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Key diagram
The three neurone types are sensory (carries impulses from receptors to the CNS), relay (connects neurones within the CNS) and motor (carries impulses from the CNS to effectors). Each has a cell body, axon and dendrites but in different arrangements.
Neurone diagrams test whether students can identify and draw the three types correctly, labelling the key structures. The differences in cell body position and axon length are the main distinguishing features.
Sensory neurone
Draw a long neurone with dendrites at one end (connected to a receptor) and a terminal (synaptic) knob at the other end. The cell body is positioned to one side along the length of the axon, on a short branch: not at either end. The axon is long and may have a myelin sheath drawn as segments along its length. A sensory neurone carries impulses from the receptor to the central nervous system (CNS).
Relay neurone
Draw a short neurone with the cell body in the centre and short dendrites extending from it. Relay neurones are found within the CNS (brain or spinal cord). They connect sensory neurones to motor neurones. They are much shorter than sensory or motor neurones and are often drawn as a simple cell body with several short projections.
Motor neurone
Draw a neurone with the cell body at one end, with dendrites branching from it. A long axon extends from the cell body, covered in a myelin sheath, ending in motor end plates that connect to the effector (muscle fibre or gland). A motor neurone carries impulses from the CNS to the effector.
Structures common to all neurones
All neurones have a cell body containing the nucleus, dendrites (short branching extensions that receive impulses), an axon (a long fibre that transmits impulses), and synaptic terminals. Many neurones have a myelin sheath: a fatty insulating layer that speeds up impulse transmission. Gaps in the myelin sheath are called nodes of Ranvier.
Label checklist
Check these labels are present and correctly positioned before finishing your drawing.
✓Cell body (with nucleus)
✓Dendrites
✓Axon
✓Myelin sheath
✓Nodes of Ranvier
✓Synaptic terminal / motor end plate
✓Direction of impulse (arrow)
Try a diagram question (2 marks)
State two structural differences between a sensory neurone and a motor neurone. [2]
Show the answer and marking guidance
In a sensory neurone, the cell body is on a side branch; in a motor neurone, the cell body is at one end.
A sensory neurone carries impulses from receptors to the CNS; a motor neurone carries impulses from the CNS to effectors.
Original Cambridge-style practice written for this site.
Common diagram mistakes
Check these against your own drawing before moving on.
Placing the cell body of a sensory neurone at the end instead of on a side branch.
Drawing relay neurones as long: they are short and found only in the CNS.
Forgetting the myelin sheath on sensory and motor neurones.
Not showing the direction of impulse transmission with an arrow.