Autonomic Nervous System Flashcards
Name some of the effects of the sympathetic nervous system, particurly on the the anatomy of the head and neck
- Constriction of smooth blood vessels, eyelid (tarsal) muscles and iris (dilator pupillae)
- Innervate sweat glands
- Arrector pili muscles (hair follices)
- Decrease secretions from salivary and lacrimal glands
Name some of the effects of the parasympathetic nervous system, particurly on the the anatomy of the head and neck
- Dilation of smooth muscle of iris (sphincter pupillae) and muscle in ciliary body that controls thickness of lens
- Stimulates lacrimal gland → tears
- Stimulates salivary and mucosal glands
- Contriction of smooth muscle of the respiratory and GI tracts
Where does the sympathetic outflow to the body arise from and where do the cell bodies reside?
Thoracolumbar region (T1-L2) of the spinal cord
Cell bodies within the lateral horn of the grey matter of the spinal cord
Where does the parasympathetic outflow to the body arise from ?
2 regions, collectively; craniosacral outflow
Cranial- 4 cranial nerves
Sacral- S2-S4 (pelvic splanchnics)
Where do preganglionic sympathetics synapse?
Synapse with the postganglionic nerve in the sympathetic nerve ganglion
Which ganglia to the preganglionic sympathetics supplying the head and neck synapse to?
3 ganglia in the neck: Superior cervical, Middle cervical and Inferior cervical ganglion
How do postganglionic neurones of the head and neck reach their target tissue?
Hitch-hike along blood vessels
Which blood vessel to postganglionic neurones follow after they leave the superior cervical ganglion?
Post ganglionics follow the common carotid artery as is branches to the external carotid artery as it branches over the face
Why can pathology involving the apex of the lung cause autonomic dysfunction in the eye and face?
Pathology of the apex of the lung can compress the common carotid artery as it exits the chest.
This can compress the post ganglionic sympathetic neurones that follow the common carotid
What are the key 3 features of Horner’s syndrome?
- Partial ptosis
- Miosis (pupil constriction)
- Anhydrosis (lack of sweating)
Why would you only get partial ptosis in Horner’s syndrome?
- The eyelid is made of 2 muscles; skeletal part is the main muscle and is innervated by occulomotor
- smooth muscle part is only a small part and is innervated by sympathetics
- Horner’s syndrome is a manifestation of the interupted sympathetic innervation therefore only the small, smooth muscle portion is compromised
Which cranial nerves carry parasympathetic fibres from the brainstem?
- Occulomotor (CN III)
- Facial (CN VII)
- Glossopharyngeal (CN IX)
- Vagus (CN X)
Which parasympathetic nuclei does the occulomotor nerve arise from? Desscribe the route of the nerve
Arises from Edinger Westphal nucleus in the brainstem
Parasympathetic Fibres from Edinger Westphal in the brainstem emerge with CNIII
Synapse on the ciliary ganglion at the back of the orbit
Innervate Ciliary muscle altering lens shape and Sphinter pupillae muscle (pupil constriction)
Explain the Pupillary Light Reflex (7 steps)
- Light shone in the Left eye
- Detected by sensory afferent the optic nerve (CNII)
- Some branches of CNII enter midbrain and synapse on pre-tectal nucleus
- Pre-tectal nucleus connects to both the left and right EDW nuclei
- Pre-ganglionic parasympathetic fibres from EDW leave brainstem with CN III (both L & R)
- Pre-ganglionic sympathetics synapse at the ciliary ganglion and become postganglionic
- Post-ganglionic reach sphincter pupillae muscle of eye causes the pupils to contrict
Explain the difference between the direct and consensual pupillary light reflex
Direct light reflex - pupil constriction in the eye the light is shone
Consensual light reflex - pupil constriction in the opposite eye
Which branches of the facial nerve do the parasympathetics reach their target tissues by, which ganglia do they synapse in and which structures do they innervate ?
- Carried on Greater petrosal → Synapse on Pterygopalatine ganglion → Innervates Lacrimal gland and mucosal glands of the nasal cavity
- Carried on Chorda Tympani → Synapse on the submandibular ganglion → innervate the submandibular and lingual salivary gland
Explain how parasympathetics run with the glossopharyngeal nerve to reach their target tissue (5)
- Parasympathetics arise from brainstem and exit with CN IX through the jugular foramen
- At exit from the from the jugular foramen, splits into a number of branches
- Parasympathetic fibres initally run along the course of the tympanic nerve (supplies sensory to middle ear)
- They then exit the middle ear as the lesser petrosal nerve and synapse at the otic ganglion in the infra temporal fossa
- Post ganglionics hitchike on brank of CN Vc to the parotid gland
Explain how parasympathetics run along the Vagus nerve to reach their target tissues
- Parasymapthetics arise in the medulla of the brainstem and exit with CN X
- Pre-ganglionics run through the branches of CN X
- Meet the ganglion at/ in the target tissue (has no defined ganglion)
- Target tissues:
- mucosal glands of pharynx/ larynx and smooth muscle of oesophagus and trachea
- Smooth muscle and mucosal glands in respiratory and GI tracts
- The Heart
Explain why a patient presenting with Horner’s syndrome should be sent for a CXR?
As they may have a cancerous growth at the apex of the lung, compressing the sympathetics running along the common carotid artery as it exits the chest
A 40 year old lady presents with history of sweating and palpations . She has no exopthalmus but on clinical examination the GP notices lid retraction. What is her underlying condition and why does this give lid retraction?
Hyperthyroidism
Thyroid hormone increases sensitivity of the sympathetic Nervous system
Levtor Palpabrae superioris smooth muscle is innervated by sympathetics, so with increased thyroid you see increased lid retraction
