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BSc module 1 > Cardiac muscle: Cells, structure & function > Flashcards

Cardiac muscle: Cells, structure & function Flashcards

1
Q

What are the cell types of the heart?

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

How many capillaries for each myocyte

A

> /=2 - V vascularised!

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3
Q

What forms inter-cell network?

A

Collagen

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4
Q

Which cell type makes up majority of cardiac tissue?

A

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

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5
Q

How many fibroblasts border each cardiomyocyte?

A

> /=1

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6
Q

Size of cardiomyocyte

A

30X100micrometres

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7
Q

Differences between cardiomyocytes and skeletal muscle

A

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

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8
Q

Histology of purkinje fibres

A

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

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9
Q

Size of purkinje fibres in relation to cardiomyocytes

A

Larger

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10
Q

What does ECM consist of

A

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

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11
Q

How are cardiomyoctes linked together?

A

Intercerlated discs

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12
Q

Types of cell junction in intercerlated disc

A
  1. Gap junction
  2. Fascia adherens junction
  3. Desmosomes
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13
Q

Purpose of IC disc

A
  1. Mechanical link for force

2. Electrical and chemical connection

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14
Q

What junction responsible for mechanical link in IC disc?

A
  1. Fascia adherens connect actins

2. Desomosomes connect intermediate filaments

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15
Q

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

A

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

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16
Q

Gap junction composition

A

Connexons - 1 from each cell

Each connexon has 6 connexins

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17
Q

How much of cardiomyocte is mitochondria?

A

30-40%

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18
Q

What is a t-tubule?

A

Invaginations of sarcolemma, at level of z disc

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19
Q

What happens to t-tubules in HF?

A

Disruption of t-tubule network

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20
Q

What is a sarcomere?

A

Repeating contractile unit of striated muscle

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21
Q

What is thick filament ban?

A

A band

22
Q

What is thin filament band?

A

I band

23
Q

What is in M band?

A

Thick filaments crosslinked

24
Q

Appearance of z-line and why?

A

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

25
Q

A band width

A

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

26
Q

Thin filament length

A

~1micrometre - not fixed in cardiac muscle

27
Q

Which bands/zones change size?

A

H and I

28
Q

Which bands/zones stay same size?

A

A

29
Q

Thick filament made of?

A

Myosin filament

30
Q

How does myosin molecule form filament?

A

Bipolar myosin filament structure

  • Antiparallel to form cerntral bare region
  • Parallel to form crossbridge region on either side
31
Q

Structure of myosin molecule

A

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)

32
Q

Thin filament made of?

A

Actin filament

33
Q

Actin filament structure

A

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

34
Q

How to make thin filament from actin?

A

Add tropomyosin and troponin

35
Q

What blocks myosin binding to actin at rest?

A

tropomyosin

36
Q

How is binding site of actin revealed?

A

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

37
Q

What do the 3 troponins bind to

A 
Troponin T (binds to tropomyosin)
Troponin C (calcium binding)
Troponin I (interface between the two)
38
Q

Crossbridge cycle - rigor

A

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

39
Q

Crossbridge cycle - ATP binding

A

Crossbridges come off and filament resets

40
Q

Crossbridge cycle - Relaxing

A

ATP release -> ATP and phosphate ion

41
Q

Weak binding

A

attached to actin . Only when ADP lost - contraction

42
Q

Cytoskeletal elements of sarcomere

A

Titin
M band
Z band
cMyBP-C

43
Q

Titin structure and function

A

Giant 3 MDa protein 1micrometre length

- forms template and responsible for resting elasticity

44
Q

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

A 
PEVK
Proline
Glultamate
Valine
Lysine
45
Q

Binding of titin to which bands

A

Z - disc
M band
Runs free in I band

46
Q

M -band structure and function

A

Compromises 3 stripes - M4’, M1, M 4

- Elasticity reorders the A band in relaxation

47
Q

Z - disc structure

A

Square lattice of actin. Mainly alpha-actinin

- Tethers opposite polarity actin filaments from adjacent structures - maintains order of thin filament

48
Q

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

A

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

49
Q

cMyBP-C structure and function

A

Organised on a disc and contacts actin

- may be a cardiac contraction regulation mechanism

50
Q

Mutations of cMyBP-C cause..

A

HCM

51
Q

Clinical use of cMyBP-C

A

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

BSc module 1 (9 decks)

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