Reflex steps

1A hammer tap stretches the tendon in the knee, stretching receptors in the extensor muscle.

3 In a monosynaptic pathway, the sensory neuron synapses with a motor neuron in the ventral horn of the spinal cord.

4 The motor neuron conducts action potentials to the extensor muscle, causing contraction.

5 A multiple synapse pathway involving a spinal interneuron inhibits firing in the motor neuron for the antagonistic muscle.

6 The leg extends.

Dorsal horn

Dorsal root (afferent nerves)

Gray matter

Inhibitory interneuron

Motor neurons

Stretch receptors fire action potentials.

Ventral horn

Ventral root (efferent nerves)

White matter