Exam 4 - Cardiac Potentials & ANS Flashcards
What does cardioplegia do
- Stops heart by decreasing [K] gradient…stops flow of K out of cell…..holding heart in a depolarized state
- Keeps K channel gates from resetting
Cardiac Action Potentials
- Very fast….happen in cardiac cells
- Created by changing permeability of Na, K, Ca channels
Phase 0
- Depolarization
- Big increase in Na permeability
- Na rushes into cell making more +
Phase 1
- The overshoot at top of peak (due to excess Na into cell)
- Na permeability DECREASE
- Ca permeability INCREASE
- K permeability STARTS INCREASE
Phase 2
- Plateau phase (pronounced in cardiac cells)
- Caused by increase Ca into cell
- Na permeability back to normal
- K permeability continues to increase (K moves out)
Which ion is needed for actual muscle contraction
- Ca
- In fast action potential cells only
Phase 3
- Repolarization phase
- Ca permeability back to normal
- Na permeability back to normal
- BIG INCREASE in K permeability
Phase 4
- Normal resting potential….cell is polarized
- RMP for cardiac cells is -90 mV
- RMP in muscle cells is stable
- RMP in SA/AV node is NOT stable
- Leaky Na channels slowly depolarize cell at phase 4
- Eventually trigger Action Potential
Speed of Muscle cells AP
Fast
Speed of AP in SA/AV node
- Slow
- Also a slowly depolarizing phase 4 (automaticity)
- Ca drives this slow depolarization
- No plateau in slow cells because Ca doesn’t contribute to contraction
Absolute refractory
- Not able to generate action potential
Relative refractory
- If given enough voltage…can cause AP
Supranormal refractory
- Smaller than normal voltage can cause AP
How is AP conduction velocity determined
- Diameter of fiber (AV is small…Purkinje are big)
- Intensity of local depolarization
- Resistance of cell junctions
Which node is pacemaker of heart
- SA node….doesn’t have to be but usually is
- Steepest phase 4 slope
What does AV node do to AP
- Slows it down
- Makes sure Ventricles can fill all the way
- Slow due to small size of cells
PR Interval
- Conduction time through atria and AV node
QT interval
- duration of ventricular systole
Velocity of AP in Atrial muscle
0.3 m/s
Velocity of AP in Internodal pathways
1.0 m/s
Delay in AV node and AV bundle system
0.13 seconds
Velocity of AP in Purkinje
1.5 - 4.0 m/s
Velocity of AP in Ventricular Muscle
0.3 - 0.5 m/s
Intrinsic rate of SA node
100 bum
Intrinsic rate of AV node
40 - 60 bpm
Intrinsic rate of Purkinje
15 - 40 bpm
What innervates the nodes
- Both the sympathetic and parasympathetic
What innervates the cardiac muscle
- Sympathetic
Parasympathetic fibers release what
- Ach
- Interacts with muscarinic receptors
- Changes RMP and phase 4 slope
- Increase K permeability in RMP
- Decreases Na permeability
- Decrease HR
Sympathetic fibers release what
- Norepi
- Interacts with B-1 receptors
- Changes slope of phase 4 only
- Increases Na and Ca permeability
- Increase HR
Chronotropic
- Affects HR
- High Ca tends to decrease HR
Dromotropic
- Affects conduction velocities
- High sympathetic tone increases velocity (affects AV node)
ANS control centers
- Spinal cord
- Brain stem
- Hypothalamus
- Visceral reflexes
Which vessels innervated by ANS
Arterioles
Hypothalamus controls…
- Food control
- H2O balance
- Temp. regulation
- All parasympathetic things
Brain stem controls….
- Bladder
- Pneumotaxic
- Cardiac speed up
- Cardiac slow down
- Respiratory center
Effector organs controlled by….
- Either sympathetic or parasympathetic….not both
Sympathetic neuron set up
- Short pre-ganglionic (Ach)
- Long post-ganglionic (Norepi)
- Fibers originate from T1 to L2
Paravertebral sympathetic ganglion chains
- two of them
- run either side of spinal cord
- can move message up and down chain
- once message received….3 transmission options
3 paravertebral ganglion chains transmission options
- synapse directly with post-ganglionic fibers
- pre-ganglionic to ciliac/hypogastric ganglia to post-ganglionic
- through sympathetic chain to adrenal medulla
Parasympathetic neuron setup
- Long pre-ganglionic (Ach) (pass all the way to organ)
- Short post-ganglionic (Ach) (located in wall of organ)
- Arise from Cranial nerves 3, 7, 9, 10…and 2-3 sacral nerves
- 75% of parasympathetic nerves are in 10
Synapse structure
- Mitochondria: make ATP for transmitter production
- Vesicles: store transmitters
- Cleft: space between
- Presynaptic terminal has voltage gated Ca channels
Transmitter release steps
- AP reaches Ca channels and activates them
- Ca rushes in to the terminal end
- Stimulates release of transmitter into cleft
- Amount of transmitter released proportional to amount of Ca
Receptor protein structure
- Outside Binding portion
- Transmembrane ionophore portion
- ionophore part can be ion channel (short term effects)
- or second messenger activator (long term effects)
Types of ion channel receptors on post-synaptic membrane
- Cation: think Na / tends to be excitatory (depolarize)
- Anion: think Cl / tends to be inhibitory (hyperpolarize)
Second messenger ionophore
- G-protein
- 3 proteins grouped on inside
- Alpha part is activator
- Beta and Gamma stay put
4 actions of alpha component
- Open ion channels
- Activate cAMP
- Activate enzymes
- Activate gene transcription
-All activate actions happen at effector organ site
Cholinergic fibers
- Release Ach
Adrenergic fibers
- Release norepi
Ach
- Parasympathetic transmitter
- Acetyl CoA + Choline = Ach
- needs choline acetyltransferase - Removed by acetylcholinesterase degradation
- choline end product transported back into terminal for recycle
Norepi sympathetic post-ganglionic exceptions
- Sweat glands, some blood vessels, pilorector muscles release Ach
Norepi production
- Tyrosine -> Dopa -> Dopamine
- Dopa -> Dopamine done in vesicles - In adrenal medulla… 80% converted to Epi….20% remain norepi
Norepi removal (3 ways)
- 50-80% moved back into terminal via active transport
- Most of the rest diffuse away
- Small amount destroyed by enzymes in liver
Norepi active time
- Several seconds unless released by adrenal medulla….then 10-30 seconds.
- 1-3 minutes to go away completely
Two types of Cholinergic receptors
- Muscarinic: on effector organ innervated by parasympathetic post-ganglionic fibers
- Nicotinic: on neuromuscular junction of muscles and postganglionic fibers of all ANS fibers
Two types of adrenergic receptors
- Alpha: 1 and 2 (affected by Norepi and Epi)
- Beta: 1, 2, and 3 (affected by Epi)
- Both can be either excitatory or inhibitory (depends on organ)
Tone
- # of impulses
- How active system is
- 1 impulse/second will maintain
- 10-20 impulse/second will fully activate
Systemic arterioles diameter
- Kept at 1/2 of normal diameter by sympathetic tone
Normal adrenal medulla tone
- 0.05 Norepi
- 0.2 Epi
- ug/kg/min
- Note if all sympathetic innervation lost…basal secretion of these two would maintain normal arterial blood pressure
- Sympathetic tone is combo of neural (synapse) and humoral (adrenal)
Alpha 1 receptors function
- vasoconstriction
- intestinal relax
- iris dilation
- bladder constriction
Alpha 2
- inhibits neurotransmitter release
Beta 1
- Increase HR
- Increase strength
Beta 2
- Vasodilation
- intestinal relax
- bronchodilation
Beta 3
- Thermogenesis
Parasympathetic effects
- Slow HR
- Dilate heart/lung vessels
- Constrict bronchi
- Increase gut activity
- Glycogen synthesis
