This is the case for cerebellar granule neurons (CGN) as well as cortical and hippocampal pyramidal neurons (PN), three of the best-studied models of neuronal polarization both in vitro and in vivo ( Gao & Hatten 1993, Hatanaka & Murakami 2002, Komuro et al 2001, Noctor et al 2004, Rakic 1971, Rakic 1972, Shoukimas & Hinds 1978). On the other hand, other neurons undergo extensive stereotypical changes of their morphology leading to polarized outgrowth of their axon and dendrite ( Figure 1C-D). This is the case for retinal ganglion cells and bipolar cells in the developing vertebrate retina ( Figure 1A-B) ( Hinds & Hinds 1978, Morgan et al 2006, Zolessi et al 2006). Careful examination of the morphological transition between neural progenitors and post-mitotic neurons reveal that neurons can inherit their axon and dendrite polarity directly from the apico-basal polarity of their progenitors. While migrating, post-mitotic neurons form a leading process and a trailing process which become the axon or the dendrite depending on the cell type ( Figure 1). In vivo, most neurons undergo axon-dendrite polarization during migration. Neuronal polarization can be divided in several specific steps: upon cell cycle exit, mammalian neurons usually migrate over a long distance before reaching their final destination. The current review will provide an updated model synthesizing a recent body of work suggesting that in vivo, neuronal polarity is most probably a result of a complex interaction between extracellular cues directing intrinsic cell polarity pathways. Based on existing data, Craig and Banker provided a conceptual framework for the experiments that, over the past decade, have improved our understanding on how neuronal polarity is established mostly using in vitro approaches. A seminal review published by Craig and Banker fifteen years ago in this journal ( Craig & Banker 1994) observed that “we almost nothing about the cellular mechanisms responsible for the compartmentation in neurons”. How are the axonal and dendritic compartments generated during development? This question has received a lot of attention both at the cellular and molecular levels over the past three decades. Dendrites integrate synaptic inputs triggering the generation of axon potentials at the level of the soma and propagates along the axon making presynaptic contacts onto the dendrite of target neurons. Neurons typically form a single axon and multiple dendrites which underlie the flow of information transfer in the central nervous system. Neurons are among the most polarized cell types in our body and are compartimentalized into two molecularly and functionally distinct domains: the axon and the dendrites. Its disruption is thought to underlie several pathological states including cell transformation and metastasis. There are only differences between fast secreting neurotransmitters (Acth, dopamine) and slow releasing neuropeptides from neuroendocrine cells.Cell polarity lies at the center of many biological processes including epithelial morphogenesis, cell migration and chemotaxis. The specific capacitance is mainly determined by the thickness and dielectric constant of the phospholipid bilayer membrane and is similar for intracellular organelles and the plasma membrane. This can be measured by increases in membrane capacitance (Cm). Another direct measure of exocytosis is the increase in membrane area due to the incorporation of the secretory granule or vesicle membrane into the plasma membrane. Meaning that upon stimulation, many neurotransmitters are being released into the synaptic cleft.īut there a thing called membrane capacitance. In the process, they cause changes in the permeability of the cell membrane to specific ions, opening up special gates or channels which let in a flood of charged particles (ions of calcium, sodium, potassium, and chloride). These chemicals then bind to chemical receptors in the dendrites of the receiving (post-synaptic) neuron. When stimulated by an electrical pulse, neurotransmitters of various types are released, and they cross the cell membrane into the synaptic gap between neurons. The more signals sent between two neurons, the stronger the connection grows. The connections between neurons are not static, though, they change over time. Meaning that a certain neuron sends multiple kinds of signals by sending different kinds of neurotransmitters.įunctionally related neurons connect to form neural networks (also known as neural nets or assemblies). Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synaptic connections.

Show picture of dendrite and axon