How is the excitation transmitted at the neuromuscular junction

Motorized end plate

The motorized end plate is the contact point between a nerve and a muscle cell. Here you will learn how it is structured and how the transmission of excitations works.

  • Motorized end plate simply explained
    in the text
  • Motorized end plate structure
    in the text
  • Neuromuscular synapse processes
    in the text

Motorized end plate simply explained

In order for you to be able to move the muscles in your leg, for example, your nerve cells (neurons) have to transmit electrical signals from the central nervous system (brain and spinal cord) to the muscle cells. To do this, the Nerve cells in contact with the muscle cells stand. You call the special junction between a neuron and a muscle cell motorized end plate or neuromuscular synapse

In general, you refer to the contact points of a nerve cell with another cell as Synapses. They serve to transmit excitations (Action potentials) In the case of the motor endplate, a motor neuron transfers the excitation to a muscle cell and releases a so-called there Endplate potential (EPP).

Motorized end plate structure

The neuromuscular endplate is constructed in exactly the same way as a "normal" synapse. That means you can break it down into three sections:

  • presynaptic membrane:corresponds to the synaptic terminal (presynaptic terminal) of the nerve cell; contains Vesicle(membrane-covered vesicles) with the messenger substance acetylcholine
  • synaptic gap:Area between the two cells; Release of the messenger substance (= Neurotransmitters)
  • postsynaptic membrane: corresponds to the membrane of the muscle cell; contains Receptors for acetylcholine in the membrane

The cell membranes involved are strongly folded. In this way, they increase the surfaces with which they are in contact. This allows the neuron to transmit the excitation better.

Neuromuscular synapse processes

Let's take a step-by-step look at which processes take place at the synapse and how the transmission of excitation works:

  1. First reached a Action potential the end button / soleplate of the nerve cell. By this you mean a deviation of the voltage from that in the resting state (resting potential). This leads to a Depolarization (Decrease in voltage).
  2. Then open Calcium ion channels. So approx2+Ions into the presynaptic cell.
  3. Thus the neurotransmitter is released Acetylcholine from the vesicles into the synaptic cleft. To do this, the vesicles fuse with the membrane. You call the process Exocytosis.
  4. After the transmitter has moved to the postsynaptic membrane, it can address specific - so-called nicotinic acetylcholine receptors - tie. You call the type of receptor a ionotropic. This means that it also forms an ion channel at the same time. The channel then opens through the binding of acetylcholine.
  5. The ion channel is unspecifically permeable to Cations (positive ions). This means that both sodium, calcium and potassium ions can pass through. The ions flow into the muscle cell and thereby depolarize the cell.
  6. A so-called end plate potential arises and spreads. After all, that solves one Muscle contraction out.

The neurotransmitter acetylcholine releases itself from its receptor after a while. A special enzyme, acetylcholinesterase, then breaks down the free acetylcholine in the synaptic gap. To do this, she splits it into acetate and choline. The molecules can then be taken up again by the presynapse and recycled. This means that the cell uses it to form new acetylcholine and repackage it in vesicles. Now a new transmission of excitation can begin.