Cranial Nerves - Blood Supply & Reflexes Flashcards
What are the 4 nuclei associated with the facial nerve and what fibre type are they associated with?
GVE fibres:
- associated with the superior salivatory nucleus
SVA fibres:
- associated with the superior (rostral) solitary nucleus
SVE fibres:
- associated with the motor nucleus of VII
GSA fibres:
- associated with the trigeminal sensory nucleus
Where is the motor nucleus of VII located and what will fibres originating here innervate?
How is the facial colliculus formed?
- at the level of the pons, it is located most medially
- motor fibres leaving the motor nucleus of VII will wrap around the abducens nucleus to create the facial colliculus
- the abducens nucleus is located more medially and more posteriorly
- these fibres are SVE fibres that will innervate the muscles of facial expression
- as the fibres arch around the abducens nucleus, they are called the internal genu of the facial nerve
Where are the nuclei associated with the facial nerve located within the pons?
What fibres form the nervus intermedius?
- the motor nucleus of VII is located most medially as it is both efferent and somatic
- the superior salivatory nucleus is also efferent, so is located close to the midline
- this is located more posteriorly than the motor nucleus
- the superior solitary nucleus is afferent, so is located more dorsolaterally
- the trigeminal sensory nucleus is located most laterally
- GSA, GVE and SVA fibres come together to form the nervus intermedius of VII
- SVE motor fibres continue independently as the motor root of VII
What fibres emerge from the superior salivatory nucleus and what do they supply?
- it gives rise to parasympathetic GVE fibres that will innervate the submandibular, sublingual and lacrimal glands
What fibres arise from the superior solitary nucleus and what do they supply?
- gives rise to SVA taste fibres that will supply the anterior 2/3 of the tongue
- these neurones have their cell bodies within the geniculate ganglion
What fibres will travel to the trigeminal sensory ganglion VII?
- GSA fibres carrying sensory information from the skin around the external ear
- fibres carrying pain & temperature information descend in the spinal tract of V to reach the trigeminal spinal nucleus
- fibres carrying discriminative touch information reach the chief sensory nucleus (pontine) at the level of the pons
What are the 5 nuclei associated with the glossopharyngeal nerve?
SVE fibres:
- associated with the rostral nucleus ambiguus
GVE fibres:
- associated with the inferior salivatory nucleus
GSA fibres:
- associated with the trigeminal sensory nucleus
SVA fibres:
- associated with the superior solitary nucleus
GVA fibres:
- associated with the inferior solitary nucleus
Where are the nuclei associated with IX located in the open medulla?
- the solitary tract and nucleus is located posteriorly and lateral to the dorsal motor nucleus of X
- the nucleus ambiguus is located more ventrally and closest to the midline
- the inferior salivatory nucleus is slightly more lateral than the nucleus ambiguus and more posterior
What fibres arise from the nucleus ambiguus?
- SVE fibres that will supply the stylopharyngeus muscle of the pharynx
What is the role of the superior solitary nucleus in relation to IX?
- it receives SVA taste fibres from the posterior 1/3 of the tongue
What is the role of the inferior solitary nucleus in relation to IX?
- it receives GVA fibres carrying viscerosensory information from the carotid sinus and carotid body
- these fibres must descend within the solitary tract to reach the inferior solitary nucleus
What is the role of the inferior salivatory nucleus?
- it sends parasympathetic GVE fibres via IX to the parotid gland
What information is carried to the trigeminal sensory nucleus from IX?
- GSA fibres carrying sensation from the pharynx, larynx and external ear
- These fibres can travel up and down via the spinal tract of V to reach the spinal nucleus, or travel to the pontine nucleus
Why does someone with a brainstem lesion often present with multiple signs / symptoms?
- The brainstem is diverse, yet anatomically compact
- A single lesion can damage several nuclei, reflex centres, tracts or pathways
- It is rare that a lesion will only damage a single structure
What are the 5 most common causes of brainstem degeneration?
- trauma
- vascular pathology
- tumours
- demyelination
- degeneration
What are the most likely deficits that would arise from plaque 3?
Hypoglossal nucleus:
- both hypoglossal nuclei are impacted, leading to bilateral weakness of the tongue
Medial lemniscus:
- this is associated with the dorsal column pathway, which brings discriminative touch, proprioception and vibration information from the body
- both MLs are implicated, so there would be loss of proprioception, discriminative touch & vibration sense from both sides of the body
Pyramidal tracts:
- leads to bilateral motor weakness in the relevant parts of the body
What 2 branches are given off by the vertebral arteries before they fuse that supply the medulla?
Anterior spinal artery:
- small branch in the midline that supplies the ventral aspects of the medulla
Posterior inferior cerebellar artery (PICA):
- this supplies the lateral aspects of the medulla
What artery arises from the PICA that supplies part of the medulla?
Posterior spinal artery:
- can also arise from the vertebral artery
- supplies the dorsolateral aspects of the medulla and the dorsal spinal cord
What 2 other branches of the basilar artery, other than the AICA, supply blood to the pons?
Transverse pontine arteries:
- these loop around the dorsolateral aspect of the pons and supply it
Superior cerebellar artery:
- this is the penultimate branch of the basilar artery, it supplies the dorsolateral aspect of the pons more rostrally
What is the terminal branch of the basilar artery?
Which 3 branches of this artery will supply structures of the brainstem?
Posterior cerebral artery (PCA):
- collicular branches will supply the tectum of the midbrain
- geniculate branches will supply the geniculate bodies
- choroid branches will supply the choroid plexus
At each level of the brainstem, what is the general name for arteries that supply the medial and lateral aspects?
Midline (paramedian) branches:
- these will penetrate the brainstem to supply the medial aspect
Circumferential (dorsolateral) branches:
- these will loop around the surface of the brainstem to supply the dorsolateral aspect
What vessels give rise to the paramedian and dorsolateral branches at the level of the medulla?
Paramedian branches:
- these arise from the anterior spinal artery and the vertebral arteries
- in the rostral medulla, the paramedian branches arise from the vertebral arteries only as there is no anterior spinal artery in this region
- these will supply the substance of the brainstem at this level - pyramids, medial lemniscus, nucleus of XII, etc.
Circumferential branches:
- arise from the posterior inferior cerebellar arteries (PICA)
What vessels give rise to the paramedian and circumferential branches at the level of the pons?
Paramedian branches:
- the basilar artery is the median artery supplying the pons, which gives rise to paramedian penetrating branches
Dorsolateral / circumferential branches:
- arise from the anterior inferior cerebellar artery (AICA) in the caudal pons
- arise from pontine arteries in the middle of the pons
- arise from the superior cerebellar artery in the rostral pons
Which vessels give rise to the paramedian and circumferential branches that supply the midbrain?
Paramedian branch:
- arises from the basilar artery
Circumferential (dorsolateral) branch:
- arise from the posterior cerebral arteries
What vessels supply the following areas?
What 3 arteries supply these territories of the closed medulla?
How can you tell that this is the closed medulla?
- central region is supplied by the paramedian branches that arise from the anterior spinal artery
- the more lateral aspects are supplied by the vertebral arteries
- the dorsal aspect is supplied by the posterior spinal arteries
- this is the closed medulla as the ventricular system is represented by the central canal (completely closed)*
What would happen if there was an infarction to the posterior spinal arteries or anterior spinal artery at the level of the closed medulla?
Posterior spinal arteries:
- loss of discriminative touch, vibration and proprioception sense
- due to involvement of the gracile and cuneate fascicles (dorsal columns)
Anterior spinal artery:
- weakness of the muscles in the body due to involvement of the corticospinal tracts (pyramids)
What blood vessels supply the medial and lateral aspects of the open medulla?
- the medial aspect is supplied by paramedian branches that arise from the vertebral artery
- there may be some input from the anterior spinal artery
- the dorsolateral aspect is supplied by the PICA, with some input from the vertebral artery
What causes lateral medullary (Wallenberg) syndrome?
What symptoms does the patient present with and why do these occur?
occurs due to ischaemia in the territory of the PICA and vertebral artery at the level of the open medulla
Vomiting & vertigo:
- due to involvement of the vestibular nuclei
Ipsilateral loss of taste:
- due to involvement of the solitary tract and nucleus
Ipsilateral cerebellar ataxia:
- due to involvement of the inferior cerebellar peduncle
Ipsilateral loss of pain & temp sensation of face:
- due to involvement of the spinal trigeminal tract & nucleus
Dysphagia:
- due to involvement of the nucleus ambiguus
Loss of sympathetic functions:
- due to involvement of descending sympathetic fibres
Contralateral loss of pain & temp sensation of body:
- due to involvement of the lateral spinothalamic tract
What vessels give rise to the paramedian and circumferential branches at the level of the pons?
- paramedian branches arise from the basilar artery
- circumferential arteries arise from different vessels depending on the level of the pons:
- from anterior inferior cerebellar arteries (AICA) in the caudal pons
- from lateral pontine arteries in the middle of the pons
- from superior cerebellar artery in the rostral pons
What vessels give rise to the paramedian and dorsolateral branches at the level of the midbrain?
- paramedian branches arise from the basilar artery
- infarct in this territory can lead to oculomotor nerve palsies as CN III fibres leave the interpeduncular fossa here
- circumferential branches mainly arise from the posterior cerebral artery
Describe the neurones involved in the somatovisceral (lacrimal) reflex
First order neurone:
- when the cornea is irritated, sensory fibres travel via the ophthalmic nerve (V1)
- cell bodies are within the trigeminal ganglion
- fibres travel to, and synapse within, the trigeminal spinal nucleus
Interneurones:
- interneurones project bilaterally from the trigeminal spinal nucleus to the superior salivatory nuclei
Preganglionic neurones:
- travel from the superior salivatory nucleus within the facial nerve (VII)
- these are parasympathetic GVE fibres
- they reach the pterygopalatine ganglion, where they synapse
Postganglionic neurones:
- travel from the pterygopalatine ganglion to the lacrimal gland to stimulate tear production
- As the interneurones project bilaterally, this is a BILATERAL response that should stimulate lacrimation in both eyes*
Describe the neurones involved in the sneeze reflex
Afferent neurone:
- irritants in the nasal cavity stimulate sensory fibres within the maxillary nerve (V2)
- their cell bodies are within the trigeminal ganglion
- fibres enter at the level of the pons and descend via the spinal tract of V to reach the trigeminal spinal nucleus
Projections from spinal nucleus of V:
- the trigeminal spinal nucleus sends bilateral projections to specific regions of the spinal cord
- projections to C3, C4 and C5 stimulate the phrenic nerve to cause contraction of the diaphragm
- projections to lower levels of the spinal cord to stimuate motor neurones travelling to the intercostal / abdominal muscles
- contraction of the diaphragm, intercostal and abdominal muscles leads to forceful expulsion of air
Describe the neurones and pathway involved in the gag reflex
Afferent neurones:
- irritation of the pharynx stimulates GSA fibres travelling in both IX and X
- these fibres enter the medulla and descend via the spinal tract of V to reach the spinal nucleus of V (closed medulla)
- they synapse within the spinal nucleus of V
Second order neurone:
- ascends from the spinal nucleus of V via the trigeminothalamic tract to reach the nucleus ambiguus on BOTH sides of the open medulla
Efferent neurone:
- GVE fibres pass from the nucleus ambiguus and travel via CN IX and X
- these will stimulate pharyngeal constrictors and muscles that will elevate the palate on both sides
Describe the neurones and structures involved in the baroreceptor reflex
GVA fibres:
- receptors in the aorta send GVA fibres via X to the solitary nucleus
- receptors within the carotid send GVA fibres via IX to the solitary nucleus
Interneurones:
- from the solitary nucleus, interneurones project to the dorsal motor nucleus of X and the lateral motor column
From the dorsal motor nucleus of X:
- interneurones stimulate parasympathetic GVE fibres that will travel in X to reach the heart
- these will induce a decrease in HR & BP
From the lateral motor column:
- if an increase in HR or BP is required, sympathetic fibres will travel from the lateral motor column to reach the heart
If there is an increase in blood pressure, what is the reflex response to counteract this?
- increased activity of GVA fibres travelling from baroreceptors in the carotid and aorta via IX and X
- these fibres travel to the solitary nucleus to stimulate interneurones
- activity of interneurones projecting to the dorsal motor nucleus of X and to the lateral motor column increases
- interneurones activate the dorsal motor nucleus of X to increase the activity of GVE fibres travelling to the heart
- parasympathetic influence on the heart will decrease HR and BP
- interneurones reaching the lateral motor column will inhibit efferent sympathetic fibres
What is the reflex response if there is a change in blood chemistry?
- if there is an increase in CO2 levels in the blood, there needs to be an increase in respiration
- activity of GVA fibres travelling to the solitary nucleus via IX and X will increase
- the solitary nucleus sends interneurones to areas of the spinal cord controlling the intercostal muscles and diaphragm (phrenic nucleus), allowing for an increase in respiration
