1
Q
Parts of a neuron
A
- soma or cell body
- dendrites: short, branches nerve fibres which receive the electrical signal from other neurons
- axons: elongated nerve cells that transmit impulses throughout a neuron
- axon terminal: transmits impulse to another neuron
- myelin sheath: allow electrical impulses to travel more quickly
- node of ranvier
- Schwann cell
2
Q
Steps of an impulse transmission
A
- Resting potential
- Action potential
- Depolarization
- Repolarization
- Refractory period
- Threshold potential
3
Q
nerve impulse definition
A
- an action potential that starts at one end of the neutron and then is propagated along the axon to the other end of the neutron
4
Q
resting potential
A
- the neuron is at rest: not transmitting a signal
- membrane potential due to an imbalance of positive and negative charges across the membrane
- resting potential maintained by active transport (Na+/K+ pump, an antiport)
- 3 Na+ ions pumped out
- 2 K+ ions pumped in
- Na+ gradient steeper than K+ gradient, results in a slight concentration gradient for each ion (outside slightly positive, inside slightly negative)
- membrane ~50x more permeable to K+ ions than Na+ ions
- K+ ions leak back out across the membrane out faster than Na+ ions
- resting membrane potential = -70mV
5
Q
action potential
A
- rapid change in membrane potential
6
Q
depolarization
A
- reversal of charge from negative to positive
- Na+ channels open, Na+ ions diffuse INTO neuron
- cell becomes positive relative to the outside
- if enough change in membrane potential is achieved (threshold potential), all the voltage gated Na+ channels open
- membrane potential = +30mV
7
Q
repolarization
A
- restoration of charge from positive to negative
- Na+ channels close
- K+ channels open
- K+ ions diffuse OUT of the neuron
- inside the cell becomes negative relative to the outside
- membrane potential = -70mV
8
Q
refractory period
A
- neutron cannot propagate another action potential
- membrane potential (electrical gradient) restored (-70mV) but ions are not in the correct location
- Na+/K+ pump re-establishes the chemical gradient: prevents the action potential from moving backwards (can only travel in one direction)
9
Q
threshold potential
A
- nerve impulse follow an all-or-nothing principle
- action potential only initiated if the threshold potential is reached: causes voltage gated Na+ channels to open
- full depolarization if threshold Is reached
10
Q
myelinated axons
A
- myelin acts as an insulator
- action potentials jump from node to node, occurring at the un-myelinated nodes of Ranvier
- very rapid conduction inside the myelinated portion (travels more quickly, up to 200 m/s compared to un-myelinated: 2 m/s)
- allows impulse to travel longer distances, reduces energy expenditure over the axon
11
Q
synapses definition
A
- junctions between neurons and other neurons/effector cells
- nerve impulse propagated along the pre-synaptic neuron (end of the neuron)
- depolarization causes Ca2+ ions to diffuse into the pre-synaptic neuron
- influx of Ca2+ ions causes vesicles containing neurotransmitters to exit the pre-synaptic neuron via exocytosis
- NT diffuse into the post-synaptic cleft and binds to receptors on the post-synaptic neuron
- binding causes Na+ channels to open
- Na+ ions diffuse into the post-synaptic neuron and neuron reaches threshold potential (depolarization)
- action potential triggered in post-synaptic neuron and propagated along the neuron
- NT broken down and removed from synaptic cleft (by enzymes), taken up by pre-synaptic neuron by active transport (re-uptake)
12
Q
example of a neurotransmitter
A
- acetylcholine: made form choline and acetyl CoA
- acetylcholine broken down by acetylcholinesterase
- choline transported back to the axon terminal and used to make more ACh
13
Q
neonicotinoid
A
- blocks receptors
- prevents neurotransmitters from binding
- used for parasites/pests
- can result in paralysis and eventually death
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