The reason behind this is that the inside of the cell has some positive charges (K +) and also other negatively charged ions (A –), while the outside of the cell has more positive ions (Na + and Ca 2+) and some negatively charged ones (Cl –). 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.

Dendrite definition