Respiratory Anatomy

Question 1

What cranial nerve innervates the posterior one-third of the tongue and carries the sensation of taste?

Answer 1

The glossopharyngeal nerve (cranial nerve IX) provides sensory innervation of the posterior one-third of the tongue and carries taste sensations

Question 2

What cranial nerve innervates the anterior two-thirds of the tongue and carries the sensation of taste?

Answer 2

The facial nerve (cranial nerve VII) provides sensory innervation of the anterior two-thirds of the tongue and carries taste sensations.

Question 3

What is the primary function of the larynx? What are two other functions?

Answer 3

The primary function of the larynx is to protect the lungs from aspiration of foreign material. The larynx also functions in respiration and in phonation.

Question 4

**What muscle acts as a barrier to regurgitation in the conscious subject?

Answer 4

In the awake subject, the cricopharyngeus muscle is the primary muscular barrier to regurgitation.

Question 5

**There are 9 laryngeal cartilages, three paired, three unpaired (single). Identify and group the 9 laryngeal cartilages by paired and single. Can you list the cartilages encountered, in order from superior to inferior, from an anterior view?

Answer 5

The 3 unpaired laryngeal cartilages are the epiglottis, thyroid, and cricoid. The 3 paired laryngeal cartilages are the arytenoids, cuneiforms, and corniculates. The 9 laryngeal cartilages encountered from superior to inferior are: epiglottis, thyroid, cuneiform (paired), corniculate (paired), arytenoids (paired), and cricoid.

Question 6

**Which intrinsic muscles close the laryngeal inlet (laryngeal vestibule)?

Answer 6

The aryepiglottic muscle pair closes the laryngeal inlet— they are sphincters of the laryngeal vestibule.

Question 7

Identify the muscles that abduct and adduct the vocal cords.

Answer 7

The posterior cricoarytenoids abduct (open) the cords; the lateral cricoarytenoids adduct (close) the cords.

Question 8

What intrinsic laryngeal muscle dilates the cords?

Answer 8

The key to answering this question is interpreting the word “dilates”. If “dilates” means that the space between the cords widens (the cords abduct), the answer is the posterior cricoarytenoids.

Question 9

Which muscle tenses the vocal cords? Will the voice go up or down in pitch when the cords are tensed?

Answer 9

The cricothyroid muscle lengthens (tightens or tenses) the vocal cords. The voice will go up in pitch when the cords are tensed.

Question 10

What muscle relaxes the vocal cords?

Answer 10

The thyroarytenoid relaxes the cords.

Question 11

What nerve provides sensation below the cords? What nerve provides sensation above the cords?

Answer 11

The recurrent laryngeal nerve, which is a branch of the vagus, provides sensation below the cords. The internal branch of the superior laryngeal nerve, which also is a branch of the vagus, provides sensations above the cords.

Question 12

What nerve provides sensation to the anterior and posterior surfaces of the epiglottis?

Answer 12

The internal branch of the superior laryngeal nerve supplies sensory fibers to the anterior and posterior surfaces of the epiglottis.

Question 13

**Laryngospasm is caused by stimulation of which nerve?

Answer 13

Stimulation of the superior laryngeal nerves may cause laryngospasm.

Question 14

What muscles are involved in laryngospasm? What motor (efferent) nerve is involved?

Answer 14

The cricothyroids are the muscles involved in laryngospasm. The cricothyroids adduct and tense the true vocal cords. Laryngospasm is mediated by the external branch of the superior laryngeal nerve. The external branch of superior laryngeal nerve provides motor innervation to the cricothyroid muscle.

Question 15

Injury to what nerve will prevent the vocal cords from coming together? What intrinsic laryngeal muscles are involved?

Answer 15

When the recurrent laryngeal nerve is damaged, the paralyzed vocal cord assumes a position intermediate between the abducted and adducted states. The paralyzed cord cannot adduct. The lateral cricoarytenoid causes adduction of the cords.

Question 16

What are the muscles of inspiration? What is the most important muscle of inspiration?

Answer 16

The muscles of inspiration are the diaphragm and the external intercostals. The diaphragm is the most important muscle of inspiration.

Question 17

**What percentage of a tidal volume breath is contributed by the diaphragm in the upright subject during quite breathing (eupnea)?

Answer 17

The answer is controversial. Stoelting states that the diaphragm accounts for approximately 75% of air that enters the lung during spontaneous respiration, without respect to position. Levitzky states that when a person is in the upright position, the diaphragm contributes one-third to one-half (33% to 50%) of the tidal volume during eupnea. Levitzky also states that the action of the diaphragm is responsible for about two-thirds (66%) of tidal volume during eupnea when supine. Summary: if body positional orientation is not given, assume about 67% to 75% of tidal volume enters the lungs due to the action of the diaphragm during eupnea.

Question 18

The diaphragm is innervated by what nerve arising from what segments of the spinal cord?

Answer 18

The diaphragm is innervated by the phrenic nerve originating from C3, C4, C5. The phrenic nerve arises chiefly from the 4th cervical nerve with contributions from the 3rd and 5th cervical nerves. Remember: C3, C4.C5 keeps the diaphragm alive.

Question 19

In what two ways does the diaphragm alter thoracic dimensions?

Answer 19

When the diaphragm contracts, the vertical dimension of the chest cavity is increased. In addition, the rib margins are lifted and moved out, causing an increase in the antero-posterior (A/P) diameter of the thorax.

Question 20

Contraction of what muscles increase the antero-posterior (A/P) diameter of the thorax? Contraction of which muscle is most responsible for increasing the antero-posterior (A/P) diameter of the thorax?

Answer 20

Both the diaphragm and the external intercostal muscles increase the antero-posterior (A/P) diameter of the thorax. Contraction of the external intercostal muscles, however, is most responsible for raising the ribs and increasing the antero-posterior (A/P) diameter of the thorax.

Question 21

Contraction of what muscle is most responsible for increasing the vertical (up and down) dimension of the thorax?

Answer 21

Contraction of the diaphragm most contributes to the increase in the vertical (up and down) dimension of the chest wall.

Question 22

Identify the two groups of muscles that may be employed to force expiration.

Answer 22

The muscles that pull the rib cage downward and permit forced expiration are: (1) the abdominal recti (and other abdominal muscles) and (2) the internal intercostal muscles.

Question 23

Define dead space.

Answer 23

Dead space is that portion of the tidal volume that does not participate in gas exchange.

Question 24

Define anatomic dead space. What percent of anatomical dead space is contained in the upper airway? Does anatomic dead space remain relatively constant throughout life?

Answer 24

Anatomic dead space is the volume of air in the conducting airways. 50% of anatomic dead space is contained in the upper airway. The anatomic dead space remains relatively constant throughout life. Note: Conducting airways are airways where gas exchange does not occur.

Question 25

**Define alveolar dead space. What causes alveolar deadspace?

Answer 25

Alveolar dead space is that volume of inhaled gas that enters non-perfused or poorly perfused alveoli. Inadequate perfusion of ventilated alveoli causes alveolar dead space.

Question 26

Define physiologic dead space.

Answer 26

Physiologic dead space is the sum of the anatomic and alveolar dead spaces.

Question 27

When are anatomic dead space and physiologic dead space almost equal?

Answer 27

In a normal, healthy adult in whom nearly all alveoli are functional, alveolar dead space is minimal. In this situation, physiologic dead space is nearly equal to anatomic deadspace.

Question 28

What is the difference between physiologic and anatomic dead space?

Answer 28

Physiologic dead space is the sum of the anatomic dead space and alveolar dead space. Physiologic dead space minus anatomic dead space is, therefore, alveolar dead space. Alveolar dead space is caused by unperfused or poorly perfused alveoli. Hence, the difference between physiologic dead space and anatomic dead space is unperfused or under-perfused alveoli.

Question 29

What is the anatomic dead space in ml/kg in the adult? Calculate the anatomic dead space in an 80 kg adult?

Answer 29

2 ml/kg is the normal adult anatomic dead space. For an 80 kg adult, anatomic deadspace is 2 ml/kg x 80 kg = 160 ml.

Question 30

Identify four situations that are associated with a significant increase in dead space.

Answer 30

Dead space increases: (1) with age, (2) during positive pressure ventilation, (3) when there is pulmonary embolism, and (4) in the patient with lung disease.

Question 31

What percent of the tidal volume in a spontaneously breathing adult is dead space? In a paralyzed, mechanically ventilated patient?

Answer 31

Dead space is 20-40% (average, 33%) of tidal volume in a spontaneously breathing adult and 40-60% in a paralyzed, mechanically ventilated patient.

Question 32

With each breath in the spontaneously breathing healthy individual, what fraction of the tidal volume mixes with alveolar air?

Answer 32

About two-thirds of the inspired gas in each breath mixes with alveolar gases, because one-third is dead space.

Question 33

What is the normal dead space to tidal volume (VD/VT) ratio, and what happens to this ratio when physiologic dead space increases?

Answer 33

Normally, anatomic dead space is almost equal to physiologic dead space (alveolar dead space is small), and Vd/Vt is about 0.33 (33%). (Recall that dead space averages 33% of tidal volume in the spontaneously breathing healthy young adult.) With lung disease, the physiologic dead space increases and the VD/VT ratio increases. In the patient with obstructive airway disease, VD/VT may increase to 0.6 to 0.7 (60-70%).

Question 34

What site in the trachea produces the strongest cough reflex when stimulated?

Answer 34

The carina.

Question 35

What respiratory cells secrete mucus?

Answer 35

Goblet cells secrete mucus.