Nerves & Reflexes

Nerve Cells Nerve cells are highly specialised. Their structure is directly linked to their function Look at the following slide & label your diagram….

How does their structure relate to their function? Long axon Dendrites on cell body Myelin sheath (fatty sheath) FUNCTION Can reach to far places in the body Allows nerve cells to connect with each other to pass on impulses (messages) Acts as insulation so the impulses do not cross over to other cells

What do nerve cells do? Nerve cells connect to receptors at one end. Some nerves carry impulses to the brain. From here the brain will decide what response is necessary. Once it has decided what to do, the brain will send another impulse through another nerve cell. These nerves connect to a muscle or gland at the other end. The muscle or gland carries out the job required

Stimulus → receptor → nerve → brain → nerve → muscle/gland → response As you can see there are 2 nerves involved in this chain. We can give these nerves special names according to the jobs they do…. We call the first nerve in the chain the SENSORY NERVE. This is because it is involved in the sensing of the stimulus. We call the second nerve the MOTOR NEURONE. This one is involved in bringing about the response to the stimulus. We can also call the muscle/gland the EFFECTOR. This is easier as it is only one word and can mean either muscle or gland. It is the part actually doing something. So our chain can now look like this: Stimulus → receptor → sensory → brain → motor → effector → response nerve neurone

Working example: See your mate → receptors in eye → sensory nerve → brain → motor neurone → arm muscles & vocal cords → wave to your friend & say ‘hello’ Try and think of your own example and write it down……

Reflexes Some responses need to be really, really quick. We need to be able to do this without thinking. If we are in danger of harming ourselves we would need to act without thinking about what to do. We call this a reflex. It is like an action that is already programmed into our nervous systems: it happens automatically. With reflexes the sensory nerves do not travel all the way to the brain. This would take too long if we were in danger. Instead the impulses are taken to the spinal cord as it is closer. Look at the next diagram and label your own.

reflexes Write down as many impulses as you can think of….. Write out the chain of events for a reflex like the chain we went through before. Pick a specific type of reflex from your list and write out the chain.

questions 1) What do these words mean: - stimulus - response - effector 2) What is the special name given to the nerve that carries the impulse from the receptor to the brain or spinal cord? 3) What is the special name given to the nerve that carries the impulse from the brain or spinal cord to the effector? 4) What is the name given to the brain and spinal cord together? 5) Write the chain of events for the following scenario: ‘a stupid year 11 boy has just thrown a pen towards a year 7 boys face. What does the year 7 boy do? Is it a reflex or does he have to think about doing it?’