RK Goit, Lecturer
Department of Physiology
Structure of Cardiac Muscle
Excitation-Contraction Coupling
Properties of Cardi...
• heart is composed of 3 major types of cardiac muscle:
atrial muscle, ventricular muscle, & specialized excitatory
& cond...
• cardiac muscle fibers arranged in a latticework, with the
fibers dividing, recombining, & then spreading again
• cardiac...
Cardiac Muscle as a Syncytium
• cardiac cells are so interconnected that when one of
these cells becomes excited, the acti...
properties of heart can be divided into 2 groups:
Beating heart Quiescent heart
• Automaticity
• Rhythmicity
• Contractibi...
Properties of cardiac muscle
• Automaticity
– capability of contract even in the absence of neural control
• Rhythmicity
–...
• Conductivity
– impulses produced in the SA node is conducted by the
specialized conducting pathway
• Distensibility
– oc...
• Long refractory period
• Extrasystole & compensatory pause
– when the ventricle is stimulated in the relaxation period
(relative refractory perio...
• All or none law
– if the heart is stimulated with subthreshold stimuli no response
is seen
– a threshold stimulus is the...
• Staircase phenomenon
– if a quiescent ventricle is stimulated repeatedly such that the
interval between consecutive stim...
• Length-tension relationship (Frank-Starling law)
– the force of contraction of cardiac muscle is directly proportional
t...
• Frequency force relationship
– changes in cardiac rate & rhythm also affect myocardial
contractility
• Load velocity relationship
References
• Ganong Review of Medical Physiology, 23/E
• Textbook of Medical Physiology, 12/E Guyton & Hall
• Understandin...
Thank You
Structure of cardiac muscle excitation contraction coupling properties of cardiac muscle
Structure of cardiac muscle excitation contraction coupling properties of cardiac muscle
Structure of cardiac muscle excitation contraction coupling properties of cardiac muscle
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Structure of cardiac muscle excitation contraction coupling properties of cardiac muscle

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Structure of cardiac muscle excitation contraction coupling properties of cardiac muscle

  1. 1. RK Goit, Lecturer Department of Physiology Structure of Cardiac Muscle Excitation-Contraction Coupling Properties of Cardiac Muscle
  2. 2. • heart is composed of 3 major types of cardiac muscle: atrial muscle, ventricular muscle, & specialized excitatory & conductive muscle fibers • atrial & ventricular types of muscle contract in much the same way as skeletal muscle, except that the duration of contraction is much longer • excitatory & conductive fibers contract only feebly • cardiac muscle fibers are made up of many individual cells connected in series & in parallel with one another
  3. 3. • cardiac muscle fibers arranged in a latticework, with the fibers dividing, recombining, & then spreading again • cardiac muscle is striated in same manner as in skeletal muscle • cardiac muscle has myofibrils that contain actin & myosin filaments almost identical to those found in skeletal muscle – these filaments lie side by side & slide along one another during contraction in the same manner as occurs in skeletal muscle
  4. 4. Cardiac Muscle as a Syncytium • cardiac cells are so interconnected that when one of these cells becomes excited, the action potential spreads to all of them, from cell to cell throughout the latticework interconnections • heart actually is composed of two syncytiums: the atrial syncytium, which constitutes the walls of the two atria, & the ventricular syncytium, which constitutes the walls of the two ventricles • division of the muscle of the heart into two functional syncytiums allows the atria to contract a short time ahead of ventricular contraction
  5. 5. properties of heart can be divided into 2 groups: Beating heart Quiescent heart • Automaticity • Rhythmicity • Contractibility • Excitability • Conductivity • Distensibility • Functional syncitium • Long refractory period • Extrasystole & compensatory pause • All or none law • The staircase phenomenon • Length-tension relationship • Summation of subminimal stimuli
  6. 6. Properties of cardiac muscle • Automaticity – capability of contract even in the absence of neural control • Rhythmicity – heart beats are extremely regular • Contractibility – cardiac muscle contracts in response to a stimulus • Excitability – ability of the cardiac muscle to respond to different stimuli
  7. 7. • Conductivity – impulses produced in the SA node is conducted by the specialized conducting pathway • Distensibility – occurs due to compliance of the cardiac muscle • Functional syncytium – due to the presence of numerous gap junctions
  8. 8. • Long refractory period
  9. 9. • Extrasystole & compensatory pause – when the ventricle is stimulated in the relaxation period (relative refractory period), the cardiac muscle may contract – It may occurs because a papillary muscle may fire an impulse before normal impulse reaches the ventricles
  10. 10. • All or none law – if the heart is stimulated with subthreshold stimuli no response is seen – a threshold stimulus is the weakest stimulus that evokes a response – amplitude of contraction in response to the suprathreshold stimuli remains the same as that with the threshold stimuli
  11. 11. • Staircase phenomenon – if a quiescent ventricle is stimulated repeatedly such that the interval between consecutive stimuli is less than 10 s, the first 3-4 contractions are progressively more forceful
  12. 12. • Length-tension relationship (Frank-Starling law) – the force of contraction of cardiac muscle is directly proportional to the initial length of the muscle fibers • Summation of subminimal stimuli – when subminimal stimuli are applied repeatedly, the stimuli summate & produce a response
  13. 13. • Frequency force relationship – changes in cardiac rate & rhythm also affect myocardial contractility
  14. 14. • Load velocity relationship
  15. 15. References • Ganong Review of Medical Physiology, 23/E • Textbook of Medical Physiology, 12/E Guyton & Hall • Understanding Medical Physiology, 4/E Bijlani & Manjunatha
  16. 16. Thank You

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