Cardiac Muscle

Question 1

List the 3 types of cardiac cells.

Answer 1

Myocardium, pacemaker, conduction cells

Question 2

Describe myocardium.

Answer 2

-atrial & ventricular
-contraction & impulse

Question 3

Describe pacemaker.

Answer 3

-automatic rhythmic electrical discharge via AP
-self excitatory
-pass from atrial to ventricle

Question 4

Describe conduction cells.

Answer 4

-conduct AP through heart
-excitatory system that controls rhythmical beating

Question 5

Describe similar characteristics of the cardiac muscle (compared to skeletal).

Answer 5

-striated
-similar sarcomere structure
-cardiac isoforms of actin & myosin
-SR & T-Tubules

Question 6

Describe different characteristics of cardiac muscle (contrasted from skeletal muscle).

Answer 6

-contracts involuntarily
-uninucleated
-fibers are shorter & branched (functional syncytium)
-intercalated disks between cells

Question 7

Describe intercalated disks.

Answer 7

-dark, dense cross-band at each end of myocardial cells
-continuous w/ sarcolemma
-cell-to-cell junctions (2):
1. gap junction channels = diffuse of ions & AP
2. desmosomes = mechanical strength

Question 8

Describe the AP in the sinus node.

Answer 8

AP in atrial & ventricle is longer than nerve & muscle cells
LOCATION:
Sinoatrial node in right atrium

THRESHOLD:
-pacemaker cells slowly depolarize (lack 0 phase) until threshold, triggering AP.
-lack Na channels, instead pacemaker Na channels = “Funny Na Channels” (If or f channels)
-close during AP & open when AP done (spontaneous depol)
DEPOL:
-after threshold, If channels close & some Ca channels open (T-type/fast) speeds approach to threshold after threshold reached, lots of Ca channels open (L-type/slow)
-Ca primarily responsible for AP in pacemaker cells
REPOL:
-after Ca channels close, K channels open and then close, and If channels open and cycle repeats

Excitation-contraction coupling source of Ca = ECF & SR

Question 9

Describe the AP in the ventricular muscle cells.

Answer 9

0. Depol:
   -Na channels open = rapid depol
1. Initial repol:
   -Na channels close
2. Plateau (absolute period)
   -K channels close & Ca channels open
   brief repol and then plateau due to K efflux & Ca influx
3. Rapid repol
   -Ca channels close & K channels open
   returns MP to resting
4. Resting potential

Refractory period= when Na channels open to when K channels start to close
Relative period= when K channels open to when K channels close

*atrial cells = shorter AP than ventricular
*atrial Ca & K channels = stay open shorter than ventricular
*NO tetanization
*AP duration same as duration of contraction (not seen in skeletal)

Question 10

What are the main sources of Ca for cardiac contraction?

Answer 10

-oxidative metabolism of fatty acids (lipid droplets/triglycerides)
-mitochondria make up 40% of cytoplasm
-10-30% energy from glucose & lactate