Transcript 10-cerebellum

General Features of Cerebellum :
The cerebellum consists of a midline
vermis and 2-lateral hemispheres.
Anatomically , it is divided into anterior
, posterior & flocculo-nodular lobes.
It controls equilibrium, it influences
posture & muscle tone and coordinates
the movements
Its surface is high convoluted, forming
folds or folia, being oriented transversely
Lateral aspect of brain
stem & cerebellum ,
showing cerebellar
peduncles.
It lies behind Pons & M.O. , separated
from them by the cavity of 4th ventricle.
It is connected to brain stem (medulla,
pons& midbrain) by inferior, middle &
superior cerebellar pedunclesrespectively.
External Features of Cerebellum :
It has anterior notch ,which is
wider and lodging the back of pons
& medulla. It is separated from
them by cavity of 4thventricle
 It has also posterior notch
occupied by falx cerebelli, which
separates the 2 cerebellar H.
Superior surface
Inferior surface : rounded on
each side and presents :
Inferior surface
a deep groove (vallecula) between
the 2-cerebellar hemispheres,which
is occupied by the inferior vermis.
-Tonsil is a small part of cerebellar
hemisphere that lies lateral to
inferior vermis.
External Features of Cerebellum :
Superior surface : lies beneath
tentorium cerebelli and has a raised superior
vermis + a large cerebellar hemisphere on
each side + primary & horizontal fissures.
1- Primary fissure V-shaped,well defined
fissure, lies on superior surface and
separates the small anterior lobe from the
larger middle lobe (or posterior lobe).
2- Horizontal fissure lies along the sides of
cerebellum, extending from anterior notch
to posterior notch, separates the superior
from the inferior surfaces.
3- Secondary (posterolateral) fissure
lies on inferior surface and separates
flocculo-nodular lobe from the ramainder
of cerebellum.
Functional subdivision of
cerebellum :
1- Archi-cerebellum =
posterior lobe
(Vestibular part) :
_ It is formed of the flocculo-
Schematic drawing of cerebellum
showing the relationships between the
anatomical & functional divisions of
cerebellum.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-cerebellum
nodular lobe + associated fastigial
nuclei, lying on inf. Surface in front
of postero-lateral fissure.
_Embryologically, it is the oldest
part of cerebellum.
_It receives afferent Fs. From
vestibular apparatus of internal ear
Via vestibulo-cerebellar tracts.
_It is concerned with equlibrium.
I- Archicerebellum
It is concerned with equilibrium.
It represents flocculo-nodular lobe.
It has connections with vestibular &
reticular nuclei of brain stem
through the inferior cerebellar
peduncle.
Afferent vestibular Fs. Pass from
vestibular nuclei in pons & medulla to the
cortex of ipsilateral flocculo-nodular lobe.
Efferent cortical (purkinje cell) Fs.
Connections of
archicerebellum
Project to fastigial nucleus, which projects to
vestibular nuclei & reticular formation.
It affects the L.M.system bilaterally via
descending vestibulo-spinal & reticulo-spinal
2- Paleo-cerebellum=
(spinal part) :
-_it is formed of midline vermis
Schematic drawing of cerebellum
showing the relationships between the
anatomical & functional divisions of
cerebellum.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-cerebellum
+ surrounding paravermis +
globose & emboliform nuclei.
_It receives afferent proprioceptive impulses from Ms.&
tendons Via spino-cerebellar
tracts (dorsal & ventral) mainly.
-it sends efferents to red nucleus
of midbrain.
-it is concerned with muscle tone
2-Paleo-cerebellum
It is concerned with muscle tone
& posture.
Afferents spinal Fs. consist of
dorsal & ventral spino-cerebellar
tract from muscle, joint &
cutaneous receptors to enter the
cortex of ipsilateral vermis & para
vermis Via inferior & superior
cerebellar peduncles .
Connections of Paleo-cerebellum.
Efferents cortical fibres pass to
globose & emboliform nuclei, then
Via sup. C. peduncle to contralateral red nucleus of midbrain to
give rise descending rubro-spinal
tract.
3- Neo-cerebellum=
(cerebral part) :
_It is the remaining largest part
of cerebellum.
_It includes the most 2-cerebellar
hemispheres + dendate nuclei.
_It receives afferent impulses
from the cerebral cortex+pons
Schematic drawing of cerebellum showing Via cerebro-ponto- cerebellar
the relationships between the anatomical &
pathway.
functional divisions of cerebellum.
-it sends efferents to V.L.nucleus
Green =archi-cerebellum,
of thalamus.
blue=paleo-cerebellum.
-it controls voluntary movements
Pink= neo-cerebellum
(muscle coordination).
3- Neo-cerebellum
It is concerned with muscular
coordination.
It receives afferents from cerebral
cortex involved in planning of
movement- to pontine nuclei ,cross to
opposite side Via middle Cerebellar
peduncle to end in lateral parts of
cerebellum (cerebro-ponto-cerebellar
tract).
Connections of Neo-cerebellum.
Neo-cerebellar efferents project to
dendate nucleus,which in turn projects to
contra-lateral red nucleus & ventral
lateral nucleus of thalamus ,then to
motor cortex of frontal lobe, giving rise
descending cortico-spinal & corticobulbar pathways.
Efferents of dentate nucleus form a
major part of superior C. peduncle.
Cerebellar Lesions
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Are usually vascular, may be traumatic or tumour.
Manifestations of unilateral cerebellar lesions :
1-ipsilateral incoordination of (U.L) arm = intention tremors : it is a
terminal tremors at the end of movement as in touching nose or button
the shirt.
2-Or ipsilateral cerebellar ataxia affects (L.L.) leg, causing wide-based
unsteady gait.
Manifestations of bilateral cerebellar lesions (caused by alcoholic
intoxication, hypothyrodism, cerebellar degeneration & multiple
sclerosis) :
1-dysarthria : slowness & slurring of speech.
2-Incoordination of both arms.= intention tremors.
3-Cerebellar ataxia : intermittent jerky movements or staggering ,
wide-based, unsteady gait.
4-Nystagmus : is a very common feature of multiple sclerosis. It is due
to impairment coordination of eye movements /so, incoordination of
eye movements occurs and eyes exhibit a to-and-fro motion.
Combination of nystagmus+ dysarthria + intension tremors constitutes
Chacot’triad, which is highly diagnostic of the disease.
Internal Structure of cerebellum :
It consists of an outer
layer of grey matter
(cerebellar cortex) , &
inner layer of white matter
containing 4-pairs of
cerebellar nuclei :
Sagittal section of cerebellum.
T.S.of cerebellum & brain at level
of 4th V. to show cerebellar nuclei.
above roof of 4th V. from
medial to lateral :
1-Fastigial nucleus.
2-Globose nucleus.
3-Emboliform nucleus.
4-Dendate nucleus.
(the only one that can be
seen clearly with the naked
eye).
Cerebellar cortex
It is highly convoluted,
forming numerous transversely
oriented folia.
T.S of cerebellar folia showing
layers of cerebellar cortex.
Afferent & Efferent connecltions and
their relationships to principal cells of
cerebellar cortex.
It contains nerve cells,
dendrites and synaptic
connections of cellular
neurones.
The cellular organization of
the cortex consists of 3-layers :
1-Outer molecular layer.
2-Intermediate, purkinje cell
layer.
3-Inner granular layer, which is
dominated by granule cell.
Cerebellar cortex
Molecular layer : contains
1-Cells : molecular cells (stellate cells) &
basket cells.
2-Nerve Fibres :
a- dendrites of Purkinje cells
(arborisations).
B-axons of granule cells. ( bifurcate to
produce 2-parallel fibres , oriented
along long axis of folium).
C-ending of climbing fibers.
Purkinje cell layer : it is formed
of one layer (unicellular) of large flaskshaped purkinje cells. Their arborisations
are at right angles to long axis to folium.
Granular layer : it is formed of
small granule cells & ending of mossy
fibres.
MThere are 3-types of
Nerve Fibres in white
Matter :
1-Axons of purkinje cells :
the only axons to leave cerebellar
cortex to end in deep cerebellar
nuclei specially dendate nucleus.
2-Mossy Fibres : end in the
granular layer.
3-Climbing Fibres : end in the
molecular layer.
Afferent Fibres to cerebellum :
Mostly end in cerebellar cortex,
excitatory to cortical neurones,
as mossy or climbing Fs. passing
through the cerebellar peduncles.
(In M.O)
The following are Afferent fibres:
1-dorsal & ventral spino-cerebellar
tract. (passing via I.C.P & S.C.P)
2-vestibulo-cerebellar Fs. (via I.C.P)
3-olivo-cerebellar Fs. (via I.C.P)/
(extrapyramidal fibres), (end as
climbing or mossy fibres)
4-ponto-cerebellar Fs. (via M.C.P).
Efferent Fibres of the
cerebellum :
M
It sends the following fibres :
1-Cerebello-vestibular Fs. to
vestibular nuclei of pons & M.O.
2-Cerebello-olivary Fs. To M.O.
3-Dendato-rubro-thalamic tract To
red nucleus of midbrain & ventrolateral nucleus of the thalamus and
finally to motor cortex of frontal
lobe to coordinate movement via
cortico-spinal & corticobulbar
tracts.
The Fourth Ventricle
It is a cavity of hindbrain.
Position : lies between pons & M.O.
anteriorly and the cerebellum posteriorly.
It is a diamond-shaped space which is
lined by ependyma.
Its superior angle is continuous with
cerebral aqueduct of midbrain.
inferior angle is continuous with
centeral canal of closed M.O.
Its lateral angles extend laterally to
form a lateral recess on each side to
open into subarachnoid space.
The Boundaries of
th
4
Ventricle
Superiolateral boundary :
-it is formed by superior cerebellar
peduncle on each side.
Inferiolateral boundary :
-it is formed by inferior cerebellar
peduncle + gracile & cuneate
tubercles on each side.
The Roof of 4th Ventricle
-it is a tent-shaped when seen
laterally, and diamond-shaped when
seen behind.
-it is formed of superior & inferior
medullary vela, which are thin sheets
of white matter /consists of :
ependyma covered by pia mater.
-Sup.medullary velum connects the 2
sup.cerebellar peduncles.
-Inf.medullary velum connects the 2
inf.cerebellar peduncles.
-Inferior vermis of cerebellum : lies
in the middle of roof of 4th ventricle.
The Roof of 4th Ventricle
The lower part of roof is
invaginated by tela choroidea of 4th
ventricle.
The tela choroidea is a double
layer of pia mater which encloses the
choroid plexus of 4th ventricle.
The choroid plexus is a vascular
capillary tuft covered by ependymal
cells and secretes C.S.F. into the
lumen of 4th ventricle.
The Openings of 4th Ventricle
The roof contains 3 aperatures
which transmit C.S.F. from ventricular
lumen to subarachnoid space.
Median aperature (foramen of
Magendie) : lies in the median plane at
lower end of inferior medullary velum,
and opens into subarachnoid space at
cistrna magna at cerebello-medullary
angle
2 lateral openings (foramina of
Luschka) : each one lies at the lateral end
of lateral recess to open into
subarachnoid space at cerebello-pontine
angle. choroid plexus partly protrudes out
through each lateral aperture.
The Floor of
th
4
Ventricle
It is called rhomboid fossa.
It is diamond-shaped and is
divided into right & left halves
by the median sulcus.
It is crossed in the middle by
transvere Fs. (ponto-cerebellar
Fs.)called medullary stria,
which divide floor of 4th
ventricle into upper (pontine)
& lower (medullary) part.
A diagram to show the floor & lateral
boundaries of 4th ventricle.
The Floor of
th
4
Ventricle
Upper pontine part : presents
on each side of median sulcus.
1-Medial eminence : a rounded
elevation produced by the abducent
nucleus.
2-Facial colliculus : an elevation
on the top of lower part of medial
eminence. It is produced by the
fibres of facial nerve which
surround abducent nucleus.
3-Superior fovea : a groove lateral
to facial colliculus.
4-Vestibular area : lateral to
superior fovea. It overlies superior,
A diagram to show the floor & lateral medial & lateral vestibular nuclei.
boundaries of 4th ventricle.
The Floor of
th
4
Ventricle
Lower medullary part :
presents on each side of the
median sulcus. 1-Inferior fovea :
inverted V-shaped groove.
2-Hypoglossal area : medial to
inferior fovea. It overlies
hypo-glossal nucleus.
3-Vagal area (triangle) : between
limbs of inferior fovea.It overlies
dorsal nucleus of vagus.
4-Vestibular area : lateral to
inferior fovea. It overlies inferior
vestibular nucleus.
A diagram to show the floor & lateral
boundaries of 4th ventricle.