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In this article we will discuss about the characteristics of skeletal, smooth and cardiac muscles of human body.
Characteristics of Skeletal Muscle:
Histology:
1. Size and Shape:
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Cylindrical; 1-40 mm long, 10 to 100 μ in diameter.
2. Striations:
Transverse, longitudinal.
3. Sarcolemma:
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Present and complete.
4. Nucleus:
Multiple, just under the Sarcolemma.
5. Sarcotubular System:
Present, T-systems are at junctions of A-l band (in mammals). Terminal cisternae is prominent.
6. Branch:
Nil.
7. Cell-to-Cell Conduction:
Nil.
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Properties:
1. Rhythmicity:
Nil.
2. Conductivity:
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Very fast.
a. All-or-None Law:
True for single fibre.
3. Contractility:
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Simple muscle curve with characteristic features.
4. Refractory Period:
Short-within latent period.
a. Tetanus:
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Possible
b. Fatigue:
Possible
5. Tonicity:
Tone depends on nerves.
Composition:
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1. Protein:
Maximum.
2. Glycogen:
Less.
3. ATP and Phosphagen:
Present.
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4. Carnosine:
Maximum.
5. Fats:
Mostly neutral fats.
6. Inorganic:
Na/K-1/5.Ca++
Action of Ions:
1. Sodium:
Excitation
2. Calcium:
Present mostly in sarcoplasmic reticulum and stimulates ATP-ase activity during muscular contraction.
3. Potassium
Reduces excitability and hastens fatigue.
Metabolism:
1. Carbohydrates:
a. Lactic Acid:
Oxidised less easily than glucose and often incomplete.
b. Glycogen:
Reduced in Starvation and Diabetes Mellitus.
2. Blood Supply and O2 Consumption
Moderate.
Distribution:
Skeletal
Control:
Under the will, so voluntary.
Nerve Supply:
Somatic with special nerve endings.
Characteristics of Smooth Muscle:
Histology:
1. Size and Shape:
Elongated, fusiform, length 0.2 mm (aver.), width—6 μ (central portion).
2. Striations:
Longitudinal (special preparation).
3. Sarcolemma:
Present and complete.
4. Nucleus:
Single, at the centre with distinct nucleoli.
5. Sarcotubular System:
Present but not so characterised.
6. Branch:
Nil
7. Cell-to-Cell Conduction:
Through nexus.
Properties:
1. Rhythmicity:
Present
2. Conductivity:
Slower.
a. All-or-None Law:
True for single fibre.
3. Contractility:
Slow and worm-like. All periods of the curve longer.
4. Refractory Period:
Longer than smooth.
a. Tetanus:
Not so.
b. Fatigue:
Possible, Difficult to demonstrate.
5. Tonicity:
Independent of nerve
Composition:
1. Protein:
Less.
2. Glycogen:
More.
3. ATP and Phosphagen:
Present.
4. Carnosine:
Less.
5. Fats:
Mostly neutral fats
6. Inorganic:
About same
Action of Ions:
1. Sodium:
Probably same.
2. Calcium:
Same as skeletal.
3. Potassium:
Probably same.
Metabolism:
1. Carbohydrates:
a. Lactic acid:
Oxidised less easily than glucose and often incomplete.
b. Glycogen:
Reduced in Starvation and Diabetes Mellitus.
2. Blood Supply and O2 Consumption:
Less
Distribution:
Hollow viscera, capsules, skin, etc.
Control:
Not so, involuntary
Nerve Supply:
Autonomic with ganglia and free nerve terminals.
Characteristics of Cardiac Muscle:
Histology:
1. Size and Shape:
Short cylindrical, rectangular in longitudinal section, polyhedral in transverse section.
2. Striations:
Both longitudinal and transverse.
3. Sarcolemma:
Present and complete.
4. Nucleus:
Single and central.
5. Sarcotubular System:
Present but without terminal cisternae. T-system is more prominent and present at Z-line (in mammals).
6. Branch:
Multiple branches. In all directions three dimensional network without cytoplasmic continuity (false syncytial appearance).
7. Cell-to-cell Conduction:
Through specialised areas of intercalated use.
Properties:
1. Rhythmicity:
Present and characteristic.
2. Conductivity:
Slower, different in different parts.
a. All-or-None Law:
True for the whole heart, because of functional syncytium.
3. Contractility:
Characteristic muscle curve. Contraction, longer than relaxation.
4. Refractory Period:
Longest, whole contraction period is absolute refractory.
a. Tetanus:
Impossible
b. Fatigue:
None. Long refractory period ensures recovery.
5. Tonicity:
Independent of nerve.
Composition:
1. Protein:
Less.
2. Glycogen:
More.
3. ATP and Phosphagen:
Present.
4. Carnosine:
Less.
5. Fats:
More phosphatides and cholesterol than in other
6. Inorganic:
Na/K-1/2 i.e., more Na Ca++
Action of Ions:
1. Sodium:
Initiates and maintains heartbeat.
2. Calcium:
Increases strength of contraction and duration of systole.
3. Potassium:
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Inhibits contraction and produces relaxation.
Metabolism:
1. Carbohydrates:
a. Lactic Acid:
Completely and more readily than glucose.
b. Glycogen:
Increased.
2. Blood Supply and O2 Consumption:
High.
Distribution:
Only in heart.
Control:
Not so, involuntary.
Nerve Supply:
Same as in involuntary.
