5.3 - Neuronal communication Flashcards
What is distinctive about the function of myelinated neurones (in comparison to non-myelinated neurones)?
Action potential conduction is faster in myelinated neurones
What do myelinated neurones have that non-myelinated neurones not have that allow myelinated neurones to have faster conduction?
Schwann Cells that produce myelin - provides electrical stimulation
What do myelinated neurones prevent?
Depolarisation / movement of ions
Where can depolarisation/action potentials only occur?
Where Na+ channels are present
In comparison to non-myelinated neurones, what do myelinated neurones have in terms of axon length and Na+ channels?
Longer axons
NO Na+ channels
Where can depolarisation/ion movement only take place in myelinated neurones?
Nodes of Ranvier
How is the action potential transmitted across myelinated neurones?
Saltatory conduction: action potential jumps from one Node of Ranvier to another (enhances local current effect)
Describe the resting potential stage of the action potential (9)
- Sodium-Potassium pump
- 3Na+ ions pumped out of neuron
- 2K+ ions pumped into neuron
- by Active Transport
- K+ channels are open
- Some K+ diffuses back out
- Fewer Na+ channels open, so less Na+ diffuses out
- Voltage-Gated Na+ channels closed
- Membrane potential approx -70mV
Describe the Threshold and Depolarisation stage of the action potential (9)
- Stimulus causes some sodium ion channels to open
- Generator potential: membrane potential changes (makes inside of axon LESS negative)
- Some voltage-gated Na+ channels open
- Na+ diffuses into axon
- Causes more voltage-gated Na+ channels to open (positive feedback)
- Threshold is reached
- All voltage-gated Na+ channels open
- Na+ diffuses into the axon
- Depolarisation ends at approx +30mV
Describe the Re-polarisation stage of the action potential (2)
- Voltage-gated K+ ion channels open
- K+ diffuses out of axon
Describe the Hyperpolarisation stage of the action potential (3)
- Voltage-gated K+ ion channels are slow to close
- Membrane potential more negative than resting potential
- Resting potential established by the sodium-potassium pump
Give 9 roles of synapses
- Allows neurones to communicate/cell signalling
- Ensures transmission between neurones is unidirectional / in one direction only
- Allows convergence / impulses from more than one neurone to be passed to a single neurone
- Allows divergence / impulses from a single neurone to be passed to more than one neurone
- Filters out low level stimuli / ensures that only stimulation is strong enough will be passed on
- Prevents fatigue / prevents over-stimulation
- Allows many low level stimuli to be amplified
- Presence of inhibitory and stimulatory responses allows impulse to follow a specific path
- Allows memory/learning/decision making
When an action potential is travelling across a neurone where does it travel to in order to deliver the impulse to a neighbouring neurone?
The presynaptic membrane
When the action potential arrives at the presynaptic membrane of the synapse, what happens?
Calcium (Ca2+) Channels open
What happens when the Calcium channels in the presynaptic membrane open?
Ca2+ diffuse into the presynaptic knob
When Ca2+ ions diffuse into the presynaptic knob, what does this initiate?
The neurotransmitter Acetylcholine, is stimulated and travels in vesicles to the presynaptic membrane and fuse with it
How does acetylcholine reach the post-synaptic neurone?
Acetylcholine is released by exocytosis into the synaptic cleft and diffuses across it
Once Acetylcholine diffuses across the synaptic cleft, what happens?
Acetylcholine binds to receptors on the post-synaptic membrane which causes Na+ channels to open
When Na+ channels open in the post-synaptic membrane, what happens?
Na+ diffuses into the post-synaptic membrane and if a threshold is reached an action potential will be generated
How is acetylcholine recycled and re-synthesised after transmission across a synapse occurs?
- Acetylcholine is hydrolysed by acetylcholinesterase
- Products diffuse back across the synaptic cleft to the presynaptic knob
- Products re-synthesised into acetylcholine
How can a synapse be inhibited (6)?
- Inhibitor binds to/occupies/competes with acetylcholine
- This prevents acetylcholine binding / blocks receptor site
- Ion channels /sodium channels don’t open
- Na+ cannot enter/K+ cannot leave the neurone
- Insufficient depolarisation / excitatory postsynaptic potential/generator potential
- Post synaptic membrane does not reach threshold
Why are synapses unidirectional (3) ?
- Acetylcholine released from the presynaptic side
- Diffusion from higher concentration to lower concentration
- Receptors only on the postsynaptic membrane
What condition must a stimulus meet to generate an action potential?
Stimuli must reach THRESHOLD
What is the all-or-nothing law?
Either an action potential occurs or it doesn’t
What is true about the magnitude of action potentials?
They’re all the same magnitude no matter how strong the stimulus
What can a strong stimulus initiate?
Produce MANY action potentials in rapid succession
