Electrical Activity of the Heart Flashcards

1
Q

What can act as a large calcium store?

A

Sarcoplasmic reticulum

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2
Q

What does calcium bind to?

A

Troponin

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3
Q

Explain why cardiac muscle can act as a functional syncytium?

A

Cardiac muscle can function like one massive cell despite being composed of many different cells

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4
Q

State 3 ways in which cells are linked together.

A
  • Desmosomes
  • Intercalated discs
  • Gap junctions
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5
Q

Desmosomes provide what type of connection?

A

Physical connection

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6
Q

Gap junctions provide what type of connection?

A

Electrical connection

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7
Q

_____ muscle can exhibit tetanus while there is no tetanus in _____ muscle

A

Skeletal

Cardiac

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8
Q

Compare the length of the action potential of cardiac muscle with that of skeletal muscle.

A

Cardiac - 250 ms (longer because more calcium is released)

Skeletal - 2 ms (shorter)

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9
Q

State why cardiac muscle cannot exhibit tetanic contraction.

A

Cardiac muscle has a long refractory period (ensures heart fully relaxes and prevents tetanic contraction)

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10
Q

Why do you not want tetanic muscle contraction in your heart?

A

It would mean your heart would beat once and there would not be another one causing ASYSTOLE (cardiac arrest).

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11
Q

What forms the intercalated discs?

A

Desmosomes and gap junctions

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12
Q

Calcium saturation troponin

A

LATER

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13
Q

What do cells which have unstable resting membrane potentials act as?

A

Pacemaker cells (these produce the electrical impulses that cause your heart to beat)

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14
Q

Graph of non - pacemaker vs pacemaker potential:

A

INSERT HERE

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15
Q

What is responsible for the resting membrane potential of non-pacemaker action potentials?

A

The permeability of potassium ions (PK+)

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16
Q

What is responsible for the initial depolarisation in non-pacemaker action potentials?

A

Increase in permeability to sodium ions (PNa+)

17
Q

What is responsible for the plateau in non-pacemaker action potentials?

A

Increase in the permeability to calcium ions (PCa2+, L-type)
And a decrease in the permeability to potassium ions (PK+)

18
Q

What is responsible for the repolarisation in non-pacemaker action potentials?

A

Decrease in the permeability to calcium ions (PCa2+)

And an increase in the permeability to potassium ions (PK+)

19
Q

What is responsible for the action potential in pacemaker action potentials?

A

Increase in the permeability to calcium ions (PCa2+, L-type)

20
Q

What is the pacemaker potential (pre-potential) due to?

A
  • Gradual decrease in the permeability to potassium
  • Early increase in the permeability to sodium
  • Late increase in the permeability to calcium (T-type)
21
Q

State 7 modulators of electrical activity.

A
  • Sympathetic and parasympathetic systems
  • Temperature
  • Drugs
  • Hyperkalemia
  • Hypokalemia
  • Hypercalcemia
  • Hypocalcemia
22
Q

Drugs: What do calcium channel blockers do to modulate electrical activity?

A

Decrease force of contraction

23
Q

Drugs: What do cardiac glycosides do to modulate electrical activity?

A

Increase force of contraction

24
Q

How does temperature modulate electrical activity?

A

Increases the heart rate by 10 beats/min/degree

25
Q

How does hyperkalcemia modulate electrical activity?

A

Fibrillation and heart block

26
Q

How does hypokalaemia modulate electrical activity?

A

Fibrillation and heart block (anomalous)

27
Q

How does hypercalcemia modulate electrical activity?

A

Increased heart rate AND force of contraction

28
Q

How does hypocalcemia modulate electrical activity?

A

Decreased heart rate AND force of contraction

29
Q

List the sequence of events occurring during excitation-contraction coupling in cardiac muscle. (8)

A
  • An action potential enters from adjacent cell
  • Voltage-gated calcium channels open and calcium enter the cell
  • Calcium induces calcium release form the sarcoplasmic reticulum through ryanodine receptor channels, which causes calcium to spark
  • Summed calcium sparks create a calcium signal
  • Calcium ions then bind to troponin, which cause tropomyosin to detach from the actin filament, exposing the actin active sites
  • Contraction occurs, myosin cross bridges alternatively attach to actin and detach, pulling the actin filaments towards the centre of the sarcomere, release of ATP hydrolysis powers the cycling process
  • Removal of calcium by active transport into the sarcoplasmic reticulum after the action potential ends
  • Tropomyosin blockage restored on active sites, contraction ends and the muscle fibre relaxes