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health & disease > L26 - cardiac muscle > Flashcards

L26 - cardiac muscle Flashcards

1
Q

describe how cardiac muscle cells are arranged

A
  • interconnecting electrically coupled cells which act in a syncytium
  • cardiac cells separated from each other but still electrically coupled
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2
Q

1% of cardiac cells are?

A

non contractile

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3
Q

structure of cardiac muscle cell

A
  1. composed of branched interconnecting cardiomyocytes
  2. striated cells
  3. electrically connected via intercalated disc
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4
Q

what are the 2 types of electrical activity of cardiac muscle cells?

A
  • pacemaker potential
  • prolonged cardiac action potential
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5
Q

what is heart rate regulated by?

A

catecholamines

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6
Q

what is the functional unit of cardiac muscle?

A

sarcomere

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7
Q

cardiomyocytes (cardiac cells) are connected by intercalated discs, what does this allow?

A

allows them to work as a single functional syncytium

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8
Q

describe the intercalated discs that connect the cells

A
  1. interdigitating folds: infold at end of cells to increase SA of cell to cell connection
  2. mechanical junctions: fascia adherens & desmosomes
  3. electrical junctions: gap junctions
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9
Q

describe the fascia adheres (type of mechanical junction between intercalated discs)

A
  • couple the membrane to the actin cytoskeleton (contractile apparatus) of the cells
  • aids transmission of contractile force between cells
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10
Q

describe the desmosomes (type of mechanical junction between intercalated discs)

A
  • provide strong structural support between cells
  • makes sure cells can withstand contractile forces of heart
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11
Q

describe the electrical junctions for the intercalated discs

A
  • gap junctions electrically couple cytoplasm of neighbouring cells
  • coupling allows ions to move between cells
  • so cardiac A.P can spread
  • so heart muscle goes under depol
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12
Q

structure of gap junctions

A
  • hexamer made of connexions
  • forms gap junction of 12 subunits
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13
Q

what does the gap/electrical junction serve as?

A

a low resistance pathway between cells

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14
Q

what is cell-cell conductance?

A

electrical coupling

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15
Q

how many gap junctions represent gap junction plaque?

A

5-500

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16
Q

blood supply in cardiac muscle

A
  • needs continuous supply of oxygen
  • rich capillary supply
  • short diffusion distances for oxygen and waste products
17
Q

excitation contraction coupling

A
  • actin-myosin based contraction
  • fundamental unit is sarcomere
  • calcium initates contraction
  • regulated by troponin-tropomyosin compelex
18
Q

cardiac pacemaker cells

A
  • not by nerve stimulation like skeletal muscle
  • but by specialised cells called pace maker cells
  • which spontaneously generate A.P
  • primary pacemaker cells in SAN (upper right atrium next to superior vena cava)
19
Q

pacemaker A.P

A
  • Na+ enters via funny channel
  • calcium enters by t type calcium channel
  • more ca2+ enters by L-type calcium channel
  • K+ leaves by voltage gated potassium channel
20
Q

cardiac action potential

A
  • na enters by voltage gated na channel
  • ca2+ enters by L type calcium channel
  • K+ leaves by voltage gated k channel
21
Q

calcium induced calcium release

A
  1. L type ca channels open during cardiac A.P
  2. small amount of ca enter cell + triggers ryanodine receptor calcium channel in sr membrane to open
  3. ca released from sr + binds to troponin, so formation of cross bridge happens
  4. calcium goes back into sr by sarcoplasmic reticulum calcium ATPase (SERCA)
  5. na/ca exchanger exchanger removes calcium out of cell
  6. membrane depolarised by k channels at end of A.P
22
Q

troponin I

A

inhibitory

23
Q

Troponin C

A

calcium binding

24
Q

Troponin T

A

tropomyosin binding

25
Q

what are troponin?

A

skeletal and cardiac muscle isoforms

26
Q

what is used to detect myocardial infarction?

A

cardiac troponins (they are fragmented and released into blood when heart muscle is damaged)

27
Q

genetic cardiomyopathies

A
  • dilated cardiomyopathy (DCM) caused by mutations in genes
  • DCM causes dilation of left ventricle, contractile failure, loss of myofibrils etc

health & disease (19 decks)

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