lesson
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The instant your bare foot steps on a sharp pin, an electrical message shoots over three feet up your leg to your spinal cord in less than a hundredth of a second.
That lightning-fast warning travels along a single specialized cell called a sensory neurone, which transmits electrical impulses from receptors (cells detecting stimuli) to the central nervous system (CNS).
What makes this cell capable of stretching across entire limbs while transmitting signals at breakneck speed?
Anatomy of a Sensory Neurone
Unlike typical star-shaped nerve cells, a sensory neurone looks like a long highway with its cell body parked on a side branch.
📊Interactive labeled anatomical diagram of a sensory neurone. Layout flows horizontally left to right on a light background (#f8f9fa). On the left: Sensory Receptors in skin (touch/pain dots). Connecting to a long, thick Dendron with segmented myelin sheaths and exposed Nodes of Ranvier. In the middle-right: an off-center rounded Cell Body (soma) containing a distinct nucleus on a short stalk. Continuing right: a shorter Axon leading to Synaptic Axon Terminals entering the CNS (spinal cord cross-section). Direction of impulse arrows (pulsing yellow/cyan dashes) moving strictly left to right. Tooltips or clear labels in dark slate (#1e2945): Receptor, Dendron, Myelin Sheath, Node of Ranvier, Cell Body, Axon, CNS Terminals.
Why is the cell body tucked away on the side rather than sitting right at the receptor where the signal starts?
The Dendron and Cell Body Location
A dendron is an elongated cytoplasmic extension that carries nerve impulses toward the cell body, while an axon carries impulses away from the cell body toward the CNS.
In sensory neurones, the dendron is exceptionally long because it must reach from distant receptors in your skin, eyes, or joints all the way to near the spinal column.
The cell body (which houses the nucleus and metabolic machinery) sits off to the side in clusters called dorsal root ganglia right next to the spinal cord, safely shielded inside bone rather than exposed to injury out in your limbs.
How does an electrical impulse travel over a meter along this delicate wire without fading or slowing to a crawl?