Anatomy and Function of the Soft Palate and Pharynx

Exam Tip: Pay close attention to the nerve supply of the Tensor Veli Palatini. While most soft palate muscles are supplied by the X and XI cranial nerves, the Tensor Veli Palatini is supplied by the third part of the fifth cranial nerve (V3).

The Pharynx

The pharynx is a muscular tube that can be categorized into three parts: the nasal pharynx, the oral pharynx, and the laryngeal pharynx. The muscles of the pharynx are divided into two functional groups: those that constrict the tube and those that elevate and dilate it.

Pharyngeal Constrictors

There are three pairs of constrictor muscles: the superior, middle, and inferior constrictors. All three insert into a midline tendon in the posterior throat wall known as the median raphe, and they overlap one another at this insertion point.

1. Superior Pharyngeal Constrictor: Originates from the medial pterygoid plate, the hamular process, and the alveolar processes of the mandible and maxilla. It inserts into the base of the skull and constricts the upper pharynx to force contents downward.
2. Middle Pharyngeal Constrictor: Originates from the upper part of the hyoid bone and the stylohyoid ligament. It inserts into the median raphe and constricts the pharyngeal opening to push food toward the esophagus.
3. Inferior Pharyngeal Constrictor: Originates from the posterior part of the thyroid cartilage of the larynx. It also inserts into the median raphe and constricts the lower end of the pharynx to force food into the esophagus.

Pharyngeal Elevators and Dilators

To receive food, the pharynx must widen and lift. This is achieved by several muscles:

• Palatopharyngeus: Technically a muscle of the soft palate, it also serves to elevate the pharynx.
• Stylopharyngeus: Originating from the medial side of the styloid process, it inserts into the lateral pharyngeal wall and the thyroid cartilage. It is the primary pharyngeal dilator, responsible for the dilation and elevation of the pharynx.
• Salpingopharyngeus: This muscle originates from the end of the auditory tube in the nasal pharynx and blends with the palatopharyngeal muscle. It lifts the pharyngeal wall during swallowing.

Functional Integration: Speech and Swallowing

The true complexity of these muscles is revealed during coordinated actions like speech and swallowing.

Speech

To speak clearly, we must pull the soft palate up and back to contact the posterior pharyngeal wall. This is primarily the job of the levator veli palatini and the muscles of the uvula. If the soft palate cannot adapt well to the pharyngeal wall—for example, due to enlarged adenoids—speech may take on a nasal sound.

Swallowing

Swallowing is a multi-step process involving the tongue, palate, and pharynx:

1. Bolus Preparation: The tongue moves up and back, shifting the food bolus into the oral pharyngeal area.
2. Sealing the Nasal Cavity: Muscles of the soft palate raise the posterior end to contact the pharyngeal wall, narrowing the fauces.
3. Pharyngeal Dilation: Elevators and dilators lift and widen the pharynx to receive the bolus.
4. Peristaltic Movement: The constrictors compress the oral pharynx and push the bolus down into the laryngeal pharynx.
5. Airway Protection: As food moves, some pharyngeal muscles elevate the thyroid cartilage of the larynx, and the epiglottis shields the laryngeal opening to ensure food enters the esophagus rather than the airway.

Summary of Nerve Supplies

Most muscles of the soft palate and pharynx are supplied by the X (Vagus) and XI (Accessory) cranial nerves. However, there are important exceptions to remember for clinical and anatomical accuracy:

• Tensor Veli Palatini: Supplied by the V3 (third part of the Trigeminal nerve).
• Stylopharyngeus: Supplied by the IX (Glossopharyngeal) nerve.