electrophysiology of the cv system

Question 1

define atria

Answer 1

receiving chambers of the heart

Question 2

define ventricle

Answer 2

discharging chambers of the heart

Question 3

Where is the tricuspid valve located ?

Answer 3

between right atrium and ventricle

Question 4

where is the bicuspid valve located ?

Answer 4

between left atrium and ventricle

Question 5

key word : membrane potential means

Answer 5

The difference in charge between the
inside and outside of the cell

Question 6

key word : polar means

Answer 6

Having ‘poles’
Positive (+) and negative (-) sides

Question 7

key word : depolarisation means

Answer 7

Membrane potential going from more
negative to less negative (or positive)
The difference in charge across the
membrane, i.e. the poles, getting smaller

Question 8

key word : repolarisation means

Answer 8

becoming polarised again
positive and negative sides become more different

Question 9

key word :ion channels means

Answer 9

Proteins which act as openings to let
specific ions move through
May be ‘gated’ – Open in response to
certain stimuli

Question 10

where are autorhythmic cells in the heart located ?

Answer 10

sinoatrial node [ SA node ]
Atrioventricular node [ AV node ]

Question 11

Describe electrical conduction to the AV node

Answer 11

• Internodal pathways connect SA & AV
  nodes
• Electrical activity spreads rapidly
  to AV node via internodal
  pathways
• Depolarization spreads more
  slowly across atrial muscle
• Conduction slows within AV node

Question 12

why does electrical conduction to AV node occur ?

Answer 12

• Action potentials pass into Bundle of His
  (Wall of the septum between the
  ventricles)
• Bundle divides into left & right bundle
  branches
• Fibres continue downward and divide into
  many small Purkinje fibres that spread
  outward among the contractile cells

Question 13

what is p wave in ECG ?

Answer 13

atrial depolarisation

Question 14

what is QRS complex in ECG ?

Answer 14

Ventricular depolarisation

Question 15

what is t wave in ECG ?

Answer 15

Indicates ventricular repolarization

Question 16

what is the PR interval in ECG ?

Answer 16

indicates delay in AV node
electrical activity of the atria

Question 17

what is the QT interval in ECG ?

Answer 17

electrical activity of the ventricles

Question 18

what are the three mechanism the cardiovascular system is regulated by ?

Answer 18

humoral- response to changing levels of ions or nutrients in the blood

neural - stimulation by nerves

hormonal - stimulation received from other hormones

Question 19

what does the motor neurons in the autonomic nervous system do ?

Answer 19

innervate smooth muscle , cardiac muscle , internal organs and skin

makes adjustments to ensure optimal support for body activities

operates via subconscious control

Question 20

what does the sympatheic fibres in the autonomic nervous system do ?

Answer 20

increase heart rate , respiratory rate and inhibits digestion and elimination

Question 21

what does the parasympathetic fibres do in the autonomic nervous system do ?

Answer 21

decrease heart and respiratory rate , allow for digestion and discarding of waste

Question 22

what neurotransmitter is involved in the sympathetic fibres ?

Answer 22

catecholamines

Question 23

what neurotransmitter is involved in the parasympathetic fibres ?

Answer 23

acetylcholine

Question 24

what happens at phase 0 [ depolarisation ] of the heart cardiac myocytes action potential ?

Answer 24

action potential from SA node opens fast Na+ channels

large but transient increase in Na+ permeability

Na+ enters

accompanied by dramatic reduction in K+
conductance

prevents K+ efflux and repolarization

Question 25

what happens at phase 1 [ repolarisation ] of the heart cardiac myocytes action potential ?

Answer 25

fast Na+ channels close membrane potential begins to fall reflects partial repolarization

Question 26

what happens at phase 2 [ plateau ] of the heart cardiac myocytes action potential ?

Answer 26

* Despite closure of fast Na+ channels, potential remains positive or near 0 for ~300 msec * Largely due to opening of voltage- gated slow Ca2+ channels * Ca2+ entry is involved in excitation-contraction coupling * Plateau because: * Na+ influx from slow Na+ channel * Slow leakage of K+ out of cell keeps potential from rising 25

Question 27

what happens at phase 3 [ reolarization ] of the heart cardiac myocytes action potential ?

Answer 27

* Intracellular K+ moves down concentration gradient - leaves cell causing it to repolarize * Repolarization facilitated by closure of Ca2+ and slow Na+ channels

Question 28

what happens at phase 4 [ resting membrane potential ] of the heart cardiac myocytes action potential ?

Answer 28

* Cell repolarized and ready for the next stimulus 26

Question 29

how does the AP spread between the cells ?

Answer 29

- gap junctions [ direct transfer of ionic current from one cells to the next ] - cells connected by gap junctions are said to be electrically coupled - flow of ions from cytoplasm to cytoplasm - very fast , fail-safe transmission - almost simultaneous AP generation

Question 30

does skeletal system depend on action potential for neural activity ?

Answer 30

yes

Question 31

does cardiac system depend on action potential for neural activity ?

Answer 31

no

Question 32

what is the resting membrane potential for skeletal system ?

Answer 32

- 85mv

Question 33

what is the resting membrane potential for cardiac system ?

Answer 33

-90mv

Question 34

what is the duration of the action potential of the skeletal system ?

Answer 34

2.5 m sec

Question 35

what is the duration of the action potential of the cardiac system ?

Answer 35

300m sec