lecture 9 Flashcards
describe action potentials of skeletal, nerve, and cardiac muscles
- Skeletal + nerve muscles- very short, discrete action potential
In cardiac, is bigger + plateaus at the top = longer repolarisation section, and a prolonged contraction phase
refer to onenote
why does the action potential of cardiac muscle have a plateau?
- Ensures adequate ejection time
- is contraction
- due to ca+ channels opening, allowing calium to come in, maintaining a positive charge
The plateau means wont be able to stimulate contractions so qucikly, allowing cardiac muscles to relax before restarting- constant contraction in heart would be BAD
describe ECGs
- Records the electrical events within the heart
- Voltameter records electrical potential across cells
On a graph, time is X-axis, amplitude is Y-axis (amplitude is proportional to no. + size of cells)
- Voltameter records electrical potential across cells
describe standard bipolar ECG limb leads
- Means that the electrical potential is recorded from 2 electrodes located on different sides of the heart
2 id larger then the others because the blood in the heart travels in the same direction as the electrodes, so the signal is going to be detected as the strongest in this arrangement
refer to onenote
describe the electrical activity of the heart
- Note electrical acitivity ALWAYS preceds mechanical response
- P-wave
○ First part
○ Depolarisation
○ Valve between the atria + ventricle opens - PQ
○ Ventricles fill with blood - Q
○ Little dip before peak starts
○ Depolarisation
○ Blood going through valve to next ventricle - R
○ Signal travels through apex
○ Atrial repolarisation
○ Ventricular contraction, pushed blood to rest of the body
○ Is the big peak - S
○ Other side of peak, little dip
○ Final depolarisation of ventricles - ST
○ Ventricles contract - T
○ Ventricular repolarisation - End
Membrane goes back to neg.
- P-wave
refer to onenote
define EDV
○ End diastolic volume
Blood bolume in the ventricle at the end fo DIASTOLE
define ESV
Blood bolume in the ventricles at the end of systole
define SV
○ Stroke volume
○ Volume of blood pumped from the left ventricle per beat
○ SV = EDV - ESV (ml)
§ Note:
□ EDV influenced by venous return (VR) (increasing VR = increasing EDV)
ESV influenced by inotropy (increased contractility = decreased ESV = increased SV)
define HR
○ Heart rate, beats/min
No. Of times per minute that the ventricles eject blood
define CO
○ Cardiac output, ml/min
CO = SV x HR (L/min)
Total blood flow being pumped by heart = cardiac output
what is preload
- Filling the pumps
- Preload- degree of stretch fo the ventricular walls by blood filling the ventricles
- Proprtional to EDV
- Depends on venous return (VR) to the heart
- Increased preload = increased EDV = SV
Relationship between preload + SV is called the frank-starling lae of the heart
explain Frank Starling law
- Uses the legnth-tension relationship
- Is the strength of contraction is related to the length of th emuscle when the contractions occur
- Increase heart filling stretches the cardiac muscle fibres more at the ened of diastole
- More cross-bridges = more force (contractility increases)
- Leads to more vigorous systolic contractions + icnreased SV
Myocardium cannot continue to stretch indefinitely
what is afterload
- Pumping blood out
- Afterload- amount of pressure that the ventricles must develop to opent the semilunar valve + eject blood into the arteries
- Depends on resistance ot blood flow out fo the ventricle
- Basically, si the back pressure exerted by the arterial blood on the semilunar valves
Increasing BP = icnrease afterload
define BP
- Is the force per unit area of blood pushing against the vessel walls that contain it (mmHg)
- BP is determined by
- CO
- PVR- peripheral vascular resistance
- BP is determined by
BP = CO x PVR
what is bradycardia
HR slower then normal
