What does a Nerve Stimulator allow us to assess?
- Muscle and neuron communication
- Depth of paralytic blocks
- NMJ status
It helps determine if the muscle can contract based on nerve stimulation.
What happens when an action potential is created in nerves?
- NMJ releases Ach
- Muscle responds based on NMJ status
- Electrical event followed by mechanical event
The response of the muscle depends on whether it is paralyzed or not.
If a muscle does not contract with a Nerve Stimulator, what could be the potential problems?
- Nerve problem
- Skeletal muscle problem
- Receptors problem
This indicates issues with the neuromuscular junction or the muscle itself.
What is a Phase II block in the context of paralytics?
- Longer recovery from non-depolarizing paralytics
- Drug clogging nAch channels
- Outcompeting Ach at receptors
This occurs when depolarizing drugs are administered over extended periods.
What happens to muscle twitches as the level of block increases?
- ¾ blocked: fourth twitch disappears- have 3 twitches
- 85% blocked: third twitch disappears- have 2 twitches
- 90% blocked: second twitch disappears-have 1 twitch
- 90-95% blocked: no twitches
This illustrates the relationship between the degree of neuromuscular block and muscle response.
What is the safety factor in neuromuscular junctions?
- High number of receptors
- Activation of 10% can produce contraction
This ensures that a significant amount of receptors must be blocked to achieve paralysis.
What is a Supramaximal stimulus?
Stimulus that guarantees enough muscle stimulation to generate a twitch
It ensures that the stimulus is sufficient to elicit a muscle response.
What are the three layers of the heart?
- Endocardium -inner most layer
- Myocardium- muscle
- Epicardium - outer most muscle
-pericardium -outer layer
What is the role of fibroblasts in heart tissue?
- Lay down scar tissue
- Replace dead or unhealthy cells
- Can impair heart function if excessive
Fibroblasts are crucial for healing but can lead to complications in heart failure.
What is a syncytium in cardiac tissue?
- Neighboring tissue acting together
- Example: 2 atria as one syncytium
- Efficient contraction
This coordination is vital for effective heart function.
What is the resting membrane potential (VRM) of SA node tissue?
-55 mV
This is the key number for initiating action potentials in the SA node.
What is the normal resting heart rate?
72 beats per minute
Athletes may have lower rates due to more efficient heart function.
What determines the heart rate during Phase 4?
- na permeability
-Time from resting to threshold potential= diastolic depolarization= pacemaker potential - Slope of Phase 4
- starting point
A steeper slope results in a faster heart rate.
-a higher point(vrm) results in faster heart rate
What effect does sodium permeability have on heart rate?
- More sodium: shorter time to threshold, increased HR
- Less sodium: longer time to threshold, decreased HR
Sodium influx during Phase 4 is critical for heart rate regulation.
What happens during repolarization in cardiac action potentials?
- Closure of Na+ and Ca++ channels
- Opening of K+ channels
This process resets the cell for the next action potential.
What is the absolute refractory period (ARP)?
Period during which a second stimulus cannot elicit another action potential
This occurs during the middle of the action potential due to none of the fast sodium channels being reset
What is the relative refractory period (RRP)?
Period after ARP where a stimulus can elicit an abnormal action potential
This can lead to premature contractions.
What is the relationship between slope and heart rate?
- Steeper slope = faster heart rate
- Gentler slope = slower heart rate
The slope affects the rate at which the heart can reach its threshold for action potentials.
How does sodium permeability affect heart rate?
- More sodium leaking in → shorter time to threshold → increased heart rate
- Less sodium leaking in → longer time to threshold → decreased heart rate
Sodium permeability plays a crucial role in the depolarization phase of action potentials.
What effect do high extracellular calcium levels have on heart rate?
Slows sodium entry → decreased heart rate
May have a higher force of contraction
High calcium levels can reduce the rate of depolarization, affecting heart rhythm.
How does a more negative resting membrane potential (VRM) influence heart rate?
- More negative VRM → longer Phase 4 → decreased heart rate
- Less negative VRM → shorter Phase 4 → increased heart rate
The resting membrane potential is critical for determining the duration of the action potential phases.
What is the effect of acetylcholine on heart rate?
- ACh activation → opens K+ channels → more negative VRM → decreased heart rate
- Atropine (ACh blocker) → less negative VRM → increased heart rate
Acetylcholine’s role in heart rate regulation is mediated through its action on muscarinic receptors.
Describe the phases of fast action potential.
- Phase 0: Fast sodium channel opening
- Phase 1: Brief repolarization
- Phase 2: Plateau (calcium influx, reduced potassium permeability)
- Phase 3: Repolarization (potassium channels reopen)
Fast action potentials are characterized by rapid depolarization and a distinct plateau phase.
What characterizes slow action potential?
- Phase 4: Steep slope, increased sodium and calcium permeability via hcn channels (funny Channels)
- Phase 0: Driven by calcium influx, slower upstroke (slow L type channels)
- Phase 3: Repolarization ( vg k channels)
- Phase 2: May not be clearly defined
Slow action potentials differ from fast ones in their reliance on calcium channels and lack of a plateau.
NO Fast Na channels
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Chapter One Guyton61
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Chapter 2 Guyton118
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Chapter 4 Guyton76
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Exam 1178
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Exam194
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LECTURE ONE109
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A And P Lecture 232
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A/P Normal Values33
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Lecture 3158
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Lecture 446
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Lecture 553
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Lecture 657
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Lecture 756
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Lecture 8110
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Lecture 960
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Lecture 1075
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Lecture 1154
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Lecture 1252
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Lecture 1346
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Lecture 1447
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Lecture 1538
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Lecture 1650
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Lecture 1758
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Lecture 1836
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Lecture 1931
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Lecture 2041
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Lecture 21 - Cardiac -ekg35
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Lecture 22 Cardiac Ekg 273
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Lecture 23 EKG 336
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Lecture 24 Ekg Plus Arrythmias40
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Lecture 25 Arrythmias And Blood Fluid Filtration38
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Lecture 26 Filtration And Absorbtion38
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Lecture 27 Filtration And Absorbtion 240
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Lecture 28 Renal Pressures/ ReAbsorption / Secretion35
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Lecture 29 Creatinine And Iv Fluids39
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Lecture 30 Kidney Anatomy38
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Lecture 31 - Proximal Tubule Transporters And Descending Loop Of Henle47
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Lecture 32 Ascending Loop Of Henle And Distal Tubule41
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Lecture 33 Rena Htn, Aldo54
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Lecture 340
