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← 🫀 Human body · usually met in Std 8-12

The nervous system

A network of cells that carries signals as electrical impulses, with the brain and spinal cord at the centre and nerves reaching everywhere else.

A reflex does not wait for the brain brain spinal cord hand on something hot 1 · sensory nerve in 2 · motor nerve out — the hand moves 3 · the brain is told afterwards, which is when you feel the pain Your hand is already moving before you know the pan was hot. Deciding to move it is a different, slower path.
Drawn for Star Student.

A neuron receives signals through branched dendrites, carries them along a long axon, and passes them to the next cell across a tiny gap called a synapse, using chemical messengers. Signals travel fast — metres per second to over a hundred metres per second along insulated fibres.

The brain and spinal cord together form the central nervous system; the nerves branching out from them are the peripheral. Some responses never reach the brain at all: a reflex arc runs sensory nerve to spinal cord to motor nerve, which is why your hand leaves a hot surface before you are aware of the heat. Deciding to move your hand is a different, slower path through the brain.

Worth knowing

  • An adult human brain holds on the order of 86 billion neurons.
  • Neurons do not touch; the synaptic gap is crossed chemically, which is where most medicines acting on the brain do their work.
  • The brain uses roughly a fifth of the body's energy while being about two per cent of its weight.

Want to see it moving? Search YouTube for “The nervous system” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.

See also

🫀 The eye🫀 The ear🫀 Sleep

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Last gone through: 1 October 2026 · How these entries are written

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