8.1.1Unit 6: Practical Skills in Biology II
Neurones: Types and Functions — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 34 of 48 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Common Features
All neurones carry electrical impulses, but they differ in structure according to their job.
Cell body
- Cell body Contains the nucleus and organelles, and is where the neurone's proteins and neurotransmitters are made.
Axon
- Axon A long extension that carries electrical impulses away from the cell body toward other cells.
Axon terminal
- Axon terminal The end of the axon, which has nerve endings that connect to other neurones or to effectors.
Dendrites
- Dendrites Short branched extensions that receive impulses from other neurones and provide many connections.
Nerve
- Nerve A bundle of many neurones wrapped together, carrying impulses between the central nervous system and the body.
Part 2 of 4Three Types of Neurone
Three Types of Neurone
Sensory neurone
- Sensory neurone Carries impulses from a receptor to the central nervous system, with its cell body off to the side of the axon and no dendrites.
Relay neurone
- Relay neurone Lies entirely within the central nervous system and links sensory neurones to motor neurones.
Motor neurone
- Motor neurone Carries impulses from the central nervous system to an effector, with a large cell body at one end and many dendrites.
Overall pathway
- Overall pathway Information flows from receptor to sensory neurone, relay neurone, motor neurone and finally effector.
| Type | Direction of impulse | Cell body position |
|---|---|---|
| Sensory | Receptor to CNS | Part-way along the axon |
| Relay | Within the CNS | Within the CNS |
| Motor | CNS to effector | In the CNS, at one end |
Part 3 of 4Myelinated and Unmyelinated Neurones
1
In a myelinated neurone Schwann cells wrap around the axon many times, forming an insulating fatty myelin sheath.
2
Small uninsulated gaps between neighbouring Schwann cells are called nodes of Ranvier.
3
The impulse in a myelinated axon jumps from one node to the next, so it travels much faster.
4
In an unmyelinated neurone there is no sheath, so the impulse must travel along the whole length of the axon membrane.
5
This makes impulses in unmyelinated neurones slower, but the fibres are suitable for responses that do not need to be fast.
Part 4 of 4Exam Checklist & Tips
8.1.1 – Key Points for the Exam
- Axon A long extension of a neurone that carries impulses away from the cell body.
- Myelin sheath An insulating layer made of Schwann cells wrapped around an axon.
- Node of Ranvier An uninsulated gap in the myelin sheath.
- Sensory neurone A neurone carrying impulses from receptors to the central nervous system.
- Motor neurone A neurone carrying impulses from the central nervous system to effectors.
Common Mistakes
- Describing myelin as a single cell; it is formed from many Schwann cells along an axon.
- Stating that sensory neurones carry impulses away from the brain.
- Saying that impulses in myelinated neurones jump along the myelin; they jump between nodes.
- Confusing a nerve with a neurone; a nerve is a bundle of neurones.
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