L2 ANS Neurotransmission

Question 1

Describe the structural organization of the ANS

Answer 1

Sensory/afferent originate from sensors in internal organs, smooth muscles
Motor/efferent is response due to sensory input, modulates organ activity

Question 2

Describe the functional organization of the ANS

Answer 2

Two main functions:

1. Maintain homeostasis: viscera are effectors, innervates smooth and cardiac muscle and glands, makes adjustments to ensure optimal activities, involuntary
2. Respond to external stimuli: fight or flight response

Question 3

How do the PS and S branches differ?

Answer 3

PS is craniosacral, rest and digest
S is thoracolumbar, fight or flight
PS and S are complementary, but produce opposing effects

Question 4

Main ANS neurotransmitters

Answer 4

NE and ACh

Question 5

Types of Autonomic receptors

Answer 5

Adrenergic: a1, a2, B1, B2 (metabotropic)
Cholinergic: nicotinic (ionotropic), muscarinic (metab.)

Question 6

a1 receptors

Answer 6

Target: GI sphincter, bladder sphincter, iris muscle, renal and splanchnic
Mechanism of Action: increase IP3 and intracell. Ca

Question 7

a2 receptors

Answer 7

Target: GI wall, presynaptic adrenergic neurons

Mechanism of Action: inhibit adenylate cyclase, decrease cAMP

Question 8

B1 receptors

Answer 8

Target: Heart, salivary glands, adipose, kidney

Mech. of Action: stimulate adenylate cyclase, increase cAMP

Question 9

B2 receptors

Answer 9

Target: Vascular smooth muscle of skeletal muscle, GI wall, bladder wall, bronchioles
Mech. of Action: stimulate adenylate cyclase, increase cAMP

Question 10

Nicotinic receptors

Answer 10

Target: Skeletal muscle, motor end plate, all postgang. neurons, adrenal medulla
Mech. of Action: EPSP, Na and K current, depolarization

Question 11

Muscarinic receptors

Answer 11

Target: All effector organs (PS), sweat glands (S)

Mech. of Action: increase IP3, increase intracellular Ca

Question 12

What is the same about all preganglionic neurons in ANS?

Answer 12

All secrete ACh, which acts on postganglionic nicotinic receptors

Question 13

Adrenal gland

Answer 13

EXCEPTION to the preganglionic rule- synapse occurs in the gland, there is no postgang. neuron
-Direct activation of gland causes global release of Epi and NE into blood (for fight or flight)

Question 14

How much Epi and NE is the adrenal medulla responsible for?

Answer 14

80% of Epi and 20% of NE into circulation

Question 15

Sweat glands

Answer 15

EXCEPTION to preganglionic and sympathetic rule- innervated by symp. branch, but postganglionic neurons are muscarinic receptors that are activated by ACh

Question 16

Location of preganglionic somas: S vs. PS

Answer 16

S: T1-T12, L1-L3
PS: Brainstem and sacral spinal cord

Question 17

Location of postganglionic somas: S vs. PS

Answer 17

S; Paravertebral ganglia (lateral to SC) and prevertebral ganglia (in abdomen)
PS: Ganglia located near or in target organ

Question 18

Length of preganglionic fibers: S vs. PS

Answer 18

S: Short
PS: Long

Question 19

Length of postganglionic fibers: S vs. PS

Answer 19

S: Long
PS: Short

Question 20

Preganglionic fiber NT: S vs. PS

Answer 20

ACh for both!

Question 21

Postganglionic fiber NT: S vs. PS

Answer 21

S: NE and Epi (except for sweat glands)
PS: ACh

Question 22

Receptor type at target organ: S vs. PS

Answer 22

S: Adrenergic receptor, slow metabotropic (a1, 2, B1, 2)
PS: Muscarinic receptor, slow metabotropic (M1-5)

Question 23

Feedback Loop for S and PS activation

Answer 23

Sensors in viscera go back to integrative system (adjusting point) via SC or CNS, cause adjustment of condition in response to any factor altering homeostasis

Question 24

Difference between ANS and CNS synapse

Answer 24

ANS: post-synaptic neuron is metabotropic, synapses by passing through fat varicosities
CNS: ionotropic postsynaptic neuron, creates E/IPSPs
-Neuromuscular jxns only happen in skeletal muscle

Question 25

Adrenergic Transmission

Answer 25

NE made and transported into vesicles
AP arrives and vesicles released
NE free flowing in cleft binds to a1 receptors (smooth muscle) or back to neuron via a2 receptors
Immediate destruction or reuptake of NE

Question 26

What happens to NE in adrenergic transmission when bound to a1 receptor?

Answer 26

Endocytosed by muscle and inactivated by MAO (monoamine oxidase) and COMT (catechol-O-methyl transferase)

Question 27

What happens to NE in adrenergic transmission when bound to a2 receptor?

Answer 27

Uptake by axon and destroyed by MAO in mitochondria

Question 28

Adrenergic vs. Cholinergic vesicles

Answer 28

Adrenergic= small, granular vesicles
Cholinergic= agranular

Question 29

Cholinergic Transmission

Answer 29

ACh released, short lived- binds to muscarinic receptor or destroyed by AChE
-Once destroyed, get free choline which is reuptaken by axon for reuse

Question 30

Two Neuron Pathway

Answer 30

Preganglionic neuron goes from SC to ganglia/nucleus nad synapses there (ionotropic receptor, need fast response)
Postganglionic neuron goes to target organ and synapses (receptor is metabotropic)

Question 31

Which nerves do pain and reflex signals travel with?

Answer 31

Pain and reflex fibers are sensory afferent fibers.
Pain travels with sympathetic nerves to the SC or CNS
Reflexes travel with PS nerves

Question 32

Baroreceptor Reflex Control

Answer 32

Increase in BP= stretch in baroreceptors at carotid sinus and aortic arch= mechanoreceptors open= increase in firing= signal travels to medulla via CN IX and X= increase PS to decrease HR, decrease Symp. to decrease HR & stroke volume and increase vasodilation= BP returns to normal

Question 33

Autonomic centers in brain

Answer 33

Reticular formation (brainstem)- most direct influence over ANS
Medulla- respiration, intake
Pons- micturition
Hypothalamus- master of master gland, temp regulation, food, fight, flee, reproduction
Amygdala- learned fear, fight or flight
Cortex- some modulatory control