22-09-23 - Cranial nerves: parasympathetic function Flashcards
Learning outcomes
- Explain the differences between the two-neurone pathways of the autonomic (visceral) sympathetic and parasympathetic efferent systems
- Describe the connections and functions of the four parasympathetic ganglia: ciliary, pterygopalatine (hay fever), submandibular and otic
- Describe the sympathetic and parasympathetic supplies to the pupil and how to differentiate between an injury to either supply
- Describe the parasympathetic supplies to the lacrimal gland and to the submandibular, sublingual and parotid salivary glands
- Describe the parasympathetic (secretomotor) supplies to nasal cavity, paranasal sinuses, palate and oral cavity
- Explain the symptoms of Horner’s syndrome
What 2 systems is the autonomic nervous system (ANS) comprised of?
What are they each responsible for?
Where are their bodies located in the spinal cord?
- 2 systems the autonomic nervous system (ANS) is comprised of:
1) Sympathetic system (Thoracolumbar)
* Fight or flight
* Cell bodies are at lateral (intermediolateral, intermediate) horn of T1-L2 spinal cord segments
2) Parasympathetic System (Craniosacral)
* Rest & digest (Rest & repose)
* Cell bodies are at brain stem or S2-4 spinal cord segments
Where are the cell bodies of the sympathetic system found?
Describe the 5 steps in a pre-synaptic sympathetic neuron leaving the spinal cord and synapsing.
How long are pre and post synaptic sympathetic fibres?
- Sympathetic system cell bodies are found between T1-L2 spinal cord segments
- The pre-synaptic neuron in the CNS synapses with the synaptic neuron in a ganglion
- 5 Steps in a pre-synaptic sympathetic neuron leaving the spinal cord and synapsing:
1) Pre-synaptic sympathetic neurons emerge from the spinal cord
2) They pass to the sympathetic trunk in white ramus communicantes (WRC), which is located close to the vertebral column
3) They ascend in the chain
4) They synapse in ganglion
5) After synapsing in a ganglion, the postganglionic fibres form grey ramus communicantes (GRC) and joins a spinal nerve in which it is distributed to the body wall
- Sympathetic ganglia are located close to the vertebral column, meaning there are short pre-synaptic fibres and long post-synaptic fibres (except splanchnic n.)
Where does each sympathetic trunk extend between?
Where do these trunks fuse? Where do sympathetic ganglia fuse?
What structures make up the:
* Superior cervical ganglia
* Middle cervical ganglia
* Inferior cervical ganglia
* Stellate ganglion
- Each sympathetic trunk extends between the atlas and coccyx
- Trunks fuse with each other in the single ganglion impar, opposite the coccyx
- Sympathetic ganglia fuse in the cervical region
- Structures make up the:
1) Superior cervical ganglia - (C1-4),
2) Middle cervical ganglia (C5-6)
3) Inferior cervical ganglia (C7-8)
4) Stellate ganglion (cervicothoracic ganglion) - Inferior cervical + T1 (C7-T1)
Sympathetic and parasympathetic pre and postsynaptic neurons (in picture)
Describe the 5 steps in the route of the superior cervical ganglion to the long ciliary.
What action does the long ciliary nerve bring about?
What nerve does it work in conjunction with?
What structure does the oculomotor nerve lack?
How does sympathetic stimulation affect the pupil?
- Route of the superior cervical ganglion to the long ciliary:
1) Pre-ganglionic sympathetic enter the sympathetic chain, and ascend to the superior cervical ganglion (C1-C4) where they synapse with post-ganglion sympathetics
2) Post-ganglionic sympathetics go to the internal carotid artery and rap around it, travelling with it and forming the carotid plexus
3) The carotid plexus goes into the carotid canal and into the cavernous sinus
4) After the cavernous sinus, the post-ganglionic sympathetics form/join the nasociliary nerve
5) These fibres then jump to the long ciliary nerve
- The nasociliary nerve innervates the dilator pupillae muscle, which is a ring of contractile cells within the iris that bring about the dilation of the pupil
- It works in conjunction with the oculomotor nerve, which innervates the Levator palpebra superioris, which elevates the upper eye lid
- The oculomotor nerve doesn’t have its own sympathetics, they are hitchhikers from the sympathetic chain
- Sympathetic stimulation results in the dilation of the pupil - LSD – Long.Sympathetic.Dilates
Sympathetic coronal section (in picture)
What causes Horner’s syndrome?
What are 4 features of Horner’s syndrome?
- Horner’s syndrome is caused by sympathetics damage in the cervical region
- 4 features of Horner’s syndrome:
1) Ptosis (drooping) of the upper eyelid
2) Pupillary constriction (miosis)
3) Anhydrosis (lack of sweating)
4) Flushing of the face due to dilated vessels - These are all factors the sympathetics have control over
Horner’s syndrome diagram
What does the parasympathetic system consist of?
Where are parasympathetic ganglia located?
How long are pre and post-synaptic ganglia?
- The parasympathetic chain consists of 2 neuron chains
- Pre-ganglionic neuron in the CNS synapses with the postganglionic neuron in a ganglion
- Parasympathetic ganglia are located close to the organ
- Parasympathetics have long pre-synaptic fibres and short post-synaptic fibres
- Cell bodies are at brain stem or S2-4 spinal cord segments
Which 4 cranial nerves have parasympathetic nuclei and fibres?
- 4 cranial nerves have parasympathetic nuclei and fibres:
1) 3
2) 7
3) 9
4) 10
What is the parasympathetic nucleus of the oculomotor nerve (CN3).
Where is it located?
Where do afferents for this nucleus come from?
- The parasympathetic nucleus of the oculomotor nerve (CN3) is the Autonomic nucleus (Edinger-Westphall)
- It is located in the midbrain
- Afferents for this nucleus come from the cortex and pretectal nucleus, bilaterally
Describe the route of the oculomotor nerve (CN3).
Where are parasympathetic located in the oculomotor nerve?
- The oculomotor nerve (CN3) enters the cavernous sinus, runs anteriorly and enters the superior orbital fissure
- CN3 then divides into superior and inferior divisions (rami), which then enter the common tendinous ring of Zinn
- The parasympathetics of the ocular nerve are all located in the inferior division
What do the superior and inferior rami of the oculomotor nerve (CN3) contain?
Where do parasympathetic fibres synapse?
What do postsynaptic fibres join?
- Superior ramus of CN3 (oculomotor nerve) contains motor fibres from oculomotor nucleus and sympathetic fibres from superior cervical ganglion to levator palpebra superioris (+SR)
- Inferior ramus (division) of CN3 contains parasympathetic fibres
- Parasympathetic fibres leave the inferior division and synapse in ciliary ganglion
- Postsynaptic fibres join short ciliary nerves
What do the short ciliary nerves run alongside?
What structures do they enter and supply?
What is the purpose of this innervation?
- Short ciliary nerves run alongside long ciliary nerves and ciliary artery
- They enter the eye ball
- The short ciliary nerves supply the Ciliary muscle and Sphincter pupilla
- To look at something near, we have to increase the thickness of the lens to increase the refractive power, for this, the ciliary muscle is used under the control of the parasympathetics
What does the light reflex test the integrity of?
What are the 2 different types of light reflex?
Describe the 6 steps in the mechanism behind the light reflex.
- The light reflex tests the integrity of the optic nerve and oculomotor nerve
- 2 different types of light reflex:
1) Pupillary light reflex
* An autonomic reflex that constricts the pupil in response to light, thereby adjusting the amount of light that reaches the retina.
2) Consensual Light Reflex
* Change in pupil size in the eye opposite to the eye to which the light is directed (e.g., if the light is shone in the right eye, the left pupil also constricts consensually).
- 6 steps in the Mechanism behind the light reflex:
1) Optic nerve picks up light sensation
2) This sensation goes along the optic tract
3) Some fibres leave the optic tract and go to the brainstem in the pretectal nucleus in the pretectal area
4) The pretectal nucleus is connected to the Edinger-Westphal bilaterally (via posterior commissure), meaning both parasympathetic nuclei will be activated
5) This stimulates the oculomotor nerve, which goes towards the ciliary ganglion
6) The signal goes through the short ciliary nerves, leading to pupillary constriction
Injury to the oculomotor nerve.
Describe the 3 potential deficits due to oculomotor nerve injury
- Injury to the oculomotor nerve
- 3 potential deficits due to oculomotor nerve injury:
1) No parasympathetic input for the pupil – leads to dilated pupil
2) Loss of motor innervation to levator palpebrae superioris – leads to ptosis
3) Loss of motor innervation to extraocular muscles except superior oblique (trochlear nerve) and lateral rectus (abducent nerve) – leads to the eyes turned outward and downward
1Facial nerve (CN7).
Where is the nucleus of CN7?
Where is it located?
Where does the CN7 leave the brainstem?
What structure does it enter after?
* Facial nerve (CN7)
- The parasympathetic fibers that travel in the facial nerve originate in the superior salivatory nucleus located in the pons
- CN7 exits the brainstem at Pontocerebellar angle
- It then enters the Internal acoustic meatus
What is the nervus intermedius?
Where is it located?
What type of fibres does it contain?
Describe the formation of the greater petrosal nerve
Describe the formation of the nerve of the pterygoid canal.
Where do the parasympathetics of the facial nerve finally synapse?
- The intermediate nerve is the part of the facial nerve (cranial nerve VII) located between the motor component of the facial nerve and the vestibulocochlear nerve (cranial nerve VIII).
- It contains the sensory and parasympathetic fibres of the facial nerve
- The facial nerve enters through the facial canal and goes into the geniculate ganglion (as it is sensory)
- The parasympathetics leave the facial nerve and form the greater petrosal nerve
- The greater petrosal nerve Joins deep petrosal nerve in foramen lacerum to form the nerve of the pterygoid canal
- Finally, these parasympathetics of the facial nerve synapse at pterygopalatine ganglion (post-synaptic ganglion of CN7) in pterygopalatine fossa
Where do the postganglionic parasympathetics from the facial jump to?
What gland do they then supply?
What is the purpose of this gland?
- Postganglionic parasympathetics from the facial jump to the Zygomatic nerve of maxillary division (V2), and then to the Lacrimal branch of ophthalmic division (V1)
- They then enter into the lacrimal gland
- The lacrimal gland is responsible for producing tears when we cry
Where does parasympathetic secretomotor fibres from the facial nerve supply?
What structure do these fibres travel in?
Where do they synapse?
- Parasympathetic secretomotor supply from the facial nerve go to the submandibular and sublingual salivary glands from the chorda tympani (branch of the facial nerve)
- These fibres travel in the Lingual nerve
- They synapse at submandibular ganglion
Glossopharyngeal nerve (CN9).
Where is the parasympathetic nucleus of CN9?
Where is it located?
Where does CN9 leave the cranial cavity?
What structures does it travel with?
- Glossopharyngeal nerve (CN9).
- The parasympathetic nucleus of CN9 is the Inferior salivatory nucleus located in the medulla
- CN9 exits the cranial cavity through the Jugular foramen, together with vagus, accessory nerve, internal jugular vein
Glossopharyngeal nerve (CN9).
What is the biggest salivary gland?
What is it supplied by?
What is the tympanic nerve?
What structure does it go through?
What structure does it become?
Where do the preganglionic parasympathetics of CN9 synapse?
What is the postganglionic parasympathetic nerve from CN9?
What does it supply?
- Glossopharyngeal nerve (CN9).
- The biggest salivary gland is the parotid gland, which is supplied by the glossopharyngeal nerve
- The tympanic nerve (Jacobson’s nerve) is a branch of the glossopharyngeal nerve found near the ear
- The tympanic nerve travels through the tympanic cavity and becomes the lesser petrosal nerve (preganglionic parasympathetics from CN9)
- The preganglionic parasympathetics from CN9 synapse in the otic ganglion in the temporal fossa
- The auriculotemporal nerve contains postganglionic parasympathetics and supplies the parotid gland
How long is the vagus nerve (CN10)?
What does it supply?
- The vagus nerve (CN10) is the longest parasympathetic nerve
- It supplies thoracic organs and some abdominal organs
Overview of the parasympathetic, secretomotor supply to the salivary glands (in picture)
