9 Biology, Ms. Mayfield
1.2 The Synapse: How the synapse works
The synapse is the connection between a neuron and the cell a neuron sends its messages to. This cell can either be another neuron, or an effector cell (e.g. a muscle cell). The neuron and the next cell are separated by a small gap, the synaptic clef. A synapse consists of three parts:
a) Presynaptic membrane: The cell membrane of the axon terminal sending the signal b) Synaptic clef: The gap between the two cells
c) Postsynaptic membrane: The cell membrane of the cell receiving the signal.
The synaptic cleft is too big for the electrical impulse to travel directly into the postsynaptic cell. That is why our body uses a different way of transport across the synaptic clef: chemicals.
Axon terminals are filled with small membrane bubbles called vesicles. The vesicles inside the axon terminal contain chemical molecules called neurotransmitters.
When an electrical impulse arrives at the axon terminal the vesicles inside it move towards the presynaptic membrane. Once they reach the membrane the vesicles open up into the synaptic cleft.
Because of this the neurotransmitter-molecules are released into the synaptic cleft.
The synaptic cleft is filled with water, just like any gap between cells in our body. The neurotransmitter-molecules can move through this water, a process called diffusion. Many neurotransmitter-molecules arrive at the postsynaptic membrane.
The postsynaptic membrane carries receptors that can bind the neurotransmitter-molecules for a short time. If enough receptors bind a neurotransmitter-molecule a new electrical signal is created at the postsynaptic membrane. The message has arrived at its destination!
But someone still has to clean up! The neurotransmitter-molecules are still in the synaptic cleft. They have to be removed from the synaptic cleft, or else they will start new electrical signals at the postsynaptic membrane all the time! This is what the enzymes inside the synaptic cleft do. The enzymes inside the synaptic cleft can bind the neurotransmitter-molecules, just like the receptors.
But when they bind a neurotransmitter-molecule they cut it into smaller pieces, so the neurotransmitter cannot activate receptors anymore.
Vocabulary
to consist of – aus etw. bestehen a chemical – eine Chemikalie a bubble – eine Blase a molecule – ein Molekül to reach sth. – etwas erreichen to release – freisetzen to remove sth. – etwas entfernen
