Midterm 1 Flashcards
What’s a receptor protein?
- A protein that is sensitive to and capable of communicating some signal
- Sensitive to neurotransmitters and to outside stimuli (light, touch, smell, taste)
What are the 2 types of receptor proteins?
- Ionotropic receptors
- Metabotropic receptors
What’s an ionotropic receptor?
- A receptor protein that is an ion channel
- When they’re activated they have an immediate effect on the membrane potential of the neuron (they either produce excitatory post-synaptic potentials or inhibitory post-synaptic potentials)
- Ionotropic receptors always have a fast and immediate effect and these effects last no more than a millisecond
What’s the excitatory post-synaptic potential?
if the pore of the ion channel lets in positively charged sodium that’ll depolarize the neuron and maybe encourage it to have an action potential
What’s the inhibitory post-synaptic potential?
if other ionotropic receptors let in negatively charged chloride. This will hyperpolarize the neuron and decrease its likelihood of firing an action potential
What’s a metabotropic receptor?
- A receptor that’s sensitive to something outside the cell and is not an ion channel
- These receptors typically trigger an intracellular signalling cascade that involves g proteins, which can produce a variety of cellular effects such as a change in gene expression or the opening/closing of g protein-gated ion channels
Where does the name “g protein” come from?
It symbolizes that these proteins use GTP molecules, instead of ATP molecules, for the energy they need to perform chemical reactions
When is a g protein at its “on”/activated state?
When it is bound to a GTP molecule
When is a g protein at its “off”/inactivated state?
When it has converted GTP to GDP and is now clipped onto GDP molecules
How do g proteins let go of GDP?
- By finding an activated metabotropic receptor which is one that’s bound to a neurotransmitter
- They use the intracellular side of an activated metabotropic receptor to pry off their GDP molecule
- When this happens, they bind another GTP molecule and the process starts over again
What are G protein coupled receptors?
They use chemical reactions inside the cell to pass along a message
What’s the relationship between g proteins and ion channels?
- We often see g proteins opening up ion channels to change the membrane potential to get a neuron to spike more or to spike less
- ## Some ion channels are normally closed and the only way they open is when activated g proteins come and bind to them intracellularly which causes them to open up and let ion channels to flow through
What’s a G protein-gated ion channel?
Some ion channels are gated by g proteins, which are a family of intracellular proteins that are involved in intracellular signalling cascades
What are advantages of metabotropic receptors?
- They can amplify a signal
- They can prolong a signal
How do metabotropic receptors amplify a signal?
One neurotransmitter binding to one receptor can cause a massive change in the membrane potential because it’s causing activated g proteins to go and open up tons of ion channels at the same time
Which type of receptor protein has a more dramatic effect on the cell? Metabotropic or Ionotropic?
- Metabotropic receptors can amplify the message and hence have more dramatic effects on the cell than ionotropic receptors do
- Ionotropic receptors have only one ion channel that opens or closes
- Metabotropic receptors also have a much more prolonged signal compared to ionotropic receptors
How do metabotropic receptors prolong a signal?
- When metabotropic receptors are activated, the process will take a minimum of 30 milliseconds and only 100 milliseconds later do we begin to see the effects on the cell
- Once the effect occurs, the ion channels can stay open for a while until g protein let’s go of them which it can hang onto them for a while
What are some downstream processes that G-protein signaling cascades can affect?
- opening g protein-gated ion channels
- changes in gene transcription
- secretion of substances from the cell
Where are receptors usually located?
Located mostly on dendrites because they’re what’s sensing the external environment in the cell determining whether they should fire an action potential
Where are the different places that synapses can form between axon terminals and …?
- dendrites (dendritic shafts) - > axodendritic synapse
- dendritic spines -> axodendritic synapse
- the soma (cell body) -> axosomatic synapse
- other axon terminals -> axoaxonic synapse
What’s the neuraxis?
Neuraxis is the imaginary line that runs along the length of the brain and spinal cord (Central Nervous System)
Why do we say that all animals with a nervous system are bilateral creatures?
Because they have bilateral symmetry and the middle part is where the spinal cord runs down the animal
What does anterior mean?
In front
What does posterior mean?
Behind
What does superior mean?
Above
What does inferior mean?
Below
What does rostral mean?
Towards the beak
What does caudal mean?
Towards the tail
What does dorsal mean?
Towards the back
What does ventral mean?
Towards the belly
What does lateral mean?
Away from the midline
What does medial mean?
Toward the midline
What’s the Golgi stain?
- A mixture of silver nitrate and potassium chromate that causes 2% of brain cells to darken in colour as silver chromate crystallizes inside of them
- Using this stain to identify the structure of the nervous system and to label the neurons
What’s the soma/cell body of a neuron?
Where the nucleus is located
What are the dendrites?
- Branched, treelike extensions from the soma
- They’re responsible for sensing the external environment (for collecting information relevant to the cell)
What are axon terminals (or terminal buttons)?
- They’re responsible for releasing neurotransmitter when there’s an action potential
- They release neurotransmitter onto the downstream cells that they are in contact with
What’s the axon?
- The axon is responsible for transmitting information (via an action potential) to downstream cells
- They’re often insulated with fatty myelin sheaths, which improve the speed and fidelity of the action potential
What are different methods of orchestrating movement from a neuro cell?
- Diffusion method
- Directed transport: having a motor protein carrying something from one way or the other
- Electrical communication
How do we measure the resting membrane potential?
- It’s measured with glass micropipets filled with solutions which conduct charge
- The micropipet is inserted through the membrane into the cell
- We also use a voltmeter that measures the difference in electrical charge between 2 points or the potential difference
- It’s measured on a relative scale
- Measured in mVs (millivolts)
How many mV is the resting membrane potential in nerve and muscle?
Between -40 to -90 mV
Where is the reference electrode placed when measuring the resting membrane potential?
- Placed in the extracellular fluid which is designed as the ground and assigned a charge of 0 mV
- Extracellular fluid isn’t neutral
Is the cell membrane permeable or impermeable in water?
Impermeable
What’s an ion?
Charged atom or molecule
What’s a cation ion?
Positively charged ion
What’s an anion ion?
Negatively charged ion
What’s the electrostatic pressure?
Attractive force between molecules that are oppositely charged (negative/positive) or repulsive force between molecules that are similar charged (positive/positive)
What are ion channels?
- Specialized protein molecules that sit in the cell membrane
- They have a pore (hole) in them through which specific ions can enter or leave cells
What are leak channels?
An ion channel protein that is in the membrane and has a pore that’s always open
Do ions naturally cross the cell membrane?
No, they make proteins and they stick them in the membrane and these proteins will have a pore or hole through which specific ions can enter the cell
What are the main elements of a cell?
CHNOPS
- Hydrogen (H) 59%
- Oxygen (O) 24%
- Carbon (C) 11%
- Nitrogen (N) 4%
- Others (Phosphorus, sulfur,…) 2%
What are examples of positively charged ions?
Monovalent cations:
- Sodium (Na+)
- Potassium (K+)
Divalent cations:
- Calcium (Ca2+)
- Magnesium (Mg2+)
What are examples of negatively charged ions?
Chloride (Cl-)
Which ions are more abundant outside of cells (in the extracellular space)?
- Sodium
- Calcium
- Magnesium
- Chloride
Which ions are more abundant inside of cells (in the intracellular space)?
Potassium
What does monovalent mean?
1 charge
What does divalent mean?
2 charges
What happens if there is an equal concentration of positively and negatively charged ions on either side of the membrane?
Then,
- Outside of cell = 0 mV
- Inside of cell = 0 mV
- 0 electric potential
What 2 proteins are responsible for setting up and maintaining the resting membrane potential of neurons?
- Sodium-Potassium transporter
- Leak potassium channels
What’s the Sodium-Potassium transporter (or sodium-potassium pump)?
- Concentrates sodium and potassium outside and inside the cell, respectively
- The function of this protein is to pump Sodium or Na+ atoms out of the cell and Potassium or K+ atoms in
Describe the Leak potassium channels
- They’re always open
- The number of these channels largely determines the resting membrane potential
What concentration gradients does the Sodium-Potassium pump create?
- Causes K+ ions to be 30x more concentrated inside the cell than out
- Causes Na+ ions to be 15x more concentrated outside the cell than in
- These concentration gradients never change, ever, unless the cell dies
- There is no electrical charge difference yet (the membrane potential = 0), because there is a similar concentration of positive/negative ions inside and outside the cell
What ions are creating potential energy with regards to the sodium-potassium pump concentration gradient?
Potassium (K+) ions are creating potential energy related to the force of diffusion because K+ ions are crowded inside the cell, and they will leave if they can
What’s the force of diffusion?
If there’s a concentration gradient and no forces or barriers to prevent free movement of molecules, then molecules will move, on average, from regions of high concentration to regions of low concentration
When is the electrostatic energy of K+ equal and opposite to the diffusional force of K+ ?
When the inside of a cell reaches -90 mV
When a cell goes down to -90mV, what do we assume is in charge of this drop?
Leak channels
What’s the membrane potential?
Electrical charge across a cell membrane; difference in electrical potential inside and outside the cell
What’s the resting membrane potential?
- Membrane potential of a neuron when it’s not being altered by signalling 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 happens when a neuron has a lot of K+ channels?
The more K+ leak channels a neuron has, the more permeable it will be to K+ relative to other ions and the closer its membrane potential will be to -90 mV
What kind of stimuli in the external world do cells use proteins to detect?
- the presence of certain molecules (e.g., neurotransmitters)
- physical pressure (movement, touch)
- electrical pressure (voltage)
- temperature
- pH (acidity, basicity)
- electromagnetic radiation (light)
What’s depolarization?
When the membrane potential of a cell becomes less negative than it normally is at rest
(Ex: -60 to -50 mV from influx of Na+ ions)
What happens when positive Na+ ions enter a neuron through an ion channel which causes membrane depolarization?
It causes K+ ions to immediately leave the cell through leak channels, which restores the resting membrane potential
What are the 5 proteins involved with the action potential?
- Sodium-Potassium transporter
- Leak potassium channels
- Voltage-gated sodium channel
- Voltage-gated potassium channel
- Voltage-gated calcium channel
What is the purpose of the Voltage-gated sodium channel in the action potential?
To initiate and propagate the action potential
What is the purpose of the Voltage-gated potassium channel in the action potential?
To restore the resting membrane potential
What is the purpose of the Voltage-gated calcium channel in the action potential?
- Located in the axon terminal
- Triggers release of neurotransmitter
Describe the voltage-gated sodium channel
- These ion channels are found all over the axon, along its entire length
- The channel is closed at resting potential
- The gate opens whenever the membrane potential becomes less negative than -40 mV
- Voltage-gated channels have electrical charges on their doors, such that they open or close when the charge difference across the membrane is greater or smaller than some number
Describe the what happens when Na+ channels open?
- The opening of an Na+ channel allows Na+ ions to rush in, propelled by both diffusion and electrostatic forces
- This influx of Na+ depolarizes the membrane further, which causes additional voltage-gated Na+ channels to open
- Soon there’s an avalanche effect as all voltage-gated Na+ channels open causing the membrane potential to shoot up to +40mV
- Sodium goes in until the cell reaches +40 mV then it doesn’t wanna go in anymore, it’s happy
What’s the action potential?
- The action potential is a brief electrical impulse that provides the basis for conduction of information along the axon
- It’s a rapid change in the membrane potential caused by the opening and closing of voltage-gated ion channels
What’s the threshold of excitation?
The value of the membrane potential that must be reached to produce an action potential
What triggers an action potential?
The initial depolarization that starts an action potential is usually driven by the activation of a receptor that lets Na+ ions enter
What’s the membrane potential at the peak of the action potential?
- The membrane potential is +40mV
Why can’t we rely on Potassium leak channels to end the action potential?
It would take too long
To speed up restoration of the membrane potential, what other voltage-gated ion channel does the cell use?
The voltage-gated potassium channel, which activate at the peak of the action potential
What’s the refractory period?
A post action potential hyperpolarization, which is caused by all voltage-gated K+ channels not closing quick enough leading to the membrane falling below what it normally is at rest
Can you start another action potential immediately after one?
No, because of the refractory period, it becomes hard and takes longer to trigger another action potential right after one is completed
When do Voltage-gated K+ channels join in the action potential?
- They open in the middle of an action potential, when the membrane potential is around 0 mV.
- The opening of the voltage-gated K+ channels helps bring the membrane potential back down to -60 mV
The initial rising phase of the action potential reflects a sudden increase in membrane permeability of which ion?
Sodium (Na+), because the voltage-gated sodium channels are open
How can the speed of conduction of an action potential be calculated?
It can be calculated from the delay between the stimulus and the action potential
What’s the concentration of calcium inside vs outside the cell?
Calcium is 1000x more concentrated outside the cell than in
When do voltage-gated calcium channels open?
when the axon terminal becomes depolarized (i.e., in response to an action potential).
What’s the primary means of communication between neurons?
Synaptic transmission
What’s 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
- It operates by diffusion
What happens when voltage-gated calcium channels open?
- The influx of calcium causes several synaptic vesicles to simultaneously fuse with the presynaptic membrane
- Upon fusion, these vesicles break open and spill their contents into the synaptic cleft
In what direction does conduction of the action potential occur?
In a unidirectional manner
What’s the rate law?
The rate law states that the strength of the stimulus is represented by the rate of the firing axon
Which protein involved in the action potential requires ATP?
Sodium-Potassium transporter
What’s a protein?
a long chain of amino acids that fold up into complex 3 dimensional structures
How do you make a hole in membrane (potassium ion channel) that lets in a bigger ion (potassium) but not a smaller one (sodium)?
- Voltage-gated potassium channels are 4 proteins coming together to make a hole
- When zooming in on amino acids there are some bumps on them that make it so that different ions can enter (bigger ones rather than smaller ones)
- Bigger ions can enter rather than smaller ions is due to the water (hydration shell) -> these charges want to be balanced and this shell of water will cover them to balance them
- Carbonyl groups are spaced exactly to remove the hydration shell from the potassium which is a perfect fit with the carbonyl groups. But sodium ions are too small and don’t fit in these carbonyl groups so they can’t pass
- Sodium is covered in the hydration shell because it’s not the perfect fit so instead of going through it, it just floats away
When wanting to make a gene, what cells to scientists usually use?
- The egg cell from frogs’ ovaries (huge cells easy to see) and these don’t have ion channels
- People take out the eggs of the frog and stick in the gene that they want to study
What’s a gene promoter?
- A region of DNA that initiates transcription of a particulargene
- Indicates what kind of cells should read the gene and when.
- Promotersare typically located just before the gene
How many genes does the human genome contain for the voltage-gated potassium channel?
- 40 distinct genes that code different voltage-gated potassium channels
- Each cell can choose to express one or any combination of them to optimize cell function
What’s neuroglia (or glia cells)?
- Glia are found all around neurons and even physically encapsulate some parts of them
- They help traffic nutrients and maintain molecular (ionic) stability in the extracellular space
- They support many functions of the nervous system
- It’s estimated that they outnumber neurons in the brain
What are 3 types of glia cells?
- Astrocyte
- Microglia
- Oligodendrocytes
What’s an astrocyte?
- 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 neurons
What’s a microglia?
- The smallest of the glial cells
- They provide an immune system for the brain and protect the brain from invading microorganisms
What are Oligodendrocytes?
- Glial cells that produce the myelin sheath, which surround many axons in the central nervous system
- The sheath is not continuous; it is a series of segments
- Speed up action potentials
What’s the node of Ranvier
The exposed axon between the myelin sheaths
What are the processes formed by oligodendrocytes shaped like?
Like canoe paddles
What’s the only place along a myelinated axon that comes into contact with extracellular fluid?
At the node of Ranvier
What’s saltatory conduction?
- the conduction of action potentials by myelinated axons
- Action potential appears to jump from one node of Ranvier to next
- At each node, the strength of the signal is regenerated with additional voltage-gated Na+ channels
The transmission of what kind of sensory information is very slow for the action potential?
The transmission of pain information, as the cell for pain takes much longer (full second to get to the brain) when you touch heat
What’s a synapse?
A junction between the axon terminal of the sending neuron and the cell membrane of the receiving neuron
How is communication across the synapse achieved?
- By the release of a molecule (neurotransmitter) from an axon terminal
- This molecule can have a simple excitatory or inhibitory effect or a complex modulatory effect on the receiving neuron
What’s the presynaptic membrane?
- The membrane of the terminal button (the sending cell)
- This is where neurotransmitter is released from
- Presynaptic side is the one that sends off information
What’s the postsynaptic membrane?
- The membrane of the receiving cell that is opposite the axon terminal
- Postsynaptic side is the one that receives info
What’s a synaptic vesicle?
- Synaptic vesicles contain molecules of neurotransmitter
- They attach to the presynaptic membrane and release neurotransmitter into the synaptic cleft
What’s the synaptic cleft?
The space between the pre and postsynaptic membranes
- It’s filled with an extracellular fluid
What’s an electron microscopy?
An electron microscopy allows us to see small anatomical structures (e.g. synaptic vesicles and details of cell organelles) using a special electron microscope
What’s the neuromuscular junction?
Where a neuron is attached to a muscle
What’s a ligand?
- A signaling molecule that binds to the binding site of a receptor
- Most cell signaling and cell communication occurs through ligand-receptor interactions
- Neurotransmitters are ligands
What are the 2 categories of neurotransmitter receptors?
- Ionotropic receptors
- Metabotropic receptors
Where can receptors be located?
- On the cell membrane (surface receptors)
- Inside the cell (intracellular pool of receptors)
Neurotransmitter receptors are generally what kind of receptors?
Surface receptors
Where are postsynaptic receptors located?
They’re located on the postsynaptic membrane
Where are presynaptic receptors located?
They’re located on the presynaptic membrane
Where are extrasynaptic receptors located?
They’re located somewhere near but outside the synapse
What’s a neurotransmitter?
A signaling molecule that will bind to a receptor
What 3 ion channels do ionotropic receptors comprise of?
- leak channel
- voltage-gated ion channel
- ligand-gated ion channel
What’s a binding site?
Location on a receptor protein to which a ligand binds