The Cerebellum Flashcards
What is the cerebellum?
the control centre for the coordination of voluntary muscle activity, equilibrium, and muscle tonus on the same side
Why does a person with cerebellar injury not become paralysed?
the cerebellum does not initiate movement
What information must the cerebellum receive to carry out its function?
- 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
Where is the cerebellum located?
in the posterior cranial fossa, between the cerebral hemisphere and brainstem
What are the 3 lobes of the cerebellum?
- anterior
- posterior
- flocculonodular
How are the 3 cerebellar lobes divided?
by the primary and posterolateral fissures
How is the cerebellum divided longitudinally?
into a midline vermis and left and right cerebellar hemispheres
How is the cerebellum connected to the brainstem?
via three bundles of axons (cerebellar peduncles)
What are the 3 cerebellar peduncles?
- superior cerebellar peduncle
- middle cerebellar peduncle
- inferior cerebellar peduncle
How is unconscious proprioception regarding the state and position of muscles and joints conveyed?
by proprioceptive fibres whose receptors are found in joints, tendons, and muscles
How do central processes of unconscious proprioceptive axons reach the cerebellum?
via the dorsal or ventral spinocerebellar tracts
What is the dorsal spinocerebellar tract?
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
Describe the pathway of the dorsal spinocerebellar tract
- axons from the DRG synapse with second-order neurons in the dorsal horn (nucleus dorsalis)
- axons from the nucleus dorsalis ascend on the same side of the spinal cord in the dorsal spinocerebellar tract
- axons enter the cerebellum through the inferior cerebellar peduncle and terminate
Where is the nucleus dorsalis found?
only in the upper part of the spinal cord (C8-L2)
Describe the pathway of the ventral spinocerebellar tract
- axons enter the junction between the dorsal and ventral horn and synapse with a neuron
- 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
Where do all spinocerebellar fibres enter the cerebellum?
on the same side as the dorsal root ganglion
What does the cerebellum receive through the vestibuocochlear cranial nerve?
input about head position and rotation from the vestibular apparatus in the inner ear
What arises from the superior and lateral vestibular nuclei?
fibres that supply information concerning the equilibrium state of the body
How do equilibrium fibres enter the cerebellum?
through the ipsilateral inferior peduncle into the flocculonodular lobe
What does the cortiocpontocerebellar tract do?
provide the cerebellum with a copy of the information being sent from the motor cortex to the lower motor neurons
Describe the pathway of the corticopontocerebellar tract
- fibres originate in the motor cortex and descend through the internal capsule
- fibres synapse on neurons in the pontine nuclei
- neurons in the pontine nuclei send their axons across the midline to terminate in the cerebellum on the opposite side of the motor cortex
How does the cerebellum integrate the information it receives to the motor cortex?
via the dentato rubro thalamo cortical pathway
What are the 2 pathways from the cerebellum to the lower motor neurons?
- cerebellum → vestibulospinal tract → lower motor neurons in ventral horm
- cerebellum → rubrospinal tract → lower motor neurons in ventral horn
What is the result of the vestibulospinal tract?
contraction of the axial musculature and proximal limb muscles to maintain balance of the body, at an unconscious level
What does the dentato rubro thalamo cortical pathway allow?
the cerebellum to coordinate movements to the motor cortex itself
Describe the pathway of the dentato rubro thalamo cortical pathway
- motor cortex
- pons
- cross the midline to opposite cerebellar hemisphere
- cross the midline to opposite red nucleus
- red nucleus
- thalamus
- motor cortex
What can the red nucleus project to?
lower motor neurons in the ventral horn of the spinal cord which causes muscle contraction to maintain balance
What is ataxia?
the loss of proper coordination between muscles
What are signs of ataxia?
the patient walking with abnormal gait or with feet spread apart
What is asynergia?
loss of coordination in performing motor acts
What are signs of asynergia?
motor acts are performed in jerky stages instead of smoothly
What is dysmetria?
the inability to judge distance and to stop movement at a chosen spot
What is hypotonia?
a state in which the muscles are floppy and weak; falling may occur, especially to the injured side
What is medulloblastoma?
the most common primary CNS tumour in children situated in the vermis or roof of fourth ventricle
What are the first signs of medulloblastoma?
headache, vomiting, and ataxia with a stumbling gait and frequent unexplained falls
