Neuronal Communication Flashcards
what are neurones?
the building blocks of the nervous system, and the connections between these are important for memory
why are neurones important for memory?
information must flow between neurones
transmission within neurones is an _______ process
electrical
transmission between neurones is an _______ process
chemical
what is resting membrane potential?
an example of electrical excitability
it underpins the ability of neurones to communicate and generate signals
how is action potential generated?
by using energy to maintain the unstable resting membrane potential
upon a trigger, the stored-up energy is released. this becomes a signal and generates electricity
what is the cell membrane of a neurone?
lipid bilayer, which consists of two layers of fatty molecules
what is the function of a sodium-potassium exchange transporter?
moves sodium ions outside of the cell in exchange to move potassium ions inside
more sodium is moved out than potassium in, accumulating in positively charged ions outside the cell
cation
+ve charge
anion
-ve charge
what is the resting membrane potential difference?
-70mV
what are the three different forces that control the movement of ions?
- electrostatic pressure
- transporter
- diffusion
what is electrostatic pressure?
similarly charged ions repel each other and opposite charged ions attract each other
what are transporters?
use energy to move specific ions in order to maintain resting potential
what is diffusion?
ions want to move from areas of high concentration to low concentration
what do semi-permeable membranes allow?
molecules and ions to pass through
moving down a concentration gradient
move from areas of high concentration to low concentration
moving against a concentration gradient
move from areas of low to high concentration
are cells positive on the outside or inside?
positive on the outside and negative on the inside
membrane potential
the difference between the electrical potential inside and outside the cell
what is membrane potential altered by?
ions moving in and out of the cell
action potential
the sudden change of the resting membrane potential
a rapid change in the polarisation (electrical charge) of the neurone to send a signal
K+
at rest, more K+ is inside the cell than outside.
diffusion- K+ ions want to move outside the cell
electrostatic pressure- K+ are attracted to the negative inside of the cell
Cl-
at rest, more Cl- is outside the cell than inside
diffusion- Cl- ions want to move into the cell
electrostatic pressure- Cl- are repelled by the negative inside of the cell
Na+
at rest, more Na+ is outside the cell than inside
diffusion- Na+ ions want to move into the cell
electrostatic pressure- Na+ are attracted to the negative inside of the cell
what is necessary to generate an action potential?
the resting membrane potential
for this signal to be sent, the neurone must gain enough action potential to reach the threshold of excitation- an all or nothing process
depolarisation
making the membrane less negative
repolarisation
returning the membrane to its negative state
what does depolarisation do?
brings the membrane closer to the threshold of excitation, and makes it more likely to fire an action potential
depolarisation is caused by opening the voltage-gated sodium channels
activation
the minimum energy required for a reaction to occur
- what happens at -55Mv?
the sodium and potassium channels open at the same time
- what happens after the channels open?
sodium cations flood into the cell (due to diffusion and electrostatic pressure)
3a. what happens to the membrane potential?
it becomes positive (membrane depolarisation as the outside is no longer more positive than the inside)
3b. once membrane depolarisation occurs, what can now leave the cell?
potassium cations, as they are no longer stopped by electrostatic pressure keeping them inside
3c. what happens when the membrane potential reaches 40Mv?
the sodium channel closes
- what remains open?
the potassium channels, and potassium cations continue to leave the cell (membrane repolarisation)
- when do the potassium channels close?
potassium cations continue to leave the cell until the membrane potential goes beyond 70Mv (this is when the potassium channels close)
where does the concentration change occur?
close to the membrane
what does action potential act as?
the basic code for information in the brain
what does the ‘all-or-nothing’ law explain about the rate of action potentials?
because the size and shape of action potentials do not change, it is the frequency (rate) of action potentials that are important in coding information
what does breaching the threshold of excitation lead to?
a release of energy
reasons that membrane depolarisation can occur
- action potential occurs in a close vicinity to the membrane, and localised movement around the area is enough to ‘breach the threshold of excitation’
- sensory receptors responding to stimulation, which creates a graded response
- chemical transmission between neurones
why is communication within the neurone fast?
it is facilitated by the myelin sheath
action potential jumps between nodes, meaning it only needs to regenerate energy at the nodes instead of the entire length of the axon
what is a synapse?
the junction between two neurones, where they communicate through a chemical process
what is the name of the small gap between the synapse and the membrane?
synaptic cleft
how does information travel between neurones?
it travels across synapse A, across the synaptic cleft, and into the receptors on neurone B
where are neurotransmitters made and stored?
made in the soma of the cell
stored in the vesicles
what is the role of neurotransmitters?
they bind to the receptor’s binding site on the postsynaptic cell
these binding sites contain ion channels
what is the role of ion channels?
these let ions in or out of the postsynaptic cell
how is a postsynaptic potential created?
by ions moving into and out of the cell
what is needed for electrical signals to pass?
the postsynaptic neurone needs to be depolarised
- the presynaptic neurone brings new information to the synapse.
what is found at the end of the axon?
there is an axonal terminal which contains vesicles (inside these are neurotransmitters)
1b. how does the presynaptic neurone release neurotransmitters into the synaptic cleft?
it ‘fuses the membrane of the vesicle to the external cell membrane of the axon’
1c. what does this allow?
the contents of the vesicle (neurotransmitters) to diffuse into the synaptic cleft
2a. where does the postsynaptic neurone recieve the information?
at the synapse, and the neurotransmitters bind to receptors
2b. what are these receptors?
ion channels
this means that the ion channel opens once the neurotransmitter binds to the receptor
- what happens when the ion channel opens?
certain ions are able to flow through, which changes the voltage of the postsynaptic neurone
this creates a postsynaptic potential
what do neurotransmitters provide the basis for understanding?
how drugs work within the brain
what are the two types of postsynaptic potentials?
EPSP and IPSP
excitatory postsynaptic potential
the receiving neurone cell is encouraged to fire, and sends messages to other neurones
inhibitory postsynaptic potential
the receiving neurone cell is discouraged from firing and sending on the message
sodium (Na+) postsynaptic potential
can only move into the postsynaptic cell and not out
if a lot moves in, EPSP occurs
the cell will become depolarised
potassium (K+) postsynaptic potential
can only move out of the postsynaptic cell
if a lot moves out, IPSP is created
the cell will become hyperpolarised
chloride (Cl-) postsynaptic potential
can only move into the postsynaptic potential
if a lot moves in, IPSP occurs
the cell will become hyperpolarised
why does EPSP occur?
because of hyperpolarisation
it brings the membrane closer to the threshold of excitation, and more likely to fire an action potential
how is EPSP achieved?
opening cation channels
why does IPSP occur?
due to the opening of anion channels, which make it less likely to fire an action potential
what are two types of receptors?
ionotropic and metabotropic
process of ionotropic receptors
the ion channel on the ionotropic receptor will only open when a neurotransmitter binds to their particular binding site
can be said that ‘the receptor is an ion channel’
what are ionotropic receptors good for?
for quick, direct updates, e.g., sight and hearing
process of metabotropic receptors
the indirect method of transmission between neurones
chain reaction of metabotropic receptors
the ligand binds to the ion channel
changes the 3D receptor shape
activates the G-protein
activates an enzyme which produces second messengers
opens the ion channel
what are metabotropic receptors good for?
more useful for things that need to last a while, e.g., taste, smell, pain
what is the difference between ionotropic and metabotropic receptors?
unlike ionotropic receptors, metabotropic receptors do not directly produce postsynaptic potentials
instead, chemical reactions occur within the neurone
what might be explained by these different types of receptors?
why certain neurotransmitters have different functions
why can receptors sometimes be found on the presynaptic neurone?
this allows for signals to go in the opposite direction towards the presynaptic neurone
this might happen due to a negative feedback loop- if the neurotransmitter release does not need to happen, it binds to presynaptic receptors to turn off unnecessary signals and avoid future release
what are postsynaptic receptors?
proteins embedded within the membrane of the postsynaptic neurone
what is ligand?
any molecule or chemical that interacts with a receptor
what is a binding site?
the area on the receptor where the ligand interacts
what is the function of receptors being 3D structures?
ligands can fit in one particular area of the structure, and receptors will only interact with molecules of a certain shape
what are also ligands?
drugs
this explains the chemical effect of binding to bodily receptors
what is conformational selectivity?
ligands and receptors have particular 3D shapes, meaning that only specific ligands will fit in a particular binding site
what is affinity?
how well a ligand binds to a receptorq
what is meant by high affinity?
receptors are saturated (bound) by very dilute solutions of ligand
this means that less ligand is needed to produce the maximum effect
what can determine the effect of the ligand to receptors?
selectivity and affinity
where are neurotransmitters clustered?
in the axonal terminal, and they are found in the synaptic vesicle
how are neurotransmitters released?
into the synaptic cleft via fusion of the vesicle to the postsynaptic membrane
process of neurotransmitter release
- nerve signal reaches the end of the axon
- this causes vesicles to merge with the cell surface membrane and eject the neurotransmitter
- neurotransmitter binds to the postsynaptic receptor to cause an effect
what are two types of neurotransmitters?
glutamate and GABA
what is glutamate?
derived from glutamic acid
what type of neurotransmitter is glutamate?
the most abundant neurotransmitter
excitatory
what receptors does glutamate bind to?
both ionotropic and metabotropic receptors
what is glutamate important for?
learning and memory
what is GABA?
made from glutamate
gamma-aminobutyric acid
what type of neurotransmitter is GABA?
the most abundant inhibitory neurotransmitter
what receptors does GABA bind to?
ionotropic and metabotropic GABA receptors, and it reduces the likelihood of neurones firing
what is glycine?
a co-agonist at NMDA receptors
what are monoamines?
a different type of neurotransmitter that mostly bind to metabotropic receptors, e.g., serotonin, dopamine, noradrenaline
