L18: Autonomic innervation of head and neck

Question 1

What is the central control of the autonomic nervous system?

Answer 1

Hypothalamus

Question 2

What does the autonomic nervous system control?

Answer 2

• Controls body functions not under conscious control

- maintains and fine tunes the internal environment (accelerates/brakes)

Question 3

How do you get from the CNS to the target tissue?

Answer 3

Sequential 2 neurone arrangement and an associated ganglion

pre-ganglionic nerve (cell body in CNS) > ganglion > post-ganglionic nerve

Question 4

What is the sympathetic chain?

Answer 4

Vertical arrangment of autonomic ganglion

Question 5

What are the target tissues of the autonomic nervous system?

Answer 5

• smooth muscle
• cardiac muscle
• glands (lacrimal, mucosal, salivary)

Question 6

Whats the difference between sympathetic and parasympathetic NS?

Answer 6

Sympathetic (fight/flight)

• smooth muscles of blood vessels (constriction), eyelid (tarsal muscle), iris (dilator pupillae)
• sweat glands
• some sympathetic innervation to salivary/lacrimal glands making it more viscous (but mostly parasympathetic)
• arrector pili muscles

Parasympathetic (rest and digest)

• smooth muscle of iris (sphincter pupillae), and ciliary muscle in ciliary body which controls lens thickness
• stimulate lacrimal, mucosal and salivary glands
• contraction of smooth muscle of respiratory and GI tract

Question 7

Where is the parasympathetic/sympathetic outflow from the CNS?

Answer 7

Sympathetic: thoracolumbar (T1-L2)
-preganglionic cell bodies lie in the lateral horn of the grey matter of the spinal cord

Parasympathetic: craniosacral

• pelvic splanchnics
• cranial nerves

They have a first neurone from the hypothalamus before the post-ganglionic neurone

Question 8

Where do the sympathetics destined for the head and neck leave the spinal cord?

Answer 8

T1/T2

Question 9

How do the sympathetics for the head and neck travel from T1/2?

Answer 9

Hitchhike on external surface of blood vessels

• pre-ganglionic nerve exits spinal cord and runs into the sympathetic chain
• runs up the sympathetic chain, once it reaches the superior cervical ganglion you find the cell bodies of the post-ganglionic sympathetic nerve
• post-ganglionic nerve will join the common carotid artery and follow the external carotid artery and its distributions on surface of face, and internal carotid artery through base of skull and cavernous sinus where it gives off a branch to the orbit (follows opthalmic artery into the eye)

Question 10

Where are the top 3 ganglion of the sympathetic chain found?

Answer 10

Neck
-they are called the cervical ganglion
(superior, middle and inferior)

Question 11

Why can pathology to the apex of the lungs and the carotid arteries cause autonomic dysfunction?

Answer 11

• You interrupt the sympathetic innervation as it heads towards the eye and face as they hitchike via the carotid arteries
• route of the nerves come from inside the chest, and rise up out the chest

Question 12

What happens when you lose sympathetic innervation to the eye? (Horner’s syndrome)

Answer 12

-miosis (constricted pupil): due to unopposed parasympathetic innervation
-partial ptosis (eyelid not completely drooped)
-anhydrosis (lack of sweating)
= Horner’s syndrome

Question 13

Why, in Horner’s syndrome, is ptosis only partial, compared to severe ptosis seen in occulomotor nerve lesion?

Answer 13

• levator palpebrae superioris elevates the eyelid, this has skeletal fibres in innervated by the occulomotor nerve
• small fraction of the LPS is smooth muscle (superior tarsal) innervated by the sympathetic nervous system

Therefore if you only lose the sympathetic innervation you still have the occulomotor nerve supplying the LPS, hence partial ptosis

In occulomotor nervelesion, the sympathetic supply is not strong enough to hold open the eyelid, resulting in severe ptosis

Question 14

How would the pupil differ in Horner’s syndrome compared to an occulomotor nerve lesion?

Answer 14

Horners: miosis due to interruption to sympathetic innervation to dilator muscle leaving unopposed parasympathetic innervation to constrictor muscle of pupil

CN3 lesion: interruption to parasympathetic innervation to constrictor muscle of pupil, leaving unopposed sympathetic innervation to dilator muscle of pupil

Question 15

Which cranial nerves carry parasympathetic fibres from the brainstem?

Answer 15

-occulomotor
-facial
-glossopharyngeal
-vagus
Pre-ganglionic parasympathetic nerve axons run with the cranial nerve

Question 16

Describe the course of parasympathetic innervation to the head and neck:

Answer 16

• arise from brainstem from parasympathetic nuclei
• hitchhike onto one of the 4 CN’s
• synapse at parasympathetic ganglia (discrete-not arranged in chain)
• post-ganglionic are very short and hitch hike on very distal branches of the trigeminal nerve
• reach target tissue

Question 17

What are the names of the parasympathetic nuclei in the brainstem?

Answer 17

• edinger westphal (relate to CN3)
• superior salivary
• inferior salivary
• dorsal motor

Question 18

What are the names of the 4 parasympathetic ganglia?

Answer 18

• ciliary
• submandibular
• pterygopalatine
• otic

Question 19

What is the course of CN3 and its parasympathetics?

Answer 19

• edinger westphal nucleus lies next to the nuclei of the other fibres associated with the occulomotor nerve
• exit brainstem together, and reach orbit
• pre-ganglionic nerve synpases at the ciliary ganglion and the post-ganglionic nerve supplies the ciliary muscle, and the sphincter pupillae muscle

Parasympathetic fibres lie on the outside of the occulomotor nerve, so if it get squashed from outside, you impinge the parasympathetic first (blown pupil), continue to squash and this impinges the occulomotor nerve

Question 20

Why do both pupils constrict when you shine a light in one eye?

Answer 20

Light shone in left pupil
-sensory afferent from left retina via optic nerve (CN2)
-some branches leave CN2 and enter the midbrain and synapse at the pre-tectal nucleus
-there is a connection to the EDW nuclei (left and right) from the nucleus
-pre-ganglionic parasympathetics from EDW leave brainstem with CN3 (left and right)
-pre-ganglionics synapse in ciliary ganglion and become post-ganglionic
-reach sphincter pupillae muscle of iris
=direct light reflex

Question 21

What is aniscoria?

Answer 21

When the pupil sizes differ

Question 22

What is the course of the parasympathetics of the facial nerve (CN7)?

Answer 22

• pre-ganglionic parasympathetics exit brainstem with other axons forming the facial nerve
• parasympathetics reach target tissues via 2 branches of the facial nerve that arise in the petrous bone: greater petrosal nerve and the chorda tympani nerve
• greater petrosal nerve leaves petrous bone and synapses in the pterygopalatine fossa at the pterygopalatine ganglion, post-ganglionic parasympathetics then go to the lacrimal and mucosal glands of nasal cavity and palate
• hitchhiking with the chorda tympani are sympathetics that are destined for the submandibular and sublingual salivary glands
• they meet the submandibular ganglion and the post-ganglionics supply the salivary glands

Question 23

What are the 2 parasympathetic ganglions associated with the facial nerve?

Answer 23

• pterygopalatine ganglion

- submandibular ganglion

Question 24

What is the function of the chorda tympani?

Answer 24

Carries taste from the anterior 2/3rds of the tongue

Question 25

What is the parasympathetic course of the glossopharyngeal nerve?

Answer 25

• parasympathetic fibres arise from brainstem and exit with CN9
• exits through jugular foramen but here it splits into many branches
• the tympanic nerve supplies the sensory to the middle ear, the parasympathetic fibres hitchhike with this
• the parasympathetics exit middle ear as lesser petrosal nerve (continuation of tympanic nerve)
• it synapses in the otic ganglion
• post-ganglionic parasympathetics hitch hike and reach the parotid gland

Question 26

What is the parasympathetic course of the vagus nerve?

Answer 26

No named parasympathetic ganglia associated with it
-parasympathetics exit the brainstem with other axons forming CN10 at the medulla
-pre-ganglionics run within CN10 and its branches
-these meet a ganglion at or in the target tissue
=heart/smooth muscle and mucosal glands within respiratory and GI tract/mucosal glands in pharynx/larynx and smooth muscle of oesophagus and trachea