{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture 21 – Nervous System III

Sub threshold potentials do not result in any ap once

Info icon This preview shows pages 4–6. Sign up to view the full content.

View Full Document Right Arrow Icon
sub-threshold potentials do NOT result in any AP once you reach threshold, not matter the stimulus size, the AP will always happen and it  will always be the same the stimulus strength is conveyed by the frequency and pattern of APS this means that an AP alone cannot convey any strength about the strength of the  stimulus Refractory Periods During an AP no stimulus can produce a second AP This is when the NA gates are INACTIVE This is called the absolute refractory period This cannot end until the membrane is repolarized The inactivation gates must be removed by closing the pore and this does not happen  until the membrane is repolarized After the absolute refractory period, there is a period when a second action potential can  be produced, but only if the stimulus is considerably stronger than usual This is the relative refractory period and it can last 1- msec or longer In this period some of the Na channels have returned to the resting closed states and  the inactivation gates are not active  Some of the K channels are still open The length of the refractory period limits the number of action potentials that can be  produced per unit of time Most neurons can produce action potentials at frequencies of 100/sec Action Potential Propagation An action potential can only travel of each point along the membrane is depolarized to  threshold as the action potential moves down the neuron Differences in potential between adjacent regions of the membrane cause current to  flow and sequential depolarization (to threshold) of those adjacent regions The refractory periods are the key in determining the direction of action potential  propagation IT cannot go backwards because the inactivation gates are closed, so no ion flow can  happen **current flow is happening in both directions, but NOT ion flow This local current causes voltage gates Na channels to open and the entire set of  feedback interactiosn that result in a depolarization in a new set a membrane of a  potential
Image of page 4

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Myelination and AP Unmyelinated  Local current loops during AP propagation The current flowa a one instant in time as a result of the action potential In the inactive zoens that are adjacent to the active zone, the outward currents lead to a  depolarization If themembrane is not in an absolute refractory period and if the deplization is large 
Image of page 5
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern