Student’s question 5: “Can you help with cardiac contraction please?”

Sure we can ! ( This post is a response to a student’s question under the post on blood grouping 

The heart has 3 layers: The Epicardium , the Myocardium and the Endocardium. The Myocardium is responsible for contraction of the heart.

Before we explain the answer, you need to recall a bit of Muscle anatomy:

 

From above, you can see that the individual muscle cell is contained in the muscle cell bundle.
Lets look a little more closely at the individual muscle cell:

structure-of-m2

 

The individual muscle fiber has thick filaments-Actin (Green lines) and thick filament – Myosin ( purple lines). It is also surrounded by the Sarcoplasmic reticulum which contains calcium.

Contraction happens when these thick and thin filaments slide over each other like this…

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But for that to happen, some other things must happen first:

    1. Sodium ions (Na+) go into the cell  from outside the cell causing depolarization (The sodium ions are the red balls):

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2.This depolarization wave is transmitted to release Calcium from the Sarcoplasmic reticulum.

What do we need the calcium for?

Well, in order for the thick and thin filaments to slide over each other, the thick filament(Myosin) has to attach itself to the thin filament(Actin) at certain attachment sites. These attachment sites on the thin filaments are covered by TROPONIN and TROPOMYOSIN, preventing the thick filament(Myosin) from attaching to the thin filament(Actin).

3. Calcium helps to remove TROPONIN and TROPOMYOSIN so that the thick filament can attach to the thin filament and they can slide over each other.

figure_38_04_05-1

 

 

When they slide over each other, we have contraction!!

Here is a short video that explains it all : Muscle contraction

Do you have any questions? Post your questions below and we will get back to you ASAP!!!

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