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Home , Ear canal, Eustachian tube, Helix (ear), Middle ear

Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use

Clinical Practice Keywords //Balance/ /Physiology Systems of life This article has been The 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 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 houses ear, as they may have to care for Failure in the development of the anti- the (organ Npatients who have chronic ear – a curved prominence of 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 , 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).

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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 Inner ear , an ear disease caused by Semi-circular canals dead skin that collects in the middle ear, causing discharge and . This can erode structures in and around the middle ear and requires surgical removal. Auditory It may be congenital or can develop as a 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 (Fig 1), is attached at its tip to the window centre of the membrane, called the umbo (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 ) 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 to its margins, of the tympanic membrane. It comprises plate of 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 l 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 l Fibrous middle layer; to the internal jugular and internal be seen. Short hairs are located above the l Mucosal layer, lining the whole of the carotid . 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 , with the skin tightly adhering to that bone; the diameter Conchal bowl 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 , 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 JENNIFER membrane (eardrum), which lies at a slant,

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they sometimes hear blood pumping in Peripheral 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 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 , with the fibres of and the footplate of the stapes sits in the which is located in the post-nasal space. the vestibulocochlear nerve distributed on at the base of the cochlea. The To optimise the environment for the walls of these sacs. Two functionally stapes measures, on average, 3mm long hearing, the middle-ear space should have different sensory receptor systems detect and 1.4mm wide; it is attached to the oval air equal to atmospheric pressure. The head movement: window by a ligament. eustachian tube allows for air entry and l Semicircular canals detect rotational Sound waves travel along the external exit to the middle ear, which helps equalise head movements; ear canal and cause the tympanic mem- the air pressure. The muscles of the soft l Utricles and detect changes in brane to vibrate. The embedded lateral pro- palate are attached to the cartilage portion the position of the head relating to cess of the malleus causes the vibrations to of the eustachian tube and contract on gravity (linear acceleration) and head continue across the to the footplate chewing, and yawning, tilts on horizontal and vertical planes. of the stapes. The middle ear reduces the allowing air to pass into the middle ear Hair cells moving at a different rate to the loudness of sound partly by transferring through the opened tube. This process endolymph cause shearing forces, and these the medium of sound from air to fluid from varies between people, but is estimated to are detected and conducted by the vestibular the ossicles to the cochlea but also by the take 0.15-0.34 seconds (Ludman and nerve to the brain, which interprets the type function of the ligaments. Sound waves Wright, 1998). of movement that has occurred. transmitted to the ossicles disturb the Children’s eustachian tubes are shorter endolymph in the cochlea and cause move- and more horizontal due to the smaller How we hear ment of the hair-like projections on the size of the skull and are less efficient at The primary function of the middle ear is . This movement of the equalising pressure. As the head grows to convert air vibrations, which have been hairs generates neural impulses, which are and the skull enlarges, the eustachian tube channelled down the external ear canal to relayed to the brain through the cochlear becomes more vertical and the efficiency the tympanic membrane, into fluid vibra- nerve (Tysome and Kanegaonkar, 2018). of equalisation of pressure in the middle tions in the cochlea. To guard against loud sounds, muscles ear improves. The three smallest bones in the body – attached to the malleus and stapes con- the malleus, incus and stapes (Fig 1) – are tract, which reduces the vibrations and Inner ear located in the middle ear. These are known protects the cochlea. This is the acoustic The inner ear consists of: collectively as the ossicles and are vital to reflex. It takes about 40 milliseconds to l The cochlea (organ of hearing); hearing. occur, so if there is a sudden loud sound, l The peripheral vestibular apparatus The malleus lies high in the middle ear, such as an explosion, it will not happen in (organ of body balance). suspended by a ligament, and its head time and noise-induced hearing damage articulates with the body of the incus by a can occur. Cochlea The cochlea is a dense, snail-like structure Fig 3. Structure of the tympanic membrane of two and three-quarter turn, which lies sideways and houses the . Its spiral canal varies in length from 29mm to Pars Flaccida 40mm and is divided into three compart- ments by partitions of bone and mem- brane. The upper (scala tympani) and Short process lower (scala vestibule) compartments are Annulus of the malleus filled with a fluid called ; the middle compartment (scala media) is filled with a fluid called endolymph. The organ of Corti is located on the lower membrane (basilar membrane) of the scala media and consists of cells with hair-like projections, connecting with the terminal ends of the auditory nerve. Each projection responds to different sound fre- Handle of the quencies, with high frequencies located at Pars tensa malleus its base and low frequencies towards the tip of the spiral canal (Hussain, 2016). The first turn of the canal bulges into Light reflex the middle ear and is called the promon- tory; the outline of this can often be seen Umbo when viewing the tympanic membrane

JENNIFER N.R. SMITH JENNIFER with a microscope.

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l Vagus (tenth cranial nerve). Table 1. Ear problems across different nursing specialties During an ear examination, stimulation Specialty Conditions and associated ear problems of the auricular branch of the can cause the patient to cough; this is called Diabetes ● Diabetes can result in neuropathy along the auditory nerve as well the Arnold’s reflex (Ryan et al, 2014). as retinopathy; people with diabetes also have ear wax at a higher The shared nerve supply between the ear pH (normal pH is 4), which can predispose them to external ear and other parts of the head and neck means infections ( externa) or other pathology in these Neurology ● Neurofibromatosis is associated with schwannomas (tumour of the regions can cause . Ear problems nerve sheath), which can affect the vestibulocochlear nerve are also associated with a range of other ● Meningitis and brain abscess are rare, but can occur as a result of conditions and can affect patients across severe middle-ear infections different nursing specialties (Table 1). ● Degeneration of the cervical spine can cause referred pain in the ear Older adults ● Degeneration of the hairs in the cochlea naturally occurs with age. It Conclusion is estimated that there are >12 million deaf and hard-of-hearing Although the ear is small in size, it is adults in the UK and that, by 2035, a fifth of the population will be essential for hearing and balance, and affected (Bit.ly/ActionHearing) problems of the ear can be linked to other ● Hearing loss increases the likelihood of older adults having accidents conditions. Understanding the structure at home, as it can cause distraction and is often associated with and function of the ear will help nurses to impaired balance pick up problems early and improve the care of patients with chronic ear problems Mental health ● Research shows a link between hearing loss and mental health: and other associated health conditions. NT people with hearing loss are more likely to experience emotional

distress, loneliness and depression and are twice as likely to develop References dementia (Nakashima et al, 2016) Harkin H (2019) impaction: why it needs to be treated in primary care. Nursing Times [online]; Dermatology ● As the external ear is lined with skin, patients with skin conditions, 115: 8, 38-40. such as Darier’s disease, can experience blocked ears caused by skin Hussain S (2016) Ear anatomy and physiology. In: debris building up in the external ear canal Logan Turner’s Diseases of the Nose, Throat and Ear. CRC Press. Learning ● There is a link between overproduction of wax and learning disability Ludman H, Wright T (1998) Diseases of the Ear. disability (Schwartz et al, 2017); this increases the risk of wax impaction, which University Press. Nakashima T et al (2016) Cerumen impaction shown can cause hearing loss, , , external ear infections or pain by magnetic resonance imaging in patients with ● cognitive impairment. Geriatrics and Gerontology Dental Assessing earache should include questions on dental health and International; 16: 3, 392-395. general health and wellbeing. Establishing the origin of ear pain will Public Health England (2019) NHS Screening ensure referral to the most appropriate specialty Programmes in England. 1 April 2017 to 31 March ● 2018. London: PHE. The ear is the closest structure to the , so Ryan NM et al (2014) Arnold’s nerve cough reflex: ear pain may signal a dental problem evidence for chronic cough as a sensory vagal neuropathy. Journal of Thoracic Disease; 6: Suppl 7, Immunology ● Patients who are immunocompromised have a higher risk of S748–S752. developing ear infections Schwartz SR et al (2017) Clinical practice guideline (update): earwax (cerumen impaction). Trauma ● The perilymph in the inner ear communicates with cerebrospinal Otolaryngology – Head and Neck Surgery; 156:S1, fluid; hearing and balance can be affected by a severe electrolyte S1-S29. imbalance Szymanski A, Geiger Z (2020) Anatomy, Head and Neck, Ear. StatPearls. ● Patients with head injury will always have an ear examination as the Tysome J and Kanegaonkar R (2018) Clinical tegmen tympani separating the middle ear from the skull can anatomy. In: ENT: An Introduction and Practical fracture, and blood can often accumulate in the enclosed middle-ear Guide. CRC Press. space as a result of bleeding from a skull-based fracture Oncology ● Patients who have tumours in the head and neck region can Nursing Times complain of referred pain in the ear Self-assessment ● Some drugs used in chemotherapy can cause irreversible damage online to the hearing nerve (vestibulocochlear eighth cranial nerve) Test your knowledge with Nursing In the foetus, the auditory cortex people socially and a person’s ability to Times Self-assessment after reading (hearing part of the brain) is fully formed, balance and move around safely helps this article. If you score 80% or more, which is why newborn screening of hearing maintain independence. you will receive a personalised is very effective and 98.5% of babies born in Although the ear is a relatively small certificate that you can download and the UK are tested in the first three months structure, it is served by five cranial : store in your NT Portfolio as CPD or after birth (Public Health England, 2019). l Trigeminal nerve (fifth cranial nerve); revalidation evidence. l Facial nerve (seventh cranial nerve); The importance of the ear l Vestibulocochlear (eighth cranial To take the test, go to: Problems with hearing or balance can be nerve); nursingtimes.net/NTSATheEar extremely debilitating. Hearing connects l Glossopharyngeal (ninth cranial nerve);

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