Question 1

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 2

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 3

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 4

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]

Question 5

A patient presents with pain in the back of the thigh and leg after lifting heavy weights. Which spinal segment is most likely involved?

Accepted Answer

S1. ***S1***
- Pain radiating to the **back of the thigh and leg** after lifting heavy weights is the classic presentation of **S1 radiculopathy**, typically from L5-S1 disc herniation.
- The S1 nerve root innervates the **posterior thigh via the sciatic nerve**, continues down the **posterior leg**, and extends to the **lateral foot and little toe**.
- Clinical findings include diminished or absent **Achilles reflex**, weakness of **plantar flexion** (gastrocnemius/soleus), and sensory changes along the posterior leg and lateral foot.
- This is the **most common** presentation of sciatica from heavy lifting.

*L3*
- L3 nerve root involvement typically causes pain in the **anterior and medial thigh** with weakness of **hip flexion and knee extension** (quadriceps).
- The pain pattern does not match the posterior distribution described in this clinical scenario.

*L4*
- L4 radiculopathy presents with pain and numbness in the **medial leg and foot**, weakness of **ankle dorsiflexion** (tibialis anterior), and diminished **patellar reflex**.
- The pain distribution is anteromedial, not posterior as described in this case.

*L5*
- L5 nerve root impingement causes pain radiating to the **lateral calf and dorsum of the foot**, weakness of **great toe extension** (extensor hallucis longus), and **foot drop**.
- While L5 can cause posterior thigh pain, the classic distribution extends laterally down the leg, not primarily posterior.

*S2*
- S2 radiculopathy is uncommon and typically presents with **perineal/perianal pain** and **saddle anesthesia** rather than isolated posterior leg pain.
- S2 contributes to bladder and bowel function; isolated S2 involvement would not present with the classic sciatica pattern described. [Practice more Anatomy questions on OnCourse]

Anatomy Questions

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Upper/Lower Limb

Thorax/Abdomen

Head & Neck

Pelvis/Perineum

Gross Anatomy

Brainstem nuclei

Corticospinal tracts

Vascular supply (Circle of Willis)

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Pharyngeal arches

Heart development

GI development

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Epithelial/Connective tissues

Organ-specific histology

Histology

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Radiologic landmarks

Imaging/Clinical

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Fascial compartments

Dermatomes and myotomes

Autonomic nervous system anatomy

Lymphatic drainage pathways

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