Muscles and Their Actions — MCQs
All of the following muscles have dual nerve supply, EXCEPT?
Trendelenburg's sign is positive in injury to which structure?
Which of the following structures is supplied by the superior gluteal nerve?
What is the condition commonly known as jumper's knee?
Injury at which of the following marked sites on the leg causes failure of dorsiflexion?
Trendelenberg test is negative in
Which of the following muscles is not supplied by the femoral nerve?
The mechanism of action of botulinum toxin A is best described by:
Name the marked structure in the image.
Identify the function of the muscles marked in red:
Muscles and Their Actions Indian Medical PG Practice Questions and MCQs
Question 1: All of the following muscles have dual nerve supply, EXCEPT?
- A. Flexor digitorum profundus
- B. Pectineus
- C. Brachialis
- D. Flexor digitorum superficialis (Correct Answer)
Explanation: No changes were made to the original explanation because none of the provided references met the relevance criteria for the specific muscles and nerves discussed. ***Flexor digitorum superficialis*** - This muscle is solely innervated by the **median nerve**. - It works to **flex the middle phalanges** of the medial four digits. *Flexor digitorum profundus* - The medial half of the muscle, which supplies the ring and little fingers, is innervated by the **ulnar nerve**. - The lateral half, which supplies the index and middle fingers, is innervated by the **anterior interosseous nerve** (a branch of the median nerve). *Pectineus* - This muscle typically receives innervation from both the **femoral nerve** and the **obturator nerve**. - Its primary action is **adduction and flexion of the hip**. *Brachialis* - While primarily innervated by the **musculocutaneous nerve**, a small component also receives innervation from the **radial nerve**. - It is a powerful **flexor of the elbow joint**.
Question 2: Trendelenburg's sign is positive in injury to which structure?
- A. Gluteus maximus
- B. Gluteus medius (Correct Answer)
- C. Quadriceps femoris
- D. Quadratus lumborum
Explanation: ***Gluteus medius*** - A positive **Trendelenburg's sign** indicates weakness or paralysis of the **gluteus medius** muscle, or problem with its innervation or hip joint. - This muscle is crucial for **abduction** and **stabilization** of the pelvis during gait; its dysfunction causes the unsupported side of the pelvis to drop. *Gluteus maximus* - The **gluteus maximus** is primarily involved in **hip extension** and external rotation, not hip abduction or pelvic stability during single-leg stance. - Weakness in this muscle would manifest more as difficulty with climbing stairs or rising from a seated position. *Quadriceps femoris* - The **quadriceps femoris** muscles are responsible for **knee extension**, essential for walking and standing. - Injury to these muscles would primarily affect the ability to **straighten the leg** and bear weight on it, not cause pelvic drop. *Quadratus lumborum* - The **quadratus lumborum** is a deep abdominal muscle involved in **lateral flexion of the trunk** and stabilization of the lumbar spine. - Dysfunction of this muscle would lead to **trunk instability** or pain, but not the specific pelvic drop seen in Trendelenburg's sign.
Question 3: Which of the following structures is supplied by the superior gluteal nerve?
- A. Gluteus minimus (Correct Answer)
- B. Gluteus maximus
- C. Piriformis
- D. All of the options
Explanation: ***Gluteus minimus*** - The **superior gluteal nerve** provides motor innervation to the gluteus medius, gluteus minimus, and tensor fasciae latae muscles. - This nerve originates from the sacral plexus **(L4, L5, S1)** and exits the pelvis through the greater sciatic foramen, superior to the piriformis muscle. *Gluteus maximus* - The gluteus maximus muscle is innervated by the **inferior gluteal nerve**, not the superior gluteal nerve. - The inferior gluteal nerve also arises from the sacral plexus **(L5, S1, S2)** and is crucial for hip extension and external rotation. *Piriformis* - The piriformis muscle receives its own direct branches from the sacral plexus **(S1, S2)** via the nerve to piriformis, distinct from the superior or inferior gluteal nerves. - It plays a key role in hip external rotation and abduction when the hip is flexed. *All of the options* - This option is incorrect because gluteus maximus is innervated by the inferior gluteal nerve, and piriformis has its own specific nerve supply. - The superior gluteal nerve specifically innervates only the gluteus medius, gluteus minimus, and tensor fasciae latae.
Question 4: What is the condition commonly known as jumper's knee?
- A. Inflammation of the patellar tendon at its insertion on the patella.
- B. Tendinopathy of the quadriceps tendon.
- C. Injury to the hamstring tendon.
- D. Patellar tendonitis due to overuse of the patellar tendon. (Correct Answer)
Explanation: ***Patellar tendonitis due to overuse of the patellar tendon.*** - **Jumper's knee** is the common term for **patellar tendonitis**, which specifically refers to inflammation of the patellar tendon. - This condition is frequently caused by **overuse**, especially in activities involving repetitive jumping and landing. *Inflammation of the patellar tendon at its insertion on the patella.* - While jumper's knee does involve inflammation of the patellar tendon, it is more commonly at its insertion on the **tibial tubercle** or specifically its origin at the **inferior pole of the patella**, not necessarily at the patella itself. - This option is less precise as it describes only one aspect of the condition without mentioning the critical role of overuse. *Tendinopathy of the quadriceps tendon.* - **Tendinopathy of the quadriceps tendon** is a distinct condition affecting the tendon above the patella, known as **quadriceps tendinopathy**. - It presents with pain proximal to the patella, differentiating it from jumper's knee, which involves the tendon distal to the patella. *Injury to the hamstring tendon.* - An **injury to the hamstring tendon** would cause pain and symptoms on the posterior aspect of the knee or thigh. - This is completely unrelated to jumper's knee, which is characterized by anterior knee pain.
Question 5: Injury at which of the following marked sites on the leg causes failure of dorsiflexion?
- A. Anterior aspect of the thigh (site 1)
- B. Medial aspect of the leg (site 4)
- C. Lateral aspect of the leg (site 3) (Correct Answer)
- D. Posterior aspect of the thigh (site 2)
Explanation: ***Lateral aspect of the leg (site 3)*** - Site 3 points to the **fibula head** and the adjacent region on the lateral aspect of the leg. This is the anatomical location where the **common fibular nerve (peroneal nerve)** wraps around. - The common fibular nerve innervates the muscles responsible for **dorsiflexion** and eversion of the foot. Damage to this nerve, often due to trauma at the fibular neck, leads to **foot drop** and an inability to dorsiflex the foot. *Anterior aspect of the thigh (site 1)* - Site 1 points to the distal femur, which is part of the thigh. Nerves in the anterior thigh (e.g., **femoral nerve**) primarily control hip flexion and knee extension. - Damage here would affect movements of the hip and knee, not directly causing failure of dorsiflexion of the foot. *Medial aspect of the leg (site 4)* - Site 4 points to the medial tibia. This area is associated with the **tibial nerve** and saphenous nerve, which primarily innervate muscles for plantarflexion and inversion of the foot, or provide sensory innervation. - Injury to the tibial nerve would result in an inability to plantarflex and invert the foot, not dorsiflexion. *Posterior aspect of the thigh (site 2)* - Site 2 points to the posterior aspect of the thigh, which is the region for the hamstrings. The **sciatic nerve** and its branches (tibial and common fibular) pass through this region. - While the common fibular nerve originates from the sciatic nerve in the posterior thigh, an injury at this level would likely cause more widespread motor and sensory deficits than isolated dorsiflexion failure, and site 3 is a more common and specific site for common fibular nerve injury isolated to foot drop.
Question 6: Trendelenberg test is negative in
- A. Polio myelitis
- B. Inferior Gluteal nerve
- C. Normal hip function (Correct Answer)
- D. Superior Gluteal nerve
Explanation: ***Normal hip function*** - A **negative Trendelenburg test** indicates that the hip abductor muscles (primarily the **gluteus medius and minimus**) are functioning correctly and can maintain pelvic stability when standing on one leg. - This suggests the absence of **weakness** or **dysfunction** in the hip abductors or their innervation. *Polio myelitis* - **Poliomyelitis** can cause **paralysis** and **weakness** of various muscles, including the hip abductors, leading to a **positive Trendelenburg test**. - The disease damages **motor neurons** in the spinal cord, impairing muscle function. *Inferior Gluteal nerve* - The **inferior gluteal nerve** primarily innervates the **gluteus maximus**, which is responsible for hip extension, not hip abduction. - Weakness due to inferior gluteal nerve damage would manifest as difficulty with activities like **climbing stairs** or **rising from a chair**, but typically would not cause a positive Trendelenburg test. *Superior Gluteal nerve* - The **superior gluteal nerve** innervates the **gluteus medius and minimus**, which are the primary hip abductors. - Damage to this nerve or weakness of these muscles would result in a **positive Trendelenburg test**, where the contralateral pelvis drops when standing on the affected leg.
Question 7: Which of the following muscles is not supplied by the femoral nerve?
- A. Pectineus
- B. Sartorius
- C. Vastus medialis
- D. Obturator externus (Correct Answer)
Explanation: ***Obturator externus*** - The **obturator externus** muscle is primarily supplied by the **obturator nerve** (L3-L4), which arises from the lumbar plexus, not the femoral nerve. - Its main function is the **lateral rotation of the thigh** at the hip joint. *Pectineus* - The **pectineus** muscle receives dual innervation, typically from both the **femoral nerve** (L2-L4) and the obturator nerve. - It aids in **adduction**, **flexion**, and **medial rotation** of the thigh. *Sartorius* - The **sartorius** muscle is entirely supplied by the **femoral nerve** (L2-L3). - It is responsible for **flexing, abducting, and laterally rotating the thigh** at the hip, and flexing the leg at the knee. *Vastus medialis* - The **vastus medialis** is one of the four muscles forming the quadriceps femoris group, all of which are exclusively supplied by the **femoral nerve** (L2-L4). - This muscle is crucial for **extending the leg** at the knee joint.
Question 8: The mechanism of action of botulinum toxin A is best described by:
- A. Slowing of myelinated nerve fiber transmission
- B. Postsynaptic receptor blockade
- C. Acetylcholinesterase inhibition
- D. Presynaptic blockade of acetylcholine release (Correct Answer)
Explanation: ***Presynaptic blockade of acetylcholine release*** - **Botulinum toxin A** acts by cleaving specific proteins (**SNARE proteins** like SNAP-25, synaptobrevin, and syntaxin) essential for the fusion of **acetylcholine-containing vesicles** with the presynaptic membrane. - This prevents the release of acetylcholine into the **neuromuscular junction**, leading to muscle paralysis. *Slowing of myelinated nerve fiber transmission* - This describes the action of agents that affect **myelin sheaths** (e.g., demyelinating diseases) or ion channels involved in action potential propagation, not the mechanism of botulinum toxin. - Botulinum toxin specifically targets the **synaptic transmission**, not the speed of nerve conduction itself. *Postsynaptic receptor blockade* - This mechanism is seen with drugs like **curare** or **neuromuscular blockers** (e.g., rocuronium, vecuronium), which compete with acetylcholine for binding to **nicotinic acetylcholine receptors** on the muscle endplate. - Botulinum toxin does not affect the postsynaptic receptors directly; its action is entirely presynaptic. *Acetylcholinesterase inhibition* - **Acetylcholinesterase inhibitors** (e.g., neostigmine, pyridostigmine) prevent the breakdown of acetylcholine in the synaptic cleft, increasing its concentration and prolonging its action. - This mechanism would enhance, rather than block, muscle contraction, which is opposite to the effect of botulinum toxin.
Question 9: Name the marked structure in the image.
- A. Gracilis (Correct Answer)
- B. Vastus lateralis
- C. Rectus femoris
- D. Vastus medialis
Explanation: ***Gracilis*** - The highlighted structure is the **gracilis muscle**, a long, thin, superficial muscle located on the **medial aspect of the thigh** - It is part of the **adductor group of muscles** and originates from the **inferior pubic ramus** and inserts at the **medial surface of the proximal tibia** (pes anserinus) - Functions: **Adduction of thigh** and **flexion and medial rotation of leg** at the knee joint - Innervation: **Obturator nerve** (anterior division) *Vastus lateralis* - This is the **largest component of the quadriceps femoris**, located on the **lateral aspect of the thigh** - It is a powerful **knee extensor**, not an adductor like gracilis - Located laterally, not medially like the structure shown *Rectus femoris* - This is the **most superficial and anterior component of the quadriceps femoris** - It is the only quadriceps muscle that crosses **two joints** (hip and knee) - Located anteriorly in the thigh, not medially like gracilis *Vastus medialis* - This is a component of the **quadriceps femoris** located on the **anteromedial aspect of the thigh** - While medially positioned, it is more **anterior** than gracilis and is part of the **knee extensor mechanism**, not the adductor group - The vastus medialis is broader and more bulky compared to the thin, strap-like gracilis
Question 10: Identify the function of the muscles marked in red:
- A. Flexion at MCP joint (Correct Answer)
- B. Flexion at IP joint
- C. Extension at MCP joint
- D. Abduction at MCP joint
Explanation: ***Flexion at MCP joint*** - The muscles shown in red are the **lumbricals**, which primarily function to **flex the metacarpophalangeal (MCP) joints** and **extend the interphalangeal (IP) joints**. - This is their most fundamental action when identifying lumbrical function, as they originate from **flexor digitorum profundus tendons** and insert into the **extensor expansion**, providing precise **MCP joint flexion**. - This unique action creates the **"lumbrical grip"** essential for precision handling. *Flexion at IP joint* - Lumbricals actually **extend the interphalangeal (IP) joints**, not flex them, making this option anatomically incorrect. - **Flexion at IP joints** is performed by the **flexor digitorum superficialis** (PIP joints) and **flexor digitorum profundus** (DIP joints). - The lumbrical insertion into the **extensor hood** produces IP extension, the opposite of this option. *Extension at MCP joint* - **Extension at the MCP joints** is primarily performed by the **extensor digitorum** and other **extrinsic extensor muscles**. - Lumbricals produce the opposite action, **flexing the MCP joints** rather than extending them. *Abduction at MCP joint* - **Abduction at the MCP joints** is primarily performed by the **dorsal interossei muscles** using the **DAB** (Dorsal ABduct) mnemonic. - Lumbricals do not contribute to **finger abduction** but rather focus on **MCP flexion, IP extension**, and **fine motor control**.
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