Which of the following muscles is innervated by the tibial nerve and is responsible for plantarflexion of the foot?

Explanation

## Tibial Nerve and Plantarflexion **Key Point:** The **tibial nerve** is the medial terminal branch of the sciatic nerve. It innervates muscles of the **posterior compartment of the leg**, the primary plantarflexors of the foot. ### Tibial Nerve Innervation Pattern | **Muscle** | **Compartment** | **Action** | **Nerve** | |---|---|---|---| | **Gastrocnemius** | Posterior (superficial) | Plantarflex + knee flexion | Tibial | | **Soleus** | Posterior (superficial) | Plantarflex | Tibial | | **Tibialis posterior** | Posterior (deep) | Plantarflex + invert | Tibial | | **Flexor digitorum longus** | Posterior (deep) | Plantarflex + flex toes | Tibial | | **Flexor hallucis longus** | Posterior (deep) | Plantarflex + flex hallux | Tibial | ### Why Gastrocnemius is the Best Answer 1. **Primary plantarflexor**: The gastrocnemius is the most powerful and clinically relevant plantarflexor 2. **Tibial nerve innervation**: Confirmed — arises from S1, S2 nerve roots via tibial nerve 3. **Dual action**: Also flexes the knee (originates above the knee joint) 4. **Clinical testing**: Ankle jerk reflex (S1–S2) tests gastrocnemius-soleus function **High-Yield:** **Mnemonic for posterior leg muscles: TIP** — **T**ibialis posterior, **I**ntrinsic foot muscles (via medial/lateral plantar branches), **P**lantarflexors (gastrocnemius, soleus). All innervated by tibial nerve. **Clinical Pearl:** Tibial nerve injury (e.g., from posterior knee dislocation or tarsal tunnel syndrome) causes loss of plantarflexion, inversion, and toe flexion, with a characteristic "steppage gait" if severe. [cite:Clinically Oriented Anatomy 8e Ch 6]