Session 6 Flashcards
What is the autonomic nervous system?
- Divided into parasympathetic and sympathetic nervous systems
- Part of the peripheral nervous system
- Controls non-voluntary actions of smooth muscle, cardiac muscle and glands
- Maintains and fine-tunes internal environment
- Many structures receiving autonomic innervation are dually innervated with sympathetic and parasympathetic fibres
What are the actions of the sympathetic nervous system?
- Retract eyelids
- Dilates pupils
- Increases activity of sweat glands
- Constricts smooth muscle of blood vessels in skin and gut
- Bronchodilates airways
- Decreases gut motility
- Increases rate and force of contraction of cardiac muscle
What are the actions of the parasympathetic nervous system?
- Constricts pupil
- Makes lens fatter (smooth muscle in ciliary body)
- Increases activity of lacrimal glands
- Increases activity of salivary glands
- Increases activity of mucosal glands
- Increases contraction of smooth muscle of respiratory and GI tract
- Decreases rate and force of contraction of heart
Where are pre-ganglionic neurones found?
- Cell bodies (nuclei) within CNS
- Axons exit CNS to synapse with another autonomic neurone
Where are post-ganglionic neurones found?
- Cell body lies within a ganglion outside of CNS
- Axon exits ganglion to synapse with tissues
Where do sympathetic fibres exit the CNS?
- Thoracolumbar outflow
- T1-L2 spinal segments only
Where do parasympathetic fibres exit the CNS?
- Craniosacral outflow
- Brainstem x4 cranial nerves
- Sacral S2-S4 pelvic splanchnics
Outline how 1st, 2nd, and 3rd order neurones reach the structures of the head and neck?
- 1st order neurone descends via brainstem into spinal cord
- Synapses onto cell body of 2nd order neurone
- 2nd order neurone exits at T1/T2 level in thoracolumbar region of spinal cord
- Then enters and ascends in sympathetic chain up into the neck
- At superior cervical ganglion 2nd order neurone synapses onto 3rd order neurone
How do 3rd order neurones travel in the head and neck?
- Hitch-hike onto blood vessels
- Runs on outside of CCA and then along ICA and ECA to reach target tissues
How do 3rd order sympathetic neurones to the eye and orbit reach their targets?
- Run with ICA
- Then into orbit
- Run alongside ophthalmic artery and distal branches of Va
- Increase retraction of upper eyelid
- Dilate the pupil
How do 3rd order sympathetic neurones to the sweat glands of the face and neck reach their targets?
- Run with branches of the ECA
What are the points where sympathetic innervation to the head and neck can be damaged?
- 1st order neurones - within the CNS
- 2nd order neurones - exiting the CNS and within the sympathetic chain
- 3rd order neurones - running with blood vessels
Which pathologies/injuries affect the sympathetic nerves reaching the head and neck?
- Pathology/injury to CCA or ICA - e.g. carotid artery dissection or aneurysm
- Apical lung cancer e.g. Pancoast’s tumour (can interrupt sympathetic innervation to head and neck and involve structures relating to eye)
What is the clinical manifestation of interruption of sympathetic innervation to face and eye?
- Horner’s syndrome:
1. Partial ptosis
2. Miosis (constricted pupil)
3. Anhidrosis (ability to sweat is lost on affected side of face)
4. Apparent enophthalmus
Why does interruption of sympathetic innervation lead to partial ptosis, not a complete or severe ptosis?
- Levator palpabrae superioris contracts to elevate (retract) upper eyelid
- Two muscle types within it contribute different amounts
- Skeletal muscle innervated by CN III (somatic) has major contribution
- Smooth muscle innervated by sympathetics has smaller contribution
Which cranial nerves carry parasympathetic fibres with them?
- Oculomotor (III)
- Facial (VII)
- Glossopharyngeal (IX)
- Vagus (X)
- Remember 1973
Describe the cranial outflow of parasympathetic innervation to the head and neck
- Parasympathetic nuclei in brainstem
- Preganglionic axons exit brainstem with 1 of 4 cranial nerves
- Parasympathetic ganglia (cell body of post-ganglionic neurone)
- Post-ganglionic axons after exiting ganglia run with the very distal branches of CN V (a, b or c)
- To target tissues
Outline the parasympathetic route starting at the Edinger-Westphal nucleus to head and neck
- Edinger-Westphal nucleus (most important nucleus)
- Parasympathetic fibres exit with CN III
-Ciliary ganglion - Target tissues are sphincter pupillae (constricts pupil) and ciliary muscle (fattens lens)
Outline the parasympathetic route starting at the superior salivary nucleus to head and neck
- Superior salivary nucleus
- Exits with CN VII
- Pterygopalatine ganglion and submandibular ganglion
- Target tissues are lacrimal glands (tears), nasal and mucosal glands (mucus) and salivary glands (submandibular and sublingual)
Outline the parasympathetic route starting at the inferior salivary nucleus to head and neck
- Inferior salivary nucleus
- Exits with CN IX
- Otic ganglion
- Target tissue is salivary gland (parotid gland)
Outline the parasympathetic route starting at the dorsal motor nucleus to head and neck
- Dorsal motor nucleus
- Exits with CN X
- No named ganglion - sits very close to or within target tissues
- Target tissues are mucosal glands and smooth muscle within respiratory tract and most of GI tract and cardiac muscle
Outline the pupillary light reflex (light in left pupil)
- Light enters left eye
- Optic nerve is sensory afferent from left retina
- Some branches leave optic nerve to enter midbrain on left and synapse on pre-tectal nucleus
- Connection with EDW nuclei is on left and right side
- Pre-ganglionic parasympathetic fibres from EDW leave brainstem with oculomotor nerve fibres
- Pre-ganglionic fibres synapse in ciliary ganglion; become post-ganglionic
- Reach sphincter pupillae muscle of iris to make both pupils constrict
What are the 2 pupillary light reflexes?
- Direct light reflex (pupil into which light shone constricts)
- Consensual light reflex (other pupil also constricts)
Outline the relationship of parasympathetics associated with the facial nerve to the facial nerve
- Parasympathetic nuclei in close proximity to facial nerve nuclei
- Parasympathetic preganglionic axons exit brainstem with other axons forming facial nerve
- Run with facial nerve into petrous bone
Which branches of the facial nerve do parasympathetic fibres run with?
- Greater petrosal nerve (associated with pterygopalatine ganglion)
- Chorda tympani nerve (associated with submandibular ganglion)
Outline the relationship of parasympathetics associated with the glossopharyngeal nerve to the glossopharyngeal nerve
- Pre-ganglionic nuclei in close proximity to nuclei of CN IX
- Axons exit brainstem with axons of CN IX
- Pre-ganglionic parasympathetic fibres hitch-hike with tympanic nerve (branch of CN IX)
- Pre-ganglionic parasympathetic fibres exit middle ear as lesser petrosal nerve which runs to Otic ganglion
- Post-ganglionic parasympathetics exit ganglion and join with auriculotemporal nerve
- Supply parotid gland
Outline the relationship of parasympathetics associated with the Vagus nerve to the Vagus nerve
- Pre-ganglionic parasympathetic fibres exit with other axons forming CN X
- Run within CN X and its branches
- Meet ganglion at or in target tissues
What are the target tissues of the parasympathetics associated with the Vagus nerve?
- Heart
- Mucosal glands in pharynx/larynx and smooth muscle of oesophagus and trachea
- Smooth muscle and mucosal glands within rest of respiratory and GI tract
