Cardiac Contractility/Pre/Afterload

Alpha motor, end-plate depolarization

Skeletal Muscle Contraction

• Each fiber is innervated by an __ __ neuron

• Motor neuron initiates an __-__ __ to trigger muscle action potential

Intercalated, gap junctions

Cardiac Muscle Contraction

• Fibers (cells) connected by __ discs

• Electrical current from adjacent cells travel through __ __ (electrical synapses) to trigger cardiomyocyte action potential

Pacemaker, contractile

Cardiac Depolarization is initiated by __ cells

Spreads through __ cells of heart via electrical synapses

SA, AV, atria, apex, upward

Cardiac Conduction/Electrical Cycle

• (1) __ node depolarizes

• (2) Electrical activity goes rapidly to __ node via internodal pathways

• (3) Depolarization spreads more slowly across __ (part of heart) → Conduction slows thru AV node

• (4) Depolarization moves rapidly thru ventricular conducting system to __ of heart

• (5) Depolarization wave spreads __ from apex

Rapidly, sustained, DHPRs, RyR

Unlike neurons/skeletal muscle cells → Cardiac action potentials: 

• __ reach threshold (phase 0), and have a __ plateau (phase 2)

• Use L-Type Ca2+ Channels = __s

  • Ca2+ influx → __ (channel) opening → Ca2+ release

Phase 0

Rapid Na+ influx thru open fast Na+ channels (Card AP)

Phase 1

Transient K+ channels open and K+ efflux returns TMP to 0 mV (Card AP)

Phase 2

Influx of Ca2+  thru L-type Ca2+ channels electrically balanced from K+ efflux thru delayed rectifier K+ channels (Card AP)

Phase 3

Ca2+ channels close but delayed rectifier K+ channels remain open and return TMP to -90 mV (Card AP)

Phase 4

Na2+, Ca2+ channels closed, open K+ rectifier channels keep TMP stable at -90 mV (Card AP)

Brief, summation

Skeletal muscle refractory period

• __ action (brief/long); facilitates __ation/tetanus

Long, diastole

Cardiac muscle refractory period

• __ action (brief/long); facilitates __ (filling chambers with blood)

SERCA, Na/Ca2+ enhancer

• Both Cardiac and Skeletal muscle relaxation rely on

  • __ pumps Ca2+ back into sarcoplasmic reticulum

• Only in Cardiac muscle relaxation is also

  • __/__ __ (NCX): Pumps Ca2+ out of cells

Ejection fraction, stroke volume

• The __ __ (ratio of heart) is directly related to cardiac force production

  • More forceful contraction means a greater __ __ (measure of cardiac force)

Myocardial fiber length, contractility

Cardiac force is affected by (2) factors

B1, S, AC, cAMP, adenyl cyclase, A, contraction

Positive ionotropic effect

• __ receptors on cardiomyocytes (ANS)

• G_ protein

• Activate __ + __ (2nd messengers)

• Protein kinase _

• Increase muscle __ (action)

Stretches, myofilament, stroke volume, cross-bridges

Frank-Starling Law

• As ventricle fills in diastole, it __

• Lengthening of myofiber optimizes__ overlap and increases contraction force (i.e. __ __)

• Overstretch in myofiber → Dysfunction

  • overworking actin and myosin filaments barely form __-__ with low overlap from overstretch

Preload, diastolic, diastolic

__load is the degree of ventricular stretch (due to volume)

• It is estimated by the end-__ volume and end-__ pressure (systolic vs diastolic)

Sarcomere, calcium

Increasing __ length also makes cardiac muscle more sensitive to __ (ion) → Increasing contractility

Catecholamines, ionotropic, lusitropic

__ (neurot class) alter ionotropy and lusitropy

• More forceful contractions favor positive __tropic effect

  • Increase opening of DHPRs → Increase Ca2+ influx and release (via RyR)

• Faster relaxation favor positive __tropic effect

  • Increase SERCA activity → Increase Ca2+ reuptake

Preload, contractility, afterload

__load and myocardial __ have a positive feedback effect to stroke volume

__load on the other hand has a negative feedback to stroke volume

Afterload

Force ventricle must overcome to circulate blood ; load against which heart ejects blood

Systolic, stenosis

• Elevated__ BP → greater afterload

• Resistance - Aortic __ (valve disease) → greater afterload

Afterload, O2, ATP

To overcome increased __ (pressure) and maintain cardiac output, heart must work harder: Increase __ and __ consumption for heart tissues

Increase in preload

Increase in afterload

failure, preload, normal curve

A = heart __ due to poor __load

B = __