cardiac muscle

Question 1

3 types of cardiac muscle

Answer 1

atrial, ventricular and excitatory and conductive muscle fibres

Question 2

cardiac muscle similarities with skeletal

Answer 2

striated, contain myofibrils (actin and myosin filaments)

Question 3

left ventricular rotation

Answer 3

wringing motion, LV is organised into complex muscle fibres that run in different directions - subepicardial spirals in a leftward direction and subendocardial rightward

Question 4

why do ions flow with ease in the intracellular fluid of cardiac muscle fibres

Answer 4

intercalated discs form gap junctions (cell membrane)

- heart muscle is a synctium of many heart muscle cells

Question 5

two synctia

Answer 5

atrial and ventricular syncytium - however potentials are not conducted between these two syncytia - instead through AV bundle

Question 6

flow of blood through the heart including respective valves

Answer 6

deoxygenated blood is pumped from the head and upper body and trunk and lower body extremities into the SVC/IVC (respectively) into the RA, the tricuspid valve then allows blood to flow from RA to RV, the pulmonary valve allows blood to flow then into the pulmonary artery which then leads this blood to become oxygenated in the lungs. From the lungs blood flows from the pulmonary veins into the LA, the mitral valves allows blood to enter the LV - blood then leaves the LV to the aorta via the aortic valves

Question 7

plateau cause

Answer 7

L-type calcium channels - calcium sodium channels : slow to open and remain open for longer - more influx of calcium and sodium ions = prolonged period of depolarisation (also the calcium ions involved in this process are responsible for the initiation of the contractile process)

Question 8

Phase 0

Answer 8

depolarisation ! voltage gated sodium channels (fast sodium channels) open and allow influx of sodium causes the membrane potential to be positive of about +20 millivolts before ti closes

Question 9

phase 1

Answer 9

initial repolarisation ! sodium channels closes - cell begins to repolarise and potassium ions leave cell

Question 10

phase 2

Answer 10

plateau !voltage gated calcium ion channels open slowly during phase 0 and 1 and calcium enters the cells, potassium channels then close as calcium influx reduces potassium permeability - combination of decreased potassium efflux and calcium ion influx causes the plateau

Question 11

phase 3

Answer 11

rapid repolarisation ! calcium ion channels close and so there is increased potassium permeability - increased efflux of potassium returns cell membrane potential to its resting level

Question 12

phase 4

Answer 12

about -80/90 millivolts