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| Question | Answer |
| What are the 4 stages of the nervous impulse? | Resting potential Nerve impulse/action potential Repolarisation Hyperpolarisation |
| What happens in the neurone during resting potential? |
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| What happens to the potential difference of the cell membrane during resting potential? | The cell membrane is polarised (at -60mV) |
| Complete the sentences: The Na⁺/K⁺ pumps move Na⁺ out of the neurone, but the membrane isn't _____________ to Na⁺ ions, so they cannot __________ back in. This creates a Na⁺ _________________ gradient. | The Na⁺/K⁺ pumps move Na⁺ out of the neurone, but the membrane isn't PERMEABLE to Na⁺ ions, so they cannot DIFFUSE back in. This creates a Na⁺ ELECTROCHEMICAL gradient. |
| What happens in the neurone during an action potential? |
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| What happens to the potential difference of the cell membrane during an action potential? | The cell membrane becomes depolarised (+40mV) |
| What happens in the neurone during repolarisation? |
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| What happens to the potential difference of the cell membrane during repolarisation? | The charge is around -75mV |
| What happens in the neurone during hyperpolarisation? |
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| What happens to the potential difference of the cell membrane during hyperpolarisation? | The repolarisation overshoots and is more negative than resting potential. The original potential difference of -60mV must be restored |
| Describe the graph showing a nerve impulse travelling through a neurone |
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| What is the refractory period? | The period when, after an action potential, the neurone cell membrane can't be excited again straight away. This is because the ion channels are recovering and can't be made to open |
| The refractory period acts as a time delay between one action potential and the next. This makes sure that action potentials..... | Don't overlap but pass along as discrete impulses Are unidirectional (only travel in one direction) |
| Complete the sentences: When an action potential happens, some of the Na⁺ ions that enter the neurone diffuse __________. This causes Na⁺ ion channels in the next region to _______ and Na⁺ diffuses into that part. This establishes a _________ __________ and initiates a wave of _________________ to travel along the neurone. | When an action potential happens, some of the Na⁺ ions that enter the neurone diffuse SIDEWAYS. This causes Na⁺ ion channels in the next region to OPEN and Na⁺ diffuses into that part. This establishes a LOCAL CIRCUIT and initiates a wave of DEPOLARISATION to travel along the neurone. |
| TRUE OR FALSE: The wave of depolarisation moves away from the parts of the membrane in the refractory period |
TRUE
The parts of the membrane in the refractory period can't fire an action potential
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| TRUE OR FALSE: A bigger stimulus causes a bigger action potential | FALSE BUT! A bigger stimulus will cause action potentials to fire more frequently. If the brain receives a high frequency of action potentials, it interprets this as a big stimulus and responds accordingly. |
| What does it mean by the "all-or-nothing" nature of action potentials? | If the threshold isn't reached, an action potential won't fire |
| TRUE OR FALSE: Once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is | TRUE |
| What are the 3 factors that affect the speed of conduction of action potentials? | Myelination Axon diameter Temperature |
| In the peripheral nervous system, what is the myelin sheath of neurones made up of? | A type of cell called a Schwann cell |
| Complete the sentences: Some neurones have a ________ ________ (an electrical conductor). In the peripheral nervous system, the myelin sheath is made of a type of cell called a ____________ _____, which is wrapped around the axon (and/or __________). Between the Schwann cells are the ______ ___ ________ where Na⁺ channels are concentrated. | Some neurones have a MYELIN SHEATH (an electrical conductor). In the peripheral nervous system, the myelin sheath is made of a type of cell called a SCHWANN CELL, which is wrapped around the axon (and/or DENDRON). Between the Schwann cells are the NODES OF RANVIER where Na⁺ channels are concentrated. |
| In a myelinated neurone, the speed of conduction is faster than in a non-myelinated neurone. Why? | In a myelinated neurone, depolarisation only happens at the nodes of Ranvier. The neurone's cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse 'jumps' from node to node. This is called saltatory conduction. In a non-myelinated neurone, the impulse travels as a wave along the whole length of the axon membrane. This is slower than saltatory conduction. |
| How does axon diameter affect the speed of conduction? | Action potentials are conducted quicker along axons with bigger diameters - there's less resistance to the flow of ions than in the cytoplasm of a smaller axon. With less resistant, depolarisation reaches other parts of the neurone cell membrane quicker. |
| How does temperature affect the speed of conduction? | The speed of conduction increases as the temperature increases - ions diffuse faster. |
| TRUE OR FALSE: When the temperature gets too high, the speed of conduction decreases | TRUE The speed only increases up to around 40°C - after that the proteins begin to denature and the speed decreases |
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