Cardiac Muscle 3

Question 1

2 sources of activator calcium in heart muscle

Answer 1

• extracellular calcium

- SR calcium stores

Question 2

Process of calcium release in myocytes

Answer 2

-calcium induced calcium release

Question 3

Couplings between SR and t-tubules in cardiac cells are termed _______.

Answer 3

Dyads

Question 4

What are the “feet” of dyads?

Answer 4

-RyR calcium channels of the SR

Question 5

What type of Ca2+ channel is the main source of ECF calcium entering cardiac cells?

Answer 5

-L-type

Question 6

What is responsible for most (2/3) of the Ca2+ removal from ICF?

Answer 6

• SERCA

- other 1/3 from Na/Ca exchanger on PM

Question 7

Cardiac muscle decays within a few beats when calcium is removed from the medium, whereas skeletal muscle can contract hundreds of times in calcium free mediu. Why?

Answer 7

-Cardiac muscle relies on external calcium to release internal stores to contract. Skeletal muscle relies only on SR calcium release to contract so external calcium is not as crucial

Question 8

If you want to change the heart rate, where do you target?

Answer 8

-SA node

Question 9

3 possible alterations to pacemaking cells that decrease heart rate

Answer 9

• reduce rate of phase 4 depolarization
• less negative threshold (need more depolarization to trigger AP)
• more negative maximum diastolic potential

Question 10

The ________ interval of SA node is the major control point. Why?

Answer 10

• diastolic interval

- AP duration is less sensitive to regulatory influences

Question 11

Changes that are due to sympathetic stimulation via E and NE

Answer 11

• faster depolarization rate due to increase Ca2+ conductance
• Increase overshoot

Question 12

Pharmacological actions of both sympathetic agonists on heart are classified as beta-adrenergic and are antagonized by ______ such as _______.

Answer 12

-Beta-blockers such as propranolol

Question 13

Mechanism of B-adrenergic stimulation

Answer 13

-GPCR that increases cAMP, which increases PKA, which p-lated and increases flux through Ca2+ channel

Question 14

Parasympathetic control _____ heart rate by?

Answer 14

• Decreases
• increases K+ permeability via (IKAch)
• direct G-protein activation of KACh

Question 15

3 alterations to increase strength of muscle contraction

Answer 15

1. increase Ca2+
2. more sensitive to calcium
3. more force at each Calcium concentration

Question 16

The rate and rhythm of beating directly influences the strength of contraction (independent of extrinsic effects) by ________________.

Answer 16

• Altering the amount of Ca2+ released into the myoplasm
• this called rate staircase
• this increase strength of contraction does not depend on a catecholamine effect, althought the body in adrenergic stimulation will often cause of accompany increased heart rate
• INTRINSIC REGULATION OF CONTRACTILE STRENGTH

Question 17

Mechanism of Frank-Starling law

Answer 17

• muscle maintains a constant total volume. When stretched, this brings the fibrils closer together and able to have more AM overlap and thus generate more force
• pCa curve is shifted to the left, indicating an increase in Ca2+ sensitivity too

Question 18

Extrinsic/Adrenergic Regulation of Contractile Strength Mechanism

Answer 18

1. increase strength of contraction by increasing magnitude of ICa and Ca2+ in SR available for release
2. Decrease duration of contraction by increasing SR pump uptake and decreases troponin affinity for Ca2+ allowing it to dissociate faster (quicker relaxation)

Question 19

How does sympathetic modulation change the pCa-tension curves?

Answer 19

-Shift them right