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Title: Action Potentials
Description: Includes: - Review of the general structure of a nerve. - Overview of action potentials. - Overview of graded potentials. - Description of the phases of impulse conduction: resting phase, depolarisation, hyperpolarisation, refractory period. - Overview of continuous conduction. - Overview of saltatory conduction and its implications for the transmission of an impulse. These notes are ideal for those taking Biology A-Level or first/second year undergraduates doing a degree with anatomy units.
Description: Includes: - Review of the general structure of a nerve. - Overview of action potentials. - Overview of graded potentials. - Description of the phases of impulse conduction: resting phase, depolarisation, hyperpolarisation, refractory period. - Overview of continuous conduction. - Overview of saltatory conduction and its implications for the transmission of an impulse. These notes are ideal for those taking Biology A-Level or first/second year undergraduates doing a degree with anatomy units.
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Action Potentials
Structure of a Nerve
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The endoneurium, the innermost layer, wraps each individual axon along with its myelin sheath
...
The perineurium holds the axon group together in bundles called fascicles
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The epineurium is the outermost covering of the entire nerve
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Extensions of this layer also fill the fascicles
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- Results in a potential difference being created across the membrane
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- Always lead to membrane depolarisation
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- Their size is proportional to stimulus strength
...
Resting Phase
1) All voltage-gated Na⁺ and K⁺ channels are closed, and the membrane is at resting potential of
-70mV: the membrane is polarised
...
3) The negative charge of the inside of the cell is maintained by Na⁺ / K⁺ ATPases, which pump 3
Na⁺ into the cell for every 2 K⁺ pumped out
...
2) There is an influx of Na⁺ ions through Na⁺ channel activation gates into the cell as they diffuse
down their concentration gradient
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Repolarisation
1) Voltage-gated Na⁺ channels close whilst voltage-gated K⁺ channels gradually open
...
3) The membrane potential drops from +30mV back towards -70mV as a negative net charge
builds up on the inside of the cell once again
...
1) The outflow of K⁺ through the now open voltage-gated K⁺ channels can cause hyperpolarisation
as the membrane potential becomes even more negative
...
Refractory Period
- This takes place after the transmission of an action potential, and is a time when it is impossible
to stimulate another action potential so that the cell can recover
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Continuous and Saltatory Conduction
Continuous
- Step-by-step depolarisation in each segment of the plasma membrane with ions flowing through
their voltage-gated channels
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Saltatory Conduction
- Occurs along myelinated axons due to uneven voltage-gated channel distribution
...
Na⁺ and K⁺ flow mainly occurs at these points
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Membrane depolarises, opening voltage-gated Na⁺ between itself and neighbouring node
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- Each node repolarises after depolarisation
...
This leads to much faster travel down the
myelinated axons than the unmyelinated
...
Title: Action Potentials
Description: Includes: - Review of the general structure of a nerve. - Overview of action potentials. - Overview of graded potentials. - Description of the phases of impulse conduction: resting phase, depolarisation, hyperpolarisation, refractory period. - Overview of continuous conduction. - Overview of saltatory conduction and its implications for the transmission of an impulse. These notes are ideal for those taking Biology A-Level or first/second year undergraduates doing a degree with anatomy units.
Description: Includes: - Review of the general structure of a nerve. - Overview of action potentials. - Overview of graded potentials. - Description of the phases of impulse conduction: resting phase, depolarisation, hyperpolarisation, refractory period. - Overview of continuous conduction. - Overview of saltatory conduction and its implications for the transmission of an impulse. These notes are ideal for those taking Biology A-Level or first/second year undergraduates doing a degree with anatomy units.