What are the two types of summation at a synapse?

Answer 1

Temporal (quickly repeated signals into one input), and Spatial (many different separate inputs); but summation occurs at axon hillock, not at the synapse.

Temporal means related to time; in this case, input signals are quickly repeated.

Spatial refers to space; in this case, in a small space leading to a neuron, many separate inputs (dendrites) all receive signals.

Temporal - Single presynaptic cell fires action potentials fast enough for the post synaptic potentials to add together and fire an action potential on the post synaptic cell

Spatial - Multiple presynaptic cells fire action potentials which converge on their target. Their individual post synaptic potentials add together to fire an action potential on the post synaptic cell

(Please note that the previous answer actually relates to summations at the AXON HILLOCK, not at a SYNAPSE. As far as I know, there is no summation at a SYNAPSE. Therefore the way it's written, the question asks about actions which do not occur. The answer above does, however, explain the two types of summations which can occur at the axon hillock very well, as long as it's understood that the actions described happen at the axon hillock, not at the synapse.)

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Answer 2

Different Types of Synapses

The human nervous system uses a number of different neurotransmitter and neuroreceptors, and they don't all work in the same way. We can group synapses into 5 types:

1. Excitatory Ion Channel Synapses.

These synapses have neuroreceptors that are sodium channels. When the channels open, positive ions flow in, causing a local depolarisation and making an action potential more likely. This was the kind of synapse described above. Typical neurotransmitters are acetylcholine, glutamate or aspartate.

2. Inhibitory Ion Channel Synapses.

These synapses have neuroreceptors that are chloride channels. When the channels open, negative ions flow in causing a local hyperpolarisation and making an action potential less likely. So with these synapses an impulse in one neurone can inhibit an impulse in the next. Typical neurotransmitters are glycine or GABA.

3. Non Channel Synapses.

These synapses have neuroreceptors that are not channels at all, but instead are membrane-bound enzymes. When activated by the neurotransmitter, they catalyse the production of a "messenger chemical" inside the cell, which in turn can affect many aspects of the cell's metabolism. In particular they can alter the number and sensitivity of the ion channel receptors in the same cell. These synapses are involved in slow and long-lasting responses like learning and memory. Typical neurotransmitters are adrenaline, noradrenaline (NB adrenaline is called epinephrine in America), dopamine, serotonin, endorphin, angiotensin, and acetylcholine.

4. Neuromuscular Junctions.

These are the synapses formed between motor neurones and muscle cells. They always use the neurotransmitter acetylcholine, and are always excitatory. We shall look at these when we do muscles. Motor neurones also form specialised synapses with secretory cells.

5. Electrical Synapses.

In these synapses the membranes of the two cells actually touch, and they share proteins. This allows the action potential to pass directly from one membrane to the next. They are very fast, but are quite rare, found only in the heart and the eye.

Source: http://www.biologymad.com/NervousSystem/synapses.htm#typesofsynapses

Answer 3

The two types of summation at a synapse are spatial summation, which involves the combined effect of multiple synapses on a neuron, and temporal summation, which results from a single synapse firing rapidly in succession to generate an action potential.

Answer 4

There is the IPSP (Inhibitory Postsynaptic potential) and the EPSP (Excitary postsynaptic potential)