ilm1993's version from 2017-07-26 02:18


Question Answer
The ANS consists of motor neurons thatOperate via subconscious control; Have viscera as most of their effectors
The effectors of the ANS arecardiac muscle, smooth muscle, and glands
Efferent Pathwaysare a two-neuron chain (preganglionic neuron - lightly myelinated axon ; ganglionic- extends to an effector organ)
All somatic motor neurons releaseACh, which has an excitatory effect
ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector

Sympathetic vs Parasympathetic

Question Answer
The sympatheticmobilizes the body during extreme situations
The parasympatheticperforms maintenance activities and conserves body energy
Energy in parasympathetic?Concerned with keeping body energy use low
D activities involved in parasympathetic digestion, defecation, and diuresis
Involves E activities in sympatheticexercise, excitement, emergency, and embarrassment

Sympathetic flow

Question Answer
Sympathetic flowT1 through L2
Sympathetic neurons producelateral horns of the spinal cord
Fibers from T5-L2 formsplanchnic nerves and synapse with collateral ganglia
Postganglionic fibersinnervate the numerous organs of the body
The paravertebral ganglia formthe sympathetic trunk or chain
Typically there are23 ganglia

A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia

Question Answer
1Synapse with the ganglionic neuron within the same ganglion
2Ascend or descend the sympathetic chain to synapse in another chain ganglion
3Pass through the chain ganglion and emerge without synapsing
Postganglionic axons enterventral rami via the gray rami communicantes
These fibers innervatesweat glands and arrector pili muscles
Rami communicantes are associated only withthe sympathetic division
Preganglionic fibers emerge fromT1-T4 and synapse in the superior cervical ganglion
Preganglionic fibersStimulate dilator muscles of the iris ; Inhibit nasal and salivary glands
Preganglionic fibers emerge from T1-T6 and synapse in thecervical chain ganglia

Postganglionic fibers

Question Answer
Postganglionic fibers servethe stomach, intestines, liver, spleen, and kidneys
Postganglionic fibers emerge fromthe middle and inferior cervical ganglia and enter nerves C4-C8
These fibers innervatethe heart, thyroid and the skin
These fibers (T5-L2)leave the sympathetic chain without synapsing
They formthoracic, lumbar, and sacral splanchnic nerves
Their ganglia includethe celiac, the superior and inferior mesenterics, and the hypogastric


Question Answer
Postganglionic fibers directly servethe heart, aorta, lungs, and esophagus
Sympathetic nerves innervating the abdomen havepreganglionic fibers from T5-L2
They travel throughthe thoracic splanchnic nerves and synapse at the celiac and superior mesenteric ganglia
Preganglionic fibers originate fromT10-L2
Most travel via the lumbar and sacral splanchnic nerves tothe inferior mesenteric and hypogastric ganglia
Postganglionic fibers servethe distal half of the large intestine, the urinary bladder, and the reproductive organs
Fibers of the thoracic splanchnic nerve pass directly tothe adrenal medulla
Upon stimulation, medullary cells secretenorepinephrine and epinephrine into the blood

Visceral reflexes

Question Answer
Visceral reflexes have the same elements as somatic reflexes
They are alwayspolysynaptic pathways
Afferent fibers are found inspinal and autonomic nerves
Pain stimuli arising from the viscera are perceived assomatic in origin
This may be due to the fact that visceral pain afferents travel along the same pathways assomatic pain fibers


Question Answer
(ACh) and(NE) areThe two major neurotransmitters of the ANS
ACh is released byAll preganglionic axons and all parasympathetic postganglionic axons
Cholinergic fibersACh-releasing fibers
Adrenergic fibersSympathetic postganglionic axons that release NE
The two types of receptors that bind ACh areNicotinic and muscarinic
The effect of ACh binding to nicotinic receptors isalways stimulatory
Nicotinic receptors are found onMotor end plates, All ganglionic neurons, adrenal medulla
Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers
Alpha receptors isgenerally stimulatory
Beta receptors isgenerally inhibitory

Sympathetic tone

Question Answer
Constricts blood vessels and causesblood pressure to rise as needed
Prompts vessels to dilateif blood pressure is to be decreased
Alpha-blocker drugsinterfere with vasomotor fibers and are used to treat hypertension

Parasympathetic tone

Action: Slows the heart, Dictates normal activity levels of the digestive and urinary systems
Question Answer
The sympathetic division can override these effectsduring times of stress
Drugs that block parasympathetic responsesincrease heart rate and block fecal and urinary retention
Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris
Sympathetic fibers causeejaculation of semen in males and reflex peristalsis in females

Unique roles of the sympathetic division

Question Answer
The sympathetic division controlsThermoregulatory responses to heat ,Release of renin from the kidneys, Metabolic effects
Systemic body temperature elevation results inwidespread dilation of blood vessels
When temperature falls, blood vesselsconstrict and blood is retained in deeper vital organs
Renin isan enzyme that promotes increased blood pressure

Metabolic effects

Question Answer
The sympathetic divisionpromotes metabolic effects
Increasesthe metabolic rate of body cells
Raisesblood glucose levels
Mobilizes fat asa food source
Stimulates the reticular activating system (RAS) of the brainincreasing mental alertness
The parasympathetic division exertsshort-lived, highly localized control
The sympathetic division exertslong-lasting, diffuse effects
Sympathetic activation is long-lasting becauseNE is released into the blood and remain there until destroyed by the liver

ANS influence

Question Answer
The main integration center of ANS activityThe hypothalamus is
Influences hypothalamic functionSubconscious cerebral input via limbic lobe connections
Other controls come fromthe cerebral cortex, the reticular formation, and the spinal cord
hypothalamus controlHeart activity and blood pressure, Body temperature, water balance, and endocrine activity, Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex), Reactions to fear and the “fight-or-flight” system