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The Structure and Function of the Ear and Its Role in Hearing and Balance

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The Structure and Function of the Ear and Its Role in Hearing and Balance Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use Clinical Practice Keywords Ears/Hearing/Balance/ Anatomy/Physiology Systems of life This article has been The ear double-blind peer reviewed In this article... ● The structure of the external, middle and inner ears ● Understanding the mechanisms of hearing and balance ● Ear problems and associated health conditions The structure and function of the ear and its role in hearing and balance Key points Author Hilary Harkin is ear, nose and throat clinical nurse specialist, Ear, Nose and Hearing and balance Throat Outpatient Department, Guy’s and St Thomas’ NHS Foundation Trust. are the two main functions of the ear Abstract The ears provide the important functions of hearing and balance. Ear problems can be debilitating for patients and may also be associated with other NT SELF- The ear is divided health conditions. Nurses may be caring for patients with chronic ear problems across ASSESSMENT into three parts: the many nursing specialties in both hospital and community settings, and they need to external, middle and understand the structure and function of the ear. inner ears Citation Harkin H (2021) The structure and function of the ear and its role in hearing The transmission of and balance. Nursing Times; 117: 4, 56-59. sound takes place in the external and middle ears urses need to understand the head are affected, it is often considered to structure and the function of the be an inherited abnormality. The inner ear houses ear, as they may have to care for Failure in the development of the anti- the cochlea (organ Npatients who have chronic ear helix – a curved prominence of cartilage of hearing) and the problems and across many different spe- that is parallel with, and in front of, the peripheral vestibular cialties, in both hospital and community helix or outer rim of the ear (Fig 2) – leads system (organ of settings. to protruding ears; this is also often an balance) The ear is divided into three intercon- inherited trait. necting sections: external, middle and inner Ear problems can be ears (Fig 1). While the external and middle External ear associated with ears are mainly concerned with the trans- The external ear canal, sometimes referred other health mission of sound, the inner ear contains the to as the external auditory canal or external conditions and cochlea – often called the organ of hearing – auditory meatus (EAM), is lined with skin patients with chronic and also houses the body’s organ of balance. and is approximately 2.5cm long. In con- ear problems are tinuation of the pinna, the outer third is seen across many Ear development composed of cartilage; skin lining this car- nursing specialties The ear starts to develop as early as in the tilage has hair follicles and wax-producing sixth week of pregnancy. During foetal glands, which are a combination of ceru- development, the pinna (the visible part of minous and sebaceous glands. the ear) forms from little bumps (hillocks) The sebaceous glands secrete an oily on the side of the head, which grow and substance called sebum into the root canal fuse. Sometimes the pinna fails to develop of the hair follicles, while the ceruminous fully – known as microtia – and in some glands are modified apocrine sweat babies the ear canal may also be absent. glands, which open into the base of the Preauricular sinus is a common con- hair follicles and produce a moist white genital abnormality in which complete secretion that darkens and thickens as it fusion of the hillocks fails to occur; it often dries, becoming sticky. It is estimated that appears as a tiny skin-lined hole in front of the ceruminous glands and hair follicles the upper ear, where the cartilage of the ear develop when the foetus is about five meets the face (Fig 2). If both sides of the months old (Szymanski and Geiger, 2020). Nursing Times [online] April 2021 / Vol 117 Issue 4 56 www.nursingtimes.net Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use Clinical Practice Systems of life Fig 1. Anatomy of the ear The pars flaccida is a triangular area above the pars tensa, which lacks a fibrous layer. This makes it more vulnerable to External ear Middle ear Inner ear cholesteatoma, an ear disease caused by Malleus Incus Semi-circular canals dead skin that collects in the middle ear, causing discharge and hearing loss. This can erode structures in and around the middle ear and requires surgical removal. Auditory It may be congenital or can develop as a nerve result of repeated ear infections. External At its outer rim, the tympanic mem- ear canal Cochlea brane is thickened and called the annulus. The malleus, the first of the three middle Round ear bones (Fig 1), is attached at its tip to the window centre of the membrane, called the umbo Stapes (Fig 3). The handle of the malleus (Fig 3), Ceruminous the most identifiable mark on the tym- glands Eustachian panic membrane, lies between the fibrous Tympanic tube and mucosal layer of the pars tensa and is membrane attached both at the umbo and the lateral process. As the membrane is slightly con- cave, shining a light on it during otoscopy (examination of the external ear canal and Unlike the rest of the body, where skin leaving a recess towards the anterior wall tympanic membrane using an otoscope) grows from the basal layers towards the of the ear canal. The pinna needs to be reveals a triangle of light towards the front surface, the skin in the external ear canal moved upwards and outwards in adults and lower aspect; this is called the light migrates from the tympanic membrane (downwards and backwards in children) to reflex and can help the viewer to orientate towards the entrance; the rate of migration be able to see down the canal to the tym- the membrane. varies between individuals. The shedding panic membrane. of migrated skin mixes with secretions The tympanic membrane divides the Middle ear from the glands to form wax; any collection external ear from the middle ear; it is The middle ear has an irregular shape and in the external ear canal – such as dead skin slightly oval in shape and approximately is lined with mucosa. Although commonly cells, dust, debris, shed hair or wax – natu- 9-10mm at its largest diameter. The pars thought of as an air-filled space, it is filled rally migrates out into the conchal bowl tensa (Fig 3) makes up the majority of this with nitrogen-rich gas (Hussain, 2016). (Fig 2). This is a constant movement from membrane and is situated at the lower part The roof of the middle ear has a thin the centre of the eardrum to its margins, of the tympanic membrane. It comprises plate of bone called the tegmen tympani then up and out of the external ear canal. three layers: separating it from the meninges and tem- As the glands are only located in the ● Epithelium continuous with the poral lobe of the brain. Its floor is formed outer third of the external ear canal, this is external ear canal; by the roof of the jugular fossa and is close the only place in the canal that wax should ● Fibrous middle layer; to the internal jugular vein and internal be seen. Short hairs are located above the ● Mucosal layer, lining the whole of the carotid artery. The proximity of the vein glands and are projected towards the canal middle ear and upper respiratory tract. and artery means people can complain that entrance to assist the migration of wax out of the ear canal; they protect the ear canal by Fig 2. The pinna trapping dust and debris and discouraging anything from entering the external ear canal. Wax is slightly acidic and protects the Triangular fossa external ear canal from bacterial and fungal Helix infection; in the outer third of the canal, the hairs lift the wax slightly away from the skin Location of a preauricular to prevent skin irritation (Harkin, 2019). Anti helix sinus if present The inner two-thirds of the ear canal are housed in the temporal bone, with the skin tightly adhering to that bone; the diameter Conchal bowl Tragus of the ear canal varies between individuals and races (Ludman and Wright, 1998). The Intertragal ear canal travels downwards and slightly notch forwards into the skull, with a slight nar- rowing and bend at the junction of the car- Lobule tilage and bone of the skull. At the end of the external ear canal is the tympanic JENNIFER N.R. SMITH membrane (eardrum), which lies at a slant, Nursing Times [online] April 2021 / Vol 117 Issue 4 57 www.nursingtimes.net Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use Clinical Practice Systems of life they sometimes hear blood pumping in Peripheral vestibular system synovial joint. Although the lateral pro- their ear. The peripheral vestibular system is cess of the malleus is the most-prominent The opening for the eustachian tube is responsible for maintaining balance, coor- point visible on the tympanic membrane, on the anterior wall of the middle ear. This dinating the position of the head and eye the incus can often be seen during otos- tube is part cartilage and part bone and con- movement. The system consists of sacs copy. The incus articulates with the stapes, nects the middle ear with the nasopharynx, filled with endolymph, with the fibres of and the footplate of the stapes sits in the which is located in the post-nasal space.
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