Ch 14 - Autonomic Nervous System

Question 1

Divisions of the Autonomic Nervous System (ANS)

Answer 1

1) Parasympathetic Division - “Rest and Digest” - directs “housekeeping” activities
2) Sympathetic Division - “Fight or Flight” - quickly mobilizes the body for action

Question 2

3 Differences Between the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS)

Answer 2

1) Effector organs - SNS = skeletal muscle; ANS = cardiac muscle, smooth muscle, glands
2) Efferent pathways and ganglia - SNS = single neuron from CNS to effector; ANS = 2-neuron chain to effector
3) Neurotransmitter effects - SNS = all release acetylcholine (ACh); ANS = release norepinephrine or ACh (can be either excitatory or inhibitory)

Question 3

Neuron Chain to Reach Effector in ANS

Answer 3

1) Preganglionic neuron - cell body in CNS, axon synapses with second motor neuron
2) Postganglionic neuron - cell body is outside the CNS, axon extends to effector organ/
3) Ganglia - site of synapse between preganglionic neuron and postganglionic neuron

Question 4

Origin of Fibers in Parasympathetic Division and Location of Ganglia

Answer 4

Originates in the Brain and Sacral Spinal Cord - Projects to Ganglia In or Near the Effector Organ

Preganglionic fibers are long, postganglionic fibers are short

Question 5

Nerves involved in the Cranial Portion of the Parasympathetic Nervous System

Answer 5

III. Oculomotor nerve: innervates smooth muscle in eyes & muscle associated with lens (changes amount of light)
VII. Facial Nerve: stimulates large glands of head (salivary glands, nasal glands, lacrimal glands
IX. Glossopharyngeal nerve: activates parotid salivary gland (largest)
X. Vagus nerve: provides fibers to neck and every organ in thoracic & abd. cavities

Question 6

Plexuses of Vagus Nerve

Answer 6

1) Cardiac plexus: supplies fibers to the heart
2) Pulmonary plexus: supplies fibers to lung
3) Esophageal plexus: fibers extend into abdominal cavity from esophageal plexus - innervates liver, gallbladder, stomach, small intestine, pancreas, proximal half of large intestine.

Question 7

Basic Difference: Parasympathetic vs Sympathetic divisions of the ANS

Answer 7

Parasympathetic = “Rest & Digest”
Sympathetic = “Fight or Flight”

Question 8

Origin of Fibers and Location of Ganglia in Sympathetic Division

Answer 8

Originates in the thoracolumnar region of spinal cord (T1-L2)
- short preganglionic, long postganglionic fibers - ganglia are thus close to spinal cord
- Cell bodies form lateral horns of spinal cord

Question 9

Which division of the ANS is more complex - why?

Answer 9

Sympathetic division is more complex.
Not only innervates smooth muscle, cardiac muscle, and glands in body cavities
ALSO innervates smooth muscle & glands in superficial regions (sweat glands, arrector pili, smooth muscle in blood vessel walls)

Question 10

Preganglionic fibers of Sympathetic division form:

Answer 10

Sympathetic trunk - allows preganglionic axons to travel to spinal nerves that are higher/lower - located on both sides of spinal cord

Question 11

Pathway of sympathetic nerves to ganglion

Answer 11

1) Preganglionic fiber exits the spinal cord
2) Fiber passes through white ramus communicans
3) Fiber enters sympathetic trunk ganglion

Question 12

What guides the preganglionic fiber to the sympathetic trunk in the Sympathetic ANS

Answer 12

White Ramus Communicans

Question 13

Where the preganglionic fibers synapse with the postganglionic fibers in the sympathetic ANS

Answer 13

Sympathetic trunk ganglion

Question 14

3 ways preganglionic & postganglionic fibers synapse in the Sympathetic ANS

Answer 14

1) Synapse at the same level - leave ventral root to sympathetic trunk ganglion at same level in spine
2) Synapse at higher/lower level - leave ventral root and pass up or down through sympathetic trunk to a different ganglion
3) Synapse at a distant collateral ganglion in abdomen or pelvis - pregang. passes through splanchnic nerve to a distant ganglion (such as the celiac)

Question 15

Sympathetic pathway with synapses in trunk ganglia

Answer 15

1) Preganglionic neuron begins at lateral horn of dark matter in spinal cord
2) Passes out through ventral root
3) Continues through white ramus communicans to sympathetic trunk
4) Synapses with postganglionic neuron in sympathetic trunk ganglion
5) Postganglionic neuron passes out through grey ramus communicans to effectors

Question 16

Sympathetic pathway to the head from synapses in trunk ganglia

Answer 16

1) Preganglionic fibers emerge from T1-T4
2) Synapse with postganglionic fibers at superior cervical ganglion of the sympathetic trunk

Postganglionic fibers serve skin and blood vessels of the head, stimulate dilator muscles of eyes, inhibits nasal and salivary glands, innervates muscles to upper eyelid, sends branches to heart

Question 17

Sympathetic pathway to the thorax from synapses in trunk ganglia

Answer 17

1) Preganglionic fibers emerge from T1-T6
2) Most postganglionic axons pass through cardiac, pulmonary & esophageal plexuses to effector organ

Question 18

Sympathetic pathway with synapses in collateral ganglia

Answer 18

1) Pregenglionic fibers from T5-L2 synapse in collateral ganglia
2) Form splanchic nerves
Greater splanchnic nerve, lesser splanchnic nerve, least splanchnic nerve
Lumbar splanchnic nerves and sacral splanchnic nerves

Function: serves abdominal viscera

Question 19

Sympathetic pathway to the abdomen and pelvis with synapses in collateral ganglia

Answer 19

1) Fibers T5-L2 innervate abdomen Function: serve the stomach, most of the intestines, liver, spleen, and kidneys
2) Fibers T10-L2 innervate pelvis Function: serves the bladder, reproductive organs, distal half of large intestine

Question 20

5 components of visceral reflex arcs

Answer 20

1) Receptor in viscera
2) Sensory neuron - non-encapsulated nerve endings
3) Integration center
4) Motor neurons (preganglionic and postganglionic)
5) Visceral effector

Question 21

ANS Neurotransmitters

Answer 21

Acetylcholine (ACh) - effect depends on receptor (nicotinic or muscarinic)
Norepinephrine (NE) - effect depends on receptor it binds (Alpha or beta)

Question 22

How Acetylcholine is released in ANS

Answer 22

Released by cholinergic fibers at:
1) All ANS preganglionic axons
2) All parasympathetic postganglionic axons at synapse with effector

Question 23

Cholinergic receptors that bind ACh

Answer 23

1) Nicotinic receptors - found in ALL postganglionic neurons, hormone-producing cells of the adrenal medulla, sarcolemma of skeletal muscle cells (binding is always stimulatory)
2) Muscarinic receptors - all parasympathetic effectors and some sympathetic effectors (stimulatory OR inhibitory)

Ex. Binding of ACh to muscarinic receptors of heart is inhibitroy
Ex. Binding of ACh to muscarinic receptors of smooth muscle of gastrointestinal tract is stimulatory

Question 24

Adrenergic receptors that bond NE

Answer 24

1) Alpha receptors - all sympathetic target organs
2) Beta receptors - heart, adipose tissue, kidneys, lungs, blood vessels

Binding of NE or epinephrine can be stimulatory or inhibitory
Ex. NE binding at beta receptors of heart increases activity
Ex. Epinephrine binding at beta receptors of bronchioles causes dilation

Question 25

Interaction between Sympathetic and Parasympathetic Divisions of ANS

Answer 25

Most organs have dual innervation - send signals at the same time
Antagonistic Interactions of the Divisions - opposite effects, determined by what signal is stronger

Question 26

Sympathetic and Parasympathetic Effects on blood vessels

Answer 26

1) Vasomotor (Sympathetic) Tone - continuous partial constriction of blood vessels, sympathetic fibers supply blood vessels & control blood vessel diameter
2) Parasympathetic Tone - present mostly in cardiac muscle tissue, smooth muscle tissue of digestive and urinary organs: slows heart rate, maintains normal activity

Sympathetic division can override parasympathetic tone

If blood pressure is low - vasomotor fibers fire more rapidly: constricts more, higher blood pressure
If blood pressure is high - vasomotor fibers fire less rapidly: muscle relaxes, blood vessels dilate

Question 27

Unique Roles of the Sympathetic Division

Answer 27

1) Thermoregulatory response to heat - blood vessels dilate in response to heat, constrict in response to cold, sweat glands activated in response to heat
2) Renin release from kidneys - increases blood pressure
3) Metabolic changes - Increases metabolic rate of cells, raises blood glucose, mobilizes fats used fuel use

Question 28

Localized vs Diffuse Effects of ANS Divisions

Answer 28

1) Parasympathetic division exerts highly localized, short-lived control
2) Sympathetic division exerts diffuse, long lasting control

Question 29

Why are the parasympathetic division’s effects localized and short-lived

Answer 29

1) One preganglionic neuron synapses with one (or a few) postganglionic neurons
2) All parasympathetic fibers release ACh - quickly broken down by acetylcholinesterase

Question 30

Why are the sympathetic division’s effects localized and short-lived

Answer 30

1) Preganglionic neurons synapse with multiple postganglionic neurons
2) NE and epinephrine prolong effects

Question 31

Homeostatic Imbalances of the ANS (examples)

Answer 31

1) Hypertension - overactive vasoconstrictor response; heart works harder
2) Raynaud’s Disease - exaggerated vasoconstriction response due to cold or emotional stress; not enough blood
3) Autonomic dysreflexia - uncontrolled activation of autonomic neurons triggered by pain; arterial blood pressure skyrockets QUADRAPLEGIC