Muscle 3

Question 1

How do DHP receptors tell ryanodine receptors that theres an AP coming through

Answer 1

They’re physically connected so when the DHP receptor on the T tubule opens from the depolarization, the ryanodine receptor is mechanically opened too, this triggers the release of calcium from the SR

Question 2

Troponin and Tropomyosin

Answer 2

Troponin: on the actin filament, binds Ca++ ion (on TnC), this activates it, changes conformation to interact with ->
Tropomyosin: on the actin filament, winds around the actin filament actually, covering up the myosin binding sites, but when Ca++ comes in and activates troponin, it exposed the sites

Question 3

Why is there a falling phase in a muscle twitch and its not instantly over

Answer 3

The calcium has to be pumped back into the SR, and until its funny packed you can still have muscle contractions, just wont be everyone

Question 4

Recruitment

Answer 4

Term we use to describe how many muscle fibres get activated in a given muscle contraction

Question 5

Summation

Answer 5

The additive effect of many closely spaces twitches, applies to individual muscle fibres

Question 6

Tetanus

Answer 6

Sustained contraction of the muscle fibre, when the summation of the twitches is so high that its just continuous

Question 7

What does recruitment have to do with force

Answer 7

The more muscle fibres/ motor units we involve in a certain contraction, the more force well be able to exert

Question 8

How do we get more ATP in muscle for contraction

Answer 8

We have a certain amount of ATP in our muscle fibres, but only enough for a few twitches, nothing long lasting
Thankfully theres creatine phosphate present, another molecule that can bind phosphate in a high energy bond, is capable of giving a phosphate back to ADP
This allows for ATP levels to stay stable but creatine phosphate goes down
Note: this is just supposed to last long enough for the metabolic processes to kick in

Question 9

How do we metabolically produce more ATP for the muscle cell

Answer 9

Through glycolysis, an anaerobic reaction which only produces a few molecules of ATP, few but fast, produces pyruvate
Pyruvate is a substrate for oxidative phosphorylation, requires oxygen, produces lots of ATP but slowly
Note: glycolysis was in cytoplasm, oxidative phosphorylation in the mitochondria

Question 10

Where does muscle get its glucose

Answer 10

It can get it from the blood, but in the moment of a muscle contraction it probably wont, it’ll go to its glycogen reserves, polysaccharides of glucose monomers, and feed that into glycolysis and eventually oxidative phosphorylation

Question 11

Types of skeletal muscle fibres (no details)

Answer 11

Fast glycolysis fibres
Slow oxidative fibres
Fast oxidative fibres

Question 12

Fast glycolytic fibres

Answer 12

Fast refers to the speed at which it goes through ATP (basically how much ATP the myosin needs), implies that they are capable of generating a lot of force very quickly, but they’ll burn through ATP fast
Glycolytic refers to the fact that they get most of their ATP by glycolysis (anaerobic), inefficient but quick
Basically: these are the muscle fibres found in the muscles we use for high intensity low duration

Question 13

Slow oxidative fibres

Answer 13

Slow: myosin cycles through ATP relatively slower, requires less ATP but not as much force
Oxidative: muscle fibres be more dependent on the oxidative phosphorylation part of the cycle
We have lots of ATP because we use it slower and take the time to go the long way with oxidative phosphorylation, best for low intensity/ endurance

Question 14

Fast oxidative fibre

Answer 14

Fast: myosin uses ATP fairly quickly
Oxidative: relies mostly on oxidative phosphorylation aspect
Function is in between fast glycolytic and slow oxidative fibres

Question 15

How do muscle fibres differ in color and why

Answer 15

Fast glycolytic fibres are “white muscle” and slow oxidative fibres are “red muscle”
Has to do with the type of fibre we have running there, what dominants is what we see

Question 16

Fast glycolytic fibres and glycolysis

Answer 16

They use glucose from glycogen storage to feed into glycolysis which produces pyruvate (that this muscle fibre doesnt use much) and lactic acid, which builds up in the muscle fibre. When theres too much lactic acid if stops your muscle from working as well, leading to muscle fatigue (which happens before ATP concentration drops)

Question 17

Slow oxidative fibres and getting its energy

Answer 17

Takes advantage of the oxidative phosphorylation and how efficient it is and mostly waits for glucose to come in via the blood, so you can look at it as having an infinite supply of energy, makes sense because its for endurance which is long term
These muscle fibres also contain myoglobin (related to hemoglobin), it can bind oxygen, so it facilitates the transfer of oxygen from the blood to the key site of oxidative phosphorylation (helps efficiency), so O2 from blood goes to myoglobin goes to right place in muscle fibre

Question 18

Why are slow oxidative fibres red

Answer 18

Because they work with myoglobin that carries O2 for the oxidative phosphorylation, and it has a red hint to it
Other fibres like the fast glycolytic fibre dont utilize the oxidative phosphorylation pathway very much so they dont need oxygen as much so dont interact much with myoglobin