Topic 6B: Nervous Coordination Flashcards
What is meant by a resting potential?
- When inside the neurone is more negative than the outside
- membrane is polarised
What is the voltage at resting potential?
-70mV (millivolts)
How is resting potential maintained?
3 Na ions are actively pumped out of the neurone for every 2 K ions pumped inside the neurone through the sodium potassium pump
-the membrane of the neurone is more permeable to potassium than sodium
If stimulus is big enough…
it causes an action potential
Stages of the changes in potential difference during an action potential
1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisation
5) Resting Potential
What happens in Stage 1-Stimulus
- excites the neurones cell membrane
- membrane increases in permeability to sodium
- sodium channels open
- sodium diffuses into the neurone
- down the electrochemical gradient
- inside of the neurone less negative
What happens at Depolarisation?
- potential difference reaches at -55mV
- more sodium channels open
- more sodium ions diffuse rapidly
What happens at Repolarisation?
- reaches +30mV
- sodium channels close
- potassium channels open
- membrane is more permeable to potassium
- potassium ions diffuse out
What is Hyperpolarisation?
- potassium ion channels are too slow to close so there is a slight overshoot where too many potassium ion diffuses out of the neurone
- potential difference becomes more negative than the resting potential
What is the refractory period?
- When ion channels are recovering and cant be opened
- acts as a time delay
The time delay in the refractory period mean…
- action potential doesnt overlap
- pass along discrete impulses
- action potential is unidirectional (travel in one direction)
What are the three factors affect the speed of conduction of action potential?
- myelination
- axon diameter
- temperature
Why is there in a time delay in the refractory period?
-so that the ion channels start to recover and so they cant be made open
When are the sodium and potassium ion in a refractory period?
- sodium ion channels closed during repolarisation
- potassium ion closed during hyperpolarisation
How does action potential move along the neurone?
-the sodium ions that enter the neurone sometimes diffuses sideways
-causes Na ions in the next region of the neurone to open
-Na ion diffuses in
-causes a wave of depolarisation that travel along the neurone
-
Once the threshold is reached, an action potential will always fire…
- at the same voltage
- maximal response
The bigger the stimulus….
the more times action potentials occur frequently
How does myelination increases the speed of conduction of action potential?
- myelin sheath is an electrical insulator
- It has a faster saltatory conduction
What is the saltatory conduction?
The neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impluses jump from node to node.
What is myelin sheath made out of?
Schwann cells in the peripheral system
Between the Schwann cells there are tiny patches of bare membrane called…
Nodes of Ranvier
What are in the nodes of Ranvier?
Concentrated in the sodium ion channels
In myelinated neurone, depolaristion happens ONLY in the…
Nodes of Ranvier
How does impluses travel along a non myelinated neurone?
- Travels along the whole length of the axon membrane
- so depolarisation occurs along the whole length of the membrane
- therefore slower saltatory conduction
How does the axon diameter affect the speed of conduction of action potential?
- bigger diameter
- less resistance
- better flow of ions
- depolarisation reaches quicker
How does the temperature affect the speed of conduction of action potential?
- as temp increase
- conduction speed increases
- because ions diffuse faster
- temp higher than 40 degrees = denaturation
What is a synapse?
a junction between a neurone and neurone OR neurone and effector
The tiny gap in synapse is called…
synaptic cleft
The end of a presynaptic nob has a…
synaptic knob
The synaptic knob contains…..
synaptic vesicles which contain neurotransmitters
Because receptors are only on postsynaptic neurone it means impulses are….
unidirectional (moves in one direction)
Outline the stages of when ACh transmits across a cholinergic synapse?
- The action potential arrives at the synaptic knob
- this stimulates the voltage gated calcium ion channels to open
- Ca ion diffuses into the synaptic knob
- influx of ca ions causes synaptic vesicles to move to the presynaptic membrane
- Causes the presynaptic membrane to fuse with synaptic vesicles
- causes a release in acteylcholine (neurotransmitter) which diffuses across the synaptic cleft
- ACh bind to complementary cholingeric receptors on the postsynaptic neurone
How does the transmission of ACh stimulate a generator potential?
- the cholingeric recptors bind to the receptors
- causes sodium ion channels to open
- sodium diffuses in to the postsynaptic membrane
- causes depolarisation
- if threshold exceed it causes an generator potential.
What happens to ACh after binding?
- It gets broken down by an enzyme called acetylcholinesterase
- the products are reabsorbed by the presynaptic neurone and is used to make more ACh
What are excitatory neurotransmitters?
-neurotransmitters that DEPOLARISES the postsynaptic membrane making it fire an action potential if the threshold is reached.
Example of excitatory neurotransmitter?
- Acetylcholine is excitatory at cholingeric synapses at the CNS
- causes an action potential
What are inhibitory neurotransmitters?
-neurotransmitters that HYPERPOLARISES the postsynaptic membrane preventing it fire an action potential
Example of inhibitory neurotransmitter?
- Acetylcholine is inhibitory at cholingeric synapses at the HEART
- When it binds it causes potassium ion channels to open on the postsynaptic membrane
- hyperpolarises it
What is a neuromuscular junction?
A synapse between a motor neurone and a muscle cell
How is the neuromuscular junction different cholingeric synapse?
- has lots of folds that form clefts. This is to store the enzyme that breaks down ACh
- more receptors on the postsynaptic neurone
- always excitatory so always triggers a response on muscle cells
What is summation?
Where the effect of neurotransmitter released from many neurones is added together
What is Spatial Summation?
Many neurones connected to one nerurone
What is Temporal Summation?
Two or more nerve impulses arrive in quick succession from the same presynaptic neurone
What does summantion allow?
it accurately processes information and the response is finely tuned
