The Respiratory System in the Head and Neck The Nose



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The Respiratory System in the Head and Neck

The Nose

The nose consists of the external nose and the nasal cavity, both of which are divided by a septum into right and left halves.


External Nose

The external nose has two elliptical orifices called the nostrils, which are separated from each other by the nasal septum. The lateral margin, the ala nasi, is rounded and mobile.

The framework of the external nose is made up above by the nasal bones, the frontal processes of the maxillae, and the nasal part of the frontal bone. Below, the framework is formed of plates of hyaline cartilage.


Blood Supply of the External Nose

The skin of the external nose is supplied by branches of the ophthalmic and the maxillary arteries. The skin of the ala and the lower part of the septum are supplied by branches from the facial artery.


Nerve Supply of the External Nose

The infratrochlear and external nasal branches of the ophthalmic nerve (CN V) and the infraorbital branch of the maxillary nerve (CN V).


Nasal Cavity

The nasal cavity extends from the nostrils in front to the posterior nasal apertures or choanae behind, where the nose opens into the nasopharynx. The nasal vestibule is the area of the nasal cavity lying just inside the nostril. The nasal cavity is divided into right and left halves by the nasal septum. The septum is made up of the septal cartilage, the vertical plate of the ethmoid, and the vomer.


Walls of the Nasal Cavity

Each half of the nasal cavity has a floor, a roof, a lateral wall, and a medial or septal wall.


Floor

The palatine process of the maxilla and the horizontal plate of the palatine bone.


Roof

The roof is narrow and is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones, in the middle by the cribriform plate of the ethmoid, located beneath the anterior cranial fossa, and posteriorly by the downward sloping body of the sphenoid.


Lateral Wall

The lateral wall has three projections of bone called the superior, middle, and inferior nasal conchae. The space below each concha is called a meatus.


Sphenoethmoidal Recess

The sphenoethmoidal recess is a small area above the superior concha. It receives the opening of the sphenoid air sinus.



Superior Meatus

The superior meatus lies below the superior concha. It receives the openings of the posterior ethmoid sinuses.


Middle Meatus

The middle meatus lies below the middle concha. It has a rounded swelling called the bulla ethmoidalis that is formed by the middle ethmoidal air sinuses, which open on its upper border. A curved opening, the hiatus semilunaris, lies just below the bulla. The anterior end of the hiatus leads into a funnel-shaped channel called the infundibulum, which is continuous with the frontal sinus. The maxillary sinus opens into the middle meatus through the hiatus semilunaris.

The middle meat is continuous in front with a depression called the atrium, Below and in front the atrium, and just within the nostril, is the vestibule. This is lined by modified skin and possess short curved hair.
Inferior Meatus

The inferior meatus lies below the inferior concha and receives the opening of the lower end of the nasolacrimal duct, which is guarded by a fold of mucous membrane.


Medial Wall

The medial wall is formed by the nasal septum. The upper part is formed by the vertical plate of the ethmoid and the vomer. The anterior part is formed by the septal cartilage. The septum rarely lies in the midline, thus increasing the size of one half of the nasal cavity and decreasing the size of the other.


Mucous Membrane of the Nasal Cavity

The vestibule is lined with modified skin and has coarse hairs. The area above the superior concha is lined with olfactory mucous membrane and contains nerve endings sensitive to the reception of smell. The lower part of the nasal cavity is lined with respiratory mucous membrane. A large plexus of veins in the submucous connective tissue is present in the respiratory region.




Function of Warm Blood and Mucus of Mucous Membrane

The presence of warm blood in the venous plexuses serves to heat up the inspired air as it enters the respiratory system. The presence of mucus on the surfaces of the conchae traps foreign particles and organisms in the inspired air, which are then swallowed and destroyed by gastric acid.


Nerve Supply of the Nasal Cavity.

The olfactory nerves from the olfactory mucous membrane ascend through the cribriform plate of the ethmoid bone to the olfactory bulbs. The nerves of ordinary sensation are branches of the ophthalmic division (V1) and the maxillary division (V2) of the trigeminal nerve.




Blood Supply to the Nasal Cavity

The arterial supply to the nasal cavity is from branches of the maxillary artery, one of the terminal branches of the external carotid artery. The most important branch is the sphenopalatine artery. The sphenopalatine artery anastomoses with the septal branch of the superior labial branch of the facial artery in the region of the vestibule. The submucous venous plexus is drained by veins that accompany the arteries.


Lymph Drainage of the Nasal Cavity

The lymph vessels draining the vestibule end in the submandibular nodes. The remainder of the nasal cavity is drained by vessels that pass to the upper deep cervical nodes.


The Paranasal Sinuses

The paranasal sinuses are cavities found in the interior of the maxilla, frontal, sphenoid, and ethmoid bones. They are lined with mucoperiosteum and filled with air; they communicate with the nasal cavity through relatively small apertures. The maxillary and sphenoidal sinuses are present in a rudimentary form at birth; they enlarge appreciably after the eighth year and become fully formed in adolescence.


Drainage of Mucus and Function of Paranasal Sinuses

The mucus produced by the mucous membrane is moved into the nose by ciliary action of the columnar cells. Drainage of the mucus is also achieved by the siphon action created during the blowing of the nose. The function of the sinuses is 1_ to act as resonators to the voice; 2_ they also reduce the weight of the skull. When the apertures of the sinuses are blocked or they become filled with fluid, the quality of the voice is markedly changed.


Maxillary Sinus

The maxillary sinus is pyramidal in shape and located within the body of the maxilla behind the skin of the cheek. The roof is formed by the floor of the orbit, and the floor is related to the roots of the premolars and molar teeth. The maxillary sinus opens into the middle meatus of the nose through the hiatus semilunaris.


Frontal Sinuses

The two frontal sinuses are contained within the frontal bone. They are separated from each other by a bony septum. Each sinus is roughly triangular, extending upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit. Each frontal sinus opens into the middle meatus of the nose through the infundibulum.


Sphenoidal Sinuses

The two sphenoidal sinuses lie within the body of the sphenoid bone. Each sinus opens into the sphenoethmoidal recess above the superior concha.


Ethmoid Sinuses

The ethmoidal sinuses are anterior, middle, and posterior and they are contained within the ethmoid bone, between the nose and the orbit. They are separated from the latter by a thin plate of bone so that infection can readily spread from the sinuses into the orbit. The anterior sinuses open into the infundibulum; the middle sinuses open into the middle meatus, on or above the bulla ethmoidalis; and the posterior sinuses open into the superior meatus.



Paranasal Sinuses and Their Site of Drainage Into the Nose

Sinus

Site of Drainage




Maxillary sinus

Middle meatus through hiatus semilunaris




Frontal sinuses

Middle meatus via infundibulum




Sphenoidal sinuses

Sphenoethmoidal recess




Ethmoidal sinuses




    Anterior group

Infundibulum and into middle meatus




    Middle group

Middle meatus on or above bulla ethmoidalis




    Posterior group

Superior meatus




Note that maxillary and sphenoidal sinuses are present in rudimentary form at birth, enlarge appreciably after the eighth year, and are fully formed in adolescence.







Crossing of Air and Food Pathways in the Pharynx

It is in the pharynx that the air and food pathways cross. This is made possible by the presence of the soft palate, which serves as a flap-valve. This flap shuts off the mouth from the oropharynx, for example, during the process of chewing food so that breathing may continue unaffected. The completely raised soft palate can shut off the nasopharynx from the oropharynx, thus preventing food entering the nasopharynx in swallowing. When it is desirable to direct the maximum amount of air in and out of the larynx, the soft palate is raised to direct air through the mouth rather than the narrow cavities of the nose. Such an arrangement permits the expectoration of mucus from the respiratory system through the mouth. It also allows the maximum expiration of air through the mouth as in the use of wind instruments such as the trumpet.


The Larynx

The larynx is an organ that provides a protective sphincter at the inlet of the air passages and is responsible for voice production. It is situated below the tongue and hyoid bone and between the great blood vessels of the neck and lies at the level of the fourth, fifth, and sixth cervical vertebrae. It opens above into the laryngeal part of the pharynx, and below is continuous with the trachea. The larynx is covered in front by the infrahyoid strap muscles and at the sides by the thyroid gland.



The framework of the larynx is formed of cartilages that are held together by ligaments and membranes, moved by muscles, and lined by mucous membrane.
Cartilages of the Larynx

  • Thyroid cartilage: This is the largest cartilage of the larynx and consists of two laminae of hyaline cartilage that meet in the midline in the prominent V angle (the so-called Adam's apple). The posterior border extends upward into a superior cornu and downward into an inferior cornu. On the outer surface of each lamina is an oblique line for the attachment of muscles.

  • Cricoid cartilage: This cartilage is formed of hyaline cartilage and shaped like a signet ring, having a broad plate behind and a shallow arch in front. The cricoid cartilage lies below the thyroid cartilage, and on each side of the lateral surface is a facet for articulation with the inferior cornu of the thyroid cartilage. Posteriorly, the lamina has on its upper border on each side a facet for articulation with the arytenoid cartilage. All these joints are synovial.

  • Arytenoid cartilages: There are two arytenoid cartilages, which are small and pyramid shaped and located at the back of the larynx. They articulate with the upper border of the lamina of the cricoid cartilage. Each cartilage has an apex above that articulates with the small corniculate cartilage, a base below that articulates with the lamina of the cricoid cartilage, and a vocal process that projects forward and gives attachment to the vocal ligament. A muscular process that projects laterally gives attachment to the posterior and lateral cricoarytenoid muscles.

  • Corniculate cartilages: Two small conical-shaped cartilages articulate with the arytenoid cartilages. They give attachment to the aryepiglottic folds.

  • Cuneiform cartilages: These two small rod-shaped cartilages are found in the aryepiglottic folds and serve to strengthen them.

  • Epiglottis: This leaf-shaped lamina of elastic cartilage lies behind the root of the tongue. Its stalk is attached to the back of the thyroid cartilage. The sides of the epiglottis are attached to the arytenoid cartilages by the aryepiglottic folds of mucous membrane. The upper edge of the epiglottis is free. The covering of mucous membrane passes forward onto the posterior surface of the tongue as the median glossoepiglottic fold; the depression on each side of the fold is called the vallecula. Laterally the mucous membrane passes onto the wall of the pharynx as the lateral glossoepiglottic fold.

Membranes and Ligaments of the Larynx

  • Thyrohyoid membrane: This connects the upper margin of the thyroid cartilage to the hyoid bone. In the midline it is thickened to form the median thyrohyoid ligament. The membrane is pierced on each side by the superior laryngeal vessels and the internal laryngeal nerve, a branch of the superior laryngeal nerve.

  • Cricotracheal ligament: This connects the cricoid cartilage to the first ring of the trachea.

  • Quadrangular membrane: This extends between the epiglottis and the arytenoid cartilages. Its thickened inferior margin forms the vestibular ligament, and the vestibular ligaments form the interior of the vestibular folds.

  • Cricothyroid ligament: The lower margin is attached to the upper border of the cricoid cartilage. The superior margin of the ligament, instead of being attached to the thyroid cartilage, ascends on the medial surface of the thyroid cartilage. Its upper free margin, composed almost entirely of elastic tissue, forms the important vocal ligament on each side. The vocal ligaments form the interior of the vocal folds (vocal cords). The anterior end of each vocal ligament is attached to the thyroid cartilage, and the posterior end is attached to the vocal process of the arytenoid cartilage.

Inlet of the Larynx

The inlet of the larynx looks backward and upward into the laryngeal part of the pharynx. The opening is wider in front than behind and is bounded in front by the epiglottis, laterally by the aryepiglottic fold of mucous membrane, and posteriorly by the arytenoid cartilages with the corniculate cartilages. The cuneiform cartilage lies within and strengthens the aryepiglottic fold and produces a small elevation on the upper border.


The Piriform Fossa

The piriform fossa is a recess on either side of the fold and inlet. It is bounded medially by the aryepiglottic fold and laterally by the thyroid cartilage and the thyrohyoid membrane.


Laryngeal Folds

Vestibular Fold

The vestibular fold is a fixed fold on each side of the larynx. It is formed by mucous membrane covering the vestibular ligament and is vascular and pink in color.


Vocal Fold (Vocal Cord)

The vocal fold is a mobile fold on each side of the larynx and is concerned with voice production. It is formed by mucous membrane covering the vocal ligament and is avascular and white in color. The vocal fold moves with respiration and its white color is easily seen when viewed with a laryngoscope.

The gap between the vocal folds is called the rima glottidis
or glottis. The glottis is bounded in front by the vocal folds and behind by the medial surface of the arytenoid cartilages. The glottis is the narrowest part of the larynx and measures about 2.5 cm from front to back in the male adult and less in the female. In children the lower part of the larynx within the cricoid cartilage is the narrowest part.
Cavity of the Larynx

The cavity of the larynx extends from the inlet to the lower border of the cricoid cartilage, where it is continuous with the cavity of the trachea. It is divided into three regions:



  • The vestibule, which is situated between the inlet and the vestibular folds

  • The middle region, which is situated between the vestibular folds above and the vocal folds below

  • The lower region, which is situated between the vocal folds above and the lower border of the cricoid cartilage below

Sinus of the Larynx

The sinus of the larynx is a small recess on each side of the larynx situated between the vestibular and vocal folds. It is lined with mucous membrane.




Saccule of the Larynx

The saccule of the larynx is a diverticulum of mucous membrane that ascends from the sinus. The mucous secretion lubricates the vocal cords.


Muscles of the Larynx

The muscles of the larynx may be divided into two groups: extrinsic and intrinsic.


Extrinsic Muscles

These muscles move the larynx up and down during swallowing. Note that many of these muscles are attached to the hyoid bone, which is attached to the thyroid cartilage by the thyrohyoid membrane. It follows that movements of the hyoid bone are accompanied by movements of the larynx.



  • Elevation: The digastric, the stylohyoid, the mylohyoid, the geniohyoid, the stylopharyngeus, the salpingopharyngeus, and the palatopharyngeus muscles

  • Depression: The sternothyroid, the sternohyoid, and the omohyoid muscles

Intrinsic Muscles

Two muscles modify the laryngeal inlet:



  • Narrowing the inlet: The oblique arytenoid muscle

  • Widening the inlet: The thyroepiglottic muscle

Five muscles move the vocal folds (cords):

  • Tensing the vocal cords: The cricothyroid muscle

  • Relaxing the vocal cords: The thyroarytenoid (vocalis) muscle

  • Adducting the vocal cords: The lateral cricoarytenoid muscle

  • Abducting the vocal cords: The posterior cricoarytenoid muscle

  • Approximates the arytenoid cartilages: The transverse arytenoid muscle

The details of the origins, insertions, nerve supply, and action of the intrinsic muscles of the larynx are given in Table below.


Intrinsic Muscles of the Larynx

Muscle

Origin

Insertion

Nerve Supply

Action

Muscles Controlling the Laryngeal Inlet

Oblique arytenoid

Muscular process of arytenoid cartilage

Apex of opposite arytenoid cartilage

Recurrent laryngeal nerve

Narrows the inlet by bringing the aryepiglottic folds together

Thyroepiglottic

Medial surface of thyroid cartilage

Lateral margin of epiglottis and aryepiglottic fold

Recurrent laryngeal nerve

Widens the inlet by pulling the aryepiglottic folds apart

Muscles Controlling the Movements of the Vocal Folds (Cords)

Cricothyroid

Side of cricoid cartilage

Lower border and inferior cornu of thyroid cartilage

External laryngeal nerve

Tenses vocal cords

Thyroarytenoid (vocalis)

Inner surface of thyroid cartilage

Arytenoid cartilage

Recurrent laryngeal nerve

Relaxes vocal cords

Lateral cricoarytenoid

Upper border of cricoid cartilage

Muscular process of arytenoid cartilage

Recurrent laryngeal nerve

Adducts the vocal cords by rotating arytenoid cartilage

Posterior cricoarytenoid

Back of cricoid cartilage

Muscular process of arytenoid cartilage

Recurrent laryngeal nerve

Abducts the vocal cords by rotating arytenoid cartilage

Transverse arytenoid

Back and medial surface of arytenoid cartilage

Back and medial surface of opposite arytenoid cartilage

Recurrent laryngeal nerve

Closes posterior part of rima glottidis by approximating arytenoid cartilages






Mucous Membrane of the Larynx

The mucous membrane of the larynx lines the cavity and is covered with ciliated columnar epithelium. On the vocal cords, however, where the mucous membrane is subject to repeated trauma during phonation, the mucous membrane is covered with stratified squamous epithelium.


Nerve Supply of the Larynx

Sensory Nerves

  • Above the vocal cords: The internal laryngeal branch of the superior laryngeal branch of the vagus

  • Below the level of the vocal cords: The recurrent laryngeal nerve

Motor Nerves

All the intrinsic muscles of the larynx except the cricothyroid muscle are supplied by the recurrent laryngeal nerve. The cricothyroid muscle is supplied by the external laryngeal branch of the superior laryngeal branch of the vagus.


Blood Supply of the Larynx

  • Upper half of the larynx: The superior laryngeal branch of the superior thyroid artery

  • Lower half of the larynx: The inferior laryngeal branch of the inferior thyroid artery

Lymph Drainage of the Larynx

The lymph vessels drain into the deep cervical group of nodes.






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