Nervous System [3]: Synapses (A Level Biology)


Uploaded by freeeschool on 02.09.2012

Transcript:
A Level Biology _ Nervous System 3 - Synapses
Thanks for joining me. This is my third video on the nervous system and we’re going to
be looking at synapses today. So, you can see on this diagram that you’ve
got two different cells here. So, you’ve got what is sometimes referred to as a pre-synaptic
cell and then a post-synaptic cell. This gap that you see in the middle here is actually
called a synapse and so, hence, pre and post. Neurone cells don’t actually touch one another,
so the pre and post synaptic cells don’t touch because they got this gap here which
is the synapse. This allows a coordinated response to a stimulus. So, if we use the
example of you may be doing a bicep curl, so you bring in your arm from a right angle
position, your hand up towards your shoulder. Essentially, you only want certain muscle
fibers contracting, the muscle fibers are going to bring your arm up, which what you
don’t want to happen in this instance, is the muscle cells which control the tricep
which move the arm down. You wouldn’t want both the bicep and the tricep to contract
at once. Synapses and gaps between neurones mean that certain muscle fibers or certain
effectors can be stimulated and others won’t be.
So, on this diagram of the synapse, you have one or two things that you may have seen before.
So, for instance, the axon, which, if you remember, is the part of the neurone that
actually carries the impulse, the synapse which is the gap, and then you have the dendrites
on the other side, which, again, provide connections between different neurones.
Now, some of the bits you haven’t probably seen before, the synaptic vesicles. Now, a
vesicle, all it is, is a membrane-bound organelle that contains, in this case, a neurotransmitter.
So, it’s a way of delivering a chemical from inside the cell throughout. So, you can
see that here, some of the vesicles, they are binding with the outer membrane of this
neurone and they cause in the release of a material called the neurotransmitter.
So, this diagram is going to take you through the steps involved with the stimulation of
a pre and post synaptic cell. So, you can see here our pre synaptic is labeled and its
got this yellow arrow coming in; the yellow arrow represents an impulse arriving. This
impulse causes the release of a neurotransmitter which are found in these vesicles. So, what
happens is one of these vesicles binds the outer membrane and it causes the release of
this neurotransmitter. The neurotransmitter then diffuses across the synapse and towards
a receptor. It then binds on to the receptor on the post synaptic cell and this induces
an impulse in the post synaptic cell. There’s a lot of difficult terminology there, but
essentially, it’s a communication method from this cell to this one.
In summary, this is going to take you through some of the points we’ve covered today,
the first one being, that synapse is a gap between neurones. When you want something
to bridge across the synapse, the first thing that needs to happen is the impulse needs
to arrive at the pre-synaptic neurone and the pre-synaptic is the one before the neurone
or before the synapse. What then happens is the neurotransmitter, which is a chemical
which is released from a vesicle into the synapse. That neurotransmitter can then diffuse
across the synapse and then it will bind to a receptor on the post-synaptic cell, the
post-synaptic being the one after the synapse. This then induces an impulse on the post-synaptic
neuron and, therefore, the impulse can then continue on to the effector or to its target
cells. This enables a coordinated response. What
this means is it means that certain cells or certain effectors can be targeted and not
all at once. The fact that you have gaps between the neurones means that some effectors can
be targeted and stimulated and others cannot.