Neuoranatomy

1. Neuroanatomy
Lecture.4

2. Midbrain

3. GrossAppearanceGrossAppearance
of Midbrain:of Midbrain:
• connectstheponsand
cerebellum with the
forebrain.
• Itslong axisascends
through theopening in the
tentorium cerebelli.
• Themidbrain istraversed
by anarrow channel, the
cerebral aqueduct,
which isfilled with
cerebrospinal fluid

4. posterior
surface
1. Four colliculi
Thesearerounded
eminencesthat are
divided by avertical and
atransversegrooveinto :
• Superior colliculi :
arecentersfor visual
reflexes
• Inferior colliculi :
arelower auditory
centers.

5. 2. Trochlear nerves:
emergeIn the
midlinebelow the
inferior colliculi,
(Theseareslender cranial
nervesthat wind around
thelateral aspect of the
midbrain to enter the
lateral wall of the
cavernoussinus).

6. • On thelateral aspect of
themidbrain,
3. Superior brachium
passesfrom thesuperior
colliculusto thelateral
geniculatebody and the
optic tract.
4. Inferior brachium
connectstheinferior
colliculusto themedial
geniculatebody.

7. Anterior aspect
1. thereisadeep depression
in themidline, called :
Interpeduncular fossa,
2. Thisdepression is
bounded on either sideby
the:
Cruscerebri.
Many small blood vessels
perforatethefloor of the
interpeduncular fossa, and
thisregion istermed the:
Posterior
perforated
substance

8. 3. Theocculomotor nerve
emergesfrom agroove
on themedial sideof
thecruscerebri and
passesforward in the
lateral wall of the
cavernoussinus.

9. Arterial supply:
issupplied by:
1. Posterior cerebral
2. Superior cerebellar
3. Basilar arteries.
Venousdrainage:
into thebasal or great
cerebral veins

10. Internal StructureOf
Midbrain

11. Level Inferior colliculi
Cavity Cerebral aqueduct
Nuclei
Inferior colliculus, Substantianigra,
Trochlear nucleus, Mesencephalic
nuclei of cranial nerveV
MotorTracts
Corticospinal and corticonuclear tracts,
Temporopontine, Frontopontine,
Medial longitudinal fasciculus,
Sensory Tracts
Lateral, trigeminal, spinal, and medial
lemnisci; decussation of superior
cerebellar peduncles

12. Nuclie:
4. Mesencephalic nuclei of
cranial nerveV
1. Inferior colliculus,
2. Trochlear
nucleus,
3. Substantia
nigra,

13. Motor Tracts:
1. Temporo-
pontine
2. Corticospinal &
corticonuclear
3. Frontopontine,
4. Medial longitudinal
fasciculus

14. Sensory tracts
1. Lemnisci (Lmn.)
Lateral Lmn.
Trigeminal Lmn
Spinal Lmn.
Medial Lmn.
2. Decussation of2. Decussation of
superior cerebellarsuperior cerebellar
pedunclespeduncles
Cerebral aqueduct

15. Level Superior colliculi
Cavity Cerebral aqueduct
Nuclei
Superior colliculus, substantianigra,
Oculomotor nucleus, Edinger-Westphal
nucleus, red nucleus, Mesencephalic
nucleusof cranial nerveV
MotorTracts
Corticospinal and corticonuclear tracts,
temporopontine, frontopontine, medial
longitudinal fasciculus, decussation of
rubrospinal tract
Sensory Tracts Trigeminal, spinal, and medial lemnisci

16. Cerebral aqueduct

17. Nuclie:
1. Superior colliculus,
2. Mesencephalic nucleusof
cranial nerveV
2. Oculomotor nucleus,
3. Edinger-Westphal nucleus,
4. Red nucleus
5. Substantianigra,

18. Motor Tracts:
1. Temporo-
pontine
2. Corticospinal &
corticonuclear
3. Frontopontine,
5. Medial longitudinal
fasciculus
4. Decussation of rubrospinal tract

19. Sensory tracts
Lemnisci (Lmn.)
Trigeminal Lmn
Spinal Lmn.
Medial Lmn.

20. Clinical Notes

21. Clinical Significance of the Midbrain
• Themidbrain formstheupper end of thenarrow stalk of the
brain or brainstem. Asit ascendsout of theposterior cranial
fossathrough therelatively small rigid opening in the
tentorium cerebelli, it isvulnerableto traumatic injury.
• It possessestwo important cranial nervenuclei (oculomotor
and trochlear), reflex centers(thecolliculi), and thered
nucleusand substantianigra, which greatly influencemotor
function, and themidbrain servesasaconduit for many
important ascending and descending tracts.
• Asin other partsof thebrainstem, it isasitefor tumors,
hemorrhage, or infarcts that will produceawidevariety of
symptomsand signs.

22. 1. Trauma to the Midbrain
• asudden lateral movement of thehead could result
in thecerebral pedunclesimpinging against the
sharp rigid freeedgeof thetentorium cerebelli.
• Sudden movementsof thehead resulting from
traumacausedifferent regionsof thebrain to move
at different velocities relativeto oneanother. For
example, thelargeanatomical unit, theforebrain,
may moveat adifferent velocity from theremainder
of thebrain, such asthecerebellum. Thiswill result
in themidbrain being bent, stretched, twisted, or
torn.

23. • Involvement of the oculomotornucleus will
produceipsilateral paralysis of thelevator
palpebraesuperioris; thesuperior, inferior, and
medial recti muscles; and theinferior oblique
muscle.
• Malfunction of the parasympathetic nucleus
of the oculomotornerve producesadilated
pupil that isinsensitiveto light and doesnot
constrict on accommodation.
• Involvement of the trochlearnucleus will
producecontralateral paralysis of thesuperior
obliquemuscleof theeyeball.

24. 2. Blockage of the Cerebral Aqueduct
Thecavity of themidbrain, thecerebral
aqueduct, isoneof thenarrower
partsof theventricular system.
• In congenital hydrocephalus,
thecerebral aqueduct may be
blocked or replaced by numerous
small tubular passagesthat are
insufficient for thenormal flow of cerebrospinal fluid.
• When thecerebral aqueduct isblocked, theaccumulating
cerebrospinal fluid within thethird and lateral ventricles
produceslesionsin themidbrain.
• Thepresenceof theoculomotor and trochlear nervenuclei,
together with theimportant descending corticospinal and
corticonuclear tracts, will providesymptomsand signsthat
arehelpful in accurately localizing alesion in thebrainstem.

25. 3. VascularLesions of the Midbrain
A. Weber Syndrome
• which iscommonly produced by
occlusion of abranch of theposterior
cerebral artery that suppliesthe
midbrain, resultsin thenecrosis
of brain tissueinvolving
oculomotor nerveand thecruscerebri.
• Thereisipsilateral ophthalmoplegiaand contralateral
paralysisof thelower part of theface, thetongue, and the
arm and leg. Theeyeball isdeviated laterally becauseof
theparalysisof themedial rectusmuscle; thereisdrooping
(ptosis) of theupper lid, and thepupil isdilated and fixed
to light and accommodation.

26. B. Benedikt Syndrome
• issimilar to Weber
syndrome, but thenecrosis
involvesthemedial
lemniscusand red nucleus,
• producing contralateral
hemianesthesiaand
involuntary movementsof
thelimbsof theopposite
side.

27. Cerebellum

28. DefinitionDefinition:
• The trilobed structure of the brain, lying posterior
to the pons and medulla oblongata and inferior to
occipital lobes of the cerebral hemispheres, thusit
liesin theposterior cranial fossa.
• Responsible for the regulation and coordination of
complex voluntary muscular movementsand the
maintainenceof postureand balance

29. GrossAppearanceof theCerebellum
• situated in theposterior cranial fossa
• covered superiorly by the tentorium cerebelli
• liesposterior to thefourth ventricle, thepons, and
themedullaoblongata
• issomewhat ovoid in shapeand constricted in its
median part.

30. It consistsof:
1. two cerebellar hemi-
spheres
2. Vermis: joining both hemi-
spheres.

31. Connected to posterior
aspect of thebrainstem by
threesymmetrical bundles
of nervefiberscalled the:
1.Superior cerebellar
peduncle
2.Middlecerebellar
peduncle
3.inferior cerebellar
peduncle

32. Thecerebellum is
divided into three
main lobes:
1. Anteriorlobe :
may beseen on the
superior surfaceof
thecerebellum and is
separated from the
middlelobeby awide
V-shaped fissure
called theprimary
fissure.

33. 2. Middlelobe:
(sometimescalled the
posterior lobe), which is
thelargest part of the
cerebellum, issituated
between theprimary and
posterolateral fissures.
• Flocculonodular lobe:
• issituated posterior to
theposterolateral
fissure.
• Formed by two flocculi
and thenodule
Inferior veiw
Superior veiw

34. Tonsils
• Are roughly spherical
lobuleson theinferior
aspect of posterior lobe.
• Thetonsil may bedisplaced
down through theforamen
magnum in conditionsof
severeraised intracranial
pressureor in congenital
malformations

35. • horizontal fissure:
that isfound along the
margin of thecerebellum
separatesthesuperior
from theinferior surfaces.

36. The vermis
• consistsof ;
A. Superior part
B. Inferior part
• SuperiorVermis
liesbetween superior
medullary velum & primary
fissure
• Iscomposed of:
1. Lingula
2. Central lobule
3. Culmuen

37. • InferiorVermis
liesbetween primary
fissureand postero-
lateral fissure, and
consistsof :
1. Declive
2. Folium
3. Tuber
4. Pyramid
5. Uvula
6. Nodule

38. longitudinal division:
1. Vermis(medial zone)
2. Paravermal Region
( Intermediatezone)
3. Cerebellar Hemisphere:
(Lateral zone)

39. Anatomically
Transverseplane
Longitudinal plane
Anterior lobe
Vermis
Posterior lobe
Paravermis
Flocculonodular
Hemisphere
Functionally
Spino-
cerebellum
Cerebro-
cerebellum
Vestibulo-
cerebellum
Phylogenetic
Paleo-
cerebellum
Neo-
cerebellum
Archi-
cerebellum

40. Functionally:
• Thevestibulocerebellum
(correspondsbest with theflocculonodular lobe) has
reciprocal connectionswith vestibular and reticular nuclei
and playsarolein control of body equilibrium and eye
movement.
• Thespinocerebellum
(correspondsbest to theanterior lobe) hasreciprocal
connectionswith thespinal cord and playsarolein
control of muscletoneaswell asaxial and limb
movements, such asthoseused in walking and swimming.
• Thecerebrocerebellum or pontocerebellum
(correspondsbest to theposterior lobe) hasreciprocal
connectionswith thecerebral cortex and playsarolein
planning and initiation of movements, aswell asthe
regulation of discretelimb movements.

41. Phylogenetically:
1. Thearchicerebellum:
theoldest zone, correspondsto theflocculonodular
lobe.
2. Thepaleocerebellum,:
of morerecent phylogenetic development than the
archicerebellum, correspondsto theanterior lobe
and asmall part of theposterior lobe.
3. Theneocerebellum:
themost recent phylogenetically, correspondsto
theposterior lobe.

42. Functional Areas of the CerebellarCortex
• cerebellar cortex isdivided into threefunctional areas.
• Thecortex of thevermis:
influencesthemovementsof thelong axisof thebody,
namely, theneck, theshoulders, thethorax, theabdomen,
and thehips.
• Intermediatezoneof thecerebellar hemisphere: This
areahasbeen shown to control themusclesof the limbs,
especially thehandsand feet.
• Lateral zoneof each cerebellar hemisphere: Appears
to beconcerned with theplanning of sequential movements
of theentirebody and isinvolved with theconscious
assessment of movement errors.

43. Arterial supply of The cerebellum is
by:
1. Superior cerebellar
2. Anterior inferior cerebellar,
3. Posterior inferior cerebellar
Venous drainage
by veinsthat empty
into the
• Great cerebral vein
• Venoussinuses.

44. IntracerebellarNuclei
• Four massesof gray matter areembedded in
thewhitematter of thecerebellum on each
sideof themidline. From lateral to medial,
thesenuclei are:
1. Dentatenucleus,
2. Emboliform nucleus,
3. Globosenucleus,
4. Fastigial nucleus.

45. Fistugial nucleus Globosenucleus
Emboliform nucleus
Dentatenucleus
4th
Ventricle
Pons

46. Afferent Cerebellar Pathways

47. Information regarding theinitiation of
movement in thecerebral cortex isprobably
transmitted to thecerebellum so that the
movement can bemonitored and appropriate
adjustmentsin thevoluntary muscleactivity
can bemade.
1. CerebellarAfferent Fibers From
the Cerebral Cortex

48. Pathway Function Origin Destination
1.1.
CortiCo-CortiCo-
pontoponto
CerebellarCerebellar
Conveyscontrol
signalsfrom
cerebral cortex
Frontal, parietal,
temporal, and
occipital lobes
Viapontine
nuclei to
cerebellar cortex
2.2.
Cerebro-Cerebro-
olivo-olivo-
CerebellarCerebellar
Conveyscontrol
signalsfrom
cerebral cortex
Frontal, parietal,
temporal, and
occipital lobes
Viainferior
olivary nuclei to
cerebellar cortex
3.3.
Cerebro-Cerebro-
retiCulo-retiCulo-
CerebellarCerebellar
Conveyscontrol
signalsfrom
cerebral cortex
Sensorimotor
areas
Viareticular
formation to
cerebellar cortex

49. Corticopontocerebellar pathway
Corticoreticulocerebellar pathway
Cortico-olivocerebellar pathway
Reticular formation
Pontine
nuclie
Inferior olivary nucleus

50. • Thespinal cord sendsinformation to thecerebellum from
somatosensory receptorsby threepathways:
(1) theanterior spinocerebellar tract:
isfound at all segmentsof thespinal cord, and itsfibers
convey musclejoint information from theupper and lower
limbs
(2) theposterior spinocerebellar tract:
receivesmusclejoint information from thetrunk and
lower limbs.
(3) thecuneocerebellar tract:
receivesmusclejoint information from theupper limb and
upper part of thethorax
2. CerebellarAfferent Fibers
From Spinal Cord

51. 3. CerebellarAfferent Fibers From
the
VestibularNerve
• Thevestibular nervereceives
information from theinner ear
concerning:
A. Motion from thesemicircular canals
B. position relativeto gravity from:
Utricle
Saccule.

52. 4. OtherAfferent Fibers
• In addition, thecerebellum receivessmall
bundlesof afferent fibersfrom:
1. thered nucleus
2. thetectum.

53. Superior cerebellar peduncle
Inferior cerebellar peduncle
Cerebellum
Inferior cerebellar peduncle
Medulla
Anterior spinocerebellar tract
(minority of fibers)
Vestibular nuclie
Dentatenucleus
Nucleuscunatus
Vestibular nucleus
Posterior spinocerebellar tract
Anterior spinocerebellar tract
(majority of fibers)

54. TheEfferent Cerebellar Pathways

55. Pathway Function Origin Destination
Globose-Globose-
emboliformemboliform
-rubral-rubral
Influences
ipsilateral
motor
activity
Globoseand
emboliform
nuclei
contralateral
red nucleus,
then via
crossed
rubrospinal
tract to
ipsilateral
motor
neuronsin
spinal cord

56. Pathway Function Origin Destination
Dento-Dento-
thalamicthalamic
Influences
ipsilateral
motor
activity
Dentate
nucleus
contralateral ventro-
lateral nucleusof
thalamus,
contralateral motor
cerebral cortex;
corticospinal tract
crossesmidlineand
controlsipsilateral
motor neuronsin
spinal cord

57. Pathway Function Origin Destination
fastiGialfastiGial
vestibularvestibular
Influences
ipsilateral
extensor
muscle
tone
Fastigial
nucleus
Mainly to ipsilateral
and to contralateral
lateral vestibular
nuclei; vestibulo-
spinal tract to
ipsilateral motor
neuronsin spinal
cord

58. Pathway Function Origin Destination
fastiGialfastiGial
reticularreticular
Influences
ipsilateral
muscle
tone
Fastigial
nucleus
neuronsof reticular
formation; reticulo-
spinal tract to ipsi-
lateral motor neurons
to spinal cord

59. CLINICAL
NOTES

60. General Considerations:
• Each cerebellar hemisphereisconnected by nervous
pathwaysprincipally with thesamesideof thebody; thus, a
lesion in onecerebellar hemispheregivesriseto signsand
symptomsthat arelimited to thesamesideof thebody.
• Theessential function of thecerebellum isto coordinate, by
synergistic action, all reflex and voluntary muscular
activity. Thus, it graduatesand harmonizesmuscletoneand
maintainsnormal body posture. It permitsvoluntary
movements, such aswalking, to takeplacesmoothly with
precision and economy of effort.
• It must beunderstood that although thecerebellum playsan
important rolein skeletal muscleactivity, it is not ableto
initiatemusclemovement.

61. Characteristic symptoms and signs of
cerebellardysfunction:
1.hypotonia:
Themusclesloseresilienceto palpation. Thereis
diminished resistanceto passivemovementsof
joints. Shaking thelimb producesexcessive
movementsat theterminal joints. Thecondition is
attributableto lossof cerebellar influenceon the
simplestretch reflex.

62. 2. Postural Changes and Alteration of Gait
• Thehead isoften rotated and flexed, and the
shoulder on thesideof thelesion islower than on
thenormal side.
• Thepatient assumesawidebasewhen heor she
standsand isoften stiff legged to compensatefor
lossof muscletone.
• When theindividual walks, staggerstoward the
affected side.

63. 3. Disturbancesof Voluntary Movement (Ataxia)
Themusclescontract irregularly and weakly.
• Tremoroccurswhen finemovements, such as
buttoning clothes, writing, and shaving, are
attempted. Musclegroupsfail to work harmon-
iously, and thereisdecomposition of movement.
• Testsfor tremor :
1. Asking thepatient to touch thetip of thenosewith
theindex finger, thefinger either passesthenose
(past-pointing) or hitsthenose.
2. asking thepatient to placetheheel of onefoot on
theshin of theoppositeleg, it will either hit the
shin or not.

64. 4. Dysdiadochokinesia:
inability to perform alternating movementsregularly
and rapidly. Ask thepatient to pronateand supinate
theforearmsrapidly. On thesideof thecerebellar
lesion, themovementsareslow, jerky, and
incomplete.

65. 5. Disturbances of Reflexes
• Movement produced by tendon reflexestendsto
continuefor alonger period of timethan normal,
e.g. pendular kneejerk, for example, occurs
following tapping of thepatellar tendon.

66. 6. Disturbancesof Ocular Movement:
• Nystagmus, which isan ataxia(incoordination) of
theocular muscles, isarhythmical oscillation of the
eyes. It ismoreeasily demonstrated when theeyes
aredeviated in ahorizontal direction.
7. Disordersof Speech:
Dysarthriaoccursin cerebellar diseasebecauseof
ataxia(incoordination) of themusclesof thelarynx.
Articulation isjerky, and thesyllablesoften are
separated from oneanother. Speech tendsto be
explosive, and thesyllablesoften areslurred.

67. CerebellarSyndromes
1. Vermis Syndrome:
• Themost common causeof vermissyndromeisa
medulloblastomaof thevermisin children.
• Involvement of theflocculonodular lobe resultsin
signsand symptomsrelated to thevestibular system.
• Sincethevermisisunpaired and influencesmidline
structures, muscleincoordination involvesthehead
and trunk and not thelimbs.
• Thereisatendency to fall forward or backward.
Thereisdifficulty in holding thehead steady and in
an upright position. Therealso may be difficulty in
holding thetrunk erect.

68. 2. CerebellarHemisphere Syndrome:
• Tumorsof onecerebellar hemispheremay bethecause
of cerebellar hemispheresyndrome.
• Thesymptomsand signsareusually unilateral and
involvemuscleson thesideof thediseased cerebellar
hemisphere.
• Movementsof thelimbs, especially thearms, are
disturbed. Swaying and falling to thesideof thelesion
often occur.
• Dysarthriaand nystagmusarealso common findings.
• Disordersof thelateral part of thecerebellar
hemispheresproducedelaysin initiating movements
and inability to moveall limb segmentstogether in a
coordinated manner but show atendency to moveone
joint at atime.

69. Thanks