Describe the blood supply and nerve supply of the nose.

Arterial Supply

• The nose has a remarkably rich blood supply, derived from both the internal and the external carotid systems, which anastomose freely.
• This explains both the excellent healing of nasal tissue and the severity of epistaxis.
• From the internal carotid, via the ophthalmic artery — the anterior and posterior ethmoidal arteries.

Nerve Supply and Lymphatics

• The nerve supply divides cleanly into three functional groups, and organising the answer this way makes it far clearer than a list:
• 1. Special sensory (olfaction) — the olfactory (first) nerve. Its receptors lie in the olfactory epithelium of the roof, the upper septum and the superior turbinate, and their unmyelinated axons pass through the cribriform plate to the olfactory bulb
• Because these fibres pass through bone with a sheath of dura and arachnoid, the cribriform plate is a route for CSF leak and for intracranial spread of infection
• 2. General sensory — the trigeminal nerve: the anterior ethmoidal nerve (from the ophthalmic division, V1) supplies the anterosuperior part; and branches of the maxillary division (V2) — the nasopalatine, greater palatine and posterior lateral nasal nerves, from the pterygopalatine ganglion — supply the posterior and inferior part
• The anterior ethmoidal nerve also supplies the external nasal skin at the tip via its external nasal branch.
• The sneeze reflex is mediated by trigeminal afferents, which is why irritation of the nasal mucosa provokes it; and the nasociliary nerve explains the PHOTIC sneeze (ACHOO) reflex
• 3. Autonomic — the group that governs nasal physiology: parasympathetic secretomotor fibres arise in the superior salivatory nucleus and travel in the nervus intermedius → greater superficial petrosal nerve → nerve of the pterygoid canal (vidian nerve) → pterygopalatine ganglion, and cause vasodilatation and secretion
• Sympathetic fibres arise from the superior cervical ganglion, travel with the deep petrosal nerve (which joins the greater petrosal to form the vidian nerve), and cause vasoconstriction and decongestion
• The balance between them explains most OF nasal physiology and pharmacology — the nasal cycle, the blockage of vasomotor rhinitis, the action of topical sympathomimetic decongestants, and the rationale of vidian neurectomy, formerly performed for intractable rhinorrhoea
• Lymphatic drainage — the anterior part drains to the submandibular nodes; the posterior part and the sinuses to the retropharyngeal and upper deep cervical nodes
• The retropharyngeal drainage is clinically important.
• Four arteries meet at Little area, which is why the antero-inferior septum accounts for about ninety per cent of nosebleeds
• The sphenopalatine is the principal artery of the nose, entering behind the posterior end of the middle turbinate
• The ethmoidal arteries come from the internal carotid, which is why external carotid ligation alone may fail to stop bleeding
• Endoscopic sphenopalatine ligation has replaced proximal ligation, being closer to the bleeding point and more reliable
• Woodruff plexus is venous and posterior, and explains the heavier posterior epistaxis of the elderly
• Children essentially always bleed from Little area, so a posterior bleed in a child should prompt a search for another cause
• The ophthalmic veins are valveless, which is the anatomical basis of the danger area of the face