14.5 control of heart rate

Question 1

what are the 2 division if the autonomic nervous system

Answer 1

• sympathetic nervous system
• parasympathetic nervous system

Question 2

what is the sympathetic nervous system

Answer 2

• stimulates effectors and sped up activity
• copes with stressful situations by heightening our awareness
• fight or flight response

Question 3

what is the parasympathetic nervous system

Answer 3

• inhibits effectors and slows down activity
• control under normal resting conditions

Question 4

what does antagonistic mean

Answer 4

• actions oppose each other
• one contracts a muscle the other relaxes it

Question 5

what is cardiac muscle

Answer 5

• heart muscle

Question 6

what does myogenic mean

Answer 6

• contraction is initiated from within the muscle itself rather than nervous impulses from outside (neurogenic)

Question 7

what is the sinoatrial node (SAN)

Answer 7

• group of cells in the right atrium
• initial stimulus for contractions originates
• pacemaker

Question 8

how does the SAN control heart rate

Answer 8

1. wave of electrical excitation spreads out from the SAN across both atria causing them to contract
2. atrioventricular septum (non conductive tissue) prevents the wave crossing to the ventricles
3. wave of excitation enters the atrioventricular node (AVN) which lies between the atria
4. AVN after a short delay conveys a wave of electrical excitation between the ventricles along the purkyne tissue which make up the bundle of His
5. bundle of His conducts the care though the AVN septum to the base of the ventricles where the bundles branches into smaller fibres of purkyne tissue
6. wave of excitation is released form the purkyne tissue causing the ventricles to contract quickly at the same time from the bottom of the heart upwards

Question 9

what modifies heart rate

Answer 9

• medulla oblongata
  -center that increases heart rate, linked to the sinoatrial node by the sympathetic nervous system
  center that decreases heart rate, linked to the sinoatrial node by the parasympathetic nervous system

Question 10

where are chemoreceptors found

Answer 10

the wall of the carotid arteries
sensitive to changes in the pH of the blood that results from changes in CO concentration

Question 11

how does control by chemoreceptors work

Answer 11

1. when the blood has a higher than normal concentration of CO its pH is lowered
2. chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate
3. this increases the frequency of impulses via the SNS to the SAN, this increases the rate of production to electrical waves by the SAN and increases heart rate
4. increased blood flow leads to more CO being removed by the longs ad so CO concentration of blood returns to normal
5. pH of blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata
6. medulla oblongata reduces the frequency of impulses to the SAN which lead to a reduction in heart rate

Question 12

control by pressure receptors when blood pressure is higher than normal

Answer 12

• pressure receptors transmit more nervous impulses to the centre on the medulla oblongata that decreases heart rate
• centre sends impulses via the PNS to the SAN of the heart which leads to a decrease in the rate at which the heartbeat

Question 13

control by pressure receptors when blood pressure is lower than normal

Answer 13

• pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate
• centre sends impulses via the sympathetic nervous system to the SAN which increases the rate at which the heat beats