Princicples Of MSK

Question 1

3 major components of MSK

Answer 1

Bone

Connective tissues

Skeletal muscle (not all skeletal muscles are voluntary)

Question 2

Functions of bone

Answer 2

Support - keep body upright

Protection - protect vital organs

Metabolic

Storage - store fat in bone marrow

Movement - i.e. joints

Haematopoiesis - make blood

Question 3

Functions of Skeletal muscle

Answer 3

Locomotion - movement of limbs

Posture - for standing up

Metabolic

Venous return - deep veins are surrounded by muscles - help blood back to the heart

Heat production - involuntary contraction of muscles - shivering

Continence - so don’t shit yourself

Question 4

Functions of connective tissues:

Tendons
Ligaments 
Fascia 
Cartilage 
Synovial membrane 
Bursa

Answer 4

Tendon - force transmission from muscle to bone - high collagen count, low elastin count

Ligament - supports bone to bone

Fascia - sheets of connective tissue - used in compartmentalisation in muscles and protection

Cartilage - articular (specifically hyaline) which decreases friction, Fibrocartilage - contains collagen fibers which is used in shock absorption and increases bony congruity

Synovial membrane - secretes synovial fluid for joint and tendon lubrication

Bursa - synovial fluid- filled sacs to protect tendons, ligaments from friction - these don’t appear well in cadavers

Question 5

Histology of Bone

Answer 5

Bone is connective tissue

ECM of bone is calcified which gives the bone its strength and rigidity due to the presence of calcium phosphate

Major fibre type is collagen (confers great tensile strength to the bone) with little elastin - also contains water GAGs and PGs

Question 6

Cells of the bone

Answer 6

Osteoblasts - synthesise new bone - migrate all over matrix and synthesise/ deposit Osteoid and matix protein of the bone - osteoid contains collagen - OB deposit CaPO4 into the Osteoid to make bone

Osteoclasts - multinucleate cells formed by fusion of progenitor cells of monocytes lineage - migrate over surface of bone and secrete acid chemicals to dissolve bone on cortical surface - surface is contact with bone has ruffled - increasing SA for absorption of minerals —> into ECM —> blood stream

Osteocytes - trapped OB in the matrix/ lacunae and become involve in signalling processes inside the bone - communicate with other osteocytes via fillipodia which extend through canals of bone

Question 7

classification of bones

Answer 7

Adult skeleton has 206 bones - skeleton divided into axial and appendicular sections

Bone types - Long, flat, short, irregular, sesamoid

Osteology is the study of the S + F of bones

Powerful muscles attach onto large bony prominences

Have indentations of bv and nerves as both are compressed against bones

Question 8

Long bones:

Answer 8

Diaphysis is the shaft of a long bone

Flares out into metaphysics which lies adjacent to the growth plate

On other side of growth plates is the epiphysis - articulating surfaces are conver with hyaline cartilage - with remainder of bony surface covered with periosteum

Medullary cavity full or red BM - involved in haematopoiesis

E.g. Femur, humerus

Question 9

Short bones

Answer 9

As long as they are wide

Provide stability and when working together can facilitate a large range of movement

E.g. the carpal bones in the wrist and the tarsal bones in the ankle

Question 10

Flat bones

Answer 10

Function is to protect the internal organs such as the brain heart

Can also provide large areas of attachment for muscles

E.g. skull, thoracic cage and pelvis

Question 11

Irregular bones

Answer 11

Vary in shape and structure - don’t fit into any category

Have complex shape which usually helps protect internal organs

E.g. vertebrae of the spinal cord

Question 12

Sesamoid bones

Answer 12

Bones embedded in tendons

Main function is to protect tendons from stress and wear - can act as a mech advantage by acting as a fulcrum for a muscle crossing a joint with a wide range of movement

E.g. patella

Question 13

Blood supple to bones

Answer 13

Nutrient artery is already present

Arteries in periosteum supply outer third of cortical bone and the periosteum itself

Rest of cortex and BM are dependent on the nutrient artery

In some bones there are additional metaphysical arteries - these enter at the site of attachment of the capsule

In a child metaphysical arteries don’t cross growth plate - epiphyseal artery then supplies ends of bone until adulthood when the 2 arteries fuse

Question 14

Avascular necrosis

Answer 14

Death of bone due to loss of its blood supply

Common cause is fracture, as well as alcoholism, excessive steroid use, radiation, hypertension and thrombosis

Question 15

Bone remodelling

Answer 15

Occurs in response to environmental factors due to a change in the Balance in activity between OB and OC

Question 16

Classification of joints

Answer 16

Connect one bone to another

Great variation in range of movement

Range of movement versus stability

3 types - fibrous, cartilaginous and synovial

Question 17

Fibrous joints

Answer 17

Fibrous joints are united by collagen fibres. They have very limited mobility (i.e. poor range of movement) and high stability.

Some examples of fibrous joints are:
• Sutures of the skull
• Inferior tibiofibular joint (at the ankle)
• Radioulnar interosseous membrane (in the forearm)
• Posterior sacroiliac joint (in the pelvis)

Question 18

Cartilaginous joints

Answer 18

Joints that use cartilage to unite bones are called cartilaginous joints.

They are typically found in the midline of the body and also in the epiphyseal plates of long bones.

They can be divided into primary and secondary cartilaginous joints.

Primary cartilaginous joints are united by hyaline cartilage and are completely immobile. Examples and include the first sternocostal joint, and the epiphyseal growth plates of the long bones.

Secondary cartilaginous joints are also known as symphyses. In these joints the articulating bones are covered with hyaline cartilage with a pad of fibrocartilage between them. They are usually found in the midline of the body.

Examples include the symphysis pubis (in the pelvis), intervertebral discs and the manubriosternal joint (between the manubrium sterni and the body of the sternum;

Question 19

Synovial joints

Answer 19

A major feature of a synovial joint is that it has a joint cavity containing synovial fluid.

It provides lubrication to the articular surfaces. Synovial joints therefore tend to have a high degree of mobility and are widespread throughout the skeleton.

The articulating surfaces within a synovial joint are typically covered with hyaline cartilage.

Hyaline cartilage usually permits smooth, low-friction movement and resists compressive forces within the joint by acting as a shock absorber.

The fibrous capsule surrounding the joint is composed of collagen in longitudinal and interlacing bundles. The capsule completely encloses the joint, except where it is interrupted by synovial protrusions which form bursae

The capsule stabilises the joint; it permits movement but resists dislocation. It is continuous with the periosteum covering the surface of the adjacent bones.

The synovial membrane is a thin highly-vascularised membrane that produces synovial fluid. It lines the joint capsule and covers any exposed osseous surfaces. It also lines tendon sheaths and bursae However, it does not cover articular cartilage or intra-articular discs / menisci.

Question 20

Different types of synovial joint

Answer 20

The shape of a synovial joint dictates the type of movement that the joint can perform.

There are:
plane joints - 2 flat surfaces slide against each other - movements in several directions e.g. carpal bones of wrist

hinge joints - joint allows for stable flexion and extension without sliding, only in 1 plane e.g. elbow joint bw humerus and ulna

saddle joints - 2 bones that fit like a rider in a saddle - allows for motion in 2 planes at the same time e.g. joint at base of thumb

condyloid (or ellipsoid) joints - looks like 2 diagonal halves of an egg coming together - e.g. Atlanta-occiptal joint at base of skull

pivot joints - rotational motion without gliding/ bending/ sideways displacement e.g. Atlanto-axial, allows head to rotate

ball and socket joints - allow stable movement in several directions without slippage e.g. hip

Question 21

Embryological development of synovial joints

Answer 21

The synovial joints will form between the adjacent cartilage models, in an area called the joint interzone

Cells at the centre of this interzone region undergo apoptosis (programmed cell death) to form the joint cavity, while surrounding mesenchyme cells from the perichondrium will form the periosteum where they lie in contact with bone, and the joint capsule and supporting ligaments where they lie in contact with the developing joint

Question 22

Joints as leavers

Answer 22

Class 1 levers: 
A first-class lever is exemplified by pair of scissors we  could think of the effort as the fingers pulling the upper handle of the scissors downwards to raise the load that is resting on the lower blade of the scissors We tend to see first- class levers in the body in places where the load is in equilibrium; for example, the head is well-balanced on the top of the neck with the weight of the posterior skull and its contents being balanced by the weight of the facial skeleton and jaw anteriorly. The posterior neck muscles contract to raise the load of the facial skeleton and jaw, using the top of the cervical spine (neck) as the fulcrum, and this enables you to look upwards. This is a first-class lever because the effort is applied on the opposite side of the fulcrum to the load.

Class 2 levers: A second-class lever is exemplified by a wheelbarrow The effort is exerted by pulling up on the handles of the wheelbarrow whereas the load is situated in the barrow itself. In the human body, an example of a second- class lever is seen when standing on tip-toes. The effort is applied through contraction of the calf muscles, the fulcrum is at the metatarsal heads (the ‘ball of the foot’) and the load is the Centre of Gravity of the body which passes straight down through the mid-foot. In a second-class lever, the load being lifted lies between the fulcrum and the effort that is applied to lift the load.

Class 3 levers: A third-class lever is like a set of forceps (fig 1.16c). The fulcrum is found where the two prongs of the forceps intersect at the hinge, the effort is applied by lifting the lower prong upwards and the load in this case is piece of tissue being held within the forceps. An example of a third-class lever in the body is seen at the elbow, where the elbow joint acts as the fulcrum, the biceps muscles are exerting the effort to flex the elbow, and the load is the weight of the forearm and hand. In a third-class lever, the effort is applied between the fulcrum and the load.

Question 23

Muscles

Function

Answer 23

Muscles produce force to:

Question 24

Attachment point of muscles

Answer 24

With the exception of the circular muscles, muscles have at least two sites of attachment to the bony skeleton.

These attachments are known as the origin and insertion. At attribution of origin and insertion is arbitrary, but there are some rules that are generally followed:

The origin is the stationary anchor point and is usually sited proximally in the limb.

The insertion is the mobile attachment point and is usually sited distally in the limb.

Muscle contraction is symmetrical, exerting equal force on the origin and insertion. It is the stabilisation of the ‘origin’ (e.g. by contraction of other muscles) that leads to the ‘insertion’ becoming the only mobile attachment point.

If the usual insertion point becomes fixed and the usual origin becomes mobile, the position of the origin and insertion will become inverted.

The action of a muscle on a joint is a function of the orientation of its fibres and the relation of those fibres to the joint

The action of the muscle is a function of the starting point of the joint

Question 25

Muscle role in movement

Answer 25

Muscles work together, almost never in isolation

The brain and spinal cord co-ordinate this complex task

Muscles that act to assist the prime mover are called synergists

Neutralisers prevent the unwanted actions of a muscle (e.g. gluteus maximas stabilises hip joint

Fixations stabilise a joint when another part of the body is moving

Question 26

Types of muscle contraction

Answer 26

Muscles can only pull, but whilst pulling they don’t always shorten!
Muscle contractions can be divided into:

Question 27

Concentric contractions

Answer 27

Concentric contractions are those which cause the muscle to shorten as it contracts. An example is flexing the elbow from full extension to full flexion by
concentric contraction of the Biceps Brachii muscle. Concentric contractions are the most common type of muscle contraction and occur frequently in daily and sporting activities.

Question 28

Eccentric contractions

Answer 28

Eccentric contractions are the opposite of concentric and occur when the muscle lengthens as it contracts. For example, eccentric contraction occurs when lowering the dumbbell down in a bicep curl exercise. The fibres within the Biceps brachii muscle are contracting to reduce the rate at which the dumbbell is lowered, but the biceps muscle is lengthening passively (due to Triceps brachii contracting and extending the elbow, and due to the effect of gravity on the dumbbell).

Question 29

Isometric contraction

Answer 29

Isometric contractions occur when there is no change in the length of the contracting muscle. For example, isometric contraction occurs when carrying an object; the weight of the object is pulling your arm downwards, but your muscles are contracting to hold the object at the same level. Another example is when you are gripping an object such as a tennis racket. There is no movement taking place in the joints of the hand, but the muscles are contracting to provide sufficient force to keep a steady hold of the racket.

Question 30

Arrangements of skeletal muscle fibres

Answer 30

The fascicles and fibres within muscles can be arranged in several different ways:

Question 31

Compartmentalisation within the limbs

predicting muscles action

Answer 31

Muscles are contained within fascial compartments. The muscles within a compartment usually share a common innervation and action

A fascial compartment is a region of the limb that contains muscles, nerves and blood vessels, surrounded by deep fascia

Each compartment usually has a separate nerve and blood supply to its neighbours. The muscles in a compartment will often be supplied by the same nerve.

Where does it attach (origin and insertion)?

Question 32

Connective tissues

Answer 32

Connective tissues are all physically connected with each other, hence the name connective tissue.
For example, there is continuity between the periosteum, joint capsule, tendons, epimysium and the collagen matrix of the bone.

Question 33

Fascia

Answer 33

Fascia (derived from the Latin for band) is a band or sheet of connective tissue.
Superficial fascia is a subcutaneous fatty layer, found in most regions of the body, serves as storage medium for fat and water, nerves BV and lymphatics

Deep fascia is entirely different in its construction. It is a thickened elaboration of the epimysium enveloping the muscle compartments

Question 34

Tendons

Answer 34

Tendons consist of dense regular connective tissue fascicles, enclosed within dense irregular connective tissue sheaths. They are anchored to bone by Sharpe

Question 35

Ligaments

Answer 35

Ligaments connect bone to bone (with the exception of the peritoneal ligaments that you will study within the abdominal cavity in the GI Unit in Semester 3). Like tendons, ligaments comprise dense regular bundles of connective tissue (mostly collagen) protected by dense irregular connective tissue sheaths.
Peri-articular (capsular) ligaments comprise thickenings of the capsule that surrounds synovial joints. They act as mechanical reinforcements for the joint.

Question 36

Aponeuroses

Answer 36

sheet-like structures that are histologically similar to tendons. Their primary function is to join muscles of the body (e.g. the aponeurosis connecting the frontalis and occipitalis muscles of the scalp;

Some aponeuroses, however, have lost contact with their original muscle but still serve a useful function.
Examples in the MSK system include the palmar aponeurosis formerly the broad expansion of the palmaris longus muscle in the anterior forearm and
plantar aponeurosis formerly the broad expansion of the plantaris muscle in the posterior leg/

Question 37

Hiltons Law

Answer 37

The nerves supplying the muscles moving the also supply the joint capsule and the skin overlying the insertions fo these muscles

Question 38

Embryology of the MSK

Answer 38

During embryonic development, humans are built from a repeating pattern of subunits called segments, arranged along the longitudinal axis. Segmentation is a crucial developmental process involved in the patterning and segregation of groups of cells with different features, generating regional properties for such cell groups and organising them into tissues.

Question 39

Hox genes

Answer 39

Segmentation is controlled by Hox genes. These genes are expressed in a segmental pattern in a cranio-caudal (top-to-bottom) axis

The order that the Hox genes are encoded on the chromosome is reflected in the order in whey are expressed in the body

These Hox genes determine the different types of vertebrae that will form in a body segment and the type of limb (arm, leg) that will develop from a limb bud. They confer segmental identity but do not form the actual segments themselves.

Mutation of Hox genes is an example of a homeotic mutation: a mutation that causes tissues to alter their normal differentiation pattern, producing integrated structures in unusual locations. One example is the generation of a sixth lumbar vertebra in place of the first sacral vertebra

Question 40

Serial homology

Answer 40

The upper and lower limbs have extremely similar development leading to extremely similar anatomy i.e. they are serially homologous. This is very helpful when learning anatomy as you will be able to draw parallels between the lower and upper limbs.

At a very basic level, the hip joint is serially homologous with the shoulder joint and the elbow is serially homologous with the knee.

Question 41

Limb buds

Answer 41

The limb buds first appear as small projections on the lateral body wall during the fourth week of development.

The limb buds consist of a mass of mesenchyme covered by a layer of ectoderm; at the tip of the bud the ectodermal cells divide to form an apical ectodermal ridge.

The limb buds elongate by the proliferation of mesenchyme. The apical ectodermal ridge is thought to exert an inductive influence on the limb mesenchyme that promotes growth and development of the limbs.

The process of endochondral ossification, which converts the cartilage models into bone, begins by the twelfth week of embryonic development.

Question 42

Rotation of limbs in development

Answer 42

The developing upper and lower limbs rotate in opposite directions and to different degrees.

The upper limb rotates externally (laterally) through 90° on its longitudinal axis; thus, the future elbows point backwards and the extensor muscles come to lie on the lateral and posterior aspects of the limb

The lower limb rotates internally (medially) through almost 90°; thus, the future knees face forward and the extensor muscles
come to lie on the anterior aspect of the lower limb.

This explains why dermatology are spiral pattern and why sartorius muscle in the anterior thigh follows an oblique path and why flexion of knee and elbow occur in different directions