Final answer:
The simplest autonomic reflexes typically involve two synapses: a sensory neuron synapsing onto a ganglionic neuron and the ganglionic neuron onto the effector organ. These synapses usually occur in peripheral ganglia and can take place without the involvement of the CNS, unlike somatic reflexes.
Step-by-step explanation:
The simplest autonomic reflexes typically involve two synapses. These reflexes involve a sensory neuron projecting to a ganglionic neuron—this constitutes the first synapse. The ganglionic neuron then activates the effector target with the second synapse. It's crucial to understand that the key difference here is that these simplest reflexes might not involve the central nervous system (CNS), setting them apart from somatic reflexes which always involve the CNS.
In a short autonomic reflex, the sensory neuron synapses directly onto the ganglionic neuron, potentially bypassing the CNS entirely. The synapses can occur in peripheral ganglia, which are clusters of neuronal cell bodies located outside the CNS. In other words, the autonomic reflex arc can be completed without the sensory input traveling all the way to the brain or spinal cord before the response is executed.
It is worth noting that in chemical signaling within the autonomic nervous system, the synapse is where an autonomic neuron connects with the target and can release neurotransmitters like acetylcholine or norepinephrine to activate the target organ.