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
The action potential involves 3 other proteins: voltage-gated ion channels
which are…
Voltage-gated sodium channel (to initiate and propagate the action potential)
Voltage-gated potassium channel (to restore the resting membrane potential)
Voltage-gated calcium channel (located at the end of the axon, the axon terminal, and cause the release of neurotransmitter-containing vesicles)
how does Voltage-gated sodium channel work
Voltage-gated channels have electrical charges on their doors. These doors open or close when the charge difference across the cell membrane is greater or smaller than some number. The classic voltage gated Na+ channel is closed when the inside of the cell is more negative than -40 mV. This channel opens anytime the voltage difference is less than -40 mV.
what can pass through Voltage-gated sodium channel work
only sodium
Remember the outside of cell is always considered to be what mV
0 mV. At rest, most neurons sit at -60 mV relative to outside.
opening a Voltage-gated sodium channel makes what happen
Opening a Na+ channel, even just for 1 ms, will result in Na+ ions rushing in, propelled by both diffusion and electrochemical forces. The opening of just one channel will cause the membrane to further depolarize, causing more and more of these channels to open. It is an avalanche effect that can make the membrane potential rise above zero, even up to +40mV
what analogy is used for the voltage gated sodium channel
ball and clog
the clog moves up to clog the door
It opens when the membrane
become less negative than it normally is. Typically, a depolarization to -40 mV from -60 mV is enough to open the door. (when it Is positive then it has th instinct to get away and it then clogs the door because it moved upwards and away from other positive charged)
Inactivation lasts until the membrane potential gets back down to -60 mV for about ½ a millsecond
what is The action potential
a brief electrical impulse that provides the basis for conduction of information along the axon. It is a rapid change in the membrane potential that is caused by the active opening and closing of ion channels.
The value of the membrane potential that must be reached to produce an action potential is called what
the threshold of excitation.
what is the process of action potential (the graph thing)
- -70 (ish) or resting
an impulse comes and the charge reaches the “threshold of excitation” which means the first collage gated channel opens
then it “trips” all the other ones which means they all open up in a chain reaction (all this time the voltage potential is getting much higher) - K+ channels open, K+ begins to leave the cell
- when it gets to 40 mV that is the max and it enters the refractory period; no more Na+ enters the cell (the ball clogs the door at this point)
- K+ continues to leave cell, causes membrane potential to return to resting level
- then the volatage starts to go down and has a period when it goes below resting state as a kind of over reaction and then gets to the regular resting state
With only the Sodium-Potassium Pump
what happens
K+ is pumped in while Na+ is pumped out.
With only the Sodium-Potassium Pump, If there are no open ion channels, then what does this mean
then there is no electrical charge difference (membrane potential = 0). There are similar amounts of positive ions inside and out, but there is a potential energy here based on the force of diffusion..
what is the process of actually Ending the Action Potential
Voltage-gate K+ channels open when the membrane potential is more positive than 0 (no difference in charge between inside and outside of the cell). The opening of the voltage-gated K+ channels helps bring the membrane potential back down to -60 mV.
An action potential is sent from where
the soma down the axon to the terminal button.
give a summary of Voltage-gated calcium channel
located at the end of the axon, the axon terminal, and cause the release of neurotransmitter-containing vesicles)
also, calcium is more concentrated out than in
The primary means of communication between neurons is what
synaptic transmission
what exactly is synaptic transmission
transmission of messages from one neuron to another via the presynaptic release of a chemical (a neurotransmitter) that crosses the synapse and binds to receptors located on the post-synaptic membrane
When action potentials are conducted down an axon (and down all of its branches), it causes what
voltage-gated calcium channels to open. The influx of calcium causes several synaptic vesicles to simultaneously fuse with the presynaptic membrane.
The primary means of communication between neurons is synaptic transmission—transmission of messages from one neuron to another via the presynaptic release of a chemical (a neurotransmitter) that crosses the synapse and binds to receptors located on the post-synaptic membrane.
When action potentials are conducted down an axon (and down all of its branches), it causes voltage-gated calcium channels to open. The influx of calcium causes several synaptic vesicles to simultaneously fuse with the presynaptic membrane.
Upon fusion, what happens
these vesicles break open and spill their contents into the synaptic cleft.
The movement of the information along the axon is referred to as what
conduction of the action potential
Conduction occurs in what kind of manner/ direction
unidirectional manner
The size of the action potential remains ____
consistent
The All-or-none law states what
the action potential occurs or does not occur, and once triggered, will propagate down the axon without growing or diminishing in size, to the end of the axon.
The rate law states what
that the strength of the stimulus is represented by the rate of the firing axon.
what are the 5 points of Conduction of the Action Potential
The movement of the information along the axon is referred to as conduction of the action potential.
Conduction occurs in a unidirectional manner.
The size of the action potential remains constant.
The All-or-none law states that the action potential occurs or does not occur, and once triggered, will propagate down the axon without growing or diminishing in size, to the end of the axon.
The rate law states that the strength of the stimulus is represented by the rate of the firing axon.
another name for Neuroglia is what
Glial cells
Glia are found where
all around neurons and even physically encapsulate some parts of them
what do Glia do
They help traffic nutrients and maintain molecular (ionic) stability in the extracellular space. They support many functions of the nervous system. It is estimated that glia cells outnumber neurons in the brain somewhere between 2:1 and 5:1
what are the 3 Supporting Cells of the Central Nervous system
Astrocyte
Oligodendrocytes
Microglia
what are Astrocyte
is a glial cell that provides physical support and cleans up debris in the brain through phagocytosis. They control the chemical composition of the surrounding environment and help nourish neuron
what are Oligodendrocytes
support axons of neurons and produce the myelin sheath, which encapsulates axons
describe myelin sheath
The sheath is not continuous; it is a series of segments. The exposed axon is called the node of Ranvier
what are Microglia
the smallest of the glial cells. They provide an immune system for the brain and protect the brain from invading microorganisms.
During development of the CNS, ________ form processes shaped something like canoe paddles
oligodendrocytes
During development of the CNS, oligodendrocytes form processes shaped something like canoe paddles
Each of these paddle-shaped processes then does what
wraps itself many times around a segment of an axon and, while doing so, produces layers of myelin that make up part of the axon’s myelin sheath.
In what order does the myelin sheath wrap around the cells
starts at back (vision) then makes its way forward to front of brain
what are the node of ranvier
exposed axon that is very small but it is as f the current is jumping from one to another
Only place where a myelinated axon comes into contact with extracellular fluid is where
at node of Ranvier, where axon is naked
In myelinated areas are there ion channels why or why not
there are almost no ion channels, and those that are there are of no consequence because there is no extracellular fluid outside the membrane
what is Saltatory conduction
the conduction of action potentials by myelinated axons
Action potential appears to jump from one node of Ranvier to next. At each one the strength of the signal is regenerated with additional voltage-gated Na+ channels
do We know a lot about voltage-gated ion channels
We know their exact shape, the arrangement of all the atoms in them (X-ray crystallography).
We know the DNA letters (the exact string of nucleic acids) that encode these proteins in numerous species. Accordingly, we also know the exact string of amino acids that form the proteins.
In genetics, apromoter is what
a region of DNA that initiates transcription of a particulargene. They indicate what kind of cells should read the gene and when.
Promotersare typically located just before the gene.
what is Avirus
a smallinfectious agentthat replicates inside the cellsof other organisms.
The DNA of a virus does what
encodes instructions on how to make more virus
what do we know about Viral-Mediated Gene Delivery
Avirusis a smallinfectious agentthat replicates inside the cellsof other organisms. The DNA of a virus encodes instructions on how to make more virus.
We know how to remove the DNA from a virus, which renders the virus “replication-deficient”. We can also add foreign DNA to the virus, DNA that encodes things like fluorescent proteins or optogenetic proteins.
When a modified virus is injected into an animal’s brain, it infects the cells it comes into contact with. Some viruses infect cell bodies (e.g., AAV), others infect axon terminals (e.g., rabies). Once the virus gets its DNA into the infected cell’s nucleus, that cell will start to transcribe it and make the foreign protein.
Almost all lab-made viral constructs contain a section of DNA that encodes a fluorescent protein (e.g., GFP). Fluorescent proteins are used to later identify the infected cells.
Allen Brain Atlas: http://www.brain-map.org/ mouse connectivity
