96 Neuroanatomy: Draw It to Know It
Parasympathetic Nervous System
Here, will draw the motor division of the parasympa-
thetic nervous system. First, draw a coronal view through
the brainstem and label the midbrain, pons, and medulla;
indicate that the brainstem contains the cranial compo-
nent of the parasympathetic system. Th en, draw a coro-
nal view of the sacral spinal cord and label it as the sacral
component.
In the midbrain, draw the Edinger-Westphal nucleus
of cranial nerve 3. Show that it innervates the ciliary
ganglion, which innervates the ciliary body and pupil-
lary constrictor muscles.
Next, in the pons, draw the superior salivatory nucleus
of cranial nerve 7, which innervates both the pterygo-
palatine and submandibular ganglia, which innervate
the majority of the major glands of the face. Indicate that
the pterygopalatine ganglion innervates the major glands
of the upper face except for the parotid gland (which the
otic ganglion innervates). Specifi cally, the pterygopala-
tine ganglion innervates the nasal, lacrimal, pharyngeal,
and palatine glands. Th en, show that the submandibular
ganglion innervates the submandibular and sublingual
glands.
Now, in the medulla, draw the inferior salivatory
nucleus of cranial nerve 9. Show that it innervates the
otic ganglion, which, as mentioned, innervates the
parotid gland. Th en, draw the dorsal motor nucleus of
the vagus nerve of cranial nerve 10. Show that it inner-
vates the ganglia of numerous pharyngeal and thora-
coabdominal glands and organs. Notably, it innervates
the abdominal foregut and midgut derivatives (but not
the hindgut derivates: its innervation stops at the splenic
fl exure of the colon). Th e target organs of the dorsal
motor nucleus of the vagus include the pharyngeal and
laryngeal mucosa, lungs, esophagus, liver, pancreas, gall-
bladder, stomach, small intestine, and colon to the splenic
fl exure. It induces bronchoconstriction and increases
gut peristalsis. As we will show in a moment, however,
the dorsal motor nucleus of the vagus provides minimal,
if any, innervation to the heart; nucleus ambiguus is
responsible for that, instead.
Next, draw the nucleus ambiguus of cranial nerves 9
and 10. Show that through its glossopharyngeal nerve
parasympathetic fi bers, nucleus ambiguus innervates
ganglia that lie within and act on the carotid body and
carotid sinus, and then show that through its vagus nerve
parasympathetic fi bers, nucleus ambiguus innervates the
cardiac ganglion, which induces heart rate deceleration.
Note that although not drawn as such here, nucleus
ambiguus and the dorsal motor nucleus of the vagus
both lie at the same rostro-caudal level of the medulla
(see Drawing 11-4, for details).
Now, let’s turn our attention to the sacral component
of the parasympathetic nervous system. Draw the sacral
nuclei of the intermediolateral cell column for sacral
levels 2–4. Th ese nuclei reside in lamina 7 in the inter-
mediate gray matter horn of the spinal cord. Show
that the visceromotor axons from sacral levels 2–4 travel
as pelvic splanchnic nerves, which relay in the ganglia
of their target organs in the abdomen and pelvis. Th eir
targets are the hindgut derivatives: the distal transverse
colon, descending colon, sigmoid colon, and rectum; and
also the anal canal, lower urinary tract, and reproductive
organs. Sacral parasympathetic activation increases blood
fl ow to the gut, increases gut peristalsis and secretion,
provides urinary bladder detrusor muscle tone, and
induces genital engorgement.^4 – 8