Why is there a synapse

They are who you are. See some synapses "Up Close and Personal". Play the Interactive Word Search Game on the neuron and neurotransmitters. Play an Outside Game to reinforce what you have learned about the synapse.

Color the synapse online: Picture 1 Picture 2. The Synapse Neurons have specialized projections called dendrites and axons. The synapse consists of: a presynaptic ending that contains neurotransmitters , mitochondria and other cell organelles a postsynaptic ending that contains receptor sites for neurotransmitters a synaptic cleft or space between the presynaptic and postsynaptic endings. Select personalised ads. Apply market research to generate audience insights.

Measure content performance. Develop and improve products. List of Partners vendors. In the central nervous system , a synapse is a small gap at the end of a neuron that allows a signal to pass from one neuron to the next.

Synapses are found where nerve cells connect with other nerve cells. Synapses are key to the brain's function , especially when it comes to memory. The term synapse was first introduced in by physiologist Michael Foster in his "Textbook of Physiology" and is derived from the Greek synapsis , meaning "conjunction.

When a nerve signal reaches the end of the neuron, it cannot simply continue to the next cell. Instead, it must trigger the release of neurotransmitters which can then carry the impulse across the synapse to the next neuron. Once a nerve impulse has triggered the release of neurotransmitters, these chemical messengers cross the tiny synaptic gap and are taken up by receptors on the surface of the next cell.

These receptors act much like a lock, while the neurotransmitters function much like keys. Neurotransmitters may excite or inhibit the neuron they bind to. Think of the nerve signal like the electrical current, and the neurons like wires. Synapses would be the outlets or junction boxes that connect the current to a lamp or other electrical appliance of your choosing , allowing the lamp to light. Synapses are composed of three main parts:. An electrical impulse travels down the axon of a neuron and then triggers the release of tiny vesicles containing neurotransmitters.

These vesicles will then bind to the membrane of the presynaptic cell, releasing the neurotransmitters into the synapse. These chemical messengers cross the synaptic cleft and connect with receptor sites in the next nerve cell, triggering an electrical impulse known as an action potential. Another subtype, the muscarinic cholinergic receptor, opens a potassium channel when it binds ACh. Stimulation of a muscarinic cholinergic receptor leads to cell hyperpolarization.

Acetylcholine can either excite or inhibit the postsynaptic cell depending on whether that cell has the nicotinic or muscarinic receptor subtype. In the example we just considered, both receptor subtypes were linked to distinct ion channels.

It is also possible for one receptor subtype to be linked to an ion channel while another subtype leads to the production of a second messenger. Opening an ion channel takes very little time compared to the complex signaling that occurs with a second messenger. The response is fast with a receptor linked to an ion channel and is slow with a receptor that leads to a second messenger cascade.

Although slower, second messenger cascades can produce more diverse cellular effects and have the advantage of amplification. Binding of a single molecule of neurotransmitter can produce many molecules of the second messenger. In contrast, if the receptor opens an ion channel, a single molecule of neurotransmitter or sometimes two molecules is needed to open a single ion channel in the postsynaptic cell. A receptor that produces a second messenger in the postsynaptic cell.

Second messengers can lead to a wide range of effects in the postsynaptic cell. An excitatory postsynaptic potential depolarizes the membrane bringing it closer to the threshold potential.

An excitatory postsynaptic potential EPSP occurs if the membrane is depolarized by the ion movement. If, on the other hand, the membrane becomes hyperpolarized when the ions move, an inhibitory postsynaptic potential IPSP is generated. Opening of sodium- or calcium channels leads to depolarization of the membrane.

If there is sufficient depolarization, the threshold potential is reached and an action potential will be produced in the postsynaptic membrane. Since an EPSP depolarizes the membrane, it facilitates action potentials.

An inhibitory postsynaptic potential hyperpolarizes the membrane taking it farther from the threshold potential. Opening of potassium- or chloride channels leads to hyperpolarization of the membrane. Since the current is outward for potassium ions, and inward for chloride ions, opening of either of these two channels will cause the postsynaptic membrane to hyperpolarize.

A hyperpolarized membrane has moved farther from the threshold potential and has less probability of producing an action potential. Since an IPSP hyperpolarizes the membrane, it inhibits action potentials. Remember that a neuron synapses with many other neurons. So a postsynaptic neuron can receive signals from many presynaptic neurons simultaneously.

Whether or not the postsynaptic cell has an action potential depends on the summation the additive effect of all the incoming signals. The net effect of all the local potentials on the trigger zone determines whether or not there is an action potential in the postsynaptic cell.

The simpler type is the electrical synapse, in which there are essentially no gaps between the cells. Instead, ions travel through what are called gap junctions and transfer an electrical charge to the next neuron.

These gap junctions may actually be better understood in other areas of the body, as they are not unique to neurons. There are other cells, like in the heart, that also have gap junctions that transmit electrical signals.

On the other hand, at chemical synapses, the electrical signal within neurons, called an action potential, is translated into a chemical signal that can travel across the synapse to the next neuron in the circuit.

This is done through the release of chemicals called neurotransmitters, which are released in packets called vesicles upon arrival of an action potential at the synapse.