cardiac muscle structures

Question 1

contractile cells of the heart

Answer 1

myocytes

Question 2

The largest cell population by number is

Answer 2

endothelial cells, followed by cardiac fibroblasts

Question 3

predominant components of the ECM are:

Answer 3

Fibrillar collagen type I and III

Question 4

disruptions in the ECM occur with

Answer 4

disease and cardiac remodeling

Question 5

Cardiac muscles are:

Answer 5

1. striated
2. not under direct neural control (unlike skeletal which are)
3. shorter, narrower
4. richer in mitochondria
5. one nucleus
6. Ca2+ binds to troponin, which regulates actomyosin interaction

Question 6

ATPase activity of myosin is

Answer 6

slower in cardiac than skeletal but faster than smooth muscle

Question 7

in cardiac muscle, Ca2+ binds to

Answer 7

troponin, which regulates actomyosin interaction

Question 8

Cardiac muscle cells are connected with each other through

Answer 8

intercalated discs

Question 9

coupling between cardiac muscle cells is

Answer 9

both mechanical and electrical

Question 10

intercalated discs

Answer 10

1. Coincide with the Z discs; contain desmosomes and gap junctions
2. Desmosomes provide adhesion and assure that the force generated in one cell passes to the other (connects to ECM)
3. Gap junctions provide low resistance pathways for electrical current

Question 11

Myofibrils and mitochondria occupy about

Answer 11

85% of the heart cell volume (the rest contains sarcolemma, T-tubules, SR, intercalated disks, gap junctions, etc)

Question 12

thick filament

Answer 12

composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex

Question 13

thin filament

Answer 13

composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex

Question 14

saracomere

Answer 14

unit of contractile activity composed mainly of actin and myosin and extending from Z line to Z line in a myofibril

Question 15

myofibril

Answer 15

end to end arrays of identical sarcomeres

Question 16

myofiber

Answer 16

a single, multinucleated muscle cell containsing all the usual cell organelles plus many myofibrils

Question 17

muscle

Answer 17

organized array of muscle fibers

Question 18

a cardiac muscle cell is made up of

Answer 18

sarcomeres

Question 19

sarcomere is defined as

Answer 19

z line to z line

Question 20

the a band is

Answer 20

thick filaments

Question 21

the I band is

Answer 21

thin filament extensions from the Z line

Question 22

major contractile protein

Answer 22

1. myosin

2. actin

Question 23

Myosin

Answer 23

1. Composed of two heavy chains and four light chains (RLC, ELC) with a mass of about 480,000 daltons.
2. Developmental regulation of isoforms (and with disease).
3. HC isoform determines ATPase activity (a vs b)

Question 24

Actin is

Answer 24

1. Similar to skeletal muscle myosin

2. Binds tropomyosin and troponin

Question 25

major regulatory

Answer 25

1. troponin C
2. troponin I
3. troponin T
4. tropomyosin

Question 26

Troponin C (TN-C)

Answer 26

A dumbbell shaped protein with the N-lobe containing only one Ca2+-binding site (unlike skeletal which contains two)

Question 27

troponin I (TN-I)

Answer 27

1. Contains a unique N-terminal extension of 32 amino acids that contains 2 PKA phosphorylation sites critical for adrenergic responsiveness of the heart.
2. This extension interacts with TN-C but is released with phosphorylation.

(KNOW THIS)

Question 28

TN-C ca2+ binding sites

Answer 28

only one calcium binding site, compared to 2 in skeletal

Question 29

Troponin T (TN-T)

Answer 29

1. Binds tropomyosin.

2. Developmental regulation of isoform expression (and perhaps pathological regulation).

Question 30

Tropomyosin

Answer 30

only the alpha isoform is in the heart