Question 1

A biopsy of the posterior wall of the pharynx reveals a stratified squamous epithelium overlying a lamina propria rich in mucous glands, with underlying skeletal muscle. A student is asked to identify the embryological origin of the epithelial lining in this region. Which of the following correctly identifies the embryologic origin of this epithelium?

Accepted Answer

Endoderm lining the foregut, independent of pharyngeal arch mesenchyme. ***Endoderm lining the foregut, independent of pharyngeal arch mesenchyme***
- The internal lining of the entire **pharynx**, including the posterior wall, is derived from the **endoderm** of the cranial-most part of the **foregut**.
- While the epithelium undergoes **metaplasia** to become stratified squamous to resist mechanical stress, its developmental origin remains the **primitive gut tube** lining.

*Ectoderm derived from the surface epithelium of pharyngeal arch 1*
- This **ectoderm** contributes to the lining of the **oral cavity** and the external covering of the arches, not the internal pharyngeal wall.
- **Pharyngeal arch 1** structures are specifically associated with the **trigeminal nerve** and components anterior to the oropharyngeal membrane.

*Neural crest cells migrating from rhombomeres 6–8*
- **Neural crest cells** are responsible for forming the **connective tissues**, bones, and cartilage of the pharyngeal region, not the epithelial lining.
- Cells from **rhombomeres** migrate into specific pharyngeal arches to form **mesenchymal** structures rather than the internal mucosa.

*Mesoderm of the lateral plate forming the buccopharyngeal membrane*
- The **buccopharyngeal membrane** is a bilayer of **ectoderm and endoderm**; the lateral plate mesoderm does not form the membrane's surface epithelium.
- **Lateral plate mesoderm** primarily contributes to the **connective tissue** and smooth muscle of the gut tube, while skeletal muscle here is derived from **paraxial mesoderm**.

*Ectoderm of the stomodeum invaginating past the buccopharyngeal membrane*
- The **stomodeal ectoderm** gives rise to the lining of the **oral cavity** (mouth) only up to the point of the former **buccopharyngeal membrane**.
- The **pharynx** is located posterior to this membrane and is therefore derived from the **endoderm** rather than the invaginating ectoderm. [Practice more Anatomy questions on OnCourse]

Question 2

Identify the arrow marked nerve

Accepted Answer

Lateral pectoral nerve. ***Lateral pectoral nerve***
  - The arrow points to a nerve originating from the **lateral cord of the brachial plexus**, traveling laterally to innervate the **pectoralis major muscle**.
  - Its position, lateral to the medial pectoral nerve and supplying the pectoralis major, confirms it as the lateral pectoral nerve.

*Medial pectoral nerve*
  - The medial pectoral nerve typically arises from the **medial cord of the brachial plexus** and passes through both **pectoralis major** and **pectoralis minor**.
  - It lies more medially and generally pierces the pectoralis minor, unlike the nerve indicated.

*Long thoracic nerve*
  - The long thoracic nerve innervates the **serratus anterior muscle** and runs along the lateral aspect of the chest wall.
  - Its course is distal and distinct from the nerve shown, which is clearly positioned in the pectoral region.

*Thoracodorsal nerve*
  - The thoracodorsal nerve innervates the **latissimus dorsi muscle** and descends on the posterior axillary wall.
  - It is not located in the shown pectoral region and has a different trajectory.

*Nerve to subclavius*
  - The nerve to subclavius arises from the **upper trunk of the brachial plexus** (C5-C6) and descends to innervate the **subclavius muscle**.
  - It has a more superior course compared to the lateral pectoral nerve and is not visible in the position indicated by the arrow. [Practice more Anatomy questions on OnCourse]

Question 3

A patient with a nerve injury was asked to form an "O" with their index finger and thumb but was unable to do so. Which muscle is most likely affected?

Accepted Answer

Opponens pollicis. ***Opponens pollicis***
  - The **opponens pollicis** muscle is responsible for **opposition of the thumb**, a complex movement involving flexion, abduction, and medial rotation of the thumb at the carpometacarpal joint.
  - Inability to form an "O" sign with the index finger and thumb is a classic clinical test for impaired opposition, often indicating a problem with the **median nerve** or the opponens pollicis muscle it innervates.

*Abductor pollicis brevis*
  - The **abductor pollicis brevis** primarily abducts the thumb, moving it away from the palm.
  - While necessary for thumb function, its primary role is not the opposition motion required to touch the fingertips in an "O" shape.

*Flexor pollicis brevis*
  - The **flexor pollicis brevis** primarily flexes the thumb at the metacarpophalangeal joint.
  - While it contributes to thumb movements, it is not the primary muscle responsible for the complex motion of opposition.

*Adductor pollicis*
  - The **adductor pollicis** adducts the thumb, bringing it towards the palm and index finger.
  - Innervated by the **ulnar nerve**, this muscle is important for pinch grip but is not the primary muscle for opposition movement.

*Palmar interossei*
  - The **palmar interossei** muscles adduct the fingers, pulling them towards the middle finger.
  - These muscles are involved in finger adduction, not direct thumb opposition, and are typically innervated by the ulnar nerve. [Practice more Anatomy questions on OnCourse]

Question 4

A patient diagnosed with sciatica has tender hamstrings. Which of the following nerves supplies a hybrid muscle that is partially spared in this patient?

Accepted Answer

Common peroneal nerve. ***Common peroneal nerve***
  - The **short head of the biceps femoris** is a unique "hybrid" muscle, supplied by the **common peroneal nerve**, while the **long head** is supplied by the **tibial nerve**.
  - If the hamstrings are tender and sciatica is present, but this specific muscle's function is spared, it points towards the common peroneal nerve being the relevant nerve for the spared portion.

*Femoral*
  - The **femoral nerve** primarily innervates the **anterior compartment of the thigh**, including the quadriceps femoris.
  - It does not supply any part of the hamstring muscles.

*Obturator*
  - The **obturator nerve** primarily innervates the **medial compartment of the thigh**, which consists of adductor muscles.
  - It does not contribute to the innervation of the hamstring muscles.

*Superior gluteal*
  - The **superior gluteal nerve** innervates the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae** muscles.
  - It does not supply any hamstring muscles.

*Tibial*
  - The **tibial nerve** innervates most of the hamstring muscles (semitendinosus, semimembranosus, and the long head of the biceps femoris).
  - If the hamstrings are tender, involvement of the tibial nerve would likely lead to more widespread hamstring weakness rather than a partially spared scenario involving the short head of the biceps femoris. [Practice more Anatomy questions on OnCourse]

Question 5

Which artery is palpated behind the medial malleolus and in front of the Achilles tendon?

Accepted Answer

Posterior tibial artery. ***Posterior tibial artery***
  - This artery is directly accessible for palpation in the **retromalleolar groove**, situated between the medial malleolus and the Achilles tendon.
  - It is a common site for assessing **peripheral circulation** in the foot.

*Peroneal artery*
  - The peroneal artery is located **deep within the posterior compartment** of the leg, making it difficult to palpate at the ankle.
  - It primarily supplies the lateral compartment and is not typically palpable at the described location.

*Anterior tibial artery*
  - The anterior tibial artery runs along the **anterior compartment** of the lower leg and, at the ankle, becomes the dorsalis pedis artery.
  - It is best palpated on the **dorsum of the foot** as the dorsalis pedis artery, not behind the medial malleolus.

*Dorsalis pedis artery*
  - This artery is a continuation of the anterior tibial artery and is found on the **dorsum of the foot**, typically lateral to the extensor hallucis longus tendon.
  - While an important pulse point, it is not located behind the medial malleolus.

*Popliteal artery*
  - The popliteal artery is located in the **popliteal fossa** behind the knee, where it can be palpated with deep pressure.
  - It is proximal to the ankle and divides into the anterior and posterior tibial arteries, making it anatomically distant from the medial malleolus. [Practice more Anatomy questions on OnCourse]

Anatomy Questions

Topics

Upper/Lower Limb

Thorax/Abdomen

Head & Neck

Pelvis/Perineum

Gross Anatomy

Brainstem nuclei

Corticospinal tracts

Vascular supply (Circle of Willis)

Neuroanatomy

Pharyngeal arches

Heart development

GI development

Embryology

Epithelial/Connective tissues

Organ-specific histology

Histology

Cross-sectional anatomy

Radiologic landmarks

Imaging/Clinical

Surface anatomy

Fascial compartments

Dermatomes and myotomes

Autonomic nervous system anatomy

Lymphatic drainage pathways

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