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Q9:
Why do we call our heart myogenic?
Solution :
1. Definition of Myogenic Heart
The term myogenic (from the Greek myo-, meaning "muscle," and -genic, meaning "originating from") refers to a heart where the rhythmic electrical impulses required for contraction are initiated by specialized cardiac muscle cells rather than by external nervous stimulation. [Per physiological definition of autorhythmicity].
2. Mechanism of Excitation
In humans and other vertebrates, the heartbeat is initiated by the Sinoatrial Node (SA node), located in the wall of the right atrium. This structure consists of specialized, modified cardiac muscle fibers known as pacemaker cells.
- Self-Excitation: These cells possess an unstable resting membrane potential, causing them to spontaneously depolarize to a threshold level without external input [Per the ionic theory of action potential generation in pacemaker cells].
- Propagation: The generated electrical impulse (action potential) spreads rapidly through the myocardium via gap junctions, ensuring a coordinated, wave-like contraction of the heart chambers.
3. Comparative Analysis: Myogenic vs. Neurogenic
| Feature | Myogenic Heart | Neurogenic Heart |
|---|---|---|
| Origin of Contraction | Modified cardiac muscle fibers | Central nervous system (ganglia) |
| Dependency | Independent of CNS; modulated by ANS | Dependent on neuronal impulses |
| Occurrence | Vertebrates (including Humans) | Most Annelids, many Arthropods |
4. Structural Representation of the Conducting System
5. Physiological Justification
The heart is termed myogenic because the primary drive for contraction is intrinsic. While the Autonomic Nervous System (ANS) can modulate the heart rate—increasing it via the sympathetic division or decreasing it via the parasympathetic division—it does not initiate the individual heartbeat. Removal of the heart from the body (if supplied with proper oxygenated, nutrient-rich physiological saline) results in the heart continuing to beat rhythmically, proving its myogenic nature [Per the principles of intrinsic autorhythmicity].
Final Solution: The heart is called myogenic because the stimulus for cardiac contraction is generated internally by specialized cardiac muscle cells within the SA node, rather than by impulses originating in the central nervous system.
More Questions from Class 11 Biology Body Fluids and Circulation EXERCISES
- Q1: Name the components of the formed elements in the blood and mention one major function of each of them.
- Q2: What is the importance of plasma proteins?
- Q3: Match Column I with Column II : Column I Column II (a) Eosinophils (i) Coagulation (b) RBC (ii) Universal Recipient (c) AB Group (iii) Resist Infections (d) Platelets (iv) Contraction of Heart (e) Systole (v) Gas transport
- Q4: Why do we consider blood as a connective tissue?
- Q5: What is the difference between lymph and blood?
- Q6: What is meant by double circulation? What is its significance?
- Q7(a): Write the differences between : (a) Blood and Lymph
- Q7(b): Write the differences between : (b) Open and Closed system of circulation
- Q7(c): Write the differences between : (c) Systole and Diastole
- Q7(d): Write the differences between : (d) P-wave and T-wave
- Q8: Describe the evolutionary change in the pattern of heart among the vertebrates.
- Q10: Sino-atrial node is called the pacemaker of our heart. Why?
- Q11: What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
- Q12: Define a cardiac cycle and the cardiac output.
- Q13: Explain heart sounds.
- Q14: Draw a standard ECG and explain the different segments in it.
CBSE Solutions for Class 11 Biology Body Fluids and Circulation
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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