Swallowing

Question 1

What are the 4 phases of swallowing?

Answer 1

1) Preparatory phase
2) Oral phase
3) Pharyngeal phase
4) Oesophageal phase

Question 2

where is the sequence of activity of swallowing preprogrammed? What happens when swallowing begins? Where is the part that is devoted to swallowing and how many cranial nerves are involved?

Answer 2

Sequence of activity is preprogrammed by specific neural centres called swallowing centres:
lies in the brainstem (medulla)

Once the centre is triggered, the neural circuit controls the action of swallowing which is almost an entirely involuntary process

Neural circuit requires:
– integrated activity of a large area of the brainstem
– involvement of six cranial nerves
– numerous receptors and muscles

Question 3

With the four phases of swallowing and which are conscious/voluntary or unconscious/involuntary?

Answer 3

1) Preparatory phase
2) Oral phase
3) Pharyngeal phase
4) Oesophageal phase

First two voluntary, second two involuntary.

Question 4

What is the 1) preparatory phase?

Answer 4

carries on from the end of the mastication of the food

involves the formation of a food bolus in the midline of the oral cavity

Question 5

What is the 2) oral phase?

Answer 5

• involves the active propulsion of the bolus from the oral cavity into the pharynx – 0.5 sec
• fast, strong force

Question 6

What is the 3) pharyngeal phase?

Answer 6

• food bolus is moved from the oro-pharyngeal location into the top of the oesophagus – 0.7 sec

Question 7

What is the 4) oesophageal phase?

Answer 7

• here the bolus is transported through the oesophagus into the stomach – takes about 3 secs for liquids; about 10 secs for foods.

Question 8

How does the preparatory phase begin? And how is the rest carried out?

Answer 8

The first stage of swallowing begins with the tip of the tongue pressing up against the anterior maxillary incisors (or against the hard palate)

Before swallowing commences, the bolus of food is moved to the midline and to the dorsum of the tongue

The lips are generally closed

If there is a cleft palate, the food will go into the nasal cavity!!

Question 9

Where is the bolus found in the preparatory phase? How does the posterior part of the tongue help? What is the seal that is called?

Answer 9

bolus is found in central depression of tongue

• posterior part of tongue presses up against soft palate to help prevent bolus from escaping
• forms a seal called the glossopalatal sphincter.

Question 10

In the oral phase what does the anterior two thirds of the tongue do? Then what does the base of the tongue do?

Answer 10

When the oral phase starts, the anterior two thirds of the tongue elevates propelling the bolus towards the oropharynx.

The base of the tongue moves downward and forward (expands the hypopharynx) and the food drops into a chute-like region.

Question 11

In the pharyngeal phase, what happen with the teeth? Then what does the posterior of the tongue do?

Answer 11

Normally the upper and lower teeth come into contact during the swallow as the food passes into the pharynx.

The pharyngeal phase involves the posterior part of the tongue acting like a piston to ram the bolus into the the hypopharynx at the top end of the oesophagus.

At this point the airway is closed off, this is important because you could aspirate food. It’s important that diaphragm muscles are inhibited at the same time that the muscles of swallowing are firing.

Question 12

In the pharyngeal phase what do contracts to assist in squeezing the food in to the oesophagus? then what happens?

Answer 12

The pharyngeal constrictors now begin to contract in a sequential contraction series to assist in squeezing the food into the oesophagus.

As it passes through the pharynx, the bolus elongates – making it easier to swallow

Question 13

In the pharyngeal phase, what happens to the larynx?

Answer 13

larynx is closed off through the epiglottis flapping over the laryngeal opening directing the food into the piriform sinuses

larynx elevates to close off the opening and the glottis muscles contract to seal off the trachea.

larynx is closed off through the epiglottis flapping over the laryngeal opening directing the food into the piriform sinuses

larynx elevates to close off the opening and the glottis muscles contract to seal off the trachea.

Flow of bolus down lateral side channels of pharynx.

Question 14

In the oesophageal phase what happens? When is it complete?

Answer 14

The oesophageal phase involves the opening of the upper oesophageal sphincter, followed by peristaltic contractions of the oesophagus to assist the bolus on its way to the stomach.

This last phase is completed when the lower oesophageal sphincter opens to allow passage of food into the stomach.

Question 15

What does pressure have to do with the oesophageal phase?

Answer 15

There are set pressure changes associated with some of these events.

At the beginning the pressure in the mouth is close to atmospheric

As the food is moved into the hypoharynx, the presure can rise to over 100 cm of H2O

The upper oesophageal sphincter is normally at a resting pressure of 16 – 60 cm of H2O
The oesophagus is at a negative pressure (due to the pleural cavity)

This negative pressure helps to push the food down into the esophagus.

Relaxation of upper sphincter occurs in conjunction with action of the pharyngeal constrictors

Once bolus passes the upper sphincter, it contracts at a pressure of 70 – 100 cm of H2O for 2 –4 secs to prevent reflux.

The lower oesophageal sphincter is normally kept at a resting pressure of about 10 cm of H2O

If there is an issue with this, you can get reflux.

Once the food has moved to the lower end of the oesophagus, it relaxes for about 3 secs to allow food to pass into the stomach and then closes at a pressure of ~ 20 – 35 cm of H2O.

If lots of food, will remain relaxed (open) till the last swallow completed and bolus passed.

Question 16

What are facultative and obligate muscles?

Answer 16

There are 31 pairs of muscles involved in the 4 phases of swallowing

During the preparative and oral stages, there are groups of muscles called facultative muscles that fire. These do not necessarily have to be active to initiate a swallow. they help to swallow, there can be disruption in these but you can still swallow.

During the pharyngeal phase there is a group of muscles involved called the obligate muscles – these are always activated during a swallowing sequence.
They have to be activated for you to be able to swallow.

Question 17

What are the facultative muscles?

Answer 17

(Muscles of mastication)

Mandibular muscles (medial pterygoid; masseter and temporalis) are often involved in stabilizing the mandible (stabilizes the base of the tongue)

Facial muscles (Orbicularis oris, buccinator) help control the lips and cheeks – develop a seal.

the tongue is also involved, anything that is involved in getting the bolus to the midline.

Question 18

Does it matter what you are swallowing for what muscles are active?

Answer 18

Yes, if you are swallowing saliva and water, the anterior temporalis and masseter will not be activated.
In other words more muscles are activated if you are eating more food.

Question 19

What are the obligate muscles?

Answer 19

Pharyngeal phase is complex. Set of muscles called the leading complex show activity in the obligate group at the beginning of a swallow. (Fig 11-8)

Can clearly see that there are a programmed sequence of contractions and inhibitions over a 1 – 2 sec period.

These obligate muscles are programmed from before birth

Question 20

What is the inhibition of various muscles for swallowing?

Answer 20

Most of the pharyngeal constrictors are actively inhibited prior to contraction. This allows the squeezing effect from superior to inferior.

Also, the diaphragmatic muscles are actively inhibited during these pharyngeal and oesophageal phases. Prevents inspiration of food/fluid into the trachea.

Question 21

For central control what are the six cranial nerves?

Answer 21

Trigeminal (V) - trigeminal sensory nucleus, sometimes you can’t swallow because of the feeling (think of survivor and people gagging up things)

Facial (VII)
Glossopharyngeal (IX)
Vagus (X)
XII (hypoglossal)

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Question 22

What does the brainstem do?

Answer 22

Coordinates the control of the swallowing mechanism and the order of firing of muscles needed.

Question 23

What is the swallowing center three components?

Answer 23

There are three components for this swallowing control centre.

Sensory input – from the oral cavity; the pharynx, larynx and oesophagus is conveyed to the nucleus tractus solitarius and the trigeminal sensory nucleus

Interneuronal connections – a series of excitatory and inhibitory interneurons (reticular formation) that co-ordinate and finely control the series of contractions through feedback

Question 24

What are the motor nuclei for the swallowing center?

Answer 24

Motor Nuclei
– specific motor nuclei in the brainstem that control various muscle groupings

trigeminal motor nucleus 	- Nerve V
facial motor nucleus	- Nerve VII
hypoglossal motor nucleus- Nerve XII
nucleus ambiguus		- Nerve IX, X
spinal cord			- Nerves C1, C2

Question 25

What are the muscles controlled? (don’t have to memorize this)

Answer 25

V - Mylohyoid, Temporalis, Masseter, Lat & Medial Pterygoids, Ant. Digastric, Tensor levator Palati

VII – Stylohyoid, Facial muscles, Post. Digastric

XII – Tongue muscles (intrinsic – hyo, genio and styloglossus), Geniohyoids, Thryrohyoids

Nuc. Ambiguus – Constrictors, Oesophagus, Arytenoids, Cricothyroids, Levator veli palati, Salpingopharyngeus, Palatopharyngeus, Palatoglossus,