PSIO202 Exam 1 Lecture 4

Question 1

What is a cardiac cycle?

Answer 1

All of the events in one heartbeat

Question 2

What is the length of the average cardiac cycle at rest?

Answer 2

0.8 seconds

Question 3

How is HR related to cycle period (T)?

Answer 3

HR=1/T x 60

Question 4

What does 1/T represent?

Answer 4

Frequency (beats per second)

Question 5

How does flow of ions impact membrane potential in the SA/AV nodes?

Answer 5

leak current of Na+ causes slow depol to threshold, increase in Ca++ permeability causes depolarization, and K+ flowing out causes repolarization

Question 6

Is control of heart rate chronotropic or inotropic?

Answer 6

chronotropic

Question 7

Other than nervous input, what else can modify heart rate?

Answer 7

emotions/limbic system, circulating hormones, cortical input, and ion concentrations

Question 8

Where are the cardiovascular control centers located?

Answer 8

caudal medulla

Question 9

Does the sympathetic nervous system affect HR, contractility, or both? What is the reasoning for this?

Answer 9

Both, because it innervates the nodes, atria, and ventricles

Question 10

Does the parasympathetic nervous system affect HR, contractility, or both? What is the reasoning for this?

Answer 10

HR only, because it only innervates the nodes and atria

Question 11

What is the pathway of sympathetic nervous input on HR? Draw it out.

Answer 11

sympathetic neurons from the cardioaccelatory center synapse onto a short preganglionic neuron, release ACh onto the ganglion, along postganglionic neuron synapses onto the SA/AV nodes, atria, and ventricles where norepinephrine is released. NE activates B1 receptors, increase Na+ and Ca++, less permeable to K+, reaches threshold more easily (and doesn’t hyperpolarize as much) which increases heart rate

Question 12

What is the pathway of parasympathetic nervous input on HR? Draw it out.

Answer 12

parasympathetic neurons in the cardioinhibitory centers send axons to the heart in the Vagus nerve (CN X), vagus nerve synapses onto the SA/AV nodes and atrial muscle. Vagus nerve releases ACh onto the cells, increase K+ diffusion out of the cell, lots of hyperpolarization, takes more time for Na+ leak to reach threshold and activate Ca++, longer cycles and slower HR

Question 13

What ion concentrations affect normal heart function?

Answer 13

hypocalcemia: low Ca++, impede crossbridge formation, depress contractility
hypercalcemia: too much Ca++, too much crossbridge formation, spastic contractions and heart irritability
hypernatremia: too much Na+, inhibits Ca++, no crossbridge formation, blocks heart contraction
hyperkalemia: too much K+, super hyperpolarized, leak current of Na+ can’t depolarize to threshold