
Little finger and toe
Which spine segments do the upper limb buds appear opposite?
Caudal cervical
Which spinal segments do the lower limb buds appear opposite?
Lumbar and sacral
Why do spinal nerves enter the limb bud early in its development?
Needed along with AER for development
What is a myotome/dermatome?
Strip of skin/muscle-group of muscles supplied by a single nerve which can be examines clinically
Why is the regular organisation of dermatomes and myotomes seen in the embryo not seen later on in development?
Distorted due to loss of symmetry and limb bud rotation
What are the ventral axial lines?
Mid axillary lines that spilt the arm in half along the longitudinal axis
How do muscles become innervated by the brachial plexus?
Muscles are compartmentalised and nerves grow into common muscle masses
What happens to all anterior divisions of the brachial plexus that innervate the flexors?
Regroup to form lateral and medial cords to supply the flexors
What happens to the posterior divisions of the brachial plexus that innervate the posterior components?
Regroup to form posterior cord to supply extensors
What forms the superior border of the cubital fossa?
Imaginary line between lateral and medial elicondyles
What forms the medial border of the cubital fossa?
Lateral border of the pronator teres
What forms the lateral border of the cubital fossa?
Medial border of brachioradialis
What is the cubital fossa?
Depression on the anterior surface of the elbow joint that marks the area of transition between the anatomical arm and forearm
What forms the floor of ten cubital fossa?
Proximally = brachialis Distally = supinator
What forms the roof of the cubital fossa?
Skin and fascia reinforced by the bicipital aponeurosis
What structure does the median cubital vein run through?
Bicipital aponeurosis
What are the contents of the cubital fossa?
Radial nerve
Biceps tendon
Brachial artery
Median nerve
Where is the radial nerve located in the cubital fossa?
Deep b/w brachioradialis and brachialis
What does the radial nerve divide into in the cubital fossa?
Deep and superficial branches
How is the biceps tendon located in the cubital fossa?
Runs through attaching to radial tuberosity
What is the function of the brachial artery?
Supply oxygenated blood to the forearm
What happens to the brachial artery at the alex of the cubital fossa?
Bifurcates into radial and ulnar arteries
Where does the median nerve exit the cubital fossa?
B/w two heads of the pronator teres
What does the median nerve innervate the majority of?
Flexor muscles in the forearm
Where are the tendon, artery and nerve located in the cubital fossa?
Closer to the medial side
What does the median cubital vein join in the cubital fossa?
Basilic and cephalic veins
Why is the medial cubital vein a good site for venepuncture?
It’s superficial location makes it clearly visible when a tourniquet is applied
Where is the brachial pulse felt?
Immediately medial to biceps tendon in cubital fossa
Where do you listen for Korotkoff sounds?
Brachial pulse site in cubital fossa
What is the function of the intrinsic back muscles?
Hold spine erect
Responsible for posture
What are the three groups of extrinsic back muscles?
Superficial
Posterior axio-appendicular
Intermediate
What is the function of the posterior axio-appendicular muscles?
Attach axial skeleton to appendicular skeleton
Which muscles make up the superficial group of the posterior axio-appendicular-appendicular back muscles?
Trapezius
Latissimus dorsi
Which muscles make up the deep group of posterior axio-appendicular back muscles?
Levator scapulae
Rhomboids
Which muscles make up the scapulo-humeral group of the posterior axio-appendicular back muscles?
Deltoid
Teres major
4 rotator cuff muscles
What are the main actions of the trapezius?
Superior part: elevation of clavicle
Middle part: retraction of scapula
Inferior part: depression of scapula
What innervates the trapezius?
Accessory nerve
How is the accessory nerve tested?
Shrug shoulders against resistance
What is the main action of the latissimus dorsi?
Adduct arms
Extend arms at shoulder joint
Medial rotation
What innervates the latissimus dorsi?
Thoraco-dorsal nerve
Where does the thoraco-dorsal nerve originate from?
Posterior cord of brachial plexus
What are the main actions of the deltoid?
Anterior fibres = flexion
Middle fibres = abduction from 15-90 degrees
Posterior fibres = extension
What innervates the deltoid?
Axillary nerve
What are the main actions of the levator scapulae?
Elevate scapula
Rotate scapula by depressing glenoid cavity
What innervates the levator scapulae?
Dorsal scapular and cranial nerves
What are the main actions of the Rhomboids major and minor?
Retract scapula
Rotate scapula by depressing glenod cavity
What innervates the rhomboids?
Dorsal scapular nerve
Where does the dorsal scapular nerve originate?
C5 root of brachial plexus
What are the main actions of Teres major?
Addicts arm
Medial rotation
What innervates teres major?
Lower subscapular nerve
How is rotation of the scapula achieved?
Superior and inferior parts of trapezius act together elevating GC
Serratus anterior aids upwards rotation
Arm abducted above horizontal
Why does the whole unit have to move in the glenohumeral joint to facilitate rotation of the scapula?
Otherwise acromion obstructs humerus
What deepens the glenoid cavity?
Glenoid labrum w/fibrocartilage rim
What causes the glenohumeral joint to be the most mobile but least stable?
Shallow glenoid cavity
Disproportion of articular surfaces
Multiplanar movements
Lax capsule
How is stability of the glenohumeral joint achieved?
Muscles of rotator cuff
Surrounding muscles
Ligaments
Capsule
What is the capsule of the glenohumeral joint attached to?
Glenoid labrum
Margins of glenoid cavity of scapula
Anatomical neck of humerus
Medially to surgical neck
What does the capsule of the glenohumeral joint bridge?
Intertubercular groove
Where does the shoulder joint synovium communicate with the subscapular bursa?
Small anterior opening of the glenohumeral capsule
Why are intramuscular injections into deltoid given higher than the surgical neck?
Axillary nerve and post circumflex artery are vulnerable here
What are the three intracapsular ligaments in the glenohumeral joint?
Superior, middle and inferior glenohumeral ligaments
What are the intracapsular ligaments of the GH joint?
3 fibrous bands part of the fibrous capsule b/w glenoid labrum and humerus
In which direction do the intracapsular ligaments reinforce the GH joint?
Anteriorly
What are the three extracapsular ligaments of the glenohumeral joint?
Coracoacromial
Coracohumeral
Transverse humerus
Which is the most important extracapsular ligament?
Coracoacromial
Where is the coracoacromial ligament located?
B/w acromion and coracoid process
Where is the coracohumeral ligament located?
Base of coracoid process to anterior greater tubercle
What is the function of the transverse humeral ligament?
Holds tendon of long head of biceps in place during shoulder movement
What forms the coraco acromial arch?
Coracoacromial ligament
Acromion
Coracoid process
Why does the coraco acromial arch prevent upper displacement of the humeral head?
Strong osseoligamentous structure overlies humeral head
What will happen before dislocation of the glenohumeral joint due to the coraco acromial arch?
Fracture of humeral head
What are the two bursae found in the glenohumeral joint?
Subscapular
Sub acromial
What is the function of the subscapular bursa?
Facilitate movement of the tendon of subscapularis muscle over scapula
What does the subscapular bursa communicate with?
Joint cavity
What does the subacromial bursa facilitate?
Movement of supraspinatus tendon under the CA
Movement of deltoid muscle over shoulder joint capsule and greater tubercle of humerus
What does inflammation of the subacromial bursa cause?
Painful arc syndrome
What is the rotator cuff?
Collective name given to the 4 short muscles closely associated with the glenohumeral joint
What is the most important factor in the stability of the glenohumeral joint?
Rotator cuff
Which four muscles make up the rotator cuff?
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Which three rotator cuff muscles attach to the greater tubercle?
Supraspinatus
Infraspinatus
Teres minor
What is subscapularis attached to on the humerus?
Lesser tubercle
How is the cuff of the rotator cuff formed?
Tendons of the muscles blend together
What part of the rotator cuff strengthens the GH joint?
Tendinous cuff fusing with the capsule
What holds the humeral head close to the glenoid cavity?
Tone in rotator cuff muscles
What is the main action of supraspinatus?
Initiation and first 15 degrees of abduction
What innervates supraspinatus?
Suprascapular nerve
What is the main action of infraspinatus?
Lateral rotation of the arm
What innervates infraspinatus?
Suprascapular nerve
What is the main action of teres minor?
Lateral rotation of the arm
Weak adduction
What innervates teres minor?
Axillary nerve
What is the main action of subscapularis?
Medial rotation of the arm
What innervates subscapularis?
Upper and lower subscapular nerves
Which muscles are used in flexion of the GH joint?
Pec. major
Anterior fibres of deltoid
Corachobrachialis
Biceps brachii
Which muscles are used in extension of the GH joint?
Posterior fibres of deltoid
Latissimus dorsi
Teres major
Which muscles are used for abduction of the GH joint?
0-20 degrees = supraspinatus
20-90 degrees = central deltoid fibres
>90 degrees = trapezius, serratus anterior
What must happen for adduction of the GH joint above 90 degrees?
Rotation of scapula
Which muscles are used in adduction of the GH joint?
Pec. major
Latissimus dorsi
Teres major
Which muscles are used in medial rotation of the GH joint?
Subscapularis
Teres major
Pec. major
Latissimus dorsi
Which muscles are used for lateral rotation of the GH joint?
Infraspinatus
Teres minor
What is the general function of muscles in the anterior forearm?
Flexion
What are the muscles of the first layer of the anterior forearm?
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
What are the muscles of the second layer of the anterior forearm?
Flexor digitorum superficialis
What are the muscles of the third layer of the anterior forearm?
Flexor pollicus longus
Flexor digitorum profundus
Pronator quadratus
What is the main action of pronator teres?
Pronation and flexion of the forearm at the elbow
What innervates pronator teres?
Median nerve
What is the main action of flexor carpi radialis?
Flex and abduct hand at wrist
What innervates flexor carpi radialis?
Median nerve
What is the main action of palmaris longus?
Flex hand at wrist
Tense palmar aponeuorsis
What innervates palmaris longus?
Median nerve
What is the main action of flexor carpi ulnaris?
Flexes and addicts hand at wrist
What innervates flexor carpi ulnaris?
Ulnar nerve
What is the main action of flexor digitorum superficialis?
Flex middle 4 phalanges at proximal interphalangeal joints
Flex proximal phalanges at metacarpophalangeal joints
What innervates flexor digitorum superficialis?
Median nerve
What is the main action of flexor digitorum profundus?
Flex distal 2-5 digits at distal interphalangeal joints
What innervates flexor digitorum profundus?
Ulnar nerve
What is the main action of flexor pollcis longus?
Flex phalanges of first digit
What innervates flexor pollicis longus?
Anterior interosseous nerve from median nerve
What is the main action of pronator quadratus?
Promate forearm
Deep fibres bind radius and ulna together
What innervates pronator quadratus?
Anterior interosseous nerve from median nerve
