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Anatomy test #2 (cardiac cycle)
Terms in this set (27)
What is cardiac cycle responsible for?
Pumping blood to the cells
When does tissue need more blood
Stress or exercise
Heart rate increases when;
Blood is needed
SA node = ____________ of heart
What does the pacemaker do?
Sends out action potentials for heart beat -w/o hormones 100bpm
What regulates the SA node?
Para and sympathetic ns
Where does the vagus nerve arise from?
Medulla oblongata & branches to SA and AV nodes
Nerves secrete Ach which;
Lessens rate of discharge of SA node and AV node (which lowers heart rate)
CN X = vagus nerve =
Brake for heart rate
parasympathetic nervous system does what to heart rate?
Changes it (impulse increases, heart slows and impulses decrease and heart speeds up)
Sympathetic fibers that go to nodes and myocardium
-fibers secrete NE (increases rate and force of contraction- thus stroke volume)
Where is cardiac center located?
Cardioinhibitor reflex center+cardio accelerator reflex center =
Purpose of cardiac center?
Maintains balance between inhibitory effects of parasympathetic fibers
Receptors from body send signals to cardiac center to tell the state of the
How does the cardiac center respond to signals?
Maintains and changes vagus and accelerator nerves discharged
Constant braking by vagus nerve
Pressoreceptors and baroreceptors are
Sensitive to changes in bp
Where are pressoreceptors and barroreceptors locates?
Aortic sinus and arch and in carotid sinuses
Bp increases, receptors stretch and send signals to cardioinhibitor center therefore;
The center sends parasympathetic impulses thru vagus nerve to heart, causing the heart rate and stroke volume to decrease
Receptors in vena cava stimulated if blood in heart is pushing back into the vena cava. This sends signals to accelerator nerves to push more blood out
What can affect heart rate?
Emotional states (pain ^ and grief decrease)
Temperature ( fever ^ or in surgery may put someone in hypothermic condition to lower it on purpose)
Ions also influence
Too little k ions
-can't keep repolarizations
Not enough ca ions
-depresses heart action
-not enough for normal depolarization
AP for Autorhythmic Cells
-rising membrane potential due to
•leaky NA channels
•decreased k permeability
RMP for autorhythmic cells;
Gradually increase to threshold (-40 mv)
-ca and na channels activated and rush in
-depolarized cells producing the AP
-100-150msec after opening, CA and NA channels inactivate and k channels open
•k diffuses out and repolarizes cell
(Hyperpolarizes cell to -55 mv because k channels take time to fully close)
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