Download Cerebellum YAYDAR 2013-2014

Cerebellum (Latin for Little Brain)
• Function
•
•
•
•
The cerebellum regulates the following 5 functions:
•
•
•
•
•
•
Muscle tone
Coordination of goal directed and spontaneous movements
Posture and balance
Eye movements
Motor learning
Some cognitive functions (e.g., language acquisition, riding a bike,
professonal musicians)
Each hemisphere of the cerebellum influences motor activity on the
ipsilateral half of the body.
The cerebellum compares the motor plan (intent) created in the cortex
with motor performance (reported from the periphery) and functions to
smoothen and coordinate the movements.
This is accomplished by making synaptic contacts with the brainstem
‘motor’ centers and the cerebral hemispheres.
Cerebellum (Latin for Little Brain)
The Cerebellum
 Its surface is highly convoluted, forming
folds or folia, being oriented transversely.
 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 peduncles,
respectively.
Cerebellum, Superior and Inferior Surfaces
• The cerebellum consists of a midline
vermis and 2 lateral hemispheres.
• Anatomically, it is divided into
anterior, posterior & flocculonodular lobes.
Vermis: (Latin for worm)
Cerebellum, Superior and Inferior Surfaces
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
the 2 cerebellar hemispheres.
occupied by falx cerebelli, which separates
Cerebellum, Superior Surface
Cerebellum, Inferior Surface
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.
 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).
 Horizontal fissure lies along the sides of
cerebellum, extending from anterior notch to
posterior notch, separates the superior from the
inferior surfaces.
External Features of Cerebellum
 Inferior surface:rounded on each side and
presents :
 A deep groove (vallecula) between 2
cerebellar hemispheres,which is occupied by
the inferior vermis and tonsil.
 Tonsil is a small part of cerebellar
hemisphere that lies lateral to inferior vermis.
 Retrotonsillar fissure seperates tonsil from
the biventer lobule.
 Secondary (posterolateral) fissure
lies on
inferior surface and separates flocculo-nodular
lobe from the remainder of cerebellum.
External Features of Cerebellum
External Features of Cerebellum
Uvula: (Latin for little grape)
Tuber: (Latin for swelling)
External Features of Cerebellum
External Features of Cerebellum
External Features of Cerebellum
Fourth Ventricle and Cerebellum
Cerebellum
Internal Features of Cerebellum
Internal Features of Cerebellum
Section in Plane of Superior Cerebellar Peduncle
Internal Features of Cerebellum
Interposed Nucleus
Cerebellar Nuclei
•
Fastigial
• Stance and gait, controls muscles only in the
modes of sitting, standing, and walking
•
Globose + Emboliform
• Segmental reflexes, speeds the initiation of
movements triggered by somatosensory cues that
guide the response, stops unwanted and
promotes wanted oscillations, stabilizes holds
•
Dentate
• Fine dexterity
Functional Subdivisions of Cerebellum
 Schematic drawing of cerebellum showing the relationships between the
anatomical & functional divisions of cerebellum.
(Paleo-cerebellum)
(Neo-cerebellum)
(Archi-cerebellum)
Functional Subdivisions of Cerebellum
Functional Subdivisions of Cerebellum
Functional Subdivisions of Cerebellum
Functional Subdivisions of Cerebellum
1- Archi-cerebellum = posterior lobe
(Vestibular part) :
 It is formed of the flocculo-nodular
lobe
+ associated fastigial nuclei, lying on
inferior surface in front of postero-lateral
fissure.
 Embryologically, it is the oldest part of
cerebellum.
 It receives afferent
fibers from vestibular
apparatus of internal ear via
vestibulocerebellar tracts.
It is concerned with equlibrium and eye
movements
Functional Subdivisions of Cerebellum
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 fibers. Pass from
vestibular nuclei in pons & medulla to the
cortex of ipsilateral flocculo-nodular lobe.
 Efferent cortical (purkinje cell) fibers.
Project to fastigial nucleus, which projects to
vestibular nuclei & reticular formation.
 It affects the L.M.system bilaterally
via
descending vestibulo-spinal & reticulospinal tracts.
Connections of
archicerebellum
Functional Subdivisions of Cerebellum
2. Paleo-cerebellum= (spinal part) :
Formed of:
 Midline vermis + surrounding
paravermis + globose & emboliform
nuclei.
 It receives afferent proprio-ceptive
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.
Functional Subdivisions of Cerebellum
• 2. Paleo-cerebellum
• It is concerned with muscle tone &
posture.
• Afferents spinal
fibers: consist of
dorsal & ventral spino-cerebellar
tracts from muscle, joint & cutaneous
receptors to enter the cortex of
ipsilateral vermis & para vermis via
inferior & superior cerebellar peduncles.
.
• Efferents cortical fibers pass to
globose & emboliform nuclei, then via
sup. c. peduncle to contra-lateral red
nucleus of midbrain to give rise
descending rubro-spinal tract.
Connections of Paleocerebellum.
Functional Subdivisions of Cerebellum
3- Neo-cerebellum= (cerebral
part):
 It is the remaining largest part of
cerebellum.
 It includes the most of 2 cerebellar
hemispheres + dendate nuclei.
 It receives afferent impulses from
the cerebral cortex + pons via
cerebro-ponto- cerebellar pathway.
 It sends efferents to V.L. nucleus
of thalamus.
 It controls voluntary movements
(muscle coordination).
Functional Subdivisions of Cerebellum
 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).
 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 &
cortico-bulbar pathways.
 Efferents of dentate nucleus form a major
part of superior C. peduncle.
Connections of Neocerebellum.
Afferent and Efferents
•
Superior Cerebellar Peduncle
(brachium conjunctivum)
• Connects with midbrain
•
Middle Cerebellar Peduncle
(brachium pontis)
• Connects with pons
•
Inferior Cerebellar Peduncle
(restiform body)
• Connects with medulla
Superior Cerebellar Peduncle
Afferent:
• Ventral spinocerebellar tract: Transmits proprioceptive and
exteroceptive information from levels below the midthoracic cord.
•, Tectocerebellar tract: Arises in the superior and inferior colliculi and
carries auditory and visual information.
• Trigeminocerebellar tract: Carries proprioceptive fibers from the
mesencephalon and tactile information from the chief sensory nucleus
of the trigeminal nerve.
• The cerulocerebellar tract: Fibers from the nucleus ceruleus
Superior Cerebellar Peduncle
Efferent: (most prominent)
• Dentatorubral tract, output to the contralateral red nucleus
• Dentatothalamic tract, output to the contralateral ventrolateral
nucleus of the thalamus
• Uncinate bundle of Russell, output to the vestibular nuclei and
reticular formation
Middle Cerebellar Peduncle
• Afferent fibers: (only)
•
Pontocerebellar (corticopontocerebellar) tract, arises in contralateral
pontine gray matter
• Transmits impulses from the cerebral cortex to the intermediate
and lateral zones of the cerebellum.
Inferior Cerebellar Peduncle
Afferents:
• Dorsal spinocerebellar tract, originating in the dorsal nucleus of
Clarke (T1–L2), carries proprioceptive and exteroceptive information
mostly from the trunk and ipsilateral lower extremity.
• Cuneocerebellar tract, originating in the external arcuate nucleus,
which transmits proprioceptive information from the upper extremity
and neck.
• Olivocerebellar tract, which carries somatosensory information from
the contralateral inferior olivary nuclei.
• Vestibulocerebellar tract, transmits information from vestibular
receptors on both sides of the body.
• Reticulocerebellar tract, arises in the lateral reticular and
paramedian nuclei of the medulla.
Inferior Cerebellar Peduncle
•
Arcuatocerebellar tract, arises from the arcuate nuclei of
the medulla oblongata.
• Trigeminocerebellar tract, arises from the spinal and
main sensory nuclei of the trigeminal nerve
Efferent:
• Fastigiobulbar tract -(through Juxtarestifrom body),
cerebellovistibular
•
Cerebelloreticular pathways
A schematic model of the motor system.
The cerebellum influences movements via connections to both the
brainstem and cerebral cortex
Vascular Supply
Vascular Supply
Vascular Supply
Vascular Supply
Vascular Supply
Vascular Supply
•
PICA
• From intracranial vertebral artery,
supplies the lateral medullary
tegmentum, inferior cerebellar
peduncle, the ipsilateral portion of
the inferior vermis, and the inferior
surface of the cerebellar
hemisphere.
• Medial branch supplies dorsolateral
medulla and medial cerebellum,
lateral branch supplies
inferiopostalateral
Vascular Supply
•
AICA
• Above the origin of the basilar artery, supplies the anterior
petrosal surface of the cerebellar hemisphere, flocculus, lower
portion of the middle cerebellar peduncle, and lateral
pontomedullary tegmentum.
•
SCA
• Distal segment of the basilar artery just below the terminal
bifurcation into the paired PCAs, and supplies the upper surface
of the cerebellar hemisphere, ipsilateral portion of the superior
vermis, most of the dentate nucleus, upper portion of the middle
cerebellar peduncle, superior cerebellar peduncle, and lateral
pontine tegmentum.
Cerebellar Lesions
• Are usually vascular, may be traumatic or tumor.
• Manifestations of unilateral cerebellar lesions :
• 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.
• Ipsilateral cerebellar ataxia affects (L.L.) leg, causing widebased unsteady gait.
• Manifestations of bilateral cerebellar lesions (caused by alcoholic
intoxication, hypothyrodism, cerebellar degeneration & multiple
sclerosis) :
• Dysarthria: slowness & slurring of speech.
Cerebellar Lesions
• Incoordination of both arms.= intention tremors
• Cerebellar ataxia: intermittent jerky movements or staggering ,
wide-based, unsteady gait.
• Nystagmus : 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 Charcot’s triad, which is highly diagnostic of the
disease.
• Loss of cerebellar function does not produce paralysis or the
inability to initiate a movement. Rather, cerebellar disease produces
disturbances in the coordination and fine control of movements and
posture.