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33 Cards in this Set
- Front
- Back
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Where do sensory neurones transmit nerve impulses from and to? |
From receptor to spinal cord |
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Where do connector/relay neurones transmit info? |
Within spinal cord |
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Where do motor neurones transmit nerve impulses from and to? |
From spinal cord to effector |
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By what process do neurotransmitters travel across the synapse? |
Diffusion |
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What is the central nervous system made up of? |
Brain and spinal cord |
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What is a motor neurone highly specialised for? |
The rapid transmission of electrical impulses |
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Was does a myelinated motor neurone have ? |
Nucleus, cell surface membrane , cytoplasm , mitochondria (v few other organelles present) |
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4 adaptations of a myelinated motor neurone? |
Dendrites on the cell body Axon Myelin sheath Nodes of ranvier |
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How are dendrites in the cell body an adaptation of myelinated motor neurones? |
Synapse with connector neurone |
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How is the axon an adaptation of a mylinated motor neurone? |
Long. Conveys nerve impulses rapidly from spinal cord to effector |
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How is the myelin sheath an adaptation of a myelinated motor neurone? |
Forms a fatty layer around the axon and increases the speed of transmission of impulses |
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What is the myelin sheath made of? |
Shwann cells wrapped around the axon |
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What are nodes of Ranvier? |
Gaps between the shwann cells when ions can move between the cells and tissue fluid |
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When does a neurone membrane have a potential difference of -70 |
During resting potential |
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What happens during resting potential? |
Sodium potassium pumps pump out 3 Na+ ions for every 2 K+ ions pumped in. Active transport so uses protein carriers and ATP.
Facilitated diffuison also takes place. K+ diffuses rapidly back out of the cell as the mem is more permeable to Na+. Na+ can only diffuse v.slowly back into the cells as the cell mem. is much less perm. to Na+
Therefore, an electrochemical gradient is produced as the tissue fluid outside the cell has more positive ions than cytoplasm inside . The membrane is polarised. |
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Definition of depolarisation? |
A rapid temporary reversal of the resting potential |
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What happens during depolarisation? |
Sodium vgc are open, potassium vgc are closed. Membrane is more permeable to sodium ions. Sodium ions diffuse into the axon. Charge diffrence is reduced across membrane and assuming above the threshold value of -40mV , an AP is produced. |
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What happens during repolarisation? |
Potassium vgc open , sodium vgc close. Membrane more permeable to potassium ions Potassium ions diffuse back out down the concentration gradient so positive charge is taken out of the neuron. Potential difference goes to -75(less than resting potential) |
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What happens during hyperpolarisation? |
Because the potential difference is more negative than resting potential. Both vgc are shut Sodium/potassium pumps quickly restore the resting potential of -70mV |
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So what is a nerve impulse? |
The depolarisation of one part of the neurone sets off the depolarisation of the next part all the way along the neurone. The action potential moves like a wave along the neurone and this is the nerve impulse. |
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What is the refractory period? |
The time when the neurone membrane is unable to respond to another action potential. |
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Why can't the neurone respond to another action potential during the refractory period? |
The sodium vgc can't open |
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3 reasons the refractory period is important? |
1) an AP can only be propergated in one direction.. it can't spread to both directions along the neurone 2) there is always a time gap between impulses.. the never nerve together, they are discrete 3) as the 2nd AP is separated from the 1st , it sets the upper limit to the frequency of impulses along the neurone |
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Size of the action potential? |
Remains exact the same size when it's propagated along the neurone. When a resting neurone is depolarised, the depolarisation is either above threshold to achieve a full size action potential or not above threshold so doesn't produce an action potential at all. This is the all or nothing response |
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How is strength of a stimulus conveyed ? |
The frequency of action potentials. Lots of APs closely followed=strong Few spaced apart = weak |
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What 3 factors determine speed of conduction? |
Axon diameter Myelin sheath Temperature |
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How does axon diameter influence speed of conduction? |
The greater the diameter, the faster conduction Non vertebrate organisms have evolved v large axons to enable to rapid transfer of AP's from one part of the body to another. But they still do not achieve the speeds that can be reached in a myelinated axon. |
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How does the myelin sheath influence speed of conduction? |
Myelinated neurone conduct APs faster than non-myelinated neurones. Myelin sheath is not continuous along whole axon. It is absent at points called the nodes of Ranvier. As sodium and potassium ions channels are only found at nodes of Ranvier, the changes in potential difference that produce an AP can only take place here. The AP effectively 'jumps' from node to node. This is called saltatory conduction. |
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How does temperature influence speed of conduction? |
The higher the temperature, the greater the speed of conduction. The quicker the diffusion of ions in depolarisation and repolarisation. However, this is only important in organisms where body temperature varies with environmental temperature. In mammals, body temperature is maintained at a constant level so varying external temperature has no effect on speed of conduction. |
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What is the potential difference at resting potential? |
-70mV |
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What is the potential difference at depolarisation? |
-40mV |
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What is the potential depolarisation? |
+40mV |
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What is the potential difference at hyperpolarisation? |
-75mV |
