Development of Musculoskeletal System — MCQs
The gene that regulates normal morphogenesis during development is?
Muscles of mastication develop from
Which is the earliest secondary ossification center to develop chronologically?
Histology of Myositis ossificans most closely mimics which of the following?
Which of the following statements provides the MOST COMPLETE description of sclerotome function during vertebral development?
Which muscle paralysis can cause winging of the scapula?
An intrauterine scan at the 13th week of pregnancy showed a fetus with multiple long bone fractures. What is commonly associated with this finding?
Which of the following is least likely to be associated with progressive congenital scoliosis?
Just before birth, which epiphysis appears?
All are derived from ectoderm except for which of the following?
Development of Musculoskeletal System Indian Medical PG Practice Questions and MCQs
Question 1: The gene that regulates normal morphogenesis during development is?
- A. FMR-1 gene
- B. P-16
- C. Homeobox gene (Correct Answer)
- D. PTEN
Explanation: ***Homeobox gene*** - **Homeobox genes** (Hox genes) are a large family of genes that play a critical role in regulating the **patterning of the body axis** and the **development of organs** and appendages during embryonic development. - They encode **transcription factors** that control the expression of other genes involved in morphogenesis. *FMR-1 gene* - The **FMR-1 gene** (fragile X mental retardation 1 gene) is associated with **Fragile X syndrome**, a genetic condition causing intellectual disability and developmental problems. - Its primary role is in **brain development** and synaptic function, not general normal morphogenesis. *P-16* - **P16 (CDKN2A)** is a **tumor suppressor gene** involved in regulating the cell cycle by inhibiting cyclin-dependent kinases. - Its main function is in preventing uncontrolled cell growth and proliferation, not directly in orchestrating embryonic morphogenesis. *PTEN* - **PTEN** is another prominent **tumor suppressor gene** that plays a crucial role in cell growth, survival, and proliferation. - Mutations in PTEN are linked to various cancers and developmental disorders such as **Cowden syndrome**, but its primary function is not in regulating the broad aspects of normal embryonic morphogenesis.
Question 2: Muscles of mastication develop from
- A. 1st branchial arch (Correct Answer)
- B. 2nd branchial arch
- C. 3rd branchial arch
- D. 6th branchial arch
Explanation: The original explanation remains unchanged because none of the provided references contained relevant medical information regarding the embryological development of branchial arches or muscles of mastication. ***1st branchial arch*** - The **1st branchial arch**, also known as the mandibular arch, gives rise to the **muscles of mastication**, which include the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. - The nerve supplying these muscles is the **trigeminal nerve (CN V)**, specifically its mandibular division, which is also derived from the 1st branchial arch. *2nd branchial arch* - The **2nd branchial arch**, or hyoid arch, develops into the **muscles of facial expression**, such as the orbicularis oculi and zygomaticus. - These muscles are innervated by the **facial nerve (CN VII)**, which is associated with the 2nd arch. *3rd branchial arch* - The **3rd branchial arch** gives rise to a single muscle, the **stylopharyngeus**, which plays a role in swallowing. - This arch is innervated by the **glossopharyngeal nerve (CN IX)**. *6th branchial arch* - The **6th branchial arch** contributes to the formation of most of the **laryngeal muscles**, which are essential for voice production. - These muscles are innervated by branches of the **vagus nerve (CN X)**, specifically the recurrent laryngeal nerve.
Question 3: Which is the earliest secondary ossification center to develop chronologically?
- A. Lower end of femur (Correct Answer)
- B. Upper end of humerus
- C. Lower end of fibula
- D. Upper end of tibia
Explanation: ***Lower end of femur*** - The **distal femoral epiphysis** is typically the first secondary ossification center to appear, often present at birth or shortly before [1]. - Its presence at birth is an indicator of **fetal maturity**, making it a key developmental landmark [1]. *Upper end of humerus* - The **proximal humeral epiphysis** typically ossifies around 6 months of age, significantly later than the distal femur. - This center contributes to the growth of the humeral head and greater tubercle. *Lower end of fibula* - The **distal fibular epiphysis** appears around the first year of life, after both the distal femur and proximal humerus. - It forms part of the ankle joint and contributes to its stability. *Upper end of tibia* - The **proximal tibial epiphysis** typically ossifies around 6-12 months of age, well after the distal femur. - This center is crucial for the growth of the upper tibia and knee joint development.
Question 4: Histology of Myositis ossificans most closely mimics which of the following?
- A. Giant Cell Tumor
- B. Ewing's tumor
- C. Osteochondroma
- D. Osteosarcoma (Correct Answer)
Explanation: ***Osteosarcoma*** - Histologically, myositis ossificans can mimic **osteosarcoma**, as both conditions show features of **ossification and bone formation** [1]. - **Age** and **location** may also help differentiate, but careful histological examination reveals similarities. *Osteochondroma* - Characterized by a **cartilaginous cap** overlying the bone, which is not present in myositis ossificans [2]. - Usually develops in patients with a **pedunculated or sessile base**, rather than the heterogeneous ossification seen in myositis ossificans. *Ewing's tumour* - This is a **malignant round cell tumor** that predominantly affects children and young adults, with specific **translocation** genetic features. - Histologically, it shows a **small, blue cell appearance**, distinct from the fibroblastic reaction and bone formation seen in myositis ossificans. *GCT* - Granulosa cell tumors (GCT) are primarily **gynecological**, with no significant **bony changes** as seen in myositis ossificans. - Histologically, GCTs show **multinucleated giant cells** and are associated with **subarticular bone lesions**, unlike the heterotopic ossification seen in myositis ossificans. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 673-674. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 672-673.
Question 5: Which of the following statements provides the MOST COMPLETE description of sclerotome function during vertebral development?
- A. The notochord forms the nucleus pulposus.
- B. The sclerotome contributes to the formation of vertebral bodies.
- C. The sclerotome surrounds the notochord and the neural tube during development. (Correct Answer)
- D. The sclerotome surrounds the notochord.
Explanation: ***The sclerotome surrounds the notochord and the neural tube during development.*** - The **sclerotome** is the part of the somite that differentiates into mesenchymal cells and migrates to surround both the developing **notochord** (which gives rise to the nucleus pulposus) and the **neural tube** (which forms the spinal cord). - This encirclement is crucial for the formation of the **vertebral column**, providing protection and a structural framework. *The notochord forms the nucleus pulposus.* - While true that the **notochord** contributes to the **nucleus pulposus**, this statement describes the fate of the notochord itself, not the function of the sclerotome. - The question asks for the function of the sclerotome, and this option only details one specific derivative. *The sclerotome contributes to the formation of vertebral bodies.* - This statement is partially true, as the **sclerotome** does indeed form the **vertebral bodies**, arches, and intervertebral discs. - However, it is not the *most complete* description of its function during development, as it omits the crucial aspect of surrounding the neural tube. *The sclerotome surrounds the notochord.* - This statement is correct but **incomplete** as it only mentions the notochord. - The **sclerotome** also surrounds the **neural tube**, which is a vital part of its developmental role in forming the vertebral canal.
Question 6: Which muscle paralysis can cause winging of the scapula?
- A. Teres minor
- B. Deltoid
- C. Serratus anterior (Correct Answer)
- D. Supraspinatus
Explanation: ***Serratus anterior*** - Paralysis or weakness of the **serratus anterior muscle**, innervated by the **long thoracic nerve**, causes winging of the scapula. - This muscle is responsible for **protraction and upward rotation of the scapula**, keeping it flat against the chest wall; without its function, the medial border of the scapula protrudes posteriorly. *Teres minor* - The **teres minor** is part of the rotator cuff and is involved in **external rotation** and **adduction of the arm**. - Its paralysis would primarily affect shoulder movement and stability, but not directly lead to **scapular winging**. *Deltoid* - The **deltoid muscle** is the primary muscle for **abduction of the arm** beyond the first 15 degrees. - Paralysis of the deltoid would result in significant difficulty lifting the arm, but it does not cause the **scapula to wing**. *Supraspinatus* - The **supraspinatus muscle** initiates **abduction of the arm** (first 15 degrees) and helps stabilize the shoulder joint. - Its paralysis would impair arm elevation but does not directly result in **scapular winging**.
Question 7: An intrauterine scan at the 13th week of pregnancy showed a fetus with multiple long bone fractures. What is commonly associated with this finding?
- A. Osteogenesis imperfecta (Correct Answer)
- B. Marfan syndrome
- C. Achondroplasia
- D. Cretinism
Explanation: ***Osteogenesis imperfecta*** - **Multiple long bone fractures** detected early in pregnancy are a classic presentation of **osteogenesis imperfecta (OI)**, a genetic disorder characterized by **bone fragility**. - OI is primarily caused by mutations in genes encoding **type I collagen**, leading to defective bone formation. *Achondroplasia* - This condition is a form of **dwarfism** characterized by disproportionately short limbs and a normal-sized trunk, resulting from a mutation in the **FGFR3 gene**. - While it affects bone growth, it typically does not cause **multiple fractures** prenatally. *Marfan syndrome* - This is a connective tissue disorder affecting the skeletal, ocular, and cardiovascular systems, characterized by **tall stature**, **long limbs and fingers**, and **aortic root dilation**. - It results from a mutation in the **fibrillin-1 gene** and is not primarily associated with prenatal long bone fractures. *Cretinism* - This is a historical term for **congenital hypothyroidism**, which results from severely deficient thyroid hormone production in a newborn. - It leads to developmental delays, growth retardation, and intellectual disability, but not to **multiple bone fractures**.
Question 8: Which of the following is least likely to be associated with progressive congenital scoliosis?
- A. Hemivertebra
- B. Unilateral unsegmented vertebra with bar
- C. Wedge vertebra (Correct Answer)
- D. Block vertebra
Explanation: ***Wedge vertebra*** - A **wedge vertebra** is a less severe form of vertebral anomaly compared to a hemivertebra, characterized by incomplete formation of the vertebral body on one side. - While it can cause scoliosis, it is significantly **less likely to progress** rapidly or severely compared to anomalies that involve complete lack of formation or fusion. *Hemivertebra* - A **hemivertebra** is a fully unsegmented vertebral body fused to one side of the adjacent segments, leading to a profound congenital deformity and a powerful growth plate on the opposite side. - This imbalance causes a **high likelihood of progression** in congenital scoliosis due to differential growth. *Unilateral unsegmented vertebra with bar* - This anomaly involves a **failure of segmentation** on one side of a vertebral body, creating a "bar" that inhibits growth on that side, while the other side grows normally. - The unrestricted growth on one side coupled with restricted growth on the other creates a significant imbalance, leading to a **high potential for progressive scoliosis**. *Block vertebra* - A **block vertebra** results from a complete failure of segmentation between two or more vertebral bodies along both sides. - While it causes a reduction in vertebral height and potentially some stiffness, it generally leads to **little or no progressive scoliosis** because the growth inhibition is symmetric and balanced on both sides of the spine.
Question 9: Just before birth, which epiphysis appears?
- A. Upper end of humerus
- B. Lower end of fibula
- C. Upper end of tibia
- D. Lower end of femur (Correct Answer)
Explanation: ***Lower end of femur*** - The **distal femoral epiphysis** is one of the first epiphyses to ossify, appearing around **36 weeks of gestation** (9th month), making it consistently present just before birth [1]. - Its presence on antenatal imaging or X-ray at birth is a reliable indicator of **fetal maturity** and is used medico-legally to assess gestational age [1]. - This is a **classic anatomical landmark** frequently tested in medical examinations. *Upper end of humerus* - The epiphysis at the **proximal end of the humerus** typically appears between **birth and 6 months of age**. - This ossification center is primarily responsible for the growth in length of the upper arm. - It is **not present at birth** in most cases. *Lower end of fibula* - The **distal fibular epiphysis** usually appears much later, typically around **1-2 years of age**. - It contributes to the formation of the lateral malleolus of the ankle joint. - This is one of the **later-appearing** epiphyses. *Upper end of tibia* - The **proximal tibial epiphysis** ossifies around the **time of birth or shortly after**, usually appearing after the distal femur. - It forms the superior part of the tibia and contributes to the knee joint. - While close in timing, it is **not as reliably present** just before birth as the distal femoral epiphysis.
Question 10: All are derived from ectoderm except for which of the following?
- A. Hair follicles
- B. Nails
- C. Lens of the eye
- D. Adrenal cortex (Correct Answer)
Explanation: ***Adrenal cortex*** - The adrenal cortex is derived from the **intermediate mesoderm**, specifically from the cells lining the posterior abdominal wall. The cells migrate to develop into the adrenal cortex. - It produces various steroid hormones, including **aldosterone**, **cortisol**, and **androgens**, which regulate diverse bodily functions. *Lens of the eye* - The lens of the eye is derived from the **surface ectoderm**. It forms from an invagination of the surface ectoderm called the lens placode. - Its primary function is to **focus light** onto the retina. *Hair follicles* - Hair follicles develop from the **surface ectoderm** [1]; they are invaginations of the epidermis that extend into the dermis. - They produce hair, which provides **insulation** and **protection** [1]. *Nails* - Nails are also derivatives of the **surface ectoderm**, forming thickened plates on the dorsal surface of the distal phalanges. - They provide **protection** to the fingertips and aid in grasping objects.
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