Shoulder & Upper Arm and Skeletal Muscle

Question 1

What is the Shoulder Girdle and what is its function?

Answer 1

It consists of the clavicle and the scapula and it connects the arm to the axial skeleton.

Question 2

Name 3 joints that are part of the shoulder girdle and one that is not.

Answer 2

Sternoclavicular joint
Acromioclavicular joint
Scapulothoracic joint

Glenohumoral joint

Question 3

Name the features of the proximal humerus.

Answer 3

The head, then the anatomical neck before the lesser tubercle (medial), intertubercular groove (for tendon for long head of biceps) and greater tubercle, then surgical neck before shaft.

Question 4

The glenohumeral joint is the most commonly dislocated joint. It has a wide range of movements in multiple planes, because it is which type of joint?

Answer 4

Synovial joint - ball and socket type.

Question 5

What is the glenoid labrum?

Answer 5

A fibrocartilage extension of the glenoid fossa, which deepens it.

Question 6

What surrounds the glenohumeral joint?

Answer 6

A loose articular capsule as well as superior, middle and inferior glenohumeral ligaments.

Question 7

Name the 3 extra capsular ligaments?

Answer 7

Coracohumeral ligament
Coracoacromonial (which creates arch, giving stability and stops superior-posterior dislocation)
Coracoclavicular ligament

Question 8

Name the 4 rotator cuff muscle’s, what they’re innervated by and where they attach.

Answer 8

Supraspinatus (suprascapular N.), Infraspinatus (suprascapular N.) and Teres Minor (axillary N.), all attach at the greater tuberosity of the humerus.
The Subscapularis (upper and lower subscapular N.) inserts on the lesser tubercle of the humerus.

Question 9

What’s the overall function of the rotator cuff and which movements do the individual muscles perform?

Answer 9

Overall it is an important stabiliser of the shoulder joint.
The supraspinatus initiates abduction at the shoulder. The infraspinatus and teres minor externally rotate the shoulder. The subscapularis internally rotates at the shoulder.

Question 10

The space between the acromion and the head of the humerus is only 1-1.5cm in size, but holds which 4 things?

Answer 10

Subacromonial Bursa - fluid filled sac reduces friction
Rotator cuff tendons
Capsule
Long head of biceps

Question 11

Which muscles contribute towards the abduction of the arm? Name their nerves if possible.

Answer 11

0-15 degrees - Supraspinatus (suprascapular N.)
15-90 - Deltoid (axillary N.)
>90 - due to scapulothoracic joint through scapular rotation - upper trapezius and serratus anterior

Question 12

Which muscles (and so nerves) are responsible for adduction of the arm?

Answer 12

Pectoralis major (medial and lateral pectoral N.), Latissimus Dorsi (thoracodoral N.) and Teres Major (thoracodorsal N.).

Question 13

Which muscles (and so nerves) are responsible for flexion of the arm?

Answer 13

Anterior fibres of the Deltoid muscle (axillary N.)
Pectoralis Major (medial and lateral pectoral N.)
Coracobrachialis (musculoskeletal N.)
Biceps Brachii (musculoskeletal N.)

Question 14

Which muscles (and so nerves) are responsible for extension of the arm?

Answer 14

Posterior fibres of the Deltoid muscle (axillary N.)
Latissimus Dorsi (thoracodorsal N.)
Teres Major (thoracodorsal N.)

Question 15

Which muscles (and so nerves) are responsible for internal rotation of the arm?

Answer 15

Subscapularis (upper and lower subscapular N.)
Teres Major (thoracodorsal N.)
Pectoralis Major (medial and lateral pectoral N.)
Latissimus Dorsi (thoracodorsal N.)

Question 16

Which muscles (and so nerves) are responsible for external rotation of the arm?

Answer 16

Infraspinatus (suprascapular N.)
Teres minor (axillary N.)

Question 17

What is the effect of the imbalance of strength in muscles which internally and externally rotate the arm?

Answer 17

An electric shock or seizure may cause internal rotation and so posterior dislocation at the glenohumeral joint.

Question 18

When there’s an arm injury, why should you always examine the neurovascular status of the limb - what in particular may be damaged?

Answer 18

The axillary artery becomes the brachial artery which has branches of the anterior and posterior circumflex arteries which wrap around the humerus and may become damaged if there’s a fracture.
A fracture or dislocation may also damage the brachial plexus with the trunks and divisions running behind the clavicle. The posterior cord provides the axillary and radial nerves which may become damaged.

Question 19

Name 6 static stabilisers of the glenohumeral joint.

Answer 19

Articular anatomy
Glenoid labrum
Capsule
Glenohumeral ligaments
Extracapsular ligaments 
Negative intraarticular pressure

Question 20

Name 3 components which are dynamic stabilisers of the glenohumeral joint.

Answer 20

Rotator cuff muscles
Biceps brachii
Muscles crossing over the shoulder

Question 21

Which type of shoulder dislocation is less common and often missed on x-rays?
What may cause it?

Answer 21

Posterior dislocation. May be caused by an electric shock or seizure - the shoulder is fixed in internal rotation.

Question 22

Acromioclavicular joint dislocations may require surgery, which ligament tears?

Answer 22

The coracoclavicular ligament.

Question 23

What happens in the degenerative condition of Calcific Tendinitis?

Answer 23

Calcium hydroxyapatite deposits cause a subacrominal impingement if they’re large. If it bursts, then there’s acute tendinitis (rapidly progressive very severe pain which resolves after 1-2 weeks).

Question 24

What may cause the appearance of the ‘Popeye muscle’? It is a cosmetic issue.

Answer 24

Long head of the biceps rupture.

Question 25

If there is an impingement of the biceps muscle, what type of pain is felt?

Answer 25

Low painful arc - as you raise arm there is pain, but when it is fully up, it does not hurt. Tenderness over tuberosity.

Question 26

How might you be able to tell if someone has torn their rotator cuff?

Answer 26

Supraspinatus test weak, Infraspinatus weak, and external rotation lag - progressive functional loss with size of tear.

Question 27

Rotator cuff arthropathy is not repairable in which group of people?

Answer 27

The elderly.

Question 28

What might happen to the acromion in glenohumeral arthritis?

Answer 28

Acromio erosion or maybe a fracture - may need shoulder replacement.

Question 29

What is a difference in the patient exp reindeer of acromioclavicular osteoarthritis and glenohumeral osteoarthritis?

Answer 29

Acromioclavicular osteoarthritis in the majority of cases is asymptomatic, whereas glenohumeral osteoarthritis will lead to progressive pain and stiffness over the years - eventually the joint may be replaced.

Question 30

A pathology known as ‘frozen shoulder’, involves severe pain, progressive nocturnal jerk pain, with progressive stiffness following which resolves after 2/3 years - may have manipulation under anaesthesia or surgical release. What is its proper name?

Answer 30

Adhesive capsulitis.

Question 31

What is meant by the fact that skeletal muscle is striated?

Answer 31

Ordered arrangement of myofibril apparatus leads to a banding pattern.

Question 32

What is the function of skeletal muscle?

Answer 32

To permit movement - usually contracted consciously and voluntarily. Also helps to maintain posture by stabilising joints (when there are no obvious movements). Inefficient chemical to kinetic energy conversions produce heat (hence shivering).

Question 33

Most commonly, muscle fibres are arranged so that they run parallel to the force-generating axis. What are the 3 categories of parallel muscle?

Answer 33

Strap muscles
Fusiform (cylinder with tapering ends)
Fan shaped (converge at 1 end)

Question 34

Pennate muscles can be either unipennate, bipennate or multipennate, what’s the difference?

Answer 34

Pennate muscles (like a feather in shape) have at least one aponeurosis running through their body from the tendon. Fascicles attach to the aponeuroses at an angle - with bipennate they attach on either side and with multipennate a central tendon has branches.

Question 35

What type of muscle acts as a sphincter to adjust openings and how?

Answer 35

Circular muscles - concentric fibres attach to skin, ligaments and fascia rather than bones.

Question 36

How can you tell the difference between a muscle’s origin and its insertion?

Answer 36

The origin is a typically proximal bone with a greater mass and more stability during contraction, whereas the insertion is the structure the muscle attaches to, which tends to be moved by contraction (greater motion) - distal bone/tendon/connective tissue.

Question 37

Limbs are divided into compartments, delineated by fascia. What can be the consequences of trauma in a compartment?

Answer 37

Internal bleeding will exert pressure on blood vessels and nerves and may give rise to Compartment syndrome - deep, constant, poorly localised pain, aggravated by passive stretch of the muscle group, paresthesia may result, may feel tense and firm, with shiny swollen skin, sometimes with bruising, prolonged capillary refill time. A fasciotomy may be needed to relieve the pressure, then the area will be covered by a graft.

Question 38

Muscles may have different roles in movements, name the five types.

Answer 38

Agonists, antagonists, synergists, neutralisers and fixators.

Question 39

Agonists, antagonists, synergists, neutralisers and fixators are the roles muscles can play in movement, what do they all entail?

Answer 39

Agonists are the prime movers.
Antagonists oppose the prime movers.
Synergists assist the prime movers.
Neutralisers prevent unwanted action of the agonist.
Fixators hold a body part immobile while another is moving (stabilise joint).

Question 40

What’s the difference between isotonic and isometric contraction?

Answer 40

In isotonic contraction, the tension is constant and there is variable muscle length (to move the load), when as isometric contraction involves constant length with variable tension (e.g. a hand grip).

Question 41

What are the 2 types of isotonic contraction?

Answer 41

Concentric - muscle shortens, such as when you lift a load with your arm.
Eccentric - muscle exerts force while extended (e.g. downhill walking, with delayed onset muscle soreness.

Passive stretch is the 4th type of muscle contraction - lengthened in passive state.

Question 42

What constitutes a first class lever? Give an example from the body.

Answer 42

Effort at one end, load at the other with a fulcrum in the middle.
Extension/flexion of the head - mechanical disadvantage in body.

Question 43

What constitutes a second class lever? Give an example from the body.

Answer 43

Effort at one end, with fulcrum at other and load in the middle.
Plantar flexion of the foot (tiptoes).

Question 44

What constitutes a third class lever? Give an example from the body.

Answer 44

Load and fulcrum at either end with effort in the middle - mechanical disadvantage, most common in body.

Question 45

What is a motor unit?

Answer 45

An alpha motor neurone and the muscle fibres it innervates.
Muscle fibres that make up a motor unit are all of the same contractile type, so each motor neurone is fast/slow contracting.

Question 46

What’s the correlation between power and number of muscle fibres part of a single motor unit?

Answer 46

As fine control gives way to power, more fibres are part of a single motor unit, so muscles in the eye will have fewer muscle fibres per motor unit than the pectoralis major muscle.

Question 47

What are muscle fibre types and what are the 3 main ones?

Answer 47

Based on myosin heavy chain (MHC) expression. Slow type I, Fast type IIa and Fast type II X.

Question 48

Which main muscle fibre type undergoes aerobic respiration, has high myoglobin levels and numbers of mitochondria, is red, with a rich capillary supply, is fatigue resistant and the first type to be recruited (e.g. for walking/running), why not the other types?

Answer 48

Slow type I.
Fast type IIA is similar, but is red-pink, has moderate fatigue resistance and is the second type to be recruited.
Fast type II X undergoes anaerobic glycolysis, has low levels of myoglobin and few mitochondria, is white with a poor capillary supply, is rapidly fatiguable and the last type to be recruited (running/sprinting/jumping).
Several intermediate types.

Question 49

What is a muscle spindle?

Answer 49

Located in the muscle belly and senses muscle stretch - intrafusal muscle fibres facilitate proprioception (sense of where limbs are).
Separated from rest of muscle by collagen sheath

Question 50

Explain the innervation of muscle spindles. What is a consequence of ‘large fibre sensory neuropathy’?

Answer 50

Innervated by 1 gamma motor neurone, which keeps fibres taught and changes sensitivity by changing tensity. 2 sensory neurones - type Ia relays rate of change in muscle length back to CNS and type II provide position sense).

Large fibre sensory neuropathy results in being unable to perform small movements accurately without vision.

Question 51

What are the names of the two ways to control muscle force?

Answer 51

Size principle and rate load.

Question 52

What is ‘size principle’ in terms of controlling muscle force?

Answer 52

Small motor neurones are recruited before large, so motor neurones with mostly fibre types: slow type I –> fast type IIa –> fast type II X are utilised.

Question 53

How does ‘rate code’ control muscle force?

Answer 53

More action potentials lead to more force, with subsequent action potentials summated up to a limit called tetany, where no further force can be stimulated.

Question 54

What term describes the state of healthy muscles never being fully relaxed (except in R.E.M. sleep), retaining an amount of stiffness and function?

Answer 54

Muscle tone.

Baseline tone is due to motor neurone activity and muscle elasticity.

Question 55

What is hypotonia and what may cause it?

Answer 55

It’s a symptom where skeletal muscle lacks tone, e.g. In floppy baby syndrome or muscular dystrophies. Cause could be primary degeneration (myopathies), lesions of lower motor neurones or lesions of sensory afferents from muscle spindles or lesions of the cerebellum/cerebral or spinal shock.

Question 56

Outline what happens at the neuromuscular junction.

Answer 56

Action potential opens VOCC and triggers vesicles fusion and ACh release.
nAChRs open, so sodium flows into the muscle cell.
ACh rapidly broken down in cleft by AChE.
Depolarisation opens voltage-gated sodium channels in muscle cell, so muscle action potential is generated.

Question 57

Briefly outline excitation-contraction coupling.

How is relaxation facilitated?

Answer 57

Voltage gated calcium channels (DHP receptors) are concentrated in T tubules in contact with the sarcoplasmic reticulum at triads. Calcium release channels (ryanodine receptors) in SR are closely related to DHP receptors, allowing rapid signalling from action potential to calcium release. Calcium binds to troponin C, tropomyosin reveals actin binding site for myosin heads.
Relaxation facilitated by calcium being pumped out of cytosol by SERCA and PMCA.

Question 58

Permeability to which ions lead to the skeletal muscle action potential?

Answer 58

Chloride channels as well as potassium channels are present, so resting membrane potential is closer to Nernst equation for Cl-. Higher chloride permeability is important for relaxation after the action potential.

Question 59

Name and explain a channelopathy.

Answer 59

Myotonia Congenita happens where you can’t relax your muscles at will. A mutation in the chloride channel leads to muscle stiffness and hypertrophy enhanced by the cold and relieved by activity. Recessive or dominant. Often no treatment (occasionally anticonvulsants). Channel forms homodimer.

Question 60

What are the differing responsibilities of chloride and potassium/sodium ions in the membrane potential of the skeletal muscle cell and how is this affected in Myotonia Congenita?

Answer 60

Sodium and potassium permeabilities are the determinants of excitability, but 70% conductance of resting fibres is from chloride flow. In Myotonia Congenita, the buffering capacity of chloride is lost.

Question 61

What are the sources of ATP in muscles?

Answer 61

Short term stores in fibres, PCr, glycolysis and oxidative phosphorylation. Anaerobic glycolysis is inefficient, incomplete metabolism of glucose and the formation of lactate which can lead to acidosis.