| Property | Skeletal | Smooth | Cardiac |
| Cell shape, size and interactions and cell organelles | Cylindrical 10 – 100 µm diameters 2-3 cm long, no electrical coupling (cell to cell conduction), no branching, prominent T- tubules, multiple nuclei, varying degree mitochondria present, triad is prominent. | Elongated fusiform 1 – 12 µm dai.,15 – 500 µm long, functional syncytium,no branching. Moderately developed sarcoplasmic reticulum system, less prominent, T- tubules, few mitochondria | Multi branched 2 –20 µm dia., 20-200 µm long, intercalated disc provide electrical coupling. Abundant mitochndria. No lateral cisternae, fairly developed sarcoplasmic reticular system. |
| Rhythmicity | Nil | Present | Present & characteristic |
| Conductivity | Very fast | Slower | Slower |
| All or none law | True for single fiber | True for single fiber | True for the whole heart. |
| Contractility | Simple muscle curve | Slow- all periods of the curve longer | Contraction longer than relaxation |
| Refractory period | Short (with in latent period) | Longer | Longest (whole contraction period is absolute refractory) |
| Tetanus | Possible | Not so | Impossible (long refractory period ensures recovery) |
| Fatigue | Possible | Possible | Impossible (long refractory period ensures recovery) |
| Tonicity | Depend on nerve | Independent of nerve | Independent of nerve |
| Action Potential | RMP = -70 mV, AP is 1 msec long, AP depends on Na+ and K+ gradient. No spontaneous activity. | RMP = – 55mV (-50 to -60), larger resting Na+ permeability. AP depends on Ca2+ gradient. AP 10 ms long, AP is Ca2+ permeability dependent (SLOW CHANNEL). Stretch and pacemaker activation. | RMP = -90 mV. AP dependent gradients of Ca2+ K+ and Na+. Spontaneous pacemaker activity, no stretch induced activity, AP 250 msec long. |
| Actomyosin ATPase | Well developed | Lowest actomysion ATPase. | Moderate amount of actomysin ATPase. |
| Ca2+ | Ca2+ removes inhibition due to troponin. Ca2+ from sacrcoplasmic reticulum only, Ca2+ increases the activity of ATPase during contraction. | No troponin system. sparse sarcoplasmic reticular Ca2+. Ca2+ form ECF (by diffusion). Ca2+ so latent period is more prolonged. Ca2+ pump works slowly causing relaxation, so more contraction time. | Ca2+ from ECF and sarcoplasmic reticulum. Troponin system present. Extensive Ca+, Na+ exchange system. Ca+ ↑es strength of contraction and duration of systole. |
| Na+ | Excitation | Probably same | Initiates and maintains heart beat. |
| K+ | Reduce excitability and hastens fatigue | Probably same | Inhibits contraction and produces relaxation |
| Protein | maximum | Less | Less |
| Glycogen | less | More | More |
| Carnosine | maximum | Less | Less |
| Fats | Mostly neutral fats | Mostly neutral fats | More phospholipids and cholesterol than in other |
| Inorganic | Na+/K+ = 1/5 Ca2+ | About same | Na+/K+ = ½ Ca2+ ie., more Na+ |
| Energy metabolism | Glycolysis and oxidative metabolism. | Primarily glycosysis | Oxidative metabolism with high O2 need. Also glycolysis & fatty acid metabolism. |
| Lactic acid | Oxidized less easily than glucose and often incomplete | Same as skeletal | Completely and more readily than glucose |
| Glycogen | Decreased metabolism of glycogen during starvation | Same as skeletal | Increased glycogen metabolism during starvation. |
| Blood supply and O2 consumption | moderate | Less | High |
| Control | Voluntary | Not so, involuntary | Not so, involuntary |
| Innervations | Single innervation with Peripheral NS A-ch as neurotransmitter. | Dually innervated by Autonomic NS. Excitation and inhibition modulates ongoing activity | Dually innervated by ANS. Parasympathetic slows down activity and sympathetic increases. |
| Electrical events | Short AP (1 ms) does not over lap with twitch event (30 ms). Summation possible. | Relatively short Ap (5-10 ms), does not over lap with prolonged twitches. Summation possible | Very long AP (250 ms), almost completely overlaps with long twitches (300 ms). No tetanus and no summation possible. |
