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A Handbook of Biology

SPÏÑÅL ÑËRVËS

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Humans have 31 pairs.

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It is divided into 5 groups. (C8Th12L5S5CO1)

SPINAL NERVE

Cervical

(8 pairs)

Thoracic

(12 pairs)

Lumbar

(5 pairs)

Sacral

(5 pairs)

Coccygeal

(1 pairs)

RËFLËX ÅÇTÏØÑ

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It is the rapid, involuntary and unconscious action of body in response

to a stimulus.

To brain

Spinal cord

Motor (efferent) neuron

Pain receptor

Flexor muscle -

withdraws foot

from stimulus

when contracted

Sensory

(afferent)

neuron

Dorsal root ganglion

Given below are some of the examples:

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Knee jerk phenomenon