1.The somatic nervous system, composed of somatic parts of the CNS and PNS, provides sensory and motor innervation to all parts of the body (G.soma), except the viscera in the body cavities, smooth muscle, and glands.
2.The somatic sensory system transmits sensations of touch, pain, temperature, and position from sensory receptors. Most of these sensations reach conscious levels (i.e., we are aware of them).
3.The somatic motor system innervates only skeletal muscle, stimulating voluntary and reflexive movement by causing the muscle to contract, as occurs in response to touching a hot iron.
Autonomic Nervous System
1.The autonomic nervous system (ANS), classically described as the visceral nervous system or visceral motor system,consists of motor fibers that stimulate smooth (involuntary) muscle, modified cardiac muscle (the intrinsic stimulating and conducting tissue of the heart), and glandular (secretory) cells.
2.However, the visceral efferent fibers of the ANS are accompanied by visceral afferent fibers.
3.As the afferent component of autonomic reflexes and in conducting visceral pain impulses, these visceral afferent fibers also play a role in the regulation of visceral function.
4.The efferent nerve fibers and ganglia of the ANS are organized into two systems or divisions: the sympathetic (thoracolumbar) division and the parasympathetic (craniosacral) division.
5.Unlike sensory and somatic motor innervation, in which the passage of impulses between the CNS and the sensory ending or effector organ involves a single neuron, in both divisions of the ANS, conduction of impulses from the CNS to the effector organ involves a series of two multipolar neurons.
6.The nerve cell body of the first presynaptic (preganglionic) neuron is located in the gray matter of the CNS. Its fiber (axon) synapses only on the cell body of a postsynaptic (postganglionic) neuron, the second neuron in the series.
7.The cell bodies of these second neurons are located outside the CNS in autonomic ganglia, with fibers terminating on the effector organ (smooth muscle, modified cardiac muscle, or glands).
The anatomical distinction between the sympathetic and parasympathetic divisions of the ANS is based primarily on
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the location of the presynaptic cell bodies.
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which nerves conduct the presynaptic fibers from the CNS.
8.A functional distinction of pharmacological importance for medical practice is that the postsynaptic neurons of the two divisions generally liberate different neurotransmitter substances: norepinephrine by the sympathetic division (except in the case of sweat glands) and acetylcholine by the parasympathetic division.