Lecture 4 Flashcards
Chapter 2c
The Action Potential in Five Proteins are:
You know 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: voltage-gated ion channels
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)
We know the DNA letters (the exact string of nucleic acids) do what
encode these proteins in numerous species
A portion of the DNA that encodes the voltage-gated potassium channel: what letters encode it
AGA
AGA encodes what
These 3 letters encode the amino acid arginine
In genetics, apromoteris 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 A synapse
is a junction between the axon terminal of the sending neuron and a portion of the cell membrane of the receiving neuron
Communication generally proceeds in one direction only, what is it (synaptic communication)
FROM the axon terminal TO the membrane of the other cell.
A synapse is a junction between the axon terminal of the sending neuron and a portion of the cell membrane of the receiving neuron.
Communication generally proceeds in one direction only: FROM the axon terminal TO the membrane of the other cell.
This communication across the synapse is achieved how
by the release of a chemical from an axon terminal
A synapse is a junction between the axon terminal of the sending neuron and a portion of the cell membrane of the receiving neuron.
Communication generally proceeds in one direction only: FROM the axon terminal TO the membrane of the other cell.
This communication across the synapse is achieved by the release of a chemical from an axon terminal. This chemical is called a what
neurotransmitter
what kind of effect does a neurotransmitter have
can have a simple excitatory or inhibitory effect or a complex modulatory effect on the receiving neuron
what are the main parts of the synapse
Presynaptic membrane
Synaptic vesicles
Synaptic cleft
Postsynaptic membrane
what is the Presynaptic membrane
the membrane of the terminal button (the sending cell). This is where neurotransmitter is released from.
what is the Synaptic vesicles
contain molecules of neurotransmitter. They attach to the presynaptic membrane and release neurotransmitter into the synaptic cleft
what is the Synaptic cleft
is the space between the pre- and postsynaptic membranes. It is filled with an extracellular fluid.
what is the Postsynaptic membrane
is the membrane of the receiving cell that is opposite the axon terminal
what is Electron microscopy
allows us to see small anatomical structures (e.g. synaptic vesicles and details of cell organelles) using a special electron microscope.
Neurotransmitters are what kind of molecules
signaling
Signaling molecules that bind to protein receptors are called what
ligands
Most cell signaling and cell communication occurs through what kind of interactions
ligand-receptor interactions.
Receptors can either be located where
on the cell membrane (surface receptors) or somewhere inside the cell (intracellular receptors).
Neurotransmitter receptors are generally what kind of receptors
surface receptors
Postsynaptic receptors are located where
on the postsynaptic membrane
Presynaptic receptors are located where
on the presynaptic membrane
Extrasynaptic receptors are located where
somewhere outside of the synapse.
Neurotransmitter receptors can also be classified as what
ionotropic receptors or metabotropic receptors
Neurotransmitter receptors can also be classified as ionotropic receptors what are these
ion channels
Neurotransmitter receptors can also be classified as metabotropic receptors what are these
protein receptors that can open ion channels through an intracellular signaling cascade
what are the 4 main Communication Between Neurons
Ligand
Binding site
Postsynaptic Receptor
Ligand-gated ion channel
what do Ligand do
General term for a signaling molecule (chemical) that binds to the binding site of a receptor. Neurotransmitters are ligands.
what is the Binding site
Location on a receptor protein to which a ligand binds
what is Postsynaptic Receptor
Receptor protein in postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter
what are Ligand-gated ion channel
A receptor that is an ion channel. Also known as an ionotropic receptor. The ion channel opens when the ligand (e.g., the neurotransmitter) binds to it.
Neurotransmitter signaling in the synapse is kept brief by two mechanisms which are…
reuptake and enzymatic deactivation
what is Reuptake
Reentry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating postsynaptic potential
what is Enzymatic deactivation
Destruction of a neurotransmitter by enzyme after its release
For example, destruction of acetylcholine by acetylcholinesterase
what is Postsynaptic potential
Alterations in the membrane potential of a postsynaptic neuron, produced by neurotransmitter release into the synapse and receptor activation.
Postsynaptic potentials can either be …
excitatory (often due to an influx of positive sodium ions)
or
inhibitory (often due to an influx of negative chloride ions).
what is Excitatory postsynaptic potential (EPSP)
Excitatory depolarization of postsynaptic membrane caused by neurotransmitter binding to a postsynaptic receptor protein
Excitatory postsynaptic potential (EPSP) are mediated how
by receptor proteins that open ion channels permeable to sodium. (Making the membrane more permeable to sodium will push the membrane potential towards +40 mV.)
what is Neural integration
If only a couple EPSPs occur at one time, the influx of sodium ions will likely not cause an action potential.
The depolarizing effect of the incoming sodium ions will be counteracted by an increase in the outflow of potassium ions through the leak channels.
Really anytime positive sodium ions come in, the likelihood that positive potassium ions will leave increases.
Thus to trigger an action potential, many EPSPs have to occur at nearly the same time. Sodium ions have to come in at a faster rate that potassium ions can leave in order to depolarize the membrane to the threshold of activation. And, this depolarization has to reach the beginning of the axon (the axon hillock) where voltage-gated sodium channels are congregated and can trigger an action potential.
what is Inhibitory postsynaptic potential (IPSP)
Inhibitory hyperpolarization of postsynaptic caused by neurotransmitter binding to a postsynaptic receptor protein.
IPSPs are mediated how
by receptor proteins that open ion channels permeable to chloride. (Making the membrane more permeable to chloride will push the membrane potential towards -80 mV.)
The interaction of the excitatory and inhibitory synapses on a particular neuron is called what
neural integration
When EPSPs and IPSPs occur at the same time what happens
the influx of negatively charged chloride ions diminish the impact of the positively charged sodium ions. IPSPs decrease the likelihood that the cell will fire.
what are the 3 main points of Communication Between Neurons:Postsynaptic Potentials
Postsynaptic potentials can be either depolarizing (excitatory) or hyperpolarizing (inhibitory)
What determines the direction of the postsynaptic potential (EPSP vs IPSP) is not neurotransmitter, but rather the receptor
Some serotonin receptors cause EPSPs and others cause IPSPs. It is up to the postsynaptic cell to determine how it wants to respond the signaling molecule.
Postsynaptic potentials can be what
either depolarizing (excitatory) or hyperpolarizing (inhibitory)
What determines the direction of the postsynaptic potential (EPSP vs IPSP) is not neurotransmitter but…
rather the receptor
Some serotonin receptors cause EPSPs and others cause IPSPs what determines how it wants to respond
It is up to the postsynaptic cell to determine how it wants to respond the signaling molecule.
what is an Ionotropic Receptor
and what does it do
A neurotransmitter receptor that is an ion channel. The properties of the pore of the ion channel (the hole) will determine if it causes EPSPs or IPSPs (i.e., if it lets sodium or chloride ions through).
what is Metabotropic receptor
and what does it do
Neurotransmitter receptor that triggers an intracellular signaling cascade that often involves g proteins. The signaling cascade can lead to ion channel opening or other cellular effects.
what is G protein-gated ion channel
and what does it do
G proteins are a family of intracellular proteins that are involved in intracellular signaling cascades. Some ion channels are gated by g proteins.
regarding Metabotropic Receptors
G-protein signaling cascades can affect multiple downstream processes, including;
opening g protein-gated ion channels
changes in gene transcription
secretion of substances from the cell
really anything the cell wants.
When the dendrites of a sensory neuron are stimulated by a noxious stimulus (such as contact with a hot object), what happens
it sends messages down the axon to terminal buttons located in spinal cord.
The sensory neuron will activate an interneuron, which in turn will active a motor neuron and cause a withdrawal reflex
When the dendrites of a sensory neuron are stimulated by a noxious stimulus (such as contact with a hot object), it sends messages down the axon to terminal buttons located in spinal cord.
The sensory neuron will activate an interneuron, which in turn will active a motor neuron and cause a withdrawal reflex
however what might also happen
However, a neuron deep in the brain may have other plans. For example, a cortical neuron could send an action potential down the spinal cord to excite an inhibitory interneuron, which is a neuron that generally causes IPSCs in downstream neurons.
This interneuron would induce IPSCs in the motor neuron and block (counteract) the withdrawal reflex
This circuit provides an example of a contest between two competing tendencies: to drop the casserole and to hold onto it
An inhibitory neuron is a neuron that does what
reliably causes IPSCs in downstream neurons (i.e., it reduces the spiking activity of downstream neurons).
An inhibitory neuron is a neuron that reliably causes IPSCs in downstream neurons (i.e., it reduces the spiking activity of downstream neurons).
Keep in mind that the net result of inhibitory neuron activity may …
not be to inhibit an animal’s behaviour.
Sometimes, inhibitory neuron activity can cause a movement. This is often the case if…
the inhibitory neuron has synaptic connections on other inhibitory neurons. Inhibition of inhibitory neurons can make a behaviour more likely to occur.
An inhibitory neuron is a neuron that reliably causes IPSCs in downstream neurons (i.e., it reduces the spiking activity of downstream neurons).
Keep in mind that the net result of inhibitory neuron activity may not be to inhibit an animal’s behaviour.
Sometimes, inhibitory neuron activity can cause a movement. This is often the case if the inhibitory neuron has synaptic connections on other inhibitory neurons. Inhibition of inhibitory neurons can make a behaviour more likely to occur.
what is The big picture
For every neuron trying to change behaviour in one way, there are probably other neurons trying to do the opposite. Both groups of neurons are often regulated by inhibitory neurons. And in turn the inhibitory neurons themselves may be regulated by other inhibitory neurons. It is not uncommon to find long chains of inhibitory neurons in a row, which can make it really hard to determine which ones are trying to cause or prevent a behaviour. The take home point is that:
Neural excitation is not the same thing as behavioural excitation.
Neural inhibition is not the same thing as behavioural inhibition.
Synapses can form between axon terminals and …
dendrites (dendritic shafts)
dendritic spines
the soma (cell body)
other axon terminals
what are the 2 Axoaxonic Synapses
Presynaptic inhibition
and
Presynaptic facilitation
what is Presynaptic facilitation
The purpose of an axoaxonic synapse can be to increases the amount of neurotransmitter released by the second neuron when it has an action potential. It depolarizes the axon terminal of that neuron, so when an action potential comes more calcium channels open.
what is Presynaptic inhibition
The purpose of an axoaxonic synapse can be to reduce the amount of neurotransmitter released by the second neuron when it has an action potential. It hyperpolarizes the axon terminal of that neuron so its calcium channels may not open at all or for very long when an action potential arrives.
what is an Autoreceptor
Receptor located on the presynaptic neuron, the neuron that is releasing the neuro-transmitter
Autoreceptors are gated by what
the neurotransmitter that the cell releases
Autoreceptors are generally metabotropic and inhibitory. They are a main source of ….
presynaptic inhibition
where are Post-synaptic
receptors located
Post-synaptic
receptor: receptor located on the receiving neuron, the one that is not releasing the neurotransmitter
Cells are sensitive to certain molecules because why
of what they represent, the information they convey. These are called signaling molecules and they trigger a cellular response (beyond digestion).
Most signaling molecules fit into two broad categories which are
Amino acids (including proteins and amino acid derivatives) Lipids (including fats and steroids)
When signaling molecules are released into the circulatory system (the bloodstream) they are called what
hormones
When signaling molecules are released into the circulatory system (the bloodstream) they are called hormones. The same substance released in the brain would be called what
a neurotransmitter
what are the The Principal Neurotransmitters
Conventional neurotransmitters
Neuropeptides
Lipid-based signaling molecules
what are Conventional neurotransmitters
mostly amino acid derivatives
The main players: glutamate, GABA, dopamine, serotonin, norepinephrine, acetylcholine
are synthesized locally in axon terminals
are usually secreted from small synaptic vesicles (SSVs) that dock very close to the site of Ca2+entry in the axon terminal
generally activate ionotropic and metabotropic receptors
are typically recaptured after secretion
usually bind receptors directly across the synapse. Even when neurotransmitters diffuse, they only act over distances of tens to hundreds of micrometers
what are Neuropeptides
short string of amino acids (i.e., a protein formed with only ~ 10-30 amino acids)
Examples from the list of >70: oxytocin, vasopressin, enkephalin, prolactin, NPY, ghrelin, CRH
are synthesized in the cell soma, transported down the axon while undergoing additional processing, and released just once.
are usually secreted from large dense core vesicles (LDCV) that dock a ways back from the site of Ca2+entry in the axon terminal
only activate metabotropic receptors (neuropeptides do not activate ionotropic receptors)
no synaptic re-use occurs of either the neuropeptides or their immediate precursors.
may diffuse long distances and exert action at a distance (non-synaptic communication)
what are Lipid-based signaling molecules
(e.g., the cannabinoids anandamide and arachidonoylglycerol)
are synthesized and released on demand (as needed)
are secreted in an unknown, non-vesicular manner typically from postsynaptic neurons
activate metabotropic receptors typically located on the presynaptic axon terminal
