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Why can't it undergo tetany ?


Impossible to tetanize heart muscle becouse very long absolute refractory period-one electrical event per mechanical event




smiling face



Can someone explain tetany and the mech behind it? I will always get confused with it. Somewhere I read that it's premature contractions....elsewhere it says, it's due to high??? Ca levels rushing into cytoplasm.... Hmmm, I am not very sure!


1. cross- bridge interaction you need cross bridge-high affinity at resting condition(myosin that can attach to the actin)
2. cycling starts when free Ca+ is available and attaches to troponin
3. contraction is the continuous cycling of cross-bridges, every time a cross bridge completes a single cycle, one ATP is hydrolyzed
4. it will be continues until you have free Ca or ATP will be depleted
5. in skeletal muscles active potential precedes the mechanical event and has very short refractory period (short duration) -- multiple action potential can occur during the mechanical event
6. Increasing the frequency of action potentials  more free Ca -> more cross bridges , big magnitude in mechanical event
7. Complete tetanus when more than enough Ca is available and a lot of cross bridges (keeping busy, never stop)
:P I hope it was helpful ,if not -let me know I try to explain it again smiling face



Thnx for ur explanation. That's exactly what I have read as well. However, when I was reading about Di George's syndrome in first aid, they just mentioned that pt presents with tetany due to low calcium levels. How could you have tetany if there is no calcium? Then I jump into physio and read something totally different.....basically what you explained. So, I don't know if it's just terminology I am getting lost in :?

Also, toward the end of ur message, u mentioned TETANUS. You meant TETANY, correct? Cuz I thought tetanus was a/w clostridium difficile.

And oh, when u have Rigor Mortis, the muscle stays contracted cuz there is no ATP to relax it, right? So what triggers an expired pt with rigor mortis to move the arm or other body parts?


Hi Bela
Tetany-by definition is a neurological disorder marked by intermittent tonic spasm that are usually paroxysmal (mean occurring repeatedly and without warning)
Tetanus-by definition is a life-threatening illness manifested by muscle rigidity and spasm; it is caused by a neurotoxin (tetanospasmin)—clostridium tetani, I thinking this is what Kaplan meant in physiology notes on page 141
I am thinking they have the same physiology explanation but different pathology trigger, I would be pleased if somebody can correct me.

About Di George syndrome
Failure of development of the 3 and the 4th pharyngeal pouches – no parathyroid, no thymus

Clinical –reduction in total and serum Ca so(Ca exist but low)—results in tetany and …..

Low ionized Ca level causes partial depolarization of nerves and muscle by lowering the threshold potential so it comes closer to the resting membrane potential, therefore a smaller stimulus is required to initiate an action potential (decreased ionized calcium increase excitability. and hypercalcemia will be decreased excitability.

Rigor mortis- the stiffness that occurs in dead bodies. You can not see it under physio conditions.
I want you thank you for all your takes time for me to find answers to but it was very helpful at least for me



Tetany-by definition is a neurological disorder marked by intermittent tonic spasm that are usually paroxysmal (mean occurring repeatedly and without warning) and involve the exremities.

sorry i miss it

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