Princicples Of MSK Flashcards
3 major components of MSK
Bone
Connective tissues
Skeletal muscle (not all skeletal muscles are voluntary)
Functions of bone
Support - keep body upright
Protection - protect vital organs
Metabolic
Storage - store fat in bone marrow
Movement - i.e. joints
Haematopoiesis - make blood
Functions of Skeletal muscle
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
Functions of connective tissues:
Tendons Ligaments Fascia Cartilage Synovial membrane Bursa
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
Histology of Bone
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
Cells of the bone
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
classification of bones
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
Long bones:
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
Short bones
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
Flat bones
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
Irregular bones
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
Sesamoid bones
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
Blood supple to bones
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
Avascular necrosis
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
Bone remodelling
Occurs in response to environmental factors due to a change in the Balance in activity between OB and OC
Classification of joints
Connect one bone to another
Great variation in range of movement
Range of movement versus stability
3 types - fibrous, cartilaginous and synovial
Fibrous joints
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)
Cartilaginous joints
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;
Synovial joints
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.
Different types of synovial joint
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
Embryological development of synovial joints
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
Joints as leavers
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.
Muscles
Function
Muscles produce force to:
Attachment point of muscles
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
Muscle role in movement
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
Types of muscle contraction
Muscles can only pull, but whilst pulling they don’t always shorten!
Muscle contractions can be divided into:
Concentric contractions
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.
Eccentric contractions
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).
Isometric contraction
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.
Arrangements of skeletal muscle fibres
The fascicles and fibres within muscles can be arranged in several different ways:
Compartmentalisation within the limbs
predicting muscles action
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)?
Connective tissues
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.
Fascia
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
Tendons
Tendons consist of dense regular connective tissue fascicles, enclosed within dense irregular connective tissue sheaths. They are anchored to bone by Sharpe
Ligaments
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.
Aponeuroses
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/
Hiltons Law
The nerves supplying the muscles moving the also supply the joint capsule and the skin overlying the insertions fo these muscles
Embryology of the MSK
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.
Hox genes
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
Serial homology
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.
Limb buds
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.
Rotation of limbs in development
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
