Chapter 16: Autonomic Nervous System

Question 1

What are the two divisions of the autonomic system?

Answer 1

1. sympathetic nervous system (SNS)
2. parasympathetic nervous system (PSNS)

the two divisions often oppose one another to maintain our bodily functions

these systems rarely work at extremes; most often there is a subtle balancing act between sympathetic and parasympathetic tone

Question 2

What is the purpose of the sympathetic nervous system? (what does it allow us to do)

Answer 2

SNS is capable of mobilizing us during extreme conditions (e.g. fear, exercise, anger) and is often referred to as the fight or flight system. It increases our heart rate and respiratory rate, increases catabolism, increased sweating , and dilates our pupils

Question 3

What is the purpose of the parasympathetic nervous system? (what does it allow us to do)

Answer 3

PSNS is capable of slowing us down and conserving energy, and is often called the rest and digest system. It increases digestion, defecation, urination, while decreasing heart rate, breathing rate, and constricts our pupils

Question 4

What is the function of the autonomic nervous system?

Answer 4

Routine homeostatic adjustment of physiological systems through ANS reflexes, regulated by centers in the hypothalamus and brain stem
- occurs independently of the somatic nervous system

Question 5

What is the organization of the autonomic nervous system?

Answer 5

Stimulated by:
1. Sensory receptors called interceptors located in blood vessels, visceral organs, muscles, and nervous system monitor conditions in the internal environment
- examples of interceptors are chemoreceptors that monitor blood pH and CO2 levels and mechanoreceptors that detect the degree of stretch in walls of organs or blood vessels (baroreceptors)

2. Motor neurons that originate in the CNS synapse with visceral motor neurons located in autonomic ganglia outside CNS and provide biofeedback response

ganglionic motor neurons directly control visceral effectors

because autonomic responses cannot be consciously altered to any great degree, some autonomic responses are the basis for polygraph (lie detector) tests

Question 6

How does a polygraph test work?

Answer 6

It records several ANS controlled physiological signs, such as;
blood pressure, pulse, respiration rate, skin conducting (sweat) while the subject is asked and answers a series of questions

Question 7

What are the 3 neuron pathways / location of the integrative centers for autonomic activity

Answer 7

1. Visceral motor neurons in hypothalamus synapse with
2. Preganglionic neurons
   - locations of cell bodies: in CNS (in autonomic nuclei or spinal cord)

preganglionic neurons synapse with Ganglionic neurons (post-ganglionic neurons), which synapse onto visceral effectors

Question 8

What is dual ANS innervation?

Answer 8

Receives impulses from both sympathetic and parasympathetic neurons, however in some cases tissues are innervated by only one ANS pathway which is either on (low, med, high) or off
- usually nerve impulses from one division stimulate an organ, and impulses from the other division decrease activity

Question 9

What are the general function and responses generated by the sympathetic nervous system?

Answer 9

called the thoracolumbar division
General function: increases metabolic rate (production of ATP)

increases:
1. metabolic rate (by as much as 2x) and activates energy reserves
2. alertness (ras activity)
3. breathing (rate and depth)
4. heart rate
5. blood pressure
6. body temperature
7. perspiration and goosebumps

decreases:
1. digestion
2. urinary function

Question 10

Location of preganglionic cell bodies of sympathetic system?

Answer 10

Between T1 and L2 of spinal cord in lateral gray horns

the sympathetic division is called thoracolumbar division even though sympathetic ganglia extend in the vicinity of the cord from cervical to sacral region..

Question 11

What are the (3) locations of ganglionic cell bodies?

Answer 11

1. Sympathetic chain ganglia
   - chain of ganglia running along each side of a vertebral column
   - innervate visceral effectors located on each side of the body in body walls, thoracic cavity, head, neck, and limbs
   - only T1-L2 spinal nerves have white rami communicants
2. Collateral ganglia
   - outside sympathetic chain (usually not paired)
   - splanchnic nerves innervates 3 collateral ganglia (celiac, superior, and inferior mesenteric)

innervate: a variety of abdominopelvic tissues and organs

3. Adrenal medulla = suprarenal medullae
   - core of adrenal gland = modified sympathetic ganglion
   - nature of ganglionic fibers: short axons, release neurotransmitters into a capillary that act as hormones to affect target cells throughout the body

Question 12

Name the sympathetic chain ganglia:

Answer 12

Cervical (3) pairs
Thoracic (11-12) pairs
Lumbar (4-5) pairs
Sacral (4-5) pairs

Question 13

What are the 3 types of preganglionic fiber pathways?

Answer 13

a) synapse within the sympathetic chain ganglia with a ganglionic neuron at same level

b) travel up or down the chain to synapse within the sympathetic chain ganglion with a more superior or inferior ganglionic neuron

c) travel right through the sympathetic chain ganglia to synapse with ganglionic neuron in collateral ganglia or adrenal medulla

Question 14

What neurotransmitters are released by sympathetic postganglionic fibers?

Answer 14

Neurotransmitters released by sympathetic postganglionic fibers: NE and E (norepinephrine and epinephrine)
- these cells are said to be adrenergic visceral motor neurons

the main neurotransmitter released by postganglionic fibers: norepinephrine

Question 15

What neurotransmitters are released by the adrenal medulla?

Answer 15

Chemical messengers released by cells of the adrenal medulla once stimulated by sympathetic preganglionic neurons (by ACh)
80% E
20% NE
released by adrenal medulla into the blood stream

Question 16

What are adrenal medulla cells said to be?

Answer 16

Neuroendocrine cells because they can release neurotransmitters that act as hormones

these hormones help to prolong the SNS effects

Question 17

Why are SNS effects last longer and more wide spread than PSNS?

Answer 17

1) release of catecholamines (mostly epinephrine) from the adrenal medulla thus enhancing the sympathetic effects via the endocrine system

2) norepinephrine is broken down more slowly than acetylcholine

3) there are more SNS axon collateral that synapse with more SNS postganglionic neurons than in the PSNS division

4) more visceral effectors have receptors for catecholamines than for acetylcholine

Question 18

What is the effect of norepinephrine and epinephrine binding to receptors on target cell?

Answer 18

Stimulate 2nd messengers within the cell

Question 19

Cells can only respond to a chemical messenger if they have _____?

Answer 19

Have receptors for that messenger in the cell membrane or inside the cell

Question 20

• What are ganglionic fibers?

Answer 20

Ganglionic fiber (axon) branches into telodendria which have variosites (swollen enlargements) filled with vesicles of NE (or sometimes ACh or NO)

• monoamine oxidase (MAO) recycles used reabsorbed neurotransmitter
• rest of neurotransmitter is broken down by COMT (catechol-o-methyltransferase)

Question 21

What are the general function and responses generated by the parasympathetic nervous system?

Answer 21

called the craniosacral division
General effects: rest and digest

increases:
- motility and blood flow to the digestive tract
- urinary function
- salivary and digestive glands

decreases:
- metabolic rate
- heart rate
- blood pressure

Question 22

Location of preganglionic and ganglionic cell bodies (PSNS)?

Answer 22

location of preganglionic cell bodies: brain stem and sacral segments of the spinal cord
- in nuclei of cranial nerves 3, 7, 9, 10 in brain stem
- lateral gray matter of 2nd-4th sacral segments of the spinal cord

location of ganglionic cell bodies:
- terminal ganglia: located near target organ
- intramural ganglia: embedded in the tissues of the target organ

Question 23

What are the 2 neuron pathways of the ANS?

Answer 23

ANS consists of 2 neuron pathway connected by ganglion (unlike single-neuron pathway of the somatic system)
- the neurons are named preganglionic and postganglionic
- all preganglionic neurons arise from the CNS and use acetylcholine as a neurotransmitter, however postganglionic cells of the sympathetic division use norepinephrine and postganglionic cells of the parasympathetic division use acetylcholine

Question 24

What are the effects of sympathetic stimulation?

Answer 24

Results primarily from the interaction of NE and E with adrenergic receptors (and associated G proteins) in the target cell’s plasma membrane

the stimulation of alpha receptors by norepinephrine, which activates enzymes on the inside of the target cell’s plasma membrane

the stimulation of beta receptors by epinephrine, which triggers changes in the metabolic activity of the target cell

*** pg 32

Question 25

pg 33

Question 26

34

Question 27

What organs do not receive dual innervation (exceptions)

Answer 27

Most vital organs and tissues receive innervations from both SNS and PSNS exceptions: - lacrimal glands (PSNS only) - sweat glands - arrector pili muscles - blood vessels (normally 1/2 diameter, can vasodilate and vasoconstrict) - adrenal gland - respiratory mucus glands - skeletal muscle - adipose tissue

Question 28

What is autonomic tone?

Answer 28

In absence of stimuli, autonomic motor neurons show a background level of activity from both SNS and PSNS - various stimuli can increase or decrease activity