How Does the Brain Control Swallowing?

Getty Images/ Joos Mind

Believe it or not, swallowing is one of the most complicated tasks that your body performs. A coordinated job carried out by the brain, the nerves and the muscles, swallowing requires almost no deliberate thought.

Swallowing occurs in three sequential phases that require the carefully coordinated function of muscles in the mouth, pharynx, larynx, and esophagus. These muscles are all under the control of a group of nerves that are called cranial nerves.

The cranial nerves are 12 pairs of nerves that emerge from the brainstem. They control functions such as smelling, tasting, swallowing, vision, eye movements, face movements, balance and shoulder shrugging. Several of the cranial nerves are involved with controlling the coordination and movements involved in chewing and swallowing.

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 Centers In the Brain

The voluntary initiation of swallowing takes place in special areas of the cerebral cortex of the brain, which is the area that commands the brain's functions. The regions of the cerebral cortex that command swallowing are located in the precentral, posterior-inferior, and frontal- gyri.

These structures of the cerebral cortex send orders via nerve axons that travel through a nerve pathway called the corticobulbar tract to a swallowing center in the medulla, which is part of the brainstem.

Sensory Nerves

Nerve signals originating in the mouth receive input about the food we are chewing. Several sensory nerves in the mouth, pharynx, and larynx bring information to the brain that allows us to know what type of material is in the mouth and throat. For instance, they "tell" the brain about the size, temperature, and texture of food.

This information is sent to the sensory cortex of the brain, and the medulla integrates with the sensory information in order to direct the efforts of the muscles of chewing, which work together to chew the food.

Nerves Involved in Swallowing

The act of chewing changes the food into a softer and more slippery food bolus that is suitable and safe for swallowing. As the swallowing reflex advances through its different phases, the nerves involved in swallowing trigger the reflexive closing of the larynx and the epiglottis. This closing off of the 'windpipe'  prevents food and liquid particles from entering the lungs.

If the windpipe dies not properly close off, or if swallowing is not well coordinated, problems such as choking can occur. Another complication of swallowing problems, aspiration pneumonia, can happen if food enters the lungs. This may happen as the result of a stroke or other neurological disorders.

The following sensory nerves are involved in swallowing:

  • Trigeminal (cranial nerve V)
  • Facial (cranial nerve VII)
  • Glossopharyngeal (cranial nerve IX)
  • Vagus (cranial nerve X)

The muscles of swallowing are controlled by several cranial nerves 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 see, there are multiple areas of the central nervous system which, if affected by a stroke or another neurological condition, could disrupt the ability to swallow.

The medulla is a relatively small area of the brainstem that contains multiple structures that are critical in carrying out the swallowing reflex. Strokes or tumors that involve the medulla are especially likely to cause swallowing problems. In fact, people with medullary strokes may require temporary or permanent feeding tube placement to prevent choking and dangerous complications of swallowing impairment.

A Word From Verywell

Swallowing is an important bodily function that is more complicated than most people realize. A number of neurological conditions, such as stroke, multiple sclerosis, bells palsy and dementia, have a significant impact on swallowing. When swallowing function is impaired, complications such as choking and aspiration pneumonia can result.

You might have a speech and swallow evaluation after a stroke, and also as part of the evaluation of other neurological problems that affect the muscles that control swallowing.  You might need to make adjustments to the types of food and liquids that you consume in order to make it easier for you to safely swallow. Sometimes, sleeping with a pillow that keeps you propped up can help prevent you from choking or aspirating on saliva during sleep. A variety of exercises and techniques can help you manage your swallowing problems, so you will be able to avoid these complications.

Living with swallowing problems certainly adds a complication to your life, but there are well designed techniques that can help you safely adapt to swallowing difficulties.

Sources

Treatment Effects for Dysphagia in Adults with Multiple Sclerosis: A Systematic Review, Alali D, Ballard K, Bogaardt H, Dysphagia. 2016 Oct;31(5):610-8

Continue Reading