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15.1.314-15 · Homeostasis and Control

Neurones — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 6 parts Lesson 18 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

15.1.3 Neurones — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the structure of sensory, relay and motor neurones and the role of myelin.Axon — a long fibre that carries impulses away from the cell body.Myelin sheath — a fatty insulating sheath made by Sch…

  • Nodes of Ranvier
  • Basic structure
  • Schwann cell
  • Node of Ranvier
  • Jumping — the impulse jumps from node to node, saving time
  • Dendrites — extensions of the cell body that connect to many other neurones and receive impulses

Part 1 of 4Features of neurones

Features of neurones
Axon
  • Axon a long fibre that carries impulses away from the cell body.
Myelin sheath
  • Myelin sheath a fatty insulating sheath made by Schwann cells wrapped around the axon.
Nodes of Ranvier
  • Nodes of Ranvier small uninsulated sections along the axon.
Jumping
  • Jumping the impulse jumps from node to node, saving time.
Dendrites
  • Dendrites extensions of the cell body that connect to many other neurones and receive impulses.

Part 2 of 4Three types of neurone

TypeRole
SensoryCarries impulses from receptors to the CNS
RelayConnects sensory and motor neurones within the CNS
MotorCarries impulses from the CNS to effectors (muscles or glands)

Part 3 of 4Motor neurone structure

Motor neurone structure
Cell body
  • Cell body large, at one end, in the spinal cord or brain.
Nucleus
  • Nucleus always in the cell body.
Dendrites
  • Dendrites many highly branched, giving a large surface area for the axon terminals of other neurones.

Part 4 of 4Sensory neurone structure

Sensory neurone structure
Basic structure
  • Basic structure the same as a motor neurone.
Cell body
  • Cell body branches off in the middle of the cell.
Position
  • Position near the source of stimuli or in a swelling of a spinal nerve called a ganglion.

Key terms

TermMeaning
AxonLong fibre carrying impulses away from the cell body.
MyelinFatty sheath insulating the axon.
Schwann cellCell forming the myelin sheath.
Node of RanvierUninsulated gap in the myelin.
DendriteExtension of the cell body receiving impulses.
GanglionSwelling of a spinal nerve containing sensory cell bodies.

Avoid these mistakes

1
Saying axons carry impulses towards the cell body — they carry impulses away.
2
Confusing sensory and motor neurones — sensory go to the CNS, motor go from it.
3
Saying the impulse passes along the whole axon in myelinated neurones — it jumps between nodes.
4
Saying the cell body of a sensory neurone is at the end — it branches off in the middle.

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