Heart Activity Flashcards
What is the dicrotic notch?
Force of aortic valve snapping shut (pressure decreases blood flow/stops back flow)
What is the Pericardium?
Layer filled with fluid to let heart slip around
Why is the heart described as a double-pump?
4 chambered double pump
2x atrium/2x ventricle
Double circulation: from heart to lungs and from heart to tissues
Where does the hearts internal innervation come from?
Sinoatrial node: rear wall of atrium
- Pacemaker: regular discharge begins firing pattern of whole heart. Maintains about 120bpm, firing spreads excitation over atria
- Shown in P wave of ECG, begins contracting pushing blood to ventricles
Atrioventricular node: wall between atrium & ventricle
- discharge passes via AV bundle to ventricles
- Begins QRS complex
How is the heart externally innervated?
Parasympathetic: acetylcholine as transmitter
Creates vagal inhibition of SA node (reduces HR)
Vagal withdrawal may increase HR (when BP drops)
Sympathetic: norepinephrine transmitter
-HR increase via increasing rate of SA node discharge
Baroreceptor Reflex: controls HR and BP links
Low BP to change firing rate -> info to 9th cranial nerve-> caria -> makes SNS increase cardiac output
What is Respiratory Sinus Arrhythmia?
Natural cycle of arrhythmia from influence of breathing on flow of sympathetic and vagal impulses -> SA node
HR variability in synchrony with restoration
R-R interval shortened during inspiration and prolonged with expiration
How do you measure heart rate?
Electrocardiogram: Waller and then Einthoven
Standard= 12 ECG leads, Use Ag/AgCl electrodes to measure R-R in mV range
Prone to movement artefact
What is directional fractionation?
John Lacey: diff physical variables show difference directions of response in particular situation
Found evidence for:
- COG= increase HR, increase SCL
-PERC= decrease HR, increase SCL
What is the Intake-Rejection hypothesis?
HR and BP influence cortical activity and therefore affect sensitivity to stimuli
Cardiac deceleration facilitates stimulus “intake”
Cardiac acceleration facilitates stimulus “rejection”
Can Heart Rate be used as an index of the Orienting Reflex?
No (may think so because people often get it confused with intake-rejection)
Phasic HR deceleration response to OR type stimulus doesn’t habituate
Because: Lacey uses tonic changes for OR
Can Heart Rate be used as an index of Vigilance?
Maybe/yes
Barry and Tremayne: vigilance increased with HR deceleration
Using Tonic measure
