Final answer:
The somatic nervous system typically involves one neuron between the spinal cord and the effector, while the autonomic nervous system involves a two-neuron chain, with both a preganglionic and a postganglionic neuron in the pathway to the effector.
Step-by-step explanation:
When comparing how many neurons are found in the ANS versus the somatic nervous system between the spinal cord and the effector, it is important to understand the structural differences in their reflex pathways. In the somatic nervous system (SNS), the usual reflex comprises just one motor neuron, the lower motor neuron, which directly innervates skeletal muscle, resulting in muscle contraction. This means there is typically only one neuron in the pathway between the spinal cord and the skeletal muscle effector. In contrast, the autonomic nervous system (ANS) involves a two-neuron chain where a preganglionic neuron originating in the CNS synapses with a postganglionic neuron in the peripheral ganglia, which then acts on the target organ, be it cardiac or smooth muscle, or glandular tissue. Therefore, in the ANS, there are two neurons involved between the central nervous system and the effector.