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46 Cards in this Set
- Front
- Back
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What is the function of the autonomic nervous system?
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The autonomic nervous system (ANS) is the motor division of the PNS that controls visceral activities, with the goal of maintaining internal homeostasis
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What does the autonomic nervous system innervate?
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The somatic (voluntary) nervous system provides motor fibers to skeletal muscles. The autonomic (involuntary or visceral motor) nervous system provides motor fibers to smooth and cardiac muscles and glands.
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What kind of ganglionic chain is used in the efferent pathway of the autonomic nervous system?
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In the somatic division, a single motor neuron forms the efferent pathway from the CNS to the effectors. The efferent pathway of the autonomic division consists of a two-neuron chain: the preganglionic neuron in the CNS and the ganglionic neuron in a ganglion
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What is the function of acetylcholine?
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Acetylcholine, the neurotransmitter of somatic motor neurons, is stimulatory to skeletal muscle fibers. Neurotransmitters released by autonomic motor neurons (acetylcholine and norepinephrine) may cause excitation or inhibition.
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What are the two divisions of the autonomic nervous system?
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The ANS consists of two divisions, the parasympathetic and sympathetic, which normally exert antagonistic effects on many of the same target organs.
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What is the function of the parasympathetic system?
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The parasympathetic division (the resting-digesting system) conserves body energy and maintains body activities at basal levels.
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What are some effects of the parasympathetic system?
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Parasympathetic effects include pupillary constriction, glandular secretion, increased digestive tract motility, and smooth muscle activity leading to elimination of feces and urine.
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What is the function of the sympathetic system?
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The sympathetic division prepares the body for activity and is called the fight-or-flight system.
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What are some effects of the sympathetic system?
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Sympathetic responses include dilated pupils, increased heart rate, increased blood pressure, dilation of the bronchioles of the lungs, increased blood glucose levels, and sweating. During exercise, sympathetic vasoconstriction shunts blood from the skin and digestive viscera to the heart, brain, and skeletal muscles.
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Where do parasympathetic preganglionic neurons come from?
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Parasympathetic preganglionic neurons arise from the brain stem and from the sacral (S2-S4) region of the cord.
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Where do preganglionic fibers synapse?
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Preganglionic fibers synapse with ganglionic neurons in terminal ganglia located in (intramural ganglia) or close to their effector organs. Preganglionic fibers are long, postganglionic fibers are short.
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Where do cranial fibers arise?
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Cranial fibers arise in the brain stem nuclei of cranial nerves III, VII, IX, and X and synapse in ganglia of the head, thorax, and abdomen. The vagus nerves serve virtually all organs of the thoracic and abdominal cavities.
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Where do sacral fibers arise?
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Sacral fibers (S2-S4) issue from the lateral region of the cord and form pelvic splanchnic nerves that innervate the pelvic viscera. The preganglionic axons do not travel within rami communicantes or spinal nerves.
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Where do preganglionic sympathetic neurons arise?
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Preganglionic sympathetic neurons arise from the lateral horn of the spinal cord form the level of T1 to L2.
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How do preganglionic axons leave the cord?
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Preganglionic axons leave the cord via white rami cammunicantes and enter the sympathetic trunk (chain) ganglia in the sympathetic trunk. An axon may synapse in a trunk ganglion at the same or at a different level, or it may issue from the sympathetic trunk without synapsing. Preganglionic fibers are short, post ganglionic fibers are long.
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How does the routing of the postganglionic fiber change when the synapse occurs in a trunk ganglion?
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When the synapse occurs in a trunk ganglion, the post-ganglionic fiber may enter the spinal nerve ramus via the gray ramus communicans to travel to the body periphery. Postganglionic fibers issuing from the cervical ganglia also serve visceral organs and blood vessels of the head, neck and thorax.
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What happens when synapses do not occur in the trunk ganglia?
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When synapses do not occur in the trunk ganglia, the preganglionic fibers form splanchnic nerves (thoracic, lumbar, and sacral). Most splanchnic nerve fibers synapse in collateral ganglia, and the postganglionic fibers serve the abdominal viscera. Some splanchnic nerve fibers synapse with cells of the adrenal medulla.
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How do visceral reflex arcs compare to somatic reflex arcs?
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Visceral reflex arcs have the same components as somatic reflexes.
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Where are cell bodies of visceral sensory neurons located?
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Cell bodies of visceral sensory neurons are located in dorsal root ganglia, sensory ganglia of cranial nerves, or autonomic ganglia. Visceral afferents are found in spinal nerves and in virtually all autonomic nerves.
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What is meant by a cholinergic or adrenergic fiber?
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Two major neurotransmitters, acytylcholine (ACh) and norepinephrine (NE), are released by autonomic motor neurons. On the basis of the neurotransmitter released, the fibers are classified as cholinergic or adrenergic.
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What structures release ACh and NE?
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Ach is released by all preganglionic fibers and all parasympathetic postganglinic fibes. NE is released by all sympathetic prostganglionic fibers except those serving the sweat glands of the skin, and some blood vessels within skeletal muscles.
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How are cholinergic and adrenergic receptors classified?
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Neurotransmitter effects depend on the receptors to which the transmitter binds. Cholinergic (ACh) receptors are classified as nicotinic or muscarinic. Adrenergic (NE) receptors are classified as alpha 1 or alpha 2, or beta 1, beta 2, or beta 3.
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How are drugs used to alter the functioning of the ANS?
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Drugs that mimic, enhance, or inhibit the action of ANS neurotransmitters are used to treat conditions caused by excessive, inadequate, or inappropriate ANS functioning. Some drugs bind with only one receptor subtype, allowing specific ANS-mediated activites to be enhanced or blocked.
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How do the sympathetic and parasympathetic systems affect visceral organs?
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Most visceral organs are innervated by both divisions; they interact in various ways but usually exert a dynamic antagonism. Antagonistic interactions mainly involve the heart, respiratory system, and gastrointestinal organs. Sympathetic activity increases heart and respiratory system activity and depresses gastrointestinal activity. Parasympathetic activity reverses these effects.
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How are the blood vessels and heart affected by the sympathetic and parasympathetic systems?
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Most blood vessels are innervated only by sympathetic fibers and exhibit vasomotor tone. Parasympathetic activity dominates the heart and muscles of the gastrointestinal tract (which normally exhibit parasympathetic tone) and glands).
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How do the two divisions of the ANS affect genitalia?
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The two ANS divisions exert cooperative effects on the external genitalia.
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What functions are unique to the sympathetic division?
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Roles unique to the sympathetic division are blood pressure regulation, shunting of blood in the vascular system, themoregulatory responses, stimulation of renin release by the kidneys, and metabolic effects.
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Contrast the parasympathetic and sympathetic systems in terms of scope and longevity.
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Activation of the sympathetic division can cause widespread, long-lasting mobilization of the fight-or-flight response. Parasympathetic effects are highly localized and short lived.
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How is autonomic function controlled?
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Autonomic function is controlled at several levels. (1) Reflex activity is mediated by the spinal cord and brain stem (particularly medullary) centers (2) hypothalamic integration centers interact with both higher and lower centers to orchestrate autonomic, somatic, and endocrine responses and (3) cortical centers influence autonomic functioning via connections with the limbic system; conscious controls of autonomic function are rare but possible, as illustrated by biofeedback training.
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What are some examples of autonomic disorders?
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Most autonomic disorders reflect problems with smooth muscle control. Abnormalities in vascular control, such as occur in hypertension, Raynaud's disease, and autonomic dysreflexia, are most devistating.
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What do preganglionic neurons develop from?
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Preganglionic neurons develop from the neural tube; ganglionic neurons develop from the embryonic neural crest.
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What are the effects of aging on the autonomic system?
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The efficiency of the autonomic nervous system declines in old age, as reflected by decreased glandular secretory activity, decreased gastrointestingal motility, and slowed sympathetic vasomotor responses to changes in position.
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All of the following characterize the ANS except:
A) two-neuron efferent chain B) presence of nerve cell bodies in the CNS C) presence of nerve cell bodies in the ganglia D) innervation of skeletal muscles |
D) innervation of skeletal muscles
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Preganglionic neurons develop from:
A) neural crest cells B) neural tube cells C) alar plate cells D) endoderm |
B) neural tube cells
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The white rami communicatntes contain what kind of fibers?
A) preganglionic parasympathetic B) postganglionic parasympathetic C) preganglionic sympathetic D) postganglionic sympathetic |
C) preganglionic sympathetic
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Prevertebral sympathetic ganglia are involved with the innervation of the:
A) abdominal organs B) thoracic organs C) head D) arrector pili E) all of these |
A) abdominal organs
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The celiac and superior and inferior mesenteric ganglia are not sympathetic trunk ganglia. What kind of ganglia are they?
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Collateral (prevertebral) ganglia
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Pre and postganglionic neurons will synapse within:
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Pathway of Preganglionic Neurons
- Once the preganglionic neuron reaches the sympathetic chain ganglion, it has three options: - It can synapse with a postganglionic neuron within the chain ganglion - Will ascend or descend the sympathetic trunk and synapse in another chain ganglion - Can pass through the chain ganglion and emerge from the sympathetic trunk as a splanchnic nerve which synapse within the prevertebral ganglia |
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The myelination of motor neurons of the ANS occurs with:
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White rami
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What is the function of the sympathetic branch of the ANS?
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The sympathetic division turns on during the 4e's:
-- Exercise -- Excitement -- Emergencies -- Emotions - will increase the activities of essential organs: heart rate, blood pressure, respiratory rate, and liver secretions - Decreases the activity of non-essential organs: renal system, digestive system |
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Postganglionic neurons that innervate structures within the thorax, synapse:
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within the sympathetic chain ganglia
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What are the three options preganglionic neurons have when they enter the sympathetic chain
ganglia? |
Pathway of Preganglionic Neurons
- Once the preganglionic neuron reaches the sympathetic chain ganglion, it has three options: - It can synapse with a postganglionic neuron within the chain ganglion - Will ascend or descend the sympathetic trunk and synapse in another chain ganglion - Can pass through the chain ganglion and emerge from the sympathetic trunk as a splanchnic nerve which synapse within the prevertebral ganglia |
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Which neural structures (or nerves) represent the parasympathetic branch of the ANS?
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- Located in the cranial and sacral regions of the spinal cord represented by:
-- Cranial nerves III, VII, IX, and X -- Pelvic splanchnic nerves S2, S3, and S4 - A long preganglionic neuron and a short postganglionic neuron - the cell bodies of the 1st motor neurons are located within the brian stem or the lateral horn of the lumbar enlargement - Terminal ganglia near or within the target organ |
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The pre and postganglionic motor neurons of the parasympathetic branch will synapse:
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Terminal ganglia near or within the target organ
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Those neurons which release the neurotransmitter acetylcholine (ACh) are called:
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- Neurons which release acetylcholine (Ach) are called cholinergic neurons
- Cholinergic receptors are: -- Nicotinic receptors excite --- Located on the membranes of postganglionic neurons -- Muscarinic receptors excite and inhibit --- Located on membranes of target tissue |
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What are Adrenergic receptors?
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- Neurons which release epinephrine or norepinephrine are called adrenergic neurons
- Adrenergic receptors are located on the target tissue - Two types are Alpha and Beta -- Alpha are excitatory: --- Cause vasoconstriction --- Contraction of the intestinal and urinary sphincters -- Beta's are either --- Excitatory (Beta1) increases heart rate and strength of contraction --- Inhibitory (Beta2) bronchiole dilation, dilation of coronary arteries |
