Depolarization Phases of cardiac cell and electrolytes influx and eflux - 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 02-16-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 324
Threads: 70
Thanked 239 Times in 144 Posts
Reputation: 249
Heart Depolarization Phases of cardiac cell and electrolytes influx and eflux

In uworld it is written that "In SA node, automaticity is the result of slow phase 4 depolarization that occurs due to a slow inward calcium current".
But in kaplan it is said that slow calcium current occurs during phase 0..
and in my understanding slow sodium influx or funny current not calcium influx occurs during phase 4 ..
can anyone explain plz?
Reply With Quote Quick reply to this message



  #2  
Old 02-16-2011
beka-CTS's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 763
Threads: 77
Thanked 1,371 Times in 349 Posts
Reputation: 1381
Default

I think Ca isn't a main factor for automaticity of SA.

the resting potential of cardiac cells is -90 mV, meanwhile in Pacemakers (SA) this value is changed during a Dyastole. In SA node occurs process called: "Slow Spontan Diastolic Depolarisation" and it is the result of special character of SA node cell membranes. They(membranes) increase Na flow into cell during Diastole and resting potential is rased to -60mV. after that Normal cycle begins.
Reply With Quote Quick reply to this message
The above post was thanked by:
Amenah (02-16-2011), Mondoshawan (02-16-2011), struggle (02-16-2011)
  #3  
Old 02-16-2011
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 9
Threads: 0
Thanked 20 Times in 7 Posts
Reputation: 30
Default

As far as I know, transient calcium channel open around ~-50mV.

Since phase 4 starts in below -60mV and then depolarizes slowly till action potential, before ~-50mV the most important current is what is called "funny current".

However, after that, there is a calcium current, that is important to the end of phase 4.


Once you've reached the threshold, Slow calcium channels open and calcium influx causes action potential.

Note there are two different calcium channels, and they play different roles in different phases of node potential.



I hope I helped you!

Last edited by GGossling; 02-16-2011 at 08:10 AM. Reason: Adding information.
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-16-2011), struggle (02-16-2011)



Reply

Tags
Cardiovascular-, 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
Cardiac Output and TPR relationship? prim USMLE Step 1 Forum 4 08-24-2012 07:26 PM
Cardiac Innervation aungawa USMLE Step 1 Forum 8 02-22-2012 02:36 AM
Pathway towards Cardiac Surgery? saeyed IMG Residency Match Forum 3 12-25-2010 09:54 AM
Biggest Mistakes in USMLE Prep and the three phases Dr.Sidd USMLE Step 1 Forum 1 11-21-2010 03:03 PM
Cardiac Bruise ecgram USMLE Step 1 Forum 2 05-22-2010 11:55 AM

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)