Lecture 5 Unit 1

Question 1

in the sympathetic division of the nervous system what do short preganglionic neurons release?

Answer 1

ACh

Question 2

in the sympathetic division of the nervous system what do long postganglionic neuron axons release

Answer 2

norepinephrine

Question 3

in the parasympathetic division of the nervous system what do long preganglionic neurons release

Answer 3

ACh

Question 4

in the parasympathetic division of the nervous system what do short postganglionic neuron axons release?

Answer 4

ACh

Question 5

what does the cardiac cycle refer to?

Answer 5

all the events associated with one heartbeat

Question 6

what is systole?

Answer 6

the period of ventricular contraction and blood ejection

Question 7

what is a diastole?

Answer 7

the period of ventricular relaxation and filling

Question 8

how long is the cardiac cycle period?

Answer 8

0.8 seconds

Question 9

how can cardiac frequency or heart rate be computed?

Answer 9

from the cardiac cycle period

Question 10

what is the formula for heart rate?

Answer 10

[1 beat/ cardiac cycle period (sec)] x 60 sec/min

Question 11

how is the heart rate modified?

Answer 11

by changes in the autonomic nervous system

Question 12

what are the effects of the ANS on heart rate called?

Answer 12

chronotropic effects

Question 13

how can ANS activity on heart rate be modified?

Answer 13

• circulating hormones

- higher brain structures

Question 14

what are the circulating hormones of the ANS?

Answer 14

Norepineprhine, epinephrine, and thyroxine

Question 15

how do higher brain structures of the ANS affect heart rate?

Answer 15

it influences sympathetic and parasympathetic neurons that send nerve fibers to the heart

Question 16

where are the neurons in higher brain structures located?

Answer 16

in the caudal portions of the medulla oblongata (in the cardiac centers)

Question 17

fibers leaving from the cardioacceleratory center are what?

Answer 17

sympathetic

Question 18

fibers leaving from the cardio inhibitory center are what?

Answer 18

parasympathetic

Question 19

what do neurons in the cardioaccceleratory center do?

Answer 19

synapse on preganglionic neurons in the lateral gray horns of the thoracic spinal cord

Question 20

what do the preganglionic neurons do after they synapse?

Answer 20

they synapse on postganglionic neurons which are located in the sympathetic chain ganglia

Question 21

what do the postganglionic neurons after they synapse in the sympathetic nervous system?

Answer 21

they send their axons to the SA node, AV node and the ventricular cardiac muscle fibers

Question 22

what do preganglionic neurons release on the sympathetic branch and where?

Answer 22

acetylcholine onto postganglionic neurons in the sympathetic chain ganglia

Question 23

where does ACh bind in the sympathetic branch and where?

Answer 23

to nicotinic receptors on dendrites and cell bodies of postganglionic neurons in sympathetic chain ganglia

Question 24

what do postganglionic neurons release and where in the sympathetic branch?

Answer 24

norepinephrine onto the heart cells activating beta 1 adrenergic receptors which have widespread effects on the cardiac nervous and muscle tissue

Question 25

what does the binding of NE to the pacemaker cells in the SA and AV nodes lead to?

Answer 25

an increase in the inward Na+ current

Question 26

what does the greater Na+ current produce?

Answer 26

an increase rate of depolarization or a steeper pacemaker potential

Question 27

what do the pacemaker cells end up reaching?

Answer 27

they are able to reach threshold more frequently (# of APs generate per unit time goes up) and heart rate rises

Question 28

how do the neurons in the cardio inhibitory center of the medulla send their signals to the heart?

Answer 28

via the vagus nerve

Question 29

what happens after the preganglionic neurons synapse in terminal ganglia near the heart in the parasympathetic nervous system?

Answer 29

postganglionic neurons carry signals to the SA node, AV node and atrial muscle fibers

Question 30

how is heart rate controlled by the parasympathetic division?

Answer 30

heart rate slows down

Question 31

how is heart rate slowed down by the parasympathetic nervous system?

Answer 31

ACh increases K+ permeability of pacemaker cells and the rate of K+ diffusion out of the cells is increased

Question 32

what happens to pacemaker cell membranes after heart rate is slowed by the parasympathetic nervous system?

Answer 32

hyperpolarization

Question 33

what is actually happening when heart rate is slowed?

Answer 33

it takes more time for the pacemaker potentials to reach the threshold for AP generation. for atrial controntaile fibers voltage gated Na+ channel opening is delayed. for pacemaker cells, voltage gated Ca2+ channel opening is delayed and heart rate slows

Question 34

what do hormone levels do to heart rate?

Answer 34

epinephrine and thyroxine increases heart rate and contractility

Question 35

what does hypocalcemia do to heart rate?

Answer 35

reduced ionic calcium depressed contractility

Question 36

what does hypercalcemia do to heart rate

Answer 36

excess ionic calcium dramatically increases heart irritability and leads to spastic contractions

Question 37

what does hyperatremia do to heart rate?

Answer 37

excess ionic sodium blocks heart contraction by inhibiting ionic calcium transport

Question 38

what does hyperkalemia do to heart rate?

Answer 38

excess ionic potassium leads to heart block and cardiac arrest