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physiology for PHYSIOTHERAPY > Pacemaker potentials > Flashcards

Pacemaker potentials Flashcards

1
Q

Compare the **% of cells in the heart that are contractile or pace maker** cells

A
  • 99% of cardiac cells are contractile, they are responsible for the mechanical work of pumping
  • 1% of cardiac cells are pacemaker cells are specialised non contractile cells
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2
Q

What is the function of cardiac pacemaker cells?

A
  • they are responsible for triggering the contraction of cardiac muscle
  • exhibit automaticity - spontaneous rhythmic action potential generation
  • they set the rhythm of cardiac contraction
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3
Q

What is the main location in the heart that contains pacemaker cells? (dominant pace maker)

A

the Sino Atrial node (SA node)

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4
Q

What is the SA node regulated by?

A

regulated by
* the ANS
* circulating hormones

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5
Q

What are the** 2 types of Ca2+ channels** involved in the pacemaker potential?

A
  • T (transient) channel
  • L (long type) channel
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6
Q

what is the Na+ channel needed for the pacemaker potential?

A
  • Na+ (F)
  • funny channel
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7
Q

How many phases are there in the pace maker potential (SA node AP)

A
  • 4 phases
  • NO PHASE 1
  • 4,0,2,3
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8
Q

Describe what occurs during phase 4 of SA node AP?

A
  • An **Na+ influx **occurs through the Na+ funny channels
  • the F type channels are not selective between K+ and Na+, but Na+ entry is favoured (inward depolarising current)
  • delayed recitifier voltage activated K+ channels (Kv) inactivate which reduces the outflow of K+
  • opening of the voltage gated T-type Ca2+ channels
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9
Q

What are important exchanger channel that is involved in phase 4 of the SA node AP?

A

The 3Na+/Ca2+ exchanger

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10
Q

What does phase 0 involve?

A
  • the opening of the T type Ca2+ channels leads to a membrane depolarisation
  • this activates the** L type Ca2+ channels** which cause a** full depolarisation** of the membrane
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11
Q

What does phase 2 involve?

A
  • The T type channels close
  • the membrane begins to repolarise
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12
Q

What does phase 3 involve in the SA node AP?

A
  • The PREVIOUS depolarisation has opened 2 types of K+ channels
  • Ikr (rapidly activating delayed outward rectifiying current)
  • Iks (slowly activating delayed outward rectifying current)
  • The Kv channels activate slowly during the AP and also inactivate slowly
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13
Q

What are the** important anatomical parts** of the heart for the cardiac conduction system?

A
  • SA node
  • AV node (atrioventricular)
  • Bundle of his
  • Purkinje fibers
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14
Q

What is the function of the bundle of His?

A
  • The bundle of His is an important part of the electrical conduction system in the heart
  • they transmit impulses that are made in the AV node down to the ventricles
  • the bundle branches out into the left and right branch
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15
Q

What is the function of the purkinje fibers?

A
  • The purkinje fibers are extremely efficient at conducting action potentials from the pacemaker cells to the endocardium (the smooth membrane that lines the inside of the heart)
  • from the endocardium the impulses travel from myocyte to myocyte via gap junctions
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16
Q

What are intercalated discs?

A
  • they are structural formations found between cardiac muscle cells
  • they play a role in connecting them together and allowing the passage of signals between them
  • they contain desmosomes and gap junctions
17
Q

What are the 3 types of cell junctions that make up the intercalated disc?

A
  1. **Fascia adherens **(anchor actin filaments of the sarcomere)
  2. desmosomes (important for cell adhesion via cadherin plaques)
  3. gap junctions
18
Q

What is the function of the gap junctions within the intercalated discs?

A
  • they provide electrical coupling for adjacent cardiac muscle cells (allows ions to flow between cells)
19
Q

In summary, how does the SA node AP arise?

A
  • **inflow of Na+ **through F type channels
    * inflow of Ca2+ through T type channels and L type channels
  • decreased outflow of K+ through delayed rectifier (Kv) k+ channels
20
Q

In summary, what is the AP depolarisation phase (0) caused by?

A

It is caused by the inflow of Ca2+ through L type Ca2+ channels

21
Q

In summary, what is the repolarisation phase caused by (2) ?

A

The repolarisation phase is caused by
* the** K+ outflow** through delayed recitifer (Kv) K+ channels
* and the **closure of the L type Ca2+ channels **

22
Q

Why are the SA node action potentials smaller and slower rising than the ventricular AP’s in cardiac myocytes?

A
  • few fast Na+ channels
  • the Ca2+ current through L type channels depolarises the membrane SLOWLY in comparision with the influence of voltage gated Na+ channels in fast response cells

physiology for PHYSIOTHERAPY (25 decks)

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