L18: Autonomic innervation of head and neck Flashcards
What is the central control of the autonomic nervous system?
Hypothalamus
What does the autonomic nervous system control?
- Controls body functions not under conscious control
- maintains and fine tunes the internal environment (accelerates/brakes)
How do you get from the CNS to the target tissue?
Sequential 2 neurone arrangement and an associated ganglion
pre-ganglionic nerve (cell body in CNS) > ganglion > post-ganglionic nerve
What is the sympathetic chain?
Vertical arrangment of autonomic ganglion
What are the target tissues of the autonomic nervous system?
- smooth muscle
- cardiac muscle
- glands (lacrimal, mucosal, salivary)
Whats the difference between sympathetic and parasympathetic NS?
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
Where is the parasympathetic/sympathetic outflow from the CNS?
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
Where do the sympathetics destined for the head and neck leave the spinal cord?
T1/T2
How do the sympathetics for the head and neck travel from T1/2?
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)
Where are the top 3 ganglion of the sympathetic chain found?
Neck
-they are called the cervical ganglion
(superior, middle and inferior)
Why can pathology to the apex of the lungs and the carotid arteries cause autonomic dysfunction?
- 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
What happens when you lose sympathetic innervation to the eye? (Horner’s syndrome)
-miosis (constricted pupil): due to unopposed parasympathetic innervation
-partial ptosis (eyelid not completely drooped)
-anhydrosis (lack of sweating)
= Horner’s syndrome
Why, in Horner’s syndrome, is ptosis only partial, compared to severe ptosis seen in occulomotor nerve lesion?
- 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
How would the pupil differ in Horner’s syndrome compared to an occulomotor nerve lesion?
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
Which cranial nerves carry parasympathetic fibres from the brainstem?
-occulomotor
-facial
-glossopharyngeal
-vagus
Pre-ganglionic parasympathetic nerve axons run with the cranial nerve
Describe the course of parasympathetic innervation to the head and neck:
- 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
What are the names of the parasympathetic nuclei in the brainstem?
- edinger westphal (relate to CN3)
- superior salivary
- inferior salivary
- dorsal motor
What are the names of the 4 parasympathetic ganglia?
- ciliary
- submandibular
- pterygopalatine
- otic
What is the course of CN3 and its parasympathetics?
- 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
Why do both pupils constrict when you shine a light in one eye?
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
What is aniscoria?
When the pupil sizes differ
What is the course of the parasympathetics of the facial nerve (CN7)?
- 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
What are the 2 parasympathetic ganglions associated with the facial nerve?
- pterygopalatine ganglion
- submandibular ganglion
What is the function of the chorda tympani?
Carries taste from the anterior 2/3rds of the tongue
What is the parasympathetic course of the glossopharyngeal nerve?
- 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
What is the parasympathetic course of the vagus nerve?
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
