Full coverage of action potentials, with well-structured subheadings to organise the material, subject material includes: introduction, active cell membranes, the membrane potential, the action potential, and a summary, along with some visual materials to summarise key information.
Action Potentials
Week 1
Learning Objectives
Describe the components of the membrane that establish the resting membrane
potential
Describe the changes that occur to the membrane that result in the action potential
Introduction
The functions of the nervous system—sensation, integration, and response—depend
on the functions of the neurons underlying these pathways. To understand how
neurons can communicate, it is necessary to describe the role of an excitable
membrane in generating these signals. The basis of this communication is the action
potential, which demonstrates how changes in the membrane can constitute a
signal. Looking at the way these signals work in more variable circumstances
involves a look at graded potentials, which will be covered in the next section
Electrically Active Cell Membranes
Most cells in the body make use of charged particles, ions, to build up a
charge across the cell membrane. Previously, this was shown to be a part of
how muscle cells work
For skeletal muscles to contract, based on excitation–contraction coupling,
requires input from a neuron. Both of the cells make use of the cell membrane
to regulate ion movement between the extracellular fluid and cytosol
The cell membrane is primarily responsible for regulating what can cross the
membrane and what stays on only one side
The cell membrane is a phospholipid bilayer, so only substances that can
pass directly through the hydrophobic core can diffuse through unaided
Charged particles, which are hydrophilic by definition, cannot pass through
the cell membrane without assistance
Transmembrane proteins, specifically channel proteins, make this possible.
Several passive transport channels, as well as active transport pumps, are
necessary to generate a transmembrane potential and an action potential
Of special interest is the carrier protein referred to as the sodium/potassium
pump that moves sodium ions (Na+) out of a cell and potassium ions (K+) into
a cell, thus regulating ion concentration on both sides of the cell membrane
The sodium/potassium pump requires energy in the form of adenosine
triphosphate (ATP), so it is also referred to as an ATPase
As was explained in the cell chapter, the concentration of Na+ is higher
outside the cell than inside, and the concentration of K+ is higher inside the
cell than outside. That means that this pump is moving the ions against the
concentration gradients for sodium and potassium, which is why it requires
energy. In fact, the pump basically maintains those concentration gradients
Ion channels are pores that allow specific charged particles to cross the
membrane in response to an existing concentration gradient
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