Ch. 15 The Autonomic Nervous System

24 July 2022
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ANS
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- a system of motor neurons that innervate the smooth muscle, cardiac muscle, and glands of the body - autonomic activation or inhibition of the viscera - two divisions: sympathetic and parasympathetic - somatic system controls voluntary muscle - somatic motor system; when an action potential causes Ach to initiate muscle contraction, *it only activates* the muscle - ANS can activate or inhibit smooth muscle, cardiac tissue to contract
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functional organization of the ANS
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sympathetic - "fight or flight" - responds to stresses (physical and emotional) - increases body functions that support physical activity - decreases digestive and urinary function - activated: heart starts pumping or muscles contract, breathing heavier, pupils dilated, reduced digestive and urinary system parasympathetic - "rest and digest" - conserve and restore body energy - decrease body functions that support physical activity - increase digestive and urinary function *for the most part, opposing functions*
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somatic motor vs. autonomic motor
somatic motor vs. autonomic motor
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*study picture* - somatic: cell body; CNS in the ventral horn; one axon to the effector organ; acetylcholine; contraction - ANS; chain of 2 neurons; cell body CNS, 2nd in a ganglion in the 1st neuron; pre-ganglionic neuron; CNS; 2nd neuron; post-ganglionic neuron; PNS - pre-ganglionic: neurotransmitter is ACh - post-ganglionic: neurotransmitter in sympathetic is NE, ACh in parasympathetic - length of axons: sympathetic = pre is relatively short, post is a little longer; parasympathetic = pre is very long, post is short
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ANS neurons
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- pre-ganglionic neuron: soma located in the CNS sympathetic: lateral horn of thoracolumbar spinal cord, T1-L2 sends its axons through the ventral root; motor-only root; synapses with post-ganglionic neuron to a tube of smooth muscle to cause contraction parasympathetic: brainstem or sacral spinal cord - post-ganglionic neuron: soma located in the PNS
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Parasympathetic Ganglia
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- terminal ganglia: located close to or within the wall of an organ ; at the site of termination - because terminal ganglia are located so near the effector organ... 1) long pre-ganglionic axons (CNS -> ganglia) 2) short post-ganglionic axons (ganglia -> effector) - cranial outflow: 4 spinal nerves - sacral outflow: sacral spinal nerves
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Cranial Nerves and the ANS
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- CNIII: oculomotor nerve; 4 of the 6 extraocular muscles, as well as the levator palpebrae (eyelid); eye movement and eyeball regulation; parasympathetic; constriction - CNVII: facial nerve; facial muscles, sensory function and taste; parasympathetic; *lacrimal gland*= above the eye to wash the eyeball; sublingual and submandibular gland = salvia for digestion - CNIX: glossopharyngeal nerve; parotid gland near the ear - CNX: vagus nerve; all visceral organs and 2/3 of the abdominal; 1/3 by the sacral spinal nerves
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Cranial Nerves with Parasympathetic Function
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- CNIII (Oculomotor) = pupillary construction - CNVII (Facial) = lacrimal gland and sublingual and submandibular salivary glands - CNIX (Glossopharyngeal) = parotid gland - CNX (Vagus) = visceral organs of the thorax and upper 2/3 of the abdomen; 90% of preganglionic parasympathetic fibers
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Sympathetic Ganglia
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- paravertebral ganglia: located in a vertical row to either side of the vertebral column - prevertebral ganglia: located anterior to the vertebral column, on the abdominal aorta - because most sympathetic ganglia are near the spinal cord: 1) short preganglionic axons (spinal cord -> ganglion) 2) long postganglionic axons (ganglion -> effector)
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Paravetebral and Prevertebral Ganglia
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- yellow dots beside the spinal column are paravertebral ganglia; chain ganglia or trunk ganglia - those located on the abdominal aorta are called the prevertebral ganglia or collateral ganglia
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Paravertebral and Prevertebral Ganglia continued...
Paravertebral and Prevertebral Ganglia continued...
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- preganglionic neurons live in the lateral horns of the spinal cord - travel to the chain ganglia or prevertebral ganglia - synapse and then post-synaptic axon synapses with an effector organ
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The Adrenal Medulla
The Adrenal Medulla
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- triangle-shaped structure above kidney; 2 parts: 1) adrenal cortex 2) adrenal medulla: chromaffin cells; modified postganglionic sympathetic neurons that secrete the amine hormones epinephrine and NE; adrenal medulla is a specialized sympathetic ganglion - another name for epinephrine is adrenaline - adrenaline rush: adrenal medulla release of E and NE - anything that has a E and NE receptor will bind to it; i.e. heart will beat faster; pounding heart rate
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Autonomic Tone
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- sympathetic and para sympathetic outflow; at specific times there is more than one compared to the other - balance between the two is referred to as autonomic tone
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Example: Autonomic Control of the Heart
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- heart; vagi's; right and left vagus nerve; innervate the region of the heart that dictates how fast the heart will beat - sympathetic cardiac accelerator nerves; not only the rate but also the muscular parts to affect the force of muscle contraction - ACh: causes a reduction in the HR - NE: causes an increase in HR and force of contraction
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Heart Rate
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- resting heart rate; feel pulse; resting 60-100 - anything over 100 = tachycardia - anything below 60 = brachycardia - vagus nerve has a higher tone at rest - withdrawal of vagal tone; less ACh release on to heart, and then with higher activity; sympathetic activity needs to be increased
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Example: Autonomic Control of the Bronchioles
Example: Autonomic Control of the Bronchioles
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- bronchioles; branching to smaller bronchioles; smooth muscle wrapped around the tubes; no cartilage there, thus can bronchoconstrict; close the lumen - brachodilate causes lumen to become larger - sympathetic; inhibition of muscle contraction; relax the smooth muscle; NE and E; bronchodilation - parasympathetic; slight constriction - epi pen will inhibit contraction of bronchiole
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Division of the ANS responsible for the fight-or-flight response describes the
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Sympathetic Division
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The parasympathetic nervous system is characterized by
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peripheral ganglia near the organs, and short post-ganglionic fibers.
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Which of these organs/tissues are NOT innervated by parasympathetic fibers, or do not exhibit parasympathetic effects? (A) blood coagulation, mental activity, and vagina (B) the eye (ciliary muscles), cellular metabolism, and heart (C) sweat glands, arrector pili muscles, and adipose tissue (D)adrenal medullae, kidney, and gallbladder
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(C)
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The ANS is the system of __________ neurons that regulates such functions as __________.
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motor / heart rate, digestion, and blood pressure
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Which region of the spinal cord does NOT contain any autonomic neurons?
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The cervical region is the only region that does not contain preganglionic sympathetic neuronal cell bodies.
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Cell body of this autonomic neuron lies within the CNS.
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pre-ganglionic neuron
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Cell body of this autonomic neuron lies outside the CNS.
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post-ganglionic neuron
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Cell bodies of the preganglionic sympathetic neurons are located within the
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lateral gray horns of the spinal cord.
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This organ contains modified sympathetic postganglionic neurons that lack nerve processes.
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Adrenal Medulla
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Adrenergic hormones are secreted into the bloodstream in this region of the adrenal gland.
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Medulla
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Which region of the central nervous system integrates the activities of the autonomic nervous system?
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Hypothalamus
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Which division of the autonomic nervous system has preganglionic fibers within the facial nerve?
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Parasympathetic
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The trunk ganglia contain what kind of cell bodies?
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Post-ganglionic sympathetic
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Cranial parasympathetic outflow is contained in all of the following cranial nerves except the accessory, vagus, glossopharyngeal, or facial?
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Accessory
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Which fibers in the motor division of the PNS are not myelinated?
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Postganglionic axons of both the sympathetic and parasympathetic divisions are nonmyelinated.
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As you are driving home from school, a car suddenly swerves toward you, forcing you to hit the brakes quickly. You feel your heart pump, and you begin to sweat a bit. Which division of the ANS has been activated?
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The sympathetic division of the ANS has been activated in this near-miss scenario.
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Where are the sympathetic ganglia located? Where are most of the parasympathetic ganglia located?
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Sympathetic ganglia are located near the spinal cord and vertebral column (in the sympathetic trunk or collateral ganglia). Most parasympathetic ganglia are located in or near the target organ.
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Are visceral sensory fibers considered part of the ANS?
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Traditionally the ANS is considered a motor division; therefore, it does not include the visceral sensory fibers.
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Which spinal nerves carry parasympathetic preganglionic fibers?
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Sacral spinal nerves (S2-S4) carry preganglionic parasympathetic fibers.
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What is the result of vagal stimulation of (a) the heart, (b) the small intestine, (c) the salivary glands?
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(a) Vagal stimulation of the heart decreases heart rate. (b) Vagal stimulation of the small intestine increases motility and secretion. (c) Vagal stimulation of the salivary glands stimulates secretion.
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Cranial nerves III, VII, and IX carry preganglionic parasympathetic fibers. Which cranial nerve carries the postganglionic fibers to the target organs innervated by these three nerves?
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The preganglionic fibers synapse in ganglia located along the pathway of the trigeminal nerve (CN V). Postganglionic fibers then travel along CN V to reach their target organs.
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Why are the white rami communicates located only on sympathetic trunk ganglia between T1 and L2 and gray rami communicates branch off each sympathetic trunk ganglion?
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The white rami communicantes carry preganglionic outflow from the thoracic and lumbar regions of the cord into the sympathetic trunk. The gray rami communicantes are postganglionic fibers that exit off the sympathetic trunk onto a spinal nerve at each level of the sympathetic trunk. These postganglionic fibers are carried on spinal nerves to all regions of the body to innervate blood vessels, sweat glands, and arrector pili
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What is the general effect of sympathetic innervation to the abdominal organs?
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Sympathetic innervation to the abdominal organs decreases activity of the glands and muscles of the digestive system.
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Which type of autonomic fibers (preganglionic, postganglionic, sympathetic, parasympathetic) are located in the thoracic and abdominal autonomic plexuses?
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The thoracic plexuses contain preganglionic parasympathetic fibers and postganglionic sympathetic fibers. The abdominal plexuses also contain preganglionic parasympathetic fibers and postganglionic sympathetic fibers. In addition, preganglionic sympathetic fibers travel through the abdominal plexuses (via the splanchnic nerves) to reach the collateral ganglia.