lecture 18

Question 1

The cardiac muscle cells

Answer 1

1. myocytes:
   - force producing cells
   - striated muscle fibers
   - can generate and action potential
2. pacemaker cells
   - they are autorythmic
   - they self excite
   - generate spontaneous muscle action potential
   - have lots of voltage gated ion channels

Question 2

why in this case are they called cells and not fibres

Answer 2

they are not long and cylindrical

Question 3

intercalated disks

Answer 3

• muscle cells are connected at these regions
• the provide physical coupling so they’re structural they keep 1 muscle cell attached to its neighbour and this is made possible by desmosones
  -bthey provide functional coupling made possible by gap junctions so when 1 cell excites all cell excites because we want heart to function has a whole

Question 4

Cardiac muscle cells vs. skeletal muscle fibers

Answer 4

• called cells because they are not long cylindrical cells that resulted from a fusion event
• they are smaller and have 1 or 2 nucleus
• they irregular shaped (branch or y shape)
• have intercalated disks
• skeletal muscle have larger t-tubules
• smaller sarcoplasmic reticulum
• have lots of mitochondria

Question 5

excitation-contraction coupling in cardiac myocytes

Answer 5

1. Action potential started from a pacemaker cell arrive and enters from adjacent cell (gap junction)
2. that wave of excitation will cause voltage gated K+ and Na+ channels to open
3. Action potential moves along plasma membrane of our cardio myocytes
4. Action potential will travel down the t-tubule
5. which will activate “L type Ca2+ channels”
   - calcium will move from ECF to in and bind to the “RyR Ca2+ channel” in the SR
   - RyR channel is ligand gated
   - in cardiac muscle calcium from ECF is critical
6. RyR channels open and now we get a bulk of Ca2+ release from SR
   - this is call “calcium induced calcium release”
7. we get a Ca2+ spark that leads to Ca2+ signal
8. Ca2+ signal
   - Ca2+ binds to troponin which pulls tropomyosin our of the way and tropomyosin is no longer blocking myosin binding sites
   - we get high force cross bridge and crossbridge cycling and heart will contract

Question 6

What is the ration of calcium from ECF and SR

Answer 6

90% from SR
10% from ECF

Question 7

Mechanism of myocyte relaxation

Answer 7

Relaxation occurs when Ca2+ is put away of kicked out
Put away: SERCA is a pump that requires energy that moves calcium back into SR
Kicked out: NCX
- sodium-calcium exchanger
- secondary active transport because Na+ move down its electrochemical and using that energy to remove Ca2+

Question 8

3 key differences between skeletal and cardiac excitation-contraction coupling

Answer 8

1. Calcium induced calcium release
2. NCX
3. Lack of summation in cardiac muscle. They contract then relax rather than entering a fused or unfused tetanus

Question 9

arteries take blood ________ from the heart

Answer 9

away

Question 10

veins bring blood _______ to the heart

Answer 10

back

Question 11

pericardium

Answer 11

minimizes friction

Question 12

The coronary artery

Answer 12

• branch right off the aorta that comes right back to the heart and feeds the heart muscle
• provides a blood supply for the heart
• related to cardiovascular diseases

Question 13

The 4 major blood vessels

Answer 13

1. Pulmonary veins: bring back oxygenated rich blood from the lungs to heart.
2. Pulmonary arteries: carrying oxygen poor blood from the heart to the lungs
3. Aorta: carries oxygen rich blood from the heart to the circulatory system
4. Vena cava (inferior/superior): entry point, both drain into right atrium

Question 14

Valves open and close to

Answer 14

prevent back flow

Question 15

Valves between the atria and ventricles are called

Answer 15

Atrioventricular valves
1. Tricuspid valve (RA to RV)
2. Bicuspid (mitral) valve (LA to LV)

Question 16

Valves between ventricles and arteries

Answer 16

1. Pulmonary semilunar valve (RV to pulmonary artery
2. Aortic valve (LV to aorta)

Question 17

chordae tendineae

Answer 17

• heart strings
• close AV valves not explode

Question 18

During ventricular contraction

Answer 18

• AV valves are closed to prevent back flow
• SV are open to eject blood to lungs or body

Question 19

During ventricular relaxation

Answer 19

• AV are open
• SV are closed to prevent back flow of blood that has entered the arteries