Hey what are you doing?
Hey students,
Did you observe my sudden movement when he
was pinching me?
My body recacted because
of the pinching.
similar is the case when
someone tickles you or you touch some hot object.
If you think more deeply
you'll realize that all these movements are controlled
and they are in response to
some external trigger or stimulus.
So in this lesson we'll see how these
movements are control and coordinated
in animals.
The control and coordination in all the animals is done by Nervous system.
Nervous system consists of
a network of neurons or nerve cells.
Some of these nerve cells
have specialized tips which detect the
external stimulus.
These specialized tips are called sensory receptors.
Now all the sensory receptors are present in the sense organs.
for example in a
ears, skin, tounge, nose etc.
For example sensory receptors present tounge are
called Gustatory receptors.
These receptors detect taste.
Because of these receptors we can say that the food sweet
or salty.
Similarly sensory receptors present in our nose are called as
Olfacto receptors.
and these receptors detect smell.
Have you ever tried eating food by blocking your nose?
this is weird right?
Just try it in food like this and you will observe that
Olfacto and Gustatory receptors are
required together to suffice your palate.
Now let's have a look on the structure of neuron.
The neuron consist of cell body,
Dendrites,
and then Axon.
Cell body is this spehrical part of the
neuron which contains nucleus.
Dendrites are the branches of the nueron
which receives the signal from the other cells.
while axon is the longest dendrite
present in the neuron and it transmits
the signal to the other cells.
Now let's see how these nerve cells or neurons functions.
The main function of these
nerve cells is to receive, conduct and
transmit the signals.
The dendrites of the nerve cells receive the signal and
sets of a chemical reaction.
This chemical reaction creates an electrical impulse.
the impulse is then transmitted
from this dendrites to the cell body and
then to the axon.
From the axon this signal is transmitted to the
dendrites of the another neuron.
and thus the signal is distributed over
all the neurons.
The junction between the axon of the first neuron and the
dendrites of the second neuron is known
as synapse.
At the end of the axon of the first neuron the electrical impulse
sets of a chemical reaction.
These chemicals generated by this reaction
they cross the synapse and generate the
electrical impulses again in the
dendrite of the next neuron.
and finally as i mentioned earlier that the impulse
from all these nerve cells is
transmitted to the cells of the sensory
organs like some muscle cells or to some glance.
Here we can see how the axons
are transmitting the information to the
muscle cells.
This quick movement of my hand away from the flames is called
reflex or reflects action.
So we can define reflex action as an involuntary
instantaneous movement
in response to the external stimulus.
When I put my hand over the flame the
signals from my hand are taken up by
the neurons and are transmitted to the brain.
These signals are detected by the
brain and then the brain prepares the
response which is transmitted back from
the brain to my hand and which made me
remove my hand from the flame.
neurons that carry the signals from all
the parts of the body and transmitted to
the brain are known as sensory neurons.
While the neurons that carry the signals
from the brain to all the parts of the
body are called motor neurons.
So now you know that the reflex responses are very quick.
but it would take much longer if
the information goes the whole way from
the sensory organs to the brain.
So the responses to these reflex actions are given up  by spinal cord.
Because the spinal cord is the meeting point of the input
that is the sensory nerves and the
output that is the motor nerves.
This shortened nerve pathway or the connection
between the sensory nerve and the Mortor nerve
that controls the reflex action is
known as reflex arc.
Now let's quickly summarize the whole lesson.
The nervous system consists of many nerve cells or neurons.
A nerve cells is made up of a cell body,
dendrites and an axon.
Dendrites receive the information from the
organs and carry on this information
as electrical impulse throughout the axon.
From the axon these impulse
set of some chemical reactions.
The chemicals made by these chemical
reactions then across the synapse and
reach as the impulse on to the dendrites
of the next neurons.
and thus the information is carried on from the sense organs to the brain.
and back from the brain to
the sense organs.
Next we studied about the reflex actions
the involuntary instantaneous movements
in response to some external stimuli are
known as reflex actions.
