Brainstem and Cranial nerves Flashcards
What is the Brainstem made up of?
- Midbrain
- Pons
- Medulla
Which CN’s have their nuclei/are connected to the brain stem?
10 out of the 12 CN’s are.
The first 2 are not - olfactory & optic
What is important in motor co-ordination?
The Cerebellum
What are the mamillary bodies part of?
The Hypothalamus, not the brain stem
What are the Crus Cerebri?
Huge fibre tracts that convey info from cortex to periphery and vice versa
also connects to higher brain centres
What do the middle cerebellar peduncles do?
Connect the brain stem to the cerebellum
What does the cerebellum overlie?
The 4th ventricle
How many pairs of Cerebellar peduncles are there?
Which one is the largest?
There are 3 pairs:
- superior
- middle
- inferior
Middle ones are the largest
What do the Superior and Inferior Colliculi do?
Superior Colliculi:
- conveys visual info from the eyes to the visual cortex
Inferior Colliculi:
- relays auditory information
Where do the Corticospinal tracts run through?
The Pyramids
Where does a larger portion of the Corticospinal tract decussate?
What is this portion?
At the level of the pyramids
80% decussate here
Which Cranial nerves attach to the Brainstem?
Cranial nerves III to XII (3 to 12)
First 2 cranial nerves (olfactory and optic) don’t connect to the brain stem
What are fibres
- in front of the optic chiasm?
- behind the optic chiasm?
In front = Optic NERVE
Behind = Optic TRACT
What happens at the Optic Chiasm?
Vast majority of the optic nerve from the eye crosses over here and then projects to the midbrain and cortex
What are the generally larger AFFERENT SENSORY nuclei?
- Trigeminal sensory nucleus
- cV, cIX, cX
- trigeminal, glossopharyngeal, vagus
- Vestibular &cochlear nuclei
- cVIII
- vestibulocochlear
- Nucleus solitarius
- cVII, cIX, cX
- facial, glossopharyngeal, vagus
What are the smaller EFFERENT MOTOR nuclei?
EOTTAFSIND
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Not Dying
- Edinger-Westphal nucleus - cIII occulomotor
- oculomotor nucleus - see above
- trochlear nucleus - cIV trochlear
- trigeminal motor nucleus - cV trigeminal
- abducens nucleus - cVI abducens
- facial motor nucleus - cVII facial
- superior salivatory nucleus - see above
- inferior salivatory nucleus - cIX glossopharyngeal
- nucleus ambiguus - cIX + cXI (accessory)
- dorsal motor nucleus of the vagus - cX vagus
- hypoglossal nucleus - cXII hypoglossal
What are the Cranial nerves involved with eye movement?
- CN III - Optic
- CN IV - Trochlear
- CN VI - Abducens
Occulomotor nerve
cIII
Which nuclei make up this nerve?
-
Edinger-Westphal nucleus
- parasympathetic nucleus - important in the papillary reflex
-
Occulomotor nucleus
- involved in voluntary movement
both found near top of brainstem
Trochlear Nerve cIV
EFFERENT MOTOR PROJECTION
What nuclei make up this nerve?
what does it innervate?
- Trochlear nucleus
- innervates Superior Oblique
- abducts the eyeball to the side
- loops around the central canal and exits DORSALLY
what are the 3 things to know about the TROCHLEAR nerve? cIV
- smallest of the cranial nerves
- only cranial nerve that exits the brainstem on the dorsal side (all others exit on the ventral side)
- only cranial nerve that decussates!!
- therefore specific defects of cIV will lead to impairment of movements on the other side
Abducens nerve cVI
what nucleus is it made up of?
what kind of nerve is it?
what does it innervate?
Where does it lie?
- Made up of the abducens nucleus
- motor nerve
- innervates lateral rectus
- attaches to the side of the eye and ABDUCTS the eyeball
- Lies at the floor of the 4th ventricle
At what level do cIII and cIV exit the brainstem?
Occulomotor and trochlear
They both exit at the level of the Crus Cerebri
What arteries does the occulomotor nerve exit between?
- posterior cerebral artery
- (supplies part of the occipital lobe)
- superior cerebral artery
Where does the abducens nerve exit?
At the junction between the pons and medulla
what side does the trochlear nerve exit on?
is this normal
Dorsal
No it is the only CN to do this
What do cIII, cIV and cVI exit the cranium via?
Superior Orbital Fissure
Rupture of what can lead to the squeezing of the cranial nerves?
THe Cavernous Sinus
it is thin-walled.
Hence complete paralysis of an eye may be an indication of cavernous sinus rupture
Trigeminal nerve cV
Has both afferent Sensory and efferent motor componets
where does it exit the brain stem?
Sensory cV
-
from the trigeminal sensory nucleus
- lies @ the floor of the 4th ventricle
- supplies the face
Motor cV
- from the trigeminal motor nucleus
- innervates the muscles of mastication
EXITS the brain stem:
- lateral to the Pons
How many branches does the sensory cV have?
What do they supply?
Has 3 divisions
-
opthalmic
- forehead, eyes, tip of nose
-
maxillary
- cheeks and upper jaw
-
mandibular
- lower jaw
Where do all the second order neurons of the trigeminal sensory nucleus project to?
What are these called?
VP (ventral posterior) nucleus of the Thalamus
The fibres are called trigeminothalamic fibres
Trigeminal sensory nucleus
What senses have their cell bodies outside the CNS like the spinal levels?
What is the ganglion called?
Touch/pressure and Pain/Temp
The Ganglion is called the Trigeminal (semilunar) ganglion
Trigeminal
Which sense has its cell body in the CNS?
What is its nucleus called?
Proprioception
Mesencephalic nucleus of the Trigeminal
Trigem. n
What is the nucleus for touch/pressure?
Chief sensory nuclueus of the trigeminal
Trigem n
What is the nucleus for pain/temp?
Nucleus of the spinal tract of the trigeminal
Facial nerve
What are its sensory and motor nerve nuclei?
Sensory - nucleus solitarius
Motor
-
superior salivatory nucleus
- parasympathetic output
- facial motor nucleus
Where does the motor component of the Facial nerve exit?
It wraps around the abducens nucleus and exits laterally
Exits at the CPA - cerebellopontine angle
the angle between the cerebellum pons and medulla
Peripheral distribution of the facial nerve fibres
Motor
- Orginates in the facial nucleus
- passes up and loops over the abducens nucleus then moves down
- Gives off a branch to the stapedius -
- smallest muscle of the body in the inner ear
- Passes through the stylomastoid foramen
- supplies the facial muscles
Peripheral distribution of the facial nerve fibres
Sensory
- nerve cell bodies lie outside the CNS in the geniculate ganglion
- fibres enter the CNS and project to the nucleus solitarius
- other fibres travel and supply the roof of the mouth whilst some travel with the chorda tympani and supply the tongue
Peripheral distribution of the facial nerve fibres
Parasympathetic
- Originate in the superior salivatory nucleus
- innervate the glands
- one set goes through the chorda tympani to the submandibular ganglion before giving branches to the sublingual and submandibular glands
- the other set goes to the pterygopalatine ganglion which then branches to the lacrimal gland and also bits of the nose and top of mouth
What is Bell’s palsy caused by?
Acute unilateral inflammation of cVII (facial nerve)
What are the motor branches of the Facial nerve?
Mneumonic:
Two Zulus Borrowed My Cat
- Temporal
- Zygomatic
- Buccal
- Marginal Mandibular
- Cervical
All are relatively superficial and prone to injury from facial laceration
Patient dribbles if the Marginal Mandibular is damaged, also opp side muscles pull mouth over
mouth muscles then can’t form an adequate seal and also it is ugly looking
Vestibulocochlear nerve cVIII
Predominantly SENSORY, tiny motor component involved
vestibular and cochlear nuclei - involved with hearing and balance
Exits at the CPA
It is at risk from Acoustic Neuroma, Neurofibromatosis
- can therefore squish CNVII
- Bell’s (facial) palsy may be an indication of the above conditions
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Afferent sensory fibres of the Glossopharyngeal nerve cIX
-
Trigeminal sensory nucleus
- general sensation
-
Nucleus Solitarius
- taste, visceral sensation
-
Nucleus Ambiguus
- pharynx, back of tongue
-
Hypoglossal nucleus
- pharynx, back of tongue
Motor component of the Glossopharyngeal nerve cIX
nucleus ambiguus
- innervates the Stylopharyngeus muscle
- this moves the head
Preganglionic parasympathetic fibres of cIX
Inferior salivatory nucleus
- postganglionic neurones to otic ganglion
- this otic ganglion innervates the parotid salivary gland
Glossopharyngeal nerve
where does it join the brainstem?
Lateral to the olive/medulla
Just inferior to the CPA
Vagus - CN X
afferent fibres
Trigeminal sensory nucleus
- sensation
Nucleus solitarius
- visceral sensation
Vagus Nerve
Motor fibres
It is a small motor compartment
Nucleus ambiguus
- muscles of soft palate
- pharynx
- larynx
- upper part of oesophagus
Vagus nerve
Parasympathetic fibres
Substantial parasympathetic portion
Dorsal motor nucles of the vagus
- Vagus nerve:*
- attaches lateral to the medull, lateral to the Olives
Accessory nerve cXI
Has 2 parts
What does it exit the neurocranium via?
2 parts from:
- nucleuus ambiguus (inferior part)
- spinal root
Exits via the Jugular foramen
Rupture of the blood vessels in the Jugular foramen can cause cranial nerve damage
Hypoglossal nerve cXII
PURELY MOTOR
Hypoglossal nucleus
- extrinsic and intrinsic muscles of the tongue
- important for speech
where do the rootlets of cXII emerege?
Between the Olives and the pyramids
Motor neurone disease
- chronic degenerative disorder (> 50 ys)
- degeneration of corticobulbar tracts
- degeneration of nucleus ambiguus and hypoglossal nucleus
- dysphonia (difficulties in phonation)
- dysphagia (difficulties in swallowing)
- dysarthria (difficulties in articulation)
- weakness, spasticity of tongue
Compression of cIX-cXII by tumours
Causes:
- dysphonia (difficulties in phonation)
- unilateral weakness, wasting and fasciculation of tongue
- suppression of gag reflex
- unilateral wasting of sternomastoid and trapezius muscles
Noradrenergic projections from the brain stem
homeostatic functions
Involved in
- arousal
- attention
- awareness
- sleep
- cognition
- cardiac reflexes
- respiration
- REM sleep
Pathology of the NA pathways leads to:
- depression
- anxiety
- stress
- opiate withdrawal
- Rett syndrome
Serotenergic pathways
involved in:
reward
sleep
nociception
Dopaminergic pathways
involved in
- reward
- cognition
- motivation
- emotional processing
- motor control
- saccadic eye movement
Key areas:
- ventral tegmental area
- substantia nigra
- locus coeruleus
Pathology of dopaminergic pathways leads to
- addiction
- schizophrenia
- insomnia
- ADHD
- Parkinson’s disease
unilateral brain stem leisons
(stroke, tumour, multiple sclerosis)
- ipsilateral cranial nerve dysfunction
- contralateral spastic hemiparesis
- hyperreflexia
- ipsilateral incoordination
- contralateral hemisensory loss
Bilateral brain stem leisons
Trauma, stroke, cancer
Coma
Death
Summary
- The brain stem consists of midbrain, pons and medulla.
- It is a conduit for ascending and descending pathways such as the corticospinal tract that decussates at the level of the pyramids.
- Cranial nerves III-XII attach to the brain stem and their sensory and motor nuclei are located within the brain stem.
- reticular formation has widespread ascending and descending projections and is involved in multiple normal and pathological processes.
- serotonergic raphe nuclei innervate every major CNS subdivision.
- The dopaminergic substantia nigra is affected in Parkinson’s disease.
- Brain stem lesions can lead to unilateral nerve dysfunction, coma and death.
