MPPSC 2025 Prelims Paper-I · Question 64 of 100

Correct — C, Stapedius. The stapedius is the smallest skeletal muscle in the human body, roughly one millimetre long. It lies inside the middle ear, arising from the pyramidal eminence of the tympanic cavity and inserting on the neck of the stapes — the smallest bone in the body. It is the effector of the acoustic (stapedial) reflex: when a very loud sound arrives, the stapedius contracts, stiffens the ossicular chain and damps the vibration passed to the inner ear. It is supplied by the nerve to stapedius, a branch of the facial nerve (cranial nerve VII), which is why a facial-nerve lesion above that branch can cause hyperacusis — ordinary sounds becoming painfully loud.

• (a)Bicep — The biceps brachii is a large two-headed muscle on the front of the upper arm that flexes the elbow and supinates the forearm — one of the most visible muscles in the body, nowhere near the smallest.
• (b)Sartorius — The exact opposite superlative: the sartorius is the LONGEST muscle in the human body, a strap muscle running diagonally across the thigh from the hip bone to the inner side of the knee. Papers pair it with stapedius precisely to catch a half-remembered fact.
• (d)Tricep — The triceps brachii is the three-headed extensor at the back of the upper arm and is bulkier than the biceps — again a large limb muscle, not a candidate for the smallest.

Sound reaches the inner ear through a chain of three tiny bones in the middle ear — malleus, incus and stapes. Two muscles control that chain: the tensor tympani (supplied by the trigeminal nerve, CN V) and the stapedius (supplied by the facial nerve, CN VII). Both work as a protective damping system for loud sound. Because the whole assembly is built at millimetre scale, the middle ear holds both the body's smallest bone (stapes) and its smallest skeletal muscle (stapedius).

This is a pure superlatives question, and the paper has stacked the options so that recall alone decides it. Biceps and triceps are there only as familiar names. The real contest is sartorius versus stapedius — and sartorius owns the opposite record, longest. Learn the pair as a unit and the question answers itself in both directions.

• Stapedius — about 1 mm long — is the smallest skeletal muscle in the human body; it acts on the stapes, the smallest bone.
• It is innervated by the nerve to stapedius, a branch of the facial nerve (CN VII); loss of that supply causes hyperacusis.
• Its function is the acoustic (stapedial) reflex — damping the ossicular chain against loud sound.
• Companion superlatives worth memorising: sartorius = longest muscle, gluteus maximus = largest muscle, femur = longest bone.

• Swapping sartorius and stapedius — sartorius is the longest muscle, not the smallest.
• Confusing smallest MUSCLE (stapedius) with smallest BONE (stapes); both sit in the middle ear, and papers exploit that.

Usually a one-line superlative, sometimes buried inside a statement set (UPSC 2004 tested 'femur is the longest bone' this way). Keep a single revision table of body superlatives.

• practice — not a real PYQ

  The smallest bone in the human body is:

  • (a)Stapes
  • (b)Incus
  • (c)Malleus
  • (d)Nasal bone

  Answer(a) Stapes — the stirrup-shaped ossicle of the middle ear, to which the stapedius muscle attaches.

• practice — not a real PYQ

  The stapedius muscle of the middle ear is supplied by which cranial nerve?

  • (a)Facial nerve (VII)
  • (b)Trigeminal nerve (V)
  • (c)Vestibulocochlear nerve (VIII)
  • (d)Glossopharyngeal nerve (IX)

  Answer(a) Facial nerve (VII) — via the nerve to stapedius; the tensor tympani, by contrast, is supplied by the trigeminal nerve.