Page 118 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 312

Motor (parasympathetic, synaptic) ganglia

The oculomotor (III), facial (VII), glossopharyngeal (IX) and vagus (X) all have such ganglia.
However, the parasympathetic efferent ganglia of the facial and glossopharyngeal nerves all lie associated with
parts of the trigeminal (Vth) nerve - which the parasympathetic system "parasitizes" as a delivery service.

Oculomotor (Illrd) nerve - ciliary ganglion associated with the oculomotor nerve in the orbit ( eye
socket). Smooth muscle of eye.

Facial (Vllth) nerve - (a) Submandibular ganglion in the floor of the mouth, associated with
the lingual nerve from mandibular division of trigeminal (V). Salivary
glands.
(b) pterygopalatine ganglion in the pterygopalatine fossa, assod1ted
with the maxillary division of the trigeminal (Vth) nerve. Salivary
glands, nasal glands and lacrimal (tear) glands.

Glossopharyngeal (IXth) nerve - otic ganglion associated with mandibular division of the trigeminal
(Vth) nerve in infra-temporal region. Salivary gland.

Vagus (Xth) nerve - diffuse ganglia in chest and abdomen. Cardiac muscle and SA/ AV
nodes; smooth muscle and exocrine glands of respiratory and
gastrointestinal tracts.

BRANCHIAL ARCHES (Branchial - “gill”) See HN 30 et seq.
The neck region of the embryo develops a series of potential gills: these are a series of deep fissures
inside and outside the developing neck region (the external fissures are branchial clefts, the internal -
outpouchings of the pharynx - are branchial pouches.) In the mammalian embryo, the clefts meet their
corresponding pouches, but the two do not normally become continuous: they remain opposed but separated by
a layer of tissue. The first cleft and pouch persist as the external and middle ear cavities respectively,
separated by the tympanic membrane (ear drum), and the middle ear connected to the pharynx. The remainder
disappear. Occasionally, however, things go wrong, and individuals are born with a small channel connecting
the pharynx to the outside world at the side of the neck (branchial fistula), or cystic remnant, usually along the
anterior border of the stemocleidomastoid, and known as a branchial or lateral cervical cyst (see HN 34). The
bars of tissue separating consecutive pouches and clefts (i.e. gills) are known as branchial arches. Up to
seven are readily discernible in mammalian embryos. These arches can be regarded as head segments or
“somite equivalents”, and each gives rise in a consistent way to specific adult structures. For example, the first
arch produces the mandible, the skeletal muscles which move it, two of the middle ear ossicles, and a few other
relatively unimportant structures. The second arch gives rise to the styloid process and part of the hyoid bone
and therefore structures linking these two, as well as to the “muscles of facial expression”, the third middle ear
ossicle and its associated muscle (stapedius). Furthermore, just as each true somite is innervated by a
chracteristic spinal nerve, each arch is innervated by a characteristic cranial (i.e. head segment) nerve. Thus
the nerve of the first arch is the fifth (trigeminal), and of the second arch the seventh (facial), and of the third
3
arch the ninth (glossopharyngeal) . It may help some of you to form complete “packages” if you can take on
board this principle and know which structures come from which arch. If you can't make use of this method,
just forget it.

K.E.W.

3 Note: The "gaps" are accounted for by cranial nerves which innervate structures not derived from branchial arches. For
example the lllrd (oculomotor) and IVth (trochlear) innervate skeletal muscles derived from true somites.
\NewCMedPhysSc\28 HN 31 O Cran Nerves.