Nervous system Flashcards
At a resting potential is the outside more positive or negative than the inside
Positive
What does polarised mean
There is a difference in charge
What is the voltage at a resting potential
-70mV
How is a resting potential maintained
The Na/K pump
Na moved out
Membrane imperméable to Na so they can’t move back in
Creates Na electrochemical gradient (more Na outside than in)
K move in
Membrane permeable to k
K moves back out (by channel proteins)
What ratio does the Na/K pump move ions
Na:K
3:2
Give the 5 stages of an action potential
Stimulus Depolarisation Repolarisation Hyper polarisation Resting potential
Explain how a stimulus starts the action potential
Excites neurone plasma membrane Na channels open More permeable to Na Na diffuse into neurone down electrochemical gradient Inside is less negative
Explain depolarisation
Potential difference reached threshold potential
More Na channels open
Na diffusés more rapidly into the neurone
Less negative
Explain repolarisation
Na channels close
K channels open
More permeable to k
K move out down conc grad
Explain hyperpolarisation
K channels are slow to close
Overshoot of how many k diffuse out of neurone
More negative than resting potential
Explain resting potential after an ap
Ion channels are rests
Na/k pump returns membrane to -70mV
What is the refractory period
After ap
Ion channels are recovering and can’t open
No action potential can happen
How do ap move along neurone
Na ions diffuse sideways
Na channels in the next region open
Na diffuse into the next part
Wave of depolarisation away from areas in refractory period
What are the effects of the refractory period
Ap don’t overlap = they are discrète Impulses
The frequency is limited
Unidirectional
Why do ap have “all or nothing” nature
If threshold reached the ap will always fire at the same voltage no matter the stimulus size. If the threshold isn’t reached then no ap
What is the effect of a bigger stimulus
More frequent ap
What is a myelin sheath
Electrical insulator
What makes the myelin sheath
Schwann cell
What structure is between the Schwann cells
Nodes of ranvier
Where are Na channels concentrated
Nodes of ranvier
Where does depolarisation happen at a myelinated neurone
At nodes of ranvier
Explain saltatory conduction
The neurone cytoplasm conducts enough electrical charge to depolarise the next node of ranvier. So depolarisation jumps from node to node
What is the benefit of salutatory conduction
Very fast
Explain the conduction in non myelinated neurones
The impulse travels along the whole length of the axon membrane so is slower
What are dendrites
Extensions of cell body that connect to other neurones
How does axon diameter effect speed of depolarisation
Big diameter = fast rate of depolarisation
Because there’s less resistance to flow of ions
How does temp effect speed of depolarisation
Temp increases = depolarisation rate increases
Because ions diffuse faster
Until 40 = channel proteins denature and speed decreases
What is a synapse
Junction between 2 neurones or a neurone and effector cell
Why are synapses uni directional
Receptors are only on the post synaptic membrane
How does the synapse stop the the impulse continually happening
Neurotransmitters are removed from cleft by enzymes or réabsorbed by presynaptic knob
What structure does the presynamptic knob have
Synaptic vesicles
What do synaptic vesicles store/release
Neurotransmitters
What is the neurotransmitter at a cholinergic synapse
Acetylcholine
How is a nerve impulse transmitted across a cholinergic synapse
- Ap arrives at presynaptic knob
- Voltage gated ça ion channels open in presynaptic neurone
- Ça diffuse into synaptic knob
- Synaptic vesicles move to presynaptic membrane and fuse
- Vesicles release ACh into synaptic cleft
- ACh binds to cholinergic receptors on the post synaptic membrane
- Na channels open on post synaptic neurone
- Post syn. Neurone is depolarised
- Ap fired when threshold reached
How is ACh removed from synaptic cleft
Broken down by enzyme: acetylcholineesterase
Products reabsorbed by presynaptic neurone
What are excitatory neurotransmitters
Cause the post synaptic membrane to be depolarised
Causing an ap when threshold reached
Give an example of an excitatory neurotransmitter
Acetylcholine
What is an inhibitory neurotransmitter
They hyperpolarise the post synaptic membrane
Preventing the ap being fired
How does acetylcholine act as a inhibitory neurotransmitter at the heart
It binds to receptors
Causes k channels to open
Hyper polarising the post synaptic membrane
What happens to the amount of neurotransmitter with a weak stimulus
Small amount released from presynaptic neurone
What is summation
The effect of neurotransmitters released from many neurones is added together
What is spatial summation
Many neurones connect to 1 neurone
The small amount of neurotransmitter released from each neurone is added together to reach the threshold
Or if inhibitory = to stop the the ap
What is temporal summation
2+ impulses arrive in quick succession from the same presynaptic neurone
More neurotransmitter released
More likely to cause ap
Where is a neuromuscular junction
Synapse Between motor neurone and muscle cell
What neurotransmitter is used at neuromuscular junctions
Acetylcholine
What does the neurotransmitter bind to at neuromuscular junctions
Nicotinic cholinergenic receptors
What are the differences between cholinergenic synapses and neuromuscular junctions
- At neuromuscular junctions the post syn. Membrane has lots of folds which form clefts. The clefts store acetylcholinesterase
- Neuromuscular junctions have more receptors
- Neuromuscular junctions always have excitatory ACh
What are agonist drugs
Drugs that have the same shape as neurotransmitters and mimic their action at receptors. So more receptors are activated
Give an example of an agonist drug
Nicotine
Binds to nicotinic receptors in the brain
What are antagonist drugs
Block receptors so can’t be activated by neurotransmitters
So fewer receptors are activated
What drug blocks nictotinic cholinergenic receptors
Curare
What is the affect of nicotinic cholinergenic receptors being blocked
Muscle paralysis
What is the effect of drugs that stop the enzyme for the neurotransmitter
More neurotransmitter in the syn cleft
More can bind to receptors on post syn membrane
More there for longer
More frequent ap
What is the effect of nerve gases
Loss of muscle control
What is the affect of amphétamines on synapses
Release more neurotransmitter from pre syn membrane
More receptors activated
What is the effect of alcohol on synapses
Inhibit the release of neurotransmitters
Fewer receptors activated
