3.6.1.3- Control of heart

Question 1

Cardiac muscle is MYOGENIC so why does it need to be controlled?

Answer 1

the myogenic muscle contracts by itself, but the RATE of contraction is controlled by nervous impulses

Question 2

What parts are involved in controlling rate of contraction of heart?

Answer 2

1) Sinoatrial node (SAN)
2) Atrioventricular node (AVN)
3) Bundle of His
4) Purkyne fibres

Question 3

SAN features=

Answer 3

• located in wall of right atrium

- known as pacemaker

Question 4

Bundle of his- features=

Answer 4

• collection of conducting tissue
• transmits electrical activity to bottom of heart & around V walls along PURKEYNE FIBRES
• located in SEPTUM

Question 5

AVN features

Answer 5

-located near border of L & R ventricle within atria

Question 6

Purkyne fibres- features

Answer 6

found in walls of ventricles

Question 7

Heartbeat process- (7)

Answer 7

1) SAN releases a WOD across atria, causing them to contract
2) AVN releases another WOD after receiving 1st
3) A non-conductive layer between A & V prevent waves crossing to V
4) Instead Bundle of his, conducts the wave down to the septum & Purkyne fibres
5) As result, short delay before apex & walls of V contract & AVN transmits 2nd WOD
6) Delay allows time for A to pump all the blood> V
7) Cells repolarise & cardiac muscle relaxes

Question 8

What triggers the control of heart rate? (1+2)

Answer 8

the medulla oblongata in brain controls the heart rate via the autonomic nervous system

1) CC linked to SAN increases heart rate via SYMPATHETIC nervous system
2) CC that decreases heart rate via PARASYMPATHETIC nervous system

Question 9

Homeostatic control of heart rate-

heart rate changes in response to changes in

Answer 9

• pH

- Blood pressure

Question 10

what detects changes in pH and blood pressure?

Answer 10

pH= chemoreceptors
BP= baroreceptors
(both found in aorta& carotid arteries)

Question 11

Homeostatic control of HR- if High CO2 & low pH (4)

Answer 11

1) Detected by chemoreceptors
2) more frequent impulses> SAN via sympathetic nervous system
3) Cardiac muscle contracts more frequently ,
4) so Heart rate increases & CO2 diffuses out> alveoli more rapidly

Question 12

Homeostatic control of HR- Response to High BP (4)

Answer 12

1) Detected by baroreceptors
2) More frequent impulses from PARAsympathetic nervous system> SAN
3) Less frequent impulses from SAN
4) cardiac muscle contracts LESS frequently so heart rate & BP DECREASES.