Chapter 18 · Class 11-12 & NEET
Locomotion & Movement
36 topics in 15 parts
Key ideas
| Biological Parameter | Primary / Normal Condition | Alternative / Specialized Variant |
|---|---|---|
| Morphological Feature | Conserved anatomical architecture | Adapted/Modified structure for specialized function |
| Energetic / Metabolic State | Basal physiological activity | Induced / Stress-responsive activation |
| Regulatory Control | Endocrine & enzymatic feedback | Autonomous / Environmental signaling |
| Evolutionary Fitness Impact | Essential for organismal survival | Enhances reproductive efficiency & niche adaptation |
Conceptual Foundation & Core Theory
The Human Circulatory System employs closed double circulation comprising pulmonary and systemic circuits. The myogenic human heart contracts autonomously under impulses generated by the Sinoatrial (SA) node, commonly termed the natural pacemaker.
1. The Cardiac Cycle & Volume Dynamics
A single heartbeat corresponds to one cardiac cycle lasting approximately 0.8 seconds at a typical resting heart rate of 72 beats per minute:
- Joint Diastole (0.4 s): All four chambers are in a relaxed state. The tricuspid and bicuspid (mitral) AV valves remain open, allowing blood from the pulmonary veins and vena cava to flow passively into the left and right ventricles respectively.
- Atrial Systole (0.1 s): The SA node fires an action potential causing both atria to contract simultaneously, boosting ventricular blood filling by roughly 30%.
- Ventricular Systole (0.3 s): The impulse conducts through the AV node, Bundle of His, and Purkinje fibers to depolarize the ventricular myocardium. Ventricular pressure rises sharply, immediately shutting the AV valves (producing the first heart sound 'LUB'). When intraventricular pressure exceeds arterial pressures, the semilunar valves open, ejecting ~70 mL of blood per ventricle (Stroke Volume).
- Ventricular Diastole: As ventricles relax, falling intraventricular pressure causes arterial backflow that snaps shut the semilunar valves (producing the second heart sound 'DUB').
2. Standard Electrocardiogram (ECG) Waves
A clinical ECG graphically records electrical voltage changes across cardiac tissue over time using surface leads (Lead I, II, III):
- P Wave: Represents electrical depolarization of both atria initiated by the SA node.
- QRS Complex: Represents rapid depolarization of both ventricles immediately preceding ventricular systole. The number of QRS complexes per minute directly determines the heart rate.
- T Wave: Represents ventricular repolarization (return of ventricles from excited to normal polarized resting state). The end of the T wave marks the end of mechanical ventricular systole.
Key Scientific Principles, Pathways & Diagnostic Points
// Hemodynamic Formulas & Quantitative Relationships
1. Stroke Volume (SV) = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV)
SV = 120 mL - 50 mL = ~70 mL per beat
2. Cardiac Output (CO) = Stroke Volume × Heart Rate (HR)
CO = 70 mL × 72 beats/min = ~5,040 mL/min ≈ 5 Litres/min
3. Cardiac Cycle Duration = 60 seconds / Heart Rate
For 72 bpm → Duration = 60 / 72 = 0.8 seconds:
- Atrial Systole = 0.1 s | Atrial Diastole = 0.7 s
- Ventricular Systole = 0.3 s | Ventricular Diastole = 0.5 s
- Complete Joint Diastole = 0.4 sECG Waves & Associated Mechanical Cardiac Events
| ECG Waveform | Electrical Event | Mechanical Consequence | Clinical Pathology Indication |
|---|---|---|---|
| P Wave | Atrial depolarization (SA node fire) | Atrial contraction (completes ventricular filling) | Enlarged P wave indicates atrial hypertrophy / mitral stenosis |
| Q-R-S Complex | Ventricular depolarization (Purkinje network) | Ventricular isovolumetric contraction & rapid ejection | Broadened QRS indicates bundle branch block / myocardial infarction |
| T Wave | Ventricular repolarization | Ventricular relaxation (closure of semilunar valves) | Flat or inverted T wave indicates cardiac ischemia / hypokalemia |
| P-R Interval | AV conduction transit time (~0.12–0.20 s) | Ensures atria empty before ventricles contract | Prolonged PR indicates first-degree AV heart block |
NEET Problem: Cardiac Output Calculation under Exercise
NEET Problem: During vigorous athletic exercise, an athlete’s heart rate increases to 150 beats/min and end-diastolic volume increases to 140 mL while end-systolic volume drops to 40 mL. Calculate their cardiac output.
Step-by-step Solution:
1. Calculate Stroke Volume: $SV = EDV - ESV = 140\text{ mL} - 40\text{ mL} = 100\text{ mL}$.
2. Calculate Cardiac Output: $CO = SV \times HR = 100\text{ mL/beat} \times 150\text{ beats/min} = 15,000\text{ mL/min} = 15\text{ L/min}$.
Result: The athlete’s cardiac output expands threefold from 5 L/min to 15 L/min.
Checkpoint
1. In a standard clinical electrocardiogram (ECG), which feature directly correlates with ventricular depolarization and can be counted to determine an individual's heart rate?
All 36 topics in Locomotion & Movement
Types of Movement
- Amoeboid Movement & Pseudopodia
- Ciliary & Flagellar Movement
- Muscular Movement & Human Locomotion
Muscle Types
- Skeletal, Visceral & Cardiac Muscle Structure
- Excitability, Contractility & Elasticity Properties
- Fascia, Tendons & Collagenous Connective Tissue
Muscle Fibre Types
- Red & White Muscle Fibres (Myoglobin Content)
- Muscle Fatigue & Lactic Acid Accumulation
Sarcomere Structure
- A-Band, I-Band, H-Zone & Z-Line Organisation
- Fascicles, Sarcoplasm & Myofibril Alignment
- Functional Unit of Contraction
Muscle Filament Proteins
- Actin Thin Filaments (F-Actin, Tropomyosin & Troponin)
- Myosin Thick Filaments (Meromyosins, Cross-Arms & Head)
Sliding Filament Theory
- Cross-Bridge Cycling & Power Stroke Mechanism
- Neuromuscular Junction & Sarcolemma Action Potential
- ATP Hydrolysis & Myosin Head Activation
Calcium & Contraction
- Sarcoplasmic Reticulum & Calcium Ion Storage
- Calcium Binding to Troponin & Masking/Unmasking Active Sites
Skeletal System
- Axial & Appendicular Skeleton Overview
- Bone Histology, Cartilage & Sesamoid Bones
Skull & Cranium
- Cranial & Facial Bones
- Occipital Condyles & Hyoid Bone
Vertebral Column
- Vertebral Regions (Cervical, Thoracic, Lumbar, Sacral & Coccygeal)
- Neural Canal & Intervertebral Discs
Rib Cage
- True, False & Floating Ribs
- Sternum & Vertebrochondral Rib Articulations
Pectoral Girdle
- Scapula & Acromion Process
- Clavicle & Glenoid Cavity
Pelvic Girdle
- Coxal Bones (Ilium, Ischium & Pubis)
- Acetabulum Cavity & Pubic Symphysis
Types of Joints
- Fibrous Joints (Sutures)
- Cartilaginous Joints
- Synovial Joints (Pivot, Hinge, Ball & Socket, Saddle & Gliding)
Musculoskeletal Disorders
- Myasthenia Gravis & Muscular Dystrophy
- Tetany, Gout & Arthritis
- Osteoporosis & Bone Mass Reduction