VPB 121: Veterinary Physiology - II (2+1)

Characteristics of different types of muscles

CHARACTERISTICS OF SKELETAL, SMOOTH AND CARDIC MUSCLES

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.