Pharynx and prevertebral region

• Pharynx

  •Upper end funnel shaped at base of skull - joins oesophagus at @C6

  •Mucous membrane – nasal, mouth, larynx, tympanic cavity

  •Ciliated columnar epithelium superiorly to stratified squamous inferiorly

  •Fibrous layer under epithelium – connect to base of skull and into submucous coat of the oesophagus

  •Muscular layer under fibrous layer has almost circular constrictor muscles and longitudinal muscles

  forms the posterior parts of the nasal cavities, the oral cavity and passes posterior to the larynx.
• Divisions

  The pharynx is divided into 3 regions based on their relationship to the surrounding structures. The nasopharynx sits posterior to the nasal cavities (above the soft palate), the oropharynx sits posterior to the mouth (between the soft palate and epiglottis) and the laryngopharynx passes posterior to the larynx to blend with the oesophagus and @C6 vertebral level.

  
• Nasopharynx

  •Behind nasal cavities, above soft palate

  •Roof = sphenoid, occipital and pharyngeal tonsil

  •Floor = soft palate – pharyngeal isthmus

  •Anterior = nasal passages

  •Posterior = roof and C1 level

  •Lateral = auditory/ Eustacian tube, salpingopharyngeal fold

  
• Nasopharynx

  The lateral wall contains the auditory tube (blue arrow on photograph), this is also called the Eustacian tube or the pharyngotympanic tube. It communicates with the middle ear and allows air to pass between the pharynx and middle ear to equalize pressure either side of the tympanic membrane (ear drum). This allows the membrane to move freely in response to sound waves. The tube has cartilage in its walls, which provide attachment for tensor and levator palatini muscles of the soft palate but also for salpingopharyngeus, a longitudinal muscle of the pharynx (shown by the star).

  
• Oropharynx

  •From soft palate to upper border of epiglottis

  •Roof = soft palate

  •Floor = post third tongue, lingual tonsil, glossoepiglottic folds

  •Anterior = mouth

  •Posterior = C2/3 level

  •Lateral  = palatoglossal and palatopharyngeal folds with palatine tonsil

  
• Palate

  Palatoglossus and palatopharyngeus form the arches at the back of the mouth. They are muscles that contribute to movements of the soft palate, tongue and pharynx.

  
• Laryngopharynx

  •Behind larynx and laryngeal opening

  •Anterior = larynx

  •Posterior = C vertebrae 3-6

  •Lateral = supported by thyroid cartilage, aryepiglottic fold and thyrohyoid membrane

  The muscle layers of the laryngopharynx blend inferiorly with the muscular wall of the oesophagus.

  
• Superior constrictor

  •Lower part (post) medial pterygoid plate, hamulus, pterygomandibular ligament, mandible, side of tongue

  •To pharyngeal tubercle of occipital bone, fibrous raphe and middle constrictor

  -Upper fibres pull posterior pharyngeal wall anteriorly to close off nasopharynx

  -Propel food to middle constrictor

  -Pharyngeal plexus (vagus)

  The superior constrictor forms part of the nasopharynx and oropharynx. There are 2 parts to each constrictor muscle, so there is a right and left side of the superior constrictor that meet in the posterior midline in a fibrous join called a raphe.

  
• Superior constrictor

  The pterygomandibular ligament provides attachment for buccinator anteriorly and the superior constrictor posteriorly, effectively closing the oral cavity by being the connection between the lateral wall (buccinator) and the oropharynx. All of the constrictor muscles push a food bolus downwards, but the superior constrictor also raises the pharyngeal wall and pulls it forwards – towards the nasal cavities. This closes the nasopharynx and prevents food passing towards the nose.

  
• Middle constrictor

  •Lower part stylohyoid ligament to greater and lesser cornua of the hyoid bone

  •To raphe but also blend with superior and inferior constrictor

  •Propel food towards inferior constrictor

  •Pharyngeal plexus (vagus)

  
• Inferior constrictor

  •Lamina of thyroid cartilage and cricoid cartilage

  •To raphe and blend with middle constrictor and oesophagus

  •Propel food to oesophagus

  •Pharyngeal plexus (vagus)

  The inferior constrictor contributes to the laryngopharynx, completes the pharynx and joins the oesophagus. It has muscle fibres that pass towards the midline in a similar fashion to the other constrictor muscles but also forms fibres that are more circular in nature.

  
• Inferior constrictor

  The muscle fibres that pass to the midline are called the thyropharyngeus part of the inferior constrictor. The more circular fibres are called the cricopharyngeus part of the inferior constrictor and are thought to help to close the end of the pharynx to prevent air passing into the oesophagus. All of the constrictor muscles receive motor innervation from the vagus nerve, mainly as it forms part of the pharyngeal plexus. Cricopharyngeus receives a different branch of the vagus nerve called the external laryngeal nerve

  
• Longitudinal muscles

  •Stylopharyngeus

  •Base of styloid process of temporal bone to posterior border of thyroid cartilage

  •Across internal carotid artery

  •Passes between superior and middle constrictors

  •Elevates larynx and pharynx during swallowing

  •Glossopharyngeal nerve

  The styloid process of the temporal bone provides the attachment site of stylohyoid, styloglossus and stylopharyngeus muscles (and the stylohyoid ligament).

  
• Salpingopharyngeus – cartilage of auditory tube to blend with palatopharyngeus

  •Elevate pharynx

  •Pharyngeal plexus (vagus)

  Palatopharyngeus – hard palate and palatine aponeurosis to lamina of thyroid cartilage (post)

  •Elevate pharynx

  •Pharyngeal plexus (vagus)

  are salpingopharyngeus which blends with palatopharyngeus to attach onto the thyroid cartilage. Salpingopharyngeus forms a fold in the lateral wall of the nasopharynx and palatopharyngeus forms a fold in the lateral wall of the oropharynx.

  
• Swallowing

  food being molded using the tongue and hard palate then pushed to the back of the mouth by the tongue to be swallowed. The soft palate is then raised, and the pharynx elevated to ensure food passes away from the nasopharynx. The larynx is raised, and the epiglottis passively bends over the larynx as the bolus of food passes it, and the aryepiglottic folds move together to ensure food passes into the laryngopharynx not the larynx.  Waves of muscular contraction push the food along the oesophagus to the stomach.

  
• Otherstructures

  other features of the pharynx, including the pathways taken by the superior laryngeal nerve (through the thyrohyoid membrane) and the recurrent laryngeal nerve (between the oesophagus and trachea then passing inferior to the inferior constrictor of the pharynx).

  
• Ring of lymphoid tissue

  the pharyngeal tonsil, the palatine tonsils and the lingual tonsil form a ring of protective lymphoid tissue around the openings into the nasopharynx and oropharynx. The general sensory innervation to the pharynx is divided between the maxillary division of the trigeminal nerve, the glossopharyngeal nerve (also gag reflex for soft palate) and the vagus nerve.

  
• Pharyngeal plexus

  Glossopharyngeal CN IX, vagus CN X and sympathetic

  CN IX and CNX contribute fibres to the pharyngeal plexus to supply the pharynx. The cranial part of the accessory nerve joins the plexus via the vagus nerve to supply the muscles of the soft palate (except tensor veli palatini CNV3). Sympathetic fibres also join the pharyngeal plexus

  
• Veins

  The pharyngeal veins form a plexus that communicates with the facial and internal jugular veins.

  
• Arteries

  •Pharyngeal branches from the maxillary artery (nasopharynx)

  •Ascending pharyngeal artery from ‘medial’ surface of external carotid

  The upper regions of the pharynx are supplied from branches of the maxillary artery (greater palatine and pharyngeal) and the ascending pharyngeal branch of the external carotid artery.

  
• Lymph

  Lymph drains to retropharyngeal and paratracheal nodes and then to deep cervical nodes.

  
• Pre-vertebral (anterior) muscles

  •Longus colli

  •Longus capitis

  •Rectus capitis anterior

  •Rectus capitis lateralis

  •Other pre-vertebral structures lie between the muscle sheath covering longus colli and longus capitis (prevertebral fascia) and the carotid sheath

  The pre-vertebral structures lie posterior to the pharynx and are composed of muscles and sympathetic ganglia.
• Longus capitis

  •Transverse processes of cervical vertebrae anterior tubercles C3-6 to base of occipital bone

  •Flexion of head

  •Ventral rami cervical spinal nerves C1-3

  
• Longus colli

  •From atlas to T3

  •Inferior oblique, superior oblique and vertical parts

  •Inferior oblique = T2/3 to anterior tubercle of cervical transverse process C5,6

  •Superior oblique = anterior tubercle C3-5 to atlantal anterior tubercle

  •Vertical = anterior aspect T1-3 to C4-6

  •Flexion of neck

  •Rotation to opposite side via inf oblique

  •Ventral rami cervical spinal nerves C2-6

  the inferior oblique fibres also allow rotation of the neck

  
• Rectus capitis anterior and lateralis

  •Anterior from anterior surface and root of transverse process of atlas to occipital bone (ant to occipital condyle)

  •Anterior flex atlanto-occipital joint

  •Lateralis from transverse process of atlas to occipital bone (inf surface of jugular process)

  •Lateralis gives lateral flexion of the head

  •Crossed by internal jugular vein

  •Ventral rami of cervical nerves C1-C2 loop

  
• Sympathetic ganglia

  •From base of skull to join to thoracic chain

  •Chain behind internal and common carotid arteries

  •Medial to vagus nerve

  •Embedded in deep fascia between carotid sheath and fascia over surface of longus capitis and longus colli

  •Superior, middle and inferior cervical ganglia

  
• Superior cervical ganglia

  •Large, immediately below skull

  •Internal carotid nerve (postgang) into carotid canal to form internal carotid plexus

  •Gray rami communicantes to C1-4 ventral rami

  •Branches to form plexus of common and external carotid arteries

  •Cranial nerve branches = CN IX, X, XII

  •Pharyngeal branches join CN IX and CN X in pharyngeal plexus

  •Superior cardiac – plexus in thorax

  This large ganglion gives fibres to wind around the carotid arteries, it contributes to the pharyngeal plexus, and to the cardiac plexus in the thorax.

  
• Middle cervical ganglion

  •Small, at level of cricoid cartilage

  •Related to loop of inferior thyroid artery

  •Gray rami communicantes to C5,6 ventral rami

  •Thyroid branches along artery to gland

  •Middle cardiac branch to cardiac plexus

  •Middle to inferior usually 2 or more nerve bundles – anterior bundle pass anterior to 1st part subclavian artery and then behind it = ansa subclavia

  This small ganglion communicates with C5 and C6 ventral rami, gives branches to the thyroid gland, and the cardiac plexus in the thorax. It forms the ansa subclavia – a loop around the subclavian artery

  
• Inferior cervical ganglion

  •Usually fused with 1st thoracic ganglion to form stellate ganglion

  •Lies behind vertebral artery between transverse process of C7 and head of 1st rib

  •Grey rami communicantes to ventral rami of C7,8

  •Arterial branches to subclavian and vertebral arteries

  •Inferior cardiac branch to cardiac plexus