Neural pathways and circuits of the cerebellum Neural pathways and circuits in the cerebellum. (+) represent excitatory synapse, while (-) represent inhibitory synapses. Cerebellar<unk> s receive excitatory input from 3 or 4 mossy fibers originating from pontine nuclei. Mossy fibers make an excitatory connection onto<unk> s which cause the<unk>  to fire an action potential. The axon of a cerebellar<unk>  splits to form a parallel fiber which innervates Purkinje cells. The vast majority of<unk>  axonal synapses are found on the parallel fibers. The parallel fibers are sent up through the Purkinje layer into the molecular layer where they branch out and spread through Purkinje cell dendritic arbors. These parallel fibers form thousands of excitatory<unk> -Purkinje-cell synapses onto the dendrites of Purkinje cells. This connection is excitatory as glutamate is released. The parallel fibers and ascending axon synapses from the same<unk>  fire in synchrony which results in excitatory signals. In the cerebellar cortex there are a variety of inhibitory neurons (interneurons). The only excitatory neurons present in the cerebellar cortex are<unk> s. Plasticity of the synapse between a parallel fiber and a Purkinje cell is believed to be important for motor learning. The function of cerebellar circuits is entirely dependent on processes carried out by the<unk> r layer. Therefore, the function of<unk> s determines the cerebellar function as a whole. Mossy fiber input on cerebellar<unk> s<unk>  dendrites also synapse with distinctive unmyelinated axons which Santiago Ramón y Cajal called mossy fibers Mossy fibers and golgi cells both make synaptic connections with<unk> s. Together these cells form the glomeruli.<unk> s are subject to feed-forward inhibition:<unk> s excite Purkinje cells but also excite GABAergic interneurons that inhibit Purkinje cells.<unk> s are also subject to feedback inhibition: Golgi cells receive excitatory stimuli from<unk> s and in turn send back inhibitory signals to the<unk> . Mossy fiber input codes are conserved during synaptic transmission between<unk> s, suggesting that innervation is specific to the input that is received.<unk> s do not just relay signals from mossy fibers, rather they perform various, intricate transformations which are required in the spatiotemporal domain. Each<unk>  is receiving an input from two different mossy fiber inputs. The input is thus coming from two different places as opposed to the<unk>  receiving multiple inputs from the same source. The differences in mossy fibers that are sending signals to the<unk> s directly effects the type of information that<unk> s translate to Purkinje cells. The reliability of this translation will depend on the reliability of synaptic activity in<unk> s and on the nature of the stimulus being received. The signal a<unk>  receives from a Mossy fiber depends on the function of the mossy fiber itself. Therefore,<unk> s are able to integrate information from the different mossy fibers and generate new patterns of activity. Climbing fiber input on cerebellar<unk> s Different patterns of mossy fiber input will produce unique patterns of activity in<unk> s that can be modified by a teaching signal conveyed by the climbing fiber input. David Marr and James Albus suggested that the cerebellum operates as an adaptive filter, altering motor behaviour based on the nature of the sensory input. Since multiple (~200,000)<unk> s synapse onto a single Purkinje cell, the effects of each parallel fiber can be altered in response to a “teacher signal” from the climbing fiber input. Specific functions of different<unk> s ;Cerebellum<unk> s David Marr suggested that the<unk> s encode combinations of mossy fiber inputs. In order for the<unk>  to respond, it needs to receive active inputs from multiple mossy fibers. The combination of multiple inputs results in the cerebellum being able to make more precise distinctions between input patterns than a single mossy fiber would allow. The cerebellar<unk> s also play a role in orchestrating the tonic conductances which control sleep in conjunction with the ambient levels of GABA which are found in the brain. ;Dentate<unk> s Loss of dentate gyrus neurons from the hippocampus results in spatial memory deficits. Therefore, dentate<unk> s are thought to function in the formation of spatial memories and of episodic memories. Immature and mature dentate<unk> s have distinct roles in memory function. Adult-born<unk> s are thought to be involved in pattern separation whereas old<unk> s contribute to rapid pattern completion. ;Dorsal cochlear<unk> s Pyramidal cells from the primary auditory cortex project directly on to the cochlear nucleus. This is important in the acoustic startle reflex, in which the pyramidal cells modulate the secondary orientation reflex and the<unk>  input is responsible for appropriate orientation. This is because the signals received by the<unk> s contain information about the head position.<unk> s in the dorsal cochlear nucleus play a role in the perception and response to sounds in our environment. ;Olfactory bulb<unk> s Inhibition generated by<unk> s, the most common GABAergic cell type in the olfactory bulb, plays a critical role in shaping the output of the olfactory bulb. There are two types of excitatory inputs received by GABAergic<unk> s; those activated by an AMPA receptor and those activated by a NMDA receptor. This allows the<unk> s to regulate the processing of the sensory input in the olfactory bulb. The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell.<unk> s in the olfactory bulb have also been found to be important in forming memories linked with scents. Critical factors for function ;Calcium Calcium dynamics are essential for several functions of<unk> s such as changing membrane potential, synaptic plasticity, apoptosis, and regulation of gene transcription. The nature of the calcium signals that control the presynaptic and postsynaptic function of the olfactory bulb<unk> s spines is mostly unknown. ;Nitric oxide<unk>  neurons have high levels of the neuronal isoform of nitric oxide synthase. This enzyme is dependent on the presence of calcium and is responsible for the production of nitric oxide (NO). This neurotransmitter is a negative regulator of<unk>  precursor proliferation which promotes the differentiation of different<unk> s. NO regulates interactions between<unk> s and glia and is essential for protecting the<unk> s from damage. NO is also responsible for neuroplasticity and motor learning.
Granule cell
Foam cell
Nurse cell
Aschoff cell
Navicular cell
Respirocyte
Sustentacular cell
Corneocyte