How do chemical synapses work

Our body performs countless movements every day. In order for you to lift your arm, for example, this information must first be passed on from the central nervous system (CNS) to your muscles in your arm. The information is transferred from one nerve cell to the next until it finally arrives in the arm. The place where two nerve cells meet is called a synapse. In the following I will explain to you how the information is transmitted there.

Synapses are the contact points between a nerve cell (presynaptic cell) and a subsequent nerve cell (postsynaptic cell). The contact point between two nerve cells is called interneuronal synapses. A synapse between a nerve cell and a muscle cell is called a motor end plate.

There are excitatory and inhibitory synapses. In addition, synapses can also be differentiated according to the type of excitation transmission (chemical or electrical synapse). More on that in a moment.

A synapse consists of the membrane of the end button of the upstream nerve cell (presynaptic membrane) and the membrane of the downstream cell (the postsynaptic membrane) as well as the space between the two membranes (synaptic gap).

Chemical synapses

Once a Action potential runs through the membrane into the terminal button, voltage-dependent calcium channels that are located in the presynaptic membrane open. Calcium now flows along the Concentration gradient in the end button. As a result, the vesicles containing neurotransmitters fuse with the presynaptic membrane (exocytosis). The neurotransmitters are released into the synaptic cleft by the exocytosis and bind to the receptors located in the postsynaptic membrane. These open through molecular structural changes and there is an influx or outflow of ions into the postsynaptic cell.

Sodium ions flow in when synapses are excited. The postsynaptic cell is depolarized (increased membrane tension).

In inhibitory synapses, they bind neurotransmitters to potassium or chloride channels. The outflow of these two ions causes hyperpolarization (reduced membrane tension).

The inhibitory and excitatory synapses counteract each other so that a movement is carried out correctly. As soon as there is an imbalance, it can lead to paralysis or excessive movements.

Then enzymes located in the synaptic gap bind to the neurotransmitters. As a result of this molecular structural change, the neurotransmitters are released from the receptors again. The transmitters are split by the influence of the enzymes. Their components are taken up again in the vesicles in the terminal button. The synapse is regenerated and a renewed transmission of excitation can occur (see Fig. 1).

© Jasmin Zorn

This video explains that Transmission of excitation at a synasp so really good.

External links:

1. Nice animations of the processes on the motorized end plate: