How is the sensorimotor nervous system different from the autonomic nervous system in structure and function?

Answer 1

The autonomic nervous system is NOT under our voluntary control. It is generally divided into two subsystems, the Sympathetic and the Parasympathetic nervous systems. The sympathetic neurotransmitter (at the target organ ) is nor-epinephrine (aka nor-adrenaline); it binds to alpha- or beta-adrenergic receptors, and indirectly, through a G-protein linked second messenger system, it opens a channel that changes the cell membrane potential, which causes its effect. It is involved in the "flight or fight" response. The parasympathetic neurotransmitter (at the target organ) is acetylcholine; it binds to a muscarinic receptor and through the same kind of second messenger system, mediates the opposite (to the sympathetic) response, a kind of rest and relaxation effect. Both subsystems involve a chain of two neurons from the spinal cord to the target organ.
The somtic nervous system IS under voluntary control. An alpha motor neuron (a single cell) goes from the spinal cord to the muscle the neuron innervates. The neurotransmitter is acetylcholine; it binds to a nicotinic receptor. This receptor has a cation channel within it; opening the channel causes an action potential in the muscle, which causes a contraction.