Cerebellum and Extrapyramidal Pathways
Competencies:
- Compile the pathways projecting through the inferior cerebellar peduncle.
- Analyze the efferents of cerebellum for coordination of motor function.
- Draw all the descending upper motor neuron pathways originating in brain stem.
To master the material presented in this
lecture:
Read ...
Purves text, Chapter 19
Haines pp 240-245, 214-216.
Look at the Review Questions below ...
Listen to the lecture and focus on
the following points ...
- The convolutions of the cerebellar cortex (folia)
increase the surface area for the computational network of cells,
and these folia continue across the midline in the vermis.
- The cerebellum is organized from medial
to lateral and referred to as:
- vermis, found in all 3 lobes. Prominent
in flocculonodular lobe, and its vestibular functions. (balance
and movement of eyes).
- paravermis, includes most of the
Anterior Lobe, and the medial posterior lobe. ‘Sensory'
homunculi indicate spinal cord connections, e.g. spinocerebellar
tracts. (Posture, muscle tone, synergy for stereotyped movements)
- hemispheres, includes mostly the
Posterior Lobe. Basilar pons connections, therefore cerebro-ponto-cerebellar
pathway. (cerebral planning, muscle tone in accurate nonstereotyped
movements)
- Primary fissure and posterolateral fissure.
- Three pairs of cerebellar peduncles carry
afferent and efferent fibers.
- Inferior Cb. Peduncle (restiform
body) - mostly sensory input from spinal cord and
brain stem (a juxtarestiform body carries the vestibular connections).
- Middle Cb. Peduncle (brachium pontis)
- cerebral cortical input.
- Superior Cb. Peduncle (Brachium
conjunctivum) - mostly efferent to VL thalamus, and
also reticular formation and red nucleus.
- Cerebellar Cortex:
- Uniformity in thickness and cytology.
- Molecular layer.
- Purkinje cell layer.
- Granule cell layer.
- Five neuronal types in the cortex:
- Purkinje cells - the only
efferent axons - GABA.
- Granule cells - parallel
fibers - glutamate.
- Basket cells - GABA - lateral
inhibition.
- Stellate cells - ?taurine.
- Golgi cells - ?GABA.
- Three types of Afferent fibers:
- Climbing fibers - excitatory
from inferior olive.
- Aminergic fibers - DA,
NE, 5HT.
- Mossy fibers - excitatory
from all other afferent tracts.
- Deep cerebellar nuclei provide most of
the efferent axons.
- Purkinje cells of cortex project to the
deep nuclei.
- Fastigial nucleus - from
vermis and flocculonodular lobe, has bilateral efferents to
the vestibular nuclei (via juxtarestiform body).
- Globose nucleus - from
paravermis.
- Emboliform nucleus - These
nuclei project mainly to red nucleus, and reticular formation.
- Dentate nucleus - from
cerebellar hemisphere. Projects mainly to contralateral
VL of thalamus, which influences motor cortex activity.
- Cerebellar disease, if unilateral, results in
ipsilateral disturbances of somatic motor activity. It may
result in falling to the ipsilateral side, and depending on location
of damage, may principally affect trunk muscles and posture (vermis),
or the voluntary movements of the limbs (hemisphere). Symptoms
tend to dissipate with time. Generally, lesions of the superior
cerebellar peduncle or deep cerebellar nuclei produce greater
deficits than cerebellar cortex lesions.
- Extrapyramidal pathways are those that arise from nuclei in the brain stem, and most are influenced directly by the cerebellum.
- Red nucleus gives rise to the rubrospinal tract which functionally parallels the pyramidal tract.
- Reticular nuclei give rise to the reticulospinal tracts which modulate posture and highly stereotyped movements such as walking.
- Superior colliculus gives rise to the tectospinal tract which influences movement of the head in relation to visual orientation.
- Vestibular nuclei give rise to:
- the lateral vestibulospinal tract which runs the length of the spinal cord to facilitate antigravity muscles, and
- the medial vestibulospinal tract (also called descending limb of MLF) to cervical levels of spinal cord for head adjustment to movement in space.
Consider the Following Questions ..
- Describe the neural circuits involved in maintaining postural tone? balance? coordination of head and eye movements?
- Why will disturbance of the right cerebellar hemisphere result in right hand ataxia?
- The single source of climbing fibers to the cerebellar cortex is from which nucleus?
- Name the tracts bringing sensory information from the spinal cord, and identify how they enter the cerebellum and how they end in the cerebellar cortex.
- Information integrated in the cerebellar cortex reaches thalamus and primary motor cortex via which pathways?
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