Chapter 15 Study Topics – ANS and Visceral Reflexes

Question 1

What are some of the primary target organs of the ANS?

Answer 1

Viscera of thoracic and abdominal cavities, some structures of the body wall (cutaneous blood vessels, sweat glands, and arrector muscles)

Question 2

Define visceral reflexes. What are they controlled by?

Answer 2

Visceral reflexes—unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors. They are controlled by ANS

Question 3

Are the actions of the ANS voluntary or involuntary?

Answer 3

Involuntary

Question 4

What changes occur within the body with the sympathetic division is triggered?

Answer 4

Increased heart rate, BP, airflow, blood glucose levels, etc. Blood flow to the skin and digestive tract are reduced.

Question 5

What changes occur within the body with the parasympathetic division is triggered?

Answer 5

Calms body functions and reduces energy usage of the body and assists in bodily maintenance like digestion and waste elimination

Question 6

What is autonomic tone? List an example of parasympathetic tone and sympathetic tone.

Answer 6

Autonomic tone is normal background rate of activity that represents the balance of the two systems according to the body’s needs.

Parasympathetic tone examples:
-Maintains smooth muscle tone in intestines
-Holds resting heart rate down to about 70 to 80 beats per minute

Sympathetic tone examples:
-Keeps most blood vessels partially constricted and maintains blood pressure

Question 7

How does the autonomic pathway compare to somatic pathways?

Answer 7

In somatic pathway, a motor neuron from brainstem or spinal cord issues a myelinated axon that reaches all the way to skeletal muscle

In autonomic pathway, a signal must travel across two neurons to get to the target organ, and cross a synapse where these two neurons meet in an autonomic ganglion.

Question 8

What are the adrenal glands? What type of hormones do they secrete?

Answer 8

Adrenal glands are paired glands located on the superior poles of kidneys; each is two glands with different functions.

Adrenal cortex—outer layer; secretes steroid hormones

Adrenal medulla—inner core; essentially a sympathetic ganglion
It secretes a mixture of hormones into bloodstream: 85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline)

Question 9

What is the enteric plexus? What organ system does it innervate?

Answer 9

The Enteric plexus (enteric nervous system) is the nervous network of the digestive tract. It innervates the GI tract

Question 10

What is Hirschsprung disease? What is a megacolon?

Answer 10

Hirschsprung disease is a hereditary defect causing absence of the enteric plexus

Megacolon is the massive dilation of bowel accompanied by abdominal distension and chronic constipation

Question 11

What are cholinergic neurons? What neurotransmitter do they secrete?

Answer 11

Cholinergic neurons are neurons that secrete ACh. ACh (Acetylcholine) is secreted by all preganglionic neurons in both divisions and by postganglionic parasympathetic neurons

Question 12

What are the two categories of cholinergic receptors? Where is each found? Which is always excitatory?

Answer 12

Muscarinic receptors—found on cardiac muscle, smooth muscle, and gland cells with cholinergic innervation
*Act through second-messenger systems
*Receptor subtypes exist, often providing contrasting effects on organs
*Example: ACh excites intestinal smooth muscle, but inhibits cardiac muscle

Nicotinic receptors—found on postganglionic neuron cell bodies in autonomic ganglia; on cells of adrenal medulla; and neuromuscular junction of skeletal muscle fibers
*Binding of ACh to receptor is always excitatory
*Open ligand-gated ion channels, produce excitatory postsynaptic potential

Question 13

What are adrenergic neurons? What neurotransmitter do they secrete?

Answer 13

Norepinephrine (NE) is secreted by nearly all sympathetic postganglionic neurons
*Nerve fibers that secrete NE are called adrenergic fibers
*Receptors for NE are called adrenergic receptors

Question 14

What are the two categories of adrenergic receptors? Which is usually excitatory? Which is usually inhibitory?

Answer 14

Two categories:
Alpha-adrenergic receptors, usually excitatory
-Two subclasses use different second messengers (α1 and α2)
Beta-adrenergic receptors, usually inhibitory
-Two subclasses with different effects, but both act through cAMP as a second messenger (β1and β2)

Question 15

List some antagonistic effects of the parasympathetic and sympathetic systems

Answer 15

Dual innervation—most viscera receive nerve fibers from both parasympathetic and sympathetic divisions

Antagonistic effects: oppose each other
* Can be exerted through dual innervation of same effector cells (example: heart rate)

• Can be exerted because each division innervates different cells (example: muscles of iris)

Question 16

List some cooperative effects of the parasympathetic and sympathetic systems.

Answer 16

Cooperative effects: two divisions act on different effectors to produce a unified overall effect

*Example: saliva production—parasympathetic stimulates serous cell secretion and sympathetic stimulates mucous cell secretion
*Even when both division innervate a single organ, innervation is not always equal or exert equal influence

Question 17

What structures in the CNS regulate the ANS? Which functions do each area control?

Answer 17

Visceral reflexes—unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors; controlled by ANS​
Visceral reflex arc:​
1. Receptors—nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli​
2. Afferent neurons—lead to CNS​
3.Integrating center—interneurons in the CNS​
4.Efferent neurons—carry motor signals away from the CNS​
Effectors—carry out end response

Question 18

What do sympathomimetics do? What do sympatholytics do? List examples of each.

Answer 18

Sympathomimetics enhance sympathetic activity and stimulate receptors or increase norepinephrine release
Example: Cold medicines that dilate the bronchioles or constrict nasal blood vessels

Sympatholytics suppress sympathetic activity and block receptors or inhibit norepinephrine release
Example: Beta-blockers reduce high BP interfering with effects of epinephrine and norepinephrine on heart and blood vessels