Contraction Of Cardiac Muscle Cells

Question 1

What are the fibres that run along the length of the cardiac muscle cell called?

Answer 1

Cardiac myofibrils- thin fibres (tubes)

Question 2

What is the network of spaces inside muscle cells and function (looks like net)

Answer 2

Sarcoplasmic reticulum and contains Ca2+ ions - storehouse

Question 3

What allows action potential to travel into interior of cardiac muscle cell?

Answer 3

Transverse tubules (T tubules)

Question 4

What happens as action potential enters the cardiac muscle cell (cell components)

Answer 4

Action potential travels down T-tubules and causes sarcoplasmic reticulum to release Ca2+ ions. The Ca are free around the cardiac myofibrals and enter they also enter muscle cell during action potential (more)

Question 5

What is the function of troponin and tropomyosin ?

Answer 5

Tropomyosin covers the binding sites in actin which myosin will attach to
Troponin holds tropomyosin in place
Contraction due to thick and thin filaments sliding past each other

Question 6

How does action potential cause contraction

Answer 6

Action potential triggers release of Ca2+ from sarcoplasmic reticulum within cardiac muscle cell
This ca2+ (plus Ca2+ that has entered from outside the cell due to action potential) binds to TROPONIN
Cell contracts ( same sliding filaments mechanism thick myosin filaments and thin actin filaments )

Question 7

What is recovery period during cardiac muscle cell action potential? (2 components)

Answer 7

Heart is recovering before it can be stimulated again and has 2 components

1. absolute refractory period where nothing you can do to make cell respond (on graph covers all action potential nearly)- can’t generate 2nd action potential
2. Relative recovery period - can generate response but have to stimulate at higher level (takes place where cardiac muscle cel is baking depolarised at end of graph)

Question 8

Why is the absolute refractive period extended ? Why important

Answer 8

Because of Ca2+ controlled plateau phase - action potential is long so refractive period is long.
Heart can’t contract so refills with blood.

Question 9

Difference between skeletal muscle contraction and cardiac muscle contraction action potential (2)

Answer 9

Greatly elongated

Can’t increase contraction because of extended action potential

Question 10

What is the function of the AV node

Answer 10

• Cells of AV Node are smaller
  than typical cardiac cell
  elsewhere so they conduct­ more slowly (signal slower)
• links between cells are less efficient (signal don’t pass as efficiently and quickly) about 100msec
• delay@ AV Node.
  important as delays ventricles so ventricles fill
  with blood (atria can pass blood onto ventricles).

Question 11

Where is AV node located

Answer 11

On floor of right atrium

Question 12

Where does signal pass from AV node ?

Answer 12

Signal passes down AV bundle (atrio-ventricles bundle) found in wall between 2 ventricles inter-ventricular septum then bundle into branches
AV Bundle is only electrical connection between atria and ventricles

Question 13

Why is the AV bundle the only electrical connection between the atria and ventricles ?

Answer 13

Only get from top to bottom of heart through av bundle due to insulating fibrous skeleton

Question 14

What happens once the signal is sent down to the apex (bottom)?

Answer 14

Distributed by purkinje fibres which delivers signal to all cardiac muscle cells and pumps blood out from hearts

Question 15

What is the equipment used to measure the electric ark changes in the heart using electrodes on the body

Answer 15

Electrocardiogram - ECG - • Hearts electrical signal so strong
that gets transmitted beyond
❤, travel through salty funds
in body, detected using electrodes
on bodies surface
• single cardiac cycle

Question 16

What are the components of the ECG and what do they stand for ?

Answer 16

P- atrial depolarisation and contraction
QRS - ventricular depolarisation and contraction
T - ventricular repolarisation and relaxation

Question 17

What is the intervals in the ECG?

Answer 17

P-r interval = time between atrial activation and ventricular activation
Q-t interval = duration of ventricular changes contracting and relaxing

Question 18

Cardiac output equation

Answer 18

CO= heart rate x stroke volume

Question 19

What is cardiac output the same as

Answer 19

Venomous return (VR) volume retuning to one atria per min

Question 20

What is stroke volume?

Answer 20

Volume pumped out from one ventricle in a beat

Question 21

What are the two centres in the cardiovascular centre in medulla

Answer 21

Cardioinhibitory centre = parasympathetic

Cardioaccelerator centre = sympathetic

Question 22

What are baroreceptors and chemoreceptors

Answer 22

Baroreceptors = detect changes in pressure of blood
Chemoreceptors = monitor blood chemistry

Question 23

Where are baroreceptors located?

Answer 23

1. Wall of right atrium
2. aortic sinuses
3. Cortoid sinuses

Question 24

Where are chemoreceptors located

Answer 24

Aortic bodies 
Carotid bodies (neck)

Question 25

What are receptors called in the parasympathetic system ?

Answer 25

Nicotinic receptors (Na+ channels) and muscarinic receptors (K+ leave cell)

Question 26

Parasympathetic effect on SA node?

Answer 26

Takes longer to reach threshold

Question 27

What are receptors in sympathetic system ?

Answer 27

No tonic receptors and adrenergic receptors

Question 28

What is sympathetic effect on SA node?

Answer 28

Takes less time to reach threshold

Question 29

What is cardiac cycle ?

Answer 29

Atria systole (shorter), ventricular systole (med) , diastole (longest)