Lecture 4: Neurotransmitter Receptors Flashcards
the portion of the DNA that encodes the voltage-gated potassium channel
AGA
a portion of DNA that encodes the amino acid arginine
AAA
How do ion channels let in potassium (a bigger ion) but not sodium (a smaller ion)?
Selectivity filters remove potassium ions’ hydration shells, allowing them to enter the channel. But other ions like sodium are too small for the filter to remove its hydration shell
promoter
a region of DNA that initiates transcription of a particular gene
transcription
the process of copying a segment of DNA into RNA
the human genome contains ___ distinct genes for the voltage-gated potassium channel
40
Neuroglia (glial cells)
help traffic neurons and maintain ions’ stability. found all around neurons and even physically encapsulates some
ratio of glial cells to neurons
2:1 - 5:1
3 types of glial cells
astrocytes, microglia, oligodendrocytes
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.
microglia
small glial cells. They provide an immune system for the brain and protect the brain from invading microorganisms.
Oligodendrocytes
produce the myelin sheath, which encapsulates axons
node of Ranvier
The exposed axon
one oligodendrocyte produces ____ myelin sheaths
50
how do oligodendrocytes produce myelin?
During the development of the CNS, they form processes shaped like canoe paddles. Each of the processes then wraps itself many times around a segment of the axon and while doing so, produces layers of myelin that make up the myelin sheath
the only place where a myelinated axon comes into contact with the extracellular fluid is
at the node of Ranvier
distribution of sodium in the action potential
- sodium flow at node generates an action potential
- sodium diffuses along the inside of the axolemma to the next node
- excitation of voltage-regulated gates will generate the next action potential
t or f: ion channels are found in myelinated areas
false; there are almost no ions channels and those that are there have no effect because there is no extracellular fluid outside the membrane
Saltatory conduction
the conduction of action potentials by myelinated axons
conduction of action potentials in myelinated axons
- action potential appears to jump from one node of Ranvier to the next
- at each one, the strength of the signal is regenerated with additional voltage-gated sodium channels
the fastest action potentials can travel is
100 m/s
the transmission of pain information travels at
1 m/s
synapse
the function between the axon terminal of the sending neuron and the cell membrane of the receiving neuron
Neurotransmitter
a molecule that can have a simple excitatory or inhibitory effect or a complex modulatory effect on the receiving neuron
Synaptic vesicles
contain molecules of neurotransmitters. They attach to the presynaptic membrane and release neurotransmitters into the synaptic cleft
synaptic cleft
the space between the pre-and postsynaptic membranes. It is filled with extracellular fluid.
presynaptic membrane
the membrane of the terminal button (the sending cell). This is where neurotransmitter is released from.
postsynaptic membrane
the membrane of the receiving cell that is opposite the axon terminal.
Electron Microscopy
Allows us to see small anatomical structures (e.g. synaptic vesicles and details of cell organelles) using a special electron microscope.
ligands
signalling molecules that bind to protein receptors
two categories of neurotransmitter receptors
ionotropic & metabotropic receptors
Ionotropic receptors
ion channels
Metabotropic receptors
protein-coupled receptors that can open ion channels through an intracellular signalling cascade
receptors can be located ___ & ____
on the cell membrane or inside the cell
surface receptors
located on the cell membrane
intracellular pool of receptors
located inside the cell
3 types of surface receptors
postsynaptic, presynaptic, extrasynaptic receptors
postsynaptic receptors
located on the postsynaptic membrane
presynaptic receptors
located on the presynaptic membrane
extrasynaptic receptors
located somewhere near but outside the synapse
binding site
located on a receptor protein to which a ligand binds
enzymatic deviation
destruction of neurotransmitter by enzyme after its release so that the next action potential can be received
reuptake
reentry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating postsynaptic potential
Postsynaptic potential
Alterations in the membrane potential of a postsynaptic neuron, produced by neurotransmitter release into the synapse and receptor activation.
excitatory
an influx of positive sodium ions depolarizes the cell
inhibitory
an influx of negative chloride ions hyperpolarizes the cell
Depolarization
When the membrane potential of a cell becomes less negative than it normally is at rest.
hyperpolarization
When the membrane potential of a cell becomes more negative than it normally is at rest
Excitatory Postsynaptic Potential (EPSP)
Excitatory depolarization of postsynaptic membrane caused by neurotransmitter binding to a postsynaptic receptor protein.
Inhibitory Postsynaptic Potential (IPSP)
Inhibitory hyperpolarization of the cell is caused by neurotransmitter binding to a postsynaptic receptor protein.
neural integration
The excitatory and inhibition synapses on a particular neuron
EPSPs and action potentials
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 than potassium ions can leave in order to depolarize the membrane to the threshold of action
IPSPs _____ the likelihood that the cell will fire
decrease
what determines the direction of the postsynaptic potential (EPSP vs IPSP)
the receptor
Interneuron
a neuron internally contained within the brain and the spinal cord
can we override reflexes?
yes, if we consciously try we can. the 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
t or f: Neural excitation = behavioural excitation.
false
t or f: Neural inhibition = behavioural inhibition
false
receptor protein
a protein that is sensitive to and capable of communicating some signal
Most cell signalling and cell communication occur through
ligand-receptor interactions
how do ionotropic receptors determine if they will produce EPSPs or IPSPs?
the properties of the pore determine if it will let in positively charged sodium ions and increase the likelihood of firing an action potential (EPSPs) or negatively charged chloride ions and decrease the likelihood of firing an action potential (IPSPs)
how do metabotropic receptors mediate their effects?
activating g proteins
g proteins
proteins that bind to the GTP molecule instead of ATP for the energy they need to perform chemical reactions
when are g proteins on
when they are bound to GTP because in this state they can trigger chemical reactions
what happens when g proteins are off
they are not bound to GTP and the g protein is converted from GTP to GDP making the g protein inactivated
can g proteins gate ion channels?
yes
where can synapses form?
between the axon terminals and
1. Dendrites (dendritic shafts)
2. Dendritic spines
3. The soma (cell body)
4. Other axons terminals (axoaxonic synapses)
Axoaxonic synapses
regulate the amount of neurotransmitter that the second neuron will release when it has an action potential
Presynaptic inhibition
axoaxonic synapse can hyperpolarize the axon terminal of the downstream neuron so that its voltage-gated calcium channels will not open at all or for very long when an action potential arrives. The net effect is to reduce neurotransmitter release when it has an action potential
Presynaptic facilitation
axoaxonic synapses can depolarize the axon terminal of the downstream neuron so that its voltage-gated calcium channels are more likely to open when an action potential arrives. The net effect is to increase neurotransmitter release when the cell has an action potential
what is the main source of presynaptic inhibition
autoreceptors
autoreceptors
a receptor located on the presynaptic membrane that gets activated when the cell releases its own neurotransmitter
metabolism
chemical reactions that occur inside cells
if the space between nodes of Ranvier was increased, the action potential would…
fail to propagate
nodes of ranvier function
allow the action potential to quickly skip along unmyelinated portions of the axon
