Cardiac muscle: Cells, structure & function

Question 1

What are the cell types of the heart?

Answer 1

1. Contractile cells -cardiomyocytes
2. Conduction cells - e.g. Purkinje fibres
3. Endothelial cells - capillaries
4. Fibroblasts (ECM)

Question 2

How many capillaries for each myocyte

Answer 2

> /=2 - V vascularised!

Question 3

What forms inter-cell network?

Answer 3

Collagen

Question 4

Which cell type makes up majority of cardiac tissue?

Answer 4

Cardiomyocytes 2/3 volume
BUT
Endothelial and fibroblasts 2/3 cell number

Question 5

How many fibroblasts border each cardiomyocyte?

Answer 5

> /=1

Question 6

Size of cardiomyocyte

Answer 6

30X100micrometres

Question 7

Differences between cardiomyocytes and skeletal muscle

Answer 7

C: striated, joined end-end IC discs = electrical and chemical conduction = synctium. Mononucleated (cenrally located). Jagged edges for branching
S = long cylindrical shape and run along whole length of muscle. Multinucleated (nuclei at surface). Voluntary control

Question 8

Histology of purkinje fibres

Answer 8

Located in subendocardium. Connected by desmosomes and GJs but not IC discs

Question 9

Size of purkinje fibres in relation to cardiomyocytes

Answer 9

Larger

Question 10

What does ECM consist of

Answer 10

Non-myocyte cells (fibroblasts, endothelial cell), fibrillar collagen and blood vessels

Question 11

How are cardiomyoctes linked together?

Answer 11

Intercerlated discs

Question 12

Types of cell junction in intercerlated disc

Answer 12

1. Gap junction
2. Fascia adherens junction
3. Desmosomes

Question 13

Purpose of IC disc

Answer 13

1. Mechanical link for force

2. Electrical and chemical connection

Question 14

What junction responsible for mechanical link in IC disc?

Answer 14

1. Fascia adherens connect actins

2. Desomosomes connect intermediate filaments

Question 15

What junction responsible for electrical and chemical connection in IC disc?

Answer 15

Gap junction - flow of AP, equilibration, regulation and growth & development

Question 16

Gap junction composition

Answer 16

Connexons - 1 from each cell

Each connexon has 6 connexins

Question 17

How much of cardiomyocte is mitochondria?

Answer 17

30-40%

Question 18

What is a t-tubule?

Answer 18

Invaginations of sarcolemma, at level of z disc

Question 19

What happens to t-tubules in HF?

Answer 19

Disruption of t-tubule network

Question 20

What is a sarcomere?

Answer 20

Repeating contractile unit of striated muscle

Question 21

What is thick filament ban?

Answer 21

A band

Question 22

What is thin filament band?

Answer 22

I band

Question 23

What is in M band?

Answer 23

Thick filaments crosslinked

Question 24

Appearance of z-line and why?

Answer 24

Square lattice of actin filaments - v dense because lots of protein present

Question 25

A band width

Answer 25

1.6 micrometres (fixed across vertebraes/cardiac/skeletal muscle)

Question 26

Thin filament length

Answer 26

~1micrometre - not fixed in cardiac muscle

Question 27

Which bands/zones change size?

Answer 27

H and I

Question 28

Which bands/zones stay same size?

Answer 28

A

Question 29

Thick filament made of?

Answer 29

Myosin filament

Question 30

How does myosin molecule form filament?

Answer 30

Bipolar myosin filament structure - Antiparallel to form cerntral bare region - Parallel to form crossbridge region on either side

Question 31

Structure of myosin molecule

Answer 31

2 heavy chains and 2 pairs of light chains | C-terminus - alpha helical coiled rod S2 (backbone of filament) and N-terminus: head S1 (protruding)

Question 32

Thin filament made of?

Answer 32

Actin filament

Question 33

Actin filament structure

Answer 33

Banded appearance Myosin head S1 can only attach at 1 angle Dual stranded helix of actin monomers Polar - contraction only in 1 direction

Question 34

How to make thin filament from actin?

Answer 34

Add tropomyosin and troponin

Question 35

What blocks myosin binding to actin at rest?

Answer 35

tropomyosin

Question 36

How is binding site of actin revealed?

Answer 36

Ca binds to Tn-C, causes activation and induces rolling of TM, revealing binding site

Question 37

What do the 3 troponins bind to

Answer 37

``` Troponin T (binds to tropomyosin) Troponin C (calcium binding) Troponin I (interface between the two) ```

Question 38

Crossbridge cycle - rigor

Answer 38

ATP depletion - crossbridges attach to actin to form strong rigor complex

Question 39

Crossbridge cycle - ATP binding

Answer 39

Crossbridges come off and filament resets

Question 40

Crossbridge cycle - Relaxing

Answer 40

ATP release -> ATP and phosphate ion

Question 41

Weak binding

Answer 41

attached to actin . Only when ADP lost - contraction

Question 42

Cytoskeletal elements of sarcomere

Answer 42

Titin M band Z band cMyBP-C

Question 43

Titin structure and function

Answer 43

Giant 3 MDa protein 1micrometre length | - forms template and responsible for resting elasticity

Question 44

Important region in Titin and what is it's composition?

Answer 44

``` PEVK Proline Glultamate Valine Lysine ```

Question 45

Binding of titin to which bands

Answer 45

Z - disc M band Runs free in I band

Question 46

M -band structure and function

Answer 46

Compromises 3 stripes - M4’, M1, M 4 | - Elasticity reorders the A band in relaxation

Question 47

Z - disc structure

Answer 47

Square lattice of actin. Mainly alpha-actinin | - Tethers opposite polarity actin filaments from adjacent structures - maintains order of thin filament

Question 48

How is z-disc different between cardiac and skeletal muscle?

Answer 48

Cardiac: Wider z-disc than fast skeletal muscle - larger overlap with more alpha actin layers

Question 49

cMyBP-C structure and function

Answer 49

Organised on a disc and contacts actin | - may be a cardiac contraction regulation mechanism

Question 50

Mutations of cMyBP-C cause..

Answer 50

HCM

Question 51

Clinical use of cMyBP-C

Answer 51

After MI - fragments of it found in blood - could be faster than troponin