Final answer:
The somatic nervous system reaches its target using only one neuron, which is a motor neuron. It controls voluntary movements by directly connecting the central nervous system to the skeletal muscles.
Step-by-step explanation:
The somatic nervous system controls voluntary movements by transmitting signals from the central nervous system (CNS) to the skeletal muscles. It achieves this via motor neurons. Each motor neuron in the somatic nervous system reaches its target with one neuron. Thus, the correct answer is 1) One neuron.
To provide further understanding, let's compare the somatic and autonomic systems. Unlike the autonomic nervous system, which usually has two synapses between the CNS and the target organ, the somatic nervous system uses a single neuron to make a direct connection. The motor neurons in the somatic nervous system carry instructions directly from the CNS to the muscles, making them contract. This system also includes sensory neurons, but in the context of reaching the target organ with motor commands, just one neuron is used.
Sensory and motor neurons play different roles. Sensory neurons transmit information from sensory receptors to the CNS, allowing perception of environmental stimuli. Motor neurons, on the other hand, transmit instructions for movement from the CNS to the muscles.
When a motor neuron transmits a nerve impulse to another neuron or to a muscle fiber, it does so through a synapse. The neurotransmitter acetylcholine, released by the motor neuron, crosses the synapse and binds to receptors on the muscle fiber, stimulating muscle contraction.