Nervous System [5]: Modified Reflexes (A Level Biology)

Uploaded by freeeschool on 02.09.2012

A Level Biology: Nervous System 5 - Modified Reflex
Hi, and welcome to my fifth video in this series and this one has to do with modified
reflexes. So, if we start off by looking at tradition reflex arc. A reflex is something
which doesn’t involve the brain or conscious thinking and in usually goes through the spinal
cord. We have our three different types of neurones; our sensory neurone, that’s the
one that takes it from the receptor to the central nervous system, the relay neurone
which is usually found in the spinal cord, and then you have the motor neurone which
is the one that carries it from the central nervous system to the effector, usually the
muscle. In a tradition reflex arc, this occurs very,
very quickly and the reason for that is it prevents further damage or potentially harm
to the individual. Now, the modified reflex, what you’re able to do is you actually are
able to physically modify the reflex so that it doesn’t go through. The best example
of this is withholding a hot cup of tea. Holding the cup of tea, the normal reflex is because
it’s hot, it’s burning your hand, is to drop it.
Now, we all know if you’ve been carrying a cup of tea, that’s probably not the best
idea if somebody sat near you or if you’re in a situation where you’ve got important
documents in front of you; you don’t want to be dropping the cup of tea and spilling
it everywhere. So, what happens is you can modify that reflex. Instead of dropping the
cup of tea, you can hold on to it. With the modified reflex, you can actively
stop a standard reflex. So, a good example of this is sword swallowing. Reflexes, they’re
involuntary. That means they don’t involve conscious thought and they’re predominantly
controlled by the spinal cord. So that means that in most instances, in most reflexes,
that the impulse never actually arrives at the brain.
So, with sword swallowing, how this works is if somebody proficient in sword swallowing
can actually block the normal gag reflex, and the gag reflex is really important. We
probably all had the experience of swallowing something and its gone down the wrong way
and the gag reflex stops any food or objects going further down the windpipe and it causes
the muscles within the windpipe to contract and to force the food back up the throat.
Now, obviously, someone who’s doing the sword swallowing doesn’t want the gag reflex
to kick in. Obviously, you’ve got a sharp knife going down your throat. It isn’t good
idea to have a gag reflex when that’s going on. Another signal from the brain basically
blocks the signal going down the motor neurone and, hence, the person doesn’t gag and performs
the trick. Modifying your behavior is a huge advance because it means you don’t always
necessarily have to react within the same way. Most simple organisms like invertebrates
like insects always acts of reflexes and very rarely act of modified behavior, hence, why
it’s such an important thing. In summary, reflexes are involuntarily, which
means that they don’t usually involve conscious thought, so they don’t usually involve the
brain. A modified reflex can block the impulse coming from a motor neuron reaching the effector
so it can effectively stop a normal reflex. Probably, the best example of this is if you
are holding a hot cup of tea. The normal reflex is to drop it, but a message is sent from
your brain towards it blocking the motor neurone and, therefore, you don’t drop the cup of
tea. This enables organisms to change their behavior, which is a huge survival benefit.
Organisms that are able to modify their reflexes are much more likely to survive than the ones
that are not, hence, why we have it.