![]() This means that the inside of the neuron is negatively charged with respect to the outside of the cell. The normal or physiological resting membrane potential of neurons is about -65 mV. To understand this, we need first to understand some intrinsic properties of neurons. The sum of many EPSPs can surpass the threshold needed for the post-synaptic neuron to start an action potential. Therefore, a net influx of negative charges (Cl –) lead to a decrease in the cell membrane potential and, consequently, to what we call a post-synaptic inhibitory potential (IPSP). Here, Cl – will flow into the post-synaptic neuron. In the case of inhibitory neurotransmitters, something similar occurs but instead of activating ligand-gated Na + and Ca 2+ channels, binding to the receptor will result in the activation of ligand-gated Cl – channels. If there are enough positive charges such that the cell membrane potential reaches a threshold value, then there is an action potential (see below under Transfer Information). there is a net influx of positive charges, then we call this a post-synaptic excitatory potential (EPSP), and the cell is depolarized. If enough positive charges enter the cell such that the cell membrane potential increases, i.e. At the same time, some K + will also exit the cell. Because it is an excitatory neurotransmitter, binding to the receptor will activate ligand-gated ion channels that allow positively charged ions to enter the cell: Na + and Ca 2+. In the case of excitatory neurotransmitters, the pre-synaptic neuron releases the neurotransmitter and the post-synaptic neuron detects it when it binds to its specific receptors. Let’s take a look at what happens in each case. Na +, Ca 2+, Cl – or sodium, calcium, chloride, respectively) or to exit the neuron (e.g. Ligand-gated ion channels enable ions to enter the neuron (e.g. The neurotransmitter receptors begin a signaling cascade that activates certain ligand-gated ion channels. This signaling cascade depends on the neurotransmitter and neurotransmitter receptor: there are excitatory neurotransmitters, such as glutamate, and inhibitory neurotransmitters, such as GABA. Once the neurotransmitter binds to the neurotransmitter receptor in the post-synaptic neuron, a signaling cascade starts that enables the information to be processed at the synapse. You can find an example of a dendritic spine in this micrograph: Some types of neurons have dendritic spines on the dendrites, which are small protrusions that project from the dendrites and which have neurotransmitter receptors that increase the detection of neurotransmitters. ![]() If, for instance, a pre-synaptic neuron releases dopamine, the post-synaptic neuron will need dopamine receptors in order to detect the signal and consequently receive the information. Examples of neurotransmitters are dopamine, serotonin, norepinephrine, GABA and glutamate. If the post-synaptic neuron does not have the specific neurotransmitter receptor, then the neurotransmitter will have no effect. The post-synaptic neuron can detect the neurotransmitters because it has neurotransmitter receptors (number 5 in the figure) to which the neurotransmitters bind. This figure shows the synapse of a pre-synaptic neuron (A) and a post-synaptic neuron (B):Īt the synapse, the pre-synaptic neuron releases neurotransmitters (number 2 in the figure), which are molecules that the post-synaptic neuron detects. More specifically, synapses are the site where two neurons exchange signals: the upstream or pre-synaptic neuron releases neurotransmitters (usually at the end of the neuron, also called axonal terminal) and the downstream or post-synaptic neuron detects them (usually in the dendrites). At the end of these projections are the synapses, which is where the information transfer occurs. The dendrites resemble the branches of a tree in the sense that they extend from the soma or body of the neuron and open up into gradually smaller projections.
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