Cardiovascular: Physiology of the Heart

Question 1

What is a HEART contraction?

Answer 1

An electrical impulse that triggers contraction of CARDIAC MUSCLE (CONTRACTILE) CELLS

Question 2

Is a contraction INTRINSIC or EXTRINSIC?

Answer 2

INTRINSIC (from within the HEART itself)

Question 3

Is stim. from the NERVOUS SYSTEM required for HEART contr.

Answer 3

Nope

Question 4

What are CONDUCTING CELLS?

Answer 4

Special CARDIOCYTES that initiate and distribute APs in the HEART

Question 5

What are NODES?

Answer 5

Clusters of CONDUCTING CELLS that initiate APs in the HEART

Question 6

The INTRINSIC CONDUCTION SYSTEM has an unstable resting potential because..?

Answer 6

Na+ is constantly leaking in at a faster rate than the pumps can keep it out.

Question 7

What develops as a result of gradual depolarization?

Answer 7

PREPOTENTIAL

Question 8

What takes place after THRESHOLD is reached?

Answer 8

The VOLTAGE-GATED Ca+ channels open (Ca+ rushes in from ECF), releasing spontaneous AP

Question 9

Contraction step 1 =

Answer 9

1) Na+ enters through LEAK CHANNELS

Question 10

Contraction step 2 =

Answer 10

2) Cell develops PREPOTENTIAL

Question 11

Contraction step 3 =

Answer 11

3) VOLT. G. Ca+ CH. open at THRESHOLD

Question 12

Contraction step 4 =

Answer 12

4) Ca+ influx causes NODAL CELLS to depol. (AP!)

Question 13

Contraction step 5 =

Answer 13

5) Ca+ channels close and VOLT. G. K+ Ch. open

Question 14

Contraction step 6 =

Answer 14

6) K+ efflux causes repol.

Question 15

AP spreads along conducting pathways through GAP JUNCTIONS at __________ ____

Answer 15

INTERCALATED DISKS

Question 16

Where are APs initiated

Answer 16

In the “pacemaker” aka the SA NODE

Question 17

How many times per min. does the SA node depol.?

Answer 17

Approx. 100 times per minute

Question 18

Via what pathway do electrical signals travel from the SA NODE to the AV NODE?

Answer 18

INTERNODAL PATHWAYS

Question 19

Why is AP delayed at the AV NODE?

Answer 19

To allow time for the ATRIA to contr.

Question 20

If the SA NODE depols 100 times per minute, why is the resting HR slower than this?

Answer 20

Because the PARASYMPATHETIC SYSTEM innervates nodes ACETYLCHOLINE which slows down the HR

Question 21

What inc.s HR?

Answer 21

The SYMPATHETIC SYSTEM innervates nodes NOREPINEPHRINE to inc. HR

Question 22

If the SA NODE isn’t working, what happens?

Answer 22

The AV NODE takes over (it fires at 40-60 bpm)

Question 23

Pacemaker firing triggers all-or-none contr. of the whole HEART because…

Answer 23

All of the cells are connected by GAP JUNCTIONS at the INTERCALATED DISKS

Question 24

What is the role of GAP JUNCTIONS at INTERCALATED DISKS?

Answer 24

They allow ions to move from cell to cell

Question 25

What are DESMOSOMES? What is their F?

Answer 25

DESMOSOMES are anchoring proteins

F - Prevent separation of contracting cells

Question 26

What is the reason there are many MITOCHONDRIA in CARDIAC MUSCLE CELLS?

Answer 26

Makes the CARDIAC MUSCLE more fatigue resistant

Question 27

Are there TERMINAL CISTERNAE in CARDIAC MUSCLE?

Answer 27

No, Ca+ is released by t-tubules from the SARCOPLASMIC RETICULUM (SR)