4. Basic concepts in MSK - Connective tissues and embryology

Question 1

What is fascia?

Answer 1

Band/sheet of connective tissue

Question 2

What is superficial fascia/subcutaneousfat/subcutis/Hypodermis?

Answer 2

Subcutaneous fatty layer

Question 3

Where is superficial fascia found?

Answer 3

not always found immediately deep to the skin. It also surrounds organs and glands, neurovascular bundles, etc.

Question 4

Function of superficial fascia?

Answer 4

Stores fat+water
Passageway for lymphatics, nerves,blood vessels
Protective padding for organs

Question 5

What is deep fascia?

Answer 5

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.

Question 6

Describe structure of tendons

Answer 6

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.

Question 7

Why do tendons heal poorly?

Answer 7

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.

Question 8

Describe structure of ligaments

Answer 8

dense REGULAR bundles of connective tissue (mostly collagen) protected by dense IRREGULAR connective tissue sheaths.

Question 9

What are Peri-articular (capsular) ligaments? Function?

Answer 9

comprise thickenings of the capsule that surrounds synovial joints. They act as mechanical reinforcements for the joint.

Question 10

What is the function of ligaments?

Answer 10

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

Question 11

Define aponeurosis? Give examples

Answer 11

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

Question 12

What is the function of aponeuroses?

Answer 12

To join muscles of the body

Question 13

Which aponeuroses have lost contact with their original muscle?

Answer 13

Palmar and plantar

Question 14

What is Hilton’s Law?

Answer 14

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.

Question 15

What controls segmentation?

Answer 15

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.

Question 16

Function of hox genes?

Answer 16

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.

Question 17

Mutation of hox genes is an example of what type of mutation?

Answer 17

Homeotic mutation - mutation that causes tissues to alter their normal differentiation pattern, producing integrated structures in unusual locations.

Question 18

Examples of homeotic hox gene mutations?

Answer 18

Generation of sixth lumbar vertebra
Extra fingers/toes - polydactyl
Cervical ribs (additional ribs)

Question 19

What can cervical ribs lead to/ how can they present clinically?

Answer 19

Compress the nearby arteries and nerves, producing a condition called thoracic outlet syndrome.

Question 20

what does serially homologous mean?

Answer 20

The upper and lower limbs have extremely similar development leading to extremely similar anatomy

Question 21

What is the upper limb equivalent of the knee?

Answer 21

Elbow

Question 22

What is the lower limb equivalent of the radial nerve?

Answer 22

Femoral nerve

Question 23

What is the upper limb equivalent of the plantaris?

Answer 23

Palmaris longus

Question 24

Describe the serially homologous features of the body

Answer 24

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

Question 25

Outline prenatal limb development?

Answer 25

> 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.

Question 26

What is limb bud made of?

Answer 26

Mass of mesenchyme covered by a layer of ectoderm

Question 27

When do the limb buds first appear post natally?

Answer 27

4th week of development

Question 28

How do they limbs buds project in early embryo before development?

Answer 28

Project laterally from trunk in coronal plane

Question 29

How do the developing limbs project?

Answer 29

• 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

Question 30

How are the dorsal and ventral components formed?

Answer 30

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

Question 31

Which features of human anatomy does limb rotation explain?

Answer 31

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)