Special Sub-Topic: Swallowing - Tongue, Palate and Pharynx
|As well as having intrinsic muscles to alter its shape, the tongue has four extrinsic muscles to alter its position. Which of the four extrinsic muscles is NOT supplied by the hypoglossal (XII) nerve?|
Palatoglossus. All of the extrinsic muscles, as their names suggest, arise from structures outside of the tongue, and insert on the tongue itself. All of the intrinsic muscles and the extrinsic muscles (excluding palatoglossus) are supplied by the hypoglossal (XII) nerve, while palatoglossus is supplied by the pharyngeal plexus of the vagus (X) nerve. The integrity of the hypoglossal nerve can be tested in the living by asking the subject to stick out their tongue; deviation to one side means that the nerve is damaged on that side as the tongue on that side is not coming out of the mouth.
|Which of the extrinsic muscles of the tongue pull the tongue forward out of the mouth?|
Genioglossus. Genioglossus arises from the mandible and attaches to the hyoid bone, forming most of the body of the tongue. The muscle has various different levels of fibers with different actions: its superior fibers move the tip of the tongue, the middle fibers depress the tongue, and the inferior fibers are primarily involved in protruding the tongue out of the mouth.
Hyoglossus arises from the hyoid bone, and pulls the sides of the tongue down toward the hyoid. Styloglossus arises from the styloid process of the temporal bone in the skull, and is involved in retracting the tongue back after it has been stuck out. Palatoglossus, arising from the soft palate, mainly pulls the soft palate down to the tongue, but is also involved in retracting the tongue.
|Which of the palates, hard or soft, is able to move up and down?|
Soft & S. The hard palate contains bone and cannot move. The soft palate, however, has no bone and consists of muscle fibers. The levator of the soft palate elevates it, and is innervated by the pharyngeal plexus of the vagus (X) nerve. The tensor muscle contracts to make the soft palate stiff, and is innervated by the mandibular branch of the trigeminal nerve (V3).
|The pharynx is surrounded by three constrictor muscles (superior, middle, and inferior) which, as their name suggests, constrict the pharynx. Onto which structure do these muscles insert?|
Pharyngeal raphe. The constrictors form most of the wall of the pharynx, which is approximately 6 inches long in a human. It lies behind the nose and mouth, and is separated into three parts; nasopharynx, oropharynx, and laryngopharynx. The fibers of each constrictor arise from different places, but all converge on the pharyngeal raphe, a fibrous line of tissue running down the posterior center of the pharynx.
|The lower fibers of the inferior constrictor are tonically (continually) contracted to form the upper oesophageal sphincter. What name is sometimes given to these fibers, as if they formed a separate muscle?|
Cricopharyngeus. Cricopharyngeus is not in fact a separate muscle, but, as the question states, is formed from the lower fibers of the inferior constrictor. The upper oesophageal sphincter opens in swallowing to allow the bolus of food to pass through; it also serves to prevent a backflow of contents from the oesophagus or the stomach into the pharynx.
|Stylopharyngeus arises from the styloid process of the temporal bone in the skull and lies across the pharynx, some of its fibers joining with the constrictors, and some with palatopharyngeus. What is its primary action?|
Elevating the pharynx. Stylopharyngeus travels from the styloid process along the superior constrictor, and moving underneath the middle constrictor at the overlap point between the two constrictors. It is supplied by the glossopharyngeal nerve (IX), and as well as elevating the pharynx during swallowing (which shortens it), it elevates the larynx and pulls the epiglottis up during swallowing and speaking.
|Which muscle contracts during swallowing to prevent the the tongue moving downward?|
Mylohyoid. When food enters the mouth, the tongue is pressed upward against the hard palate, which is ridged to facilitate the breaking up of the food. This food (called a bolus) moves gradually backward to the back of the mouth. To prevent the tongue's depression, a muscle in the floor of the mouth called mylohyoid contracts - you can feel this in yourself. Place your fingers below your chin and swallow; you will feel your mylohyoid muscle contract.
|When the bolus is at the very back of the mouth, which of these does not facilitate its entry into the pharynx?|
Soft palate moving downward. The soft palate actually moves upward when swallowing, engaging with the ridge at the back of the pharynx. Stylopharyngeus contracts to elevate the pharynx; effectively this causes the pharynx to jump up and "grab" the food bolus. Of course, if the food is sitting at the back of the mouth with nothing underneath it, gravity will cause it to fall downward. The uvula helps to close off the nose so that food does not enter it.
|Swallowing causes a certain structure to open due to the contraction of a muscle called salpingopharyngeus. Which structure is this?|
Eustachian tube. Salpingopharyngeus arises from the Eustachian tube in the nose and its fibers blend into the palatopharyngeus in the pharynx. It helps stylopharyngeus in raising the pharynx during swallowing. It is important in equalizing air pressure in the middle ear, which is why swallowing a lot on airplanes helps "pop" your ears.
|Swallowing is an autonomic (involuntary) action.|
f. While swallowing is very difficult to stop when started, thus appearing to be an autonomic action, it is actually voluntary. All the muscles involved are striated voluntary muscle. You can work out it is voluntary as you can choose to swallow even when there is no food in your mouth.
Did you find these entries particularly interesting, or do you have comments / corrections to make? Let the author know!
Send the author a thank you or
Submit a correction