BM1042 Lecture Notes - Lecture 4: Cardiac Output, Qrs Complex, Autonomic Nervous System
Week 4
Describe the coordination of the cardiac muscle contraction
and control
• Heart is a muscle (cardiac muscle)
• The cardiac cycle (mechanical events)
• AV vales closed
• Blood returns to atria
• AV valves open
• Atria contract
• Blood fills ventricles (diastole)
• Atria relax
• Ventricle starts to contract, AV valves close (isovolumetric contraction)
• SL valves open
• Ventricle completes contraction
• Blood flows out through arteries
• SL valves close
• Ventricles relax
Screen clipping taken: 15/08/2018 11:03 AM
• Contraction of atria and ventricles is controlled by cardiac action potential
• Contraction of left ventricle opens AORTIC valve
• Cardiac conduction system is the coordinator
• Requires action potential for activation
o Action potential needs to flow in coordinated and sequential pattern so heart
beats properly
o Conduction system in heart allows for coordination and sequential
o Action potential NOT initiated by nervous system (like skeletal ms), initiated within
heart itself by PACEMAKER cells in sinoatrial node in atrium
• Pacemaker cells have unstable membrane potential
• Sometimes instability of membrane adds up to threshold -> action potential
-> flows through conducting system in heart
• Leads to contraction of cardiac muscle
• Beating sequence is ALWAYS atrium THEN ventricles
• AP travels through heart, can measure that as electrical output of heart
using electrocardiogram
▪ Waveforms can be used to see what's happening in heart
o Electrical activity in the heart flow order:
• SA node
• AV node
• Down intraventricular septum
• Up ventricle walls
Screen clipping taken: 15/08/2018 11:29 AM
• Cardiac output is static
• Setting/modification of rhythm of beat comes from autonomic nervous system input
• Cardiac output can be varied by changing
o Preload
o Afterload
o Contractility
o Autonomic nervous system input
o Sodium ion availability
Document Summary
Sometimes instability of membrane adds up to threshold -> action potential. Sa node: av node, down intraventricular septum, up ventricle walls. Screen clipping taken: 15/08/2018 11:29 am: cardiac output is static, cardiac output can be varied by changing. Setting/modification of rhythm of beat comes from autonomic nervous system input: preload, afterload, contractility, autonomic nervous system input, sodium ion availability. Screen clipping taken: 15/08/2018 11:29 am: qrs complex -> where atria would repolarise. If sa node taken out, av node would take over: p point would disappear. Contraction occurs just after depolarisation: e. g. after atrial depolarisation (p), contraction would occur between p and q. Explain the role of cardiac output in the maintenance of homeostasis. Cardiac output: the amount of blood pumped out of each ventricle per minute. Amount of blood pumped through heart per minute. Diastole = ventricles relaxed and filled with blood. Screen clipping taken: 16/08/2018 9:07 pm: co = stroke volume (sv) x heart rate (hr)
