00:00
So now that we've
talked about
how a muscle contraction
happens,
let's talk a little bit
about
what makes the muscle have
the ability to contract?
So pop quiz.
00:12
How do muscles derive the ATP
or the energy
necessary to power this
contraction cycle?
So there are three different ways
that we're going to be able
to derive enough ATP
in order to power
the contraction cycle.
00:35
First,
we have the creation of
creatine phosphate.
00:39
Second,
anaerobic glycolysis.
00:43
And lastly,
cellular respiration.
00:46
Let's look at these
a little more closely.
00:50
So inside of our muscle fibers,
we have a molecule
known as creatine.
00:56
Creatine has the ability
to bind to phosphate.
01:00
This allows for us to recycle
or reuse the phosphates
between
the creatine and the ATP.
01:09
The way this happens is ATP
combines to the creatine,
and the creatine is going to take
the phosphate from ATP,
also referred to as
adenosine triphosphate
and it will then become
adenosine diphosphate.
01:25
So it now only has two phosphates
and the creatine has the other.
01:30
Then there is an enzyme known as
creatine kinase,
which will then re hydrolyze the
creatine phosphate
and remove the phosphate from
the creatine back to ATP.
01:43
This cycle allows for us to have
about 15 seconds of energy.
01:49
An anaerobic glycolysis
we're going to get
a little bit more energy
as we are going to create
two ATP molecules
that can be used for
energy expenditure.
02:00
In this process,
we take glucose
from either the blood
or from glycogen
stored in our muscles.
02:07
And we're going to go through a
series of steps
in order to elicit
two ATPs and
two Pyruvate molecules.
02:17
If we are doing this process in the
absence of oxygen,
this ends with the production of
lactic acid.
02:23
So when you are
performing a function
or when you're using
your muscles
and you start to feel sore,
this soreness is due to the buildup
of lactic acid from this process.
02:37
Anaerobic glycolysis,
unlike the creatine phosphate
is going to give us
a little bit more energy
and that you can get about
two minutes of energy
per glucose molecule.
02:51
The final way that we get ATP
is cellular respiration.
02:56
So under aerobic conditions
or conditions where there is
ample oxygen
the pyruvic acid is
going to actually enter
into the mitochondria
found inside of our muscle fibers.
03:08
And from there,
it's going to undergo
a series of
oxygen requiring steps
that leads to a large amount
of ATP.
03:16
In this process,
we're going to get glucose
from either the blood
or from the breakdown of
fatty acids,
or from pyruvic acid.
03:25
Again, the proving acid
will enter into the mitochondria
and undergo
cellular respiration.
03:32
Out of this process,
we can get anywhere
from 28 to 34
ATP molecules.
03:39
This process,
unlike the others,
is going to provide
minutes up to hour's
worth of energy.
03:47
Sometimes we're using our muscles
so much
that we start to lose the ability
for our muscles to contract.
03:53
This is referred to
as muscle fatigue.
03:57
Muscle fatigue can be brought on
by several different factors.
04:02
Muscle fatigue can be due to an
inadequate release of calcium
from the sarcoplasmic reticulum.
04:09
It can also be due to a depletion
of the creatine phosphate,
or oxygen and nutrients necessary
to make more ATP.
04:19
Also, the buildup of lactic acid
or that soreness,
as well as a buildup of ATP instead
of an adequate amount of ATP
can lead to muscle fatigue.
04:30
And finally,
an insufficient release
of acetylcholine
at the neuromuscular junction.
04:37
Sometimes central fatigue
can occur,
and in this case,
the central nervous system
takes over
and generally results
in a cessation of exercise.
04:48
So sometimes you're using
your muscles so much
that you may pass out.
04:54
Pop quiz:
Why do you continue
to breathe heavily
for a period of time
after stopping excercise?
The answer,
is to pay back
your oxygen debt.
05:12
Recall that in
cellular respiration,
we're going to be
using oxygen
in order to make more ATP.
05:18
So this is kind of like
you're paying oxygen
in the beginning,
and now you're
breathing heavy
in order to restore
your oxygen levels.
05:29
The extra oxygen
can then be use
to replenish
the creatine phosphate stores.
05:35
Also,
to convert that lactic acid
back into pyruvate.
05:41
And third,
to reload oxygen onto myoglobin.
05:46
Myoglobin is the molecule
that's very similar to hemoglobin,
but it's specific for
muscle fiber cells.