Synaptic Transmission Flashcards
(16 cards)
what is Synaptic Transmission
synaptic transmission is the process for transmitting messages (communication) from neuron to neuron
label/draw a synapse
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outline process of synaptic transmission
- action potential (electrical signal) created in pre-synaptic neuron. it travels from the dendrites down the axon until it reaches the presynaptic terminal (end of the neuron). All signals within the neuron are electrical.
- each neuron is separated from the next by a tiny gap called a synapse. electrical signal can’t cross the synapse so must become chemical. to do this it stimulates vesicles (sacs containing neurotransmitters) to release neurotransmitters (chemical messengers) into the synapse.
- neurotransmitters crosses gap, binds with receptors on the dendrites of the postsynaptic neuron. this enables the signal/info to be transmitted.
- the effect will depend on the neurotransmitter being excitatory or inhibitory. a neuron can receive both excitatory and inhibitory NTs at the same time - the likelihood of the cell firing is therefore determined by adding up the excitatory (more likely to fire) and inhibitory (less likely to fire) synaptic input (summation)
- neurotransmitters can travel back to the presynaptic neuron. This process is known as ‘reuptake’ which allows the neurotransmitter to be stored and made available for later use (recycling programme)
neurotransmitters
several types of neurotransmitters (chemical messengers) have been identified in the brain.
each NT has its own specific structure that fits perfectly into a post-synaptic receptor site (lock and key).
NTs have specialist functions
- eg. acetylcholine (ACh) is found at each point where a motor neurons meets a muscle. when released it causes muscles to contract.
- eg. dopamine affects the NS including emotional arousal, pleasure, voluntary movement.
excitation and inhibition
NTs have either an excitatory or inhibitory effect on the neighbouring neuron.
Inhibitory NTs (eg seratonin) cause inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire.
If the message is likely to be stopped at the post synaptic neuron, it is an inhibitory synapse.
Hyperpolarisation: positively charged Potassium ions leave the postsynaptic cell
Excitatory NTs (eg. adrenaline) cause excitation of the post synaptic neuron by increasing its positive charge and making it more likely to fire.
If a synapse is more likely to cause the post-synaptic neuron to fire, its is an excitatory synapse.
Depolarisation: positively charged Sodium ions enter the postsynaptic cell
excitatory potential like the accelerator and an inhibitory potential is like the brake.
normal brain function depends on regulated balance between excitatory and inhibitory influence.
summation
a neuron can receive both excitatory and inhibitory NTs at the same time.
the likelihood of the cell firing is therefore determined by adding up the excitatory and inhibitory synaptic input. known as summation.
if more excitatory NTs bind with receptors, the overall net effect will be a positive charge and the neuron will be more likely to fire (if a threshold is reached, a new action potential will form in the post synaptic cell)
if more inhibitory NTs bind with receptors, the overall net effect will be a negative charge and the neuron will be less likely to fire
what is depolarisation
depolarisation refers to the reduction of the negative charge inside a neuron, making it more positive and likely to fire an electrical signal
Neurons communicate through electrical impulses.
At rest, a neuron has a negative charge inside compared to the outside (this is called the resting potential).
When a neuron is stimulated, sodium (Na⁺) ions rush into the cell, making the inside less negative.
This shift in charge is called depolarisation.
If the change reaches a certain threshold, it triggers an action potential, allowing the nerve signal to travel down the neuron.
what is hyperpolarisation
Hyperpolarisation refers to the stage in a neuron’s electrical cycle when the inside of the neuron becomes more negative than its resting potential.
Normally, a resting neuron has a negative charge inside,
During an action potential, the neuron depolarises (becomes more positive) and then repolarises (returns to negative).
In hyperpolarisation, too many potassium ions (K⁺) exit the neuron.
This makes the inside even more negative than it was at rest.
As a result, the neuron is temporarily less likely to fire again.
Hyperpolarisation is part of the refractory period, a safety mechanism that:
- Prevents overstimulation
- Ensures signals travel in one direction down the neuron.
- Allows the neuron to reset before firing again.
Hyperpolarisation is when a neuron’s internal charge becomes more negative than usual, making it harder to trigger another nerve impulse immediately.
what is the refractory period
The refractory period is a short time after a neuron fires when it cannot fire again immediately.
After a neuron sends an action potential (a nerve impulse), it needs a moment to reset. During this time the neuron can’t be stimulated to fire again.
what is the resting potential
Resting potential refers to the electrical charge inside a neuron when it’s not actively sending a signal.
When a neuron is at rest, the inside of the cell is negatively charged compared to the outside.
the resting potential prepares the neuron to fire when it gets stimulated.
Once a strong enough stimulus is received, depolarisation starts, and an action potential is triggered.
what is the action potential
Action potential is the brief electrical charge that travels along a neuron when it fires — this is how information is transmitted in the nervous system.
When a neuron is stimulated strongly enough:
The inside of the neuron becomes less negative (this is depolarisation).
If the charge reaches a threshold, an action potential is triggered.
This causes an electrical impulse to travel down the axon.
what is repolarisation
Repolarisation is the process where a neuron returns to its negative resting charge after an action potential has occurred.
After a neuron fires (depolarises), it needs to reset.
During repolarisation:
Potassium ions (K⁺) move out of the neuron.
This causes the inside of the neuron to become more negative again.
This helps restore the resting potential.
stages of neuronal transmission
1) Resting Potential: Neuron is at rest (inside more negatively charged than outside the cell)
2) Depolarisation: Neuron stimulated. positive Sodium ions (Na⁺) rush in → inside becomes positive.
3) Action Potential: electrical impulse triggered once threshold is reached. travels down and transmitted to next neuron.
4) Repolarisation: Positive Potassium ions (K⁺) move out → neuron starts returning to negative.
5) Hyperpolarisation: Too many K+ ions move out, Neuron becomes more negative than resting.
6) Refractory Period: Neuron resets and cannot fire again immediately.
transport proteins
Transport proteins are proteins in the neuron’s membrane that move ions such as sodium and potassium in or out of the cell. T
hey are essential for maintaining the resting potential and generating action potentials.
allow for reabsorption of NTs during reuptake
unidirectional
info passed chemically (neurotransmission) between neurons can only be passed in one direction.
this is due to the synapse structure eg location of the receptors
reuptake
NTs reabsorbed into the presynaptic cell after transmitting a neural impulse
this happens at transport proteins in the synapse
prepares the cell to fire again by being stored and made available for later use (recycling programme)
