[14.5] control of heart rate

Question 1

what does the autonomic nervous system control?

Answer 1

involuntary activities of internal muscles and glands

Question 2

what are the 2 subdivisions of the ANS?

Answer 2

• sympathetic nervous system
• parasympathetic nervous system

Question 3

what does the sympathetic nervous system do?

Answer 3

• stimulates effectors so speeds up any activity
• helps us cope with stressful situations by heightening awareness and preparing us for activity (fight or flight response)

Question 4

what does the parasympathetic nervous system do?

Answer 4

• inhibits effectors so slows down any activity
• controls activities in normal resting conditions
• wants to conserve energy and replenish body’s reserves

Question 5

in what way are the actions of the sympathetic and parasympathetic nervous systems antagonistic?

Answer 5

• normally oppose one another
• if one system contracts a muscle, the other relaxes it
• activities of internal glands and muscles are regulated by a balance of the two systems

Question 6

describe the muscle of the heart

Answer 6

• known as cardiac muscle
• myogenic (contraction is initiated from within muscle itself)

Question 7

what 4 features of the heart that are involved in heart rate?

Answer 7

• sinoatrial node (SAN)
• atrioventricular node (AVN)
• purkyne fibres (PFs)
• bundles of his (BoH)

Question 8

what is the SAN and where is it found?

Answer 8

cluster of neurons embedded in wall of right atrium (top left corner of RA)

Question 9

why is the SAN known as the pacemaker?

Answer 9

has a basic rhythm of stimulation that determines the beat of the heart

Question 10

what does the SAN do?

Answer 10

sends a wave of depolarisation across both atria, causing them to contract (systole)

Question 11

why does the SAN’s wave not cross to the ventricles?

Answer 11

there is a layer of non-conductive tissue (atrioventricular septum) that prevents this

Question 12

where is the AVN?

Answer 12

bottom right corner of RA, between the atria

Question 13

what does the AVN do?

Answer 13

• picks up wave of excitation
• brief pause
• conveys a wave of electrical excitations between the ventricles along PFs which make up BoH

Question 14

what are the BoH and where are they found?

Answer 14

collection of neurons in the septum

Question 15

what is the role of the BoH?

Answer 15

conducts wave through atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of purkyne tissue

Question 16

what are PFs and where are they found?

Answer 16

neurons in muscle wall at base of ventricles

Question 17

what is the role of the PFs?

Answer 17

• wave of excitation is released from purkyne tissue
• causes ventricles to contract from base of heart upwards, forcing blood in that direction

Question 18

what are changes to heart rate controlled by?

Answer 18

region of brain called medulla oblongata

Question 19

what 2 coordinators in the medulla oblongata control heart rate?

Answer 19

• cardio-acceleratory centre
• cardio-inhibitory centre

Question 20

what does the cardio-acceleratory centre do?

Answer 20

sends impulses to SAN via sympathetic motor neurons

Question 21

what does the cardio-inhibitory centre do?

Answer 21

sends impulses to SAN via parasympathetic motor neurons

Question 22

what 2 receptors control heart rate?

Answer 22

• chemoreceptors
• pressure receptors

Question 23

what do chemoreceptors do?

Answer 23

• detect changes in blood pH due to excess production of carbon dioxide from aerobic respiration
• pH becomes more acidic so is lower
• increased frequency of impulses to centres medulla oblongata

Question 24

where are chemoreceptors and pressure receptors found?

Answer 24

aortic and carotid bodies (clumps of cells in walls of aorta and carotid arteries)

Question 25

what do pressure receptors do?

Answer 25

• detect changes in blood pressure
• sends more impulses to centres in medulla oblongata based on this

Question 26

why is having too high or low blood pressure bad?

Answer 26

• high = damage to tissues and cells
• low = interrupts delivery of blood to parts of body