Structure and Function
Control and coordination
Follow an impulse along a neuron and round a reflex arc, name what each region of the brain looks after, and tell a plant's tropic growth from an animal's hormone response.
Your hand leaves a hot pan before you have decided anything about it. That is not carelessness on the brain's part — it is the body routing round the brain on purpose. Thinking means passing impulses through dense networks of neurons, and that takes time you do not have when your skin is burning. So the nerve that feels the heat is wired to the nerve that moves the muscle at the first place they meet: the spinal cord.
Electrical, then chemical, then electrical again
An impulse is electrical while it is inside one neuron and chemical where it crosses to the next. Information arrives at the dendritic tip, a chemical reaction there sets up an electrical impulse, the impulse runs to the cell body and down the axon, and at the far end it releases chemicals that cross the gap — the synapse — and start the whole thing again in the next cell. The same kind of junction hands the message on to a muscle.
Worked example
Why is a chemical signal worth having, when an electrical one is so much faster?
An electrical impulse reaches no cell that nervous tissue does not connect.
A squirrel that has just seen a dog needs half its body made ready at once, and much of that body has no nerve running to it.
Try it together
A cyclist swerves round a pothole, wobbles, and steadies herself without thinking about it.
Work out which part of the nervous system did what.
1.Keeping her balance and making the turn precise is the work of which part of the hind-brain?
Have a go
Have a go on your own. Where in the body is a reflex arc made?
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.