Edexcel A Level (IAL) Biology -8.1 Neurones: Types and Functions- Study Notes- New Syllabus

Structure & Function of Neurones

🌱 Introduction

Neurones transmit electrical impulses in the nervous system.
There are three main types: sensory, relay, and motor neurones.
They work together to detect stimuli, process information, and trigger responses.
Schwann cells and myelination help impulses travel faster.

📌 1. Sensory Neurones

Structure

• Long dendron carries impulse from receptor to cell body.
• Short axon carries impulse from cell body to CNS.
• Cell body is outside CNS in a ganglion.
• Myelinated in most cases.

Function

• Transmit impulses from receptors (skin, eyes, ears) to CNS.

📌 2. Relay (Inter) Neurones

Structure

• Many short dendrites and a single short axon.
• Found entirely within CNS (brain/spinal cord).
• Usually unmyelinated for short local connections.

Function

• Connect sensory neurones to motor neurones.
• Integrate information and coordinate responses.

📌 3. Motor Neurones

Structure

• Cell body inside CNS.
• Long axon carries impulse from CNS to effector (muscle/gland).
• Short dendrites receive impulses from relay neurones.
• Myelinated for faster conduction.

Function

• Transmit impulses from CNS to effectors to trigger a response.

📌 4. Schwann Cells & Myelination

Schwann Cells

• Wrap around axon of neurones.
• Produce myelin sheath in PNS.

Myelin Sheath

• Fatty layer surrounding axon.
• Acts as insulator → speeds up electrical impulses.
• Impulses jump between nodes of Ranvier (gaps in myelin) — called saltatory conduction.
• Advantages: faster, more efficient, less energy loss.

📊 Summary Table