Neurones and nerve impulses
Nerve impulses are electrical signals transmitted along neurones. Many neurones grouped together form a nerve.
Different neurone types transmit impulses through different parts of the nervous system.
| Type of neurone | Role |
|---|---|
| Sensory neurone | Transmits impulses from receptor cells towards the CNS. |
| Relay neurone | Forms a link between sensory and motor neurones inside the CNS. |
| Motor neurone | Transmits impulses away from the CNS towards an effector. |
Recognising a motor neurone
A motor neurone can be identified by a cell body positioned at one end within the CNS, an extended axon and terminal endings associated with the effector.
- Cell body: contains the nucleus and most of the cell structures.
- Dendrites: provide connections with other neurones.
- Axon: forms the long pathway along which the impulse travels towards the effector.
- Axon terminal endings: occur at the target end of the motor neurone.
Structure linked to function
| Feature | Why it is useful |
|---|---|
| Long axon | Enables one motor neurone to transmit an impulse across a large distance between the CNS and its target. |
| Dendrites | Provide sites through which the motor neurone can connect with other neurones. |
| Myelin sheath | Allows nerve impulses to be conducted more rapidly along the axon. |
Exam Tip: For a structure–function question, name the adaptation and then state its consequence. For example, link the length of the axon to transmission across a large distance, or link myelination to faster impulse conduction.