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FHB I - Cardiac Unit > Autonomic NS > Flashcards

Flashcards in Autonomic NS Deck (24):

Describe the ANS.

CNS- brain (CN and retina, and spinal cord)

PNS- peripheral ganglia, sensory receptors, peripheral portions of spinal and cranial nerves)

Autonomic- selected portions of CNS and PNS


Describe visceral sensory/motor.

sensory (afferent) originate from sensors in organs (DRG)

motor (efferent) modulate organ activity..ventral


Describe two main ANS functions.

maintain homeostasis or steady state internal environment (viscera are its effectors, innervates smooth and cardiac muscle and glands, makes adjustments to ensure optimal support for body activities, involuntary)

to respond to external stimuli "fight or flight" response

(receptors on CNS... to ANS...)


What are ANS subdivisions?

sympathetic, parasympathetic and enteric (GI)


Describe major NTs

Ach, NE
ATP, NO, 5HT, GABA, dopamine, glutamate
Epi. functions as a hormone in ANS


Describe ANS synapses vs CNS synapses.

ANS synpases ('en passant') are not as well defined as CNS synapses; contain varicosities

their synaptic cleft distance is variable (20-40 nm to mm); the post-synaptic receptors located at target organs are all metabotropic, slow acting, producing neuromodulatory effects


Describe adrenergic neurotransmission.

NE is synthesized in vesicles from dopa. NE release occurs near target cells but it is not closely coupled. After release and interaction with alpha or beta adrenergic receptors, NE is taken back into cytosol and degraded by specific enzymes (MAO, COMT)
degrading enzymes also exist in mitochondria and in the circulation.
(Graph slide 10)


Describe cholinergic neurotransmission.

Ach is synthesized in the cytosol from choline and transported to vesicles. After release and interaction with its receptors, Ach is inactivated by hydrolysis via acetyl cholinesterase (AchE). Choline is re-uptaken inot presynaptic terminal for reuse
(graph slide 11)


How does sarin gas/nerve agents work?

nerve agents (sarin gas) inhibit AChE and prevent Ach degradation, causing death in minutes by over-stimulation (convulsions, paralysis, and ultimate respiratory failure). Current treatment involves a drug cocktail with Diazepam (benzodiazepine) a sedative to prevent seizures, atropine to block muscarinic AChRs and ...


Describe the four types of adrenergic receptors.

alpha 1- vascular smooth muscle, skin, renal, splanchnic, GI tract, sphincters; radial muscle, iris- increases IP3, increases intracellular Ca

alpha 2- GI tract, wall, presynpatic adrenergic neurons, act to inhibit adenylate cyclase, reduce cAMP

Beta 1- heart, salivary glands, adipose tissue, kidney, acts to stimulate adenylate cyclase and increase cAMP

Beta 2- vascular smooth muscle of SkM, GI tract, wall; bladder, wall; bronchioles, acts to stimulate adenylate cyclase, increase cAMP


Describe the 2 types of cholinergic receptors.

nicotinic- skeletal muscle, motor end plate, all postganglionic neurons; adrenal medulla, increase EPSP, Na and K current, depolarization

muscarinic- all effector organs (parasymp); sweat glands (symp) increase IP3 and increase intracellular Ca


Describe the differences between ANS and CNS synapses (neuron-neuron, neuron-viscera, neuron-SkM):

synapse, synaptic cleft distance, post synaptic receptor type, NT effect, postsynaptic potential

synapse- well defined
synapse cleft distance- 20 to 40 nm
post synaptic receptor type- ionotropic, fast, e.g. nAChR
NT effect- direct
postsynaptic potential- EPSP/IPSP

synapse- 'en passant'; varicosities
synaptic cleft distance- variable viscera 20-40 nm, large blood vessels 1-2 mm
post synaptic receptor type- metabotropic, slower, mAChR, alpha, beta, ARs
NT effect: variable, may induce neuromodulator activity
postsynaptic potential- junction potential, EJP, IJP

synapse- NMJ
synaptic cleft distance- 20 to 40 nm
post-synaptic receptor type- ionotropic, fast, nAChR
NT effect-direct
postsynaptic potential- EPP


Describe the organization of the ANS (two neuron system).

preganglionic is located within CNS in spinal cord and synapses with a postganglionic neuron located in an autonomic ganglion. postganglionic neuron synapses with the target organ.

many sites innervated by the ANS have a "basal tone" or resting level of activity that permits both increases and decreases from that level


What do preganglionic neurons secret and what do they act on?

all preganglionic neurons secrete Ach which acts on post-ganglionic nicotinic receptors (ionotropic, fast acting)


All preganglionic neurons secrete ACh, which acts on post-ganglionic nicotinic receptors (ionotropic, fast-acting). What are two major exceptions?

adrenal gland- synapse in gland, no post ganglionic neuron
direct cholinergic activation causes body-wide release of Epi and NE secretion directly into blood stream

An exception to the sympathetic activation of post-ganglionic adrenergic receptors are the sweat glands, which are innervated by the sympathetic branch, but are activated via acetylcholine (ACh) binding to muscarinic metabotropic receptors.


Describe the role of the adrenal medulla.

preganglionic axons pass through the splanchnic nerve and directly synapse with the medulla. So there is no post-ganglionic neuron: chromaffin cells in the adrenal medulla secrete epi and NE directly into the blood stream as a response from the direct activation of cholinergic pre-ganglionic fibers; the adrenal medulla is responsible for the secretion of 80 percent of E and 20 percent of NE into the circulation


What kind of receptors do NE and E have?

metabotropic receptors that are coupled to a G protein cascade


Describe the following characteristics for sympathetics...
Location of preganglionic somas-
Location of postganglionic somas-
Length of preganglionic fiber-
Length of postganglionic fiber-
Preganglionic fiber NT-
Postganglionic receptor Agonist-
Postganglionic fiber NT-
Receptor at the target organ, receptor type, Agonist-

Function- homeostatis, fight or flight
Location of preganglionic somas- SC: T1-T12 (C8) and upper lumbar L1-L3

Location of postganglionic somas- paravertebral ganglia (2 sets lateral to SC) and prevertebral ganglia in abdominal cavity)

Length of preganglionic fiber- short

Length of postganglionic fiber- long

Preganglionic fiber NT- Ach

Postganglionic receptor Agonist- nicotinic (fast, ionotropic) nicotine

Postganglionic fiber NT- NE, E (80 percent of E comes from adrenal medulla) (an exception is sweat glands, Ach)

Receptor at the target organ, receptor type, Agonist- adrenergic receptor (slow, metabotropic), alpha 12, beta 123, alpha AR, phenylephrine, Beta AR, isopropternol


Describe the following characteristics for parasympathetics...
Location of preganglionic somas-
Location of postganglionic somas-
Length of preganglionic fiber-
Length of postganglionic fiber-
Preganglionic fiber NT-
Postganglionic receptor Agonist-
Postganglionic fiber NT-
Receptor at the target organ, receptor type, Agonist-

Function- homeostasis, complements sympathetic response

Location of preganglionic somas- brainstem and sacral spinal cord

Location of postganglionic somas- ganglia located near or in the walls of target organs

Length of preganglionic fiber- long (somas are in brainstem or sacral SC)

Length of postganglionic fiber- short (somas are by target organs)

Preganglionic fiber NT- Ach

Postganglionic receptor Agonist- nicotinic (fast, ionotropic) nicotine

Postganglionic fiber NT- Ach

Receptor at the target organ, receptor type, Agonist- muscarinic (slow, metabotropic): M1, M2, M3, M4, M4, muscarine


Describe how the reflex arc response occurs.

ANS efferent (motor) fibers are accompanied by sensory afferent fibers traveling from the periphery to the SC and the CNS. These fibers provide information from sensory receptors in the viscera, resulting in a reflex arc response


How are pain receptors in the viscera activated?

How do pain signals travel and what do they do?

Pain receptors in viscera are activated by excessive distension, ischemia or obstructions. Pain signals travel through sympathetic nerves (splanchnics) to SC, activating interneurons that trigger reflex arcs, and also activating projection neurons that trigger pain signals to the brain

other visceral afferents travel in parasympathetic nerves; these are usually involved in reflexes rather than pain sensation. Glossopharyngeal nerve baroreceptor afferent fibers from the carotid sinus enter the brainstem (nucleus of the solitary tract) and activate interneurons which in turn synapse onto pre-ganglionic neurons that control HR and BP


What do afferent fibers use as the preferred nt?

use glutamate

neuromodulators may be co-released


Describe the origin of referred pain. How it is perceived by CNS?

referred pain is pain originating in viscera but perceived by the CNS as originating elsewhere (are of skin for instance)...results from the convergence of somatic and visceral afferent fibers from the same SC level of the spinal cord


Describe BP control

when BP increases from basal levels, baroreceptor reflex is activated; negative feedback loop that controls arterial pressure.

(baroreceptors are mechanoreceptors located in the nerve terminals in the carotid sinus and the aortic arch; these "stretch-activated channels" are activated when arterial pressure increases, resulting in depolarization and increase in AP firing rate of the nerve.

these afferent fibers join the IX and X nerves ending at the vasomotor and cardioregulatory centers of the medulla in the brainstem. Activation of this centers during increased BP produces:
-decrease of symp. input to heart resulting in decreased HR and contraction strength (via withdrawal of B adrenergic receptor stimulation)
-increase in parasym. input to the heart, resulting in decreased HR (via muscarinic receptors)
-decrease of sym. input to vascular smooth muscle, resulting in relaxation (via withdrawal of alpha1 adrenergic receptor stimulation
-decreased symp. input to adrenal chromaffin cells, resulting in decreased epi and NE secretion into the lood stream, and less activation of peripheral alpha and beta receptors...
overall these lead to decrease in arterial pressure

(in contrast... decreases in stretch of mechanoreceptors due to low arterial pressure result in firing rates lower than normal in baroceptors terminals; eliciting the opposite neural responses which lead to increased arterial pressure