Reflex Pathways

Fruit being loaded into a bowl puts weight on an arm muscle and stretches it. Will the bowl drop? NO! Muscle spindles in the muscle’s sheath also are stretched.

Stretching stimulates sensory receptor endings in this muscle spindle. Action potentials are propagated toward spinal cord.

 In the spinal cord, axon terminals of the sensory neuron release a neurotransmitter that diffuses across a synaptic cleft and stimulates a motor neuron.

The stimulation is strong enough to generate action potentials that self-propagate along the motor neuron’s axon.

ACh released from the  motor neuron’s axon terminals stimulates muscle fibers.

 Stimulation makes the stretched muscle contract. Ongoing stimulations and contractions hold the bowl steady.