22.1 Vagus Nerve

Question 1

a) List the nuclei of the vagus nerve. (10%)

Answer 1

> > Dorsal (vagal) nucleus.

> > Nucleus ambiguus.

> > Solitary nucleus
(nucleus of the tractus solitarius).

> > Spinal trigeminal nucleus:
fibres supplying sensation to the pharynx and
larynx are carried by the vagus to the spinal nucleus of the trigeminal nerve.

Question 2

b) Describe the immediate relations of the right vagus nerve in the neck at C6 (15%) and thorax at T4. (15%)

Answer 2

C6
» Lies within the carotid sheath with
carotid artery anteromedially,
internal jugular vein anterolaterally.

> > Anteriorly:
omohyoid and thyroid gland.

> > Posteriorly:
longus coli, anterior scalene, phrenic nerve.

> > Medially:
sympathetic trunk.

> > Laterally:
sternocleidomastoid

T4
» Anteriorly:
phrenic nerve, superior vena cava.

> > Posteriorly:
oesophagus and right lung.

> > Medially:
trachea.

> > Laterally:
azygos vein and right lung.

Question 3

c) List the branches of the vagus nerve. (30%)

Answer 3

Jugular fossa:
» Meningeal branch.
» Auricular nerve.

Neck:
>> Pharyngeal nerve.
>> Superior laryngeal nerve.
>> Right recurrent laryngeal nerve.
>> Cardiac branches.

Thorax:
>> Oesophageal branches.
>> Pericardial branches.
>> Left recurrent laryngeal nerve.
>> Branches to cardiac plexus.
>> Branches to pulmonary plexus.

Abdomen:
» Gastric branches.
» Hepatic branch.
» Coeliac branches.

Question 4

d) Which clinical situations commonly produce vagal reflex bradycardia? (30%)

Answer 4

> > Central afferent pathway triggered by stress or pain.

> > Oculocardiac reflex caused by traction
on extra-ocular muscles during surgery.

> > Trigeminocardiac reflex during maxillofacial surgery.

> > Stimulation of larynx during intubation,
laryngoscopy or with suctioning.

> > Peritoneal stretch during laparoscopic surgery.

> > Manipulation of abdominal and pelvic organs.

> > Cervical or anal dilatation during surgery or examination.