Electrical and mechanical properties of heart muscles and phases of cardiac cycle- cardio-physio.ppt

Electrical and mechanical properties of heart muscles.

1. Electrical and
Mechanical
Properties of
Heart Muscles
and Phases of
Cardiac cycle

3. Cardiac muscle = myocardium
Combines features of skeletal and smooth muscle.
Specialized for continuous, rhythmic contraction.
Shows both electrical and mechanical activity.
Found only in the walls of the heart.
The heart muscle is a unique tissue designed for endurance and
coordination.
It has properties that allow it to beat over 100,000 times per day
without tiring.
The myocardium helps the heart contract and pump blood to the
whole body.
It works involuntarily (without conscious control) and continuously,
even during sleep.
Heart muscle cells are branched, have one nucleus, and are connected
by intercalated discs which help the heart beat in a coordinated way.

4. Characteristics of Cardiac
Muscle Tissue
•Striated like skeletal muscle, but
involuntary like smooth muscle.
•Composed of branched cells with
one or two central nuclei.
•Contains intercalated discs –
specialized connections between cells
that allow rapid signal transmission.
•Rich in mitochondria for continuous
energy production.
•Controlled by the autonomic
nervous system and pacemaker
cells.

5. Types of Cells in Heart Muscle
CONTRACTILE CELLS
•Function: Responsible for pumping action of
the heart.
•Make up about 99% of heart muscle cells.
•Do not initiate impulses but respond to them.
•Generate force through synchronous
contraction.
•Found mainly in atria and ventricles.
•Contain actin and myosin for contraction.
•Connected by intercalated discs to allow
coordinated beating
CONDUCTING CELLS
OR (AUTORHYTHMIC)
•Function: Generate and conduct electrical
impulses.
•Make up about 1% of heart muscle cells.
•Have automaticity – can self-generate action
potentials.
•Do not contract strongly – they are mainly
electrical
•Found in specialized areas of the cardiac
conduction system

6. The cardiac conduction system is the heart’s electrical
wiring system. It’s made up of specialized cells and
structures that generate and carry electrical impulses,
which control the rhythm and rate of your heartbeat. This
system ensures that your heart beats in a coordinated and
efficient way to pump blood throughout your body.
Each time your heart beats, electrical signals travel
through your heart. These signals cause different parts of
your heart to expand and contract. These actions regulate
blood flow through your heart and body.

7. What are the parts of your heart’s
conduction system?
The conduction system in your heart
contains specialized cells and nodes that
control your heartbeat.
These are the:
•Sinoatrial node
•Atrioventricular node
•Bundle of His (atrioventricular bundle)
•Purkinje fibers
Your cardiac conduction system sends
signals through your heart to tell it
when to beat.

8. •Sinoatrial (SA) Node -
Known as the heart’s natural
pacemaker, it’s located in the
right atrium. It starts the
electrical impulse that makes the
heart beat.
•Atrioventricular (AV) Node -
Located between the atria and
ventricles, it delays the signal
slightly to allow the atria to
contract before the ventricles.
•Bundle of His -
This pathway carries signals
from the AV node down to the
ventricles.
•Right and Left Bundle
Branches –
These branches carry the signal
through the ventricles.
•Purkinje Fibers –
These fibers spread throughout
the ventricles and cause them
to contract.
Key Components of the Cardiac Conduction System:

9. SA Node (Sinoatrial Node)
↓
Atria Contract
↓
AV Node (Atrioventricular Node)
↓
Bundle of His
↓
Right & Left Bundle Branches
↓
Purkinje Fibers
↓
Ventricles Contract
Electrical Impulse Pathway

10. ELECTRICAL PROPERTIES
Heart generates and conducts electrical impulses
PROPERTY DESCRIPTION
Automaticity
Ability to generate impulses without external
stimulus
Generates impulses without nerve input
Conductivity
Rapid spread of impulses via gap junctions
Conducts impulses from cell to cell
Excitability
Responds to stimuli by generating action
potentials
Responds to stimuli (like an electric signal)
Refractoriness
Rest period after an impulse
Time during which the heart muscle cannot be
re-excited
Rhythmicity
Regular generation of impulses (esp. SA node)
Beats in a regular rhythm

11. •These properties ensure the heart beats on its own and in a coordinated fashion.
•The electrical signals originate in the SA node and spread through the conduction
system.
•These properties ensure orderly depolarization and contraction.
•Refractoriness is vital for avoiding sustained, non-relaxing contractions
•SA node = natural pacemaker of the heart
•Impulse travels through AV node, Bundle of His, Purkinje fibers
•Causes coordinated contraction of atria and ventricles
•Maintains normal heart rhythm (sinus rhythm)
•Important ions: Na , K , Ca²
⁺ ⁺ ⁺

12. MECHANICAL PROPERTIES
Heart muscle contracts to pump blood
PROPERTY DESCRIPTION
Contractility
Forceful contraction when stimulated
Heart muscle contracts to pump blood
Elasticity Ability to stretch and return to original shape
Tension
Generates active tension via sarcomeres
Creates force for pumping
Intercalated Discs
Mechanical & electrical connection between cells
Connect cells, allow smooth contraction
Fatigue Resistance
High endurance due to many mitochondria
Does not get tired easily

13. •Mechanical function is tightly linked to electrical activity.
•The heart adapts to workload while avoiding fatigue
•Contractility depends on calcium and sarcomere length.
•Intercalated discs ensure the heart functions as a syncytium (unit)
•Muscle is striated (like skeletal muscle)
•Has many mitochondria – produces energy
•Works non-stop throughout life
•Helps maintain blood flow and pressure

14. What is the Cardiac Cycle?
•The cardiac cycle describes a whole heartbeat from
its onset to the start of the following pulse. It
consists of the diastole, the systole, and the interval
in between. A heart rate, which is normally
expressed as beats per minute, serves as an
example of how a cardiac cycle occurs.
•It includes the contraction and relaxation of the
atria and ventricles.
•There are 72 cardiac cycles per minute for a
healthy human heart, or 72 beats per minute.
•Duration: ~0.8 seconds in a healthy adult.
•Purpose: To pump blood efficiently through the
heart and to the body.

15. PHASES OF THE CARDIAC CYCLE
•Atrial Systole (0.1 sec):
•Atria contract
•Blood pushed into ventricles
•Ventricular Systole (0.3 sec):
•Ventricles contract
•Blood pumped into the aorta and
pulmonary artery
•Diastole (0.4 sec):
•All chambers relax
•Blood flows passively into atria and
ventricles

16. Phase 1 – Atrial Systole
•Both atria contract due to depolarization (P wave in ECG).
•This contraction pushes the remaining 20–30% of blood into the
relaxed ventricles (ventricles are already partially filled
passively).
Valves Status:
•AV valves (tricuspid & mitral): Open
•Semilunar valves: Closed
Importance:
•Atrial systole ensures maximum filling of the ventricles before
they contract.
ECG: P wave
Duration: ~0.1 seconds

17. Phase 2 – Ventricular Systole
Divided into two parts:
a. Isovolumetric Contraction
•Ventricles begin to contract, but all valves are closed.
•This increases intraventricular pressure sharply.
•No change in blood volume ("iso" = same, "volume" = volume).
b. Ventricular Ejection
•When pressure in ventricles exceeds pressure in arteries, semilunar valves open.
•Blood is ejected into:
•Aorta (from left ventricle)
•Pulmonary artery (from right ventricle)
Valves Status:
•AV valves: Closed
•Semilunar valves: Open
ECG Correspondence: QRS complex (ventricular depolarization) and T wave
(repolarization)
Duration: ~0.3 seconds

18. Phase 3 – Diastole (Relaxation)
Also called Joint Diastole (atria + ventricles relax).
This phase also has two parts:
a. Isovolumetric Relaxation
•Ventricles begin to relax after ejection.
•All valves are closed, so no blood enters the ventricles yet.
•Intraventricular pressure drops rapidly.
b. Ventricular Filling
•Once ventricular pressure falls below atrial pressure, AV valves
open.
•Blood flows passively from atria to ventricles (about 70% of
filling).
•Atrial systole later completes the remaining 30%.
Valves Status:
•AV valves: Open
•Semilunar valves: Closed
Duration: ~0.4 seconds

19. Heart Sounds (S1 & S2)
•S1 ("Lub"): Closure of AV valves
(beginning of ventricular systole)
•S2 ("Dub"): Closure of semilunar valves
(end of ventricular systole)

20. Clinical Relevance
•SA Node Dysfunction → Bradycardia (slow heart rate)
•AV Node Block → Heart Block (may need pacemaker)
•Abnormal Rhythm → Arrhythmias (like atrial fibrillation)
•ECG Changes → Help detect heart attacks, electrolyte imbalances
•Weak Heart Muscle → Heart Failure (less pumping capacity)
•Valve Problems → Heart Murmurs (extra sounds heard)
•S1 & S2 Sounds → Used to check valve function
•Frank-Starling Law → Fails in advanced heart failure
•Ion Imbalance (K , Ca² ) → Can cause irregular heartbeat
⁺ ⁺
•Pacemakers/Defibrillators → Support in rhythm disorders