L5.3 Neural control of the heart Flashcards Preview

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Flashcards in L5.3 Neural control of the heart Deck (10):
1

Electrical conduction pathway

  • SA → AV → Bundle of His → Purkinje fibres
    • AP spreads passively through neighbouring gap junctions

2

Cardio ventricular AP

  • (1 AP = 1 contraction)
  • Fast Na channel opens
  • L type channels close
  • L type channels open
  • K channels open
  • Stable RMP

3

Intrinsic pacemaker AP

  • Threshold = -40
  • No fast Na current
  • T-type Ca channel
  • I-funny (I-f) channels open Na entry
    • T-type & I-f channels propagates AP to threshold → I-f closes & L-type Ca opens → Ca influx (depol) → K channel opens (repol)

4

Which is the dominant pacemaker?

  • Most cardiac cells capable of becoming pacemaker 
  • Normally cells in SA that is fastest takes lead (well connected together)
  • Depol & injured cells risk becoming ectopic pacemaker → causes arrthymia 
    • E.g. Fom ischemia

5

Autonomic innervation dominance

  • Blocks NS to the heart → Nerves might regrow but not necessarily → usually leads to increase SNS or PNS depending on dominance
    • I.e. if all N are cut in situ and an increase in HR is exhibited → Means PNS was dominant before (ACh > NA)
    • Dominance of PNS increases with training

6

Sympathetic regulation

  • INcrease Ca depol current
  • NA activates G-protein signaling → change in conformation
  • Mech:
    • GTP binds to a-subunit → dissociates from b & gamma subunit → activates adenylyl cyclase → generates cAMP → Phosphorylate and stimualtes I-Ca (T&L channels) & I-f → Net Na flux 

7

PNS regulation

  • Increase hyperpol K current → slower depol
  • GTP binds to a-subunit (Gai) → dissociates from b & gamma subunit → b & gamma binds K-channels → directly increase conductance (NO SECONDARY MESSENGERS)

8

Refractory period

  • Unresponsive to stimuli
  • Skeletal muscles refractory period ~10ms
    • Period not as important →force generated through tetanus
  • Cardiac muscle refractory period ~250ms
    • AP is longer from incoming Ca before K repol
  • Refractory period due to:
    • Delay inactivation of L-type Ca channel
    • Protects against early re-excitation
    • Allows 1 AP = 1 contraction 

9

Baroreceptor reflex

  • High pressure R at aortic arch & carotid sinus → controls BP 
  • Stretched → Decrease BP (Vice versa)

10

Bainbridge reflex

  • Low range pressure R, controls BV
  • Atria, pulmoanry A, RV
  • Increases VR = increased stretch → renal vasodilation → increase urine → decrease BV → decrease stretch of R