Otorhinolaryngology (ENT)
Anatomy and Physiology of the Ear, Nose and Throat
Ear, nose and throat anatomy and physiology for MBBS: tympanic membrane, ossicles, cochlea, sinus drainage and laryngeal nerve supply, mapped to NMC codes EN1.1 and EN1.2.
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Anatomy and Physiology of the Ear, Nose and Throat
Ear, nose and throat anatomy and physiology for MBBS: tympanic membrane, ossicles, cochlea, sinus drainage and laryngeal nerve supply, mapped to NMC codes EN1.1 and EN1.2.
This chapter lays the anatomical and physiological groundwork for all of ENT. It covers the structure of the external, middle and inner ear, the nose and paranasal sinuses, the larynx and pharynx, and the physiology of hearing, balance, smell and voice that every later clinical chapter depends on.
High-yield: Anatomy and Physiology of the Ear, Nose and Throat
- The ear has three parts: the external ear up to the tympanic membrane, the middle ear cleft, and the inner ear with the cochlea and vestibular apparatus.
- The tympanic membrane has a pars tensa and a small pars flaccida, and the cone of light is normally seen in the anteroinferior quadrant.
- The middle ear ossicles are the malleus, incus and stapes, and the stapes footplate sits in the oval window.
- The facial nerve runs through the middle ear in its horizontal (tympanic) segment and is at risk in ear surgery.
- The Eustachian tube connects the middle ear to the nasopharynx and equalises pressure; it is shorter and more horizontal in children, which favours otitis media.
- The organ of Corti sits on the basilar membrane inside the cochlea and converts sound vibration into nerve impulses.
- High-frequency sounds are detected at the base of the cochlea and low-frequency sounds at the apex, a tonotopic arrangement.
- The nasal septum has a vascular area called Little's area (Kiesselbach's plexus) on its anterior part, the commonest site of epistaxis.
- The paranasal sinuses are the maxillary, frontal, ethmoidal and sphenoidal; the maxillary sinus is the largest and drains high on its medial wall.
- The osteomeatal complex in the middle meatus is the common drainage pathway of the frontal, maxillary and anterior ethmoidal sinuses.
- The larynx has three parts: supraglottis, glottis and subglottis, and the vocal cords lie at the glottis.
- All intrinsic laryngeal muscles are supplied by the recurrent laryngeal nerve except the cricothyroid, which is supplied by the external laryngeal nerve.
- The posterior cricoarytenoid is the only muscle that abducts (opens) the vocal cords, so its paralysis is dangerous for the airway.
- The Waldeyer ring of lymphoid tissue guards the upper airway and includes the palatine tonsils, adenoids and lingual tonsil.
- The maxillary sinus is the first sinus to develop and is present at birth, whereas the frontal sinus develops later in childhood.
Laryngeal muscle nerve supply
- **All intrinsic muscles except cricothyroid:** Recurrent laryngeal nerve.
- **Cricothyroid:** External laryngeal nerve (branch of superior laryngeal nerve). Tenses the cords.
- **Posterior cricoarytenoid:** The only abductor. Opens the glottis. Vital for the airway.
- **Sensation above the cords:** Internal laryngeal nerve (branch of superior laryngeal nerve).
NMC competencies in this chapter
- **EN1.1:** Anatomy and physiology of the ear, nose, throat, head and neck
- **EN1.2:** Pathophysiology of common disorders of the ear, nose and throat
Frequently Asked Questions
Why do children get more middle ear infections than adults?
The Eustachian tube in children is shorter, wider and more horizontal, so nasopharyngeal infection reaches the middle ear more easily, making otitis media common in childhood.
Which laryngeal muscle opens the vocal cords?
The posterior cricoarytenoid is the only abductor of the vocal cords. Its paralysis is serious because it can compromise the airway.
Where does most nasal bleeding come from?
From Little's area on the anterior nasal septum, where several vessels anastomose to form Kiesselbach's plexus, the commonest site of anterior epistaxis.
Why is this chapter important for exams?
ENT clinical reasoning is built on this anatomy. Cone of light, ossicles, sinus drainage and laryngeal nerve supply recur across otology, rhinology and laryngology questions.
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