L5: ANS

Question 1

The ANS controls important visceral functions

Answer 1

“automatic functions”
– Heart rate
– Blood pressure
– Digestion
– Glandular secretion
– Sweating
– Pupillary aperture

Question 2

General Organization
of the Nervous System: Anatomy

Answer 2

Nervous System

1. Central NS: brain and spinal cord
2. Peripheral NS: cranial and spinal nerves
   - Autonomic NS: not under direct conscious control, innervates internal organs/glands/smooth and cardiac muscles
   - Somatic NS: motor portion concerned with conscious functions, innervates SKM

Question 3

Sensory (afferent) neurons

Answer 3

ARRIVING
-Transmit information about external and internal environments from periphery to CNS

Question 4

Motor (efferent) neurons

Answer 4

EXITING
-Transmit “instructions” from CNS to periphery

Question 5

ANS and SNS neurons

Answer 5

ANS: visceral sensory and motor neurons

SNS: somatic sensory and motor neurons

Question 6

Structure of Motor Neurons

Answer 6

• Dendrites receive input from adjacent neurons -> soma
• Information transmitted from soma along axon in form of an action potential
• Nerve terminal synthesizes a neurotransmitter (NT) and stores it in vesicles
• When action potential arrives at nerve terminal, NT is released by exocytosis

Question 7

Neurotransmission in the ANS

Answer 7

ANS motor neurons: mostly 2 neuron system (from CNS to Effector cell)

Question 8

Neurotransmission in the SNS

Answer 8

SNS motor neurons: one neuron system

Question 9

Functions of the ANS

Answer 9

• Controls:
  – Cardiac muscle
  – Smooth muscle
  – Secretory glands

*Sympathetic: Fight or Flight
*Parasympathetic: Rest and Digest

Question 10

Fight or Flight

Answer 10

• pupil dilation
• bronchodilation
• sweating
• inc. heart rate / contractile force
• blood glucose
• dec. GI motility, inc. SM sphincter tone
• dec. bladder SM tone, inc. SM sphincter
• vasoconstriction in viscera
• vasodilation in skeletal muscle

Question 11

Rest and Digest

Answer 11

• pupil constriction
• bronchoconstriction
• dec. heart rate
• inc. GI motility, dec. SM sphincter tone
• inc. bladder SM tone, dec. SM sphincter tone
• inc. glandular secretions

Question 12

Only the sympathetic division innervates and controls:

Answer 12

• Most blood vessels
• Sweat glands
• Adrenal medulla
• Ventricles (very little parasympathetic input)

Question 13

Sympathetic division - Thoracolumbar division

Answer 13

Preganglionic neurons
Somas
-Thoracic and lumbar spinal cord
Fibers
* Spinal nerves T1-L2/L3
* Branch extensively (widespread responses)

Postganglionic neurons
Somas
-In peripheral ganglia near spinal cord
* Paravertebral ganglia
* Prevertebral ganglia
Fibers
* Usually longer than preganglionic fibers

Question 14

Parasympathetic division - Craniosacral division

Answer 14

Preganglionic neurons
Somas
-In brain stem and sacral spinal cord
Fibers
* In cranial nerves III, VII, IX, X and spinal nerves S2-S4
* Limited branching (= localized responses)

Postganglionic neurons
Somas
-In peripheral ganglia near innervated structures
* Terminal ganglia
* Intramural ganglia
Fibers
* Usually shorter than preganglionic fibers

Question 15

Autonomic NTs

Answer 15

Acetylcholine (ACh)
-all synapses in peripheral ganglia
-all NEJs in parasympathetic division
-some NEJs in sympathetic division (most sweat glands)
-all NMJs in SNS

Norepinephrine (NE) (aka Noradrenaline)
-most NEJs in sympathetic division
-exceptions: sympathetic NEJs with cholinergic transmission
-Most sweat glands <- sympathetic cholinergic

Question 16

Neurochemistry of the Adrenal Medulla

Answer 16

ANS motor neurons: mostly 2 neuron system
-Exception: Adrenal medulla
(= Specialized peripheral ganglion)
-Cells are homologous to autonomic postganglionic neurons (without postganglionic fibers!)

-Adrenal medulla secretes EPI and small amounts of NE
-EPI and NE are secreted into the blood, to function as neurohormones
-Responses to sympathetic stimulation include effects of EPI and NE from the adrenal medulla

Question 17

Neurotransmission Steps

Answer 17

1. Synthesis and storage of NT
2. Release of NT by exocytosis
3. Diffusion of NT to postsynaptic cell
4. Binding of NT to receptors on postsynaptic cell, initiating a response
5. Termination of action of NT

Important mechanisms:
* Enzymatic inactivation of NT
* Reuptake of NT by presynaptic fiber

Question 18

ACh: Enzymatic Inactivation

Answer 18

Rapid hydrolysis by acetylcholine esterase (AChE

Question 19

NE Reuptake

Answer 19

-Transport back into nerve terminal by NET (Na+- dependent amine transport system)
-Re uptake allows “recycling” of NE

Question 20

Enzymatic Inactivation of ACh is _____ than Reuptake of NE

Answer 20

FASTER

Sympathetic
* Produces sustained responses

Parasympathetic
* Produces responses of short duration

Question 21

Cholinergic Receptors

Answer 21

nAChRs
(nicotinic acetylcholine receptors)
- ligand gated ion channels

mAChRs
(muscarinic acetylcholine receptors)
- GPCRs

Question 22

Soma in ____
Ganglia in ____

Answer 22

Soma in CNS
Ganglia in PNS

Soma - preganglionic neuron - synapse - postganglionic axon

Question 23

First neurotransmitter is always

Answer 23

ACh

-Parasympathetic and Somatic will release ACh as well

-Sympathetic will release NE
-EXCEPT in sweat glands (release ACh)

Question 24

nAChRs

Answer 24

1. Binding of ACh to nAChR
2. Opening of ion channel
3. Na+ influx
4. Depolarization of postsynaptic membrane
   EPSP

Everything Nn except SKM (Nm)

Question 25

mAChRs

Answer 25

M2: Gi -Effector cells at parasympathetic NEJs -Inhibition of heart M3: Gq -Effector cells at parasympathetic NEJs: smooth muscle contraction + glandular secretion -At sympathetic cholinergic NEJs: sweating

Question 26

Alpha 1

Answer 26

Gq smooth muscle contraction

Question 27

Alpha 2

Answer 27

Gi presynaptic receptor, modulatory functions

Question 28

Beta 1

Answer 28

Gs stimulation of heart, increase renin secretion

Question 29

Beta 2

Answer 29

Gs smooth muscle relaxation, metabolic effects (epi from medulla)

Question 30

ACh is the neurotransmitter in peripheral ganglia in

Answer 30

BOTH the sympathetic division and the parasympathetic division

Question 31

NE is the neurotransmitter at most _____

Answer 31

-sympathetic NEJs the adrenergic term, which does NOT apply to the peripheral ganglia of the sympathetic division

Question 32

Extensive branching of preganglionic fibers is a characteristic of the

Answer 32

sympathetic division (not the parasympathetic division)

Question 33

The peripheral ganglia are close to (or in the walls of) the effector organs in...

Answer 33

in the parasympathetic division -so preganglionic fibers are long while the postganglionic fibers are short

Question 34

the peripheral ganglia are relatively close to the spinal cord (paravertebral ganglia, prevertebral ganglia), in the...

Answer 34

in the sympathetic division -so the preganglionic fibers are short while the postganglionic fibers are long

Question 35

in the ____, the termination of ACh’s effects at NEJs is accomplished by enzymatic hydrolysis of ACh by AChE, which is extremely ___

Answer 35

in the parasympathetic division fast

Question 36

the termination of NE’s effects at _____ NEJs is accomplished primarily by reuptake of NE by NET, which is relatively ____

Answer 36

sympathetic division slow

Question 37

the _____ has exclusive control of a greater number of effector organs. Most importantly, most _____ are controlled exclusively by the ____

Answer 37

the sympathetic division -most blood vessels and all sweat glands are controlled exclusively by the sympathetic division -adrenal medulla also

Question 38

the dominant tone at rest to most effector organs is

Answer 38

parasympathetic -most important exceptions are the blood vessels and sweat glands (sympathetic)