Lecture for the medical students

1. CEREBELLUM AND ITS
CONNECTIONS
Dr. Abdul Qadeer
MBBS; FCPS; FICS
Assistant Prof. of Surgery

2. An overview about cerebellum
1. It controls the posture and voluntary
movements
2. It coordinates the actions of the voluntary
muscles
3. Each cerebellar hemisphere controls
muscular movements on the same side
of the body
4. It has no direct pathway to the LMNs but
exerts its control via the cerebral cortex
and the brainstem

3. Gross appearance of the
cerebellum
 It is situated in the posterior cranial fossa
 It is covered superiorly by the tentorium
cerebelli
 It is the largest part of the hind brain
 It lies posterior to the 4th ventricle, pons &
medulla

4. Lateral veiw of the cerebellum

5. Gross appearance of the
cerebellum
 It consists of two cerebellar hemispheres
 Both hemispheres are joined by vermis
 It is connected to the brainstem by three
bundles of nerve fibers called:
1. Superior cerebellar peduncle
2. Middle cerebellar peduncle
3. Inferior cerebellar peduncle

7. Gross appearance of the
cerebellum
 Cerebellum is divided into 3 main lobes
1. Anterior lobe
2. Middle(or Posterior) lobe
3. Flocculonodular lobe

10. Gross appearance of the
cerebellum
 Anterior lobe may be seen on the superior
surface of the cerebellum
 It is separated from the middle lobe by a wide
V-shaped fissure called the primary fissure
 Middle lobe is the largest part of the
cerebellum. It is situated between primary &
uvulonodular fissures
 Flocculonodular lobe is situated posterior to
the uvulonodular fissure
 An insignificant horizontal fissure is also

13. Internal structure of the
cerebellum
1. Gray matter (Cortex): is the outer
covering
2. White matter: inner contents
3. Intracerbellar nuclei: are the masses of
gray matter within the white matter

14. Structure of the cerebellar
cortex
 Cerebellum is made up of folds (Folia)
 Folia give branched appearance Called
arbor vitae
 Gray matter of the cortex may be divided
into 3 layers
1. External (molecular) layer
2. Middle (Purkinje cell) layer
3. Internal (granular) layer

16. Molecular layer of cerebellar
cortex
 This layer contains 2 types of neurons
1. The outer stellate cell
2. The inner basket cell

18. Purkinje cell layer of cerebellar
cortex
 These cells are large Golgi type-I neurons
 They are flask shaped
 They are arranged in a single layer
 The dendrites of these cells pass to the
molecular layer and are branched
 The axon arises at its base & passes
through the molecular layer to enter into
the white matter

20. Purkinje cell layer of cerebellar
cortex
 The axons of these cells synapse with the
cells of one of the intracerebellar nuclei
 The collateral branches of their axons also
synapse with the dendrites of basket &
stellate cells
 Few of their axons pass directly to end in
the vestibular nuclei of the brainstem

22. Granular layer of cerebellar
cortex
 This layer contains many small cells
 The dendrites of these cells synapse with
the mossy fibers
 Their axons pass into the molecular layer
and bifurcate at a T-junction. The
branches run parallel (hence called
parallel fibers) to the cerebellar folium &
the purkinje cells

24. Functional areas of the cerebellar
cortex
 Vermis influences the movements of the
long axis of the body i.e. neck, shoulders,
thorax, abdomen & hips
 Intermediate zone controls the muscles
of the distal parts of the limbs i.e. hands
and feet
 Lateral zone of each cerebellar
hemisphere is concerned with the
planning of sequential movements of the
entire body & conscious assessment of

26. Intracerebellar nuclei
 Four masses of gray matter are
embedded in the white matter of the
cerebellum on each side of the midline
 Their axons take part in the formation of
superior & inferior cerbellar peduncles
 These nuclei (from lateral to medial)
include:
1. Dentate nucleus
2. Emboliform nucleus
3. Globose nucleus
4. Fastigial nucleus

28. Dentate nucleus
 The largest of the cerebellar nuclei
 Shape like a crumpled bag with the
opening facing medially
 Interior of the bag is filled with white
matter
 Efferent fibers leave the nucleus through
the opening to form the large part of
superior cerebellar peduncle

29. Emboliform nucleus
 It is ovoid in shape
 Situated medial to the dentate nucleus

30. Globose nucleus
 Situated medial to the emboliform nucleus
 Consists of one or more rounded cell
groups

31. Fastigial nucleus
 It lies near the midline in the vermis
 Lies close to the roof of 4th ventricle
 It is larger than globose nucleus

32. White matter of the cerebellum
 The white matter is made up of 3 groups
of fibers
1. Intrinsic
2. Afferent
3. Efferent

33. Intrinsic fibers of white matter of
the cerebellum
 These fibers do not leave the cerebellum but
connect its different regions
 Some connect folia of the cerebellar cortex
with vermis
 Others connect the two cerebellar
hemispheres together

34. Afferent fibers of white matter of
the cerebellum
 These form the greater part of the white matter
 These proceed to the cerebellar cortex
 They enter the cerebellum mainly through the
inferior and middle cerebellar peduncles

35. Efferent fibers of white matter of
the cerebellum
 These fibers form the output of the
cerebellum
 These are actually the axons of the Purkinje
cells
 Their majority of fibers pass to & synapse
with the neurons of the cerebellar nuclei (i.e.
fastigial, globose, emboliform & dentate)
 Their minority of fibers bypass the cerebellar
nuclei & leave the cerebellum without
synapsing

36. Efferent fibers of white matter of
the cerebellum
 Fibers from dentate, emboliform &
globose nuclei leave the cerebellum
through the superior cerebellar peduncle
 Fibers from the fastigial nucleus leave the
cerebellum through the inferior cerebellar
peduncle

37. Cerebellar cortical mechanisms
 Cerebellar cortex also consists of:
1. Climbing fibers
2. Mossy fibers
 These fibers are excitatory to the Purkinje
cells
 A single Purkinje neuron makes synaptic
contact with only one climbing fiber
 One climbing fiber makes contact with 1 to 10
Purkinje neurons

39. Cerebellar cortical mechanisms
 The stellate, basket & Golgi cells serve as
inhibitory interneurons and influence the
degree of Purkinje cell excitation produced
by the climbing & mossy fiber input
 Therefore the Purkinje cells form the
center of a functional unit of the
cerebellar cortex

40. Intracerbellar nuclear
mechanisms
 The deep cerebellar nuclei receive
information from two sources:
1. Inhibitory axons from the Purkinje cells of
the cortex
2. Excitiatory axons from the climbing &
mossy fibers that are passing to the
cortex

41. Cerebellar cortical
neurotransmitters
 The excitatory climbing & mossy fibers
use glutamate i.e. GABA (gamma
aminobutyric acid) as the excitatory
neurotransmitter
 Other fibers liberate norepinephrine &
serotonin as the neurotransmitter

42. Cereballar peduncles
 The cerebellum is linked to other parts of
CNS by afferent and efferent fibers that
are grouped together on each side into
three large bundles or peduncles
1. Superior cerebellar peduncles:
connect the cerebellum to the midbrain
2. Middle cerebellar peduncles: connect
the cerebellum to the pons
3. Inferior cerebellar peduncles: connect
the cerebellum to the medulla oblongata

43. Cerebellar afferent fibers
 These include:
1. From the cerebral cortex
2. From the spinal cord
3. From the vestibular nerve
4. Other afferent fibers

44. 1. Cerebellar afferent fibers from
the cerebral cortex
 The cerebral cortex sends information to
the cerebellum by 3 pathways
a. Corticopontocerebellar pathway
b. Cerebro-olivocerebellar pathway
c. Cerebro-reticulocerebral pathway

45. Corticopontocerebellar pathway
 Theses fibers run from all the lobes of the
cerebral cortex to the pons
 From the pons, the fibers run as the
transverse fibers of the pons, cross the
midline & enter the opposite cerebellar
hemisphere as the middle cerebellar
peduncle

46. Cerebro-olivocerebellar
pathway
 The cortico-olivary fibers arise from all the
lobes of the cerebral cortex to the inferior
olivary nuclei
 From here, the fibers cross the midline to
enter the opposite cerebellar hemisphere
through the inferior cerebellar hemisphere

47. Cerebro-reticulocerebellar pathway
 The fibers arise from many areas of the
cerebral cortex, especially the sensori-
motor areas
 Reach to the reticular formation on the
same & opposite sides in the pons &
medulla
 The reticulo-cerebellar fibers then enter
the cerebellar hemisphere on the same
side through the inferior and middle
cerebellar hemispheres

48. 2. Cerebellar afferent fibers from
the spinal cord
 Includes 3 pathways:
a. Anterior spinocerebellar tract
b. Posterior spinocerebellar tract
c. Cuneo-cerebellar tract

49. Anterior spinocerebellar tract
 Sensory axons enter the spinal cord via
posterior root and synapse with the
neurons of the nucleus dorsalis (Clarke’s
column)
 Most of the fibers cross to the opposite
side as the anterior spino-cerebellar tract
in the contralateral white column
 The fibers enter the cerebellum through
the superior cerebellar peduncle &
terminate as mossy fibers in the cerebellar

50. Anterior spinocerebellar tract
 It is believed that those fibers that cross
over to the opposite side in the spinal cord
cross back within the cerebellum
 This tract conveys muscle joint information
from the muscle spindles, tendon organs
and joint receptors of the upper, lower
limbs, skin & superficial fascia

51. Posterior spinocerebellar tract
 Sensory axons enter the spinal cord via
posterior root and synapse with the
neurons of the nucleus dorsalis (Clarke’s
column)
 The fibers run on the same side as the
posterior spino-cerebellar tract in the
lateral white column & reach to the
medulla oblongata
 The tract then enters the cerebellum
through the inferior cerebellar peduncle &

52. Posterior spinocerebellar tract
 This tract conveys muscle joint information
from the muscle spindles, tendon organs
and joint receptors of the trunk and lower
limbs

53. Cuneocerebellar tract
 The fibers originate in the nucleus cuneatus
of the medulla oblongata
 Then enters the cerebellar hemisphere on the
same side through the inferior cerebellar
peduncle
 The fibers terminate as mossy fibers in the
cerebellar cortex
 This tract conveys muscle joint information
from the muscle spindles, tendon organs and
joint receptors of the upper limbs and upper

54. 3. Cerebellar afferent fibers from
the vestibular nerve
 Vestibular nerve receives information from
the inner ear
 Motion movements from the semicircular
canals
 Position relative to gravity from the utricle
and saccule
 The vestibular nerve sends many afferent
fibers directly to the cerebellum on the
same side through the inferior cerebellar
peduncle

55. 3. Cerebellar afferent fibers from
the vestibular nerve
 Other vestibular fibers pass first to the
vestibular nuclei in the brainstem, then
pass to the cerebellum on the same side
through the inferior cerebellar peduncle
 All the afferent fibers from the inner ear
terminate as mossy fibers in the
flocculnodular lobe of the cerebellum

56. 4. Other afferent fibers to the
cerebellum
 These include the fibers from the:
1. Red nucleus and
2. Tectum

57. THE AFFERENT CEREBELLAR PATHWAYS
Pathway Function Origin Destination
Cortico-ponto-
cerebellar
Conveys control
from cerebral cortex
Frontal, parietal and
occipital lobes
Via pontine nuclei &
mossy fibers to
cerebellar cortex
Cerebro-olivo-
cerebellar
Conveys control
from cerebral cortex
Frontal, parietal and
occipital lobes
Cerebro-
reticulo-
cerebellar
Conveys control
from cerebral cortex
Sensorimotor areas Via reticular
formation
Anterior spino-
cerebellar
Conveys information
from muscles &
joints
Muscle spindles, tendon
organs and joint
receptors
Via mossy fibers to
cerebellar cortex
Posterior spino-
cerebellar
Conveys information
from muscles &
joints
Muscle spindles, tendon
organs and joint
receptors
Via mossy fibers to
cerebellar cortex
Cuneo-
cerebellar
Conveys information
from muscles &
joints
Of upper limb
Muscle spindles, tendon
organs and joint
receptors
Via mossy fibers to
cerebellar cortex
Vestibular nerve Conveys information Utricle, saccule and Via mossy fibers to

58. Cerebellar efferent fibers
 The entire output of the cerebellar cortex
is through the axons of the Purkinje cells
 These mostly influence through the
cerebellar nuclei. Few may influence
directly on the lateral vestibular nucleus
 The efferent fibers from the cerebellum
connect with the:
1. Red nucleus 2. Thalamus
3. Vestibular complex 4. Reticular
formation

59. Cerebellar efferent fibers
 The cerebellar efferent pathways include:
1. Globose-Emboliform-Rubral pathway
2. Dentothalamic pathway
3. Fastigial vestibular pathway
4. Fastigial reticula pathway

60. Globose-Emboliform-Rubral
Pathway
 Axons of neuron in the globose & emboliform
nuclei travel through the superior cerebellar
peduncles & cross to the opposite side in the
decussation of the superior cerebellar
peduncles
 From here the fibers cross back the midline
again to the red nucleus to influence the
rubrospinal tract
 Therefore, the globose-emboliform nuclei
influence motor activity on the same side of

61. Dento-thalamic pathway
 Axons from the neurons of the dentate
nucleus travel through the superior
cerebellar peduncle & cross the midline in
the decussation of the superior cerebellar
peduncle
 From here, the fibers end in the ventrolateral
nucleus of the thalamus, which again reach
to the primary motor cortex of the cereberum
via internal capsule & corona radiata

62. Dento-thalamic pathway
 By this pathway, the dentate nucleus can
influence motor activity of the opposite
cerebral cortex. The impulses from the
motor cortex are transitted to the spinal
cord through the cortico-spinal tract after
decussation in the pyramid
 Hence, the dentate nucleus is able to
coordinate muscle activity on the same
side

63. Fastigial-vestibular pathway
 Axons from the fastigial nucleus travel
through the inferior cerebellar peduncle
and end on the neurons of the lateral
vestibular nucleus on both sides
 The neurons from the vestibular nucleus
form the vestibulospinal tract
 This nucleus influences mainly on the
ipsilateral extensor muscle tone

64. Fastigial-reticular pathway
 The axons from the fastigial nucleus travel
through the inferior cerebellar peduncle
and synapse with the neurons of the
reticular formation
 Hence, this nucleus influences spinal
motor activity through the reticulospinal
tract

65. The efferent cerebellar
pathways
Pathway Function Origin Destination
Globose-
emboliform-
rubral
Influences
ipsilateral motor
activity
Globose &
emboliform
nuclei
To contralateral red
nucleus, then via
crossed rubrospinal
tract to ipsilateral motor
neurons in spinal cord
Dentothalamic Influences
ipsilateral motor
activity
Dentate
nucleus
To contralateral
ventrolateral nucleus of
thalamus, then to
contralateral motor
cerebral cortex;
coticospinal tract
Fastigial
vestibular
Influences
ipsilateral
extensor muscle
tone
Fastigial
nucleus
To laterla vestibular
nuclei; then via
vestibulospinal tract

66. Functions of cerebellum
 To coordinate, by synergistic action, all
reflex and voluntary muscular activity
 It harmonizes muscle tone & maintains
normal body posture
 It permits voluntary movements, such as
walking, to take place smoothly with
precision & economy of effort
 It is NOT able to initiate muscle movement

67. Clinical notes
 Lesions in one cerebellar hemisphere give
rise to signs & symptoms that are limited to
the same side of the body. The causes may
include:
1. Acute alcohol poisoning
2. Congenital agenesis or hypoplasia
3. Trauma
4. Infections
5. Tumors
6. Multiple sclerosis
7. Vascular disorders e.g. thrombosis
8. Poisoning with heavy metals

68. Signs & symptoms of cerebellar
disorders
1. Hypotonia
2. Postural changes & alteration of gait
3. Disturbances of voluntary movements (Ataxia)
4. Dysdiadochokinesia
5. Disturbances of reflexes
6. Disturbances of ocular movement
7. Disorders of speech e.g. dysarthria
8. Cerebellar syndromes e.g.
a) Vermis syndrome b) cerebellar hemisphere
syndrome

69. Hypotonia
 The muscles lose resilience to palpation
 Diminished resistance to passive
movements of joints
 Shaking the limb produces excessive
movements at the terminal joints

70. Postural changes & alteration of
gait
 Head is often rotated & flexed
 Shoulder on the side of the lesion is lower
on the normal side
 The patient assumes a wide base when
stands
 The patients stands on stiff legs to
compensate loss of muscle tone
 While walking, the patient lurches and
staggers toward the affected side

71. Ataxia
 The muscles contract irregularly & weakly
 Tremor occurs while fine movements are
attempted, such as buttoning clothes,
writing, shaving
 Muscle groups fail to work harmoniously
 There is decomposition of movement e.g.
past-pointing or hitting the nose and
putting the heel on the shin of opposite leg

72. Dysdiadochokinesia
 It is the inability to perform alternating
movements regularly and rapidly
 Example: Ask the patient to pronate &
supinate the forearm rapidly. On the side
of the cerebellar lesion, the movements
are slow, jerky & incomplete

73. Dysorders of reflexes
 Pendular knee jerk

74. Disturbances of ocular
movement
 Nystagmus:
1. Pendular nystagmus: rythmic oscillation
of the eyes may be of the same rate in
both directions
2. Jerk nystagmus: oscillation of the eyes
quicker in one direction than the other

75. Disorders of speech
 Dysarthria: occurs due to ataxia of the
muscles of larynx

76. Vermis syndrome
(Medulloblastoma)
 The vermis is unpaired and influences
midline structures. Hence in its lesions:
 The patient may fall forward or backward
 Difficulty in holding the head staedy and in
an upright position

77. Cerebellar hemisphere
syndrome
 May occur due to the tumors of the
cerebellar hemisphere
 So it involves the muscles of the same
side
 Swaying & falling to the side of the lesion
 Dysarthria & nystagmus

84. The end