comparison of somatic and autonomic nervous systems

autonomic nervous system (ANS)
Visceral sensory (afferent) and visceral motor (efferent) neurons.
-Autonomic motor neurons, both sympathetic and parasympathetic, conduct nerve impulses from the central nervous system to smooth muscle, cardiac muscle, and glands.
-So named because this part of the nervous system was thought to be self‐governing or spontaneous.
Somatic Nervous System
-includes both sensory and motor neurons.
Somatic Nervous system: 
Somatic Sensory Neurons
Somatic Nervous system:
Somatic Sensory Neurons
-convey input from receptors for:
1. somatic senses (tactile, thermal, pain, and proprioceptive sensations)
2. special senses (sight, hearing, taste, smell, and equilibrium).
-All these sensations normally are consciously perceived.
Somatic Nervous System: 
Somatic Motor Neurons
Somatic Nervous System:
Somatic Motor Neurons
-innervate skeletal muscles—the effectors of the somatic nervous system—and produce both reflexive and voluntary movements.
Somatic Motor Neurons: muscle stimulation
Somatic Motor Neurons: muscle stimulation
-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
-The main input to the ANS comes from autonomic (visceral) sensory neurons.
-Mostly, these neurons are associated with interoceptors.
Autonomic Nervous System:
Interceptors
-sensory receptors located in blood vessels, visceral organs, muscles, and the nervous system that monitor conditions in the internal environment.
-Examples of interoceptors are chemoreceptors that monitor blood CO2 level and mechanoreceptors that detect the degree of stretch in the walls of organs or blood vessels.
Autonomic Nervous System:
Interceptors are not consciously perceived all of the time:
-these sensory signals are not consciously perceived most of the time, although intense activation of interoceptors may produce conscious sensations.(Unlike those triggered by a flower’s perfume, a beautiful painting, or a delicious meal)
-Two examples of perceived visceral sensations are pain sensations from damaged viscera and angina pectoris (chest pain) from inadequate blood flow to the heart. Input that influences the ANS also includes some sensations monitored by somatic sensory and special sensory neurons. For example, pain can produce dramatic changes in some autonomic activities.
Autonomic Nervous System: 
Autonomic motor neurons
Autonomic Nervous System:
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).
-examples:
Changes in the diameter of the pupils, dilation and constriction of blood vessels, and adjustment of the rate and force of the heartbeat.
Autonomic Nervous System:
Function & damage to ANS
-Unlike skeletal muscle, tissues innervated by the ANS often function to some extent even if their nerve supply is damaged.
-example: 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.
Autonomic Nervous System: 
autonomic motor pathways
Autonomic Nervous System:
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.
-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.
In comparison: (the axon of a single, myelinated somatic motor neuron extends from the central nervous system (CNS) all the way to the skeletal muscle fibers)
Autonomic Nervous System: 
autonomic neurotransmitters
Autonomic Nervous System:
autonomic neurotransmitters
(all somatic motor neurons release only acetylcholine (ACh) as their neurotransmitter)
-autonomic motor neurons release either ACh or norepinephrine (NE) as their neurotransmitters.
Ganglion
Ganglion
a collection of neuronal cell bodies in the PNS.
autonomic ganglion
autonomic ganglion
A cluster of cell bodies of sympathetic or parasympathetic neurons located outside the central nervous system.
output part of the ANS has two divisions:
1. the sympathetic division.
2. the parasympathetic division.
sympathetic division
sympathetic division
-having cell bodies of preganglionic neurons in the lateral gray columns of the thoracic segment and the first two or three lumbar segments of the spinal cord.
-primarily concerned with processes involving the expenditure of energy.
-often called the fight‐or‐flight division.
-activities result in increased alertness and metabolic activities in order to prepare the body for an emergency situation.
Sympathetic division: Fight or flight: restoring homeostasis
-Responses to such situations, which may occur during physical activity or emotional stress.
-a rapid heart rate, faster breathing rate, dilation of the pupils, dry mouth, sweaty but cool skin, dilation of blood vessels to organs involved in combating stress (such as the heart and skeletal muscles), constriction of blood vessels to organs not involved in combating stress (for example, the gastrointestinal tract and kidneys), and release of glucose from the liver.
parasympathetic division
parasympathetic division
-having cell bodies of preganglionic neurons in nuclei in the brain stem and in the lateral gray horn of the sacral portion of the spinal cord.
-primarily concerned with activities that conserve and restore body energy.
-rest‐and‐digest division.
parasympathetic division: Rest and Digest: restoring homeostasis
-its activities conserve and restore body energy during times of rest or digesting a meal; the majority of its output is directed to the smooth muscle and glandular tissue of the gastrointestinal and respiratory tracts.
-replenishes nutrient stores.
dual innervation
-organs that receive impulses from both sympathetic and parasympathetic neurons.
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