14.5 Control of heart rate

Question 1

autonomic system

Answer 1

controls involuntary activities of internal muscles and glands

divided into sympathetic and parasympathetic nervous system

Question 2

sympathetic nervous system

Answer 2

stimulates effectors and speeds up any activity
heightens awareness and prepares for activity

-emergency controller for stressful situations
e.g. excercise or powerful emotions

Question 3

parasympathetic nervous system

Answer 3

inhibits effectors and slows down activity
conserves energy and replenishes body reserves

-controller for normal resting conditions

Question 4

sympathetic and parasympathetic nervous system

Answer 4

antagonistic
- oppose one another and regulate one another to be balanced

Question 5

myogenic

Answer 5

contraction initiated form muscle itself
-e.g. cardiac muscle

Question 6

neurogenic

Answer 6

contraction initiated by nerve impulses from outside

Question 7

sinoatrial node

Answer 7

group of cells in wall of right atrium

stimulates initial contraction
has basic rhythm
e.g. pacemaker

Question 8

sequence of basic heart rate

Answer 8

1. wave of electrical excitation spreads from sinoatrial node across both atria so they contract
2. the atrioventricular septum prevents wave crossing to ventricles
3. wave of excitation enters atrioventricular node
4. atrioventicular node conveys a wave of electrical excitation between ventricles along bundle of His
5. bundle of His conducts wave through atrioventricular septum to base of ventricles where bundle branches into smaller fibres of Purkyne tissue
6. wave of excitation is released from Purkyne tissue causing ventricle to contract quickly at same time from bottom of heart upwards

Question 9

atrioventricular node

Answer 9

group of cells between atria

Question 10

atrioventricular septum

Answer 10

a layer of non-conductive tissue

Question 11

bundle of His

Answer 11

series of specialised muscle fibre called Purkyne tissue

Question 12

medulla oblongata

Answer 12

region of brain that controls changes to heart rate

has 2 centres to do with heart rate

Question 13

2 medulla oblongata centres

Answer 13

centre that increases heartrate- linked to sinoatrial node by sympathetic nervous system

centre that decreases heart rate- linked to sinoatrial node by parasympathetic nervous system

Question 14

chemoreceptors

Answer 14

found in wall of carotid arteries

sensitive to changes in pH of blood from changes in CO2 conc

Question 15

Control by chemoreceptors when CO2 increases

Answer 15

-when blood has higher conc of co2, pH is lowered

• chemoreceptors and aorta detect and increase frequency of nerve impulses to centre of medulla oblongata that increases heartrate

-centre increases frequency of impulses via sympathetic to sinoatrial node

• increases rate of production of electrical waves by sinoatrial node which increases heart rate
• increases blood flow causes more co2 removed from lungs so Co2 conc returns to normal

Question 16

Control by chemoreceptors when CO2 levels return to normal

Answer 16

• pH of blood rise to normal

-chemoreceptors and aorta reduce frequency of nerve impulses to medulla oblongata

-medulla oblongata reduces frequency of nerve impulses to sinoatrial node

• reduction in heart rate

Question 17

when blood pressure is higher than normal

Answer 17

pressure receptors transmit more nerve impulses to medulla oblongata

centre sends impulses via parasympathetic nervous system to sinoatrial node

decrease in heart rate

Question 18

when blood pressure is lower than normal

Answer 18

pressure receptors transmit more nerve impulses to medulla oblongata

centre sends impulses via sympathetic nervous system to sinoatrial node

increases heart rode