BRAINCAKESpeed of Nerve Impulses
The speed at which an impulse travels along a neurone, its conduction velocity, depends on three main factors.
1. Myelination. Myelinated axons conduct much faster than unmyelinated axons, because depolarisation happens only at the nodes of Ranvier.
2. Axon diameter. The wider the axon, the faster the impulse. A wider axon has less resistance to the flow of ions in its cytoplasm, so local currents spread further and depolarise the next section of membrane sooner. Some invertebrates, such as the squid, have unmyelinated giant axons up to about 1 mm across that conduct fast enough for escape responses.
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More in Mammalian Nervous System
- Nervous System
- Structure and Function of Neurones
- Nerve Impulses
- Myelinated Neurones
- Investigating Nerve Impulses
- Resting Potential
- Action Potential
- Depolarisation
All 38 lessons in Mammalian Nervous System · All Edexcel A-level Biology topics