Cardiac Conduction System

Question 1

Explain conduction system pathway

Answer 1

1. Cells of SA node depolarise - present in lateral wall of RA
2. Signal progresses to both atria
3. Reaches the ventricles via the AV node - found in the interatrial septum
4. Reaches Bundle of His - In interventricular septum (near tricuspid valve)
5. Through right and left bundle branch
6. Reaching Purkinje Fibres

Question 2

Why is there a delay at the AV junction?

Answer 2

Ensures atria have ejected their blood into the ventricles first before the ventricles contract

Question 3

Why is the SA node called a pacemaker?

Answer 3

Because cells of the SA node depolarise much faster than the other cells of the heart

Question 4

Name the differences between the Skeletal and Cardiac muscle membranes

Answer 4

SKELETAL:

1. STAYS polarised until something depolarises it
   - Depolarisation causes contraction

CARDIAC:

1. Has a membrane that SPONTANEOUSLY depolarises
   - Then repolarises etc
   - No need to stimulate with external source

SKELETAL:

2. ELECTRICALLY ISOLATED from neighbouring cells
   - when one cell depolarises the adjacent cells ar enot affected
   - As there is no communication

CARDIAC:

2. Cardiac muscles do communicate with each other
   - Electrically continuous
   - Have gap junctions at intercalated discs
   - So adjacent cells will also depolarise when one depolarises
   - But dont depolarise at same rate

Question 5

What is the SA node supplied by?

Answer 5

RCA

Question 6

What is the AV node supplied by?

Answer 6

PDA