6.2 Nerve impulses and synapes Flashcards
What are the 2 types of cells in the nervous system
- Neurones
- Neuroglia
What is the role of the neurones
To transmit impulses
What is the role of neuroglia
Provide either structural and/ or metabolic support to neurones
What is the name of the neuroglia used in the AQA spec
Schwann cells
Draw and label a motor neurone
Look at 6.2 slide 4 ppt
How do you identify a motor neurone
The cell body is at 1 end of the neurone
What is an axon
A single extension that transmits impulse away from cell body
When are dendrites
Multiple extension that transmit impulse towards cell body
Where does the motor neurone transmit impulse from and to
From the central nervous system
To the effectors
Where do the sensory neurones transmit impulses from and to
From receptors
To central nervous system
Where do the intermediate neurones transmit impulses from and to
From sensory neurone
To motor neurone
In a sensory neurone, what in the name of the single extension that comes from the dendrites and goes towards the cell body
Dendron
What produces a nervous impulse
A potential difference across a membrane
What is a potential difference measured in
mV
When speaking about a potential difference, what charge is relative to what
Charge on inside of membrane relative to the charge on the outside of the membrane
What measures the potential difference
Cathode ray oscilloscope (C.R.O)
How does a cathode ray oscilloscope work
Uses microelectrodes which produces a graphical trace if change in potential difference over time
What causes a potential difference
Distribution of ions
What ions are used to create a potential difference
Sodium ions
Potassium ions
If there are fewer ions on the inside of the membrane, describe the charge
Inside of membrane is negative relative to the outside of the membrane
When the inside of the membrane is negative relative to the outside, what is the membrane said to be
Polarised
The membrane is at _________ when the inside is negative relative to the outside
Resting potential
What is the potential difference of a membrane at resting potential, AQA value
- -70 mV
There are more ions inside the membrane than the outside, describe the charge
Inside of the membrane is positive relative to the outside
When the inside of the membrane is positive relative to the outside, what is the membrane said to be
Depolarised
The membrane is at ________ when the inside of the membrane is positive relative to the outside
Action potential
What is the potential difference of a membrane at action potential, AQA value
+ 40 mV
When the SAN sends out a wave of depolarisation, what happens to the ions
The ions move into the membrane to make the inside of the membrane positive relative to the outside of the membrane
Are the majority of neurones myelinated
Yes
What does myelin provide
Electrical insulation
When myelin is around a neurone, what cannot happen
Ions cannot move in or out of the membrane so the axon cannot depolarise
When there is myelin around a neurone, what is the name of the section where depolarisation can occur
Node of Ranvier
On a graphical trace of the changes in p.d. across the axon membrane, when the graph increases from resting potential, what is the name of the process
Depolarising
What happens to the ions when the membrane is depolarising
The ions are moving into the membrane
When the membrane is repolarising, what happens to the ions
The ions are moving out of the membrane
In the node of Ranvier, how many sodium ions are transported, and are they transported in or out of the membrane per 1 ATP
3 Sodium ions are transport out of the membrane
In the node of Ranvier, how many potassium ions are transported, and are they transported in or out of the membrane per 1 ATP
2 Potassium ions are transported into the membrane
What cells are in the myelin sheath
Schwann cells
What is resting potential
When no nerve impulse has been generated
Define action potential
A sudden, fast, transitory, and propagated change of resting membrane potential
When membrane is at resting potential, what one word is used to describe the membrane
Polarised
What are the 2 proteins in the membrane that are responsible to keep membrane at resting potential
- Sodium ions and potassium ion pump
- Leakage channels
Is the axon membrane more permeable to potassium ions or sodium ions
Potassium ions
When the membrane is at resting potential, what leakage channel is open, name the ion
Potassium ion leakage channel
How does the sodium ion, potassium ion pump help keep the axon membrane at resting potential
For every 2 potassium ions pumped in, 3 sodium ions are pumped out, so overall more ions leave the membrane making the inside of the membrane negative relative to the outside, so at resting potential
How do the leakage channels help the axon membrane remain at resting potential
The axon membrane is more permeable to potassium ions, so potassium ions diffuse out of the membrane which makes the inside of the membrane negative relative to the outside, so at resting potential
During action potential, what voltage gated channel protein opens
The sodium ion voltage gated channel protein
At roughly what voltage do the voltage gated sodium ions channels open
Roughly -55 mV
When the sodium gated channels open during action potential, what happens
Sodium ions rapidly diffuse/ influx into the axon which makes the inside of the membrane positive relative to the outside which momentarily depolarising the membrane
What voltage gated channel protein is closed when the membrane is at action potential
The potassium ion
When the axon membrane repolarises, what happens to the potential difference
Falls
When the axon membrane repolarises, what happens to the voltage gated channel proteins, state what happens to both
- Sodium ion gates close
- Potassium ion gates open
At roughly what voltage do the sodium gated channel proteins close
+40 mV
At roughly what voltage do the potassium ion gated channel proteins open
+ 40 mV
What 2 proteins in the axon membrane are used to repolarise the membrane
- Sodium ion, potassium ion pump
- Potassium gated channel protein
How does the potassium ion gated channel protein cause the membrane to repolarise
Potassium ions rapidly diffuse out of the membrane/ outflux which makes the inside of the membrane negative relative to the inside, which leads to the membrane being repolarised
What is the main channel protein that restores resting potential
The sodium ion, potassium ion pump
When looking at a graphical trace from a C.R.O, what is the name of the process that causes the potential difference to drops lower than the resting potential after the membrane has been repolarised
Hyperpolarisation
If at 1 node of Ranvier there’s an action potential, what happens to the sodium ions
The sodium ions move to the next Node of Ranvier
When the sodium ions move into the next Node of Ranvier as they move down the axon, what does this lead to
The impulse moves down the axon, so the next Node of Ranvier has a more positive membrane relative to the outside, so then the sodium ions are pumped out of the membrane
What is the potential difference in the refractory period
Less than -70mV
What is the charge of the inside of the membrane relative to the outside of the membrane at the refractory period
Negative inside relative to the outside
What is the name of the conduction that occurs in myelinated neurones
Saltatory conduction
What does saltatory conduction describe
The ‘jumping’ action of the action potential from one node of Ranvier to the next
Why does saltatory conduction occur in myelinated neruones
Since the membrane can only be depolarised at the node of Ranvier, so this results in a ‘jumping’ effect on the action potential, opposed to the every section of the membrane being depolarised
What is meant by the absolute refractory period
Absolutely not possible to generate another action potential, regardless of the strength of the stimuli
When is the absolute refractory period
When the membrane is depolarising, at action potential, and then repolarising
What is meant by the relative refractory period
Highly unlikely for another action potential to be generated but is possible if the stimuli is really strong
When is the relative refractory period
During hyperpolarisation and when the membrane reaches resting potential again
What are the 2 benefits of hyperpolarisation/ the relative refractory period
- Ensures impulse don’t merge- so only one action potential occurs
- Ensures a unidirectional transmission- so the membrane behind the impulse doesn’t get depolarised again
What has to be reached in order for a generator potential to be reached
The threshold value
If the threshold value isn’t reached, what happens
A failed initiation, so the membrane doesn’t get depolarised so an action potential doesn’t occur
If a threshold value is reached, what happens
An action potential occurs
What is meant by the all or nothing principle
If the threshold value is reached, all action potentials have the same amplitude regardless of the strength of the stimuli.
If the threshold value isn’t reached, no action potential will occur
If all action potentials have the same amplitude regardless of the strength of the stimuli, what causes a strong response
A strong stimuli is reflected in the frequency of the action potential
What limits the frequency of the action potential
The refractory period as it stops the merge of impulse, so limits the frequency a little
What are the 3 factors that affect conduction velocity
- Myelination
- Axon diameter
- Temperature
What is the name of the type of conduction that happens in a non-myelinated neurone
Step by step conduction
Why is step by step conduction slower than saltatory conduction
Since every section needs to be depolarised in step by step whereas in saltatory conduction the membrane is only depolarised at the node of Ranvier
What is the relationship between axon diameter and conduction velocity
As the axon diameter increases, the conduction velocity also increases
Why does a larger axon diameter result in an increase in conduction velocity
Since there’s less resistance from axon plasma
List the 4 reasons in order associated with the increase in conduction velocity as axon diameter increases
- Less resistance from axon plasma
- So the sodium ions can move more
- The voltage gated sodium channels are more spread out
- Fewer sections that need to be depolarised
How does temperature effect the conduction velocity
- Increase temperature
- Increases conduction velocity
- Since the sodium ions have more kinetic energy, so move faster through the axon, and both ions diffuse faster which results in faster transmission of an impulse
Explain how a resting potential is maintained across the axon membrane in a neurone (3 marks)
- Higher concentration of potassium ions inside and higher
concentration of sodium ions outside (the neurone)
OR
potassium ions diffuse out
OR
sodium ions diffuse in; - (Membrane) more permeable to potassium ions (leaving
than sodium ions entering)
OR
(Membrane) less permeable to sodium ions (entering
than potassium ions leaving); - Sodium ions (actively) transported out and potassium ions in;
Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon (3 marks)
- Myelination provides (electrical) insulation;
- (In myelinated) saltatory (conduction)
OR
(In myelinated) depolarisation at nodes (of Ranvier); - In non-myelinated depolarisation occurs along whole/length (of axon);
A scientists investigated the ffect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from -70mV to 0mV.
Explain why (3 marks)
- No/less ATP produced;
- No/less active transport
OR
Sodium/potassium pump inhibited; - Electrochemical gradient not maintained
OR
(Facilitated) diffusion of ions causes change to 0 mV
OR
(Results in) same concentration of (sodium and
potassium) ions (either side of membrane)
OR
No net movement of (sodium and potassium) ions;
Describe what nodes of Ranvier are
In between the Schwann cells along the axon there are gaps
Explain what is meant by the refractory period
The time following an action potential during which another action potential cannot take place
What is a synapse
Junction between neurones
What does synapes prevent
Electrical impulses passing directly from one neurone to the next
What do the synapses ensure happens to the direction of the impulse
The impulse passes in one direction
What are the 2 types of synapses
- Where 2 neurones meet
- Between a neurone and a muscle (neuromuscular junction)
What type of biological molecule are neurotransmitters
Protein
What type of protein are neurotransmitters
Globular, teritary structure
What is the name of the 2 neurotransmitters on the AQA spec
- Acetylcholine
- Noradrenaline
From the axon, where does the action potential then arrive
At the axon terminal of the presynaptic neurone
When the impulse reaches the presynaptic neurone, what happens to the membrane
Depolarised
When the membrane of the presynaptic neurone gets depolarised, what gated channels open
Calcium ions
When the calcium ion gated channels open in the presynaptic membrane, what happens
Calcium ions diffuse rapidly into the presynaptic neurone
What triggers the synaptic vesicles to move towards the presynaptic membrane
The calcium ions entering the presynaptic neurone
What do the synaptic vesicles contain
Neurotransmitters (acetylcholine)
What happens to the synaptic vesicles, after the calcium ions have diffused into the presynaptic neurone
Synaptic vesicles move towards and fuse with presynaptic membrane
By what process, are the neurotransmitters (acetylcholine) released from the presynaptic neurone
Released by exocyotosis
When the neurotransmitters (acetylcholine) are released from the presynaptic neurone, where do they go
Into the synaptic cleft
When the neurotransmitters are in the synaptic cleft, what happens
They diffuse across the cleft
After the neurotransmitters have diffused across the synaptic cleft, what happens
The neurotransmitters bind to protein receptors in the post synaptic membrane
What is the knock on effect of the neurotransmitters binding to the protein receptors on the postsynaptic membrane
The sodium ion gated channels open and sodium ions rapidly diffuse into the post synaptic neurone
What happens to the post synaptic membrane when the sodium ions diffuse in
Gets depolarised
What must be reached in the post synaptic membrane for the action potential to be passed down the neurone
The threshold value
If the threshold value is met in the post synaptic neurone, what happens
The action potential is propagated
As long as there are neurotransmitters bound to the protein receptors in the post synaptic membrane, what remains open
The sodium ion gated channels
What must happen in order for the sodium ion gated channels to close in the post synaptic membrane
The neurotransmitters need to be hydrolysed
What is the name of the enzyme that hydrolyses acetylcholine
Acetylcholinesterase
What are the products of the hydrolysis of acetylcholine
- Ethanoic acid
- Choline
What happens to the products of acteylcholine hydrolysis
Diffuse back across the synaptic cleft
By what process are the products of acetylcholine hydrolysis taken back into the presynaptic neurone
Endocyotosis
When the products of acetylcholine hydrolysis are taken back into the pre synaptic neurone, what happens
They reform into acetylcholine
What organelle is very heavily concentrated into the pre synaptic neurone, and why
Mitochondria
- Endocyotosis is an active process
- Reforming acetylcholine is also an active process
Explain why synaptic transmission is unidirectional
- Neurotransmitters are contained in vesicles only in the pre synaptic neurone
- Protein receptors for the neurotransmitter are only found on the post synaptic membrane
What is the main function of the synapse
Transmit impulses between neurones
What 3 things ensure that synapses maintain a unidirectional transmission of impulse
- There’s only synaptic vesicles in the pre-synaptic neurone
- Calcium ion channels are only present in the pre-synaptic neurone
- There are only protein receptors on the post-synaptic membrane
How do synapses filter out background/ low level stimuli
- Low frequency action potential
- Results in a low concentration of neurotransmitters into the synaptic cleft
- So for the threshold value to be reached in the post-synaptic neurone- multiple action potentials are needed
How do synapses protect against overstimulation of effector by synaptic fatigue
- The rate of neurotransmitter release is greater than the rate of neurotransmitter regeneration
In synaptic terms, what are the 2 types of summation
- Temporal summation
- Spatial summation
List examples of processes that result in synapses preventing merging of action potentials
- Active transport of calcium ions out of the neurone to repolarise the neurone
- The hydrolysis of neurotransmitters
- Regeneration of neurotransmitters
- Endocytosis
What is temporal summation
When multiple nerve impulses arrive at the same synaptic knob within a short period of time
What is spatial summation
When multiple presynaptic neurones form a junction with a single neurone
What is an example of spatial summation
Rod cells
What are the 2 types of synapses
- Excitatory
- Inhibitory
Do inhibitory synapses make it more or less likely for an action potential to continue in post synaptic neurone
Less likely
In inhibitory synapses, what ions channels open when the neurotransmitters attach
- Potassium ions
OR - Chlorine ions
With inhibitory synapses, what happens to the post synaptic membrane
Becomes hyperpolarised
If a membrane gets hyperpolarised, is it harder or easier to exceed the threshold potential
Harder
In inhibitory synapses, when the post synaptic membrane becomes hyperpolarised, what does this mean for the action potential
No action potential is propagated in post synaptic neurone
Do excitory synapses make it more or less likely for an action potential to continue
More likely
In excitory synapses, what ion channels open when the neurotransmitters bind to the receptor proteins
Sodium ion
Drugs that inhibit transmission lead to what
Paralysis
Drugs that amplify transmission lead to what
Tetany (Muscle spasms)
Zinconotide blocks the calcium ion channels at some of the synapses which use glutamate (a neurotransmitter that transmits nerve impulses from pain receptors to the brain). The transmission of glutamate at synapses is similar to that of acetylcholine. Explain how ziconotide reduces severe, constant pain. (5 marks)
- No/fewer calcium ions enter synaptic knob
OR
No/less calcium enter synaptic knob via calcium
ion channels; - No/fewer synaptic vesicles move to/fuse with
presynaptic membrane and no/less glutamate
is released; - No/less glutamate diffuses across (synaptic
cleft); - No/less (glutamate attaches) to receptors on the
postsynaptic membrane; - No/fewer sodium ions enter (postsynaptic
neurone) so no/ fewer impulses (sent to brain);
When the patients recorded the intensity of pain, suggest 2 reasons why it was important to use a statistically valid scale (2 marks)
- (Sensation of) pain is subjective
OR
Pain sensitivity/threshold/tolerance varies; - To ensure that differences (in pain detection)
were (statistically) significant
OR
For (valid) comparison;
Describe the role of the sarcolemma at the neuromuscular junction
- Acetylcholine is released from the motor neurone and binds to receptors on the sarcolemma
- This binding causes sodium ion/ channels to open, leading to influx of sodium ions and depolarisation of the sarcolemma
- The depolarisation spreads along the sarcolemma and into the muscle fibres via T-tubules
- Depolarisation of the T-tubutles causes the sarcoplasmic reticulum to release calcium ions, which initiates muscle contraction via the sliding filament mechanism
Describe the role of the post-synaptic membrane at a synapse
- Neurotrasmitter diffuse across the synaptic cleft and bind to specific receptors on the post-synaptic membrane
- Binding on neurotransmitters causes gated sdoium ion channels to open, allowing sodium ions to enter the post-synaptic neurone
- If sufficient sodium ions enter the threshold potential is reached, the membrane depolarises, triggering an action potential in the post-synaptic neurone
- The neurotransmitter is broken down by enzymes and reabsorbed into the presynaptic neurone to stop transmission
Explain the importance of the autonomic nervous system in raising heart rate
- The autonomic nervous system controls involuntary functions, including heart rate
- The sympathetic branch of the autonomic nervous system, stimulates the SAN, which increase heart rate
- This increase inn heart rate ensures more oxygen and nutrients are delivered to tissues during activities like exercise or stress
Give two reasons why transmission across a cholinergic synapse is unidirectional (2 marks)
- (Only) the presynaptic
neurone/knob/membrane releases/has
neurotransmitter/acetylcholine;
2.(Only) the postsynaptic
neurone/membrane has receptors
OR
No receptors in the presynaptic
neurone/membrane;
