1-s2.0-S0169409X01001727-main

Advanced Drug Delivery Reviews 51 (2001) 5–19www.elsevier.com/ locate /drugdeliv

The nose and paranasal sinuses physiology and anatomy*Nick Jones

University Hospital, Nottingham NG7 2UH, UK

Abstract

The paranasal sinuses and nose are much more than two cavities behind a projection on the centre of the face. Theyhumidify, filter, warm, and sense what we breathe. The anatomy and physiology interact forming a dynamic system. Theanatomy, airflow, nasal resistance, its turbulence, the nasal cycle – a process by which the turbinates or cushions lining thenose alternatively swell and congest from side to side, can all potentially influence the nasal delivery of drugs. Along withthese factors mucus rheology and mucociliary clearance influence the removal of substances delivered to the nose. Thehealth of the nose and its immunological response to what is inhaled, be it pollutants, allergens, drugs or vaccines, all need tobe considered. It is a fascinating sensor for the body, not only detecting the potentially harmful substances such as smoke,but its psychosexual aspects have far reaching implications and the olfactory pathway has potential as a pathway for thedelivery of drugs. 2001 Elsevier Science B.V. All rights reserved.

Keywords: Nose; Paranasal sinuses; Physiology; Anatomy

Contents

1. Physiology.............................................................................................................................................................................. 61.1. Olfaction ......................................................................................................................................................................... 61.2. Sensation......................................................................................................................................................................... 81.3. Immunology .................................................................................................................................................................... 81.4. Mucociliary clearance ...................................................................................................................................................... 8

1.4.1. The clearance mechanism ....................................................................................................................................... 81.4.2. Factors affecting mucociliary clearance ................................................................................................................... 91.4.3. Measurement of mucociliary clearance .................................................................................................................... 9

1.5. Filtration ......................................................................................................................................................................... 101.6. Humidify......................................................................................................................................................................... 101.7. Nasal cycle and airflow dynamics...................................................................................................................................... 10

2. Anatomy ................................................................................................................................................................................ 102.1. The external structure ....................................................................................................................................................... 102.2. The nasal bones ............................................................................................................................................................... 112.3. The nasal vestibule........................................................................................................................................................... 112.4. The septum, the upper and lower lateral cartilages .............................................................................................................. 112.5. Nasal mucosa .................................................................................................................................................................. 152.6. Olfactory mucosa ............................................................................................................................................................. 15

*Tel.: 1 44-115-924-9924.E-mail address: [email protected] (N. Jones).

0169-409X/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S0169-409X( 01 )00172-7

6 N. Jones / Advanced Drug Delivery Reviews 51 (2001) 5 –19

2.6.1. Paranasal and sinus anatomy ................................................................................................................................... 162.6.2. The ethmoid sinuses ............................................................................................................................................... 162.6.3. The maxillary sinus ................................................................................................................................................ 162.6.4. The ostiomeatal complex ........................................................................................................................................ 162.6.5. The frontonasal recess ............................................................................................................................................ 162.6.6. The nasolacrimal system......................................................................................................................................... 162.6.7. The sphenoid sinus................................................................................................................................................. 172.6.8. Anatomical variations............................................................................................................................................. 172.6.9. Potential factors affecting the delivery or use of nasal vaccines ................................................................................. 18

References .................................................................................................................................................................................. 18

1. Physiology activate cAMP specifically and others to activate IP ,3

it is not known if these affect the same or differentWhat does the nose do? We breathe in about 12 to membrane ion channels [1].

24 times a minute, inhaling approximately 10 000 The precise mechanism by which the vast numberlitres of air a day of differing temperature, humidity of smells is recognised and discriminated is un-and which contains dust and organisms. known, but possible theories include; specific odour-

It has the following functions that are often taken ants exciting specific receptors which are randomlyfor granted until they are lost: grouped or aggregated, the differing solubility’s of

odourant allowing a temporospatial distribution of1. Olfaction the odourant across the olfactory mucosa, or a2. Sensation response to the molecules’ vibration spectra within3. Immunology an inelastic electron tunnel formed by olfactory4. Mucociliary clearance receptors and their associated G-protein. The struc-5. Filtration ture based theories on their own cannot explain6. Warm and humidify differences in smell between identical substances7. Nasal cycle and airflow dynamics such as acetophenone and its fully deuterated ana-

logue acetophenone-d8. The vibration theory has1.1. Olfaction received media prominence recently – it proposes

that it is the vibrational frequency of a moleculeHumans can detect more than 10 000 different which is detected. When it attaches to a receptor it

odours and discriminate between 5000. The olfactory detects that vibrational mode and allows electrons toepithelium has several million olfactory sensory jump across the receptor and then trigger the neu-neurones [1] (Fig. 1a and 1b). Odourant binding rone. It might be possible for one receptor to detect aproteins (OBP’s) bind and solubilise hydrophobic range of vibrational energies. The olfactory mucosamolecules, increasing their concentration up to of mammals is high in enzymes including cyto-10 000 times that in ambient air. The OBPs may also chrome P-450 glutathione and UDP-transferase andremove the odourant molecules after transduction, these may play a part in metabolising odourants.which occurs after specific interactions between the Adaptation is a characteristic of olfaction and inodourant molecules and receptor proteins on the the past has been thought to be due to receptorsurface of the olfactory cilia. Olfactory transduction phosphorylation which modulates the normal signalis probably then mediated via a unique olfactory transduction and activation of the adenyl cyclase /epithelium G -protein coupled cascade, with CAMP cyclic AMP second messenger system. More recentolf

and /or IP (phosphoinositide specific phosphodies- work suggests that the effect is downstream and a321terase C) as an intracellular 2nd messenger, exciting modulation of the cAMP-gated channel from Ca

an ion channel in the cilia, which depolarises the feedback.olfactory neurone. Recently through molecular clon- Whole scalp neuromagnetic signals to olfactorying a cyclic nucleotide-gated olfactory channel has stimulation suggest that the area around the superiorbeen identified. Some odourants have been found to temporal sulci of both hemispheres are involved in

N. Jones / Advanced Drug Delivery Reviews 51 (2001) 5 –19 7

Fig. 1. (a) Electron micrograph of olfactory mucosa. (b) Line diagram of 1a.


olfactory processing. Established odour associations variety of conditions which affect the activity of thecan last at least 1 year, three times as long as for cilia. About 20–40 ml of mucus are secreted from

2visual stimuli [2]. the normal ‘resting’ nose each day from 160 cm ofOdourants have biological meaning, a child prefer- nasal mucosa [5]. Nasal mucus provides a continu-

ring its mothers’ smell after only 6 to 10 days, this ous blanket lining the nasal cavity onto whichalso mediating the child’s attachment between 3 and particles in the turbulent inhaled airstream can5 years of age. There are other effects caused by impact and stick. Eighty percent of particles largersmell such as pheromones having a strong psycho- than 12.5 mm are filtered from the air before itsexual influence [3]. reaches the pharynx. The blanket of mucus can be

moved by the co-ordinated waves of cilia from the1.2. Sensation front of the nose to the nasopharynx where they can

be swallowed or expectorated. The properties ofThe common chemical sense in the nose which mucus are geared to fulfil these two roles: trapping

originate from free nerve endings scattered through- and transporting airborne particles.out its lining is different from olfaction and provides The periciliary fluid is a lubricating layer in whichthe sensation of irritation or burning when stimulated the cilia beat, and is functionally distinct, but struc-by substances such as ammonia and chilli peppers. turally continuous from the viscous layer of mucusThis is mediated by branches of the trigeminal nerve above the gel layer. Soluble material such as sac-and the glossopharyngeal nerve which all input to the charin will dissolve and be transported through thisspinal trigeminal nucleus, thalamus and somatosen- layer, and it has been suggested that transportsory cortex. Both sensations have a protective role through the periciliary layer is more efficient than inand can initiate a protective sneezing reflex, tears or the mucus layer. Cilia in isolation are sensitive to thenasal secretions. effects of temperature, working optimally at 35–

408C, and above and below these temperatures the1.3. Immunology natural beat frequency drops. Mucociliary systems

are very sensitive to drying but within usual atmos-As well as the protective effect of mucus being pheric conditions there is little alteration in nasal

secreted and mechanically cleared, nasal secretions mucociliary transport rate and this is due to thehave constituents that have immunological proper- warming and humidifying functions of the nose.ties. Nasal secretions contain immunoglobulins IgA, In the human nasal fossa the direction of theIgG, IgM, IgE, enzymes such as lysozymes and mucus flow is predominantly posterior towards thelactoferrin, protective proteins such as complement nasopharynx, streaming above and below the tubaland as well as neutrophils and lymphocytes in the opening. Differences in mucociliary transport ratesmucosa. In rodents and many other mammals there is between different sites in the nose depend on ciliarya rich lymphatic system in the nasal airway. This beat frequency, density of the ciliary population,does not appear to be the case in humans and the length of the cilia and mucus quality. The rate ofmacroscopic collections of lymphatic tissue are mucociliary transport is 1–2 mm/h just behind theconfined to the tonsils and nasopharynx. At the anterior portion of the inferior turbinate, and in-mucosal level antigen presenting cells and both B creases to 8–10 mm/h on the posterior portion of theand T lymphocytes play a role in local immunity as inferior turbinate. Where there is an obstruction towell as allergy [4]. the normal path of mucociliary transport, different

phenomena have been reported. Where spurs on the1.4. Mucociliary clearance septum or other mucosal irregularities present large

obstructions, or are associated with alterations in the1.4.1. The clearance mechanism epithelial surface such as squamous metaplasia, the

Nasal mucociliary clearance is a fundamental pathway is around these obstructions. If the bonyfunction required to maintain the health and defence spur is small and it has retained functioning ciliatedof the nose. Mucociliary transport is disturbed in a epithelium on its surface, and the mucus is of


adequate viscosity to move up a slope, then the mucosa. Their ciliated surface can undergo squam-mucus blanket will travel over the obstacle. If there ous metaplasia. Where the mucociliary blanket isis a defect in the mucosal surface, and the cohesive preserved the mucus is moved in a normal fashion,properties of the mucus is preserved then the mucus but due to the pedunculated swelling of the mucosacarpet can move undisturbed from one edge of intact the direction of the mucus may be lost [21–25].epithelium to the next. If there is a defect associated Patients with nasal polyposis have disturbed muco-with squamous metaplasia normal mucociliary trans- ciliary function as measured by saccharin clearanceport at this site will be lost [6]. and gamma scintigraphy.

The commonly used intranasal preparations which1.4.2. Factors affecting mucociliary clearance have steroids or antihistamines as active agents have

Disruption of cilia by viruses and bacteria such as not been shown to be detrimental to nasal muco-Haemophilus influenzae, Streptococcus pneumoniae, ciliary function in humans, despite reports thatStaphylococcus aureus and Pseudomonas produce isolated cilia beat less effectively when perfused withspecific toxins that disrupt epithelial cells with loss these drugs or the preservatives that are added toof a confluent cilial field [7]. Neutrophils which these drugs [26].gather at the sites of purulent infection produce an Between 5 and 10 percent of the cilia showelastase that is directly toxic to respiratory epi- abnormalities in children and adults who have nothelium. Viruses responsible for the common cold apparent nasal disease [6]. In Kartagener’s syndromedisrupt the ciliated cell’s microtubules and there is an there is absence of the dynein arms of the nineincrease in mucus tethering at the sites of mucus peripheral microtubules. These individuals have onlyglands making it difficult for the remaining cilia to 40% of their ciliated cells working and they also lacktransport mucus [6]. co-ordination or metachronicity. In primary ciliary

Changes in cilial structure occur in patients with dyskinesia impaired mucociliary clearance has beenlong-standing allergic rhinitis and changes in se- shown to be due to structural defects of the ciliarycreted mucus occur at times of acute allergen axoneme [27–29].challenge [8]. The changes to mucus that occur In cystic fibrosis the primary abnormality is notduring an acute allergic nasal reaction are secondary with the cilia, but with the production of abnormalto a variety of inflammatory mediators. There is mucus, possibly secondary to defective chloridelikely to be an improvement in mucociliary transport transport.due to alterations in the rheological properties of themucus and an increase in ciliary beat frequency. The 1.4.3. Measurement of mucociliary clearanceresults from experiments on the patients with allergic Several techniques have been used to measurerhinitis are inconclusive, some suggesting there is an ciliary function including measurement of ciliaryincrease and some a reduction in nasal mucociliary beat frequency using a photosensitive cell thattransport in response to allergen challenge. In pa- converts the reflections of light from beating ciliatients with positive skin tests and a positive response into an electric current and then an oscilloscopeto methacholine challenge saccharin clearance times display via an amplifier [30–33]. Alternatively videoare prolonged [9]. images of beating cilia from a monitor with the

In patients with chronic rhinosinusitis areas of altering light intensities of individual pixels or pixelciliary denudement have been demonstrated, but in groups, or interruptions of a light source or scatteringareas where cilia were preserved ciliary motility of a laser beam by the cilia can be utilised. All theseappears normal. Prolonged saccharin clearance in can be transduced to an electrical signal which canpatients with maxillary sinusitis has been attributed be amplified, filtered, and then digitised. A computerto the effects of bacterial toxins. Mucosa of patients using fast Fourier transformation can then be used towith chronic sinusitis show changes including calculate, and display the ciliary beat frequencyoedema, shedding of epithelial cells, squamous results, and include some statistical analysis.metaplasia and cilial abnormalities [10–20]. When studying preparations with beating cilia it is

Nasal polyps are oedematous swellings of nasal important they are maintained at consistent tempera-


ture, the pH and the osmolality are maintained in a 1.5. Filtrationphysiologic range. Ciliary beat frequency showsconsistent readings in the temperature range 32 to Particles larger than 30 mm are removed as there408C. Between 19 and 328C it increases in a linear is a large degree of air-mucosa contact time due tofashion, and above 408C it declines [33]. Cilia air turbulence in the nasal airway which increasesobtained with a nylon brush can be examined under with a faster respiratory rate. A substantial propor-the electron microscope. The ciliary beat axis is tion of smaller particles down to 12 mm are alsoperpendicular to a line drawn through the centres of filtered. Vibrissae, or hairs in the nostrils, help trapthe two central microtubules. In a group of cilia much larger particles.sectioned axially and displayed on an electronmic-rograph, the angle subtended by each cilia can be 1.6. Humidifymeasured and the mean ciliary angle can be calcu-lated. From this the ciliary deviation can be calcu- In spite of a wide range of inspired air the noselated – that is the standard deviation of the ciliary manages to humidify the air to a humidity over 80%angle for the cilia sectioned can be determined. In before it enters the lungs. Air is heated throughnormal patients the ciliary angle is 148, and at the tip conduction, convection and radiation with blood flowthe ciliary deviation is 48. in the opposite direction to incoming airflow that

A biopsy of nasal cilia is straightforward, but the improves the efficiency of warming [34]. The tem-equipment required to measure ciliary beat frequency perature of the nasopharynx only varies by 2–38C.and measure ciliary angles is complex and expensiveand will only be available in a few centres. 1.7. Nasal cycle and airflow dynamics

The Saccharin test involves the placement of aparticle or solution of saccharin on the anterior end The upper airway is responsible for up to 70% ofof the inferior turbinate or nasal septum, behind the the total airway resistance. This is needed to allowarea of slow anterior clearance [6]. A 1 mm diameter the lungs to expand optimally whilst allowing venousor quarter fragment of a saccharine tablet is placed return.just behind the anterior end of the inferior turbinate, The nasal cycle occurs in approximately 80% ofand the patient is asked to sit quietly with their head normal people with each side of the nose alter-forward, not to sniff, sneeze, eat or drink. The time natively congesting and decongesting every 3–7 h. Ittaken from the placement of the tablet to the first is unclear why this cycle exists but the total nasalperception of the sweet taste is the saccharin clear- airway resistance is almost unchanged. There are aance time. The saccharin dissolves in the mucus range of activities and reflexes which can affect thelayer and presumably the periciliary fluid layer, and nasal airway. Exercise usually decreases nasal resist-is transported to the nasopharynx and the base of the ance. Dust, smoke and alcohol usually increase nasaltongue. This is a useful screening test, those with resistance. Pressure on one side of the body inducestimes greater than 30 min have significantly dis- reflex nasal congestion on that side [35].turbed mucociliary transport. In these patients it isnecessary to confirm their ability to taste saccharin.The average saccharin clearance time for an adult 2. Anatomypopulation free from nasal disease would be between7 and 15 min. When using the saccharin clearance 2.1. The external structuretest it must be taken in conjunction with the patientssymptoms and proper examination of the nasal • The nasal bones usually comprise only the uppermucosa. Other techniques include the tracking of third of the nose (Fig. 2).intranasal radioisotopic particles, observing the clear- • The septum forms the central strut or scaffoldingance of dyes, and a radiographic method measuring of the nose and separates the two nasal airwaysthe movement of radiopaque 1 mm diameter discs (Fig. 3a and b).ana fluoroscopic image intensifier [6]. • The anterior part of the central strut or septum is


2.2. The nasal bones

The nasal bones are much shorter than manypeople imagine and often make up only a third of thelength of the nose. The nasal bones are attachedlaterally to the maxilla (Fig. 2) by a syndesmosis, astrong fibrous attachment. The nasal bones and themaxilla complete the bony inlet to the face called thepiriform aperture (Fig. 2). This aperture is smaller inwomen and occasionally it can be a significant factorin narrowing the nasal airway, particularly after afracture involving the maxilla.

2.3. The nasal vestibule

Laterally the nasal vestibule is the term used todescribe the entrance area to the nose (the areawhich might accept the end of the index finger in anosepicker!) and is lined by squamous epitheliumwith vibrissae or hairs and sebaceous glands. Afterapproximately half a centimetre the squamous epi-thelium becomes mucosa.Fig. 2. The nasal bones and the paranasal sinuses.

2.4. The septum, the upper and lower lateralmade up of the quadrilateral cartilage which is cartilagesattached behind to the vomer and vertical plate ofethmoid and below to the maxillary crest and The anterior quadrilateral cartilage rests on thespine. anterior nasal spine of the maxilla, and an intact strut

• The middle third of the nose is made up of the of cartilage which rests on the spine is crucial forupper lateral cartilages which are a lateral con- good support of the nasal tip (Figs. 3a,b and 4). Itstinuation of the septum. They are attached to the attachment to the spine is strong via very fibrousundersurface of the nasal bones (Fig. 4). connective tissue. Posteriorly, the quadrilateral cartil-

• The lower third of the nose is supported by the age abuts onto the vomer and the perpendicular platelower lateral cartilages which are delicate and of the ethmoid. The septum is in continuity with theusually rest in the upper lateral cartilages for upper lateral cartilages and through these is attachedsupport. Their contour makes up the tip and gives to the nasal bones. The nasal bones overlap the lowerit its round contour (Fig. 4). lateral cartilages and if they become separated, they

• A surface marking of the level which divides the can collapse the middle third of the nose and causenasal airway from the brain, called the skull base, unsightly narrowing and nasal obstruction with con-is the line between the medial corner of the eyes striction of the nasal valve. The attachment of the– the intercanthal line. upper lateral cartilages to the nasal bones provides

• The nasal valve area is the area of maximum useful support for the septum. The nasal valve isnasal resistance in the nasal airway and is formed important, as it is the part of the airway which oftenby the returning or overlap between the upper and has the smallest cross-sectional area, and thereforelower lateral cartilages, the inferior turbinate (a anything which influences it is likely to affect nasallateral vascular cushion which acts like a radiator airflow (Fig. 5). The nasal valve is made up laterallyto the nose warming the air as well as humidify- by the upper lateral cartilage which is normallying it) and the septum (Fig. 5). under the lower lateral cartilages with its end or


Fig. 3. (a) Lateral view of the septum in a cadaver. (b) Line diagram of 3a.

‘returning’ just supporting the upper edge of the between the upper and lower lateral cartilages be-lower lateral cartilages. The part of the upper lateral comes less and the inherent elasticity within thecartilage which overlaps and may project to a tissues is also reduced and these factors can result invariable extent past its contact with the lower lateral collapse and impingement on the nasal valve. Incartilage into the airway. With age the overlap some individuals (17% of the population) there is no


overlap between the cartilages and they can be‘floppy’ collapsing and reducing the airway when theperson breathes in. The rest of the nasal valve ismade up of the inferior turbinate and the septum. Asmentioned the bony lateral boundary is the piriformaperture. A poorly recognised fact is that the septumis very thick at this point because of the ‘Tuberculumof Zuckerkandl’, a very thick area of mucosa withglandular tissue which has no erectile or cavernoustissue. Anterior cuts of any coronal CT scans of thenose invariably show this significant area (Fig. 6).

The lower lateral or alar cartilages lie closer to thelongitudinal axis of the nose than many imagine andnot along the rim of the nostrils (Fig. 4), with theirlong axis lying at approximately 30 degrees from thebase of the nose and not along the rim of the nostrils.The lower lateral cartilages have one medial crura, orfoot, that stands next to its fellow on the other side,both just either side of the midline and this helps tomake up part of the columella. The medial crurabecome thin intermediate crura as the edge of thenostril starts to curve laterally at the apex of thenostril. It then becomes the lateral crura which is thelarger part of the lower lateral cartilage and this rides

Fig. 4. Line diagram to show the relationship between the nasalbones, the upper and lower lateral cartilages.

Fig. 5. The nasal valve. Fig. 6. Coronal CT scan showing the Tuberculum of Zuckerkandl.


upwards to form much of the contour and support of incoming air. The septum is supplied posteriorly by athe lower third of the nose. The medial crura meet large branch of the sphenopalatine artery, superiorlyanteriorly in front of the septum with fibrous strands by a branch from the anterior ethmoid artery andjoining them. The lateral crura are delicate cartilages antero-inferiorly by a branch from the superior labialand whilst the skin over the lower third of the nose is branch of the facial artery. Inferiorly there is also aoften sebaceous and will disguise some irregularity, supply from the greater palatine artery. The lateraltheir domes – or the area which reflects the light – wall of the nose is supplied anteriorly by the anteriorare readily apparent, and a minor degree of ethmoid artery and the majority of the rest is fromasymmetry can have a marked cosmetic effect. The the sphenopalatine artery. The turbinates, or vascularLevator Labii Superioris Alequae Nasi is a respirato- cushions which line the lateral nasal wall and act as ary muscle which dilates the nares on inspiration and radiator to the airway, are very vascular (Fig. 7).is attached to the side of the lower lateral cartilages. They contain erectile tissue which has large

The columella is the part of the nose between the sinusoids which form a large cavernous plexus andnostrils or nares. It is primarily made up of the nasal their drainage is controlled by veins which containseptum and medial crura of the lower lateral cartil- longitudinal muscle. This system allows both shunt-ages. ing of blood through the system but also venous

The arterial supply of the nose is very rich pooling which causes congestion and swelling.particularly on the septum where the squamous Externally a branch of the facial artery runs up toepithelium becomes respiratory epithelium lies Kies- the lateral aspect of the piriform aperture beforeselbach’s plexus, a 1.5 (squared) mm area of capil- giving off an angular branch which heads towardslary loops. The majority of nosebleeds come from the medial part of the eye along with a variety ofthis area. branches which pass to the alar cartilage.

It is interesting that the direction of arterial blood The root of the nose is called the nasion. Theflow in the nose runs anteriorly against inspiration. nasolabial angle is usually about 90 degrees in menThe direction of blood flow may help in warming and more open in women.

Fig. 7. A photograph of the lateral nasal wall showing the inferior, middle and superior turbinate.


2.5. Nasal mucosa

The nasal lining has the same lining as the rest ofthe respiratory tract with pseudostratified ciliatedcolumnar epithelium. There are up to 200 cilia percell whose tips lie in the superficial gel layer (seesection on mucociliary transport for more detail). Atthe anterior end of the inferior and middle turbinate,which is the area which has most contact withinspired air, there can be metaplasia with cuboidalcells which have no cilia [35].

2.6. Olfactory mucosa

The olfactory epithelium covers an area of about2370 mm lying partly on the nasal septum and partly

on the superior and middle turbinate. There is avestigial olfactory organ called Jacobson’s organ orthe vomero-nasal organ which can be seen as ablind-ended pit on the side of the septum (Fig. 8). Inman there is no good evidence that any centralconnection exists but in other mammals such as therat it is functional.

The olfactory neuroepithelium is composed ofolfactory sensory neurones, sustentacular or support-ing cells which ensheath the receptor neurones –

Fig. 8. Endoscopic view of Jacobson’s organ or the vomero-nasalthese maintain the normal extracellular potassiumorgan, macroscopically a pit on either side of the nasal septum.levels needed for neuronal activity and basal cells

which replace the neuroepithelium approximatelyevery 40 days.

The olfactory neurone dendrite is bipolar with a When neuronal axons penetrate the cribriformround cell body and has 10–23 cilia on its surface plate they become covered by Schwann cells. Onewhich are up to 200 m long and may overlap with Schwann cell contains 5–10 fibres, but occasionallythe cilia of adjacent neurones. The cilia have a nine up to 100. Olfactory sensory neurones are bipolarplus two pattern of microtubules characteristic of and about 15 000 olfactory receptor cells convergemotile cilia but towards the tip there is only a central on one mitral cell or tufted cell in the olfactory bulb.pair. The olfactory organ is unique in the central The olfactory bulb is 12.2 (range 6–16) mm long.nervous system, being the only part in direct contact Both mitral and tufted cells project a single primarywith the environment and in its ability to regenerate dendrite to a single glomerulus and emit severaldamaged or lost neurones. The olfactory sensory dendrites within the external plexiform layer. Perig-neurone tapers into an unmyelinated axon and lomerular cells, granule cells and short axon cells aresynapses in the olfactory bulb. Basal cells are small interneurones connecting glomeruli. Granule cellspolygonal cells in contact with the underlying base- connect to mitral cells and inhibit them. From thement membrane and are the stem cells for receptor olfactory bulb tract the main axons originate in theand sustentacular cells. They may play a vital role in mitral or tufted cells and give off striae which pass toregeneration after viral damage. The underlying the olfactory tubercle and then projections go to thelamina propria contains olfactory nerve fascicles and amygdala, the prepyriform cortex, the anterior olfac-mucus-secreting tubuloalveolar Bowman’s glands. tory nucleus and the entorhinal cortex as well as the


hippocampus, hypothalamus and thalamus. The ol-factory axons have both convergent and divergentprojections and are not point to point like the visualor somatosensory systems.

2.6.1. Paranasal and sinus anatomyThe paranasal sinuses comprise the maxillary,

sphenoid, frontal and the ethmoid sinuses whose roofis formed by the frontal bone lateral to the cribriformplate and the crista galli in the midline.

2.6.2. The ethmoid sinusesThere are approximately 8–15 ethmoidal air cells

which form a bony labyrinth in the upper and lateralaspect of the nasal cavity (Fig. 2). A condensation ofthe bony partitions which make up the divisions ofthe ethmoidal air cells is called the ground lamella Fig. 9. A line diagram of the lateral nasal wall.and this divides the anterior from the posteriorethmoidal air cells. The most anterior ethmoidal air semilunaris is a consistent large air cell, the ethmoi-cells are termed agger nasi cells and their size and dal bulla.number vary.

2.6.4. The ostiomeatal complex2.6.3. The maxillary sinus This is a term which has become popularised and

The maxillary sinus is housed in the maxilla with refers to the area under the middle turbinate intothe roots of the upper premolars and molars project- which the maxillary sinus (via the infundibulum), theing into its floor but its medial wall is open but is anterior ethmoidal air cells, and the frontal sinusfilled by the inferior turbinate, the uncinate bone drain (Fig. 10). The sphenoid sinus and the posteriorabove this, and the ethmoid behind. The maxillary ethmoidal air cells drain into the sphenoethmoidalostia, or hole, drains into a slit like opening into the recess which lies at the posterosuperior aspect of thenasal airway and this also aerates the sinus. The nasal cavity.uncinate bone is a thin but important bone as itmakes up the medial wall of a slit, the infundibulum,

2.6.5. The frontonasal recesswhich passes from the hiatus semilunaris to theThe term recess is a variable three dimensionalmaxillary sinus. The maxillary ostium is a hole but it

space whose boundary is influenced by the size anddoes not open directly into the nasal airway as it isheight of the anterior ethmoid or agger nasi cellsshielded medially by the uncinate process which lieslaterally and anteriorly and the way the uncinatemedial to it. Accessory ostia occur in about 30% ofprocess joins either the lateral wall, the middleindividuals. These ostia occur in areas where there isturbinate or the anterior skull base.no bone, just mucosa of the lateral wall of the nose

and the medial wall of the maxillary sinus, called theanterior or posterior fontanelles. The posterior edge 2.6.6. The nasolacrimal systemof the uncinate process may be barely discernible Tears drain into small holes, or puncta, at the innerlooking up the nose, but sometimes it curves slightly aspect of the upper and lower eyelid. Tears then flowmedially. Behind its free edge lies the hiatus through small tubes, or canaliculi, into the lacrimalsemilunaris, a two dimensional area (Fig. 9), which sac. The nasolacrimal sac then becomes the lacrimalmarks the inlet to the infundibulum or crevice which sac to drain into the lateral nasal wall. It opens intogoes to the maxillary sinus. Behind the hiatus the inferior meatus, under the inferior turbinate,


Fig. 10. A line diagram showing the path of mucociliary clearance through the ostiomeatal complex.

approximately 1 cm behind the anterior end of theinferior turbinate.

2.6.7. The sphenoid sinusThe ostium of the sphenoid sinus lies in the

posterior wall of the nose approximately 1 cm abovethe area where the posterior choana falls away intothe oropharynx. Its size varies. It is closely related tothe optic nerve and the carotid artery which lie in itslateral wall.

2.6.8. Anatomical variationsComputerised tomography scans (CT) have led to

a series of descriptive papers describing differentbony anatomical structures [36]. These are importantwhen it comes to navigating around the paranasalsinuses but their contribution to disease has beenquestioned as the ‘anomalies’ are as prevalent in anasymptomatic population as in a group with provenrhinosinusitis. The most common variation, which isfound in about 30%, is a pneumatised anterior end ofthe middle turbinate or concha bullosa (Fig. 11). Theposterior half of the middle turbinate is always Fig. 11. A coronal CT scan of the paranasal sinuses showing apneumatised as it comes off the lateral nasal wall. In concha bullosa, present in one in three people.


[2] S.S. Schiffman, Clinical physiology of smell and taste11% the middle turbinate has a concave medialdisorders, Ear, Nose and Throat Disorders 68 (1993) 297–surface instead of being convex and this is termed a308.

paradoxical middle turbinate. The cribriform plate [3] M.J. Russell, G.M. Switz, K. Thompson, Olfactory influ-may be asymmetrical in about 8% and this is more ences on the human menstrual cycle, Pharmacol. Biochem.

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