(6) Brainstem Flashcards
are divisions of the brainstem clearest anteriorly/posteriorly
anteriorly
what is the pyramidal decussation
dividing line between medulla and spinal cord
corticospinal fibres cross one side to another
what is the pontomedullary junction/sulcus
where pons are separated from medulla
cranial nerves emerge at side
midbrain begins at levels of the …
cerebral peduncles
what are the cerebral peduncles
connect brainstem with white matter of cerebrum
form 2 thick band of fibers
brainstem 3 components (top to bottom)
midbrain
pons
medulla
medulla ends where?
just above the vagal trigone
what is the vagal trigone?
small elevation on the floor of 4th ventricle produced by the underlying dorsal motor nucleus of the vagus
pons beings where?
at lower border of the inferior colliculus
upper margin of midbrain is extent of..
rostral extent of superior colliculus
rostral vs caudal
rostral= upper/above
caudal= lower/below
rostral and caudal midbrain divided by
line between superior and inferior colliculi
rostral and caudal pons divided by
line where the superior cerebellar peduncle forms the roof of the 4th ventricle (called superior medullary velum)
medulla sections open/closed
rostral= open (upper)
caudal= closed (lower)
- no 4th ventricle
rostral and caudal medulla divided by
caudal limit of the 4th ventricle called obex
above the obex, each level of brainstem is adjacent to ventricular space (name them)
midbrain= anterior and posterior to cerebral aqueduct
pons= anterior and posterior to the 4th ventricle
medulla= anterior to the 4th ventricle
what is the obex
caudal limit (lower) of the 4th ventricle
3 general areas identified in cross section at any level above obex
1) tectum
2) tegmentum
3) large structures appended to anterior surface of the brainstem
what is the tectum
area posterior to the ventricular space (mostly found in midbrain)
- consist of superior and inferior colliculi
what is the tegmentum
area anterior to the ventricular space
- consist of reticular formation, cranial nerve nuclei and tracts, ascend/descending pathways
large structures appended to anterior surface of the brainstem consist of …
- most of the pons of tegmentum are appendages
- pyramids and other structures are appendages of tegmentum
brainstem is a conduit for… (2)
1) ascending tracts to reach thalamus and cerebellum
2) descending tracts to reach spinal cord
cranial nerve nuclei associated with brainstem
- mostly all associated
only one cranial nerve no direct association with brainstem= olfactory (CN1)
brainstem intrinsic features (2)
- reticular formation
- associated projections
what is reticular formation?
- stuff left over
contains neurons, nucleus fibres, don’t for discrete components
- neurons and processes
descending motor tracts, brainstem conduits
Corticospinal fibres travel in most ANTERIOR past of the brainstem
cerebral peduncle (basis pedunculi)–> basal pons –> medullary pyramids
at highest level if brainstem, corticospinal fibres are found
in basis pedunculi (cerebral peduncles)
located ANTERIOR part of brainstem
at any level of the brainstem, where are corticospinal fibers located?
ANTERIOR/ventral part of brainstem
cerebral peduncles also carry what type of fibres? (2)
corticobulbar (corticonuclear) fibres
corticopontine fibres
what are corticobulbar fibres?
descending, mostly bilateral, motor input to cranial nerve nuclei
- travel to innervate cranial nerve nuclei in brainstem
- come from cortex, innervate lower motor neuron targets in brainstem
what are cortipontine fibres?
- descending input to pontine nuclei
- fibres originate from nucleus in cerebral cortex, descend and go to level of pons, innervate pontine nuclei
what are pontine nuclei
groups of neurons on the pons that project to the cerebellum
corticopontine pathway important for
processing by cerebellum
3 tracts from cerebrum to cerebral peduncles
corticospinal fibres
corticobulbar fibres
corticopontine fibres
where are corticopontine tracts located
at medial and lateral extreme of cerebral peduncle
ascending sensory tracts, brainstem conduits
spinothalamic fibres are found LATERALLY
spinothalamic fibres carries sensation of (3)
pain
temperature
crude touch
posterior column medial lemniscus pathway carries info for (3)
ascending sensory pathways (brainstem conduits)
fine touch
vibration
conscious proprioception
the posterior columns terminate where?
posterior column nuclei
2 posterior column nuclei (lower/upper limb)
lower= gracilis (medial)
upper= cuneatus (lateral)
projections from posterior column nuclei decussate where?
in medulla as internal arcuate fibres to form the medial lemniscus
medial lemniscus location in the posterior column medial lemniscus pathway
start out as midline (medial) structure posterior to pyramids
move progressively laterally, rotate nearly 180 degrees as they ascend
- relative to spinothalamic fibres
ascending (brainstem conduits) to the cerebellum carry what type of info
unconscious proprioception
3 ascending (brainstem conduits) pathways to the cerebellum
anterior spinocerebellar tract
posterior spinocerebellar tract
cuneocerebellar tract
anterior spinocerebellar tract (brainstem conduit)
crossed projections, primarly from the leg to superior cerebellar peduncle
posterior spinocerebellar tract (brainstem conduit)
uncrossed projections from leg, via Clarke’s nucleus, inferior cerebellar peduncle
cuneocerebellar tract (brainstem conduit)
uncrossed projections form arm, via lateral cuneate nucleus, inferior cerebellar peduncle
ascending (brainstem conduits) to the cerebellum are all positioned what way?
LATERALLY
neurons within reticular formation
integrative participating in complex motor patterns, respiratory and cardiovascular activity and regulation of level of consciousness
what 5 structures are present at the CAUDAL MEDULLA (near spinomedullary transition)
- pyramidal decussation
- pyramids (most anterior part of brainstem)
- spinothalamic tract (lateraly)
- posterior columns (most posterior)
- caudal regions of posterior columns
central canal in caudal medulla
remnants of neural tube formation in development
posterior columns in caudal medulla cross and terminate in
nucleus gracilis (lower)
- not much end in cuneatus (upper)
what 3 main structures are present at the caudal medulla caudal/lower to the obex
- medial lemniscus
- internal arcuate fibres
- nucleus cuneatus and gracilis prominent
position of medial lemniscus in caudal medulla caudal to obex
2 parallel band medially
in the caudal medulla, caudal to the obex what do the the medial lemniscus and internal arcuate fibres do
- they are obvious here
- make spinothalamic and posterior spinocerebellar tracts more obvious
is fasciculus gracilis present in caudal medulla, caudal to obex
NO
- fibers end in NG
- there is FC and NC present here
what is alteral to the nucleus cuneatus
lateral/external cuneate nucleus
axons of the lateral cuneate nucleus form the
cuneocerebellar tract that is adjacent to posterior spinocerebellar tract
medial longitudinal fasciculus in caudal medulla (Caudal to obex)
- its the caudal extend of MLF
- fibre bundle runs from caudal medulla to midbrain
- connects different cranial nerve nuclei to coordinate eye and head movements
what is the inferior olivary nucleus, where is it present?
- gray matter, posterior to pyramids
- visible in caudal medulla, caudal to obex
what structure is most obvious in the rostral (open) medulla
inferior olivary nucleus (IO)
inferior olivary nucleus forms
swellings visibly called the olives, because it is so large
IO projects to … and is associated with …
projects to the cerebellum via inferior cerebellar peduncle
- associated with motor coordination and motor learning
what other 8 structures are present at the rostral (open) medulla
- well defined pyramids
- medial lemniscus
- medial longitudinal fasciculus
- spinothalamic tract (most lateral)
- lateral cuneate nucleus
- ASCT
- PSCT
- CCT
caudal pons is at the level of the
facial colliculus
what is the facial colliculus
2 swellings in floor of 4th ventricle
- under are fibres associated with facial nerves
what 5 structures are present at caudal pons
- superior peduncle
- inferior peduncle
- middle peduncle
- medial lemniscus (rotated 90 degrees)
- corticospinal tract (about same position as medulla)
in the caudal pons what is between and posterior to corticospinal tract fibres?
pontine nuclei and transverse pontine fibres
fibres from pontine nucleus cross midline and give rise too… (in caudal pons)
give rise to middle cerebellar peduncle
mid pons are at the level of
trigeminal nerve
what structures are present at level of mid pons
- similar structure to caudal pons
- anterior spinocerebellar tract lateral to the superior cerebellar peduncle
- NO posterior spinocerebellar tract
why is there no posterior spinocerebellar tract at the level of the mid pons?
because it is above the level of inferior cerebral peduncle where fibres enter cerebellum
what structures are present at rostral pons, near pons-midbrain junction
- similar structure as caudal pis
- posterior wall of 4th ventricle now formed by superiorly medullary velum
- medial lemniscus rotated above 90 degrees
- pontine nuclei- give rise to transverse pontine fibres
locus ceruleus in rostral pons
group of pigmented (melanin) cells
- largest group of CNS neurons that are noadrenergic (uses noradrenaline)
- the pigment is a byproduct of synthesis of the NT noradrenaline
- part of the reticular formation, have widespread projections to cerebrum
neurons of locus ceruleus
inactive during sleep
active when awake
very active during periods of attention and vigilance
serotonin containing neurons in rostral pons
also contains serotonin-containing neurons in the dorsal raphe nucleus
- no pigment, occupy discrete region
what 5 structures are present at caudal midbrain at level of inferior colliculus?
- cerebral peduncles
- medial lemniscus (curving posteriorly)
- MLF
- spinothalamic tract (pain/temperature)
- PAG: reticular formation region, descending pain control pathway
superior cerebellar peduncles at level of the caudal midbrain
here they decussate
- only output fibres from the cerebellum
Periaqueductal gray-raphe nuclei pathway
- PAG neurons receive inputs from spinothalamic tract collaterals
- PAG neurons project to serotonin containing neurons in nucleus raphe magnus in rostral medulla/caudal pons (in reticular formation of lower pons)
- the raphe magnus neurons then project to posterior (dorsal) horn of the spinal cord
pain and temperature signals can pass directly/indirectly
directly to neurons in nucleus proprious
indirectly via neurons in adjacent substantia gelatinosa
pain and temperature projecting indirectly (pathway)
- spinothalamic tract collaterals project to enkephalin-containing inhibitory interneurons
- these can inhibit inhibitory interneurons that normally suppress pain-control pathway
- PAG projections neurons are disinhibited
- the serotonergic neurons of the raphe magnus project to the substantia gelatinosa (can reduce pain transmission)
how do the serotonergic neurons of the raphne nucleus reduce pain transmission (3 ways)
1) presynaptically inhibit nociceptive primary afferets
2) post-synaptically inhibit spinothalmamic neurons
3) excite inhibitory enkephalin-containing interneurons that project to spinothalamic neurons
summary: pain temperature signals
there is a descending inhibitory pathway that involves serotonergic neurons, dorsal raphe nucleus neurons and through variety of pathways can inhibit flow of pain information through dorsal horn
what 5 structures are present at rostral midbrain at level of superior colliculus
- cerebral peduncles
- rostral margin of superior cerebellar peduncle (etc.)
- brachium of the inferior colliculus
- substantia nigra
- red nucleus
what is the brachium of the inferior colliculus (at rostral midbrain)
connection from inferior colliculus to the medial geniculate nucleus of the thalamus (auditory pathway)
substantia nigra position at level of rostral midbrain
it is posterior to the cerebral peduncles, and anterolateral to the medial lemniscus
substantia nigra can be divided into … (at rostral midbrain)
posterior compact part
anterior reticular part
- both regions have connections with basal ganglia
compact part of the substantia nigra (in rostral midbrain) is source of
dopaminergic projections to the basal ganglia
dopaminergic neurons in compact part can be seen without stain because
a byproduct of dopamine synthesis is melanin (dark pigment)
substantia nigra= black substance
supply of dopamine to basal ganglia is critical for…
normal function
decrease/loss of DA leads to
dysfunction of basal ganglia= Parkinson disease
red nucleus in rostral midbrain receives..
projections from the cerebellum
- has iron-containing neurons that give it a red-pink appearance
- iron gets iodized to rust
