Musculoskeletal Practice MCQs: Jan-APR 08 c. Rhodes Phd

Scoliosis is not a congenital anomaly that results in a reduced number of cervical vertebrae. Scoliosis is a condition characterized by an abnormal curvature of the spine, which can occur in any part of the spine, not just the cervical region. The cause of scoliosis is not fully understood, but it is not primarily related to a reduced number of cervical vertebrae.

Syndactyly is a malformation of the hand or foot resulting in fusion of two or more digits. This means that the individual's fingers or toes are joined together, either partially or completely, due to the failure of proper separation during development. This condition can vary in severity, with some individuals having only a small webbing between the digits, while others may have complete fusion. Syndactyly can occur in both hands and feet and can be present at birth or develop later in life. Surgical intervention may be necessary to separate the fused digits, depending on the functional and aesthetic concerns of the individual.

Neural crest cells are not a component of the developing limb. The developing limb primarily consists of mesenchyme, which gives rise to the bones, muscles, and connective tissues of the limb. The apical ectodermal ridge is a specialized region of the ectoderm that plays a crucial role in limb development by directing the outgrowth and patterning of the limb. Hyaline cartilage is a type of connective tissue that provides support and structure to the developing limb. The ectoderm is the outermost layer of cells that gives rise to the skin and nervous system. Neural crest cells, on the other hand, are a group of cells that originate from the neural tube and give rise to various tissues and structures outside of the developing limb, such as the peripheral nervous system and certain facial structures.

Trunk musculature arises from the myotome region of the somite. The myotome is responsible for the development of skeletal muscles, including those found in the trunk. These muscles play a crucial role in providing support, stability, and movement to the trunk region of the body. Therefore, it is the myotome region that gives rise to the trunk musculature.

Thalidomide is a concern for women of childbearing age because it can cause severe limb defects if taken during the critical period of limb development. This means that if a woman takes Thalidomide during the time when her baby's limbs are forming, it can lead to serious abnormalities in the baby's limbs. This is particularly important for women of childbearing age because they may not be aware that they are pregnant during this critical period, and taking Thalidomide could have devastating effects on the developing fetus.

The correct answer is the intraembryonic mesoderm. During embryonic development, the mesoderm layer gives rise to various structures, including the muscle system. The mesoderm differentiates into different types of mesenchymal cells, which further differentiate into myoblasts. These myoblasts then fuse together to form muscle fibers, ultimately forming the muscle system.

All of the listed muscles (scalenes, prevertebral, geniohyoid, infrahyoid, flexor muscles of the trunk, quadratus lumborum, and pelvic diaphragm) are derived from the hypaxial divisions of the myotomes.

The limb musculature is derived from the somatic mesoderm. The somatic mesoderm is the layer of mesoderm that gives rise to the muscles, bones, and connective tissues of the limbs. This layer develops from the lateral plate mesoderm and is responsible for the formation of the musculoskeletal system in the limbs. Therefore, the somatic mesoderm is the correct answer in this case.

The viscerocranium gives rise to the bones of the face. The viscerocranium is a part of the skull that develops from the embryonic pharyngeal arches. It includes bones such as the maxilla, mandible, zygomatic bone, and nasal bones, which form the structure of the face. The chondrocranium, membranous neurocranium, pre-chordal chondrocranium, and cartilaginous neurocranium are all different parts of the skull but do not give rise to the bones of the face.

Craniosynostosis refers to the premature fusion of one or more fibrous sutures in the skull. The fibrous sutures are the areas where the skull bones join together. When these sutures fuse too early, it can lead to abnormal skull growth and shape. This condition can cause various complications, such as increased pressure on the brain, developmental delays, and facial deformities. Treatment for craniosynostosis often involves surgery to release the fused sutures and allow for normal skull growth.

The bones that develop from the structure labeled 'A' do not form by intramembranous ossification.

The statement is false because the diaphyseal plate is not a growth plate where chondrocytes proliferate to elongate the growing bone. The diaphyseal plate, also known as the epiphyseal plate or growth plate, is actually a layer of cartilage located near the ends of long bones in children and adolescents. It is responsible for longitudinal bone growth by allowing the proliferation and ossification of chondrocytes. Once the bone has reached its full length, the diaphyseal plate closes and is replaced by solid bone, marking the end of bone growth.

Each vertebral myotome bridges two vertebrae to permit spinal movement. This statement is correct because the myotomes, which are muscle groups formed from the somites, are responsible for movement in the vertebral column. The myotomes extend from one vertebra to the next, allowing for flexion, extension, and rotation of the spine.

During the fourth week of development, limb buds become first perceptible. This is the stage when the embryo starts developing its limbs, and small protrusions called limb buds begin to form. These limb buds will eventually grow and differentiate into the arms and legs of the developing fetus.

The bones of the chordal chondrocranium develop only through endochondral ossification. This process involves the replacement of cartilage with bone tissue. In endochondral ossification, a cartilage model is first formed and then gradually replaced by bone as osteoblasts deposit new bone tissue. This process is responsible for the development of most of the bones in the body, including those in the skull. Membranous ossification, on the other hand, involves the direct ossification of mesenchyme without a cartilage intermediate and is responsible for the formation of flat bones, such as those in the skull.

Molding refers to the adaptation of the skull bones to the birth canal, allowing them to overlap during birth. This process occurs to facilitate the passage of the baby through the narrow birth canal, ensuring a safer and easier delivery. The other options mentioned in the question do not accurately describe the concept of molding.

During embryogenesis, neural crest cells differentiate into a variety of tissues, including flat skull bones. This process occurs during the early stages of development when the embryo is forming its basic structures. The differentiation of neural crest cells into flat skull bones is a crucial step in the formation of the skull and occurs before the second trimester or the fetal period. Therefore, the correct time point for this differentiation is during embryogenesis.

During week 6 of development, the limb skeleton consists of cartilage. This is because during early embryonic development, the skeleton initially forms as a template made of cartilage before it is replaced by bone in a process called ossification. By week 6, the limb buds have developed and the cartilage is present to provide structure and support for the developing limbs.

Limb rotation is necessary for correct muscle positioning because it allows the muscles to align properly with the bones and joints, ensuring optimal movement and function. Without proper rotation, the muscles may be misaligned, leading to inefficient movement and potential injury.

The notochord degenerates along its length specifically in segments where vertebral bodies form. The notochord is a flexible rod-like structure that serves as the primary axial support in the early development of vertebrate embryos. As the embryo develops, the notochord is gradually replaced by the formation of vertebral bodies, which make up the backbone or spine. This process is known as vertebral segmentation, and it involves the degeneration and replacement of the notochord with bony structures called vertebral bodies.

The zone of polarizing activity (ZPA) is responsible for patterning the anteroposterior axis of the developing limb bud. This means that it helps to determine the positioning and formation of structures along the front-to-back axis of the limb, such as fingers and toes.

During development, mesenchymal cells migrate from the paraxial mesoderm to different regions of the embryo. In this case, the failure of these cells to migrate beneath the surface ectoderm has resulted in an abdominal wall defect in the newborn infant. This defect suggests that the paraxial mesoderm cells responsible for abdominal wall formation did not reach their proper destination, leading to the defect. Therefore, the correct answer is paraxial mesoderm.

The correct answer states that the ZPA (zone of polarizing activity) produces SHH (sonic hedgehog) which diffuses to form a concentration gradient. This is correct because during limb development, the ZPA is a specialized region in the posterior limb bud that secretes SHH. SHH then forms a concentration gradient, with higher levels near the ZPA and lower levels in the anterior limb bud. This concentration gradient helps to determine the pattern of digit formation by influencing the expression of specific genes in the developing limb.

The ventrolateral lip (VLL) is the myogenic region that will give rise to the external intercostal muscles. The VLL is located in the somite, which is a segment of the developing embryo. It is responsible for the formation of skeletal muscles, including the intercostal muscles that are found between the ribs. The external intercostal muscles play a role in expanding the ribcage during inhalation, helping with the process of breathing.