Something which converts energy from one form to another. sensory receptors are transducers
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What is a stimulus?
A change in energy level in the environment
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Which receptor detects sound?
Hair cells in the cochlea
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Which receptor detects movement?
Hair cells in the semi circular canals in the ears
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Which receptors detect pressure?
Panacian corpsucles in the skin
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Which receptors detect light touch?
Meissner's corpscules in the skin
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Which receptors in the skin detect heat/temperature?
Ruffini's endings
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What are olfactory cells?
Receptors in the nose which detect volatile chemicals.
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What do taste buds detect?
Soluble volatile chemicals
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What are dendrites?
fibres which transmit impulses towards the cell body
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What is a Node of Ranvier?
A section of the axon with no myelination
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How does the axon length compare in a sensory neurone to a motor neurone?
Sensory-shorter axon/ motor-longer axon
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Where is the location of the dendrites for a sensory neurone and a motor neurone?
Sensory) at the end of the axon and dendron/ Motor) connected to the cell body and the axon
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In which neurone are dendrons absent?
Motor neurones
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What is the function of the myelin sheath?
A layer of fat which surronds the axon. it speeds up the transmission of a nerve impulse and provides insulation+protection e.g. if you fall over
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How is a potential difference/polarisation achieved in the plasma membrane?
Na+/K+ pump pumps 3Na+ out of cell and 2K+ ions in. Membrane also more permeable to K+ so they diffuse out/more positive on outside compared to in.
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What is the resting potential value for most neurones?
-70Mv
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Once the sodium-voltage gated ion channels are opened why do Na+'s flood into the cell?
due to the electrochemical gradient
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At what potential difference will the Na+ voltage-gated ion channels open?
+40mV
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What happens during repolarisation?
K+ diffuses out of the cell down its electrochemical gradient restoring the potenial difference.
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What happens during hyperpolarisation?
Too many K+ ions leave the cell making the inside of the axon more negative than the rest. Both ion channels close in order to restore resting potential.
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Describe saltatory conduction.
Action potential jumps from one node of Ranvier to the next as the area covered by the myelin sheath cannot depolarise.
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What type of cell makes up the myelinated sheath?
Schwann cells.
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How does your brain tell the difference between a strong and a weak stimulus?
The stronger the stimulus the greater the frequency of the action potentials (more APs stimulated)
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Give some examples of organisms with giant axons
Squids, earthworms, lobsters, fan-worms
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What is happening during the refractory period?
Ion channels are recovering-can't open/Na+ channles closed during repolarisation/K+ion channels closed during hyperpolarisation/cell membrane can't be excited again straight away
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Why is transmission of an impulse slower in a non-myelinated neurone?
Because the impulse/AP must travel all the way along the axon as oppose to jumping from node to node.
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How does an action potential move along the neurone?
As a wave of depolarisation- the wave moves away from the parts of the neurone in the refractory period
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What is the synaptic cleft?
The tiny gap between neurones at a synapse
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What are the three stages involved in transmitting nerve impulses between neurones?
1)AP triggers Ca2+ influx 2) Ca2+ influx causes neurotransmitter release 3) Neurotransmitter triggers and AP in the postsynaptic neurone
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How does an influx of calcium ions into the presynaptic knob result in neurotransmitter relase?
They cause synaptic vesicles containing neurotransmitters to move to the presynaptic membrane and fuse with it.
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