Physiology and Microscopic Anatomy of Nasal Cavity

Kyung Shik Suh, M.D.

Physiological functions of the nose

1. Respiration

2. Heat exchange

• direction of blood flow
• latent heat of evaporation
• thermoregulation

3. Humidification

• anterior serous glands
• mixed serous and mucous glands
• capillary permeability
• other body fluids, e.g. tears

4. Filtration

• vibrissal
• air flow pattern: laminar/turbulent

5. Nasal resistance

• anatomical, fixed
• neurovascular, variable

6. Nasal fluids and ciliary function

• mucus, mucins
• proteins including immunoglobulins
• ciliary structure and function

7. Nasal neurovascular reflexes

Parasympathetic

• Acetylcholine(Ach)
• vasoactive intestinal polypeptide(VIP)

Sympathetic

• Noradrenaline(NA)
• neuropeptide Y(NPY)

Sensory

• axon reflexes
• substance P(SP)

8. Axon reflexes

• Sneezing
• Central nasopulmonary reflexes
• Nasal cycle
• Reflexes initiated in the nose(Nasofugal)
• Reflexes acting on the nose(Nasopetal)

9. Olfaction

코의 미세해부학 microscopic anatomy

2 가지상피 조직

호흡상피와 후각상피로 구성

1) 호흡상피 respiratory epithelium

기도airway의 대부분을 차지

이관을 포함한 중이강 및 유양동, 비인강 일부 및 비강에서 기관지 이하까지의 기도 전체

호흡상피의 구성세포

1) PCCE = pseudo ciliated columnar epithelium

2) goblet cells 배세포

3) seromucinous glands 장액점액선

4) marked lymphoid cell zone

5) well-developed venous cavernous spaces in turbinates and around sinus ostia

6) basal cell 기저세포

# stratified squamous epithelium in upper aerodigestive tract

keratinized

• vestibule of nose

nonkeratinized

• oral cavity
• pharynx including tonsils(transitional area to respiratory epitheluim)
• laryngeal surface of epiglottis
• false vocal cords=vestibular folds
• true vocal cords

2) 후각 상피 olfactory epithelium

후신경의 신경섬유가 비강내로 돌출

후열부 olfactory fissure

비중격과 중비갑개의 내측 사이에 존재

1. 사골판(사상판)을 덮는 점막 mucosa over cribriform plate
2. 상비갑개 점막 일부part of superior turbinate
3. 상비갑개에 해당하는 반대편 비중격 점막, the septum lying opposite to superior turbinate 　

후각상피의 구성세포

1) 후신경세포 olfactory nerve cells = ciliated olfactory receptors

2) 융모세포 microvillar cells

3) Bowman's gland

4) 지지세포 supporting(sustentacular) cells

5) 기저세포 basal cells

후점막 olfactory mucosa의 특징

• 1 cm2 each side
• 1.5 % of total nasal area

흡기 inspirated air의 특성

• 50 % - pass through middle and inferior meatus
• 15% - flows through the olfactory region

비강내 혈관의 특성 (기능적 구분, functional classification)

1) resistent vessels : determines regional blood flow

• small arteries
• arterioles
• A-V anastotomosis

2) exchange vessels : transport to and from the interstitial fluid

• controlled by pre- and post-capillary sphincters
• capillaries

3) capacitance vessels : determines nasal patency by tones of vessels

• venules
• venes
• cavernous sinusoids

# typical pale look of nasal in chronic rhinitis, allergic and nonallergic is due to constriction of resistance vessels and dilatation of capacitance vessels

# changes of nasal resistance - produced by alterations in the blood flow

• The capillaries drain into a superficial venous system
• The venous sinusoids are a cavernous plexus of large tortuous anastomotic veins without valves.
• The sinusoids receive both arterial and venous blood. The drainage of the sinusoids is regulated by cushion or throttle veins which have a circular muscle coat and an incomplete longitudinal crest.
• They do not close the lumen completely but are able to regulate the flow into the bone through the deep venous plexus.
• The vascular arrangement within the turbinates is often called pseudoerectile because of similarities to the blood supply of the penis.

Blood flow

As the nasal resistance is related to blood flow, rhinometry may be used to assess blood flow indirectly. Capillary leakage may be gauged either by the appearance of labeled albumin in nasal secretion following intravenous injection or by the xenon wash-out method.

코 점막의 구조

• 1. mucosa epthelium(PCCE)
• 2. BM basement membrane 기저막
• 3. lamina propria(submucosa, 고유층)
• 4. small seromucinous gland - 120,000 = 8/mm2
• 5. large serous gland - 250 , anterior part of nose

비강 점액의 특성

점막 표층은 2 중층의 구조로 되어 있으며 상층인 점액층(mucous layer)와 하층인 장액층(pericliary fluid layer)으로 되어 있으며, 이를 mucus blanket 혹은 mucosal blanket이라고 한다 .

두께는 섬모가 약 6 μm정도이고, 섬모의 첨단부에서점액 표층까지의 두께가 약 20 μm 를 넘지 않는다고 한다.

이 섬모의 미세 구조를 보면 6 μm의 길이, 0.3μm의 굵기를 가지고 있으며, 세포당 약 200개의 섬모가 존재한다.

이 섬모안에는 9+2 구조의 미세관(microtubule)을 가지고 있는데, 미세관 주변에는 subfiber A, B, C가 존재하고 subfiber A와 B사이에는 ATPase를 함유한 dynein arm이 있어 섬모운동을 추진 시키게 되어 있으며이외에 탄력 섬유인 nexin 등도 존재한다.

outer paired microtubules - linked together by nexin links

outer pairs - inner and outer dynein arms - ATPase

microtubules become the basal body, the outer pairs become triplets, and the inner pair disappear

MCT(Mucociliary Transport: 점액섬모운동)

　# 섬모의 운동은 빠른 실효기(effective stroke)와 상대적으로 느린 회복기(recovery stroke)으로 구성되어서 periciliary fluid 상측의 점액을 효과적으로 운반하게 된다.

　beat frequency : 10 - 20Hz at body temperature

• Energy is produced by the conversion of ATP to ADP by the ATPase of the dynein arms and the reaction is dependent on Mg2+ ions.
• Motion is initiated by the pair of outer microtubules sliding in relation to each other. ATP is generated by the mitochondria near the cell surface next to the basal bodies of the cilia.
• The mucous blanket is propelled backwards by the metachronous movement of the cilia, which means that only those at right angles to the direction of flow are in phase.
• Initiation of ciliary movement is by mechanicaI action, a reversible domino effect.
• Most mucus passes around the Eustachian orifice and is then swallowed.

The time taken for the cilia to transport mucus may be measured by the progress of saccharin, dye and radiolabelled particles. Saccharin is very inexpensive and is reliable clinically. The time taken is variable and lies between 5 and 20 minutes.

Factors affecting ciliary action

• Drying will stop the movement of the cilia but reversible.
• Temperature will also affect function, with cessation of movement below 10 C and above 45 C.
• Isotonic saline will preserve activity, but solutions(concenturations) above 5% and below 0.2% will cause paralysis.
• Cilia will beat between pH 6.4 and of pH 8.5 for long periods.
• The commonest factor affecting ciliary function in vivo is an upper respiratory tract infection, which may damage the epithelium to such a degree that the surface cells slough away.
• Drugs

acetylcholine increases the rate while adrenaline decreases the rate
ephedrine have not been shown to affect function
cocaine hydrochloride, in solutions above 1O%, causes immediate paralysis
corticosteroids have been shown to reduce the rate of saccharin clearance following one week's therapy

비강 점액내 물질

Nasal secretions

• Nasal secretions are composed of two elements, namely glycoproteins and water with ions.
• The glycoproteins are produced by the mucous glands, and the water and ions are produced mainly from the serous glands and indirectly from transudation from the capillary network.
• There are two secretory cell types in the mixed nasal glands, the mucous and serous cells. The glycoproteins found in mucus are produced in two cell types, the goblet cells within the epithelium and the glandular mucous cells.
• Glandular mucous and goblet cells contain large secretory granules which can be seen as lucent areas on electron microscopy and which contain the acidic glycoproteins.
• Serous cells contain electron dense granules which are discrete; the granules may have material of two densities and the cores of these are of a greater density .
• The serous cells contain neutral glycoproteins, enzymes such as lysozymes, and lactoferin, as well as immunoglobulins of the IgA type class.
• The IgA dimers are conjugated with a secretory components(SC) which is produced in the serous cells. The submucosal glands may be mixed and are arranged around ducts. The anterior part of the nose contains serous glands only in the vestibular region. When stimulated, these glands produce a copious watery secretion. The sinuses have goblet cells and mixed glands although lower in density.

Composition of Mucus

　The water, ions and some enzymes may arise outside the nose, for example in tears, and the watery layer in mucus merges gradually into the more viscous upper layer. The two layers may be considered a sol layer and a gel layer. The gel layer contains more of the glycoproteins which contribute many of the properties of mucus.

table. Nasal secretions

Water and ions from transudation

Glycoproteins

Enzymes

Circulatory proteins: complement

(2-macroglobulin, C-reactive protein

Immunoglobulins

Cells

Glycoproteins form about 80% of the dry weight of mucus

• A single sugar side chain and a polypeptide chain which are linked covalently
• These units are polymerized by disulphide linkages.
• Complexes in secretions may weigh up to 106 daltons. These polymers interact with water and ions to form a gel.

Table. Glycoproteins are classified as neutral or acidic 　

acid glycoproteins

• sialic acid(sialomucins)
• sialomucins can be subdivided by digestion by sialidases or not
• sulphate group(sulphomucins)

neutral glycoproteins

• contain fucose(fucomucins)

The glycoproteins give mucus its two most commonly measured properties, namely viscosity and elasticity.

Proteins in nasal secretion

sources:

from circulation or mucosa or surface cells.

some compounds, such as lactoferrin, are present only in nasal secretions

Lactoterrin

• Present in nasal secretions and is not present in serum.
• Its action is to bind iron in a similar way to transferrin. They both bind two divalent metal ions, particularly iron, and have a molecular weight of 76,000-77,000 daltons.
• Lactoferrin is produced by the glandular epithelium, mainly by the serous cells. Its action of removing heavy metal ions prevents the growth of certain bacteria, in particular Staphylococcus and Pseudomonas spp.

Lysozymes

• These are produced by secretion in the nose from the serous glands, but some originate from tears which gain entry by way of the nasolacrimal duct.
• They are also produced from leucocytes which are found in nasal secretions and mucosa.
• The action of lysozymes is non-specific and depends on the absence of bacterial capsules for effect.

Antiproteases

• A number of different antiproteases have been demonstrated and they increase with infection.

Complement

• C3 - made in the liver, locally by macrophages
• activation by nonspecific ot specific immunological responses

Ion and water

• Na+, Cl-

Immunoglobulins

• mucosal defence, IgA and IgE, have been found to be present in greater quantities than in serum

Surface cells

• These consist of epithelial cells, leucocytes, basophils, eosinophils, mast cells and macro-phages.
• Leucocytes and macrophages are important for phagocytosis on the surface and may help prevent bacterial or viral invasion.
• Cytology of the secretion may help in diagnosis.
• The surface cells migrate through the interstitium from the circulation.

비강의 기능

1) respiration

2) temperature control = warming or cooling

3) humidification

4) filtering = cleaning

5) protecton = local defence

6) reflex organ

7) olfaction

8) resonance

Note:

The nose warms, moistens, and cleans the atmospheric air.

코는 들여마신 공기를 덥히고 습도를 조절하고 먼지를 걸러준다.

1) respiration

코 - 인간에서 유일한 호흡의 생리적 통로

평균적인 비호흡 통계- 생리적 호흡 속도 6 liter/ min

최대 호흡 속도 50 to 70 liter/min

비역 nasal valve, limen nasi

정상인 코에서 가장 단면적이 좁은 부위

nozzle 역할을 한다

이 부위에서의 공기의 속도는 매우 빠르다.

비강내 비역과 하비갑개 앞쪽부위는 diffuser의 역할

= 기류의 속도를 줄이고 turbulence를 늘린다.

기류의 분류 column of air stream

1) laminar flow 판형 기류

2) turbulent flow 와류

흡기류 inspiratory air stream는 비강내의 중앙부를 주로 지나는데 이 때 발생하는 turbulence에 의하여 온도 및 습도의 조절이 비갑개를 포함한 비강 벽과 이루어져 안정된 온도습도의 공기를 허파로 보내게 된다.

이러한 laminar 기류와 turbulent 기류의 비율이 비강 점막의 기능과 상태를 결정하는데 매우 중요하다.

호기류expitatory air stream에 있어서는 비강내의 중앙부를 turbulence가 적게 빠져나가는데 이는 흡기시 보다 호기시에 온도 및 습도 손실을 줄이기 위한 생리적인 기능으로 설명되어 질 수 있다.

코로 숨을 들이 마시고, 입으로 숨을 내뱉는 경우에는 코 점막의 빠른 건조가 올 수 있다.

비저항 nasal resistance

= the difference of pressure between nasal introitus and nasopharynx

비강 초입부와 비인강 사이의 압력차

비호흡의 원활성을 나타내는 값 = 비 폐색(코막힘)의 정도를 나타내는 값

정상 = 8 - 20 mm H2O

> 20 mm H2O - 비역 nasal valves 가 숨 쉴때 커지기 시작한다.

> 40 mm H2O - 구호흡 mouth breathing 을 시작한다.

long term mouth breathing ==> deep seated mucosal changes

mechanical obstruction within the nose

• e. g., septal deviation,
• hypertrophy of the turbinates,
• cicatricial stenoses, etc.,

---> mouth-breathing ---> damaging consequences and mucosal diseases of the nose and nasal sinuses

nasal patency 를 결정하는 요소

1. temperature
2. humidity of the surrounding air
3. position of the body
4. bodily activity
5. changes of body temperature
6. influence of cold on different parts of the body e. g., the feet, hyperventilation
7. psychologic stimuli
8. state of the pulmonary function, of the heart, and of the circulation
9. endocrinologic disorders such as pregnancy, hyper- or hypofunction of the thyroid gland
10. some local, oral, or parenteral drugs, e.g., antihypertensive drugs such as rauwolfia, ephedrine, epinephrine 등

Air flow

The nasal air flovv is very different between rest, and exercise; Most studies have been performed during quiet respiration. The flow is maximal at the centre of the tube and drops towards the edge. Near the boundaries, flow is further retarded by viscosity of the medium, and at the edge it is zero. Pressure changes which result from viscous changes are irreversible - that is energy is used in overcoming viscosity.

If there is a change in velocity then the pressure will also alter. This process is reversible and is described by Bernouilli's equation:

However, because some viscous forces are always active in the nose, the Bernouilli equation is not strictly applicable. The nose has a variable cross-section and therefore the pressure and velocity will alter continuously. The pressure also varies independently during respiration. The inspiratory phase lasts approximately 2 seconds and reaches a pressure of -10 mm H2O, whereas expiration last about 3 seconds and reaches a pressure of 8 mmH2O. The respiratory rate is between 10-18 cycles a minute in adults at rest.

Nasal resistance

the nose = 1/2 of total airway resistance

nasal valve - narrowest part of nose

made by lower edge of upper lateral cartilage, anterior end of inferior turbinate, adjascent nasal septum surrounding soft tissues

EMG dilator naris - contraction during inspiration

loss of innervation - alar collapse

Nasal cycle

The air flow and nasal resistance are modified by mucosal changes. These changes are produced by vascular activity in particular by the veins of the pseudoerectile tissue of the nose (capacitance vessels). The changes are cyclical and occur between every 4 and 12 hours; they are constant for each person. The cycle consists of alternate nasal blockage between passages, which passes unnoticed by the majority of people. The cycle has been known by yogis since antiquity.

The nasal cycle can be demonstrated in over 80% of adults, but it is more difficult to demonstrate in children. It has been shown to be present in early childhood. The cycle may be demonstrated both by rhinomanometry or by thermography. The physiological significance has not been established but, in addition to a resistance and flow cycle, nasal secretions are also cyclical, with an increase in secretions from the side with the greatest air flow.

A number of factors may overcome or modify the nasal cycle; these include allergy, infection, exercise, hormones, pregnancy, fear, emotions generally and sexual activity. The nasal cycle is controlled by the autonomic nervous system and vagal overactivity may cause nasal congestion.

Drugs which block the action of noradrenaline may cause nasal congestion in the same way as hypotensive agents. The anticholinergic effects of antihistamines can block the parasympathetic activity and produce an increase of sympathetic tone, hence an improved airway. Times of hormonal changes, such as puberty and pregnancy, will affect the nasal mucosa. The hormones act directly on the blood vessels.

Estrogens are actively concentrated in nasal tissue, and levels up to a thousand times the serum levels Inave been demonstrated . They also inhibit the function of acetylcholinesterase and so may affect the autonomic sensitivity of the nose as well.

Rhinometry

The nasal air flow is usually measured as a volume flow in litres/minute and plotted against pressure.

2) temperature control - warming

1) 코를 통한 들여마신 공기의 warming은 매우 효과적이다.

2) 들여마신 공기의 온도는 항상 안정되게 유지되어 하기도로 공급된다.

3) 코 점막은 공기를 덥히고 습도를 조절하는 역할

4) 비인강에서의 흡기의 온도는 외부 공기의 영향을 거의 받지 안고 항온성을 유지한다.

= constant at 31_C to 34_C independent of external temperature

5) 당연히 외부 공기온도가 낮으면 비강내에서의 열의 전도가 많아져 항상 하기도로 항온의 공기를 공급

3) humidification

1) 사람이 코의 기능에 불편하지 않게 느끼는 대기의 최적 상대 습도는50% 에서 60% 정도

optimal relative humidity of room air for subjective well-being and function of nasal mucosa

2) 비인강에서는 흡기류가 코에서 물기가 공급되어 80% 에서 85%의 습도를 유지하며, 하기도에서는 더욱 일정하여 95%에서 100%의 습도를 유지

3) water vapor secreted by the entire respiratory tract per 1,000 liters of air can reach 30 g <== 대부분 콧속에서 공급

4) 콧속의 점액층 mucosal blanket은 코 점막이 습기를 공급하면서 물기를 너무 많이 잃어 코 점막이 마르게 되는 것을 방지해 주는 기능도 한다.

Water production

　It is generally assumed that the water from humidification comes directly from the capillaries to the surface epithelium. However, fluorescent studies have shown that, except during acute inflammation, little water comes directly through the surface epithelium, but originates in the serous glands which is extensive throughout the nose. During the nasal cycle, reduction of secretions occurs on the more obstructed side.

Additional water comes from the expired air, the nasolacrimal duct and the oral cavity.

4) filtering function

1) 흡기류에서 foreign bodies, bacteria, dust 등을 걸러 준다.

2) 코안에서만 크기가 4.5 μm 이상되는particles을 85% 이상 제거

3) 그러나 크기가 1 μm 이하의 particles는 5% 만이 코안에서 제거

The nose is able to achieve this level of filtration because of its morphology. The inspired air travels through up to 180 degree and during this time not only the direction but also the velocity changes, dropping markedly just after the nasal valve.

Turbulence encountered in the flow will increase the deposition of particles.

Particles in motion will tend to carry on in. the same direction: the larger the mass, the greater the tendency. The resistance to change in velocity will be greater in irregular particles because of the larger surface area and the number of facets or surfaces.

The nasal hairs(vibrissae) will stop only the largest particles and are therefore relevant only to other organisms, which try to crawl into nose.

5) protection

점액섬모수송 mucociliary transport

정상적인 비강내 섬모수송은외부 물질 및 감염에 대한 주 방어 기전을 하는 비강내 중요한 기능 중의 하나이다.

호흡상피의 섬모의 비강 점액 섬모수송 에 의한 비강내 점액(mucus, secretory film)은 후비공을 통하여 비인강으로 넘어간다.

비강내 filtering에 의해 침착된 이물질들은 점액 상층부의 점액층에 얹어지게 되고, 이러한 이물질들은 끊임없는 점액하층부의 장액층내의 섬모운동에 의하여 마치 conveyer belt 위를 따라 움직이는 화물과 같이 후비공을 향하여 이동하게 된다.

하루에 약 600 - 700 ml의 비즙이 정상적인 환경에서 비강에서 비인강으로 넘어가게 되며, 정상 조건에서는 하비갑개 앞쪽에 위치한 비강내 이물질들은 약 10 에서 20 분 정도면 후비공에 도달한다.

비강의 길이를 약 6 - 7 cm라고 할 때, 비강 점액섬모수송 속도는약 6 - 14 mm/min의 속도를 갖는다 하겠다.

섬모운동의 영향을 주는 인자들

1) cold and dried air - 대기의 온도및상대습도(RH, relative humidity)

2) 체온

3) serotonin, acetylcholin등의 신경전달물질

4) 아황산(SO2)등의 대기오염화학물, 크롬과 니켈등의 중금속

5) 먼지

6) 항원성 흡입물질(allergennic inhaler)

7) 급성 상기도 감염

8) cocaine과 같은 국소마취제등의 약물

9) immotile cilia syndrome(Katagener syndrome) : disturbances mucosal blanket and ciliary activity ---> marked influences on the physiology of the nasal cavity

The nasal mucosa protects the entire body by making contact with and providing resistance against animate and inanimate foreign material in the environment.

# Nasal defense zones can be distinguished in the nasal mucosa

1) mucosal blanket and the epithelium

2) vascular connective tissue of the lamina propria

Resistance factors of the first defensive zone (mucosal blanket 과 epithelium에서의 방어 인자):

(1) physical cleaning by the mucociliary apparatus

(2) nonspecific protective factors in the secretions

• lysozymes
• interferon
• secretory protease inhibitors
• complement system
• secretory glucosidases

(3) specific protective factors

• immunoglobulin A (sIgA) - secretory IgA, superficial protective mechanism
• immunoglobulin M (IgM)
• immunoglobulin G (IgG)

Resistance factors of the second defensive zone (lamina propria에서의 방어 인자):

(1) nonspecific protection factors and structures

• ground substance and fibrils
• micro- and macrophages
• mast cells
• vessels
• autonomic nernous system
• hormones
• interferon
• protease inhibitors
• complement, etc.

(2) specific defensive factors

• sensitized B- and T-lymphocytes
• eosinophil granulocytes
• surface basophils
• immunoglobulin IgG, IgM, and I gE.

6) olfaction

The human sense of smell is poorly developed compared to most mammals and insects.

Despite that, it is still very sensitive in the human and is almost indispensable for the individual.

Functions of Olfaction

1. protection - 경계 vigilance ,Smelling provides warning of rotten or poisonous foods and also of toxic substances e. g., gas, fire.

2. related with psychological state, The sense of smell is particularly important in the feld of psychology: Marked affects may be induced or inhibited by smells.

3. related with taste and appetite, Taste is only partially a function of the taste buds since these can only recognize the qualities of sweet, sour, salty, and bitter. all other sensory impressions caused by food such as aroma and bouquet are mediated by olfaction. This gustatory olfaction is due to the fact that the olfactory substances of food or drink pass through the olfactory cleft during expiration while eating or drinking. The sense of smell can stimulate appetite but can also depress it.

4. related with occupations, A good sense of smell is essential for those in certain occupations, e. g., cooks, confectioners, wine, coffee and tea merchants, perfumers, tobacco blenders, and chemists.

The physician needs a "clinical nose" for making his diagnosis.

5. 생식 - sexual stimulations

후각상피의 구조

The olfactory area of the nose is relatively small.

olfactory cells, i.e., the bipolar nerve cells, sensory cells and first-order neurons.

---> about 20 fibers in the olfactory nerves which run to the primary olfactory center of the olfactory bulb

---> neurons of the bulb run via the olfactory tract to the secondary olfactory center

---> tertiary cortical olfactory field lies in the dentate and semilunate gyri

후각의 기전

The mode of action of the scent molecules on the olfactory cells is not known with certainty. There are numerous current theories of the mechanism of action, including:

1) emission of scent corpuscles

2) selective absorption

3) specific receptors on the sensory cells

4) enzymatic control, molecular vibrations

5) electrobiologic processes such as changes in cell membrane potential, etc.

only volatile substances can be smelled by humans

These substances must be soluble in water and lipids/ only a few molecules suffice to stimulate the sense of smell = 10-15 molecules per ml of air are sufficient stimulation on average to exceed the threshold

about 30,000 different olfactory substances in the atmosphere : humans can perceive about 10,000 and are able to distinguish among 200

adaptation

• The sense of smell, like other senses, demonstrates the phenomenon of adaptation . The sensitivity of the olfactory organ depends also on hunger:
• several olfactory factors can be smelled better if the subject is very hungry than shortly after eating, a very useful physiologic regulation.

abnormalities of smell

Anosmia and hyposmia may be caused by obliteration of the olfactoiy cleft (polyps, etc.), causing respiratory anosmia(conductive anosmia).

• Inability of the olfactory substances in food : drink to pass from the mouth and throat to the olfactory epithelium of the nose because of obstruction of the nasal cavity or the choana is described as gustatory anosmia. 　
• Central anosmia(sensorineural anosmia) is caused by a disorder of the central nervous parts of olfactory system in the presence of a patent airway. Causes include: traumatic rupture of the olfactory nerve, cerebral contusion, and cerebral diseases. 　
• Essential anosmia is due to local damage to the olfactory epithelium, e. g., due to influenza, with an open olfactory cleft.

Sniffing

• The maximum exposure of the olfactory area to the smell is produced by sniffing which causes a turbulent air flow. Animal studies suggest that by increasing the velocity of air flow, the olfactory stimulus is increased.

Stimulus

• Odours are absorbed into the water of the mucus, and the lipid reacts with the lipid bilayer of the receptor cells at specific sites, which causes K+ and CI- to flow out and thus to depolarize the cells. After a latent period of up to 400 ms, a slow compound action potential may be recorded from the olfactory mucosa, and this is called the electro-olfactogram.
• The speed of the rising phase varies with the intensity of the stimulus. The recovery phase or falling phase is an exponential decay with time constant of 0. 9- 1.45 ms.

Threshold

• The olfactory response shows variation in both threshold and adaptation. The threshold concentration can vary depending on the chemical nature of the stimulus. The threshold of perception is lower than identification: that is, a smell is sensed before it is recognized. Threshold values vary widely between studies and they reflect the nature of smell and the different methods of detection. Smell does not have an absolute threshold, but the threshold depends on the level of inhibitory activity which is generated by the higher centres.

Adaptation

• The olfactory response shows marked adaptation:the threshold increases with exposure and recovery of the electro-olfactogram is rapid when the stimulus is withdrawn.

Pathways

• There is no interaction between the individual receptor cells, and receptor cells are connected to the olfactory bulb by non-myelinated nerve fibres.
• These fibres end on olfactory glomeruli; about 25,000 fibres end on each glomerulus, which then acts as an integrator. The conduction time between the receptor cells and the glomerulus is 50 ms for, even though the fibres are slow, they are short. The glomerulus fires with an all or none response into the mitral or tufted cells whose axons transport the signal through the lateral olfactory tract. Inhibition comes from feedback from the high cortical centres.
• Higher centres : to the opposite bulb and to the ipsilateral forebrain through the anterior commissure. The primary olfactory cortex lies rostral to the telencephalon and includes the olfactory tubercle, the prepyriform and preamygdaloid areas. There are projections into the thalamus where they are integrated with taste fibres, and there are also projections to the hypothalamus. Communication between the receptor cell and the brainstem occurs with only two synapses.
• Trigeminal input : Most smell is independent of the trigeminal nerve, but at high concentrations irritation occurs which is a factor in detecting the intensity of certain compounds, such as butyl acetate, and may account for 30% of the odour intensity. Patients who are anosmic can distinguish only sweet, sour, salt and bitter and whether a compound is irritant. The irritant effect cannot be bypassed in normal people and does contribute to the nature of smell. It is important when testing olfaction to use compounds which are not irritant.

Classifications of odours

• There is no satisfactory classification of odours.
• The human being has difficulty in detecting and recognizing variation in intensity of more than  odours. Furthermore, because the human being does not rely on conscious detection of odour, only its quality, training is necessary for scientific experiments and for occupations which require a 'good nose'. An obvious discriminatory mechanism has not been found in the nose at either the receptor site or in the olfactory bulb.
• Some cells in the olfactory bulb increase their discharge rate and some decrease their rate of discharge on stimulation.

Olfactory mucosa morphology 　

• The pattern of the stimulus within the mucosal configuration of the receptor cells detects the nature of the smell. This theory of discrimination is based partly on specific receptor sites and partly on their position within the olfactory mucosa .
• Olfaction may well be an analogue system. A number of different patterns from a few receptor sites would give rise to a large number of different smells.

Olfaction and behaviour

• Olfaction is important in regulating behaviour in all animals, including man and insects. The degree of development depends on the species. Smell is used in four main areas of behaviour: the detection and consumption of food, recognition, territorial markings, and sexual behaviour. In humans, eating and sexual behaviour are highlighted.
• Eating : Olfaction is related to two aspects of eating, namely the recognition of food types and the initiation of digestion. The initiation of digestion is mediated by way of the lateral and ventromedial hypothalamus, and it causes salivation and increases the output of gastric acid and enzymes.
• Sexual behavior : Pheromones were first described in relation to insects. The term was used to describe the chemicals which were produced by glands and were responsible for sexual attraction. They have since been encountered widely in all animals.

  Three types of pheromone have been described, which are releaser pheromones, primer pheromones and imprinting pheromones. Releaser pheromones produce an immediate and reversible response and act through the nervous systems, whereas primer pheromones require prolonged stimulation and act on the anterior pituitary where they cause hormones to be released. Imprinting pheromones, which are chemicals encountered during development, modify behaviour and may subsequently initiate a response.

  The degree of involvement in human behaviour is uncertain but the influence of smell is probably underestimated as most activity occurs at the subconscious level.

7) reflex organ

Specific nasal reflex mechanisms may arise

• Within the nose and affect the nose itself
• From other parts of the body or organs and affect the nose
• In the nose and affect other parts of the body

A reflex system which is obviously confined to the nose but whose purpose is unknown is the nasal cycle.

One cycle lasts between 2 and 6 h. Provided that both halves of the nasal cavity are of normal patency, the lumen widens and narrows alternately, lowering or increasing the respiratory resistance in each half of the nose. However, the resistance of the entire nose remains constant in the ideal case. This reflex phenomenon is controlled by the action of the autonomic nervous system on the cavernous spaces of the vascular system of the nasal mucosa.

# Nasopetal(to the nose) reflexes arise, e. g., from cooling of the extremities, which changes the respiratory resistance. They may also arise from the lungs and bronchi and from other autonomic control points.

# Important nasofugal(from the nose) communications exist between the nose and the lung, the heart and circulation, the metabolic organs, and the genitals.

In addition, there are sneezing, lacrimal, and cough reflexes, and under certain emergency situations, reflex respiratory arrest.

cf) -petal: -으로 향하는

-fugal: -으로부터 오는

Autonomir nervous system

Reflexes

Reflexes may be mediated through the brainstem, but axon reflexes may occur through the sensory nerves alone.

Axon reflexes

Reflexes from nasal stimulae

• Chemical irritation, temperature change and physical stimuli of the nose may all cause widespread cardiovascular and respiratory responses. The degree of the response depends on the intensity of the stimulus, and ranges from sneezing to cardiorespiratory arrest. Sneezing is associated with facial movements, lacrimation, nasal secretions and vascular engorgement. More usually, a change in respiratory rate with closure of the larynx and a variable cardiovascular response occurs.

Nasopulmonary reflexes

• increasing the air flow through one side of the nose is associated withan increased ventilation of the homolateral lung. This follows the nasal cycle.
• Blowing air through the nose will cause the broncheal muscle to relax on the same side and icrease its respiratory activity.

Reflexes acting on the nose

• cutaneous stimulation
• In nasal resistance. Cooling will result in vasoconstriction. Adaptation to both will occur and is followed by rebound. Pressure to the axilla on the dependent side will cause ipsilateral nasal blockage.

8) resonance - influence of the nose on speech

• The nose influences the sound of speech. During the formation of the consonants "m," "n," and "ng," e. g., the air streams through the open nose whereas during the formation of the vowels the nose and the nasopharynx are more or less closed off by the soft palate from the resonating cavity of the mouth and pharyngeal cavity.
• It Is doutful whether the sinuses have any effect on modifying the voice, although they may help with auditory feedback. Transmission of sound through the facial skeleton helps monitor voice quality.