Vermis

1. Vermis Peduncles Dentate nucleus Interposed nucleus (emboliform and globose nuclei) Fastigial nuclei Hemisphere 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).

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

3. Somatotopical Projections on the Cerebellum

4. Basket cell Stellate cell Molecular layer Purkinje cell layer Golgi cell Granular layer Granule cell White matter Climbing fiber Mossy fiber Output (to cerebellar nuclei and then to thalamus, brain stem, and vestibular nuclei) Neurons of the Cerebellum 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. Golgi cell axon Rosette Mossy fiber Granule cell dendrites A Glomerulum 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. Granule cells Purkinje cells Mossy fibers (spinocerebellar tract and brain stem nuclei) Climbing fibers (inferior olive) Inputs Into the Cerebellum 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. Complex spike Simple spike Simple and Complex Spikes 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. Distant Purkinje cells Basket cells Parallel fibers Purkinje cells Golgi cells Climbing fiber Stellate cells Granular cells Mossy fibers Glomeruli 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.

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

11. Climbing fibers Purkinje cell Parallel fibers 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.