PPT Notes Chapter 14

Question 1

Autonomic Nervous System (ANS)

Answer 1

The ANS consists of motor neurons that:
Innervate smooth and cardiac muscle and glands
Make adjustments to ensure optimal support for body activities
Operate via subconscious control
Other names
Involuntary nervous system [due to its subconscious control]
General visceral motor system [indicating the location of most of its effectors]

Question 2

Somatic and Autonomic Nervous Systems

Answer 2

The two systems differ in:
Effectors
Efferent pathways (and their neurotransmitters)
Target organ responses to neurotransmitters

Question 3

Innervation of Effectors

Answer 3

Somatic nervous system
Skeletal muscles
ANS
Cardiac muscle
Smooth muscle
Glands

Question 4

Efferent Pathways

Answer 4

Somatic nervous system; one motor neuron
The cell bodies of the neurons are in the spinal cord and their axons extend to the skeletal muscle they innervate.
ANS pathway is a two-neuron chain
Pre-  (before)
Post- (after)
Let’s take a look:

Question 5

Neurotransmitter Effects

Answer 5

Somatic nervous system
All somatic motor neurons release acetylcholine (ACh)
Effects are always stimulatory
ANS
Preganglionic fibers release ACh
Postganglionic fibers release norepinephrine or ACh at effectors
Effect is either stimulatory or inhibitory, depending on type of receptors

Question 6

Two Divisions of the ANS

Answer 6

Sympathetic division
Parasympathetic division
Dual innervation
Almost all visceral organs are served by both divisions, but they cause opposite effects

Question 7

Functional Role of the Parasympathetic Division: “rest and digest”
Promotes maintenance activities and conserves body energy
Its activity is illustrated in a person who relaxes, reading, after a meal
Blood pressure, heart rate, and respiratory rates are low
Gastrointestinal tract activity is high
Pupils are constricted and lenses are accommodated for close vision

Answer 7

Promotes maintenance activities and conserves body energy
Its activity is illustrated in a person who relaxes, reading, after a meal
Blood pressure, heart rate, and respiratory rates are low
Gastrointestinal tract activity is high
Pupils are constricted and lenses are accommodated for close vision

Question 8

Functional Role of the Sympathetic Division:“fight or flight”

Answer 8

Mobilizes the body during activity; is the “fight-or-flight” system
Promotes adjustments during exercise, or when threatened
Blood flow is shunted to skeletal muscles and heart
Bronchioles dilate
Liver releases glucose

Question 9

Sympathetic (Thoracolumbar) Division

Answer 9

Preganglionic neurons are in spinal cord segments T1 – L2
Sympathetic neurons produce the lateral horns of the spinal cord
Preganglionic fibers pass through the white rami communicantes and enter sympathetic trunk (paravertebral, or chain) ganglia

Question 10

Sympathetic Trunks and Pathways

Answer 10

There are 23 paravertebral ganglia in the sympathetic trunk (chain)
3 cervical
11 thoracic
4 lumbar
4 sacral
1 coccygeal
Upon entering a sympathetic trunk ganglion a preganglionic fiber may do one of the following:
Synapse with a ganglionic neuron within the same ganglion
Ascend or descend the sympathetic trunk to synapse in another trunk ganglion
Pass through the trunk ganglion and emerge without synapsing

Question 11

Visceral Reflexes

Answer 11

Visceral reflex arcs have the same components as somatic reflexes
Main difference: visceral reflex arc has two neurons in the motor pathway

Question 12

Referred Pain

Answer 12

Visceral pain afferents travel along the same pathway as somatic pain fibers, contributing to the phenomenon of referred pain.
Pain stimuli arising in the viscera are perceived as somatic in origin

Question 13

Neurotransmitters

Answer 13

Cholinergic fibers release the neurotransmitter ACh
All ANS preganglionic axons
All parasympathetic postganglionic axons
Adrenergic fibers release the neurotransmitter NE
Most sympathetic postganglionic axons
Exceptions: sympathetic postganglionic fibers secrete ACh at sweat glands and some blood vessels in skeletal muscles

Question 14

Receptors for Neurotransmitters

Answer 14

Cholinergic receptors for ACh

Adrenergic receptors for NE

Question 15

Cholinergic Receptors

Answer 15

Two types of receptors bind ACh
Nicotinic 
Muscarinic
Named after drugs that bind to them and mimic ACh effects
[nicotine & muscarine]

Question 16

Nicotinic Receptors

Answer 16

Found on
Motor end plates of skeletal muscle cells (Chapter 9)
All ganglionic neurons (sympathetic and parasympathetic)
Hormone-producing cells of the adrenal medulla
Effect of ACh at nicotinic receptors is always stimulatory

Question 17

Muscarinic Receptors

Answer 17

Found on
All effector cells stimulated by postganglionic cholinergic fibers
The effect of ACh at muscarinic receptors
Can be either inhibitory or excitatory
Depends on the receptor type of the target organ

Question 18

Adrenergic Receptors

Answer 18

Two types 
Alpha () (subtypes 1, 2)
Beta () (subtypes 1, 2 , 3)
Effects of NE depend on which subclass of receptor predominates on the target organ

Question 19

Interactions of the Autonomic Divisions

Answer 19

Most visceral organs have dual innervation
Dynamic antagonism allows for precise control of visceral activity
Sympathetic division increases heart and respiratory rates, and inhibits digestion and elimination
Parasympathetic division decreases heart and respiratory rates, and allows for digestion and the discarding of wastes

Question 20

Sympathetic Tone

Answer 20

Sympathetic division controls blood pressure, even at rest
Sympathetic tone (vasomotor tone)
Keeps the blood vessels in a continual state of partial constriction
Sympathetic fibers fire more rapidly to constrict blood vessels and cause blood pressure to rise
Sympathetic fibers fire less rapidly to prompt vessels to dilate to decrease blood pressure
Alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension

Question 21

Parasympathetic Tone

Answer 21

Parasympathetic division normally dominates the heart and smooth muscle of digestive and urinary tract organs
Slows the heart
Dictates normal activity levels of the digestive and urinary tracts
The sympathetic division can override these effects during times of stress
Drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention

Question 22

Cooperative Effects

Answer 22

Best seen in control of the external genitalia
Parasympathetic fibers cause vasodilation; are responsible for erection of the penis or clitoris
Sympathetic fibers cause ejaculation of semen in males and reflex contraction of a female’s vagina

Question 23

Unique Roles of the Sympathetic Division

Answer 23

The adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels receive only sympathetic fibers
The sympathetic division controls
Thermoregulatory responses to heat
Release of renin from the kidneys [rennin is a protein involved with raising blood pressure]
Metabolic effects
Increases metabolic rates of cells
Raises blood glucose levels
Mobilizes fats for use as fuels

Question 24

Localized Versus Diffuse Effects

Answer 24

Parasympathetic division: short-lived, highly localized control over effectors
Sympathetic division: long-lasting, bodywide effects

Question 25

Effects of Sympathetic Activation

Answer 25

Sympathetic activation is long lasting because NE
Is inactivated more slowly than ACh
NE and epinephrine are released into the blood and remain there until destroyed by the liver

Question 26

Control of ANS Functioning

Answer 26

Hypothalamus—main integrative center of ANS activity
The brainstem appears to exert the most direct influence over autonomic functions.
Other controls come from the cerebral cortex, the reticular formation of the brain stem, and the spinal cord

Question 27

Hypothalamic Control

Answer 27

Control may be direct or indirect (through the reticular system)
Centers of the hypothalamus control
Heart activity and blood pressure
Body temperature, water balance, and endocrine activity
Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex)
Reactions to fear and the “fight-or-flight” system