The cerebellum is located in the posterior cranial fossa. It consists of gray matter on the outside forming the cortex, and white matter on the inside. The cerebellum is divided into three lobes - the flocculonodular lobe, anterior lobe, and posterior lobe - by two fissures. It performs important roles in motor control and coordination through connections with other parts of the brain and spinal cord. Lesions of the cerebellum can cause ataxia, tremor, and other movement abnormalities. The fourth ventricle is located between the brainstem and cerebellum.

1. The Cerebellum
Dr. Mohammed Mahmoud Mosaed

2. Cerebellum
 Position Located in the posterior cranial fossa,
beneath the tentorium cerebelli and behind the
pons and medulla
 The cerebellum is extensively concerned with the
processing of sensory information.
 Although it has few ways to influence motor
neurons directly, it is considered part of the motor
system and concerned with equilibrium, muscle
tone, postural control, and co-ordination of
voluntary movements

4. The cerebellum
 The cerebellum consists of two large bilateral
hemispheres connected by a narrow median portion
called the vermis
vermis
Cerebellar
hemisphere

5.  Histologically the cerebellum consists of:
(1) an outer gray layer, the cortex,
(2)Medullary core of white matter composed of
nerve fibers projecting to and from the
cerebellum,
(3)Four pair of deep cerebellar nuclei (fastigial,
globose, emboliform and dentate).
The globose and emboliform nuclei together
constitute the interposed nucleus.

6. Internal structures
Cerebellar cortex
Dentate nucleus
Fastigial nucleus
Globose nucleus
Emboliform nucleus
medullary center

8. External features
 The cerebellar surface is corrugated into
parallel, long, narrow “gyri” called folia. These
are mostly oriented transversely.
 about 15% of the cortex is exposed to the
outer surface, where as 85% faces the sulcal
surfaces between the folia.
 If the cortex could be drawn out into a flat
sheet, it would be over 1 meter long.
 Beneath the cortex is a mass of white matter,
the medullary center of the cerebellum

9. surfaces of the cerebellum
 The upper surface of the vermis is raised and is called the
superior vermis.
 The inferior surface of the vermis is called the inferior vermis
and lies in the depression between the 2 cerebellar
hemispheres called vallecula
 The upper surface of each hemisphere is flat and slopes
downwards and laterally from the center to the periphery under
the tentorium cerebelli
 The inferior surface of each hemisphere is nearly convex
and rests on the floor of posterior cranial fossa lateral to the
internal occipital crest
 The anterior surface of the cerebellum is called anterior
cerebellar notch
 The posterior surface of the cerebellum is called the
posterior cerebellar notch which lodges the falx cerebelli.

10. Lobes of the cerebellum
 The cerebellum is divided into three main lobes: the anterior
lobe, the middle lobe, and the flocculonodular lobe.
 The anterior lobe may be seen on the superior surface of the
cerebellum and is separated from the middle lobe by a wide V-
shaped fissure called the primary fissure.
 The middle lobe (the posterior lobe), which is the largest part
of the cerebellum, is situated between the primary and
posterolateral (uvulonodular) fissures.
 The flocculonodular lobe is situated posterior to the
uvulonodular fissure.
 A deep horizontal fissure that is found along the margin of the
cerebellum separates the superior from the inferior surfaces; it
is of no morphologic or functional significance

11. Fissures in the cerebellum
 Posterolateral Fissure
 The 1st
fissure to appear during development is the
posterolateral fissure.
 It separates the flocculonodular lobe from the
corpus cerebelli.
 The corpus cerebelli is larger than the
flocculonodular lobe.
 The posterolateral fissure is so deep that the
flocculus of each side is almost pinched off from
the rest of the cerebellum.
 Primary Fissure
 It subdivides the corpus cerebelli into anterior and
posterior lobes.

12. Lobs
Primary fissure
Posterolateral fissure
Flocculonodular lobe
Anterior lobe
Posterior lobe
corpus of
cerebellar

14. External features
 Tonsil of cerebellum
two elevated masses
on inferior surface of
hemispheral portion
just nearby foramen
magnum

16. Lobes of the cerebellum
 Two fissures, the primary and posterolateral fissures
divide the cerebellum into three lobes
 1. The flocculonodular lobe, behind the
posterolateral fissure, consists of paired appendages
called flocculi located posteriorly and inferiorly and
joined medially by the nodulus (part of the vermis). It is
also called the archicerebellum because it is
phylogenetically the oldest part of the cerebellum and
the vestibulocerebellum because this lobe is
integrated with the vestibular system.
 The flocculonodular lobe plays a significant role in
regulation of muscle tone and maintenance of
equilibrium and posture through influences on the trunk
(axial) musculature.

17.  2. The anterior lobe, located rostral to the
primary fissure, is also called the
paleocerebellum because it is
phylogenetically the next oldest part. This lobe
together with the vermal and paravermal
portions of the posterior lobe constitute the
spinocerebellum
 The spinocerebellum plays a role in the
regulation of muscle tone, receives
proprioceptive and exteroceptive inputs from
the body and limbs via the spinocerebellar
pathways, and from the head via fibers from
the brainstem

18.  3. The large posterior lobe is located
between the primary fissure and the
posterolateral fissure. This phylogenetically
newest lobe (neocerebellum) receives input
from the cerebral cortex via a relay in the basilar
pons.
 It performs a significant role in planning and
programming of movements important for
muscular coordination during phasic activities.

19. Lobs
Primary fissure
Posterolateral fissure
Flocculonodular lobe
Anterior lobe
Posterior lobe
corpus of
cerebellar

20. Functional divisions of the cerebellum
 It is subdivided functionally into three zones:
 1. Medial or vermal;
 2. Paramedial, paravermal, or intermediate;
 3. Lateral or hemispheric. In addition to the cortex,
 each zone consists of underlying white matter and a
deep cerebellar nucleus to which it topographically
projects, vermis to fastigial nucleus, paravermal
cortex to interposed nuclei, and hemisphere to
dentate nucleus

22. Functional divisions of the
cerebellum
 Three functional divisions
 Vestibulocerebellum (archicerebellum)
 Flocculonodular lobe
 Spinocerebellum (paleocerebellum)
 Vermis and intermediate zone
 Cerebrocerebellum (neocerebellum)
posterior lobe

23. Vestibulocerebellum
 Connections
 Afferents: receive input from vestibular
nuclei
 Efferents: projects to the fastigial nucleus
and to the vestibular nucleus →
vestibulospinal tract and medial longitudinal
fasciculus
 Function: involved in eye movements
and maintain balance

24. Spinocerebellum
 Afferents: receive somatic sensory information via
spinocerebellar tracts
 Efferents:
 Vermis projects to the fastigial nucleus → vestibular
nuclei and reticular formation → vestibulospinal tract
and reticulospinal tract → motor neurons of anterior
horn cells
 Intermediate zone projects to the interposed nuclei
 Contralateral red nucleus → rubrospinal tract →
motor neurons of anterior horn
 Contralateral intermediate ventral nucleus of the
thalamus → cerebral cortex → coticospinal tract→
motor neurons of anterior horn cells
 Function: play an important role in control of muscle
tone and coordination of muscle movement on the
same side of the body

25. Afferent of the spinocerebellum
 Vermis receives somatosensory information (mainly from
the trunk) via the spinocerebellar tracts and from the spinal
nucleus of trigeminal nerve.
 It receives a direct projection from the primary sensory
neurons of the vestibular labyrinth, and also visual and
auditory input from brain stem nuclei.
 Intermediate hemisphere receives somatosensory
information (mainly from the limbs) via the spinocerebellar
tracts (the dorsal spinocerebellar tract, from Clarke’s
nucleus of the lower limb, and the cuneocerebellar tract,
from the accessory cuneate nucleus of the upper limb,
both enter via the ipsilateral inferior cerebellar peduncle)

26. Efferent of spinocerebellum
 1. to fastigial nucleus, which projects to
 A) the medial descending systems: (1)
reticulospinal tract (2) vestibulospinal tract
 B) an ascending projection to VL thalamus
 C) to the reticular grey of the midbrain
 2. to interposed nuclei, which project to the lateral
descending systems: (1) magnocellular portion of
red nucleus (2) VL thalamus (3) reticular nucleus
of the pontine tegmentum; (4) inferior olive (5)
spinal cord intermediate grey

27. Cerebrocerebellum
 Connection
 Afferents: receives input from the
cerebral cortex via a relay in pontine
nuclei
 Efferents: projects to dentate nucleus →
primary motor cortex → corticospinal tract
→ motor neurons of anterior horn
 Function: participates in planning
movements

28. Cerebellar peduncles
Three peduncles
 Inferior cerebellar peduncl
Connects the cerebellum with medulla
contain both afferent and efferent
fibers
 Middle cerebellar peduncle
connect with pons, contain afferent
fibers
 Superior cerebellar peduncle
connect with midbrain, contain mostly
efferent fibers

29. Superior cerebellar peduncle
 It extends from the anterior cerebellar notch upwards
and medially on the side of the upper part of the fourth
ventricle.
 It joins the back of the midbrain below the tectum
Afferents passes though the superior cerebellar peduncle
 1. Ventral spinocerebellar tract
 2. Tectocerebellar fibers from the superior and inferior
colliculi
 3. Hypothalamocerebellar fibers
Efferents passes though the superior cerebellar peduncle
 Dentatorubal fibers
 Dentatothalamic fibers

30. Middle cerebellar peduncles
 It is the thickest of the cerebellar peduncles.
 It passes from the lateral aspect of the pons and passes
posterolaterally to enter the white center of the cerebellar
hemisphere
Afferents passes though the middle cerebellar
peduncle
Pontocerebellar fibers which form the main bulk of the peduncle
Reticulocerebellar fibers from the reticular formation of the pons
Efferents passes though the middle cerebellar
peduncle
Cerebelloreticular fibers
Cerebellopontine fibers

31. Inferior cerebellar peduncle (restiform body)
 It connects the medulla with the cerbellum
 It arises from the dorsal aspect of the medulla and ascend upwards and laterally
towards the anterior cerebellar notch
 It curves posteriorly between the superior cerebellar peduncle medially and middle
cerebellar peduncle laterally to enter the cerebellar hemisphere
Afferents passes though the middle cerebellar peduncle
 Dorsal spinocerebellar fibers
 Olivocerebellar fibers
 Paraolivocerebellar fiber
 Vestibulocerebellar fibers
 Dorsal external arcuate fibers
 Ventral external arcuate fibers
 Reticulocerebellar fibers
 Trigeminocerebellar fibers from the main sensory nucleus and nucleus of
spinal tract of the trigeminal nerve from the main and the same side
Efferents passes though the middle cerebellar peduncle
 Cerebelloolivary fibers
 Cerebellovestibular fibers
 Cerebelloreticular fibers

32. Blood supply of the cerebellum
 Superior cerebellar artery from the basilar artery
 Anterior inferior cerebellar artery from the basilar
artery
 Posterior inferior cerebellar artery from the
vertebral artery

34. Cerebellar lesions
 Causes
vascular causes, Trumatic causes and Tumours in the adjacent structures
 Manifestations
Hypotonia of muscles
Cerebellar ataxia in the form of intermittent jerky movements
Disturbance of equilibrium in the form of unsteady gait with a wide base
Intention tremor it’s a terminal tremor at the end of movement
Decomposition of movements (Asynergy) which is evident by postpointing
Adiadochokinesis which is evident by asking the patient to do rapidly alternating
movements as supination and pronation, the movement appears jerky, slow and
incomplete.
Nystagmus in the form of jerky movement of the eye
Cerebellar vermain syndrom if the vermis is only affect, the muscles of the head,
neck and trunk are only affected the limbs are free
Cerebellar hemispheral syndrom: When one hemisphere is affect the
manifestations are restricted to the side of the lesion, the muscles of the upper
and lower limbs are affected on the side of the lesion with the tendency to fall
towards the side of lesion
Archicerebellar syndrom: lesion of the floculonodular lobe lead to disturbance of
equilibrium with unsteadiness, the patient walks with the a wide base and sways
from side to side

35. FOURTH VENTRICLE
 The fourth ventricle lies between the pons and
medulla oblongata anterior and the cerebellum
posterior.
 Rostrally it is continuous with the cerebral aqueduct,
and caudally with the central canal of the spinal cord.
 In sagittal section, the fourth ventricle has a
characteristic triangular shape, and the apex of its
roof protrudes into the inferior aspect of the
cerebellum. While a lateral recess on both sides
extends to the lateral border of the brain stem. At this
point the lateral aperture of the fourth ventricle
(foramen of Luschka) provides access to the
subarachnoid space at the cerebellopontine angle,
and CSF flows through it into the lateral extension of
the pontine cistern.

38. Boundaries of the 4th
ventricle
 Superolateral boundary: is formed by the superior
cerebellar peduncle on each side
 Inferolateral boundary: is formed by the inferior
cerebellar peduncle, gracile and cuneate tubercles on
each side
 Roof: is formed by the superior and inferior medullary
vela which are thin sheet of ependyma covered by pia
mater
 The roof contains 3 apertures which transmit CSF from
the ventricular lumen to the subarachoid space, one
aperature median (foramen of magendie) which open
into cerebellomedullary cistern and 2 lateral (foramen of
luschka) which lies at the lateral end of lateral recess

40.  The floor of the fourth ventricle is a
shallow diamond-shaped, or rhomboidal,
depression (its lower part formed by the
back of the open medulla. While its
upper part formed by the back of the
pons
 At the level of the lateral recess of the
ventricle, a variable group of nerve fibre
fascicles, known as the striae medullaris,
runs transversely across the ventricular
floor and passes into the median sulcus.

41.  The floor is divided into medullary part and
pontine part separated by stria medullaris
 The inferior part (medullary part) of the floor
of the fourth ventricle shows an inverted
eleveted triangle close to the median sulcus,
the hypoglossal triangle (trigone), which lies
over the hypoglossal nucleus. Laterally, the
sulcus limitans widens to produce an
indistinct inferior fovea. Caudal to the inferior
fovea, between the hypoglossal triangle and
the vestibular area, is the vagal triangle
(trigone), which covers the dorsal vagal
nucleus.
 The stria medullares are aberrant
pontocerebellar fibers and arcucerebellar
fibers

42.  The superior part (pontine part) of the
ventricular floor
 On each side of medline, a sulcus (sulcus limitans) divides
the area into 2 parts (from medial to lateral):
 1. Medial eminence: overlies abducent nucleus
 2. Vestibular area: overlies vestibular nuclei
 The inferior end of the medial eminence is slightly
expanded to form the facial colliculus which is produced
by the facial nerve winding around the nucleus of abducent
nerve
 The medial eminence is bounded laterally by the sulcus
limitans
 Lateral to the sulcus limitans is area vestibuli produced by
the underlying vestibular nuclei