brain stem Flashcards
components of brain stem
- long tracts
- cranial nerve nuclei: deal with motor and sensory functions of the head and neck
- cerebellar circuits: related to cerebellum
- reticular formation
long tracts include
- dorsal columns
- spinothalamic
- corticospinal
brain stem sections
- medulla
- pons
- midbrain
medulla includes…
- decussation of pyramids
- closed medulla (D.C. nucleus, medial lemniscus)
- open medulla (inf. olive, cerebellar peduncle)
pons includes…
- caudal portion (cerebellum, basis pontis, middle cerebellar peduncle)
- rostral portion (superior cerebellar peduncle)
midbrain includes…
- caudal portion (decussation of s.c.p., inf. colliculi)
- rostral portion (red nucleus, cerebral peduncle, sup. colliculi)
descending tracts
- lateral CST
- ventral CST
ascending tracts
- spinothalamic tract
- dorsal spinocerebellar tract
- ventral spinocerebellar tract
- fasciculus gracilis
- fasciculus cuneatus
the pyramidal decussation location
- the lowest part of the medulla
- marks the boundary between the brain stem and the spinal cord
where is the reticular formation?
- part of brain stem’s central core
the brain stem gives rise to what?
- cranial nerves 3 and 12
cross section of closed medulla @ decussation (most caudal, 1st cross section that looks different from spinal cord)
- you can see the decussation of the pyramids
- the corticospinal tract crosses at this level
- the fibers cross over and slice through the gray matter
- the crossing is responsible for voluntary movement (corticospinal/pyramidal tract)
what is a distinction between the spinal cord and the closed medulla cross-section? why does this change occur? (1st cross-section above spinal cord)
- the substantia gelatinosa becomes the spinal trigeminal tract and nucleus
- this change occurs because the zone of lissauer receives dorsal roots from spinal segments which are no longer received once you enter the brain.
- in the brain, that area receives cranial nerves thus the name changes because it is now receiving from the trigeminal nerve
zone of lissuaer and substantia gelatinosa receive what kind of messages in the spinal cord?
messages of pain and temperature sensation
trigeminal tract and nucleus (AKA descending tract of V)
- the tract and synapsing nucleus of the trigeminal nerve (= CN V)
- is an ascending pathway but actually travels in descent toward the brain stem
- the fibers turn downward through the medulla and the pons
afferent fibers in spinal cord and brain stem
spinal cord = dorsal roots
brain stem = trigeminal nerve
cell body in spinal cord and brain stem
spinal cord = DRG
brain stem = trigeminal ganglion
terminals in spinal cord and brain stem
spinal cord = zone of lissauer
brain stem = tract of (spinal) descending V
synapse in spinal cord and brain stem
spinal cord = substantia gelatinosa
brain stem = nucleus of (spinal) descending V
what signaling does cranial nerve V (trigeminal nerve) carry?
pain and temperature SENSATION from face and head
how does the descending V tract and nucleus relate to zone of lissauer and substantia gelatinosa?
same thing, just get signals form head and neck instead of spinal nerves
the trigeminal descending pathway
- pseudounipolar sensory fibers
- enter the pons
- fibers descend through the medulla
- synapse at the nucleus of the descending V
- pass the midline
- turn back up to the thalamus and cortex
As you ascend in the medulla, what are the differences of what you can see? (2nd cross-section above spinal cord)
- pyramids are above decussation on the ventral surface
- the fasciculus gracilis and fasciculus cuneatus start to turn into nuclei (grey matter)
where does the dorsal column (white matter) turn into nuclei (grey matter)
at the pyramids of the closed medulla above the decussation
fasciculus gracilis and fasciculus cuneatus are part of
the spinal cord
- dorsal column pathways
- terminate in the nucleus gracilis and cuneatus respectively
nucleus gracilis and nucleus cuneatus:
- contain second order neuron of dorsal column-medial lemniscus pathway
- give rise to internal arcuate fibers
- project via the medial lemniscus of the thalamus
what are internal arcuate fibers?
fibers that arise from the nucleus gracilis and nucleus cuneatus and FORM the contralateral medial lemniscus
what is the medial lemniscus?
basically the pathway of the second order sensory neuron where crossing over occurs in dorsal column pathway
when does the order of a neuron change?
after synapsing
- 1st order prior to synapse
- 2nd order after synapse
- 3rd order after another synapse
where does the medial lemniscus receive neuron signals from?
the contralateral (opposite side) nucleus gracilis and nucleus cuneatus
what makes the medulla open in the cross sections?
the presence of the 4th ventricle
what is the major change from the closed medulla to the open medulla?
the presence of the inferior olive
where is the inferior olive located?
lateral to the pyramids
what does the inferior olive do?
- receives input from spinal cord and cortex
- then sends signal to cerebellum
- function is tied to cerebellar function
where do the fibers from the inferior olive go to?
the inferior cerebellar peduncle
what is a peduncle?
a structure that connects the cerebellum to the brain stem and cerebrum
how does the spinocerebellar tract relate to the inferior olive?
the spinocerebellar tract joins with the inferior olive fibers and they enter the cerebellum via the inferior cerebellar peduncles
what pierces the pons?
THE PYRAMIDAL FIBERS PIERCE THE PONS
as you ascend in the cross sections, what changes are there as you enter the pons? (caudal pons)
- pontine nuclei
- pyramidal fibers of corticospinal tract pierce the pons
- middle cerebellar peduncle
- cerebellum
why does the medial lemniscus appear to move more dorsally as you enter the pons cross-sections?
- the fibers are destined to terminate in the thalamus
- are on an angle to approach the thalamus
where does the medial lemniscus send signals to?
the ventral posteriolateral nucleus of the thalamus (VPL)
changes and structure in the cross-section of rostral pons?
- superior cerebellar peduncle
- 4th ventricle gets a little smaller and begins to look like something else… the aqueduct
- central tegmental tract
changes to the cross section as you enter the caudal midbrain?
- perioaqueductal grey (pain)
- cerebral aqueduct
- decussation of superior cerebellar peduncle
- inferior colliculus
how many colliculi are there in the brain?
4 total
2 superior, 2 inferior
what changes as you enter the rostral midbrain cross sections?
- red nucleus
- superior colliculi
- cerebral penduncle
what does the cerebral penduncle consist of?
- substantia nigra (nucleus)
- crus cerebri (pathway)
what does the crus cerebri contain?
all the output of the cerebral cortex going down to the brain stem and spinal cord
- pyramidal tract
- corticospinal tract
also contains input to the cortex and all the stuff that goes to the pontine nuclei
LOTS OF AXONS
why is the substantia nigra important?
- it has dopaminergic neurons and damage to those neurons can cause Parkinson’s disease
what is the interpedunclular fossa?
- the space between the 2 cerebral peduncles
- 3rd cranial nerve is attached there
