Neuron doctrine: The nervous system, as all other living systems, is built from individual separate elements (Ramon Y Cajal). He actually invented the fact that information flows along an axon to a dendrite and then to cell body. So he thought that these two elements (axon & dendrite) should be somehow connected. A neuron consists of three parts: a) the dendritic tree, b) the axon and c) the cell body (soma). Dendrites (dendritic spines) are the input devices and axons (axon terminals) are the output devices of neurons.
1. AIS (Action Initial Segment): an electrically "hot" region which enables the initiation of the spikes if it decides that a certain threshold of potential has been reached due to the activity of EPSPs and IPSPs. The spikes then propagate along the axon. It's a propagating wave of activity without attenuation, "full-blown".
2. Nodes of Ranvier: Little gaps on the axon between myelin sheaths (or inter-nodes) which (the internodes) are electrically isolated lipid wrapping parts of the axon (they wrap the axon). Myelin sheaths are made of a special set of cells which are not neurons (sometimes they are called glial cells). The myelin is the isolation element that blocks current travel out of the axon. The Nodes are not isolated. They are excitable, amplification, boosting regions for spikes.
3. Axon terminals: Along the axon or at the end of it, there are little varicosities that consist of the neurotransmitters, the chemicals which eventually interact to another neuron. Inside a varicosity there may be are thousands of vesicles consisting of molecules of neurotransmitters (i.e. dopamine). So the spike propagates through the axon until it reaches the varicosities and triggers them to transmit (or transfer) the signal via neurotransmitters to the receptors of the spine of the next neuron.
Neuron Types (classes):
1. By function - Excitatory Vs. Inhibitory. Excitatory cells are also called "principal" because their axon projects to other brain regions. Inhibitory cells are also called "interneurons" because they demonstrate local axonal projection.
2. By anatomy - Pyramidal, etc.
3. By electrical/spiking activity pattern - some fire more, other less (bursters, stutterers, etc).
4. By chemical characteristics
5. By gene expression.
The Synapse: The contact point between two neurons, a chemical device, a small gap between a varicosity of an axon terminal of a pre-synaptic cell and a dendritic spine of a dendritic tree of a post-synaptic sell. It can be also seen as a digital to analog converter through chemical interaction since it communicates a digital signal (spike) to an analog, degraded signal (post-synaptic potential). The strength of a synapse is the strength of the ratio between the pre-synaptic signal and the post-synaptic signal. Synapse is a chemical element that enables memory, the effect of drugs, learning, etc.
- An MRI Brain Atlas
- European Data Alliance for the Brain
- Make a Mad Mad Neuron (flash game!)
- Label the Diagram of a Neuron (flash exercise!!)
- http://wps.aw.com/bc_marieb_ehap_8/25/6527/1670985.cw/index.html (quizzes)
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