MSK Session 2 - Shoulder and Upper Arm Flashcards

Question

What is the cubital fossa?

Answer 1

The cubital fossa is an area of transition between the anatomical arm and the forearm. It is located as a depression on the anterior surface of the elbow joint.

Answer 2

- **Lateral border** – The medial border of the brachioradialis muscle. **- Medial border** – The lateral border of the pronator teres muscle. **- Superior border** – An imaginary line between the epicondyles of the humerus.

Answer 3

- The **floor** of the cubital fossa is formed proximally by the brachialis, and distally by the supinator muscle. - The **roof** consists of skin and fascia, and is reinforced by the bicipital aponeurosis. - Within the roof runs the **median cubital vein**, which can be accessed for venepuncture.

Answer 4

The contents of the cubital fossa include vessels, nerves and the biceps tendon (lateral to medial): - **Radial nerve** – This is not always strictly considered part of the cubital fossa, but is in the vicinity, passing underneath the brachioradialis muscle. As is does so, the radial nerve divides into its deep and superficial branches. **- Biceps tendon** – It runs through the cubital fossa, attaching to the radial tuberosity, just distal to the neck of the radius. **- Brachial artery** – The brachial artery supplies oxygenated blood the forearm. It bifurcates into the radial and ulnar arteries at the apex of the cubital fossa. **- Median nerve** – Leaves the cubital between the two heads of the pronator teres. It supplies the majority of the flexor muscles in the forearm.

Answer 5

The muscles of the back can be divided into three groups – superficial, intermediate and deep: **- Superficial** – associated with movements of the shoulder. **- Intermediate** – associated with movements of the thoracic cage. **- Deep** – associated with movements of the vertebral column.

Answer 6

- The deep muscles develop embryologically in the back, and are thus described as **intrinsic** muscles. - The superficial and intermediate muscles do not develop in the back, and are classified as **extrinsic** muscles. - The superficial back muscles are situated underneath the skin and superficial fascia. - They originate from the vertebral column and attach to the bones of the shoulder – the clavicle, scapula and humerus. - All these muscles are therefore associated with movements of the upper limb. - The muscles in this group are the trapezius, latissimus dorsi, levator scapulae and the rhomboids. - The trapezius and the latissimus dorsi lie the most superficially, with the trapezius covering the rhomboids and levator scapulae.

Answer 7

- The shoulder joint (glenohumeral joint) is a ball and socket joint between the **scapula** and the **humerus**. - It is the major joint connecting the upper limb to the trunk. - It is one of the most mobile joints in the human body, at the cost of joint stability.

Answer 8

- The shoulder joint is formed by the articulation of the **head** of the humerus with the **glenoid cavity** (or fossa) of the scapula. - This gives rise to the alternate name for the shoulder joint – the glenohumeral joint. - Both the articulating surfaces are covered with **hyaline cartilage** – which is typical for a synovial type joint. - The head of the humerus is much larger than the glenoid fossa, giving the joint inherent instability. - To reduce the disproportion in surfaces, the glenoid fossa is deepened by a fibrocartilage rim, called the **glenoid labrum.**

Answer 9

- The joint capsule is a fibrous sheath which encloses the structures of the joint. - It extends from the anatomical neck of the humerus to the border of the glenoid fossa. - The joint capsule is lax, permitting greater mobility (particularly abduction). - The **synovial membrane** lines the inner surface of the joint capsule, and produces synovial fluid to reduce friction between the articular surfaces. - To reduce friction in the shoulder joint, several **synovial bursae** are present. A bursa is a synovial fluid filled sac, which acts as a cushion between tendons and other joint structures

Answer 10

- **Subacromial** – Located inferiorly to the deltoid and acromion, and superiorly to the supraspinatus tendon and the joint capsule. It supports the deltoid and supraspinatus muscles. Inflammation of this bursa is the cause of several shoulder problems. **- Subscapular** – Located between the subscapularis tendon and the scapula. It reduces wear and tear on the tendon during movement at the shoulder joint.

Answer 11

- In the shoulder joint, the ligaments play a key role in stabilising the bony structures. - The majority of the ligaments are thickenings of the joint capsule.

Answer 12

- **Glenohumeral ligaments** (superior, middle and inferior) – Consists of three bands, which runs with the joint capsule from the glenoid fossa to the anatomical neck of the humerus. They act to stabilise the anterior aspect of the joint. **- Coroacohumeral ligament** – Attaches the base of the coracoid process to the greater tubercle of the humerus. It supports the superior part of the joint capsule. **- Transverse humeral ligament** – Spans the distance between the two tubercles of the humerus. It holds the tendon of the long head of the biceps in the intertubercular groove.

Answer 13

- The other major ligament is the **coracoacromial ligament.** - Unlike the others, it is not a thickening of the joint capsule. It runs between the acromion and coracoid process of the scapula, forming the **coraco-acromial arch.** - This structure overlies the shoulder joint, preventing superior displacement of the humeral head.

Answer 14

- Arterial supply to the glenohumeral joint is via the anterior **and posterior circumflex humeral arteries**, and the **suprascapular artery**. Branches from these arteries form an anastomotic network around the joint. - The joint is supplied by the **axillary, suprascapular and lateral pectoral nerves**. These nerves are derived from roots C5 and C6 of the brachial plexus. Thus, an upper brachial plexus injury (**Erb’s palsy**) will affect shoulder joint function.

Answer 15

As a ball and socket synovial joint, there is a wide range of movement permitted: - Extension - Flexion - Abduction - Adduction - Medial Rotation - Lateral Rotation

Answer 16

- **Extension** **(upper limb backwards in sagittal plane)** produced by the posterior deltoid, latissimus dorsi and teres major. **- Flexion** **(upper limb forwards in sagittal plane)** produced by the biceps brachii (both heads), pectoralis major, anterior deltoid and coracobrachialis.

Answer 17

- **Abduction (upper limb away from midline in coronal plane)** The first 0-15 degrees of abduction is produced by the supraspinatus. The middle fibres of the deltoid are responsible for the next 15-90 degrees. Past 90 degrees, the scapula needs to be rotated to achieve abduction – that is carried out by the trapezius and serratus anterior. **- Adduction** (upper limb towards midline in coronal plane) produced by contraction of pectoralis major, latissimus dorsi and teres major.

Answer 18

- **Medial Rotation (rotation towards the midline, so that the thumb is pointing medially)** produced by contraction of subscapularis, pectoralis major, latissimus dorsi, teres major and anterior deltoid. **- Lateral Rotation** **(rotation away from the midline, so that the thumb is pointing laterally)** produced by contraction of the infraspinatus and teres minor.

Answer 19

- **Type of joint** – It is a ball and socket joint. **- Bony surfaces** – Shallow glenoid cavity and large humeral head – there is a 1:4 disproportion in surfaces. A commonly used analogy is the golf ball and tee. - Laxity of the **joint capsule.**

Answer 20

- **Rotator cuff muscles** – These muscles surround the shoulder joint, attaching to the tubercles of the humerus, whilst also fusing with the joint capsule. The resting tone of these muscles act to ‘pull’ the humeral head into the glenoid cavity. **- Glenoid labrum**: This is a fibrocartilaginous ridge surrounding the glenoid cavity. It deepens the cavity, reducing the risk of dislocation. **- Ligaments** – The ligaments act to reinforce the joint capsule, and forms the coraco-acromial arch.

Answer 21

- The scapula is also known as the **shoulder blade**. - It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk. - It is a **triangular**, flat bone, which serves as a site for attachment for many (17!) muscles.

Answer 22

- The anterior surface of the scapula is termed ‘costal’, this is because it is the side facing the **ribcage**. - This side of the scapula is relatively unremarkable, with a **concave** depression over most of its surface, called the **subscapular fossa.** The subscapularis muscle, one of the rotator cuff muscles, originates from this side. - Originating from the superolateral surface of the costal scapula is the **coracoid process**. It is a hook-like projection, which lies just underneath the clavicle. - The short head of the **biceps brachii** and the **pectoralis minor** attach here, while the **coracobrachialis** muscle originates from this projection.

Answer 23

- The lateral surface of the scapula faces the humerus. It is the site of the glenohumeral joint, and of various muscle attachments. **- Glenoid fossa** – A shallow cavity, which articulates with the humerus to form the glenohumeral joint. The superior part of the lateral border is very important clinically, as it articulates with the humerus to make up the shoulder joint, or glenohumeral joint. **- Supraglenoid tubercle** – A roughening immediately superior to the glenoid fossa, this is the place of attachment of the long head of the biceps brachii. **- Infraglenoid tubercle** – A roughening immediately inferior to the glenoid fossa, this is the place of attachment of the long head of the triceps brachii.

Answer 24

- The posterior surface of the scapula faces outwards. It is a site of attachment for the majority of the rotator cuff muscles of the shoulder. **- Spine** – The most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two. **- Infraspinous fossa** – The area below the spine of the scapula, it displays a convex shape. The infraspinatus muscle originates from this area. **- Supraspinous fossa** – The area above the spine of the scapula, it is much smaller that the infraspinous fossa, and is more convex in shape. The supraspinatus muscle originates from this area. **- Acromion** – projection of the spine that arches over the glenohumeral joint and articulates with the clavicle.

Answer 25

- The clavicle (collarbone) extends between the sternum and the acromion of the scapula. - The clavicle is a slender bone with an ‘S’ shape. Facing forward, the medial aspect is convex, and the lateral aspect concave. It can be divided into a sternal end, a shaft and an acromial end. - It is classed as a **long bone**, and can be palpated along its length. In thin individuals, it is visible under the skin. - The clavicle has three main functions: I. **Attaches** the upper limb to the trunk. II. **Protects** the underlying neurovascular structures supplying the upper limb. III. **Transmits** force from the upper limb to the axial skeleton.

Answer 26

- Sternal (medial) End - Shaft - Acromial (lateral) End

Answer 27

- The sternal end contains a **large facet** – for articulation with the manubrium of the sternum at the [sternoclavicular joint](http://teachmeanatomy.info/upper-limb/joints/sternoclavicular/). - The inferior surface of the sternal end is marked by a rough oval depression for the **costoclavicular ligament** (a ligament of the SC joint).

Answer 28

The shaft of the clavicle acts a point of origin and attachment for several muscles – deltoid, trapezius, subclavius, pectoralis major, sternocleidomastoid and sternohyoid.

Answer 29

- The acromial end houses a small facet for articulation with the acromion of the scapula at the [acromioclavicular joint](http://teachmeanatomy.info/upper-limb/joints/acromioclavicular/). - It also serves as an attachment point for two ligaments: I. **Conoid tubercle** – attachment point of the conoid ligament, the medial part of the coracoclavicular ligament. II. **Trapezoid line** – attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament. - The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.

Answer 30

- The humerus is the bone that forms the upper arm, and joins it to the shoulder and forearm. - The proximal region articulates with the scapula and clavicle, forming part of the **shoulder joint.** - Distally, the humerus articulates with the forearm bones (radius and ulna), to form the **elbow joint.** - The humerus acts as an attachment site for many muscles and ligaments, resulting in various raised roughening on the bony surface.

Answer 31

- The proximal region of the humerus articulates with the **scapula** to form the glenohumeral joint (shoulder joint). - The important **anatomical features** of the proximal humerus are the head, anatomical neck, surgical neck, greater and lesser tubercles and intertubercular sulcus.

Answer 32

A tubercle is a round nodule, and signifies an attachment site of a muscle or ligament.

Answer 33

- The **head** of the humerus projects medially and superiorly to articulate with the **glenoid cavity** of the scapula. The head is connected to the tubercles by the **anatomical neck**, which is short in width and nondescript. - The **greater tubercle** is located laterally on the humerus. It has an anterior and posterior face. The greater tubercle serves as attachment site for three of the **rotator cuff muscles** – supraspinatus, infraspinatus and teres minor. - The **lesser tubercle** is much smaller, and more medially located on the bone. It only has an anterior face. It is a place of attachment for the last rotator cuff muscle – subscapularis.

Answer 34

- Separating the two tubercles is a deep depression, called the **intertubercular sulcus**, or groove. - The tendon of the **long head of biceps brachii** runs through this groove. - The edges of the intertubercular sulcus are known as lips. - Tendons of the pectoralis major, teres major and latissimus dorsi attach to the lips of the intertubercular sulcus. - The surgical neck runs from the tubercles to the shaft of the humerus.

Answer 35

- The shaft of the humerus contains some important bony landmarks such as the deltoid tuberosity and radial groove, and is the site of attachment for various muscles. - On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the **deltoid tuberosity**. - The radial groove is shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The **radial nerve** and **profunda brachii** artery lie in this groove.

Answer 36

The following muscles attach to the humerus: **- Anteriorly:** Coracobrachialis, deltoid, brachialis, brachioradialis **- Posteriorly:** Medial and lateral heads of the triceps

Answer 37

- The distal part of the humerus articulates with the ulna and radius at the elbow joint. - Here, the bone adopts a flattened, almost 2-D shape.

Answer 38

- The lateral and medial borders of the humerus form medial and lateral **supraepicondylar ridges**. - The lateral supraepicondylar ridge is more roughened, as it is the site of attachment for many of the **extensor muscles** in the posterior forearm.

Answer 39

- Immediately distal to the supraepicondylar ridges are the **lateral** and **medial epicondyles** – projections of bone. - Both can be palpated at the elbow (the medial more so, as it is much larger). - The **ulnar nerve** passes into the forearm along the posterior side of the medial epicondyle, and can also be palpated there.

Answer 40

- The **trochlea** articulates with the ulna. - It is located medially, and extends onto the posterior of the bone. - Lateral to the trochlear is the **capitulum,** which articulates with the radius. - Also found on the distal portion of the humerus are three depressions, known as the **coronoid**, **radial** and **olecranon** **fossae**. - They accommodate the forearm bones during movement at the elbow.

Answer 41

- Anterior dislocations (in which the humeral head is displaced anteriorly in relation to the glenoid), account for as many as 95-98% of shoulder dislocations. - The reason is that the muscular and ligamentous support anterior to the humeral head is much less robust than the substantial muscular and bony support afforded posteriorly by the rotator cuff and scapula.

Answer 42

- **Traumatic Posterior Dislocation:** Posterior shoulder dislocations make up a small minority of total shoulder dislocation cases, accounting for 2-4% of presentations. - However, because of a low level of clinical suspicion and insufficient imaging, they are often missed. - Approximately half of posterior shoulder dislocations go undiagnosed on initial presentation. This can be causes by electric shock or a seizure.

Answer 43

- Acromioclavicular joint - A simple joint with six different ways of dislocating - The coracoclavicular ligaments are important - Some need surgery

Answer 44

- 80% of cases are undisplaced - 20% of cases are displaced - A function of the clavicle is to transmit forces from the upper limb to the axial skeleton. Thus, the clavicle is the most commonly fractured bone in the body. - Fractures commonly result from a fall onto the shoulder, or onto an outstretched hand. - The most common point of fracture is the junction of the medial 2/3 and lateral 1/3. - After fracture, the lateral end of the clavicle is displaced inferiorly by the weight of the arm, and medially, by the pectoralis major. The medial end is pulled superiorly, by the sternocleidomastoid muscle. - The suprascapular nerves (medial, intermedial and lateral) may be damaged by the upwards movement of the medial part of the fracture. These nerves innervate the lateral rotators of the upper limb at the shoulder – so damage results in unopposed medial rotation of the upper limb – the ‘waiters tip’ position.

Answer 45

- Low painful arc - Tender over tuberosity - Hawkins test +ve - Ultrasound scan I. Bursitis II. Tendinopathy III. Dynamic impingement - Treatment I. Steroid and physio II. Surgical decompression.

Answer 46

- Degenerative condition - Calcium hydroxyapatite deposit - Subacromial impingement if large - If bursts - acute calcific tendinitis I. 2 day history II. Rapidly progressive pain III. 10/10 severity IV. Resolves 1-2 weeks

Answer 47

- Full thickness large/massive tears I. Impingement signs II. Supraspinatus test weak III. Infraspinatus weak & ER lag IV. Subscapularis push off & belly press weak V. Progressive functional loss with size of tear VI. Open repair, augmentation with allograft - Rotator cuff arthropathy I. Elderly II. Cuff not repairable III. Glenohumeral arthritis IV. Acromial erosion +/- fracture V. Reverse anatomy shoulder replacement

Answer 48

- There are three types of **muscle cells**: skeletal, cardiac and smooth. - Skeletal and cardiac are classed as striated muscle due to the ordered arrangement of the myofibrillar apparatus producing a characteristic banding pattern when viewed under the microscope. - Skeletal muscles function to permit movement and are usually contracted voluntarily and consciously. - Muscular contractions also help maintain body posture by stabilising joints even when there is no obvious movement.

Answer 49

- A significant amount of body heat is also produced by skeletal muscle as this tissue is inefficient at converting chemical energy into mechanical work. - Estimates vary, but about 80% of the chemical energy is lost as heat as a by-product of muscle activity. - This inefficiency is utilised by the physiological process of shivering to raise core body temperature by the involuntary activation of skeletal muscle.

Answer 50

- There are about 640 skeletal muscles within the human body, most of which are present as bilateral pairs (e.g. left and right deltoid muscles). - These muscles vary in their overall size, the angles at which the muscle fibres are oriented and their contractile properties. - The organization and composition of each muscle is related to the functions it performs.

Answer 51

- Muscle fibres within muscles can be arranged in several different ways. - The most common arrangement is for the fibres to run parallel to the force-generating axis. - There are three main categories of **parallel** muscles: **strap, fusiform and fan shaped**. I. **Strap muscles** *(e.g. sartorius)* are, as the name suggests, shaped like strap or belt with the fibres running longitudinally, parallel to the direction of contraction. II. **Fusiform muscles** *(e.g. biceps brachii)* are cylindrical and are wider in the centre with tapering off at the ends. III. **Fan shaped muscles** *(e.g. pectoralis major)* have fibres that converge at one end.

Answer 52

- **Pennate muscles** have one or more aponeuroses running through the muscle body from the tendon and the fascicles of muscle fibres attach to these aponeuroses at an angle (called the pennation angle) to the direction of movement. - These can be **unipennate** where all the fascicles are on the same side as the tendon, **bipennate** with fascicles on both sides of a central tendon or **multipennate** where a central tendon branches.

Answer 53

- Finally, there are also **circular muscles** where the fibres form concentric rings around a sphincter or opening. - Such muscles attach to skin, ligaments and fascia of other muscles rather than to bone. *E.g. orbicularis oculi around the eye and orbicularis oris around the mouth.*

Answer 54

- The prime muscle (or muscles) responsible for a particular movement are referred to as the **agonist**(s) whereas the muscles which oppose this movement are called **antagonists**. - For example, for flexion at the elbow joint, brachialis and biceps brachii are the agonists whereas triceps brachii opposes this movement and so is the antagonist. This opposition of the action of agonists by antagonists is required for the fine control of movement.

Answer 55

- Muscles that act to assist the prime mover are called **synergist**s *(e.g. brachioradialis and pronator teres in elbow flexion).* - Acting alone they cannot perform the movement of the agonist but their angle of pull assists the agonist.

Answer 56

- **Neutralisers** prevent the unwanted actions that an agonist can perform. - For example, the rotator cuff muscles stabilise the glenohumeral joint whilst biceps, (whose long head acts to cause shoulder flexion) acts to cause flexion at the elbow joint.

Answer 57

- **Fixators (stabilisers)** act to hold a body part immobile whilst another body part is moving. - In most activities, proximal joints are stabilised whilst distal joints move. - An example is stabilising the shoulder whilst flexing the elbow. The fixators active in elbow flexion are the muscles that stabilise the position of the scapula and those that stabilise the shoulder joint. - NB. Neutralisers prevent the unwanted actions of a **muscle**; fixators stabilise a **joint.**

Answer 58

- When a muscle contracts, there is not necessarily a shortening of the muscle associated with the contraction. - This concept may seem contradictory at first but the term ‘contraction’ refers to the active cycling of cross-bridges between the actin thin filaments and the myosin thick filaments within the sarcomeres, rather than what is happening to the muscle on a gross physical level.

Answer 59

**Isotonic contraction** (lit. 'equal tension') is where the tension within the muscle remains constant and the length changes. There are two types of isotonic contractions: concentric and eccentric.

Answer 60

- **Concentric contraction** is where the muscle shortens, for example when flexing the elbow to lift a load, the biceps shortens. **- Eccentric contraction** refers to active contraction of muscles whilst they are lengthening. Classic examples of this are walking, when the quadriceps (knee extensors) are active just after heel strike whilst the knee flexes, or setting an object down gently (the arm flexors must be active to control the fall of the object).

Answer 61

**Isometric contractions** (lit. 'equal length') occur when the load against the muscle equals the contractile force being generated, e.g. holding a weight in a fixed position, or trying to push a brick wall. In both these cases the muscle is generating tension but is not shortening.

Answer 62

**- Passive stretch** is a fourth type of muscle 'contraction'. As the name implies, the muscle is being lengthened while in a passive state (i.e. not being stimulated to contract). - An example of this would be the pull felt in the hamstrings whilst touching the toes.

Answer 63

- The structures responsible for passive tension are outside of the cross-bridge itself since muscle activation is not required. - The protein titin is now known to be important in the contraction of striated muscle tissues. - Titin connects the Z line to the M line in the sarcomere. - It contributes to force transmission at the Z line and resting tension in the I band region. - Titin limits the range of motion of the sarcomere in tension, thus contributing to the passive stiffness of muscle.

Answer 64

- Each skeletal muscle is supplied by a number of motor neurons which stimulate the muscle fibres to contract. - The type of motor neurons innervating skeletal muscle fibres are called α-motor neurons and the cell bodies of these neurons are either located in the ventral horn of the spinal cord, for muscles of the limbs and trunk, or in the motor nuclei of the brainstem for the muscles of the head and face. - The axons of α-motor neurons leave the central nervous system and form part of a peripheral nerve, to supply the muscle fibres of a skeletal muscle.

Answer 65

- The neuromuscular junction is a specialised synapse between an a motor neurone and a skeletal muscle fibre. - An action potential arriving at the synapse triggers opening of voltage-gated calcium ion channels. - The resulting increase in intracellular Ca²⁺ causes vesicles containing acetylcholine (ACh) to release their contents into the synaptic cleft. - Acetylcholine activates **nicotinic** ACh receptors (a type of ligand gated ion channel) in the muscle fibre plasma membrane resulting in an influx of sodium ions and depolarisation of the muscle fibre membrane potential. - This local depolarisation activates voltage sensitive sodium channels resulting in the generation of an action potential in the muscle fibre. - Acetylcholine is rapidly broken down in the synaptic cleft by the enzyme acetylcholinesterase.

Answer 66

- A motor unit is defined as an α-motor neuron and the group of individual muscle fibres that it innervates. - Any single muscle fibre is innervated by only one α-motor neuron, but each α-motor neuron can innervate a number of different muscle fibres. - The number of muscle fibres in a motor unit varies between different muscles and depends on the function of the muscle. - Muscles that perform precise fine movements, such as inferior rectus which moves the eyeball have around ten muscle fibres in each unit motor unit whereas powerful muscles, where fine control is less important, such as gastrocnemius may have several thousand muscle fibres in each motor unit.

Answer 67

- All muscle has some degree of baseline tone (degree of tension) due to the elasticity of the muscle tissue and low levels of motor neuron activity. - Skeletal muscle tone is controlled by motor control centres in the brainstem. - The locus coeruleus, which contains noradrenergic cells, projects ascending axons to spinal motor neurons, where it facilitates muscle tone. - Muscle tone is lost in REM sleep when the locus coeruleus cells shut off. - A lack of skeletal muscle tone is known as **hypotonia.** This could result from damage to the motor cortex or cerebellum or spinal cord. Alternatively, there could be degeneration of the muscle itself (myopathy).

Answer 68

- The number of muscle fibres per motor unit and the proportion of the different fibre types varies between muscles depending on their function. - The contractile force produced by a muscle depends on two factors: I. The **size principle** and the rate code. The size principle simply means that small motor neurons are recruited before large ones. In general, this means that motor units with slow type I fibres are recruited first followed by those containing mostly fast IIa fibres and then those containing fast IIX fibres. II. The **Rate code** refers to the frequency at which the muscle fibres are stimulated by their α-motor neuron. Consecutive action potentials in a repetitive train result in **summation** giving a slightly larger force with each contraction. Eventually a limit is reached where no further force can be produced termed **tetany**.

Answer 69

- **Malignant hyperthermia** is a rare life-threatening condition triggered by some volatile anaesthetic agents and succinylcholine, a neuromuscular blocking agent. - In genetically susceptible individuals such drugs can lead to an uncontrolled increase in oxidative metabolism and increase in body temperature, which can be fatal if not immediately treated. - Polymorphism in the **ryanodine receptor** is the most common genetic cause and this receptor is activated by some volatile anaesthetic agents leading to a massive increase in intracellular calcium from intracellular stores. - The muscle cell SERCA pump (which consumes ATP in its action) is therefore working at a dramatically increased rate ultimately leading to excessive heat production. - Such patients can be treated with dantrolene, a muscle relaxant which antagonises the ryanodine receptor.

Answer 70

- Very little ATP is stored in muscle fibres and this is sufficient for only a few seconds of contraction. Additional short term stores in the form of **creatine phosphate** can be used to rapidly replenish ATP, but again this is only sufficient to provide immediate energy for an initial burst of activity lasting a few seconds. - Further energy to supply the contractile apparatus with the ATP it requires must come from glycolysis (anaerobic or aerobic) and oxidative metabolism (aerobic). Glycolysis can typically provide ATP sufficient for maximum muscle contraction for around 30-40 seconds.

Answer 71

- The advantage of using glycolysis for immediate rapid activity is that this pathway can function under anaerobic conditions and so is not reliant on the blood supplying oxygen at the rate required for maximal contraction. - Anaerobic glycolysis is therefore typically used in fast type II muscle fibres to produce short duration maximum force movements such as jumping or sprinting over a short distance. - The disadvantage of using glycolysis under anaerobic conditions is that lactate is produced from pyruvate by the action of lactate dehydrogenase.

Answer 72

The accumulation of lactate is associated (although not necessarily the direct cause) with acidification of the muscle cell environment leading to “cramps” and underlies one of the reasons why maximal activity such as sprinting rapidly fatigues muscle.

Answer 73

- Glycolysis under anaerobic conditions is also very inefficient in that only 2 molecules of ATP are produced when the pathway terminates at pyruvate. - Glycolysis under aerobic conditions however allows the pyruvate produced to enter mitochondria where it is oxidized by the tricarboxylic acid (TCA) cycle to produce the high- energy electron donors utilised by the electron transport chain allowing much more ATP to be produced per molecule of glucose. - For prolonged activity, however, such as running for several miles, the muscle needs to switch to beta oxidation of fatty acids released from triacylglycerol stored in adipose tissue.

Answer 74

- Skeletal muscle fibres differ in the speed at which they contract, the amount of force that they generate and in their energy requirements/susceptibility to fatigue. - Different types of muscle fibre differ in the isoforms of contractile proteins they express, most notably the myosin heavy chain.

Answer 75

- Slow muscle fibres (Type I) express the type I myosin heavy chain, they contract relatively slowly and produce low amounts of force. - Type I fibres are however extremely resistant to fatigue due to their high mitochondria content and use of oxidative metabolism to produce the ATP they consume.

Answer 76

- Fast muscle fibres **(Type II)** contract relatively quickly and produce large amounts of force. - There are two types of fast muscle fibres in human skeletal muscle termed fast IIA and fast IIX. - The fast IIX muscle fibres are classified as Fast Glycolytic, while IIA fibres are Fast Oxidative/Glycolytic. - Type IIA fast fibres therefore represent an intermediate form of muscle fibre between oxidative Type I fibres which produce low force but are fatigue resistant and the fast IIX fibres which rely on glycolytic metabolism, produce greater amounts of force and fatigue rapidly.

Answer 77

- The muscle fibres making up each motor unit tend to be all of the same contractile type, so each motor unit is either fast, intermediate or slow contracting. - Slow motor units are very well-vascularised, with a high myoglobin content and can maintain contractions for long periods of time. - These motor units are therefore typically found in postural muscles and those used for low intensity long duration activities such as walking. - The soleus muscle in the leg for example is composed almost exclusively of slow type I muscle fibres. - Fast type II muscle fibres have a glycolytic metabolism, and produce ATP quickly to enable a fast, powerful contraction but they also fatigue quickly. - Most muscles are composed of a mixture of different fibre types and motor unit types and the proportion of fast to slow fibres depends on the typical function of the muscle.

Answer 78

- Rotator cuff tendonitis refers to inflammation of the tendons of the rotator cuff muscles. - This usually occurs secondary to repetitive use of the shoulder joint. - Over time, this causes degenerative changes in the subacromial bursa, and the supraspinatus tendon. This increases friction between the structures of the joint. - The characteristic sign of rotator cuff tendonitis is the painful arc pain in the middle of abduction, where the affected area comes into contact with the acromion.

Answer 79

- The most common cause of accessory nerve damage is iatrogenic (i.e. due to a medical procedure). - In particular, operations such as cervical lymph node biopsy or cannulation of the internal jugular vein can cause trauma to the nerve. - To test the accessory nerve, trapezius function can be assessed. This can be done by asking the patient to shrug his/her shoulders

Answer 80

- A complete rupture of any tendon in the body is rare. However, the long head of the biceps brachii is one of the more common tendons to rupture. - This produces a characteristic sign on flexing the elbow a bulge where the muscle belly is, called the Popeye Sign. - The patient would not notice much weakness in the upper limb due to the action of the brachialis and supinator muscles.

Answer 81

- The brachial pulse can be felt by palpating immediately medial to the biceps tendon in the cubital fossa. - When measuring blood pressure, this is also the location in which the stethoscope must be placed, to hear the korotkoff sounds. - The median cubital vein is located superficially within the roof of the cubital fossa. - It connects the basilic and cephalic veins, and can be accessed easily – this makes it a common site for venepuncture.

Answer 82

- A mid-shaft fracture could easily damage the radial nerve and profunda brachii artery, as they are tightly bound in the radial groove. - The radial nerve innervates the extensors of the wrist. In the event of damage to this nerve, the extensors will be paralysed. This results in unopposed flexion of the wrist occurs, known as wrist drop. - There is also some sensory loss over the dorsal (posterior) surface of the hand, and the proximal ends of the lateral 3 and a half fingers dorsally.

Answer 83

- Supracondylar fractures and medial epicondyle fractures are common fracture types of the distal humerus. - A supraepicondylar fracture occurs by falling on a flexed elbow. - It is a transverse fracture, spanning between the two epicondyles. - Direct damage, or swelling can cause interference to the blood supply of the forearm from the brachial artery. - The resulting ischaemia can cause Volkmanns ischaemic contracture - uncontrolled flexion of the hand, as flexor muscles become fibrotic and short. There also can be damage to the median, ulnar or radial nerves. - A medial epicondyle fracture could damage the ulnar nerve, a deformity known as ulnar claw is the result. - There will be a loss of sensation over the medial 1 and 1/2 fingers of the hand, on both the dorsal and palmar surfaces.

MSK Session 2 - Shoulder and Upper Arm Flashcards

(107 cards)