Question

1. A. Compare the action potentials observed in cardiac muscle and skeletal muscle.

B. Then describe the action potential associated with the sinoatrial node.

C. Describe the conduction system of the heart.

2.A. State the equations used to determine SV and CO. State the average values for all components.

B. What happens to stroke volume when: i. ESV increases and decreases ii. EDV increases and decreases iii. increased sympathetic innervation iv. increased parasympathetic innervation v. afterload increases and decreases

C. Describe the RAS system that is activated when BP decreases in afferent arterioles supplying the glomerular capsule.

Answer 1

1. A)

	skeletal muscle	cardiac muscle
Membrane potential	- 70 mV	-90 mV
Ion channel for reaching threshold	Na+ entry by ACh channel	Depolarisation through gap junction
Depolarisation	Na entry	Na entry
Repolarisation	Rapid; by K+ efflux	Prolonged with plateau caused by Ca2+, entry ; rapid phase by efflux of K+
hyperpolarisation	By excessive K+ efflux	none
Refractory period	Small	Long

Action Potential of SA node : SA node is the pacemake of the heart with its intrinsic firing rate of approx 100-110/min.

- Prepotential phase (Phase 4) - The resting membrane potential of SA nodes oscillates between -60mV and -40 mV. It is also called as "Spontaenous diastolic depolarization". Ion responsible - Decrease in K+ current, Funny curret (If) & Influx of calcium ions by T type of calcium channel

Depolarisation phase (phase 0) : Primarily by relatively slow, inwar Ca++ currents throug L-type calcium channel

Repolarisation phase (phase 3) : Primarly by efflux of k+ by delayed rectifier potassium channel,

c) conduction system of heart : SA node --> three inter nodal pathway --> AV node --> Bundle of Hiss --> right and left bundle branch --> purkinje fiber --> ventricular myocardium

2)

A) Cardiac Output = Stroke volume x Heart Rate

Stroke volume = end diastolic volume - end systolic volume

In a avrage male, EDV = 120 ML; ESV = 50 ML & HR = 72/MIN

SV = 120-50 = 70 ML

CO = 70 X 72 = 5040 ML/min i.e. Approx 5 liter/min

B)What happens to stroke volume when:

i. ESV increases and decreases - Stroke volume = end diastolic volume - end systolic volume

ESV increses = stroke volume decreases, ESV decreases - stroke volume increases

ii. EDV increases and decreases -

EDV increses = stroke volume increases, EDV decreases - stroke volume Decreases

iii. increased sympathetic innervation - Increases stroke volume

iv. increased parasympathetic innervation - Decreases stroke volume

v. afterload increases and decreases

3) RAAS System :

When blood pressure is decreased, it leads to decreased delivery of NaCl to the DCT, which is sensed by the macula densa cells --> which stimulate Juxta glomerular apparatus --> secrete Renin --> Increases angiotensin II and aldosterone --> Increases salt and water retention & also vasoconstriction by Angiotensin II normalises the blood pressure.