CH 10: Organization of the brainstem and CNs Flashcards
what is the medulla?
the most caudal part of the brainstem
extends rostrally for 2.5 cm to the caudal border of the pons
the central canal of the SC continues through the ____ and flares open into the ____?
through the caudal half of the medulla
at a point called the obey, flares open into the wide cavity of the 4th ventricle
the rostral part of the medulla occupies the?
floor of the 4th ventricle
the roof of the 4th ventricle consists of the ?
tela choroidea
the choroid plexus
cerebellum
what is the tela choroidea?
a thin sheet of apposed ependyma and pia mater
what is the choroid plexus
tela choroidea with good vessels between the ependyma and pia
what can be seen from the anterior aspect of the medulla?
the pyramids
what are they pyramids?
formed by the pyramidal (corticospinal and corticobulbar) tracts
forms 2 longitudinal ridges on either side of the ventral median fissure
the decussation of the pyramids can be seen as bundles of fibers crossing and obliterating the fissure at the extreme caudal end of the medulla
what can be seen from the lateral aspect of the medulla?
the ventrolateral sulcus
dorsolateral sulcus
olive
what is the ventrolateral sulcus?
what exits from this groove?
extends along the lateral border of the pyramid
the rootlets of the hypoglossal nerve (12) exit
what exits from the dorsolateral sulcus?
cranial portion of the accessory nerve (9)
vagus nerve (10)
glossopharyngeal nerve (11)
how does the accessory nerve exit?
the cranial portion exits through the dorsolateral sulcus
the spinal portion originates in the gray matter of C2-5. its rootlets exit through the lateral funiculus of the cord, join, and then ascend along the lateral surface of the medulla
what is the olive?
the prominent oval swelling of the lateral area of the medulla between the ventrolateral and dorsolateral sulci
marks the site of the inferior olivary nuclear complex inside the medulla
what can be seen from the posterior aspect of the medulla?
fasciculus gracilis
fasciculus cuneatus
what marks the termination of the FC and FG?
FC= cuneate tubercle
FG= clava
the axons of neurons in the nucleus gracilis and nucleus cuneatus extend ventrally into the?
tegmentum (floor) of the medulla
thus, at the rostral end of these nuclei, the dorsal area “opens up” exposing the floor of the fourth ventricle rostral to the obex
what are the 2 pairs of swellings seen in the floor of the 4th ventricle?
vagal trigone
hypoglossal trigone
what is the vagal trigone?
lateral ridge in the floor of the 4th ventricle
bulge indicates the location of the dorsal motor nucleus of the vagus
what is the hypoglossal trigone?
medial ridge of the floor of the 4th ventricle
bulge indicates the location of the hypoglossal nucleus
what is the striae medullares of the 4th ventricle?
what do these fibers mark laterally?
ridges formed by fibers passing toward the cerebellum
laterally, these fibers mark the location of the lateral recesses
what is the lateral recess?
where opening in the 4th ventricle (foramina of Luschka) allow CSF to flow from the 4th ventricle into the subarachnoid space
how does CSF leave the 4th ventricle?
lateral recesses
foramen of Magendie- a single, midline opening at the Obex
what is the pons?
a large tissue mass rostral to the medulla
on the ventral surface of the brainstem, the cerebral peduncles pass into the pons from above, and the pyramids emerge from below
what can be seen on the anterior aspect of the pons?
a band of thick transverse fibers- constitute the pons proper or the “bridge”- occupies the entire anterior aspect
the basal sulcus-
what is the basal sulcus?
what coincides with it ?
shallow furrow extends along the midline and coincides with the course of the basilar artery
what CN exits from the inferior pontine sulcus?
the abducens nerve (6) at the caudal border of the pons close to the pyramids
what can be seen from the lateral aspect of the pons?
middle cerebellar peducles (brachia pontis)
what is the middle cerebellar peduncle?
transverse fibers of the pons converge to form compact lateral bundles that attach the pons to the overlying cerebellum
what does the cerebellopontine angle consist of?
the triangular space formed between the caudal border of the middle cerebellar peduncle, the adjoining part of the cerebellum and the upper part of the medulla
what CNs emerges from the cerebellopontine angle?
facial (7)
vestibulocochlear (8)
where does the trigeminal nerve (5) emerge?
penetrates the brachium pontis near the middle of the lateral surface of the pons
what can be seen on the posterior aspect of the pons?
forms the rostral part of the floor of the 4th ventricle
at its widest point, this triangular area contains the pontomedullary junction and the lateral recesses of the ventricle.
the facial colliculus superior cerebellar peduncles
anterior medullary velum
what is the facial colliculus and what forms it?
lies rostral to the lateral recess in the floor of the 4th ventricle.
the abducens nucleus and the fibers of the facial nerve that cross over the nucleus of abducens form this colliculus (little hill)
what do the superior cerebellar peduncles form?
what joins it to form the roof of the ventricle?
forms the walls of the 4th ventricle at this level
the cerebellar vermis in the caudal pons and the anterior medullary velum rostrally join these peduncles in the midline and complete the roof
what does the midbrain consist of?
a short segment of brain stem between the pons and the diencephalon
what is the cerebral aqueduct?
a markedly narrow tubular passage connecting the 3rd and 4th ventricles
what can be seen from the anterior aspect of the midbrain?
2 rope like bundles of fibers- cerebral peduncles or crura cerebra and a deep interpeduncular fossa that separates them, form the inferior surface
the optic tract skirts around each cerebral peduncle just before it disappears into the cerebral hemisphere above.
at its caudal end, the peduncle passes directly into the basilar portion of the pons
what CN exits from the sides of the interpeduncular fossa?
the oculomotor nerves
and emerge on the surface at the transverse groove between the pons and the midbrain
what can be seen from the posterior aspect of the midbrain?
corpora quadrigemina
the posterior surface of the midbrain=
tectum
what is the corpora quadrigemina?
4 rounded elevations
superior colliculi
inferior colliculi
what nerve emerges from the tectum?
the trochlear nerve (4)
smallest CN
emerges from tectum just behind the inferior colliculi after decussating in the anterior medullary velum
what arteries provide the primary source of blood to the brain stem?
vertebral arteries
direct branches of the L and R vertebral arteries supply the ..
anterolateral parts of the medulla
the anteromedial medulla receives blood from the
anterior spinal artery
at the pontomedullary junction, the 2 vertebral arteries..
join to form the basilar artery
the basilar artery supplies..
branches to the pons and the midbrain
branches of both the vertebral and basilar arteries wrap ..
what do these arteries include?
dorsally around the brain stem to supply the dorsal aspect of the brain stem and the entire cerebellum
posterior inferior cerebellar arteries
anterior inferior cerebellar arteries
superior cerebellar arteries
the posterior inferior cerebellar arteries supply the
medulla as well as the cerebellum
the anterior inferior cerebellar arteries provide blood for the
pons and the cerebellum
the superior cerebellar arteries distribute to ?
both the midbrain and the cerebellum
at the rostral end of the midbrain, the basilar artery terminates by …?
dividing into the R and L posterior cerebral arteries
where does the R and L posterior cerebral arteries provide blood for?
passes superior to the tentorium cerebelli to supply the posterior and ventral surfaces of the cerebral hemispheres
what is the posterior portion of the pons?
tegmentum
what is the anterior portion of the pons?
basilar portion
what is the roof portion of the pons?
tectum
overlying the cavity of the ventricle
becomes expanded and specialized to form the cerebellum
where do the corticospinal tracts appear in the pons ?
in a central location in the basilar portion
the gray matter that surrounds the corticospinal tracts in the pons contains cells of the ?
pontine nuclei
transverse pontine fibers (pontocerebellar tract) crossing from one side to the other, posterior and anterior to the corticospinal tracts, consist of axons from cell bodies in the pontine nuclei
the fibers from the pontine nuclei of one side form the ___ and terminate in the ____?
contralateral middle cerebellar peduncle and terminate in the cerebral cortex
the pontine nuclei receive input from the ___?
what do their projections to the cerebellum constitute?
ipsilateral cerebrum
their projections to the cerebellum constitute a major route by which the cerebral cortex communicates with the cerebellar cortex (travels through the cerebral peduncle of the pons)
how is the medial lemniscus oriented in the medulla ?
in the anterior-posterior axis (CTLS)
how is the medial lemniscus oriented in the lower pons?
in the tegmentum of the pons the ML has shifted and the long axis of the ellipse extends transversely along the boundary with the basilar portion of the pons
what is the position of the MLF in the lower pons? what does it primarily consist of at this level?
retains its position near midline in the floor of the fourth ventricle
MLF primarily consists of ascending fibers- these fibers arise in the vestibular nuclei and project to the nuclei supplying the extra ocular muscles
the descending interstitiospinal and pontine reticulospinal tracts become partially intermingled with the MLF at this level
what is the trapezoid body?
an auditory relay structure- appears as a prominent band of decussating fibers in the anterior part of the tegmentum
its fibers interlace at right angles with the rostrocaudally oriented fibers of the ML
what is the central segmental tract/bundle?
an isolated bundle in the anterior part of the RF that contains descending pathways (mainly rubroolivary tracts) and part of the important ascending RF projections to the thalamus and hypothalamus
also carries ascending taste fibers from the solitary nucleus to the ventral-postero-medial nucleus of the thalamus
what is the position of the spinal nucleus of V at the level of the lower pons?
spinal nucleus and tract of V have NOT changed their position but fibers of the middle cerebellar peduncle cover the lateral side
what CNs appear in the lower pons?
what are their functional components?
CN 5:
spinal nucleus of V – GSA
CN 6- abducens nucleus– GSE
CN 7- motor nucleus of 7– SVE
CN 8- vestibular nucleus– SSA
before leaving the BS, the fibers of the facial nerve form an internal loop “___”
what is the course of the loop?
where does it exit?
“internal genu of the facial nerve”
courses posteromedially toward the floor of the 4th ventricle and passes close and just caudal and medial to the nucleus of the abducens nerve
then courses rostrally and laterally around the abducens nucleus and takes a direct course anterolaterally and slightly caudally to its exit at the pontomedullary junction
what do the fibers of the motor nucleus of the facial nerve innervate?
branchiomeric muscles underneath the skin of the face– controls facial expression SVE
what is the course of the abducens nerve?
where does it exit?
fibers take a straight course through the tegmentum of the pons and exit close to the lateral border of the pyramidal tract on the anterior aspect of the BS
what does the abducens nerve innervate?
the lateral rectus muscle in the orbit
GSE
where does the vestibular nucleus lay in the lower pons?
what does it include?
vestibular nuclei continue to occupy a lateral area in the floor of the 4th ventricle
the individual sub nuclei at this level include the lateral, superior and medial sub nuclei
the spinal (inferior) nucleus remains confined to the medulla
the basilar portion of the pons in the middle pons is..
wider and thicker
what are the 2 oval shaped nuclei that lie side by side in the posterolateral part of the tegmentum?
laterally- the main (principal) sensory nucleus of the trigeminal (GSA- discriminative sensation to the face)
medially- the motor nucleus of the trigeminal nerve (SVE- muscles of mastication)
cells from the mesencephalic nucleus of V carry ___?
signals from stretch receptors in the muscles of mastication
most make monosynaptic connections with the motor nucleus of CN V and contribute the afferent signals for the jaw reflex
small filaments of this nerve pass posteriorly and rostrally to the?
pass to the mescencephalic tract of V
trigeminal nerve fibers emerge from the pons by:
passing directly through the middle cerebellar peduncle
the superior cerebellar peduncles appear :
in the walls of the fourth ventricle of the middle pons as large compact bands
what is the anterior medullary velum?
forms the roof of the ventricle
what does the upper pons consist of?
basilar portion MLF RF LSTT VTTT ML mesencephalic nucleus of V
the corticospinal and corticobulbar tracts occupy the ____ in the midbrain?
cerebral peduncle
what is the substantial nigra?
where is it?
lies between the cerebral peduncle and the tegmentum
produces dopamine
where is the ML in the caudal midbrain?
displaced laterally and slightly rotated
lies closely to the LSTT
the lateral lemniscus contains:
ascending auditory fibers – fibers terminate dorsally into the nucleus of the inferior colliculus
what CN is located in the caudal half of the midbrain?
where is it located?
CN 4- trochlear- GSE
lies near the MLF in there anterior part of the central periaqueductal gray matter
in the rostral midbrain, the cerebral peduncle and the substantial nigra …
continue to occupy the basal portion of the midbrain
the crossed fibers of the superior cerebellar peduncle pass into the ?
red nucleus; others pass forward to the thalamus
what does the red nucleus do?
rubrospinal tract
distal movement
What CN nucleus lies in the rostral midbrain?
CN III- oculomotor:
GSE
GVE- Edinger-wesphal nucleus
the nuclear complex of the oculomotor nerve lies in the anterior part of the central gray matter with the MLF beside it
the root fibers of the oculomotor nerve stream..?
what does CN 3 do?
ventrally through and around the red nucleus before converging at their exit in the interpeduncular fossa
from there, the root fibers travel to the orbit where they inner vat 4 of the 6 muscles that control eye movements and one muscle that elevates the eyelid (GSE)
the nerve also contains preganglionic parasympathetic fibers which constrict the pupil and change the shape of the lens within the eye (Edinger-wesphal- GVE)
in transverse sections through the rostral midbrain, where the midbrain joins the diencephalon, the _____ appear to be protrusions on the lateral surfaces of the midbrain
medial geniculate bodies/nuclei (vision)
not a BS structure, but the most ventral, caudal nuclei of the thalamus
