HC 2 Physiology

Question 1

Explain the “chambers” and “sphincters” in this part of the alimentary tract.

Answer 1

Oral cavity + oropharynx + esophagus = a series of expanding and contracting chambers, divided by muscular sphincters: m. orbicularis oris, soft palate & UES

Question 2

How is the propulsion of the bolus towards the stomach being established?

Answer 2

It’s a result of

• forces or positive pressure developed behind the belous
• vacuum or negative pressure developed in front of the bolus

Question 3

Which phases do we see in the act of deglutition?

Answer 3

1. preparatory phase
2. oral phase
3. pharyngeal phase
4. esopagheal phase

Question 4

Explain the preparatory phase. What is done? Where? Voluntarily or involuntarily?

Answer 4

• Preparation of the bolus:
• mastication
• mixing with saliva
• dividing for transport
• voluntary, can be interrupted at any time
• in the first chamber of the swallowing system: the oral cavity, between orbicularis oris (1st sphincter) and soft palate (2nd sphincter)

Question 5

Which facial muscles, tongue muscles and mastication muscles play a role in the bolus preparation?

Answer 5

* facial muscles: maintaining bolus on the the tongue and between the teeth:

• buccinator: contraction to keep bolus between teeth, to prevent food from pooling in the cheek pockets
• orbicularis oris: prevent spilling from mouth corner

* tongue muscles: movement & positioning of the bolus

• intrinsic muscles: alter shape and tone of the tongue
• extrinsic muscles: movement of the tongue (up, down, left, right,…)
• sensory function: information about the bolus size/consenstency,…

° mastication muscles: masseter, temporatlis, pterygoideus lateralis, pterygoideus medialis

Question 6

Explain the position of the tongue and soft palate during preparatory and oral phase. Why?

Answer 6

1. preparatory phase: to keep the bolus from escaping prematurely into the pharynx:

• posterior part tongue up against soft palate
• soft palate pushes downward

2. oral phase: to close off the nasopharynx and open the pharynx

• top of the tongue on the superior alveolar ridge behind maxillary central incisors
• voluntary opening pharynx: posterior part tongue depresses, soft palate elevates

Question 7

Explain the importance of saliva

Answer 7

• mucous: lubricates the bolus
• enzyme for digestion
• dilutes the bolus
• maintaining healthy oral tissues

=> 1-1.5 liter per day

Question 8

Explain the oral phase. What is done? Volutary or involuntary?

Answer 8

• propulsion of bolus from oral cavity to pharynx
• start = voluntary

Question 9

What muscles are involved in the oral phase and why?

Answer 9

• levator veli palatini: elevation soft palate => close nasopharynx (to avoid bolus going upward into nasopharynx, to avoid escape of air pressure), open pharynx
• hyoglossus + styloglossus: depression posterior tongue => open pharynx
• pharyngeus constructor superior: more forceful closure of the nasopharynx
• orbicularis oris + buccinator: maintain oral air pressure
• mylohyoid: early hyoid elevation as a preparation to the pharyngeal phase

Question 10

Explain the pharyngeal phase. What is done? Voluntary or involuntary? Biggest challenge?

Answer 10

• passage of food through the pharynx into the esophagus
• involuntary and irreversable mechanism
• challenge: coordination of respiration and swallowing

Question 11

When does the pharyngeal phase start and end?

Answer 11

• onset:
• tongue -> bolus into oropharynx
• mandibular muscles stabilize tongue base
• mandible closed
• pharynx elevates + contracts = descending peristaltic wave
• end:
• soft palate and hyoid return to original position
• larynx is reopened for respiration

Question 12

Explain the mechanism in which the bolus is driven from the oropharynx into the PE segment

Answer 12

Oropharynx closed at time of bolus passage

+ pressure of tongue

+ contraction pharyngeal walls

=> tongue driving force that drives the bolus downwards

SIMULTANUOUSLY:

• suprahyoid muscles pull hyoid and larynx up and forward => hypopharynx expands => pressure decreases in PE segment => bolus is sucked into PE segment
• gravity

Question 13

Which mechanisms protect the airway during swallowing? In what phase of the swallowing act?

Answer 13

In the pharyngeal phase:

• hyoid and larynx rise + pulled forward
• closure of vocal folds
• epiglottis folds down (because of 1. elevation hyoid and larynx and 2. contraction of thyrohyoid muscles)

Question 14

How does the larynx protect the airway?

Answer 14

From below upward:

1. true vocal folds
2. vestibular folds
3. lower vestibule
4. upper vestibule

Question 15

What systems are needed to open the PES?

Answer 15

1. laryngeal elevation (elevate cricoid and thyroid cartilages)
2. bolus driving forces
3. cricopharyngeal relaxation (inhibition of tonic contraction of PE segment) by brainstem

Question 16

The oropharyngeal phase is a complex sequence of ….? How is it triggered and controlled?

Answer 16

… excitatory and inhibitory events, less then 1 sec.

Triggered and controlled by a group of neurons in the reticular formation of the brainstem = “central pattern generator” = drives a sequence of complex and repetitive movements

Question 17

In which systems is the central pattern generator divided?

Answer 17

1. afferent input system: sensory signals from receptors in the muscles and mucosa of the pharynx to the generator
2. efferent system corresponding to the motor outputs: excitatory and inhibitory signals to the muscles of the oropharynx
3. organizing system

Question 18

Explain the afferent input to the central pattern generator

Answer 18

= 3 cranial nerves provide peripheral sensory feedback: trigeminal, glossopharyngeal, vagus (SLN superior laryngeal nerve)

• stimulation of sensory receptors in pharynx by the posterior movement of the bolus initiates the involuntary pharyngeal phase
• this afferent input modulates the central network activity: the swallowing muscle sequence is the same, but is adapted to bolus constistency and size

Question 19

What is thought to initiate the involuntary pharyngeal phase?

Answer 19

Stimulation of sensory receptors in the pharynx by the posterior movement of the bolus

Question 20

What is the nucleus tractus solitarius?

Answer 20

• in brainstem
• all afferent fibers involved in initiating or facilitating swallowing converge here
• fibers of glossopharyngeus (IX) and SLN (X)

Question 21

Why do scientist think that also higher cortical input influences the coordination of swallowing by the central pattern generator?

Answer 21

• many of the neurological disorders do not involve the brainstem
• swallowing can be initiated voluntarily (dry swallow) without stimulation of the pharynx by a bolus

=> a widespread network of brain regions (cortex, subcortex, insula, cerebellum) participate in the control of swallowing

Question 22

Which cranial nerves contain the main motor nuclei of the brainstem?

Answer 22

• hypoglossal (XII) -> tongue muscles
• ambiguus (X) -> larynx, pharynx, esophagus

Question 23

What are brainstem interneurons?

Answer 23

• Connect sensoric input and motoric output (programming and coordination)
• Connect multiple areas of the brainstem and other areas in CNS => integration of swallow and airway-protective reflexes

Question 24

Explain the esophageal phase. What is done? Voluntary or involuntary? How is it modified?

Answer 24

• bolus transported down the esophagus into the stomach
• involuntary
• peristaltic wave of contraction: variable speed and strength based on sensory feedback (bolus characteristics)

Question 25

What's the difference between primary and secondary wave?

Answer 25

- primary = normal starting wave, starting from top - secondary = peristalsis without a preceding oropharyngeal phase, in response to stimulation of esophageal sensory receptors (e.g. due to bolus size)

Question 26

Explain the neural control of the esophagus

Answer 26

- smooth muscle contraction controlled by autonomic nervous system - striated muscle contraction controlled by the motonuclei of the brainstem (nucleus ambiguus, n. X) - excitatory and inhibitory input to the muscles

Question 27

Which cranial nerves are involved in sensory/motor input/output during swallowing?

Answer 27

zie 'nerves swallowing act'