Functional Anatomy Practice Questions

Q: When forces are applied on the lateral surface of the mandibular angle region, compression is generated on:

Lateral surface. ***Lateral surface*** - When a force is applied to the **lateral surface** of the mandibular angle, this is the **point of direct impact and compression**. - According to **biomechanical principles**, compression occurs at the site where external force is applied to bone [1]. - In bending mechanics, the side receiving the load experiences **compressive stress**, while the opposite side experiences tensile stress [1]. - This principle is fundamental in understanding **mandibular fracture patterns** and surgical plating techniques. *Medial surface* - The medial surface, being **opposite to the point of force application**, experiences **tensile (tension) forces**, not compression [1]. - In beam bending theory, when one side is compressed, the opposite side is under tension [1]. - This is why fracture lines in the mandible often propagate from the tension side (medial) when lateral forces are applied. *Inferior surface* - The inferior border of the mandible is classically described as the **tension side during mastication and functional loading**, not lateral impact forces. - When lateral forces are applied to the angle, the inferior surface experiences complex stress patterns but is not the primary site of compression. - The inferior border-superior border axis is different from the lateral-medial force axis described in this question. *Superior surface* - The superior (alveolar) border typically experiences **compression during mastication**, but this relates to occlusal forces, not lateral impact. - For lateral forces applied to the mandibular angle, the superior surface does not experience primary compression. - This surface is more relevant for bite forces and dental occlusion mechanics.

Q: The main antagonistic muscle of the rectus abdominis muscle is

Erector spinae. ***Erector spinae*** - The **rectus abdominis** flexes the trunk, while the **erector spinae muscles** extend the trunk. [1] - This direct opposition in primary function makes the erector spinae the main antagonist to the rectus abdominis. *Psoas major* - The **psoas major** primarily functions as a **hip flexor** and contributes to lumbar stabilization. - While it has some action on the trunk, its main antagonistic relationship is with hip extensors, not primarily the rectus abdominis. *Latissimus dorsi* - The **latissimus dorsi** is a large muscle of the back that primarily extends, adducts, and internally rotates the arm. - It has a minimal direct antagonistic role to the rectus abdominis, which focuses on trunk flexion. *Quadratus lumborum* - The **quadratus lumborum** acts to laterally flex the trunk and stabilize the lumbar spine. - Its primary actions are distinct from the rectus abdominis's main function of trunk flexion, making it an antagonist for different movements, not directly for trunk flexion/extension.

Question 1

A 28-year-old woman undergoes excision of an enlarged lymph node in the posterior triangle of the neck. Two weeks post-operatively she is unable to shrug her left shoulder. Nerve conduction studies confirm injury to the arrowed nerve (Image 1). She also has a newly noted medial scapular winging accentuated by pushing against a wall and impaired scapular protraction on the ipsilateral side. Which of the following best explains why TWO distinct nerve injuries are required to account for both motor deficits observed in this patient?

Accepted Answer

D. The arrowed nerve (CN XI) supplies only the trapezius and sternocleidomastoid; serratus anterior is innervated exclusively by the long thoracic nerve (C5–C7), so injury to both nerves is necessary to produce the combined deficit of shoulder-shrug weakness and winged scapula

Answer

A. The arrowed nerve supplies both the trapezius and the serratus anterior, travelling superficially across the posterior triangle before piercing the deep cervical fascia

Answer

B. The arrowed nerve supplies the trapezius directly and communicates with the long thoracic nerve within the posterior triangle, jointly innervating serratus anterior

Answer

C. The arrowed nerve supplies the trapezius, and a separate branch arising at the same level in the posterior triangle independently innervates serratus anterior

Question 2

When forces are applied on the lateral surface of the mandibular angle region, compression is generated on:

Accepted Answer

Lateral surface

Answer

Medial surface

Answer

Superior surface

Answer

Inferior surface

Question 3

What is the function of the muscle shown in the image?

Accepted Answer

Muscle contraction that decreases the angle between body parts

Answer

Movement towards the midline of the body

Answer

Movement away from the midline of the body

Answer

Muscle contraction that increases the angle between body parts

Question 4

The main antagonistic muscle of the rectus abdominis muscle is

Accepted Answer

Erector spinae

Answer

Psoas major

Answer

Latissimus dorsi

Answer

Quadratus lumborum

Functional Anatomy — MCQs

Functional Anatomy — MCQs

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