Frog Heart Stimulation Flashcards
(33 cards)
Explain why the heart continues to beat after destruction of the spinal cord.
Because the heart depends on respiratory movements, not the central nervous system. The heart is kept in Ringer’s solution which contains electrolytes.
Label this frog heart diagram.
Where is the ‘pacemaker’ located in the frog heart and human heart?
Frog heart - Sinus Venosus.
Human heart - SAN.
What three effects does adrenaline have on heart rate?
- Increases heart rate.
- Increases atrial force of contraction.
- Increases ventricular force of contraction.
What effect does adrenaline have on the pacemaker of the heart?
It increases the activity of the pacemaker.
What receptors on cardiac muscles does adrenaline act upon?
β1 – adrenoceptors.
How does Acetylcholine (ACh) affect heart rate and why?
It slows down heart rate because it stimulates parasympathetic nerve fibres and acts upon the sinus venosus. It also slows down atrial contraction, but ventricular contraction remains the same.
What receptors on cardiac muscles does Acetylcholine (ACh) act upon?
Muscarinic acetylcholine receptors.
What enzyme does Physostigmine inhibit?
Acetylcholinesterase.
What effect does Physostigmine have on the heart when it works independently?
It decreases the heart rate very slightly.
What effect does Physostigmine and Acetylcholine have on the heart when working together?
The heart rate decreases significantly.
Atropine is a competitve inhibitor for what receptor?
The Acetylcholine muscarinic acetylcholine receptor.
What effect does Atropine have on the heart when it works independently?
It increases heart rate slighlty.
What effect does Atropine and Acetylcholine have on the heart when working together?
It brings heart rate to a normal rate.
What effect does temperature have on the heart? Why?
As temperature increases, heart rate increases. This is due to enzymes having higher kinetic energy.
Define poikilothermic.
They are cold blooded organisms whose temperature varies with the temperature of its environment.
Define refractory period.
The period during which a nerve or muscle is incapable of responding to stimulation, especially immediately following a previous stimulation.
Define absolute refractory period.
There is a total inability to respond.
Define relative refractory period.
There is a repsonse to very large stimuli.
What effect does electrical conduction have during ventricular contraction?
There is no effect as the heart is in a refractory period.
What effect does electrical conduction have during ventricular relaxation?
Ventricular contraction will take place once again.
Define extra systole.
Where another ventricular contraction takes place in what is meant to be ventricular relaxation.
Define compensatory pause.
A pause in the heartbeat following an extra systole that is long enough to compensate for the prematurity of the extra systole.
Out of skeletal muscle and cardiac muscle, which has the longest refractory period?
Cardiac muscle.
