Brainstem Flashcards
What is inside the brainstem?
- 14 CN nuclei
- Tracts connecting CN nuclei
- Tracts to and from spinal cord, cortex and cerebellum (ascending/descending)
- Reticular formation (reticular system nuclei)
What is the reticular formation?
A network of neurons responsible for core physiological processes and states of consciousness
What structures in the brainstem continuous with?
Thalamus and cortex above, cerebellum posteriorly and spinal cord below
Where do the cranial nerves (CN) emerge off of the brainstem?
Above pons:
I: links to piriform cortex
II: links to lateral geniculate body
III + IV: midbrain
In/around pons:
V: pons
VI-VIII: ponto-medullary junction
In medulla:
IX + X: lateral medulla
XII: ventral medulla
XI: C1-C5 spinal cord
What would a fracture at the foramen ovale cause?
Sensory loss on the face and motor loss of mastication as CN Vc leaves the skull floor through this hole
Where do cranial nerves (CNs) leave the cranium in the skull floor via the foramen generically?
Typically quite close to where they leave the brainstem
Why are the pons so big and rounded?
Masses of fibres cross their to enter the cerebellum
Where are the cerebral peduncles? What goes through them?
In upper midbrain anteriorly
Descending CST and CBT
Where are the pyramids? What goes through them?
Upper medulla anteriorly
Descending CST (pyramidal tracts)
What happens at the pyramidal decussation?
CST fibres become the lateral CST in the cord
What cranial nerve (CN) emerges at the interpeduncular fossa of midbrain?
CNIII
What nuclei can be seen in the lower medulla posteriorly?
Dorsal column nuclei for ascending sensory fibres:
- Nucleus cuneatus (arms) - innermost
- Nucleus gracilis (legs) - outermost
What do the superior, middle and inferior cerebellar peduncles do?
Connect cerebellum and brainstem
What is the only cranial nerve (CN) to arise from the dorsal side of the brainstem?
CNIV - making it more susceptible to raised ICP
What is the function of the superior and inferior colliculus posterior of brainstem?
Superior: visual relay nucleus
Inferior: Auditory relay nucleus
What does cranial nerve (CN) VII wrap round posteriorly in brainstem?
Around CNVI’s nucleus causing a bulge in brainstem just under 4th ventricles so a 4th ventricular tumour will compress both causing facial palsy and no lateral movement of eye, convergent squint and horizontal diplopia (worst when looking to affected side)
What are the origins of the motor cranial nerves?
Most are controlled by UMNs coming from primary motor cortex
However, CNIII, IV and VI for eye movements originate from centres in occipital lobe and frontal eye field cortex
What other fibres hitchhike along cranial nerve (CN) V’s sensory route?
Most nociception fibres from CNVII, IX and X - all enter brainstem, synapse on CNV sensory nuclei, fibres decussate and all ascend along trigeminal lemniscus fibre bundle to VPM of thalamus to synapse onto 3rd order neuron
What happens at cranial nerve (CN) motor nuclei in the brainstem?
Where typically both contralateral and ipsilateral UMNs synapse onto a LMN where the major tract contribution comes from the contralateral cortex so a lesion on one side means the CN can maintain some function due to bilateral innervation of corticobulbar tract
What structure of the internal capsule do motor tracts for the face travel through?
The genu
What cranial nerve (CN) nuclei is the exception to having both a contralateral and ipsilateral innervation?
CNVII
What is special about cranial nerves (CNs) III, IV and VI?
They have a different innervation pattern to other motor CNs of the face as they innervate the eye muscles
What is the structure of cranial nerves (CNs) VII motor nucleus in brainstem?
Split in half where top part associated with top of face receiving BILATERAL innervation whereas bottom part is associated with bottom of face receiving UNILATERAL innervation by contralateral cortex
What is an example of an upper motor neuron (UMN) lesion of cranial nerve (CN) VII?
Stroke - would cause forehead sparing as symptoms would only show in the lower face quadrants
What is an example of a lower motor neuron (LMN) lesion of cranial nerve (CN) VII?
Bell’s palsy - would knock out 1 whole half of the face
What does the word bulb refer to?
The brainstem - more specifically the pons and medulla
What is bulbar palsy?
LMN lesion affecting CNVII-XII causing paralysis of pharynx, soft palate, larynx, tongue (sometimes face + mastication), dysarthria, dysphonia, drooling, poor swallowing, aspiration, flaccid paralysis, wasting and fasciculations caused by polio, radiotherapy or CVE
What is pseudobulbar palsy?
Bilateral corticobulbar tract disorder (UMN lesion) presenting initially as LMN lesion although LMN and reflex arc remain functional but bilateral damage significant with similar symptoms of bulbar palsy but can develop spastic paralysis of pharynx and larynx (airway occlusion emergency) caused by head injury, CVE or high brainstem tumour
What cranial nerves (CNs) would be affected if the posterior inferior cerebellar artery (PICA) was lesioned?
CNIX-XII as the artery is around the lower medulla and so are these CNs nuclei
What vessels are cranial nerves (CNs) III and IV close to? What is the clinical significance of this?
CNIII: superior cerebellar artery
CNIV: posterior cerebral artery
Can be compressed w/ aneurysm
What is the arterial system that supplies the brainstem and cerebellum?
Vertebrobasilar
What is the blood supply to the midbrain?
Anterior: posterior cerebral artery (PCA)
Posterior: Superior cerebellar artery (SCA)
What is the blood supply to the pons?
Pontine arteries
What is the blood supply to the medulla?
Posterior: posterior inferior cerebellar artery (PICA)
Medial: anterior inferior cerebellar artery (AICA)
Anterior: anterior spinal
What can occur if the anterior spinal artery is damaged?
Medial lemniscus (dorsal column tract) and pyramids (CST tracts) affected
What is the nuclear arrangement of the brainstem?
Outermost: somatic sensory (CNV sensory (CNVII, IX + X hitchhike along) + CNVIII)
Medial: visceral motor and visceral sensory
Innermost: somatic motor (CNIII, IV, VI + XII)
What are the 4 major medial structures of the brainstem (all start with M!)?
- Motor nuclei (CNIII, IV, VI and XII)
- Medial longitudinal fasciculus (eye movements)
- Medial lemniscus (contralateral dorsal column continuation)
- Motor corticospinal (corticospinal fibres not yet decussated)
What are the 4 major lateral structures of the brainstem (all start with S!)?
- Sensory nucleus (CNV)
- Sympathetic nerves
- Spinocerebellar tract
- Spinothalamic tract (spinal lemniscus)
What fibres does cranial nerve (CN) contain?
Motor: involved in eyeball and eyelid movements - damage leads to exotropia and a full ptosis
Edinger-Westphal (PS) nucleus: pupillary light reflex - damage leads to ipsilateral loss of accommodation and reflex
Where does cranial nerve (CN) IV decussate?
Before exiting the posterior brainstem so a brainstem lesion would show ipsilateral symptoms whilst after the brainstem, contralateral symptoms would show
What is the structure of the cranial nerve (CN) V sensory nucleus?
Spans the entire brainstem and split into 3 sensory modalities:
- Mesencephalic: proprioception
- Principal: touch
- Spinal: pain + temp (shared with CN VII, IX + X)
What is contained within the somatic sensory part of the brainstem?
CNV sensory (CNVII, IX + X hitchhike along as they dont have their own nucleus)
CNVIII
What is contained within the somatic motor part of the brainstem?
CNIII
CNIV
CNVI
CNXII
What is contained within the visceral motor and sensory part of the brainstem?
CNIII (PS - Edinger Westphal)
CN V branchio-motor
CNVII branchiomotor
Salivatory PS nuclei (superior + inferior)
Nucleus ambiguous branchiomotor
Dorsal vagus nucleus (PS - vagus n. outflow to body)
Nucleus solitarius
What is in the motor nucleus ambiguous?
PS cardiac supply
Branchiomotor muscle: pharyngeal/laryngeal/palatal innervation IX (stylopharyngeus + larynx) and X (pharynx larynx + upper 1/3 of oesophagus)
What is in the sensory nucleus solitarius?
Sympathetic + PS fibres:
- Taste from VII + IX
- CV baroreceptor/chemoreceptor input (carotid body + sinus), visceral afferents from resp. receptor and GI tract (IX + X)
What are the functions and associated nuclei of the cranial nerve (CN) IX?
- Spinal nucleus of CNV: sensation from pharynx, mid. ear etc.
- Nucleus solitarius: taste from tongue (post 1/3) and carotid body + sinus input
- Nucleus ambiguus: motor to stylopharyngeus
- Inferior salivatory nucleus: parotid gland secretions
What are the functions and associated nuclei of the cranial nerve (CN) X?
- Spinal nucleus of trigeminal: sensation from pharynx, larynx + external ear
- Nucleus solitarius: general visceral afferents (GI, heart, lung)
- Nucleus ambiguus: motor to larynx, pharynx + soft palate
- Dorsal motor n.: PS to GI, CV + resp. systems
What are the functions and associated nuclei of the cranial nerve (CN) XI?
- Nucleus ambiguus: contributes to CNX motor
2. C1-5 ventral grey horn: motor to trapezius + SCM
What side do most cranial nerve (CN) nuclei produce symptoms on? What is the exception?
Ipsilaterally EXCEPT CNIV
How is the reticular formation of the brainstem involved in being awake?
Cholinergic neurons adjacent to cerulean excite cortex via thalamus
Hypothalamic nucleus (tuberomammillary)
Basal nucleus of Meynert above optic chiasm also active
How is the reticular formation of the brainstem involved in sleep?
Midbrain raphe nuclei (5HT)
Cerulean nucleus active in REM sleep
Hypothalamus metabolises CSF 5HT to produce sleep-inducing molecule
What symptoms would a lateral brainstem lesion cause?
- SCT - ipsilateral limb ataxia
- STT - contralateral loss of limb pain + temp
- CNV sensory nucleus - ipsilateral facial pain + temp sensation loss
- Sympathetic fibres - ipsilateral horner’s syndrome
- Smaller CNs at lateral medulla (CNIX-XI) + pontine (V-VIII)
What symptoms would a medial brainstem lesion cause?
- CST - contralateral weakness of UL/LL
- Medial lemniscus (DC) - contralateral loss of vibration + proprioception
- Medial longitudinal fasciculus - no ipsilateral eye adduction on lateral gaze
- Motor nuclei of CNIII, IV, VI + XII - ocular or lingual palsy depending on lesion level
