1. Lecture 15:
Cerebellum
The cerebellum consists of two hemispheres and a medial area called the vermis. The cerebellum is connected to other neural structures by three pairs of peduncles. The figure shows a dorsal view of the cerebellum, and the peduncles and cerebellar nuclei are obscured (shown by black areas).
Vermis
Hemisphere
Peduncles
Dentate nucleus
Interposed nucleus (emboliform and globose nuclei)
Fastigial nuclei

2. Cerebellar Lobes
Primary fissure
Anterior lobe
Posterior lobe
Posteriorlateral fissure
Flocculonodular lobe
Nodulus
Flocculus
The cerebellum is divided into three lobes: the anterior lobe, the posterior lobe, and the flocculonodular lobe.

3. Somatotopical Projections
on the Cerebellum

4. Neurons of the Cerebellum
Output (to cerebellar nuclei and then to thalamus, brain stem, and vestibular nuclei)
White matter
Molecular layer
Purkinje cell layer
Granular layer
Basket cell
Granule cell
Climbing fiber
Mossy fiber
Golgi cell
Stellate cell
The cerebellar cortex consists of three layers and five types of neurons. Inputs to the cerebellum are carried by mossy fibers (from the inferior olive) and by climbing fibers (from pontine nuclei, the vestibular system, and the spinal cord). The only output system of the cerebellum is the axons of Purkinje cells.

5. Cerebellar Neurons

6. A Glomerulum
Mossy fiber
Golgi cell axon
Granule cell dendrites
Rosette
A single glomerulum consists of an incoming mossy fiber, clusters of small dendrites (called rosettes) from a few dozen granule cells, and the axons of the Golgi cells.

7. Inputs Into the Cerebellum
Mossy fibers (spinocerebellar tract and brain stem nuclei)
Granule cells
Climbing fibers (inferior olive)
Purkinje cells
Excitatory inputs to the cerebellum are provided by mossy fibers and climbing fibers. The mossy fibers originate in the spinocerebellar tract and in brain stem nuclei; they excite granule cells. The climbing fibers originate in the medulla (the inferior olive); they make synapses on Purkinje cells.

8. Simple and Complex Spikes
Simple spike
Complex spike
In response to a single excitatory stimulus, a Purkinje cell may generate
a single action potential (a simple spike, in response to mossy fiber input), or
a larger action potential, followed by a few smaller action potentials (a complex spike, in response to a signal from climbing fibers).

9. Wiring of the Cerebellum
Stellate cells make inhibitory synapses on the dendrites of Purkinje cells. Parallel fibers activate Purkinje cells, basket cells, stellate cells, and Golgi cells. Basket cells inhibit relatively distant Purkinje cells. Golgi cells inhibit granular cells, decreasing their response to mossy fibers.
Glomeruli
Parallel fibers
Golgi cells
Basket cells
Purkinje cells
Distant Purkinje cells
Stellate cells
Granular cells
Mossy fibers
Climbing fiber

10. Neuronal Population Vectors of the Purkinje
Cells and Neurons in the Cerebellar Nuclei

11. Cerebellar Memory?
If an action potential in a climbing fiber and another action potential in a parallel fiber arrive simultaneously at a Purkinje cell, the cell may “remember” this
event with the help of a chemical mechanism, changing the synaptic efficacy.
Climbing fibers
Parallel fibers
Purkinje cell