circulatory system part 3

Question 1

control of contraction in vertebrate hearts

Answer 1

myogenic
cardiomyocytes produce spontaneous rhythmic depolarizations
don’t require nerve signal
electrically coupled by gap junctions

Question 2

pace maker cells

Answer 2

in the sinus venous in fish
in the right atrium of vertebrates
- sinoatrial node (SA)
- atrio ventricular node (AV)

Question 3

characteristics of pacemaker cells

Answer 3

small, few myofibrils & mitochondria
dont contract
have unstable resting membrane potential

Question 4

increasing heart rate

Answer 4

norepinehpherine - sympathetic neurons
epinephrine - adrenal medulla
pacemaker (funny) and Ca channels open
frequency of action potentials increase

Question 5

funny channel

Answer 5

If - funny current

inward Na - contributes to depolarization

Question 6

T-ype Ca channel

Answer 6

Ca in - contributes to depolarization

Question 7

decreasing heart rate

Answer 7

acetylcholine - parasympathetic neurons
K channels open
pacemaker cells hyperpolarize
takes longer to depolarize, less APs
vagal parasympathetic influences dominate at rest

Question 8

receptor involved increasing heart rate

Answer 8

B receptor of autorhymthic cells

G alpha s subunit phosphorylates funny and T type Ca channels allowing influx

Question 9

receptor involved in decreasing heart rate

Answer 9

muscarinic receptor of autorhymthic cells

G alpha I subunit inhibits T type Ca channels and allows K to leave

Question 10

action potentials in cardiomyocytes

Answer 10

plateau phase - extended depolarization

• long refractory period that lasts as long as contraction
• caused by Ca entry via L type channel
• prevents tetanus

Question 11

what are the effects of norepinephrine on increasing the heart rate (protein kinase)

Answer 11

• phosphorylates L type Ca channels which allows Ca to enter the cell (stimulates contraction)
• phosphorylates Ca channels on sarcoplasmic reticulum allowing Ca to move to cytoplasm (stimulates contraction)
  phosphorylates myosin (stimulating contraction)
• phosphorylates sarcoplasmic Ca ATPase, removes Ca from cytoplasm (decreases relaxation time)

Question 12

what are modified cardiomyoctes

Answer 12

elongated and pale
dont contract
work to spread action potentials rapidly

Question 13

p wave (electrocardiogram)

Answer 13

atrial depolarization

wave of depolarization from SA node throughout atria

Question 14

QRS complex

Answer 14

ventricular depolarization

ST segment corresponds to plateau phase

Question 15

T wave

Answer 15

ventricular repolarization

Question 16

cardiac output

Answer 16

heart rate x stroke volume

rate of contraction in beats/min

Question 17

bradycardiastroke volume = end diastolic volume - end systolic volume

Answer 17

decreased heart rate

Question 18

tachycardia

Answer 18

increased heart rate

Question 19

what modulates the stroke volume?

Answer 19

various nervous, hormonal and physical factors

Question 20

how does the level of sympathetic activity affect the length tension relationship

Answer 20

increased sympathetic activity - increased stroke volume

decreased sympathetic activity - decreased stroke