08Brain_stem-External_Features (2).pdf snells

Neuro anatomy brain stem extrrnal
Featurs reference snells

2. Objectives
•At the end of the class students should be able
to:
•Explain medulla external features.
•Draw & label cut sections of medulla at
different levels.
•Applied anatomy of medulla.

3. BRAIN STEM
•The brainstem occupies the
posterior cranial fossa of the
skull.
•It is stalk ikein shape and
connects the narrow spinal
cord with the expanded
forebrain, is made up of
•medulla oblongata
•the pons
•the midbrain
•CONNECTIONS WITH
CEREBELLUM:
•Each part of brain stem is
connected to cerebellum by
cerebellarpeduncles
(superior, middle & inferior).
MB
Pons

4. SAGITTAL SECTION OF BRAIN
CerebellumMid brain
Pons
Medulla
Superior
Cerebellar
peduncle
Thalamus

6. FUNCTIONS OF BRAIN STEM
•The brainstem has three broad
functions:
•(1) it serves as a conduit for the
ascending tracts and descending
tracts connecting the spinal cord
to the different parts of the
higher centers in the forebrain.
•(2) it contains important reflex
centers associated with the
control of respiration and the
cardiovascular system and with
the control of consciousness.
•(3) it contains the important
nuclei of cranial nerves III
through XII.

7. BRAIN –VENTRAL SURFACE
Showing cranial nerves attachment

8. Gross Appearance of the
Medulla Oblongata VENTRAL SURFACE
•The medulla oblongata is conical in
shape, its broad extremity being
directed superiorly.
•The central canal of the spinal cord
continues upward into the lower half
of the medulla; in the upper half of
the medulla, it expands as the cavity
of the fourth ventricle.
Ventral median fissure:
•Continuation of ventral median
fissure of spinal cord
•Divides the medulla into 2 halves
•Its lower part is masked by
decussationof most of pyramidal
(corticospinal) fibers (75%-90%).
Pyramid:
•An elevation, lies on either side of
ventral median fissure
•Produced by corticospinaltract.

9. Olive:
•An elevation, lies lateral
to the pyramid.
•Produced by inferior
olivarynucleus
(important in control of
movement).
Nerves emerging from
Medulla (4 nerves):
•Hypoglossal (12
th
): from
sulcusbetween pyramid
& olive
•Glossopharyngeal(9
th
),
vagus(10
th
) &
•cranial part of accessory
(11
th
): from sulcus
dorsolateralto olive
(from above
downwards)

11. •The features
differ in the
caudal part
(closed
medulla) and
the cranial
part (open
medulla)
MEDULLA –DORSAL SURFACE
open medulla
closed medulla

12. CLOSED
MEDULLA
Cavity: central canal.
Composed of:
•Dorsal median sulcus:
divides the closed medulla
into 2 halves.
•Graciletubercle: an
elevation produced by the
underlying gracilenucleus.
•Cuneatetubercle: an
elevation produced BY the
cuneatenucleus.

13. OPEN MEDULLA
Cavity:4
th
ventricle
On either side, an
inverted V-shaped
sulcusdivides the area
into 3 parts (from
medial to lateral):
1.Hypoglossal triangle:
overlies hypoglossal
nucleus.
2.Vagaltriangle: overlies
dorsal vagalnucleus.
3.Vestibular area: overlies
vestibular nuclei.
Shown after removing cerebellum

15. Internal Structure of medulla
oblongata
•The internal structure of the medulla
oblongata is considered at four levels:
(1) level of decussation of pyramids
(2) level of decussation of lemnisci
(3) level of the olives
(4) level just inferior to the pons
8

16. Level of the Decussation of the
Pyramids
•This is themajor decussation point of
thedescending motor fibres. Roughly 75% of
motor fibreshoused within
thepyramidscross diagonally and posteriorly,
and continue down the spinal column as the
lateral corticospinal tracts.
•At this level, the central portion of the
medulla containsgray matter, while the outer
portions consist ofwhitematter.

17. •The posterior white matter contains
thefasiculus gracilisand the more
lateralfasiculus cuneatus. Corresponding
portions of gray matter extend to these
regions and are the nucleus gracilis and
nucleus cuneatus respectively.

18. •Unchanged from the spinal cord,
thespinocerebellar tracts(posterior and
anterior) are locatedlaterally, with the lateral
spinothalamic tract situatedbetween them.
The large trigeminal nucleus and tracts can be
found posterior to these tracts.This is a
continuation of the substantia gelatinosa of
the spinal cord.

20. Level of Decussation of the Medial
Lemniscus
•This level marks thesensory decussation
occurs of the medial lemniscus.Purple lines
have been used to represent theinternal
arcuate fibresas they run from the nucleus
gracilis and nucleus cuneatus around and
anterior to the central gray matter to form the
medial lemniscus.

21. •Lateral to the medial lemniscus, the trigeminal
nucleus andspinal tractcan once again be
seen, as can thespinocerebellar tracts and the
lateral spinothalamic tract. Similarly, the
posterior structures are much the same at this
level.

22. •Centrally, thehypoglossal nucleusand medial
longitudinal fasciculus are seen. Moving
laterally, the nucleus ambiguous can be seen.
Between this structure and the pyramids is
theinferior olivary nucleus.

24. Level of the Olives
•This level shows significant change in structure
both externally and internally when compared
with previous levels. The central canal has
now expanded into the fourth ventricle and as
such makes this region theopen medulla.
•The largeinferior olivary nucleusis
responsible for the external expansion of the
olives. The related medial and dorsal
accessory olivary nuclei can be seen medial
and posterior to this structure respectively.

25. •The large inferior cerebellar peduncles come
into view and are surrounded by multiple
nuclei. The twovestibular nuclei(medial and
inferior) are both found towards the midline
while the two cochlear nuclei are found
somewhat above and below the peduncles.
Now a much smaller structure, the trigeminal
tract and nucleusis seen adjacent to the
peduncle.

26. •Thenucleus ambiguousremains as it was
previously, while the hypoglossal nucleus has
migrated with the central canal posteriorly,
joined by the medial longitudinal fasciulus. An
additional cranial nucleus comes into view
lateral to the hypoglossal –the dorsal vagal
nucleus. Moving further lateral, the nucleus of
tractus solitarius comes into view.

27. •Centrally, themedial lemniscushugs the
midline posterior to the pyramids, as does the
tectospinal tract.
•Between the peduncle and the olivary nuclei
resides the lateral spinothalamic tract and the
more lateral anterior spinocerebellar tract.

29. Level Just Inferior to the Pons
•There are no major changes, in comparison to
the previous level, in the distribution of the
gray and white matter.
•The lateral vestibular nucleus has replaced the
inferior vestibular nucleus, and the cochlear
nuclei now are visible on the anterior and
posterior surfaces of the inferior cerebellar
peduncle.

33. Clinical Significance of the
Medulla Oblongata
•The medulla oblongata not only contains many
cranial nerve nuclei that are concerned with vital
functions (e.g., regulation of heart rate and
respiration),but it also serves as a conduit for the
passage of ascending and descending tracts
connecting the spinal cord to the higher centers of
the nervous system.
•These tracts may become involved in demyelinating
diseases, neoplasms, and vascular disorders.

34. Arnold –Chiari phenomenon
Congenital anomaly
•Herniation of
cerebellum ,tonsils &
medulla from foramen
magnum into vertebral
canal. This results in the
blockage of the exits in
the roof of the fourth
ventricle to the
cerebrospinal fluid,
causing internal
hydrocephalus

35. Vascular Disorders of the Medulla
Oblongata
•Lateral medullary syndrome of Wallenberg:
•Lateral part supplied by PICA (vertebral artery).
•NA:dysphagia&dysarthriaduetoipsilateral
paralysisofpalatal&pharyngeousmuscles.
•Spinaltractoftrigeminalnerve
•Vestibularnuclei
•Horner’ssyndrome
•Ipsilateralcerebellersigns
•Spinothalamictractleison

37. •Medial Medullary Syndrome
•The medial part of the medulla oblongata is supplied
by the vertebral artery. Thrombosis of the medullary
branch produces the following signs and symptoms:
•contralateral hemiparesis
•(pyramidal tract), contralateral impaired sensations
of position and movement and tactile discrimination
(medial lemniscus),
•and ipsilateral paralysis of tongue muscles with
deviation to the paralyzed side when the tongue is
protruded(hypoglossal nerve).

39. Gross Appearance
of the Pons
•Largest part of the brain stem.
•The Pons is anterior to the cerebellum and
connects the medulla oblongata to the
midbrain.
•It is about 1 inch (2.5 cm) long and its
appearance, is that of a bridge connecting the
right and left cerebellar hemispheres.

41. PONS –VENTRAL /anterior SURFACE
•The anterior surface is
convex from side to side
and shows many
transverse fibers that
converge on each side to
form the middl
cerebellar peduncl.
•There is a shallow groove
in the midline, the basilar
groove, which lodges the
basilar artery.

42. •On the anterolateral surface of the pons, the
trigeminal nerve emerges on each side. Each
nerve consists of a smaller, medial part,
known as the motor root, and a larger, lateral
part, known as the sensory root.
•In the groove between the pons and the
medulla oblongata, there emerge, from
medial to lateral, the abducent, facial,and
vestibulocochlear nerves

44. •The posterior surface of the pons is hidden
from view by the cerebellum.
•It forms the upper half of the floor of the
fourth ventricle and is triangular in shape.
•The posterior surface is limited laterally by the
superior cerebellar peduncles and is divided
into symmetrical halves by a median sulcus.
PONS –DORSAL SURFACE

45. •Lateral to this sulcus is an elongated
elevation, the medial eminence, which is
bounded laterally by a sulcus, the sulcus
limitans .
•The inferior end of the medial eminence is
slightly expanded to form the facial colliculus,
which is produced by the root of the facial
nerve winding around the nucleus of the
abducent nerve.

47. •The floor of the superior part of the sulcus
limitans is bluish-gray in color and is called
the substantia ferruginea; it owes its color to
a group of deeply pigmented nerve cells.
•Lateral to the sulcus limitans is the area
vestibuliproduced by the underlying
vestibular nuclei

50. •Thestria medullarisof the fourth ventricle is a
bundle of nerve fibres crossing transversely
from the lateral aspect into the midline. They
mark the posterior border between the pons
and the medulla.

52. INTERNAL STRUCTURE
OF THE PONS
•For purposes of description, the pons is commonly
divided into a posterior part, the tegmentum, and an
anterior basal part by the transversely running
fibers of the trapezoid body.
•The structure of the pons may be studied at two
levels:
•(1) transverse section through the caudal part,
passing through the facial colliculus, and
•(2) transverse section through the cranial part,
passing through the trigeminal nuclei.
r

54. Transverse Section Through
the Caudal Part
•The medial lemniscus rotates as it passes from the medulla
into the pons.It is situated in the most anterior part of the
tegmentum, with its long axis running transversely. The
medial lemniscus is accompanied by the spinal and lateral
lemnisci.
•The facial nucleus lies posterior to the lateral part of the
medial lemniscus. The fibers of the facial nerve wind around
the nucleus of the abducent nerve, producing the facial
colliculus.
•The fibers of the facial nerve then pass anteriorly between
the facial nucleus and the superior end of the nucleus of the
spinal tract of the trigeminal nerve.

56. •The medial longitudinal fasciculus is situated beneath the
floor of the fourth ventricle on either side of the midline . The
medial longitudinal fasciculus is the main pathway that
connects the vestibular and cochlear nuclei with the nuclei
controlling the extraocular muscles (oculomotor, trochlear,
and abducent nuclei).
•The medial vestibular nucleus is situated lateral to the
abducent nucleus and is in close relationship to the inferior
cerebellar peduncle. The superior part of the lateral and the
inferior part of the superior vestibular nucleus are found at
this level.
•The posterior and anterior cochlear nuclei are also found at
this level.

58. •The spinal nucleus of the trigeminal nerve and its
tract lie on the anteromedial aspect of the inferior
cerebellar peduncle.
•The trapezoid body is made up of fibers derived
from the cochlear nuclei and the nuclei of the
trapezoid body. They run transversely in the anterior
part of the tegmentum.

59. Trapezoid body & Lateral laminiscus
•Trapezoid body present in
ventral part of tegmentum
of Pons
•Formed by fibers from
cochlear nuclei, dorsal
nuclei of trapezoid body of
same & opposite side
•Its efferent fibers form
Lateral leminiscus
•Both form components of
auditory pathway

61. •The basilar part of the pons, at this level, contains small of
nerve cells called pontine nuclei.
•The corticopontine fibers of the crus cerebri of the midbrain
terminate in the pontine nuclei. The axons of these cells give
origin to the transverse fibers of the pons, which cross the
midline and intersect the corticospinal and corticonuclear
tracts, breaking them up into small bundles.
•The transverse fibers of the pons enter the middle cerebellar
peduncle and are distributed to the cerebellar hemisphere.
•This connection forms the main pathway linking the cerebral
cortex to the cerebellum.

63. Transverse Section Through
the Cranial Part
•The internal structure of the cranial part of the pons
is similar to that seen at the caudal level , but it now
contains the motor and principal sensory nuclei of
the trigeminal nerve.
•The motor nucleus of the trigeminal nerve Is
situated beneath the lateral part of the fourth
ventricle within the reticular formation .
•The emerging motor fibers travel anteriorly through
the substance of the pons and exit on its anterior
surface.

65. •The principal sensory nucleus of the
trigeminal nerve is situated on the lateral
side of the motor nucleus.
•It is continuous inferiorly with the nucleus of
the spinal tract. The entering sensory fibers
travel through the substance of the pons and
lie lateral to the motor fibers.

67. BLOOD SUPPLY OF THE PONS
•The blood supply of the pons is formed by branches of
thevertebrobasilar system:
•Most of the pons is supplied by thepontine arteries,
branches of the basilar artery.
•A smaller part of its blood supply comes from theanterior
inferior cerebellar arteryand thesuperior cerebellar
artery(AICA and SCA).
•The venous drainage of the pons consists of theanterior
pontomesencephalic vein, which drains superiorly into the
basal vein, that in turn drains into thecerebral veins.
Inferiorly, the pons drains into theinferior petrosal sinus,
which drains into the internal jugular veins.

69. Clinical Significance of the Pons
•The pons, like the medulla oblongata and the
cerebellum, is situated in the posterior cranial fossa
lying beneath the tentorium cerebelli.
•It is related anteriorly to the basilar artery, the
dorsum sellae of the sphenoid bone, and the basilar
part of the occipital bone.
•In addition to forming the upper half of the floor of
the fourth ventricle, it possesses several important
cranial nerve nuclei (trigeminal,abducent,facial,and
vestibulocochlear.

70. •serves as a conduit for important ascending and descending
tracts ( corticonuclear, corticopontine, corticospinal,medial
longitudinal fasciculus and medial, spinal, and lateral
lemnisci).
•Tumors, hemorrhage, or infarcts in this area of the brain
produce a variety of symptoms and signs. For example,
involvement of the corticopontocerebellar tracts will produce
marked cerebellar ataxia, and voluntary movements are
accompanied by a rhythmic tremor that develops and
becomes further accentuated as the movements proceed
(intention tumor).

71. MID BRAIN –VENTRAL SURFACE
large column of
descending fibers (crus
cerebrior basis
pedunculi), on either
side, separated by a
depression called the
interpeduncularfossa.
Nerve emerging from
Midbrain (one):
•Occulomotor(3
rd
): from
medial aspect of crus
cerebri.

72. MID BRAIN –DORSAL SURFACE
Marked by 4 elevations:
1.Two superior colliculi:
concerned with visual
reflexes.
2.Two inferior colliculi:
forms part of auditory
pathway.
Nerve emerging from
Midbrain (one):
•Trochlear(4
th
): just
caudal to inferior
colliculus(The only
cranial nerve emerging
from dorsal surface of
brain stem).

73. SUMMARY
The brain stem is composed (from above
downwards) of: midbrain, pons& medulla
oblongata which are continuous with each other,
with diencephalon above & with spinal cord below.
The brain stem is connected with cerebellum
through three pair of cerebellarpeduncles.
The brain stem is the site of cranial nuclei, the
pathway of important ascending & descending
tracts & the site of emergence of cranial nerves
(from 3
rd
to 12
th
).
Cranial nerves (with the exception of 4
th
) emerge
from ventral surface of brain stem.

74. QUESTION 1
The cranial nerve that emerges from dorsal
surface of midbrain is:
1.Occulomotor(3
rd
).
2.Trochlear(4
th
).
3.Abducent(6
th
).
4.Facial (7
th
).

75. QUESTION 2
Regardingthe medulla oblongata:
1.The pyramid is lateral to olive.
2.The hypoglossal nerve is the most lateral
nerve emerging from it.
3.The cuneatetubercle is lateral to gracile
tubercle.
4.The cerebellum is connected to it by middle
cerebellarpeduncle.

76. thank you