Structure of Myelinated Motor Neuron
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of neurones and the nervous system from GCSE. You can test your knowledge on these below.
What is the role of a neurone?
To transmit electrical impulses around the body.
What is the function of a motor neurone?
To carry electrical impulses from the central nervous system (CNS) to effectors (muscles or glands).
What does the myelin sheath do?
It insulates the axon and increases the speed of electrical impulse transmission.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains structure of myelinated motor neurone or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What is a Motor Neurone?
- A motor neuron carries electrical impulses from the CNS to effectors (e.g. muscles, glands).
- It is part of the somatic nervous system, controlling voluntary movement.
- It is myelinated, meaning it has a fatty sheath (myelin) that speeds up impulse conduction.
Structure of a Myelinated Motor Neurone
| Part | Description & Function |
| Cell Body | Contains the nucleus, mitochondria, and rough ER (for neurotransmitter production). Located in the CNS. |
| Dendrites | Thin branched extensions that receive impulses from other neurones. |
| Axon | A long fibre that carries impulses away from the cell body to the effector. |
| Myelin Sheath | A fatty insulating layer made of Schwann cells. Increases impulse speed. |
| Schwann Cells | Surround and insulate the axon, forming the myelin sheath. |
| Nodes of Ranvier | Gaps in the myelin sheath. Allow saltatory conduction (impulse jumps between the nodes). |
| Axon Terminal | Passes the impulse to the effector via a synapse. Contains neurotransmitters. |
Myelin & Saltatory Conduction
- In myelinated neurones, impulses "jump" from node to node (called saltatory conduction).
- This is much faster than in non-myelinated neurones.
- Myelin also prevents ion leakage, preserving the strength of the impulse.
Summary Table
| Feature | Myelinated Motor Neurone |
| Direction of impulse | From cell body to axon terminal (towards the effector). |
| Myelin Sheath | Yes – made of Schwann cells. |
| Speed of conduction | Fast – due to saltatory conduction. |
| Location | Cell body in CNS, axon travels to muscle or gland. |
| Main Function | Transmit impulse to effector to trigger response (e.g. muscle contraction). |
Key Terms
- Motor neuron: A neurone that carries impulses from the CNS to an effector.
- Myelin sheath: A fatty layer surrounding the axon that insulates and speeds up impulse transmission.
- Schwann cell: A cell that produces the myelin sheath around the axon.
- Node of Ranvier: A gap in the myelin sheath that allows saltatory conduction.
- Saltatory conduction: The jumping of action potentials between nodes of Ranvier, speeding up transmission.
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Exam Tip
Examiner reports note students often confuse dendrites with axon terminals – remember, dendrites receive electrical impulse, axon terminal transmit them.
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Describe the structure of a myelinated motor neurone and explain how it helps to transmit impulses efficiently. (6 marks)
- A motor neurone has a cell body with nucleus, located in the CNS.
- Dendrites extend from the cell body to receive impulses.
- A long axon carries the impulse toward the effector.
- The axon is surrounded by a myelin sheath made by Schwann cells.
- There are gaps in the sheath called nodes of Ranvier.
- Impulses travel by saltatory conduction – jumping from node to node – which speeds up transmission.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!