Study Guides (238,653)
Canada (115,282)
HK 2810 (37)

HK Midterm 3 Textbook Notes.docx

30 Pages
Unlock Document

Human Kinetics
HK 2810
Coral Murrant

HK3940Midterm 3 Notes Rhythmical Excitation of the Heart p 116124THE HEART generates electrical impulses to cause rhythmical contraction of the heart muscleconducts these impulses rapidly through the heart Atria first then ventriclesEXITATORY AND CONDUCTIVE SYSTEM OF THE HEARTSinus Node SA node where normal rhythmical impulse is generated AV Node where the impulse from the atria is delayed before being passed on to the ventriclesPurkinje Fibersconduct cardiac impulse to all parts of the ventricles 1 SA NODE specialized cardiac muscle in the wall of the right atriumalmost no contractile muscle filamentsfibers connect directly with atrial muscle fibers any AP beginning in the SA node will spread immediately to the atrial muscle wallcapable of self excitation causes automatic rhythmical contraction Resting membrane potential between 55 and 69mV less negative than ventricular muscle fiber90mV because it is leaky to Na and KImportant membrane ion channelsfast sodium channelsspike of AP in ventricular muscle rapid influx of sodium ionsslow sodiumcalcium channelsplateau of ventricular AP potassium channelsallows diffusion of large amounts K ions outward and returns membrane to resting level which is much less negativewhen the membrane potential falls below 55mV only the sodiumcalcium channels can open cause AP atrial nodal AP is slower to develop return to negative membrane potential is slow as wellfast for ventricular fiber Self Excitationhigh sodium ion concentrationoutside nodal fiberalready open sodium channelspositive ions from outside tend to leak inside slow rise in resting membrane potential between heartbeatsthreshold voltage 40mVactivation of sodiumcalcium channelsAPselfexcitation due to leakiness of membraneprevention of constant depolarization caused by leakiness 1 sodiumcalcium channels close2 potassium channels open large quantities of positive ions diffuse outwards bringing membrane pot Back to negative continued negativityhyperpolarizationIn Sum 1 selfexcitation causes AP 2 hyperpolarization after AP is over 3 drift of resting potential to threshold 4 reexcitation for another cycle Internodal Pathwaysends of the SA nodal fibers connect with atrial muscle fibers Aps travel through these and spreads through atrial muscle mass to AV nodeincreased velocity of conduction between nodes caused by Purkinje fibers of ventricles conduction fibers2 AV NODE organized so signal doesnt travel from atria to ventricles too quicklyallows time for atria to empty blood into ventricles before ventricular contractionAV node delays this transmissionin posterior wall of right atriumimpulse goes from SA node to AV node in about 003 seconds delay in the AV node of 009sec before entering AV bundletotal delay in AV node and AV bundle is 013 seconds 003sec016sec before reaching ventricular muscles Slow Conduction caused by diminished number of gap junctionsgreat resistance to conduction of excitatory ions 3 Purkinje Fibersfrom AV node through AV bundle to ventricleslarge fibers that transmit Aps at 15 to 4 msec almost instantaneous transmission of cardiac impulse to ventricular musclerapid transmission caused by high level of leakiness of gap junctions ions transmitted easily OneWay Conduction Through AV Bundle APs cant travel backwards from ventricles to atriaonly forward conductionatrial and ventricular muscle is separated by a continuous fibrous barrierinsulator for passage of cardiac impulse between atrial and ventricular muscleLeft and Right Bundle Branchesends of the fibers penetrate 13 of the way into the muscle mass then become continuous with cardiac muscle fibers in ventriclescardiac impulse enters purkinje system and spreads to entire ventricular muscle mass In Sum lapse between origin of cardiac impulse in SA node and appearance in the heart delay in AV nodal region about 1sec before appearing in ventricular AV bundlespreads through purkinje fibers to endocardial surfaces of the ventricles
More Less

Related notes for HK 2810

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.