Musculoskeletal System (Somites + Limb Buds)

Question 1

Which of the following bones develop mainly from endochondral ossification?

clavicle

humerus

sternum

frontal bone

Answer 1

Humerus and sternum

Question 2

The failure of the chondrification centres of the neural arch to fuse results in the formation of what congenital condition?

Answer 2

Spina bifida

Question 3

Concerning the number of primary/secondary ossification centres that develop in bones: (more than one statement may be correct)

2 primary ossification centres in a typical vertebra

3 secondary ossification centres in a typical radius

3 primary ossification centres in a typical ossa coxa

7 secondary ossification centres in a typical humerus

6 primary ossification centres in a typical sternum

Answer 3

3 and 5

Question 4

Concerning the development of the limbs

ossification of the appendicular skeleton commences in week 7

the skeletal muscles of the limbs are derived from cells migrating from the sclerotome

the upper and lower limb buds appear at the same time

the apical ectodermal ridge secretes Sonic hedgehog (Shh) to establish the proximodistal axis in the limbs

Answer 4

ossification of the appendicular skeleton commences in week 7

Question 5

Name the stages of endochondral ossification in order

Answer 5

-proliferation of chondrocytes
-hypertrophy of chondrocytes
-formation of periosteal collar
-invasion of blood vessels into chondrification cells
-formation of primary and secondary ossification centres
-formation of epiphyseal line

Question 6

Match each adult derivative with its correct embryological precursor

Ribs
Deep back muscles
Skin of the back
Femur

Sclerotome
Dermatome
Lateral plate mesoderm
Hypomere of myotome
Epimere of myotome

Answer 6

Ribs- sclerotome
Deep back muscles- epimere of myotome
Skin of back- dermatome
Femur- lateral plate mesoderm

Question 7

Which part of the mesoderm contributes to the formation of the somites?

Answer 7

Paraxial mesoderm

Question 8

What would be consequence to ossification if Runx2 was not expressed during embryological development?

Answer 8

Runx2 needed for bone formation. No transcription

Question 9

What embryological structure is the nucleus pulposus derived from?

Answer 9

Notochord that degenerates within primordial centrum

Question 10

What type of tissues are sutures and fontanelles composed of?

Answer 10

Membranous connective tissue

Question 11

What is the importance of apoptosis in the formation of the digits?

Answer 11

apoptosis is essential for the refinement and separation of digits during embryonic limb development, ensuring that they form as distinct and functional structures, rather than remaining webbed together.

Question 12

What is the importance of the apical ectodermal ridge in limb development?

Answer 12

The apical ectodermal ridge is a critical signaling and structural component in limb development. Its role in maintaining proliferation, patterning, and growth is essential for the proper formation of limbs with the correct size, shape, and organization of their various structures.

Question 13

Why do the facial and cranial bones grow disproportionately during the foetal period of development?

Answer 13

Brain Growth: The most significant factor contributing to the apparent disproportion is the rapid growth of the brain. The fetal brain undergoes significant expansion and development during the latter part of pregnancy. The cranial bones need to accommodate this brain growth. The growth of the skull, especially in the cranial vault area, is a direct response to the growth of the brain to ensure that there is adequate space for the developing brain.

Birthing Adaptations: The relative size and shape of the fetal skull are adapted to the process of birth. The fetal skull is not a single, solid structure but rather consists of several bones separated by sutures and fontanelles. This allows the skull to be somewhat flexible during passage through the birth canal. The facial and cranial bones need to be adaptable to facilitate the birthing process while still protecting the developing brain.

Growth at Different Rates: Various bones in the fetal head and face grow at different rates and in response to different developmental signals. For example, the bones of the cranium respond to brain growth, while the development of the facial bones is influenced by factors such as the formation of facial features and structures.

Postnatal Growth: After birth, the growth of facial and cranial bones continues. The skull and face undergo significant changes during infancy and childhood to attain a more proportionate and mature appearance.

Question 14

How do cells in the limb buds know whether to produce a femur or a tibia or a tarsal bone?

Answer 14

the development of specific bones in the limb buds is guided by a combination of genetic information and signaling molecules that provide positional cues. The unique combination of genetic instructions, morphogen concentrations, and interactions between neighboring cells determines which type of bone will form in a particular location within the limb bud. This highly coordinated process ensures the proper development of various bones in the limbs.

Question 15

What developmental anomaly can result in congenital scoliosis?

Answer 15

Hemivertebrae: Hemivertebrae are wedge-shaped vertebrae that can develop asymmetrically. When a child is born with one or more hemivertebrae, it can cause a curvature of the spine.

Unilateral Bar: A unilateral bar is a bony or cartilaginous bridge that forms between two adjacent vertebrae on one side of the spine. This can disrupt the normal growth and alignment of the spine.

Failure of Segmentation: In some cases, the vertebrae may not form properly, leading to abnormalities like butterfly vertebrae or block vertebrae. These anomalies can result in curvature of the spine.

Failure of Formation: Sometimes, vertebrae may not form at all or may be severely underdeveloped. This can lead to congenital scoliosis when it affects the overall alignment of the spine.

Neurological Anomalies: Congenital scoliosis can also be associated with neurological abnormalities, such as tethered spinal cord or myelomeningocele (a type of spina bifida). These conditions can affect the development and alignment of the spine.

Question 16

What is polydactyly?

Answer 16

Growth of supernumerary in digits of fingers and toes

Question 17

In terms of a long bone, where do you typically find the primary and secondary ossification centres?

Answer 17

Primary- diaphysis
Secondary- epiphysis

Question 18

Which bones have primary ossification centres that develop after birth?

Answer 18

Sesmoid bones eg pisiform. Some skull bones eg sphenoid, ethmoid

Question 19

Which bones have secondary ossification centres that develop before birth?

Answer 19

Femur, tibia + fibula

Question 20

Where are accessory ribs most commonly located? Do they cause any functional deficits?

Answer 20

Found in thoracic region at C7. Can affect respiration or compress blood vessels or nerves

Question 21

Why does the symphysis menti fuse earlier than the metopic suture in a child skull?

Answer 21

the fusion of the symphysis menti is essential for facial and mandibular development and occurs earlier in life, while the metopic suture’s later fusion allows for the growth of the frontal bone and the expansion of the cranial vault to accommodate brain growth.

Question 22

What is the function of the basicranial synchondrosis? How does it differ from other temporary synchondroses in the body?

Answer 22

The basicranial synchondrosis is a specific type of cartilaginous joint in the human skull located at the base of the cranial vault. It is primarily formed by the cartilaginous connection between the occipital bone (specifically, the basioccipital bone) and the sphenoid bone. This synchondrosis serves several important functions:

Growth and Development: The basicranial synchondrosis is a crucial site for growth and development of the cranial base and, by extension, the entire skull. During childhood and adolescence, the cartilaginous tissue in this area allows for elongation and expansion of the cranial base, which is necessary to accommodate the growing brain.

Facilitation of Brain Growth: As the brain continues to grow and develop, the cranial base needs to adapt and expand to accommodate this growth. The basicranial synchondrosis allows for this dynamic growth, contributing to the overall shape and size of the skull.

Support for Neurocranial Structures: The basicranial synchondrosis provides support for various structures of the neurocranium, including the brain and the cranial vault. It plays a role in distributing and bearing the weight of the brain and surrounding structures.

Differences from Other Temporary Synchondroses:

Location: The basicranial synchondrosis is unique because it is located in the cranial base, specifically where the base of the skull interfaces with the brain. In contrast, other temporary synchondroses are found in long bones like the femur, tibia, or humerus.

Question 23

Describe the process of skull moulding and its importance in parturition

Answer 23

skull molding is a natural and adaptive process that allows the fetal skull to change shape temporarily during childbirth, facilitating the safe passage of the baby through the birth canal. This mechanism helps protect the baby’s brain, ensures a smoother delivery, and is part of the intricate process of childbirth. Over time, the baby’s skull typically assumes a more typical shape as the bones and sutures naturally adapt.

Question 24

Consider the case of craniosynostosis in the foetus. How would this affect parturition and development of the nervous system?

Answer 24

Craniosynostosis is a congenital condition in which one or more of the cranial sutures, which are the fibrous joints between the bones of an infant’s skull, close prematurely. Craniosynostosis can lead to an unusually shaped head due to the prematurely fused sutures, potentially making it more challenging for the infant to pass through the birth canal. This can result in a difficult or prolonged labor.

Development of the Nervous System:
Increased Intracranial Pressure: Craniosynostosis can lead to increased intracranial pressure within the infant’s skull. Because the cranial sutures are closed prematurely, there is limited room for the growing brain. Increased pressure within the cranial cavity can lead to developmental issues and compromise the health of the nervous system.

Risk of Brain Compression: In cases of severe craniosynostosis, where there is limited space for the growing brain, there’s a risk of brain compression. This can affect brain development, potentially leading to intellectual or developmental disabilities.

Facial and Skull Deformities: The premature closure of cranial sutures can result in an abnormal head shape and facial deformities. These craniofacial abnormalities can lead to issues with visual, auditory, and respiratory functions and may necessitate corrective surgical interventions.

Question 25

What is the difference between lumbarisation and sacralisation? What is more common? How do they develop embryologically?

Answer 25

Lumbarization:
Definition: Lumbarization is a condition where one or more of the sacral vertebrae take on characteristics similar to lumbar (lower back) vertebrae. In other words, there is an extra lumbar-like vertebra above the sacrum.
Development: Lumbarization occurs due to a failure of the lower sacral segments to fuse properly during embryonic development. This results in an extra, separate vertebra that resembles a lumbar vertebra. Lumbarization can vary in terms of the number of affected sacral vertebrae.
Commonality: Lumbarization is generally less common than sacralization.

Sacralization:
Definition: Sacralization is the opposite of lumbarization. It is a condition where one or more of the lumbar vertebrae take on characteristics similar to sacral vertebrae, typically by becoming fused with the sacrum.
Development: Sacralization occurs when one or more of the lower lumbar vertebrae fail to differentiate fully from the sacrum during embryonic development. As a result, they become partially or completely fused with the sacrum.
Commonality: Sacralization is more common than lumbarization.

Question 26

What effect does sacralisation have on body function?

Answer 26

Lower back pain, reduced flexibility, altered posture, nerve compression