Lecture 3 Flashcards
Chapter 2b
how do cells communicate in the nervous system
Electrical Signals
what is Membrane potential
Electrical charge across a cell membrane; difference in electrical potential inside and outside the cell
what is Resting potential
Membrane potential of a neuron when it is not being altered by signaling molecules that cause excitatory or inhibitory postsynaptic potentials; At rest, the membrane potential ranges between -40 and -90 mV across different types of neurons
what makes neurons special
evolved for fast communication
how do neurons do fast communication
regulating membrane potential
what Two proteins are responsible for setting up and maintaining the resting membrane potential of neurons:
Sodium-Potassium transporter (requires ATP; concentrates sodium outside the cell and potassium inside the cell.)
Leak potassium channels (always open; the number of these channels dictates the resting membrane potential.)
how do Sodium-Potassium transporters open
requires ATP
what does the Sodium-Potassium transporter do
concentrates sodium outside the cell and potassium inside the cell
how do Leak potassium channels open
always open
what do Leak potassium channels do
the number of these channels dictates the resting membrane potential.
is the number of Sodium-Potassium transporters a limiting factor for neurons?
The number of these pumps and their activity is never a limiting factor for neurons. These pumps make it so there is basically 100x more K+ inside the cell than out and 100x more Na+ outside the cell than in. These relative concentration differences never change, never ever, no matter what, unless the cell dies
The cell membrane of neurons is permeable to K+, why
and how do the leak potassium channels dictate the electrical potential of the cell
This is because their membranes contain the always-open K+ leak channels. The more of these channels there are in the membrane, the more permeable their membrane is to K+. If the membrane is fully permeable to K+, the electrical potential of the membrane will settle at -90 mV. This is when the force of diffusion encouraging K+ to leave (because K+ is 100x more concentrated in than out) is equal to the electrostatic pressure driving K+ in (because inside the cell is -90mV relative to outside). If the membrane is only partially permeable to K+, the membrane potential will be less negative than -90 mV.
If you give K+ ions the freedom to leave the cell (by putting open potassium channels in the membrane), will they?
they will do so due to the force of diffusion.
These channels are called potassium leak channels (it is a pore in the membrane… a hole)
in the leak potassium channels, explain the state of; Potassium ions, Chlorine ions and sodium ions
Potassium– wants to leave cell because force of diffusion (less outside of cell) but wants to stay in cell because of electrostatic pressure (it is negative inside and positive outside and because it is a positive ion it wants to stay inside) and so it is at a balanced state
Chlorine– is a negative ion so wants to stay outside because of electrostatic pressure (it is positive outside) and wants to come in because of force of diffusion (way less crowded inside) so it is balanced
Sodium– is positive and wants to come inside because there is less inside AND because it is negative inside so it is not balanced
explain how the electrical field is created in the leak potassium channel
the sodium and chorine atoms are opposite charges and they are attracted to eahother so they come together and make this in/ charge which creates this electric field in the membrane
and proteins in the membrane can feel this because they are sensitive to it
Cell membranes are full of proteins that act as sensors what are these called
receptors
Cell membranes are full of proteins that act as sensors (receptors). These proteins are sensitive to specific features of the extracellular environment give an example
For example, cells use many different proteins to detect and pull in nutrients from the extracellular space. (Nutrients include many proteins, fats, sugars, vitamins and minerals.)
Lots of stuff in the external world is informative but not necessarily nutritious. Cells use proteins to detect all kinds of different stimuli in the external world, including:
the presence of certain molecules (via chemical interactions) physical pressure (movement, touch) electrical pressure (voltage) temperature pH (acidity, basicity) electromagnetic radiation (light)
When the appropriate stimulus activates a receptor protein what happens
the protein responds by changing shape (a conformational change) or by undergoing/catalyzing a chemical reaction that involves a change in molecular structure
When the appropriate stimulus activates a receptor protein, the protein responds by changing shape (a conformational change) or by undergoing/catalyzing a chemical reaction that involves a change in molecular structure. What happens next is up to the cell. How does the cell want to respond to this information?
In cell biology, receptor proteins typically launch intracellular signaling cascades (e.g., a receptor protein activates enzyme 1, which activates enzyme 2, which activates etc. etc.). The net effect could be a change in gene expression or maybe the cell might physically move in some direction.
Neurons use these common receptor protein signaling cascades like all cells do. However, they also use receptor proteins to tightly control their membrane potential, which gives rise to electrical communication. Stimuli that activate or inhibit neurons typically change the ionic permeability of the cell membrane (i.e., these stimuli cause a receptor protein to open or close an ion channel or activate/deactivate an ion pump
The opening or closing of an ion channel changes what
the ionic permeability of the membrane. An influx of positive ions will depolarize the neuron (make it less negative relative to the outside).
what are the 2 options in changes in membrane potential
Depolarization
and Hyperpolarization
what is Hyperpolarization
When the membrane potential of a cell becomes more negative than it normally is at rest. An influx of negative ions like Cl- (our outflow of positive ions like K+) can hyperpolarize a neuron from -60 to -70 mV. The hyperpolarization of a neuron decreases its (spiking) activity
what is Depolarization
When the membrane potential of a cell becomes less negative than it normally is at rest. An influx of positive ions like Na+ can depolarize a neuron from -60 to -50 mV. The depolarization of a neuron increases its (spiking) activity.
what is neuronal activity? What does it mean for a neuron to be active?
An active neuron is one that is firing (spiking), which means it is experiencing a rapid change in membrane potential known as an action potential
what does action potential.
involve
Action potentials involve three types of proteins
how does action potential work
These proteins are all ion channels located in the membrane, which have doors (pores) that are normally closed. On these doors are electrical charges, and the doors can be pulled open or closed by changes in the membrane potential.
what are the 2 proteins that set up the resting membrane potential:
Sodium-Potassium transporter (requires ATP; concentrates sodium and potassium outside and inside the cell, respectively)
Leak potassium channels (always open; sets up the resting membrane potential)
The action potential involves 3 other proteins which are classified as what
voltage-gated ion channels
