Brainstem Flashcards
What’s inside the brainstem?
- Brainstem includes:
- ascending and descending tracts connecting the spinal cord to the cerebral cortex and cerebellum, cranial nerve nuclei and the reticular formation.
- 14 cranial nerve nuclei
- Reticular formation nuclei
- Tracts to and from spinal cord to cortex and cerebellum
- Tracts connecting cranial nerve nuclei
What is the reticular formation?
- Reticular formation = network of neurones responsible for core physiological processes and states of conciousness.
What is the brainstem continuous with?
- Brainstem is continuous with the thalamus and cortex above, the cerebellum posteriorly and the spinal cord inferiorly.
What is the general rule for knowing where cranial nerve nuclei are located?
- Generally location of where the cranial nerve arises off the brainstem indicates its position within the brainstem.
List the cranial nerves and where they originate from
- Olfactory- originate in cerebrum
- Optic- originate in cerebrum
- Oculomotor - midbrain
- Trochlear- midbrain
- Trigeminal - pons
- Abducens - ponto medullary junction (medial)
- facial - ponto medullary junction (lateral)
- vestibulocochlear- pontomedullary junction (lateral)
- Glossopharyngeal- lateral medulla
- vagus- lateral medulla
- accessory- C1- C5 spinal cord
- Hypoglossal - ventral medulla
Label the image
What are the pyramids formed from?
What are the cerebral peduncles?
- Cerebral peduncles- part of the brainstem that link the midbrain to the thalami and therefore the cerebrum. Descending tracts from both corticospinal and corticobulbar tracts.
- Pyramids- formed from the corticospinal tract, 80-90% of which becomes the lateral corticospinal tract at the pyramidal decussation point and descends to innervate skeletal muscles on the contralateral side of the body.
Label the image
Label this posterior aspect of the brainstem
What are the functions of superior and inferior colliculi?
What do the superior, middle and inferior cerebellar peduncles allow?
Which cranial nerve would raised ICP affect?
- Superior colliculus- visual relay centre
- Inferior colliculus -auditory relay centre
- Superior cerebellar peduncle- connects cerebellum to the midbrain
- Middle cerebellar peduncle- connects cerebellum to the pons
- Inferior cerebellar peduncle- connects cerebellum to medulla
- Cranial nerve 4 is particularly susceptible to raised ICP.
What are the two humps seen on the posterior aspect of the 4th ventricle formed from?
What symptoms could a tumour of the 4th ventricle show as?
- Humps and bumps just anterior to 4th ventricle are formed by CN VII and VI –> Called the facial colliculus
- CN VII nucleus starts laterally compared to CN VI nucleus, but to get out of the brainstem CN VII fibres wrap around CN VI nucleus before it exits anteriorly.
- Looping around of CN VII around CN VI nucleus causes this bump on the surface of the 4th ventricle
- If you have a tumour in the 4th ventricle area- you will see facial palsy.
What are the two nuclei in the image shown?
- More medially- nucleus gracilis
- More laterally- nucleus cuneatus
- At the level of this cross section see the two nuclei where the dorsal column 1st order neurones synapse with 2nd order neurons.
- Anteriorly see the two pyramids formed by the corticospinal tracts
Cranial nerves carry sensory, motor, and autonomic fibres:
Describe the route of information flow for sensory and motor fibres
When considering the motor nuclei of cranial nerves which cranial nerves are different?
- Cranial nerves are very similar to spinal nerves: they carry sensory, motor and/ or autonomic fibres
- Cranial nerve sensory neurons carry sensory information (mainly from the contralateral side) to the CNS
- CN motor nuclei are controlled by an UMN that comes from the primary motor cortex and synapse with a LMN within the cranial nerve nucleus.
- Exception: CN III, IV, VI that control eye movements:
- Eye movements come from centres within the frontal eye field cortex and occipital lobe.
What areas of the thalamus do the sensory fibres from the body synapse?
What areas of the thalamus from the head?
- From the body, sensory fibres synapse within the VPL - ventroposterolateral nucleus
- From the face, sensory fibres synapse with the VPM- ventroposteromedial nucleus.
Describe the dorsal column pathway.
How does sensory information from the face differ from sensory information from the body?
- 1st order neuron from either the arms/ legs enters the spinal cord and ascends ipsilaterally to synapse with a 2nd neurone in the lower medulla.
- These 2nd order neurones ascend to the VPL of the thalamus in the medial lemniscus (medial lemniscus= ribbon of white matter).
- 2nd order neurons synapse with 3rd order neurons in the thalamus which project up to the primary somatosensory cortex.
- Sensory information from the face is carried by the trigeminal nerve, which enters the brainstem and synapses with sensory nuclei within the trigeminal nucleus.
- These 2nd order neurons from the trigeminal sensory nucleus ascends to the thalamus via the trigeminal lemniscus.
- These 2nd order neurons synapse with 3rd order neurones within the VPM of the thalamus.
- These 3rd order neurones ascend to the primary somatosensory cortex.
What other cranial nerves synapse with CN V sensory nuclei?
What areas do they carry sensory information from?
- I love the 1975- 10/9/7 synapsed with CN 5 sensory nuclei
- CN X, XI, and VII all hitchhike withthe trigeminal lemniscus up to the primary somatosensory cortex, synapse with nuclei within the CN V sensory nucleus.
- CN X- sensory from external auditory meatus, larygopharynx and larynx, abdominal and thoracic viscera.
- CN IX- sensory from posterior 1/3 tongue, oropharynx, eustachian tube and middle ear, carotid bodies/sinus
- CN VII- sensory to the concha of the auricle
Describe how cranial nerves with motor function may innervate their targets
- Generally cranial nerves with motor function still have an upper motor neuron from the primary motor cortex, which will descend to synapse with a LMN within a cranial nerve motor nucleus.
- LMN’s within cranial nerve nuclei tend to have bilateral innervation by UMN’s from both R and L cortex- but mainly from the contralateral side.
- This means loss of one side may be compensated for by the ipsilateral side.
- The LMN leaves the nucleus as part of the cranial nerve.
What is the key point about innervation to cranial nerve motor nuclei?
What is the name of the tract that innervates LMN’s of cranial nerves?
What are the exceptions to this innervation pattern?
- All cranial nerve motor nuclei receive both IPSILATERAL and CONTRALATERAL innervation from the motor cortexes.
- Corticobulbar tract sends UMN’s/innervates the LMN’s residing in CN nuclei
- Majority from the contralateral side but some from the ipsilateral side
- Upper motor neurons to the face travel within the Genu of the internal capsule.
- These LMN’S then leave the brainstem as cranial nerves
- Exceptions to this innervation pattern are: cranial nerves III, IV, VI. The extraocular eye muscles have a different pattern of innervation.
- Further exception is CN VII (facial). There is bilateral innervation of the muscles of the face only in the upper quadrants, not the lower quadrants.
What would happen if there were a lesion at the lightning bolt?
CN V does motor innervation to the muscles of mastication.
The motor nuclei of the trigeminal nucleus recieves innervation from both the right and left cortex. Therefore a lesion on the right cortex may show as a slight defecit in function, but the left trigeminal motor nucleus would still receive motor innervation from the ipsilateral left cortex too.
What is special about the motor nuclei of cranial nerve VII?
- The motor nucleus of cranial nerve VII is split in half in the brainstem.
- The top portion of the motor nucleus innervates the upper part of the face, and receives bilateral innervation from both the R and L cortex.
- The bottom part of the nucleus innervates the bottom part of the face and receives only innervation from the contralateral motor cortex.
What would happen to motor innervation of the face in the following lesion?
- In the event of a left motor neuron lesion (e.g. stroke in the motor cortex portion that innervates the face):
- Bilateral innervation of upper portion of both R and L motor nuclei of CN VII, therefore in the R upper portion of the nucleus it will still receive innervation from R cortex despite L cortex loss.
- Upper quadrant of the face will have no symptoms
- In the Lower portion of the motor nucleus of CN V II, there is only unilateral innervation, meaning that R CN VII innervation to the lower quadrant of the face is lost- presents with R sided lower quadrant paralysis.
- Known as Forehead Sparing
What would be the consequence of a LMN lesion in CN VII?
- LMN in cranial nerve VII would lead to unilateral paralysis in both the upper and lower quadrant on the ipsilateral side of the face to the lesion, as no motor neuron can reach the muscles of facial expression on the side of the lesion.
What is Bulbar Palsy?
What are potential causes?
What does it lead to?
What are symptoms in the patient?
- Bulbar palsy= LMN lesion to CN VII- CN XII
- Potential causes: Cerebrovascular event, Polio, radiation therapy
- Leads to paralysis of:
- Pharynx (all motor to pharynx CNX except to stylopharyngeus (CNIX) ( sensory innervation all via CN IX plus in, nasopharynx via V2, laryngopharynx innervated by CN X)
- Larynx - CN X
- Soft palate-all motor innervation CN X (except tensor veli palatini V3) , snesory via V2.
- Tongue -CN XII
- Mouth/ facial muscles - CN VII
- Symptoms:
- Dysphonia- diffuculty producing speech
- Dysarthria- diffuculting articulating speech
- Dysphagia- difficultly swallowing
- Increased risk aspiration
- Drooling
- Plus LMN symptoms:
- Flaccid paralysis
- fasciculations
- muscle wasting
What is pseudobulbar palsy?
Pseudobulbar palsy = bilateral upper motor neurone lesion affecting corticobulbar tracts and UMN innervation to motor nuclei of CN’S: V , VII, IX, X, XI, XII.
Presents initially as a LMN lesion, however LMN and reflex arc are both intact. Jaw jerk reflex and gag reflex are exaggerated in psuedobulbar palsy, but absent in bulbar palsy.
Other symptoms present similar to bulbar palsy- dysphagia, dysarthria, dysphonia however presents with UMN lesion symptoms:
- No tongue muscle wasting or fasciculations ( whereas bulbar palsy has both)
- Spastic paralysis of the pharynx and larynx - AIRWAY OCCLUSION AND EMERGENCY.
Causes: head trauma, high brainstem tumour, Cerebrovascular event.
What cranial nerves may be affected by aneurysm/ pathology in the posterior cerebral artery or superior cerebellar artery?
- CN III and CN IV exit the brainstem very close to the superior cerebellar artery and posterior cerebral artery.
- Aneurysm in either of these arteries can compress and damage these cranial nerves leading to cranial nerve palsy.
What is the blood supply to the lateral and ventral medulla?
What cranial nerves can be affected by pathology of these arteries?
- Medulla split into upper and lower medulla:
- Lower medulla supplied anteriorly by the anterior spinal artery, laterally by the vertebral arteries and posteriorly by the posterior spinal artery.
- Upper medulla supplied anteriorly by the anterior spinal artery, laterally by the vertebral arteries and posteriorly by the PICA. Lateral medulla supplied by the posterior inferior cerebellar artery
- Pathology here can affect CN’s IX, X, XI
- Anterior spinal artery supplies the ventral medulla and pathology here can affect CN XII.
What arterial system supplies the brainstem and cerebellum?
Describe this arterial system and what region each branch supplies
- The vertebrobasilar system supplies the cerebellum and brainstem
- Vertebrobasilar system formed by the union of the two vertebral arteries which arise directly off the subclavian vessels and travel up the cervical vertebra in the foramen transversarium.
- They enter the brain via the foramen magnum.
- They unite over the pons, becoming the basilar artery which gives off small pontine arteries- supplying the pons.
- Basilar artery then splits off giving two superior cerebellar arteries and the posterior cerebral artery. These arteries supply the midbrain.
- The two vertebral arteries also give off the posterior inferior cerebellar artery, the anterior spinal artery (formed by union of vessels off the two vertebral arteries) and the anterior inferior cerebellar artery.
- Anterior spinal artery runs over and supplies anterior median fissue of spinal cord. Also supplies the anterior medial portion of the medulla.
- The posterior inferior cerebellar artery supplies the posterolateral aspect of the medulla.
- The vertebral arteries themselves supply the antero-lateral portion of the medulla.
What can damage to the anterior spinal artery lead to?
What can damage to the posterior inferior cerebellar artery lead to?
- Damage to anterior spinal artery can damage the corticospinal tracts/ pyramids and the medial lemniscus/ dorsal column tract
- Damage to the PICA can lead to PICA syndrome:
- Damages vestibular nuclei, inferior cerebellar peduncles, lateral spinothalamic tract, spinal trigeminal nucleus, nucleus ambiguus and descending sympathetic fibres.
- leads to imbalance and vertigo (vestibular nuclei)
- ipsilateral cerebellar ataxia (inferior cerebellar peduncle)
- contralateral loss pain and temp from the body (spinothalamic tract)
- ipsilateral loss of pain and temp from the face (trigeminal sensory nucleus)
- larynx, pharynx and palatal hemiparalysis, dysphagia and hoarseness, absent gag reflex (nucleus ambiguus which affects vagus and glossopharyngeal).
- ipsilateral horners syndrome (descending sympathetic fibres).
What is the general layout of the brainstem nuclei?
- Somatic sensory - sides
- Visceral motor and sensory - lateral
- Somatic Motor- medial
- Imagine the spinal cord layout and pull the dorsal horns forward, the general layout persists in the brainstem.
What is the Rule of 4’s in the brainstem?
- 4 medial structures all beginning with M
- 4 lateral structures all beginning with S
- 4 CN nuclei in the medulla, 4 in the pons and 4 above the Pons (2 in the midbrain).
- The motor nuclei in the midline are all the CN’s that completely divide into 12 except 1 and 2. Therefore: CN 3, 4, 6, 12.
- Therefore can decuce all others: 5/7/9/11 are in the lateral brainstem.
Label the image and explain what defect would be seen in the case of an infarct?
Starting with lateral S structures:
1) top structure is the sensory nucleus for CN V. Infarct would lead to loss of pain and temp sensation to the face ipsilaterally.
2) Sympathetic fibres- infarct would lead to Horner’s syndrome (Ptosis, Anhydrosis, Miosis).
3) Spinocerebellar tract - infarct would cause ipsilateral ataxia of limbs
4) Spinothalamic tract - infarct would cause contralateral loss of pain/ temp/ simple touch
Medial structures beginning with M”
1) Motor nuclei for CN 3/4/6/12- infarct would cause cranial nerve ocular / lingual palsy.
2) medial longitudinal fasciculus - formed by ascending/ descending tracts, main central connection for oculomotor/ trochlear/abducens. Infarct leads to loss of ipsilateral adduction of eye on lateral gaze.
3) Medial leminiscus - part of dorsal column pathway, once 2nd order neurone has synapsed with nucleus gracilis/cuneatus. Infarct leads to loss of concious proprioception/ discriminitive touch/ vibration sense on contralateral side.
4) Corticospinal tract - infarct leads to paralysis/ paresis on contralateral UL/LL.
In a brainstem lesion, apart from the Rule of 4 structures- what other structures may be affected?
- Also need to consider other smaller, relevant cranial nerves that leave the brainstem at these levels:
- Lateral medulla infarction - CN IX , X, XI
- Lateral pontine infarction - CN V- VIII
What key structures (nuclei and tracts) need to be considered in an upper midbrain lesion?
-
CN III emerges from the upper midbrain and contains both motor and parasympathetic fibres. Nuclei involved:
- CN III motor nucleus- damage leads to eye positioned down and out at rest and a full ptosis (paralysis of levator palpabrae superioris).
- Edinger Westphal nucleus - parasympathetic nucleus involved in pupillary light reflex. Damage leads to ipsilateral loss of accommodation and pupil light reflex.
- CN V sensory nucleus - which spans the length of the brainstem. (likely the mesencephalic proprioceptive nucleus).
- Substantia nigra- part of basal ganglia and degrades in parkinsons - therefore could see akinesia/ dyskinesia.
- Crus cerebri ventrally- corticospina and corticobulbar pathways.
What structures (Nuclei/ nerves) need to be considered in a lower midbrain lesion?
- CN IV motor nucleus lies in medial lower midbrain, CN IV exits the midbrain on the dorsal side. Its nerve decussates before leaving the midbrain.
- Therefore L CN IV nucleus projects to the right eye, R CN IV nucleus projects to the left eye.
- Damage to CN IV nuclues leads to loss of superior oblique function. Loss of ability to adduct eye.
- Diploplia when reading/ descending stairs, head tilted towards the site of damage nucleus.
- (Also be aware in lower midbrain lesion CN V sensory nucleus there- again proprioception likely affected).
Describe the Trigeminal nucleus and the pathway taken to the cortex
- Trigeminal nucleus is a large sensory nucleus that spans the length of the entire brainstem
- Split into three parts that detect different sensory modalities:
- 1) mesencephalic nucleus (superior- midbrain)- detects proprioception
- 2) Principal nucleus (middle- Pons)) - detects Touch
- 3) Spinal nucleus (inferior- medulla) - detects pain and temperature
- 1st order neuron enters brainstem and synapses with 2nd order neurones in the appropriate part of the CN V nucleus before decussating and ascending to the VPM of the thalamus
- Pathway from CN V nucleus to VPM is called the Trigeminal lemniscus. 2nd order trigeminal neurones cross over at different levels but ascend as trigeminal lemniscus.
what cranial nerves share the Spinal nucleus (pain and temp) of CN V?
- 1975:
- Cranial nerve X, IX, VII share the spinal nucleus of the CN V nucleus- hitchhike on it
Label the image
What is each nucleus and its function?
Sensory nuclei laterally:
- Large red nucleus spanning entire brainstem length = Trigeminal nuclues
- Top arrow - mesencephalic nucleus - proprioception
- Middle - Principal nucleus - touch
- Bottom - Spinal nucleus - pain and temperature
- Green nucleus on floor of 4th ventricle = vestibulocochlear nucleus for hearing and balance.
Motor nuclei medially:
- Upper midbrain - near superior colliculus - Oculomotor nucleus. Innervated 4/6 extraocular muscles and raises the eyelid.
- Lower midbrain - near inferior colliculus - Trochlear nucleus- innervates the superior oblique muscle, allows us to adduct the eye
- Midline of 4th ventricle- Abducens nucleus- innervates lateral rectus allowing us to abduct the eye.
- Bottom nucleus at junction of 4th ventricle and medulla- CN XII - Hypoglossal nucleus - motor innervation to the tongue.
Label the nuclei shown and what is their function?
- All nuclei shown are visceral sensory or visceral motor, beginning at the top on the right
- Top= Edinger Westphal nucleus –> parasympathetic innervation to the eye, involved in the pupillary light reflex and accomodation reflex.
- Brachiomotor CN V nucleus –> muscles of mastication
- Brachiomotor CN VII nucleus –> muscles of facial expression
- Salivatory nuclei (superior and inferior) —> parasympathetic innervation to the salivatory glands
- Nucleus ambiguus –> Brachiomotor to pharynx/larynx/ soft palate, Parasympathetic to the heart
- Dorsal Vagal nucleus –> parasympathetic vagal outflow to the body
- Bottom left= Nucleus solitarius —> Taste from VII and IX, visceral afferents from IX and X, cardiovascular baroreceptor input and respiratory receptor inputs from IX and X.
What is the nucleus shown?
what are the three component parts and what are their functions?
- Nucleus shown = nucleus ambiguus - motor function for CN IX, X, XI
- Nucleus ambigus houses LMN’s on which UMN synapse
- Does motor supply to the branchiomotor muscles in the pharynx/ larnyx/ palate
- Upper portion is innervation to stylopharyngeus via CN IX
- Middle portion is innervation to the pharynx, larynx and soft palate by CN X
- Inferior portion is innervation to the larynx via CN XI (cranial portion of accessory nerve also innervates the pharynx/larynx/ palate)
What is the nucleus shown?
What are its component parts and what is their function?
- Nucleus Solitarius
- Superior portion - receives taste sensation from CN VII, and CN IX
- Middle portion- receives visceral afferent info from the GI tract and respiratory system via CN X and CN IX
- Inferior portion - receives afferent info from baroreceptors and respiratory receptors via CN IX and CN X.
For CN IX: Glossopharyngeal: Fill the blanks and explain
- Nucleus involved in sensation from the pharynx/ middle ear etc - know that CN IX sensory innervation hitchhikes on the spinal portion of CN V nucleus.
- Taste from posterior 1/3 tongue and carotid body/sinus input –> nucleus solitarius
- Output from the nucleus ambiguus –> motor to the stylopharyngeus muscle
- Inferior salivatory nucleus output —> parasympathetic to the parotid gland
For the Vagus nerve fill in the blanks
What are the two portions of CN XI?
What are their functions?
- CN XI has both a cranial portion and a spinal portion (arises from C1-C5).
- Cranial portion arises as part of the cells of the nucleus ambiguus and travels with CN X, essentially considered as part of CN X. Does motor innervation to the larynx/ pharynx/ soft palate.
- The spinal portion arises from ventral grey horn of C1-C5 and innervates the sternocleidomastoid and trapezius muscle.
Explain the symptoms that would be seen if a lesion were to occur at each of these sites?
- In oculomotor nucleus –> ipsilateral paralysis of 4/ 6 extraocular muscles, leading to down and out eye and divergent squint. Diplopia at rest, worse when looking away from lesion. Pupillary light reflex may be fine if the EWP nucleus intact.
- In trochlear nucleus –> Paralysis of superior oblique muscle on contralateral side –> leads to inability to adduct eye inward. Diplopia when looking down
- In abducens nucleus –> ipsilateral loss innervation to lateral rectus muscle, inability to abduct eye. Diplopia at rest and worse when looking towards lesioned side.
- In hypoglossal motor nucleus –> flaccid hemiparalysis of the tongue muscles on ipsilateral side ,deviation towards the side of the lesion when protruded.
- Trgieminal sensory nucleus –> loss of proprioception (mesencephalic), touch (principal) and pain/ temp (spinal). Damage to spinal nucleus may also affect CN ‘S X , XI and VII that hitchhike on it.
What are each of the nuclei shown?
What can occur if there is damage to each?
- Top - Erdinger Westphal nucleus - parasympathetic innervation to ciliary muscles and pupillae constrictor muscles. Leads to loss of pupillary light reflex and accomodation reflex in eye affected. Contralateral reflex will be preserved.
- Visceral motor to muscles of mastication –> paralysis muscles mastication ipsilaterally
- Visceral motor to facial muscles –> paralysis of facial muscles ipsilaterally
- Superior salivatory nucleus –> parasympathetic innervation to salivary glands (except parotid), lacrimal glands. Loss leads to reduced saliva and tear production on ipsilateral side.
- Inferior salivatory nucleus –> parasympathetic innervation to Parotid gland, loss leads to lack of saliva production on ipsilateral side.
- Nucleus ambiguus (orange) –> loss of parasympathetic to cardiac regions and loss of motor to the pharynx/ larynx/ soft palate. Dysphagia and soft palate deviation away from the lesion.
- Dorsal vagal nucleus –> loss vagal output to the body, patient can die suddenly following lateral medullary stroke.
- Upper left - Vestibulocochlear nucleus –> balance issues to contralateral side, vertigo, nystagmus, some hearing loss
- Nucleus solitarius –> lack of visceral sensation - taste, carotid body and sinus
What is the reticular formation?
what are the parts involved in sleep?
What are the parts involved in wakefullness?
- Reticular formation is a neural network located throughout the brainstem formed of poorly defined cell columns, has many functions but one is sleep and wakefullness cycle.
- Brainstem damage can affect your level of conciousness.
- Nuclei involved in sleep:
- Midbrain raphe nuclei - secrete serotonin
- Cereulean nucleus active in REM sleep
- Hypothalamus metabolises CSF serotonin to produce sleep-inducing molecule
- Nuclei involved in wakefullness:
- Nuclei next to the cerulean nucleus has cholingergic neurones that excite the cortex via thalamus
- Hypothalamic nucleus - tuberomamillary nucleus
- Basal nucleus of meynert above optic chiasm also active
