Lecture #4 Control of Heart Rate

Question 1

What is a Cardiac Cycle?

Answer 1

All the events associated with ONE HEARTBEAT

Question 2

Is the period of ventricular contraction and blood ejection?

Answer 2

Systole

Question 3

Is the period of ventricular relaxation and filling?

Answer 3

Diastole

Question 4

How long does it take for the cardiac cycle to rest?

Answer 4

0.8 seconds

Question 5

_______, can be computed from the cardiac cycle period.

Answer 5

Cardiac frequency or heart rate.

Question 6

How do you calculate heart rate?

Answer 6

Heart rate is expressed in beats/minute = 1/ cycle period (sec) x 60 sec/min

Question 7

How does Autonomic Nervous System control heart rate?

Answer 7

Heart rate is modified by input from the ANS which is chronotropic effects.

Question 8

How is ANS modified?

Answer 8

By circulating hormones and by higher brain structures.

Question 9

In what area does the sympathetic neurons send nerve fibers to the heart?

Answer 9

Cardiovascular center–is in the caudal portion of the medulla oblongata

Question 10

How does the sympathetic nervous system control heart rate?

Answer 10

Sympathetic neurons in the CV center synapse upon preganglionic neurons in the intermediolateral cell columns of the thoracic spinal cod.

Question 11

After the preganglionic neurons synapse, what comes next?

Answer 11

It synapses to postganglionic neurons, which are located in the sympathetic chain ganglia.

Question 12

Where does the signals of the postganglionic neurons go?

Answer 12

Send their axons to the SA and AV nodes, the cardiac muscle fibers.

Question 13

Preganglionic neurons release_______ onto postganglionic neurons.

Answer 13

Acetylcholine (ACh)

Question 14

Postganglionic neurons then release ______ onto target cells.

Answer 14

Norepinephrine (NE)

Question 15

_______is the postganglionic neurotransmitter for the sympathetic nervous system.

Answer 15

Norepinphrine (NE)

Question 16

NE activates ______, which have wide-spread effects on the cardiac nervous and muscle tissue.

Answer 16

Beta-1 receptors

Question 17

What are the mechanisms of heart rate control?

Answer 17

The neurons are brought to threshold more frequently, leading to an increase in the number of action potentials in a given unit of time

Question 18

An increased ______ in the cells of the SA and AV nodes, due to an increase in the inward Na+ current

Answer 18

Rate of Depolarization

Question 19

How does the Parasympathetic Nervous System control heart rate?

Answer 19

Parasympathetic neurons in the CV centers of the brain stem send their axons to the heart in the vagus nerves

Vagal motoneurons synapse directly on the SA and AV nodes, and on the atrial muscle fibers

Vagal motoneurons release ACh onto the postsynaptic cells, leading to slowing of heart rate.

Question 20

What is the mechanism of PNS to control Heart Rate?

Answer 20

ACh increases potassium permeability of the cells so the rate of potassium diffusion out of the cells is increased

Question 21

Are the results of the PNS HR control Depolarized, hyperpolarized, or repolarized?

Answer 21

Hyperpolarization of the cell membrane.

Question 22

What happens when the membrane potential reach a threshold for Ca++ channel activation?

Answer 22

It takes more time for a spontaneous upward drift in membrane potential

Question 23

What chemicals regulate the heart?

Answer 23

Hormones, epinephrine, and thyroxin increase heart rate.

Intra and extra cellular ion concentrations tightly regulate for normal heart function.

Question 24

Reduced Ionic calcium depresses contractility is called _______.

Answer 24

Hypocalcemia

Question 25

Dramatically increases heart irrability and leads to spastic contractions is called ______.

Answer 25

Hypercalcemia

Question 26

Blocks heart contraction by inhibiting ionic calcium transport is called ______.

Answer 26

Hypernatremia

Question 27

Leads to heart block and cardiac arrest is called _____.

Answer 27

Hyperkalemia