Cranial nerves: parasympathetic function

Question 1

State the organisation of the Sympathetic Autonomic (Visceral) Efferent nervous system.

Answer 1

-Efferent neurons are characterised by two-neurone chains.

BOTH SNS AND PSNS

-Cell body of 1st (pre-ganglionic, pre-synaptic, primary, 1y) neurone lies in the CNS

-Cell Body of 2nd (post-ganglionic, post-synaptic, secondary, 2y) neurone is located in a ganglion

-Axon of 1st neurone synapses on cell body of 2nd neurone in the ganglion

SNS
-Preganglionic cell bodies lie in the lateral grey matter of the thoracic spinal cord between T1 and L2 (AKA THORACOLUMBAR OUTFLOW)
-The sympathetic preganglionic (1y) neurones emerge from the cord in the T1 to L2 spinal nerves
-They pass to the sympathetic trunk in white rami communicantes (WRC) and either synapse immediately in the adjacent ganglion or they travel up or down in the trunk to be distributed above T1 and below L2
-Postganglionic cell bodies lie in a sympathetic ganglion
-After the snyapse, post-ganglionic neurone may become a grey ramus communicantes (GRC) that joins a spinal nerve in which it is distributed to the body wall
-They either “hitch-hike” along somatic nerves and/or arteries and are distributed widely, all over the body
OR they supply adjacent viscera through autonomic plexuses
-The cell bodies of the postganglionic neurones are in 2 chains of linked ganglia that lie, one on each side, alongside all the vertebral bodies (atlas to coccyx) – the sympathetic trunks (i. e. short pre-ganglionic neurons, long post-ganglionic neurons)
-Each sympathetic trunk extends as far as the atlas and they fuse with each other in the ganglion impar opposite the coccyx
-There are superior, middle and inferior cervical ganglia, the latter often fuses with the T1 ganglion to form the Stellate Ganglion that lies on the neck of the 1st rib
-Sympathetic fibres that ascend in the sympathetic trunks to synapse in the superior cervical ganglion send their 2y (postganglionic) neurones to form a plexus on the carotid arteries

Question 2

Which factor of autonomic efferent neurons determines the length of the axons ?

Answer 2

The position of the ganglion determines the length of the axons

Question 3

Identify some of the effects of the SNS on the heart, lungs, eyes, skin.

Answer 3

Body uses energy (increased heart and respiratory rates; sweating; pupil dilatation)

Question 4

State the organisation of the Parasympathetic Autonomic (Visceral) Efferent nervous system.

Answer 4

-Efferent neurons are characterised by two-neurone chains.

BOTH SNS AND PSNS

-Cell body of 1st (pre-ganglionic, pre-synaptic, primary, 1y) neurone lies in the CNS

-Cell Body of 2nd (post-ganglionic, post-synaptic, secondary, 2y) neurone is located in a ganglion

-Axon of 1st neurone synapses on cell body of 2nd neurone in the ganglion

PSNS (SECRETOMOTOR)

• Ganglion is in the periphery, close to the effector organ (i.e. long 1y and short 2y neurons)
• Parasympathetic nerves only distributed to head, neck and viscera, no supply to skin or limbs
• 2y neurons ‘hitchhike’ with the cranial (or sacral spinal) nerves that supply only the head, neck, thoracic, and abdomino-(pelvic) viscera (AKA CRANIOSACRAL OUTFLOW)

Question 5

Describe structures in close proximity to internal carotid artery, and the implications of this.

Answer 5

Close proximity of the internal carotid artery and its sympathetic plexus to the divisions of the trigeminal nerve (V).
Therefore, branches of the Trigeminal (V) are often carrying postganglionic sympathetic and parasympathetic neurones.

Question 6

Describe Pancoast’s tumour.

Answer 6

Pancoast’s tumour: at the apex of the lung may affect the sympathetic trunk or stellate ganglion on the neck of the 1st rib at the thoracic inlet, compromising sympathetic supply to the head and neck on the same side, and therefore cause:

Question 7

Describe Horner’s syndrome, explaining how it can occur.

Answer 7

Injury to the sympathetic trunk (e.g. Pancoast tumor, at the apex of the lung, may affect the sympathetic trunk or stellate ganglion on the neck of the 1st rib at the thoracic inlet, compromising sympathetic supply to the head and neck on the same side) will remove the sympathetic supply to levator palpebrae superioris and to the pupil dilator, as well as the sympathetic supply to the blood vessels and sweat glands of the face on the same side. This causes Horner’s Syndrome –

• Ptosis (drooping) of the upper eyelid
• Pupillary constriction (miosis)
• Anhydrosis (lack of sweating)
• Flushing of the face

Question 8

Describe the path of sympathetics from the superior cervical ganglion.

Answer 8

Sympathetics from the superior cervical ganglion go to the carotid plexus, and then to the nasociliary (V1) and oculomotor (III) nerves, and the ciliary ganglion:

• The sympathetics in the oculomotor (III) supply the smooth muscle of levator palpebrae superioris
• The sympathetics in the nasociliary branch of V1 (picked up as V1 passes the carotid artery in the cavernous sinus) and then in the long ciliary nerve dilate the pupil (thorugh Dilator Pupillae)

Question 9

Identify the organisation of parasympathetics to the eye.

Answer 9

1) Some preganglionic parasympathetic fibres (green) run in the oculomotor nerve (III). They synapse in the ciliary ganglion and the post ganglionic fibres pass in the short ciliary nerve to the pupil constrictor, and ciliary muscle for accommodation.
2) Also in the orbit, the lacrimal gland is under the control of the parasympathetic (secretomotor) system

Question 10

Describe the consequences of an injury to the oculomotor nerve, explaining the nervous processes behind it.

Answer 10

Injury to the oculomotor nerve will cause the following:

• The left lid is drooping AKA ptosis (loss of levator palpebrae superioris)
• The eye is turned downwards (superior oblique IV) and outwards lateral rectus VI)
• The pupil is dilated (loss of parasympathetic supply for pupil constriction

Question 11

Describe the pupillary light reflex.

Answer 11

Pupillary Light Reflex

• Pupil constricts when a light is shone into the eye (thanks to Sphincter Pupillae, under PSNS control)
• But in the tectum, nerve fibres cross the midline to stimulate the opposite EW nucleus to cause the Consensual Light Reflex – both pupils constrict when a light is shone in 1 eye

Question 12

Which muscle is responsible for pupil dilation ? Which part of the NS is responsible for this ?

Answer 12

Dilator Pupillae, under Sympathetic control (LSD – Long Sympathetic Dilates)

Question 13

Identify the structures supplied by the Greater Petrosal nerve.

Answer 13

Lacrimal Gland
Glands in nasal cavity
Paranasal sinuses

Question 14

Explain how hayfever happens, in the context of cranial nerves.

Answer 14

Pterygopalatine (Hay Fever) Ganglion sends parasympathetic innervation to hitchhiking along with branches of the trigeminal nerve, to the lacrimal gland in the orbit, and the secretomotor fibers to the glands in the nasal cavity and paranasal sinuses.

Question 15

Identify the main cranial nerve nuclei of the facial nerve, stating the main function of each.

Answer 15

-VII motor nucleus (muscles of facial expression)
-Solitary nucleus (taste (and visceral sensation)) (also for IX and X)
-VII Superior salivatory nucleus (parasympathetic, secretomotor to lacrimal gland, nasal and oral cavities, submandibular and sublingual glands)
“Contains the cell bodies of parasympathetic axons within the intermediate nerve.”

Question 16

What kinds of fibers does the Greater Petrosal nerve carry ?

Answer 16

The Greater Petrosal, carries visceral efferent (parasympathetic/secretomotor) and special visceral afferent (taste) from the Nervus Intermedius (VII)

Question 17

What two nerves form the nerve of the Pterygoid canal ?

Answer 17

The sympathetic plexus on the internal carotid (in carotid canal) gives the Deep Petrosal nerve

The Greater Petrosal and Deep Petrosal combine as the Nerve of the Pterygoid Canal, which passes through the pterygoid canal into the pterygopalatine fossa

Question 18

Describe the parasympathetic fibers associated with the Trigeminal nerve.

Answer 18

Branches of the Trigeminal (V) are the carriers for p’symp (and taste), originating in the Nervus Intermedius component of VII

Question 19

Describe the anatomical location of the pterygopalatine fossa. What does this mean, physiologically ?

Answer 19

The Pterygopalatine Fossa lies: just lateral to the upper aspect of the nasal cavity and nasopharynx; just behind the orbit; and just above the hard and soft palates – poised to send nerves to them all

Question 20

Name the origins of the pre-ganglionic and destinations of post-ganglionic fibers which synapse in the pregyopalatine ganglion. Where in the skull does this occur ?

Answer 20

-Preganglionic parasympathetic fibres (from nervus intermedius [VII], via greater petrosal and nerve of pterygoid canal) synapse in the Pterygopalatine Ganglion, IN THE PREGYOPALATINE FOSSA
-Postganglionic fibres hitch-hike with branches of the Maxillary (V2) and some branches of the Ophthalmic (V1)
All branches of V2 are also accompanied by branches of the Maxillary artery

Question 21

Describe the parasympathetic supply to the lacrimal gland.

Answer 21

• Superior salivatory nucleus sends preganglionic fibres in nervus intermedius to facial nerve (VII)
• They leave in greater petrosal nerve, then nerve of pterygoid canal to
• Synapse in pterygopalatine (hay fever) ganglion
• Hitch-hike to lacrimal gland on zygomatic (and zygomaticotemporal) branches of maxillary (V2) to reach lacrimal branch of ophthalmic (V1) (which carries parasympathetic, secretomotor fibres from the pterygopalatine ganglion to the lacrimal gland)

Question 22

Describe the nerve supply to the nasal cavity and sinuses.

Answer 22

• PSNS fibres join the frontal and nasociliary nerves, that send branches to the nasal cavity and sinuses.
• Supra-orbital nerve supplies the frontal sinus, ethmoidal nerves supply the ethmoidal sinuses, the lateral wall of nasal cavity, and the nasal septum
• The infra-orbital nerve, along with the superior alveolar nerves (ant, middle and post) on their way to the teeth and gums carry the parasympathetic supply to the maxillary sinus
• LATERAL WALL OF NASAL CAVITY: Supply derived from the Ophthalmic and Maxillary branches of the Trigeminal Nerve – Cranial V1 and V2; plus Parasympathetic from VII – Nervus Intermedius
• Anterior, superior, (lateral) nasal nerves from V1, mainly via the ant ethmoidal nerve (branch of nasociliary, continues to become external nasal nerve to supply tip of nose)
• The greater and lesser palatine nerves (from V2) pass inferiorly in the palatine canal, lateral to the nasal cavity to reach the hard and soft palates
• Posterior, inferior, (lateral) nasal nerves from V2, mainly via the greater palatine nerve

• MEDIAL WALL/SEPTUM OF NASAL CAVITY: Supply derived from the Ophthalmic and Maxillary branches of the Trigeminal Nerve – Cranial V1 and V2

• Posterior, inferior, (medial) nasal nerves from V2, mainly via the nasopalatine nerve (that enters the nasal cavity via the sphenopalatine foramen)
• Anterior, superior, (medial) nasal nerves from V1
• Nasopalatine nerve passes through incisive foramen to supply the anterior palate

• All the nerves are accompanied by arteries and by parasympathetics from the pterygopalatine (Hay Fever) ganglion

Question 23

Identify an example of nerve that is capable of regeneration.

Answer 23

Olfactory nerves are capable of regeneration

Question 24

Which part of the nasal cavity is responsible for olfaction ?

Answer 24

Olfaction is restricted to the roof and over the superior concha, and to the upper aspect of the septum

Question 25

Explain what other effects Shingles (herpes zoster) at the tip of the nose might result in. Explain why.

Answer 25

Shingles (herpes zoster) at the tip of the nose may herald corneal involvement (because anterior ethmoidal nerve continues to become the external nasal nerve to supply the tip of the nose; the ant. ethmoidal is a branch of the nasociliary (V1) that supplies the cornea)

Question 26

What structures accompany branches of the Maxillary nerve ?

Answer 26

Branches of the Maxillary nerve (V2) are accompanied by branches of the maxillary branch of the external carotid artery

Question 27

What structures accompany branches of the Ophthalmic nerve ?

Answer 27

Branches of the Ophthalmic nerve (V1) are accompanied by branches of the ophthalmic branch of the internal carotid artery

Question 28

Describe the anatomical path of the chorda tympani.

Answer 28

-Facial nerve gives off chorda tympani just before the stylomastoid foramen.
-The chorda tympani passes anteriorly through the middle ear, between the incus and malleus, just medial to the tympanic membrane
-It emerges (leaves the skull) through the petrotympanic fissure to join the lingual nerve (branch of V3) in the infra-temporal fossa, just below the foramen ovale
-Chorda tympani contains parasympathetic (sup. saliv. nuc. VII), and taste fibers. While the taste fibers supply the anterior 2/3 of the tongue, the parasympathetic fibers synapse in the
submandibular Ganglion and the postganglionic (2y) neurones pass to the submandibular and sublingual glands.

Question 29

Describe the nerve supply of the mouth.

Answer 29

After being combined with the Chorda Tympani from the Facial Nerve (VII), the Lingual Nerve - carries somatic (touch, pain, temp) and taste sensation from the anterior 2/3 of the tongue, the floor of the mouth and the lingual gum; it also carries parasympathetic, secretomotor supply to the submandibular and sublingual glands.
Glossopharyngeal supplies taste fibres from the posterior 1/3 of the tongue

Question 30

Describe the anatomical path of the Glossopharyngeal nerve.

Answer 30

• Originates in the medulla oblongata of the brain.
• Emerges from the anterior aspect of the medulla, moving laterally in the posterior cranial fossa.
• The nerve leaves the cranium via the jugular foramen (with X and XI) adjacent to the wall of the pharynx. At this point, the tympanic nerve arises, which synapses in the tympanic plexus and gives off lesser petrosal nerve, which escapes from the middle ear and lies on the surface of the petrous temporal bone in the middle cranial fossa, before emerging through the foramen ovale.

Question 31

Identify the muscle of the third pharyngeal arch.

Answer 31

Stylopharyngeus

Question 32

Describe the Parasympathetic secretomotor supply to the parotid gland.

Answer 32

Tympanic nerve (branch of IX to the middle ear) contains preganglionic, parasympathetic neurones from the inf. salivatory nucleus to the tympanic plexus (also receiving somatic sensation via IX). These neurones leave the typmanic plexus in the lesser petrosal nerve, which passes through foramen ovale and synapses in the otic ganglion (suspended from V3).
Post gang. fibres pass to the Auriculo-temporal, which sends a branch to the parotid

Question 33

State the parasympathetic, secretomotor supply of the submandibular and sublingual glands.

Answer 33

Superior salivatory nucleus to facial nerve (nervus intermedius) and the submandibular
and sublingual glands

Question 34

Describe the anatomical path of the lingual nerve.

Answer 34

• The lingual nerve enters the oral cavity between mylohyoid and hyoglossus; it lies lateral to the submandibular duct, then passes inferior to the duct to ascend into the tongue on its medial side
• Preganglionic, p’symp. fibres leave the lingual and synapse in the submandibular ganglion (the parasympathetic submandibular ganglion hangs from the lingual nerve)
• Postganglionic branches pass to the submandibular and sublingual salivary glands