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Flashcards in L13 ANS Deck (26):

What are the 4 nervous systems?

CNS: brain and spinal cord

PNS: afferent division (sensory and visceral stimuli) and efferent division (somatic and autonomic branches)

Somatic: motor neurons innervate skeletal muscle

Autonomic: (sympathetic, parasympathetic and enteric)


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What are some features of ANS?

The autonomic division (of efferent PNS) is independent of conscious thought or control.

It is widely distributed, innervating heart, blood vessels, glands, smooth muscles, and visceral organs

It controls or influences cardiac output, blood pressure, blood flow, contraction and relaxation of smooth muscle, digestion, exocrine and some endocrine secretions, and some aspects of intermediary metabolism.

Autonomic pathways originate in the brain or spinal cord, and consist of a preganglionic and a postganglionic nerves connected in series by a ganglion.


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Somatic vs Autonomic Structure

Somatic division:

  • Cell bodies of motor neurons reside in CNS (brain or spinal cord)
  • Their axons (myelinated in spinal nerves) extend all the way to their skeletal muscles

Autonomic system: chains of two motor neurons

  • 1st = preganglionic neuron (in brain or cord)
  • 2nd = postgangionic neuron (cell body in ganglion outside CNS)
  • Slower because lightly myelinated or unmyelinated

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What determines the division?

What do autonomic ganglia contain?

What do pre-ganglionic fibers release? What receptor?

What do post-ganglionic fibers release? What recptor?

This division is based on anatomy. Parasympathetic nerves leave the spinal cord at the cranial and sacral levels. Sympathetic pathways leave the spinal cord in thoracic and lumbar levels.

The fibers leaving the brain stem or the spinal cord terminate in autonomic ganglia, which contain the nerve endings of pre-ganglionic fibers and the cell bodies of post-ganglionic fibers.

All pre-ganglionic fibers release acetylcholine onto nicotinic receptors in the ganglia.

Post-ganglionic fibers of the parasympathethic division release acetylcholine onto muscarinic receptors in the target organs.

Post-ganglionic fibers of the sympathethic division release norephinephrine onto adrenergic receptors in the target organs; although those innervating sweat glands release acetylcholine, and those innervating renal vasculature release dopamine.

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The adrenal medulla is a modified part of which nervous system?

How is unique from the system it's derived from?

What does stimulation of preganglionic fiber prompt?


Adrenal medulla is a modified part of sympathetic nervous system

Modified sympathetic ganglion that does not give rise to postganglionic fibers

Stimulation of preganglionic fiber prompts secretion of hormones into blood (80% epinephrine, 20% norepinephrine)

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What is stimulated by PNS and SNS?

Salivary glands and gallbladder (bile excretion)

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Summary of fiber type receptors and signaling molecules for the following effector organs:

Skeletal muscle (somatic)

Preganglionic (SNS and PNS)

Smooth muscle (SNS)

Sweat glands (SNS)

Smooth muscle (PNS)

Skeletal muscle: motor neuron releases ACh for nicotinic receptors

All pre-ganglionic fibers release acetylcholine onto nicotinic receptors in the ganglia.

Post-ganglionic fibers of the parasympathethic division release acetylcholine onto muscarinic receptors in the target organs (smooth muscle).

Post-ganglionic fibers of the sympathethic division release norephinephrine onto adrenergic receptors in the target organs(smooth muscle); although those innervating sweat glands release acetylcholine, and those innervating renal vasculature release dopamine.

Preganglionic fibers are myelinated, Postganglionic aren't

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What is the location of cell bodies, myelination, primary neurotransmitter and primary postsynaptic receptor
 for pre/postganglionic SNS and pre/postganglionic PNS?

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How is Acetylcholine synthesized?

How is it degraded in the synaptic cleft?

Is there much Acetylcholine circulation in blood?

What diseases can acetylcholinase inhibitors treat?

Synthesized from AcCoA and choline by choline acetyl transferase (Chat)

Broken down in the synaptic cleft by the enzyme acetylcholinesterase

There is very little circulating ACh in the blood

Clinically, acetylcholinesterase inhibitors are used to treat glaucoma, to increase GI motility, to treat myasthenia gravis.


How is norepeinephrine synthesized?

What receptors does NE act on?

How is NE reabsormed and what inhibits uptake?

What happens after reuptake?

Is NE detectable in circulation?


NE is a catelcholamine (need to know for biochem). Synthesis: Tyrpsine to DOPA to Dopamine to NE

NE acts on adrenergic receptors (alpha and beta subtypes)

NE is reuptaked by an active pump NET which is inhibited by cocaine and tricyclic antidepressents

After reuptake NE is metabolyzed by MAO and COMT

NE is detectable in plasma.

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Whatre the different types of cholinergic receptors (acetylcholine)

Muscarinic and Nicotinic, each with multiple subtypes.

(she says on the slide we don't need to memorize the subtype of these. She says the same thing for the adrenergic receptors and dopaminergic receptors)


What is Tonic Activity and Reflex Activity (concerning the ANS)?

Tonic Activity:
active under "resting conditions"
ability to increase/decrease activity (fine control)
SNS and PNS are tonically active to most organs
ratio of PNS/SNS determines net effect
ex. GI tract during exorcise vs feeding

Reflex Activity:
Response to a change in environment
modulated by inputs to CNS or higher brain centers


What is a visceral reflex arch?

Reflex arches are a fast way for neurons to to produce a change based on a stimulus, because the synapse occurs in the spinal cord and not the brain, the signal doesnt have to travel all the way up to the brain and be sent back down.

The visceral reflex arch is composed of a visceral (sensory) fiber that sends a signal to the spinal cord where it synapses with an autonomic neuron which sends a signal to a visceral organ. Basically a visceral stimulus and response by the ANS to stimulate a change in a visceral organ or tissue.

A somatic reflex arc  is similar with a sensory receptor sending a signal to the spinal cord, the difference is the sensory neuron synapses with a motor neuron that sends its signal to skeletal muscle.
ex: placing your hand on a hot stove, your hand jerks away before you feel the pain.

note: the somatic arch stuff wasn't on her slide but I came across it online while trying to figure out exactly what was going on with the visceral arch which I couldn't find in the book.

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Describe reciprocal vs cooperative effects of the ANS

Reciprocal: one system (SNS or PNS) inhibits while the other stimulates the target organ. Allows fine control over organ function.
ex: control of HR and intestinal motility

Cooperative Effects: Both systems promote the same goal.
ex: salivary glands and male sexual response


What is the general rule of dual reciprocal innervation and what are some exceptions?

Organ function usually depends on the ratio of SNS and PNS stimulation (dual reciprocal innercation)

Exceptions: Arteriols, veins and sweat glands only receive sympathetic stimulation. Salivary glands receive innervation from both but it's cooperative not reciprocal.


Compare SNS (fight/flight; "stress") effects to PNS (rest/digest) effects.


  • inhibits digestion
  • increases HR (tachycardia)
  • dilates pupils (mydriasis)
  • stimulates hepatic glyconeogenesis, inhibits insulin release


  • Enhance digestion
  • slows HR (bradycardia)
  • constricts pupil (miosis)
  • release insulin from pancreas to store energy

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Innervation of heart, blood vessels and lungs

(PNS on left, SNS on right)

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Innervationof glands and eyes:

(PNS on left, SNS on right)

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Innervation of GI track:

(PNS on left, SNS on right)

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Innervation of Genitourinary Track:

(PNS on left, SNS on right)

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Autonomic Control of bladder function:

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Regions of CNS involved in controlling ANS activity

Can be influenced by prefrontal association complex through its involvement with emotional expression characteristic of individual’s personality

Hypothalamus plays important role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states

Medulla within brain stem is region directly responsible for autonomic output

Some autonomic reflexes, such as urination, defecation, and erection, are integrated at spinal cord


Three areas of central control of ANS:

Amygdala: main limbic region for emotions
Stimulates sympathetic activity, especially previously learned fear-related behavior.
Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala.
Some people can regulate some autonomic activities by gaining extraordinary control over their emotions.

Hypothalamus: main integration center

Reticular formation: most direct influence over autonomic function

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ANS centers in hypothalamus and brainstem:

(visceral reflex control)

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What are agonists and antagonists?

Agonists bind to same receptor as transmitter and mimic the effects of that neurotransmitter.

Antagonists bind with receptor and block neurotransmitter signaling.


Chart of Agonists and Antagonists.
(she said we don't need to memorize all drugs, so I don't know if we need to know any of this or not.)

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