--- title: "Recurrent Laryngeal Nerve Course - Why is it different on both sides?" description: "Understand the embryological and anatomical reasons behind the asymmetric course of the Recurrent Laryngeal Nerve - an important short question in ENT exams." source: "The ENT Resident" canonical_url: "https://www.theentresident.com/ent-notes-lectures/recurrent-laryngeal-nerve-different-course" categories: ["Larynx and Trachea", "Short Questions in ENT"] video: "https://www.youtube.com/watch?v=SDCFfkLBNIY" image: "https://media.theentresident.com/og-images/recurrent-laryngeal-nerve-different-course.png" --- # Recurrent Laryngeal Nerve Course - Why is it different on both sides? Understand the embryological and anatomical reasons behind the asymmetric course of the Recurrent Laryngeal Nerve - an important short question in ENT exams. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=SDCFfkLBNIY ## Why Does the Recurrent Laryngeal Nerve Have a Different Course on Each Side? The **recurrent laryngeal nerves (RLNs)** — branches of the vagus nerve (cranial nerve X) — are essential for **motor and sensory innervation** of the larynx. Interestingly, they follow **asymmetrical paths** on the right and left sides. Let's understand why. --- ### 📍 Origin of the Recurrent Laryngeal Nerve - **Right RLN**: - Arises from the right vagus nerve at the **root of the neck**, near the **T1 vertebral level**. - Loops around the **first part of the right subclavian artery**. - **Left RLN**: - Arises from the left vagus nerve in the **thorax**, at the **T3 vertebral level**. - Loops around the **arch of the aorta**, **posterior to the ligamentum arteriosum**. --- ### 🛣 Course of the Nerve After looping around their respective arteries: - Both nerves ascend in the **tracheoesophageal groove**. - Pass deep to the **inferior constrictor muscle**. - Enter the larynx **behind the cricothyroid joint**. - Divide into **motor and sensory branches**. --- ### 🧬 Embryological Explanation The asymmetry is explained by the **development of aortic arches**: #### Left Side: - The **dorsal part of the 6th aortic arch** persists as the **ductus arteriosus** in fetal life and becomes the **ligamentum arteriosum** after birth. - The **left RLN** gets "hooked" beneath the arch of the aorta due to this persistent ligament. - The **4th aortic arch** contributes to the arch of the aorta. #### Right Side: - The **5th and 6th aortic arches** regress completely. - The **4th aortic arch** forms the **proximal part of the right subclavian artery**. - The **right RLN** loops around this artery instead of a structure in the thorax. As a result: - The **left RLN has a longer and deeper course** in the thorax. - The **right RLN** takes a **shorter course in the neck**. --- ### 🧠 Summary Table | Feature | Right RLN | Left RLN | | --- | --- | --- | | Origin | Root of neck (T1) from right vagus | Thorax (T3) from left vagus | | Loops Around | Right subclavian artery (from 4th arch) | Arch of aorta (near ligamentum arteriosum) | | Embryological Arch | 4th arch only | 4th and persistent 6th arch | | Relative Course | Shorter, in neck | Longer, in thorax | | Enters Larynx | Behind cricothyroid joint | Behind cricothyroid joint | --- ### 📝 Viva Tip When asked _"Why is the RLN course different on both sides?"_ — always link your answer to **embryological arch derivatives** and **anatomical development** for full marks. --- ## About This Note This note on Recurrent Laryngeal Nerve Course - Why is it different on both sides? is one of the free ENT study notes published by The ENT Resident. 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