Why Hypocalcemia causes Contraction and Hypercalcemia causes Weakness? - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 11-16-2010
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 2
Threads: 1
Thanked 5 Times in 1 Post
Reputation: 15
Fire Thread Why Hypocalcemia causes Contraction and Hypercalcemia causes Weakness?

The s/s of hypercalcemia: muscle weakness
hypocalcemia: muscle convulsion or tetancy

But in pysiology, calcium cuases muscular contraction, isn't it?
Isn't there any opposite between theory and clinnical manifestation? Why?

Thx a lot!
Reply With Quote Quick reply to this message
The above post was thanked by:
Jingwei (01-20-2016), pkul85 (12-05-2011), StepTaker (11-16-2010), Taiwan_Guy (05-19-2011), TBS2017 (02-18-2017)



  #2  
Old 11-16-2010
USMLE Forums Guru
 
Steps History: 1+CK+CS+3
Posts: 363
Threads: 18
Thanked 312 Times in 149 Posts
Reputation: 322
Default

More likely to Depolarize- Low Ca - thus you get muscle spasm, tetany, cramps

Less likely to depolarize- high Ca thus you get weakness

All muscles contract because of INTRAcellular Ca.

I think your getting confused on Intracellular and Extracellular calcium.
Reply With Quote Quick reply to this message
The above post was thanked by:
smita (04-16-2015)
  #3  
Old 11-16-2010
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 3,263
Threads: 147
Thanked 5,053 Times in 1,567 Posts
Reputation: 5149
Info Plasma Calcium affecting Neuronal Excitibility

Low plasma calcium increases the permeability of neuronal membranes to sodium ions, causing a progressive depolarization. This increases the ease with which action potentials can be initiated. If the plasma Ca2+ decreases to less than 50% of the normal value action potentials may be spontaneously generated, causing contraction of peripheral skeletal muscle.

The reverse is true in hypercalcemia. High Calcium causing decreased permeability and thence muscle weakness.

So in essence it's about neuronal excitation rather than the muscle itself. That's why you have signs such as the Chvostek's sign (tapping of the inferior portion of the zygoma will produce facial spasms) it's because you are tapping on the nerve (not the muscle) further exaggerating the neuronal excitation.
Reply With Quote Quick reply to this message
The above post was thanked by:
browndowntown (04-18-2016), cafs1000 (10-13-2015), daniel1987 (04-15-2013), dr-ahmed (11-16-2010), Dr.Tiger (04-15-2013), gokulramani (01-05-2016), im99 (02-25-2011), inno (03-10-2012), Linc (11-27-2015), Master shifu (04-18-2013), meghakotha (01-06-2016), organo14 (11-10-2013), pkul85 (12-05-2011), riya rai (04-16-2013), swwal (04-15-2013), TBS2017 (02-18-2017), varunshetty00 (11-16-2010), Wale Nan (08-09-2015)
 
  #4  
Old 11-16-2010
dr-ahmed's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS
Posts: 333
Threads: 61
Thanked 391 Times in 90 Posts
Reputation: 401
Default many thanks

many thanks to you ,, I had the same confusion previously but now it's all clear to me ,,
Reply With Quote Quick reply to this message
  #5  
Old 11-16-2010
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,466 Times in 358 Posts
Reputation: 1476
Arrow hypocalcemic tetany

1. increased neuronal exitibility--- when extracelluler ca level dec this inc neuronal memb permeability to sodium ions allowing easy initiation of action potential in other words dec threshold for exitation.

2. ca req for relaxation---ca ATPase( ca activated) p/in memb of SR pumps ca back into SR. so in this condition ca will still be released but not pumped back at the same rate and thus contr will persist....tetany

hope this helps

Reply With Quote Quick reply to this message
The above post was thanked by:
TBS2017 (02-18-2017)
  #6  
Old 11-17-2010
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 2
Threads: 1
Thanked 5 Times in 1 Post
Reputation: 15
Default

Thank you a lot!!

Clinically, there is a Trousseau sign of latent tetany, which means hand convulsion while using tourequit.

We also find that pregnant women in 3rd trimester often complain calf muscle convulsion, esp in supination.

We highly suspect hypoperfusion exacerbates tetancy in hypocalcemia pt.

But I can't explain.


Besides, if the plasma Ca++ is low, intracellular Ca++ should be suspected at low level, too. Since Ca++ would shift out initially at hypocalcemia, isn't it?

THX a lot.
Reply With Quote Quick reply to this message
  #7  
Old 04-15-2013
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 1
Threads: 0
Thanked 10 Times in 1 Post
Reputation: 20
Default The answer

This is a good question.

It actually has very little to do with the RMP or intracellular Ca. Remember membrane potential is determined by electrochemical (electrical and concentration) gradients and conductance. K and Cl are really the only ions that have a high conductance at RMP (Na conductance is small until threshold). Equilibration potentials for ions are:

K ~ -90 mV
Cl ~ - 70 mV
Na ~ +60 mv
Ca ~ +125 mV

RMP is about -70 to -80 mV, close to the only two ions (K and Cl) that have high conductances. Both the Na/K ATPase and leaky K channels help maintain RMP until the cell is depolarized.

Because Ca has essentially zero conductance at RMP, hyper-/hypocalcemia will not alter the resting membrane potential in any significant manner. However, Ca does have the important role of modulating the behavior of Na channels.

Divalent cations (E.g. Ca) have a small affinity for the Na channel and can essentially "plug" it up during the influx of Na. At normal Ca levels, this acts as an important modulator of excitability. Hyper-/hypocalcemia can alter that modulating activity as follows:

Hypercalcemia: there are more Ca ions to "plug" the Na channel, thus Na influx will be reduced in neurons transmitting impulses resulting in muscle weakness, constipation, etc.

Hypocalcemia: there are less Ca ions to "plug" the Na channel, thus Na influx will be increased in the neurons transmitting impulses resulting in muscle twitching, tetany, etc.

The literature states that changing extracellular Ca is like changing the threshold potential. For example hypercalcemia would increase (make less negative) threshold potential, while hypocalcemia would decrease (make more negative) threshold potential. Thus at RMP, each scenario would required wither more or less input to reach threshold and thus and action potential. However, in reality, RMP does not change.
Reply With Quote Quick reply to this message
The above post was thanked by:
Ahmad Sayed (12-02-2014), browndowntown (04-18-2016), drdhruv (04-17-2015), gokulramani (11-25-2015), hmzbrd (2 Days Ago), Jingwei (01-20-2016), Linc (11-27-2015), Master shifu (04-18-2013), riley2021 (11-26-2015), riya rai (04-16-2013)
  #8  
Old 04-16-2015
USMLE Forums Newbie
 
Posts: 1
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default

Really good explanation, just the last statement...I think that hypocalcemia should INCREASE (make less negative) RMP, because it decreases positive charge of ECF, therefore it decreases the difference between inside and outside and makes it less negative, or?
Reply With Quote Quick reply to this message
  #9  
Old 11-25-2015
USMLE Forums Newbie
 
Steps History: CK Only
Posts: 7
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default

Thank you for posting this information!)
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message
  #10  
Old 01-05-2016
gokulramani's Avatar
USMLE Forums Addict
 
Steps History: 1 + CS
Posts: 114
Threads: 13
Thanked 35 Times in 25 Posts
Reputation: 45
Default Found an interesting article.

Reference attached. Here's the summary

Quote:
The inverse relationship between extracellular calcium and neuronal excitability could be explained by several complementary molecular events (summarized in Table 1 and Figure 2). External calcium inhibits NALCNs, shifts the voltage dependency of voltage-gated Na+ channels, stabilizes CNG channels, reduces inward current through AMPA channels, and depresses the release of excitatory neurotransmitters. Conversely, it enhances transient K+ current and KCa channels and perhaps potentiates GABA sensitivity. Some of these modulatory effects may depend on CaSR while others may require calcium influx. It is these processes that we theorize may help shed light on the calcium paradox and lead to further understanding of the mechanisms behind production of seizures through hypocalcemia
http://www.ncbi.nlm.nih.gov/pmc/arti...0/#!po=19.5652
Reply With Quote Quick reply to this message
  #11  
Old 02-18-2017
USMLE Forums Newbie
 
Steps History: ---
Posts: 1
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default Why does supplemental calcium cause cramps/spasms

If I ingest any amount of supplemental calcium I get painful cramps/spasms throughout my body. If I don't take magnesium(800m) daily I get the same cramping.
If calcium relaxes muscles why am I getting cramping?
Reply With Quote Quick reply to this message



Reply

Tags
Musculoskeletal-, Physiology-

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hypercalcemia and Hypocalcemia, How to proceed! aasiaafzal USMLE Step 2 CK Bits & Pieces 8 06-29-2015 02:07 AM
The cause of hypocalcemia? Ace3 USMLE Step 2 CK Forum 1 04-18-2012 05:56 AM
Hypercalcemia scopusmount USMLE Step 1 Forum 5 11-03-2011 09:16 AM
hypocalcemia sonu.agarwall USMLE Step 2 CK Forum 5 11-01-2011 12:32 AM
MCC of Hypocalcemia jattdoc USMLE Step 1 Forum 4 09-03-2011 06:07 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)