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The swallowing process – from mouth to stomach

On this page, you can read about the swallowing process. It is the body’s way of transporting food and drink from the plate to the stomach. It is a sophisticated process preprogrammed in the brain, involving both muscles and nerve pathways.

What is the swallowing process?

The swallowing process is a sequence of events that occurs from just before we put a bite of food or a sip of liquid in our mouths until it lands in the stomach. In between, there are many small moments to navigate, and a total of 148 muscles that must function flawlessly.

The swallowing process can be divided into four phases. The first phase starts from the moment we see and smell the food until we put it in our mouths. The second phase is when the food is in the oral cavity, where we chew it.

In these first two phases, we have control over the muscles. We can decide how our teeth should chew the food and how the tongue moves. But when the food is in the mouth, it stimulates nerves that signal the muscles further down in the body that food is on the way. These muscles start preparing to receive the food.

In the third phase, the food is in the throat. There is much happening here that we do not consciously control. For instance, the larynx rises, and the epiglottis falls over the windpipe to prevent food and drink from entering the lungs.

The final phase is the food’s journey through the esophagus and into the stomach. Here, too, there are muscles beyond our control. These include the ones that open the esophagus mouth in the throat, the muscles that help transport the food through the esophagus, and those that open the stomach mouth below the diaphragm so that the food can finally reach the stomach.

The phases of the swallowing process

The body’s swallowing process is constantly active. On average, we swallow about 600 times a day, including 350 times during the day, 200 times during meals, and 50 times during sleep. Therefore, significant problems arise when the swallowing process does not function properly.

Phase 1: The Pre-Oral Phase

The swallowing process begins with the pre-oral phase. It involves transporting food from the plate to the mouth using hands and any utensils. Even here, our eyes and sense of smell inform the body that food is on its way to the stomach, and certain systems start working.

Phase 2: The Oral Phase

The Oral Phase, when the food is inside the mouth, is voluntary and controlled from the cerebral cortex. It occurs when the piece of food enters the mouth. During this phase, we chew the food. As soon as the chewed food passes the front palate towards the throat (pharyngeal phase or swallowing phase), the swallowing reflex takes over, which is controlled from the brainstem.

Both phases, the oral and pharyngeal phases, are, however, dependent on the so-called sensorimotor reflex arc. In other words, signals are sent via sensory inputs such as taste, pressure, touch, and temperature up to the brain (via afferent nerve pathways) and down to the muscles (via efferent nerve pathways).

  1. Brain stem: controls non-voluntary “unconscious” automatic functions such as breathing, blood pressure, heart rhythm, the reflex swallowing phases; and also functions as a communication node between the cerebrum, the cerebellum, the spinal cord and the peripheral nervous system.
  2. Cortex: controls our voluntary “conscious” most advanced functions such as language, thinking, fine-motor skills and the voluntary swallowing phases.
  3. Cerebellum: co-ordinates our movements, our balance and our ability to act in response to our immediate surroundings.
  4. Corpus callosum: connects the two brain hemispheres’ cortex areas with each other. It consists of some 200 to 800 million nerves that co-ordinate the activities of the brain’s two hemispheres

Based on the afferent signals from the oral cavity to the brainstem, the brain can control breathing and swallowing, as well as muscles in the face, mouth, esophagus, diaphragm, down to the stomach, intestines, and to the rectum. This rapid connection to the brain is crucial for controlling the entire swallowing process and is also the key to accessing the vital functions mentioned above in the human body.

How the brain works

Before moving on to the other stages of swallowing, we’ll describe more detailed how the brain works here:

In the brain stem we find the Nucleus Tractus Solitarius (NTS), the afferent nucleus. The NTS is the core that gathers all incoming sensory signals from the oral cavity and pharynx via the afferent nerve pathways, and transmits them either to the brain’s cortex or directly to the network-like system in the brain stem called the Formatio Reticularis (FR).

In the FR the afferent signals from the NTS and the cortex are first interpreted and then passed through various distribution nodes on to the efferent nuclei:

  1. Nucleus Ambiguus
  2. Nucleus Dorsalis Nervi Vagi.

These efferent nuclei, in their turn, send impulses to the appropriate muscles and glands – the effect organs – that are to be activated. How these function during swallowing we will explain in more detail below.

In the FR there are three of these distribution nodes (swallowing centres) that are key to the swallowing process; and also a number of other centres that control, amongst other functions: breathing, chewing, coughing, vomiting, evacuation of the bowels and bladder, and those muscles that control the body’s posture.

Phase 3: The Pharyngeal Phase

The pharyngeal phase, also known as the swallowing phase, is reflex-controlled.

When the chewed food reaches the front palate, the swallowing reflex takes over. This causes the larynx to rise, and at the same time, as the tongue begins its backward movement, the epiglottis falls over the windpipe, allowing the food to pass through the throat. This phase lasts for 0.5-1 second.

The pharyngeal phase in the swallowing process.
The Pharyngeal Phase in the Swallowing Process

Coordination between breathing and swallowing

The coordination between breathing and swallowing is essential to avoid food ‘going down the wrong pipe’.

Breathing and swallowing are guided by different centres in the brain stem. However, all the muscles that are active in these two functions are controlled from the same concentrated grouping of specialised nerve cells, nucleus, in the brain stem. This means that for a couple of breaths during the act of swallowing, the swallowing centre takes control.

To prevent food being ingested into the air pathway, the body ‘holds its breath’ for two seconds, thus twice as long as it takes for the swallow to pass the pharynx (see the Pharynx phase, as described above). When the oral phase signals that swallowing is underway, the body breathes in.

During the subsequent exhalation, the food portion is driven to the back of the tongue and the exhalation stops and the body holds his or her breath for two seconds. The swallow then passes the pharynx and breathing is resumed with a continued exhalation.

This exhalation, which is controlled by one of the brain’s swallowing centres, drives aromas up into the nose and the olfactory nerves, which is crucial for the smell and taste experience. Only now, after this has happened passed, does the person breathe in again.

Phase 4: The Esophageal phase

The fourth and final part of the swallowing process is the phase where the food is transported through the esophagus down into the stomach.

The esophagus’ longitudinal musculature is now activated, forming a stiff pipe and allowing the entrance to the upper esophagus – esophageal sphincter or the Posterior Esophageal Sphincter (PES) – to relax and open to allow the passage of the food portion into the esophagus.

At the same time the entrance to the lower esophagus – Lower Esophagus Sphincter (LES) or the upper stomach mouth – opens to complete the transfer of the food to the stomach[2,4] This phase takes around 7 seconds to complete.

As well as the outer longitudinal layer of muscles, the esophagus has also an inner layer of circular musculature. To transport the food down to the stomach, the circular muscles produce coordinated wave motions – peristaltic waves. This explains why we can swallow even when we are lying down.

The muscle function and the downwards transport of the food mass is controlled by the Vagus nerve and a branch of the Glossopharyngeal nerve. Together these nerve pathways build a local network in the esophagus Plexus Pharyngeus. There are two different types of muscle in the esophagus: voluntary skeletal striated muscles and involuntary smooth muscles:

  • The voluntary musculature is the same type as we have in our arms and legs: so-called skeletal striated muscles which are attached to the skeleton or tissue, and that are voluntarily controlled. They can be trained for increased strength and performance and can react quickly, but have relatively short term endurance.
  • The smooth musculature has better long term endurance, but works relatively slowly. They cannot be controlled voluntarily but are instead controlled by the autonomic nervous system: functioning unconsciously and involuntarily. These muscles are stimulated via one of the three motor neurons in the brain stem which send signals to the involuntary musculature. Read more about this under the heading above: “The signals down to the muscles and glands are conducted via motor neurons in the brain stem”.[7]

The esophagus’ upper third consists of skeletal striated muscles, the middle third is a mixture of skeletal striated muscles and smooth musculature, and the bottom third is solely smooth muscle. [6]

The four nerv pathways in the mouth

The structure of the chewed food or drink, its taste, temperature, and contact with the lips, cheeks, throat, as well as the tongue’s contact with the palate and front palate, stimulate the sensory nerves in the oral cavity. These nerves send information to the brainstem via the sensory, upward-transmitting afferent nerve pathways. The four sensory nerves, known as cranial nervs (CN) are:

  • Trigeminus (CN 5)
  • Facialis (CN 7)
  • Glossopharyngeus (CN 9) och
  • Vagus (CN 10)
The four sensory nerves in the oral cavity stimulated by IQoro.
The four nerves in the mouth

The function of the three swallowing centres

The NTS in the brain stem, which gathers all incoming signals from the oral cavity and the pharynx, sends a part of this information directly to the first of the three swallowing centres in the brain stem, whilst the remainder of the information continues upwards to the cortex to be processed before being switched back to the first swallowing centre.

First swallowing centre

If the combination of the information received from these two sources is interpreted as that something is to be swallowed, for example a piece of food, this instruction is sent to the second swallowing centre.

Second swallowing centre

The second swallowing centre transmits signals to the muscles via the motor nerves – the downward-transmitting efferent nerve pathways. Here there is a pre-programmed ‘go/no-go’ response: ‘swallow’ or ‘don’t swallow’ – a so-called stereotypical muscle reponse.

When something is to be swallowed the command is sent first to the Nucleus Ambiguus (NA) an efferent nucleus which, in its turn, sends the instruction to swallow to the major components of the swallowing musculature via the motor, downward-transmitting, efferent nerve pathways. Concurrently, the impulses are also sent to the third swallowing centre.

The five motor nerves that are important for swallowing are: CN Trigeminus, Facialis, Glossopharyngeus, Vagus and Hypoglossus. The first four are both sensory (afferent) and motor (efferent) nerve pathways which send information both to and from the brain.

Third swallowing centre

The third swallowing centre transmits information to the Nucleus Dorsalis Nervi Vagi (NDNV) an efferent nucleus, and then onwards to the esophagus’ musculature to complete the swallowing action and to transport the food portion downwards to the stomach.

Important nerv signals

The nerves can be thought of as cables that contain various fibres, motor neurons, that conduct signals to the muscles and glands. [6] In the brain stem there are three different kinds of motor neurons that are important in the act of swallowing:

  1. General Somatic Efferent (GSE)
    The GSE transmits signals onwards to the tongue’s and the eyes’ voluntary musculature, (skeletal striated muscles).
  2. Special Visceral Efferent (SVE)
    The SVE transmits signals to the voluntary musculature in the mouth, chewing muscles, facial musculature, pharynx, larynx, esophagus and diaphragm. Note however that the neurological connection to the diaphragm is somewhat more complex.
  3. General Visceral Efferent (GVE)
    The GVE transmits signals to the glands, blood vessels and smooth muscles in the pharynx, stomach and rectum.

The signal pathways from the above-named motor neurons are:

  • CN (V) Trigeminus – signals via the SVE
  • CN (VII) Facialis – signals via the SVE and the GVE
  • CN (IX) Glossopharyngeus – signals via the SVE and the GVE
  • CN (X) Vagus – signals via the SVE
  • CN (XII) Hypoglossus – signals via the GSE

The sum of all the above signals to the brain stem set off a pre-programmed cooperation between all 148 muscles that are involved in the transport of each food bite from the mouth down to the stomach.

Reference sources

  1. Svensson, P. (2008) I Hartelius, L., Nettelbladt, U. & Hammarberg, B. (red.). Logopedi. Lund: Studentlitteratur.
    (English translation, “Speech therapy”)
  2. Logemann, J.A. (ProEd) (1998). Evaluation and treatment of swallowing disorders(2nd) Austin, Texas: San Diego College
  3. O’Neill, P.A. (2000). Swallowing and prevention of complications. British medical bulletin, 56(2), 457-65.
  4. Tibbling-Grahn L, broschyr 03 Svenska Dysfagiförbundet, Stoppar maten upp i bröstet när du äter? Mellangärdesbråck – En vanlig matstrupssjukdom i alla åldrar., (PDF).
    (English translation, “Does food get stuck in your chest when you eat? Hiatus hernia – a common medical condition in people of all ages”)
  5. Kjellén G, Tibbling L. Manometric oesophageal function, acid perfusion test and symptomatology in a 55-year-old general population. Clinical Physiology. 1981; 1:405-15
  6. Ekberg O, (2011), Röntgendiagnostiska avdelningen, Universitetssjukhuset MAS, Malmö, Normal sväljning inclusive anatomi och fysiologi, (PDF). Downloaded 2015-12-05 
    (English translation, ”Normal swallowing including anatomy and physiology”)
  7., (2016), Muskler och senor, Downloaded 2016-09-20–halsa/sa-fungerar-kroppen/muskler-och-senor/
    (English translation, ”Muscles and sinews”)