4. Basic concepts in MSK - Connective tissues and embryology Flashcards
What is fascia?
Band/sheet of connective tissue
What is superficial fascia/subcutaneousfat/subcutis/Hypodermis?
Subcutaneous fatty layer
Where is superficial fascia found?
not always found immediately deep to the skin. It also surrounds organs and glands, neurovascular bundles, etc.
Function of superficial fascia?
Stores fat+water
Passageway for lymphatics, nerves,blood vessels
Protective padding for organs
What is deep fascia?
It is a thickened elaboration of the epimysium enveloping the muscle compartments and comprises collagen bundles and elastin fibres oriented in a wavy pattern parallel to the direction of pull. It is flexible and able to resist great unidirectional forces.
Describe structure of tendons
dense regular connective tissue fascicles, enclosed within dense irregular connective tissue sheaths.
They are anchored to bone by Sharpey’s fibres.
There is a low ratio of elastin to collagen, hence minimal waste of energy transfer between the muscle and bone.
Why do tendons heal poorly?
Tendons have a relatively poor blood supply, which impedes their healing after injury. They also have a low water content, limiting the diffusion of nutrients and further impeding tendon healing.
Describe structure of ligaments
dense REGULAR bundles of connective tissue (mostly collagen) protected by dense IRREGULAR connective tissue sheaths.
What are Peri-articular (capsular) ligaments? Function?
comprise thickenings of the capsule that surrounds synovial joints. They act as mechanical reinforcements for the joint.
What is the function of ligaments?
The major role of ligaments to help stabilise joints and limit their range of movement. However, some ligaments (e.g. in the foot) store energy to assist with propulsion. As with tendons, ligaments have a relatively poor blood supply, which compromises their healing after injury
Define aponeurosis? Give examples
a sheet of pearly-white fibrous tissue that takes the place of a tendon in sheetlike muscles having a wide area of attachment e.g. sole of foot, abdominal wall, skull
What is the function of aponeuroses?
To join muscles of the body
Which aponeuroses have lost contact with their original muscle?
Palmar and plantar
What is Hilton’s Law?
The nerves supplying the muscles moving the joint also supply the joint capsule and the skin overlying the insertions of these muscles.
Hence, if you know the nerve supply of the muscles that move the joint, you can work out: the nerve supply of the joint (capsule) and the nerve supply of the skin overlying the insertion of the muscles.
What controls segmentation?
Hox genes. Expressed in segmental pattern in cranial-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.
Function of 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 what type of mutation?
Homeotic mutation - mutation that causes tissues to alter their normal differentiation pattern, producing integrated structures in unusual locations.
Examples of homeotic hox gene mutations?
Generation of sixth lumbar vertebra
Extra fingers/toes - polydactyl
Cervical ribs (additional ribs)
What can cervical ribs lead to/ how can they present clinically?
Compress the nearby arteries and nerves, producing a condition called thoracic outlet syndrome.
what does serially homologous mean?
The upper and lower limbs have extremely similar development leading to extremely similar anatomy
What is the upper limb equivalent of the knee?
Elbow
What is the lower limb equivalent of the radial nerve?
Femoral nerve
What is the upper limb equivalent of the plantaris?
Palmaris longus
Describe the serially homologous features of the body
the hip joint is serially homologous with the shoulder joint and the elbow is serially homologous with the knee. Other examples of serial homology include the femur in the thigh and humerus in the arm, the great toe and the thumb, the palmaris longus tendon in the forearm and the plantaris tendon in the leg; the radial nerve in the arm and the femoral nerve in the leg et
Outline prenatal limb development?
> The limb buds first appear as small projections on the lateral body wall during the fourth week of development.
> At the tip of the bud, the ectodermal cells divide to form an apical ectodermal ridge. Upper limb buds first then lower few days later.
> Buds elongate by 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.
> Cells aggregate to form mesenchymal skeleton in limb. Limb skeleton is CARTILAGINOUS (Hyaline).
> Primary ossification centres appear in middle of long bones.
> Endochondral ossification.
Remember epiphyseal plate hyaline cartilage remains throughout childhood to allow bone lengthening. Also retained as articular cartilage that covers surfaces of synovial joints.
What is limb bud made of?
Mass of mesenchyme covered by a layer of ectoderm
When do the limb buds first appear post natally?
4th week of development
How do they limbs buds project in early embryo before development?
Project laterally from trunk in coronal plane
How do the developing limbs project?
- 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 backward
- lower limb rotates internally (medially) through almost 90°. - thus, the future knees face forward
How are the dorsal and ventral components formed?
As bones are forming, myoblasts aggregate and develop a large muscle mass in each limb bud. In general, this muscle mass separates into dorsal (extensor) and ventral (flexor) components.
At first the flexor aspect of the limb is ventral and the extensor aspect dorsal. The pre-axial border is cranial and postaxial border is caudal
Which features of human anatomy does limb rotation explain?
The spiral pattern of the dermatomes in the lower limb in the Keegan and Garret dermatome map
Why flexion of the elbow and flexion of the knee send the distal limb in different directions
Why the sartorius muscle in the anterior thigh follows an oblique path (see separate flashcard)
