External features of brain stem (Anatomy).pdf

Anatomy of brainstem

1. External Features of Brainstem
Midbrain
Pons
Medulla
Midbrain
Pons
Medulla

2. DISCLAIMER:
•The presentation includes some descriptions taken from googleimages or books.
•Some of the contents are for educational purposes and not claim of ownership

3. Ventrolateral View
Midbrain
Cerebral peduncles
Pons
Basis pontis
Medulla
Pyramid Olive

4. Boundaries of the brainstem
Forebrain
(Superiorly)
Cerebellum
(Posteriorly)
Spinal Cord
(Inferiorly)
Midbrain
Pons
Medula
Lateral View

5. Terms of the Brainstem

6. Major Brainstem Activities
•Conduit
–Ascending and descending pathways
•Integrative functions
–Complex motor patterns
–Respiratory and cardiovascular activity
–Regulation of arousal and level of consciousness
•Cranial Nerve functions

7. Connections of the brainstem to
other adjacent structures

8. Vental view
Lateral view
Cerebral peduncle
Superior cerebellar
peduncle
Middle cerebellar
peduncle
Inferior cerebellar
peduncle
Cerebellum
Forebrain
Pons
Medulla
Midbrain
Spinal cord
Interpeduncular fossa

9. Emergence of
Cranial Nerves from Brain stem

10. Forebrain
Midbrain
Pons
Medulla
3
4
5
5
6
6
7
7
8
9
10
11
12
12
11
10
9
4
3
8
Pineal gland
.
.
Vental view
Lateral view

11. Internal Columns of Nuclei
III, IV, VI, XII
V, VII, N. ambiguus, XII
EW, Salivatory, DMN X
V, VII, IX, X
N. Solitary tract
VIII

12. Midbrain

13. Midbrain
•Cerebral Peduncles (Anteriorly)
–Interpeduncular cistern
•Origin of CN III --Oculomotor Nerve
•Origin of CN IV –Trochlea Nerve
•Corpora Quadrigemina (Posteriorly)
–Superior Colliculi
–Inferior Colliculi

14. Midbrain
Corpora
quadrigemina
Cerebral
peduncles
Interpeduncular
cistern
CN III
Posterior viewLateral view
Anterior view

15. Internal structure of the midbrain

16. Internal structure of the midbrain
•Broadly, the midbrain is
divided into two by a
transverse line (TL) which
passes through the cerebral
aqueduct of sylvius
–The part posterior to the TL is
the tectum
–the part anterior to the TL is
the cerebral peduncles divided
into:
•Crus cerebri
•Substantial nigra
•Tegmentum

17. Crus cerebri: made up of large
longitudinal fibres from the cerebral
cortex
–Corticopontine
–Corticospinal
–Corticonuclear
•It is divided into 3 parts:
–medial 1/6 occupied by Corticopontine
fibres from the frontal lobe
(frontopontinefibres)
–Lateral 1/6 occupied by Corticopontine
fibres from the parietal, temporal and
occipital lobes(frontopontinefibres)
–Intermediate 2/3 occupied by
corticospinaland corticonuclearfibres

18. Substantial nigra:This is
immediately behind the crus
cerebri.
•It is dark due to neuromelanin
•It is divided into: dorsal part
(pars compacta) containing
dopaminergic and cholinergic
neurones and ventral (pars
reticularis) containing
GABAergicneurones
•Main connections (afferent
and efferent) are with caudate
nucleus and putamen

19. •Tegmentum: it lies between
the substantial nigra and the
tectum
•the tegmentum on both sides
is continuous at the midline
•Contains masses of grey
matter such as: Red nucleus
which is the largest and
present in the upper half of the
midbrain
•Contains reticular formation
which is continous with the
pons and medulla below,
•The internal structure of the
tegmentum differs depending
on the level of the midbrain
being considered

20. •Superior colliculus
•Inferior colliculus
Sections through the midbrain

21. Section through the inferior colliculus
1.Inferior colliculus (IC)
2.Medial to the IC is the
mesencephalic nucleus (MN) of
trigeminal nerve (continuation of
the sensory N of CN V)
3.Medial to the MN is the trochlear
nucleus with the fibres running
dorsally and decussate before
emerging
4.Just posterior to the substantial
nigra & lateral to the RED
NUCLEUS from medial to lateral:
•Medial lemniscus
•Trigeminal leminiscus
•Spinal lemniscus

22. 6. The medial londitudinal
fasciculus (MLF) lies ventral to the
trochlear nucleus
7. Ventral to the MLF is the
tectospinal tracts
8. Ventral to the tectospinal tracts is
the decussation of the fibres of
superior cerebellar peduncle (to red
nucleus or thalamus)
9. Ventral to the decussation of the
superior cerebellar peduncle is the
rubospinal tracts
•The inferior colliculusis concern with
reflexes involving the auditory stimuli
•Receives fibres of lateral lemniscus
•Impulses are relayed to the medial
geniculate body through the inferior
brachium

23. 1.Superior colliculus(SC)
2.Red nucleus (2 large oval mass)
posteromedial to the substantial
nigra. It is an important motor
nucleus of extrapyramidal system
3.Occulomotornuclei (fused) form a
complex ventral to the central
grey matter
4.EdingerWestphalnucleus forms
part of the occulomotorcomplex
(supplies sphincter papillae and
ciliarismuscle)
5.Ventral to the occulomotor
complex is the medial longitudinal
fasciculus
6. Ventral to the superior colliculus is
the pretectal nucleus concern with
pathways for the pupillary light reflexes
–It receives fibres from SC, optic tracts
and visual cortex
Section through the superior colliculus

24. 7. The medial lemniscus,
trigeminallemniscus and spinal
lemniscus lies more dorsally than
at the lower level
8. Lateral lemniscus is absent at
this level as fibres end in the
inferior colliculus
9. Inferior brachium that convey
auditory fibres to the medial
geniculate body can be seen
10. Two decussation can be seen
–Dorsal tegmental decussation
consist of fibres from SC cross to
opposite side to descend as the
tectospinal tracts
–The ventral tegmental decussation that
consists of fibres from the red nucleus
that decussate to form the rubrospinal
tracts

25. Pons

26. Pons
•CerebellarPeduncle (Anteriorly)
–Middle (Bridge of the pons)
Trigeminal nerve (CNV)
–Pontomedularyjunction
CNVI, VII, VIII
–Basilar artery
•Floor of the 4th Ventricle (Posteriorly)

27. PonsLateral view Posterior view
Anterior view

28. Pons
Middle cerebellar peduncle

29. Pons
Middle cerebellar peduncle
Inferior cerebellar peduncles
Superior cerebellar peduncles

30. Pons
•4th Ventricle
–Inflow from aqueduct of
Sylvius
–Sulcus limitans

31. lateral view
•Posterior boundary of the pons:
formed by the upper ½ of the floor of
the 4
th
ventricle

32. Internal structures of the pons

33. •The pons can be divided into two
parts
–Anterior (basilar part)
–Posterior (tegmental part)
Trapezoid body (separates the basilar
and tegmental parts)

34. The basilar part
This contains two important structures
•Fibres (i. descending longitudinal and ii. transverse)
•Pontine nuclei
Fibres
i. descending longitudinal fibres-this consists of three components:
–Corticospinaltracts which traverse the pons and form the pyramids in the
medulla
–Corticonuclearfibres which descend along side the corticospinaltracts to from
the pyramid in the medulla but end up in the contralateral motor nuclei of cranial
nerves
–Corticopontinefibres: arises from the frontal, parietal, temporal and occipital
cortices and terminate on ipsilateralpontinenuclei
•ii. Transverse fibres (pontocerebellartracts). These arise from the
pontinenuclei and cross to the opposite side to form the middle cerebellar
peduncle

35. Pontine nuclei
•Also known as nuclei pontisare small scattered mass of grey
matter between the longitudinal and transverse fibres. They
constitute a relay station between the cerebral cortex and
contralateral cerebellar hemisphere.
–They receive corticopontinefibres from the cerebral cortex
–Efferent fiberesmoves to the contralateral cerebellar hemispheres
–Also receives inputs from tectum, lateral geniculate body, nuclei gracilis
and cuneatus, reticular formation, hypothalamus, cerebellar nuclei
The tegmental part
•It’s a continuation of the part of the medullar behind the pyramids
•It is continuous with the tegmentumof the midbrain
•It is bounded posteriorly by the fourth ventricle
•It is bounded superolaterallyby the superior cerebellar peduncle
•It is bounded inferolaterallyby the inferior cerebellar peduncle

36. Cross section of the Pons at two levels
Based on the differential
structures in the
tecmentum of the pons, it is
necessary to study the
internal structures at two
levels
•Level of trigeminal
nerve (CN V)
•Level of facial colliculi

37. Section through the lower pons (Level of
facial colliculi)
•At the surface level: Two
cranial nerve nuclei are
located to the floor of the
fouth ventricle
•i abducent (medial)
•ii vestibular nuclei (lateral)
•At the deeper level: Another
two cranial nerve nuclei are
evident i. facial nuclei
(medial)and ii. Spinal
nucleus of the trigeminal
nerve (lateral)

38. •The dorsal and ventral nuclei are
related to the dorsal and ventral surface
of the inferior cerebellar peduncle
respectively
•Facial colliculiformed by the projecting
fibres of the facial nuclei
•Vestibular nuclei occupy the vestibular
area on the lateral part of the floor of
the 4
th
ventricle
•Other tracts: lateral lamniscus
–Anterior spinothalamictracts
–Lateral spinothalamictracts
–Spinotectaltracts
•Superior olivarycomplexes lying
dorsomediallyto the lateral lemiscus
•Medial lemiscusand trapezoid body
•Pontine nuclei,
•corticospinaland nuclei tracts
•Pontocerebellartracts

39. Section through the lower pons (Level of trigeminal
nerve)
•Superior cerebellar peduncle (SCP)
•Medial to SCP is the sensory
nucleus of trigeminal nerve
–It sends fibre to the spinal nuclus of
trigeminal nerve in the medulla (pain &
Temperature)
–It is continuous in the midbrain with the
mesencephalic nucleus (proprioceptive
impulses)
•Medial to the sensory N. CN (v) is
the motor N. CN (v).

40. Section through the lower pons (Level of trigeminal
nerve)
•Trapezoid body and nuclei
•Medial & lateral lemnisci
•Reticular formation
•Middle cerebellar peduncle
–Pontine nuclei,
–corticospinal and nuclei tracts
–Pontocerebellar tracts
•Median longitudinal fasciculus
which extend to the CN (III & IV)
in the midbrain

41. Medulla

42. Medulla
ANTERIORLY
•Pyramids (Anterior median fissure)
•Pyramidal decussation (lower part)
•Inferior olive
–anterolateral sulcus between pyramids & Olive (Anterior)
–posterolateral sulcus between olive and inferior cerebellar peduncle
(Anterolateral)

43. POSTERIORLY
•Posterior medial sulcus
•Lower part of the floor of 4
th
ventricle (upper part)
•Obex (inferiormost point of the 4th ventricle)
•Three tubercles (lower part) (from inferiomedial to superior
lateral)
–Gracile tubercle (nucleus gracilis)
–Cuneate tubercle (nucleus cuneatus)
–Trigeminal tubercle (trigeminal nucleus)
Obex

44. Medulla
Pyramids
Obex
Inferior olive
Lateral view Posterior view
Anterior view

45. Internal structure of the medulla

46. Internal Structure of Medulla
Cross section at three levels
•Level of pyramidal decussation
•Level of lemniscal decussation
•Level ofinferior olivary nuclei

47. Section through the medulla oblongata at
the level of Pyramidal Decussation
•It is similar to section
through the spinal cord.
•The central canal is
surrounded by central
grey matter
•The ventral grey
columns are separated
from the central grey
latter by decussating
pyramidal fibres

48. •The reticular formation
occupies the space between
the ventral grey matter and
spinal nucleus of trigeminal
nerve
•Posterior to the cental grey
matter is the fasciculus
gracilis medially and
fasciculus cuneatuslaterally
•Closely related to the
fasciculi are the
corresponding nucleus
gracilisand nucleus
cuneatus
•Laterally, we have spinal nucleus of
trigeminal nerve

49. •The main descending
fibres-corticospinal
tract, runs backward
and medially to cross in
the midline-
decussation of the
pyramids.
•After crossing, it
continues as the lateral
corticospinal tract
•The uncrossed fibres
continue as the ventral
corticospinal tracts

50. •Other descending
tracts evident at this
level are:
•Rubrospinal tract
•Vestibulospinal tract
•Olivospinal tract
•Tectospinal tracts

51. •Ascending tracts seen at
this level include the
following:
•Fasciculus gracilis and
fasciculus cuneatus
•Spinothalamic tract
•Spinocerebellar tract
•Spinotectal tract
•Spino-olivary tract

52. Section through the medulla oblongata at
the level of Sensory Decussation
•The central canal is
surrounded by the
central grey matter
•The pyramids, spinal
nucleus of trigeminal
nerve, nucleus gracillis
and nycleus coneatus
occupy same position
as it apperars at lower
level

53. •The nuclei gracilis and
cuneatus are larger and no
longer continuous with
central grey matter
•Internal arcuate fibers
arising in these nuclei cross
the midline which constitute
the lemniscal or sensory
decussation
•After crossing the midline,
the become the medial
lemniscus
•The fibersfrom the nuclei
gracilisand cuneatuscross
each other so that fibers
from nucleus gracilislie
ventral to that of nucleus
cuneatus

54. •The most medial fibres (from
the leg) lie anteriorly in the
medial lemniscus followed
by the trunk and the upper
limb
•At higher levels there is
change in the orientation so
that the most anterior fibers
now lie laterally while the
posterior fibers lie medially
•The medial lemniscus is
joined by the anterior
spinothalamic tract

55. •Fibers in the medial lemniscus
are arranged in layers.
•Those from C1 are most
medial while those from S4
are most lateral
•Accessory cuneate nucleus is
placed dorsolateral to the
cuneate nucleus
•It receives proprioseptive
impulses from the upper limb.
•Efferent fibers constitute the
posterior external arcuate
fibers
•They get to the cerebellum
through the inferior cerebellar
peduncle

56. •Some cranial nerve nuceipresent
at this level are related to the
central grey matter.
–Hypoglossal nucleus is located
ventral to the central canal
–Nucleus of the solitary tract is
located dorsal to the central
canal
–Nucleus ambiguuslie medial to
the nucleus of spinal tract of
trigeminal nerve
Other grey matter present at this
level are:
–Inferior olivarynucleus
–Medial accessory nucleus
–Lateral reticular nucleus
–Arcuatenuclei Anterior to the
pyramids
•Reticular formation which lie
lateral to the medial lemniscus

57. •The ascending tracts present
at this level are:
–The gracile and cuneate
fasciculi
–Spinothalamic tract
–Spinocerebellar tract
–Spinotectal tract and
–Spino-olivary tracts all of
which lie in the anterolateral
region
•The descending tracts
present at this level are:
–Pyramids
–Rubospinaltracts
–Vestibulospinaltracts
–Olivospinaltracts
–Medial longitudinal fasciculus
which includes the tectospinal
tract

58. Section through medulla oblangata at the
level of olive (mid-olivary level)
•The pyramids, medial
lemniscus, spinal nucleus
and tract of the trigeminal
are present at similar
position as it is at the
lower levels.
•The medial lemniscus is
larger at this level and
expanded at the anterior
end.
•The inferior cerebellar
peduncle is located lateral to
the spinal nucleus and tract of
trigeminal nerve –it connects
the medulla to the cerebellum

59. •Some cranial nerves located
at the floor of the 4
th
ventricle
from medial to lateral are:
–Hypoglossal nucleus
–Dorsal vagal nucleus
–Vestibular nuclei
•Solitary tract and nucleus lie
ventrolateral to the dorsal
vagal nucleus
•The nucleus ambiguous is
located dosomedial to the
reticular formation
•The dorsal and ventral cochlea
nuclei are seen closely
associated with the inferior
cerebellar peduncle

60. •Other masses of grey matter
are:
•Medial and dorsal accessory
olivary nuclei lying medially
and dorsally to the inferior
olivary nucleus
•Lateral reticular nucleus
•Arcuate nuclei
•Pontobulbar body

61. •The descending tracts
seen at this level are:
•Pyramids
•Tectospinal tract
•Vestibulospinal tract
•Rubrospinal tract
•Spinal tract of the
trigeminal nerve
•The ascending tracts
seen at this level are:
•Medial lemniscus
•Spinothalamictract
•Spinocerebellartract
•Spinotectaltract