The Cerebellum

Question 1

What is the cerebellum?

Answer 1

the control centre for the coordination of voluntary muscle activity, equilibrium, and muscle tonus on the same side

Question 2

Why does a person with cerebellar injury not become paralysed?

Answer 2

the cerebellum does not initiate movement

Question 3

What information must the cerebellum receive to carry out its function?

Answer 3

• position of the body parts in space, and tone of muscles in the body
• equilibrium state of the body (head)
• commands that are being sent from the motor cortex to the lower motor neurons

Question 4

Where is the cerebellum located?

Answer 4

in the posterior cranial fossa, between the cerebral hemisphere and brainstem

Question 5

What are the 3 lobes of the cerebellum?

Answer 5

• anterior
• posterior
• flocculonodular

Question 6

How are the 3 cerebellar lobes divided?

Answer 6

by the primary and posterolateral fissures

Question 7

How is the cerebellum divided longitudinally?

Answer 7

into a midline vermis and left and right cerebellar hemispheres

Question 8

How is the cerebellum connected to the brainstem?

Answer 8

via three bundles of axons (cerebellar peduncles)

Question 9

What are the 3 cerebellar peduncles?

Answer 9

• superior cerebellar peduncle
• middle cerebellar peduncle
• inferior cerebellar peduncle

Question 10

How is unconscious proprioception regarding the state and position of muscles and joints conveyed?

Answer 10

by proprioceptive fibres whose receptors are found in joints, tendons, and muscles

Question 11

How do central processes of unconscious proprioceptive axons reach the cerebellum?

Answer 11

via the dorsal or ventral spinocerebellar tracts

Question 12

What is the dorsal spinocerebellar tract?

Answer 12

a somatosensory part of the sensory nervous system that relays unconscious proprioceptive information from the lower limbs and trunk of the body to the cerebellum

Question 13

Describe the pathway of the dorsal spinocerebellar tract

Answer 13

1. axons from the DRG synapse with second-order neurons in the dorsal horn (nucleus dorsalis)
2. axons from the nucleus dorsalis ascend on the same side of the spinal cord in the dorsal spinocerebellar tract
3. axons enter the cerebellum through the inferior cerebellar peduncle and terminate

Question 14

Where is the nucleus dorsalis found?

Answer 14

only in the upper part of the spinal cord (C8-L2)

Question 15

Describe the pathway of the ventral spinocerebellar tract

Answer 15

1. axons enter the junction between the dorsal and ventral horn and synapse with a neuron
2. axons from this neuron cross the midline to ascend on the opposite side, but then cross back to the side of the DRG to enter the cerebellum

Question 16

Where do all spinocerebellar fibres enter the cerebellum?

Answer 16

on the same side as the dorsal root ganglion

Question 17

What does the cerebellum receive through the vestibuocochlear cranial nerve?

Answer 17

input about head position and rotation from the vestibular apparatus in the inner ear

Question 18

What arises from the superior and lateral vestibular nuclei?

Answer 18

fibres that supply information concerning the equilibrium state of the body

Question 19

How do equilibrium fibres enter the cerebellum?

Answer 19

through the ipsilateral inferior peduncle into the flocculonodular lobe

Question 20

What does the cortiocpontocerebellar tract do?

Answer 20

provide the cerebellum with a copy of the information being sent from the motor cortex to the lower motor neurons

Question 21

Describe the pathway of the corticopontocerebellar tract

Answer 21

1. fibres originate in the motor cortex and descend through the internal capsule
2. fibres synapse on neurons in the pontine nuclei
3. neurons in the pontine nuclei send their axons across the midline to terminate in the cerebellum on the opposite side of the motor cortex

Question 22

How does the cerebellum integrate the information it receives to the motor cortex?

Answer 22

via the dentato rubro thalamo cortical pathway

Question 23

What are the 2 pathways from the cerebellum to the lower motor neurons?

Answer 23

• cerebellum → vestibulospinal tract → lower motor neurons in ventral horm
• cerebellum → rubrospinal tract → lower motor neurons in ventral horn

Question 24

What is the result of the vestibulospinal tract?

Answer 24

contraction of the axial musculature and proximal limb muscles to maintain balance of the body, at an unconscious level

Question 25

What does the dentato rubro thalamo cortical pathway allow?

Answer 25

the cerebellum to coordinate movements to the motor cortex itself

Question 26

Describe the pathway of the dentato rubro thalamo cortical pathway

Answer 26

1. motor cortex
2. pons
3. cross the midline to opposite cerebellar hemisphere
4. cross the midline to opposite red nucleus
5. red nucleus
6. thalamus
7. motor cortex

Question 27

What can the red nucleus project to?

Answer 27

lower motor neurons in the ventral horn of the spinal cord which causes muscle contraction to maintain balance

Question 28

What is ataxia?

Answer 28

the loss of proper coordination between muscles

Question 29

What are signs of ataxia?

Answer 29

the patient walking with abnormal gait or with feet spread apart

Question 30

What is asynergia?

Answer 30

loss of coordination in performing motor acts

Question 31

What are signs of asynergia?

Answer 31

motor acts are performed in jerky stages instead of smoothly

Question 32

What is dysmetria?

Answer 32

the inability to judge distance and to stop movement at a chosen spot

Question 33

What is hypotonia?

Answer 33

a state in which the muscles are floppy and weak; falling may occur, especially to the injured side

Question 34

What is medulloblastoma?

Answer 34

the most common primary CNS tumour in children situated in the vermis or roof of fourth ventricle

Question 35

What are the first signs of medulloblastoma?

Answer 35

headache, vomiting, and ataxia with a stumbling gait and frequent unexplained falls