Autonomic NS

Question 1

Describe the ANS.

Answer 1

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

Question 2

Describe visceral sensory/motor.

Answer 2

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

motor (efferent) modulate organ activity..ventral

Question 3

Describe two main ANS functions.

Answer 3

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 organ…to CNS… to ANS…)

Question 4

What are ANS subdivisions?

Answer 4

sympathetic, parasympathetic and enteric (GI)

Question 5

Describe major NTs

Answer 5

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

Question 6

Describe ANS synapses vs CNS synapses.

Answer 6

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

Question 7

Describe adrenergic neurotransmission.

Answer 7

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)

Question 8

Describe cholinergic neurotransmission.

Answer 8

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)

Question 9

How does sarin gas/nerve agents work?

Answer 9

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 …

Question 10

Describe the four types of adrenergic receptors.

Answer 10

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

Question 11

Describe the 2 types of cholinergic receptors.

Answer 11

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

Question 12

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

Answer 12

neuron-neuron
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

neuron-viscera
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

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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.

Question 16

Describe the role of the adrenal medulla.

Answer 16

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

Question 17

What kind of receptors do NE and E have?

Answer 17

metabotropic receptors that are coupled to a G protein cascade

Question 18

Describe the following characteristics for sympathetics...
Function-
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-

Answer 18

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

Question 19

Describe the following characteristics for parasympathetics...
Function-
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-

Answer 19

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

Question 20

Describe how the reflex arc response occurs.

Answer 20

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

Question 21

How are pain receptors in the viscera activated?

How do pain signals travel and what do they do?

Answer 21

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

Question 22

What do afferent fibers use as the preferred nt?

Answer 22

use glutamate

neuromodulators may be co-released

Question 23

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

Answer 23

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

Question 24

Describe BP control

Answer 24

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