Cranial Nerves - Blood Supply & Reflexes

Question 1

What are the 4 nuclei associated with the facial nerve and what fibre type are they associated with?

Answer 1

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

Question 2

Where is the motor nucleus of VII located and what will fibres originating here innervate?

How is the facial colliculus formed?

Answer 2

• 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

Question 3

Where are the nuclei associated with the facial nerve located within the pons?

What fibres form the nervus intermedius?

Answer 3

• 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

Question 4

What fibres emerge from the superior salivatory nucleus and what do they supply?

Answer 4

• it gives rise to parasympathetic GVE fibres that will innervate the submandibular, sublingual and lacrimal glands

Question 5

What fibres arise from the superior solitary nucleus and what do they supply?

Answer 5

• 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

Question 6

What fibres will travel to the trigeminal sensory ganglion VII?

Answer 6

• 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

Question 7

What are the 5 nuclei associated with the glossopharyngeal nerve?

Answer 7

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

Question 8

Where are the nuclei associated with IX located in the open medulla?

Answer 8

• 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

Question 9

What fibres arise from the nucleus ambiguus?

Answer 9

• SVE fibres that will supply the stylopharyngeus muscle of the pharynx

Question 10

What is the role of the superior solitary nucleus in relation to IX?

Answer 10

• it receives SVA taste fibres from the posterior 1/3 of the tongue

Question 11

What is the role of the inferior solitary nucleus in relation to IX?

Answer 11

• 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

Question 12

What is the role of the inferior salivatory nucleus?

Answer 12

• it sends parasympathetic GVE fibres via IX to the parotid gland

Question 13

What information is carried to the trigeminal sensory nucleus from IX?

Answer 13

• 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

Question 15

Why does someone with a brainstem lesion often present with multiple signs / symptoms?

Answer 15

• 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

Question 16

What are the 5 most common causes of brainstem degeneration?

Answer 16

1. trauma
2. vascular pathology
3. tumours
4. demyelination
5. degeneration

Question 17

What are the most likely deficits that would arise from plaque 3?

Answer 17

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

Question 18

What 2 branches are given off by the vertebral arteries before they fuse that supply the medulla?

Answer 18

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

Question 19

What artery arises from the PICA that supplies part of the medulla?

Answer 19

Posterior spinal artery:

• can also arise from the vertebral artery
• supplies the dorsolateral aspects of the medulla and the dorsal spinal cord

Question 20

Where does the anterior inferior cerebellar artery (AICA) arise from?

Which aspects of the brainstem does it supply and what branch does it give off?

Answer 20

• arises from the basilar artery
• loops around the caudal pons to supply its dorsolateral aspect before reaching the cerebellum
• gives off the labyrinthine artery (which can branch directly from basilar artery) which accompanies the vestibulocochlear nerve
  
  • Ischaemia of VIII can lead to hearing loss

Question 21

What 2 other branches of the basilar artery, other than the AICA, supply blood to the pons?

Answer 21

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

Question 22

What is the terminal branch of the basilar artery?

Which 3 branches of this artery will supply structures of the brainstem?

Answer 22

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

Question 23

At each level of the brainstem, what is the general name for arteries that supply the medial and lateral aspects?

Answer 23

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

Question 24

What vessels give rise to the paramedian and dorsolateral branches at the level of the medulla?

Answer 24

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)

Question 25

What vessels give rise to the paramedian and circumferential branches at the level of the pons?

Answer 25

**_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***

Question 26

Which vessels give rise to the paramedian and circumferential branches that supply the midbrain?

Answer 26

**_Paramedian branch:_** * arises from the **_basilar artery_** **_Circumferential (dorsolateral) branch:_** * arise from the **_posterior cerebral arteries_**

Question 27

What vessels supply the following areas?

Answer 27

Question 28

What 3 arteries supply these territories of the closed medulla? How can you tell that this is the closed medulla?

Answer 28

* **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)*

Question 29

What would happen if there was an infarction to the posterior spinal arteries or anterior spinal artery at the level of the closed medulla?

Answer 29

**_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)

Question 30

What blood vessels supply the medial and lateral aspects of the open medulla?

Answer 30

* 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**

Question 31

What causes lateral medullary (Wallenberg) syndrome? What symptoms does the patient present with and why do these occur?

Answer 31

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**

Question 32

What vessels give rise to the paramedian and circumferential branches at the level of the pons?

Answer 32

* paramedian branches arise from the **_basilar artery_** * circumferential arteries arise from different vessels depending on the level of the pons: 1. from **_anterior inferior cerebellar arteries_** (AICA) in the ***caudal*** pons 2. from **_lateral pontine arteries_** in the ***middle*** of the pons 3. from **_superior cerebellar artery_** in the ***rostral*** pons

Question 33

What vessels give rise to the paramedian and dorsolateral branches at the level of the midbrain?

Answer 33

* 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_**

Question 34

Describe the neurones involved in the somatovisceral (lacrimal) reflex

Answer 34

**_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*

Question 35

Describe the neurones involved in the sneeze reflex

Answer 35

**_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 1. projections to **C3, C4 and C5** stimulate the **_phrenic nerve_** to cause **contraction of the diaphragm** 2. 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

Question 36

Describe the neurones and pathway involved in the gag reflex

Answer 36

**_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

Question 37

What is the principle behind the baroreceptor reflex?

Answer 37

* receptors within the aorta and carotid artery can sense the **blood pressure** and **blood chemistry** * this information is sent to the brainstem, where it is integrated and projected to areas that are capable of eliciting a response **at the level of the heart** * the response involves i**ncreasing / decreasing the heart rate / blood pressure**

Question 38

Describe the neurones and structures involved in the baroreceptor reflex

Answer 38

**_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

Question 39

If there is an increase in blood pressure, what is the reflex response to counteract this?

Answer 39

* 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

Question 40

What is the reflex response if there is a change in blood chemistry?

Answer 40

* 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