Synapse

The idea

At the end of the axon the impulse releases chemicals that cross the gap, or synapse, and start a similar impulse in a dendrite of the next neuron; synapses also deliver impulses to muscle cells or glands.

A gap in the path

Two nerve cells lie end to end, but the end of the first one and the start of the next do not touch. There is a gap between them.

How do you think the message gets across this gap?

• Chemicals cross the gap and start a new impulse
• The axon grows longer until it fills the gap
• The message cannot cross, so it stops

Cross the gap

Press Next step to follow the message across.

A chemical bridge

The impulse is electrical inside a neuron. At the gap, chemicals carry the message over, and a new electrical impulse starts on the other side.

At the end of the axon the impulse releases chemicals. They cross the gap, or synapse, and start a similar impulse in a dendrite of the next neuron. Synapses also deliver impulses to muscle cells or glands.

Notes

At the end of an axon the impulse releases chemicals that cross the gap, or synapse, and start a similar impulse in a dendrite of the next neuron. Synapses also deliver impulses to muscle cells or glands.

Check yourself

What is released at the end of the axon?

What is the gap between two neurons called?

What do the chemicals do after they cross the gap?

Besides other neurons, synapses deliver impulses to which cells?

• Some chemicals — correct. Yes!
• A new axon. No new axon is made. Chemicals are released at the end of the axon.
• A muscle cell. Muscle cells are a different kind of cell. At the end of the axon, chemicals are released.
• A dendrite. A dendrite is the part of the next neuron that receives the chemicals. The gap is the synapse.
• A synapse — correct. Yes!
• An axon. The axon is the long thread of the first neuron. The gap after it is the synapse.
• Carry the same impulse back to the first neuron. The chemicals cross the gap towards the next neuron and start an impulse there.
• Join the two neurons into one cell. The neurons stay separate cells with a gap between them, which the chemicals cross.
• Start a similar electrical impulse in a dendrite of the next neuron — correct. Yes!
• Muscle cells or glands — correct. Yes!
• Red blood cells. The book says synapses deliver impulses to other cells such as muscle cells or glands.
• Cells of the bony box. Synapses deliver impulses to other cells such as muscle cells or glands.