Compare the structural and functional differences between the somatic and autonomic parts of the nervous system.

Somatic Nervous System
includes both sensory and motor neurons.
Sensory neurons
Sensory neurons
convey input from receptors for somatic senses (tactile, thermal, pain, and proprioceptive sensations; and from receptors for the special senses (sight, hearing, taste, smell, and equilibrium
somatic motor neurons
somatic motor neurons
innervate skeletal muscles—the effectors of the somatic nervous system—and produce both reflexive and voluntary movements
When a somatic motor neuron stimulates the muscle
When a somatic motor neuron stimulates the muscle
it contracts; the effect always is excitation
If somatic motor neurons cease to stimulate a muscle
the result is a paralyzed, limp muscle that has no muscle tone
Autonomic Nervous System
( monitor conditions in the internal environment.

)The main input to the ANS comes from autonomic (visceral) sensory neurons. Mostly, these neurons are associated with interoceptors

sensory receptors located in blood vessels, visceral organs, muscles
Examples of interoceptors
Examples of interoceptors
chemoreceptors that monitor blood CO2 level and mechanoreceptors that detect the degree of stretch in the walls of organs or blood vessels.
Autonomic motor neurons
Autonomic motor neurons
regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, and glands).
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the heart continues to beat when it is removed for transplantation into another person, smooth muscle in the lining of the gastrointestinal tract contracts rhythmically on its own, and glands produce some secretions in the absence of ANS control.
Comparison of Somatic and Autonomic Motor Neurons
Comparison of Somatic and Autonomic Motor Neurons
that the axon of a single, myelinated somatic motor neuron extends from the central nervous system (CNS) all the way to the skeletal muscle fibers in its motor unit ; By contrast, most autonomic motor pathways consist of two motor neurons in series, that is, one following the other (The first neuron (preganglionic neuron) has its cell body in the CNS; its myelinated axon extends from the CNS to an autonomic ganglion. (Recall that a ganglion is a collection of neuronal cell bodies in the PNS.) The cell body of the second neuron (postganglionic neuron) is also in that same autonomic ganglion; its unmyelinated axon extends directly from the ganglion to the effector (smooth muscle, cardiac muscle, or a gland). Alternatively, in some autonomic pathways, the first motor neuron extends to specialized cells called chromaffin cells in the adrenal medullae (inner portions of the adrenal glands) rather than an autonomic ganglion.)
chromaffin cells
chromaffin cells
What kind of cells is the adrenal medulla made of? (secrete epinephrine and noriepinephrine)
What does dual innervation mean?
Dual innervation means that a body organ receives neural innervation from both sympathetic and parasympathetic neurons of the ANS.
From somatic senses and special senses.
SOMATIC NERVOUS SYSTEM Control of motor output
Voluntary control from cerebral cortex, with contributions from basal ganglia, cerebellum, brain stem, and spinal cord.
SOMATIC NERVOUS SYSTEM Motor neuron pathway
One-neuron pathway: Somatic motor neurons extending from CNS synapse directly with effector.
SOMATIC NERVOUS SYSTEM Neurotransmitters and hormones
All somatic motor neurons release only acetylcholine (ACh).
Skeletal muscle.
Contraction of skeletal muscle.
Mainly from interoceptors; some from somatic senses and special senses.
AUTONOMIC NERVOUS SYSTEM Control of motor output
Involuntary control from hypothalamus, limbic system, brain stem, and spinal cord; limited control from cerebral cortex.
Usually two-neuron pathway: Preganglionic neurons extending from CNS synapse with postganglionic neurons in autonomic ganglion, and postganglionic neurons extending from ganglion synapse with visceral effector. Alternatively, preganglionic neurons may extend from CNS to synapse with chromaffin cells of adrenal medullae.
AUTONOMIC NERVOUS SYSTEM Neurotransmitters and hormones
acetylcholine (ACh).
All sympathetic and parasympathetic preganglionic neurons release ACh. Most sympathetic postganglionic neurons release NE; those to most sweat glands release ACh. All parasympathetic postganglionic neurons release ACh. Chromaffin cells of adrenal medullae release epinephrine and norepinephrine (NE).
Smooth muscle, cardiac muscle, and glands.
Contraction or relaxation of smooth muscle; increased or decreased rate and force of contraction of cardiac muscle; increased or decreased secretions of glands.
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