THE PHARYNXprime.edu.pk/infoserver/Dr_Muhammad_Imran_Qureshi/… · · 2017-12-05foundation or...

THE PHARYNX

By

Prof. Dr. Muhammad Imran Qureshi

Introduction

The pharynx is the most cranial end of the foregut.

It extends from the base of the skull down to the lower border of the cricoid cartilage (C6), where it continues into the esophagus.

The internal structure of the pharynx is much like that of the rest of the gut. It is lined by a mucous membrane,

has an intermediate muscle layer, and

has an external fibrous layer called tunica fibrosa. The tunica fibrosa of the pharynx is more often referred

to as Buccopharyngeal membrane or fascia.

Introduction

However, some differences do exist between the pharynx and the rest of the gut.

One of them is the absence of a well defined submucosal layer except in the region immediately inferior to the skull base. Here, a submucosal layer is developed at this site because

here, both side walls of pharynx are devoid of muscle.

This limited submucosal layer of the pharynx is called pharyngobasilar fascia.

A second difference is that in the pharynx, the muscle is striated (not smooth) and is derived from somites associated with the vagus nerve.

Finally, at the sites where the embryonic nasal and oral cavities ruptured into the pharynx, this gut tube misses an anterior wall.

Introduction

Posteriorly, both pharynx and oesophagus are in contact with the prevertebral fascia, which provides a foundation or basis upon which they can freely slide during swallowing and movements of the neck.

The “dead space” between the pharynx and the prevertebral fascia not only allows for free mobility of the pharynx and oesophagus, but also permits the extension of infection from one side of the neck to the other . It continues below into the posterior mediastinum.

The Pharyngobasilar Fascia

Since the muscle does not extend up to the base of the skull; here the immobile wall of the nasopharynx consists of a rigid membrane, the Pharyngobasilar fascia.

This is simply a dense thickening of the submucosa that fills in the gap between the skull and the upper border of the superior constrictor.


The thickening can be traced down to the level of the soft palate, making a fourth but fibrous cup stacked inside the other three.

Its stiffness keeps the nasopharynx always open for breathing, and food does not enter it.

We can trace the attachments of this fascia as follows:


Start from the pharyngeal tubercle, which is a midline thickening. The pharyngeal raphe is attached to it, which receives fibres from the constrictor muscles.

The attachment of the fascia then passes laterally, convex forwards over longus capitis and the back part of the foramen lacerum to the petrous part of the temporal bone just in front of the carotid foramen.

From this point its attachment is to the cartilaginous part of the auditory tube, not to the skull.

Below the orifice of the auditory tube it is attached to the sharp posterior border of the medial pterygoid plate, down to the hamulus.


Suspended from the base of the skull, and sweeping around from one medial pterygoid plate to the other, reinforced posteriorly by the pharyngeal raphe, the pharyngobasilar fascia makes a rigid wall that holds the nasopharynx permanently open for breathing.

The lower edge of the pharyngobasilar fascia lies at the site of Passavant's ridge, level with the hard palate, inside the superior constrictor muscle.

The ridge acts like a purse string on the lower free margin of the pharyngobasilar fascia.

Below this the mucous membrane lies on a loose submucosa.

Divisions

Anatomists divide the pharynx into three regions.

1. The uppermost region lies between the base of the skull and the palate. Because it opens up into the nasal cavities, it is called the nasopharynx. The nasopharynx has no anterior wall

One may consider the back edge of the nasal septum as all that is left of an anterior wall after the nasal cavities rupture into the pharynx during development.

2. Below the palate and above the epiglottis is a region of pharynx that opens forward into the oral cavity. The palatoglossal arches mark the boundary between this oropharynx and the oral cavity.

Divisions

Divisions

Due to the oblique disposition of

the epiglottis, the oropharynx is

taller in front than in back. Like the

nasopharynx, the oropharynx has

not much of an anterior wall.

However, it must be remembered

that the dorsum of tongue is a

curved structure. Its anterior two

thirds faces superiorly, but its

posterior one third faces backward.

Thus, just above the hyoid bone,

the oropharynx has an anterior wall

composed of the posterior third of

the tongue.

Divisions

3. Below the oropharynx is the laryngopharynx.

In embryonic life the laryngotracheal diverticulum

formed as an outpocketing of the anterior wall of the

foregut at the lower end of the pharynx.

The opening into this laryngotracheal diverticulum

was the primitive laryngeal aperture.

The diverticulum grew downward into the chest,

hugging the anterior wall of the esophagus along the

way.

The cranial part of the laryngotracheal diverticulum

becomes the larynx.

Divisions

During its development, “the

larynx” pushes backward

and upward into the lower

part of the pharynx, raising

the laryngeal aperture so

that it lies behind and partly

above the hyoid bone, and

causing the anterior wall of

the lower pharynx to curve

around the sides of the

larynx (hence the pyriform

recesses).

Divisions

Nasopharynx

Oropharynx

Laryngopharynx

Pharyngeal Muscles

The Pharyngeal muscles comprise of:

1. The Constrictors:

The lateral and posterior walls of the pharynx are

composed primarily of the three pharyngeal

constrictor muscles:

1. Superior Constrictor,

2. Middle Constrictor, and

3. Inferior Constrictor.

Pharyngeal Muscles

2. Supplementing small muscles:

1. Stylopharyngeus,

2. Palatopharyngeus, and

3. Salpingopharyngeus

Attachments of Pharyngeal Muscles

Let us revise some of the osteology before the study of the superior, middle, and inferior constrictor muscles.

The diagram shows a few relevant features of the inferior aspect of the skull as seen from the side.

Identify the mastoid process (MP), zygomatic arch (ZA), external auditory meatus (EAM), lateral pterygoid lamina (LPL), medial pterygoid lamina (MPL) (visualized through LPL), pterygoid hamulus (PH) (literally "a little hook", of the MPL).


Identify also the styloid process (SP), hyoid bone with its body (B), lesser horn (LH), and greater horn (GH), The thyroid cartilage (T) has a superior horn (SH), an inferior horn (IH), and an oblique line (OL) on each lamina. The inferior horn articulates with the lamina of the cricoid (ring like) cartilage (CC) to form the cricothyroid joint (CTJ).

Before introducing fibrous connective tissue structures, identify the pterygopalatine fossa (PF) and the posterior wall of the maxillary sinus (PWMS) which forms the anterior wall of the pterygopalatine fossa (PF).


There are four connective tissue structures of significance to understanding the three constrictors:

1. The pterygomandibular ligament (PL);

2. The stylohyoid ligament (SL);

3. The pharyngeal raphe (PR);

4. A tendinous arch (TA) extending between the inferior tubercle on the oblique line of the thyroid cartilage and the arch of the cricoid cartilage.


The Pterygomandibular ligament (PL) is attached to the pterygoid hamulus (PH) of the medial pterygoid lamina and to the posterior end of the mylohyoid line (ML) of the mandible.

Although the mylohyoid line is on the medial side of the mandible it is superimposed on the lateral view of the bone as though the bone were transparent.

Two muscles are intimately related to this pterygomandibular ligament: The Superior Constrictor and

The Buccinator.


The stylohyoid ligament (SL) extends from the tip of the styloid process to the lesser horn of the hyoid bone.

With the greater horn of the hyoid bone, the stylohyoid ligament and lesser horn form an osseo-tendinous angle from which arises the middle constrictor muscle.


The pharyngeal raphe

drops vertically from the

pharyngeal tubercle on the

basiocciput of the skull

base.

All three constrictors

attach to the raphe.


The oblique line, the

tubercle at its inferior end

and the tendinous arch (TA)

between the inferior

tubercle of the oblique line

and the cricoid cartilage

serve as attachments for

the inferior constrictor

muscle of the pharynx.


The tendinous arch (TA) bridges across one of the intrinsic muscles of the larynx, the cricothyroid.

Contraction of the cricothyroid approximates the anterior portion of the two cartilages and tenses the vocal cords. Movement occurs at the cricothyroid joint (CTJ) on each side.


All of the skeletal elements to which the constrictor muscles are attached (e.g., mandible, hyoid bone, thyroid cartilage) are open posteriorly except the cricoid cartilage.

The portion of the inferior constrictor which is attached to the tendinous arch is called the cricopharyngeus muscle.

If it goes into spasm, swallowing can be difficult or impossible because it applies lateral pressure against the posterior surface of the cricoid cartilage and closes this part of the pharynx.


The arrangement of the three pairs of constrictor muscles of the pharynx are likened to three flower pots fitted one inside the other. OR

These muscles overlap posteriorly, being telescoped into each other like three stacked cups

Attachments of Superior Constrictor

The anterior attachment (origin) of the Superior Constrictor is to the lower part of the posterior edge of the medial pterygoid lamina, the pterygoid hamulus, pterygomandibular ligament, and posterior end of the mylohyoid line (ML).

From these origins the fibers pass posteriorly to their insertion into the pharyngeal tubercle (PT) and raphe (PR).

Attachments of Middle Constrictor

The anterior attachment (origin) of the Middle Constrictor is to the stylohyoid ligament, the lesser horn, and the greater horn of the hyoid bone, where these three structures meet to form an acute angle.

From this attachment they pass posteriorly to insert into the pharyngeal raphe.

Attachments of Inferior Constrictor

Anteriorly the Inferior Constrictor arises from the oblique line of the thyroid cartilage and the tendinous arch between the inferior tubercle of the oblique line and the cricoid cartilage (this arches over the cricothyroid muscle). The part of the Inferior Constrictor

attaching to the tendinous arch is called the Cricopharyngeus muscle.

Spasm of these fibers can cause great difficulty in swallowing because the cricoid cartilage is a complete ring.

Gaps between the Constrictors

There is a space between the upper border of the superior constrictor and the base of the skull. Through here passes the cartilaginous part of the auditory tube, the tensor & levator veli palitini muscles and tonsillar branch of ascending pharyngeal artery. The rest of the space is closed by the firm pharyngobasilar fascia.

There is a gap laterally between the superior and middle constrictors. This is plugged by the back of the tongue and traversed by structures that pass from outside the pharynx to inside the mouth, namely stylopharyngeus, the glossopharyngeal nerve and the lingual nerve.

Gaps between the Constrictors

The gap between the middle and inferior constrictors is closed by the thyrohyoid membrane, which joins the hyoid bone to the thyroid cartilage and walls in the laryngeal part of the pharynx at the piriform recess.

Passing through this gap by piercing the membrane are the internal laryngeal nerve and superior laryngeal vessels.

Outer Surface of the Pharynx

The outer surface of the pharynx is covered by the delicate epimysium of the pharyngeal constrictors.

This thin tissue is continuous over the pterygomandibular raphe with the epimysium over buccinator, so it has been called the buccopharyngeal fascia.

The junction between thyropharyngeus and cricopharyngeus near the midline is a potentially weak area of the pharyngeal wall, and through this area (Killian's dehiscence) a pouch of mucosa may become protruded (pharyngeal diverticulum).

As it enlarges the pouch hangs down at the side of the oesophagus, and although it may be called an “oesophageal” diverticulum the origin is above the cricopharyngeus.

Lesser Pharyngeal Muscles

These are the Stylopharyngeus, Palatopharyngeus, Salpingopharyngeus.

These three small pharyngeal muscles have common insertions. Their fibers run more or less longitudinally.

1. The Stylopharyngeus: It is the biggest of all the three. It arises from the medial surface of the styloidprocess (i.e., that surface closest to the pharynx). The fibers pass medially and downward to contact the external surface of the lower fibers of the superior constrictor. The stylopharyngeus then slips deep to the upper border of the middle constrictor and continues deep to it and then to the inferior constrictor all the way to an insertion on the posterior border of the thyroid lamina and the actual connective tissue of the pharyngeal wall.


2. The palatopharyngeus: It arises from the connective tissue of the soft palate and descends almost straight vertically deep to the superior constrictor (thus, separated by it from the stylopharyngeus). At the lower border of the superior constrictor, the palatopharyngeus and stylopharyngeus meet and pass together to a common insertion.

3. The salpingopharyngeus: It arises from the medial end of the cartilaginous auditory tube and descends almost straight vertically deep to the superior constrictor to contact the back edge of the palatopharyngeus and pass with it to join the stylopharyngeus.

Function of Pharyngeal Muscles

The pharyngeal muscles play role in swallowing.

The constrictors are activated in sequence, from top

to bottom, to propel food toward the esophagus.

The longitudinal muscles elevate the larynx and

pharynx at the initiation of the swallow.

Blood Supply and Lymph Drainage

Branches of many arteries take blood to the pharynx:

Ascending pharyngeal, ascending palatine, lingual, tonsillar, greater palatine, the artery of the pterygoid canal, and the superior and inferior laryngeal arteries.

Venous blood is largely collected into the pharyngeal venous plexus which like the nerve plexus is situated at the back of the middle constrictor; it drains to the pterygoid plexus or directly into the internal jugular vein. From the lowest part blood finds its way to the inferior thyroid veins.

Lymph drainage

Lymph passes to retropharyngeal lymph nodes and via these or directly to upper and lower deep cervical groups.

Nerve Supply

For the motor nerve supply of the pharynx the general statement is that all the muscles are supplied by the pharyngeal plexus except for stylopharyngeus, which is the only muscle supplied by the glossopharyngeal nerve.

The cricopharyngeus part of the inferior constrictor may be supplied by the recurrent laryngeal nerve, or have an additional or even sole supply from the external laryngeal.

The cell bodies that supply all six muscles on each side are in the middle part of the nucleus ambiguus, no matter by what named nerves they reach their destination.

Nerve Supply

The pharyngeal plexus lies on the posterolateral wall

of the pharynx, mainly over the middle constrictor,

and is formed by the union of pharyngeal branches

from the vagus and glossopharyngeal nerves and the

cervical sympathetic.

The glossopharyngeal component is purely afferent;

The pharyngeal fibres of the vagus carry some motor

fibres from the cranial part of the accessory nerve as

well as afferent fibres.

The sympathetic element is vasoconstrictor.

Nerve Supply

The mucosa of the nasopharynx is supplied from the

maxillary nerve through the pterygopalatine ganglion,

whose pharyngeal branch reaches the nasopharynx

via the palatovaginal canal.

Most of the oropharynx receives its sensory supply

from the glossopharyngeal nerve, but the vallecula is

supplied by the internal laryngeal nerve, and all the

rest of the pharyngeal mucosa is innervated by the

internal and recurrent laryngeal nerves.

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