In turn, cranial nerves are controlled by “processing centers” in the brain where information related to swallowing is processed. These centers include areas located in the cerebral cortex, the medulla oblongata, and the cranial nerve nuclei.
Swallowing CentersThe voluntary initiation of swallowing takes place in special brain areas located in the precentral, posterior-inferior, and frontal- gyri. These structures send orders via axons that travel inside a nerve bundle called the corticobulbar tract, to a third swallowing center in the medulla.
The latter integrates these orders with information carried by several sensory nerves in the mouth, pharynx and larynx, in order to deliver final orders to the muscles that carry out the swallowing reflex.
Sensory NervesNerve signals originating in the mouth bring information to the brain about the food we are chewing. For instance they "tell" the brain about the size, temperature and texture of food. This information directs the efforts of the muscles of chewing which work together to generate a food bolus that is suitable for swallowing. As the swallowing reflex advances through its different phases, these nerves trigger the reflexive closing of the larynx and the epiglottis, which prevent food and liquid particles from entering the lungs.
Here are the sensory nerves involved in swallowing:
- Trigeminal (cranial nerve V)
- Facial (cranial nerve VII)
- Glossopharyngeal (cranial nerve IX)
- Vagus (cranial nerve X)
Cranial Nerve NucleiThe muscles of swallowing are controlled by several cranial nerve nuclei. These are:
- The nucleus ambiguous (of the vagus and glossopharyngeal nerves)
- The dorsal motor nucleus (of the vagus nerve)
- The hypoglossal nucleus (of the hypoglossal nerve)
How Is Swallowing Affected by Stroke?As you can gather from the information written above, there are multiple areas of the central nervous system which, if affected by a stroke, could disrupt the ability to swallow. This is especially true for strokes of the medulla, as this is a relatively small area that contains multiple structures that are critical in carrying out the swallowing reflex. In fact, people with medullary strokes frequently require temporary or permanent feeding tube placement.
Richard Snell; Clinical Anatomy Fifth Edition; Little Brown and Company; 1995