Chapter 15 The Autonomic Nervous System

Question 1

What is the main function of the ANS?

Answer 1

Maintain homeostasis by conveying motor output from the CNS to smooth muscle, cardiac muscle, and glands for appropriate responses to integrated sensory information.

Question 2

What are the two divisions of the motor (efferent) division of the PNS?

Answer 2

The somatic nervous system and the autonomic nervous system.

Question 3

Which ANS system typically operates under voluntary control?

Answer 3

The ANS usually operates without conscious control but is regulated by centers in the hypothalamus and brainstem.

Question 4

What structures in the body do the somatic nervous system and autonomic nervous system target?

Answer 4

The SNS targets skeletal muscles, while the ANS targets cardiac muscle, smooth muscle, and glands (visceral effectors).

Question 5

What is the main difference between somatic and autonomic motor control?

Answer 5

The SNS usually operates under voluntary control, while the ANS operates involuntarily and regulates visceral functions.

Question 6

What is the role of the autonomic nervous system in organ function?

Answer 6

Regulates the activity of cardiac muscle, smooth muscle, and glands, controlling actions such as heart rate, blood vessel dilation, and digestion.

Question 7

What are interoceptors and what do they monitor?

Answer 7

Sensory receptors in the body that monitor conditions such as blood CO2 levels and the degree of stretch in organ walls or blood vessels.

Question 8

What are the two main divisions of the autonomic nervous system?

Answer 8

The sympathetic nervous system and the parasympathetic nervous system.

Question 9

What is the difference between the sympathetic and parasympathetic nervous systems?

Answer 9

The SNS prepares the body for emergency situations (fight-or-flight), while the PNS promotes rest-and-digest activities (conserving energy during rest).

Question 10

What is dual innervation in the context of the ANS?

Answer 10

Refers to most organs receiving input from both the sympathetic and parasympathetic divisions, with one division stimulating activity (excitation) and the other inhibiting it.

Question 11

What is the function of the enteric nervous system?

Answer 11

Regulates the gastrointestinal (GI) tract, controlling smooth muscle contractions and secretion of GI tract glands, operating involuntarily.

Question 12

How many neurons are typically involved in autonomic motor pathways?

Answer 12

Most autonomic pathways involve two motor neurons: a preganglionic neuron and a postganglionic neuron.

Question 13

What are chromaffin cells and where are they found?

Answer 13

Chromaffin cells are specialized cells in the adrenal medulla that secrete epinephrine and norepinephrine in response to autonomic input.

Question 14

What neurotransmitters are released by somatic and autonomic motor neurons?

Answer 14

Somatic motor neurons release ACh, while autonomic motor neurons release either ACh or NE.

Question 15

How does the autonomic nervous system affect heart rate?

Answer 15

The sympathetic division increases heart rate, while the parasympathetic division slows it down.

Question 16

What is the first motor neuron in an autonomic motor pathway called?

Answer 16

The first motor neuron is called a preganglionic neuron. It has its cell body in the brain or spinal cord.

Question 17

What type of fiber is the axon of a preganglionic neuron?

Answer 17

A small-diameter, myelinated type B fiber.

Question 18

Where does the axon of a preganglionic neuron synapse?

Answer 18

With a postganglionic neuron in an autonomic ganglion.

Question 19

What type of fiber is the axon of a postganglionic neuron?

Answer 19

A small-diameter, unmyelinated type C fiber.

Question 20

What is the difference between the sympathetic and parasympathetic divisions of the ANS in terms of the location of preganglionic neuron cell bodies?

Answer 20

The sympathetic division has preganglionic neuron cell bodies in the thoracic and lumbar segments of the spinal cord (thoracolumbar division). The parasympathetic division has preganglionic neuron cell bodies in the brainstem and sacral segments of the spinal cord (craniosacral division).

Question 21

What are the two major groups of autonomic ganglia?

Answer 21

The sympathetic ganglia (part of the sympathetic division) and parasympathetic ganglia (part of the parasympathetic division).

Question 22

What are sympathetic trunk ganglia?

Answer 22

Located in a vertical row on either side of the vertebral column and synapse between sympathetic preganglionic and postganglionic neurons.

Question 23

What is the function of prevertebral ganglia?

Answer 23

Located anterior to the vertebral column and innervate organs below the diaphragm.

Question 24

What is the term for the network of sympathetic and parasympathetic axons forming tangled networks in the thorax, abdomen, and pelvis?

Answer 24

Autonomic plexuses.

Question 25

What is the largest autonomic plexus and what does it supply?

Answer 25

The celiac (solar) plexus is the largest autonomic plexus and supplies the stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medullae, testes, and ovaries.

Question 26

What are the four pathways through which postganglionic axons leave the sympathetic trunk?

Answer 26

1. Enter spinal nerves,
2. Form cephalic periarterial nerves,
3. Form sympathetic nerves,
4. Form splanchnic nerves.

Question 27

What is the function of gray rami communicantes?

Answer 27

Structures that contain sympathetic postganglionic axons and connect the sympathetic trunk to spinal nerves.

Question 28

Where do sympathetic preganglionic neurons that ascend to the superior cervical ganglion synapse, and what do they innervate?

Answer 28

They synapse in the superior cervical ganglion and innervate the skin of the face, smooth muscle of the eye, lacrimal glands, pineal gland, nasal mucosa, and salivary glands.

Question 29

What do sympathetic nerves to the heart innervate?

Answer 29

Innervate the heart, specifically the heart muscle and the coronary blood vessels.

Question 30

What are the two classifications of autonomic neurons based on the neurotransmitter they release?

Answer 30

Cholinergic and adrenergic neurons.

Question 31

Which neurons in the ANS release ACh?

Answer 31

All sympathetic and parasympathetic preganglionic neurons, sympathetic postganglionic neurons that innervate most sweat glands, and all parasympathetic postganglionic neurons.

Question 32

What are the two types of cholinergic receptors?

Answer 32

Nicotinic receptors and muscarinic receptors.

Question 33

What is the role of nicotinic receptors?

Answer 33

Cause depolarization (excitation) of postsynaptic cells and are found in the dendrites and cell bodies of both sympathetic and parasympathetic postganglionic neurons, chromaffin cells of the adrenal medullae, and the neuromuscular junction.

Question 34

What effect do muscarinic receptors have when activated by ACh?

Answer 34

can cause either depolarization (excitation) or hyperpolarization (inhibition) depending on the cell type.

Question 35

How are the effects of cholinergic neurons terminated?

Answer 35

The effects of cholinergic neurons are brief due to the inactivation of ACh by the enzyme AChE.

Question 36

What is released by adrenergic neurons in the ANS?

Answer 36

Norepinephrine (NE), also known as noradrenalin.

Question 37

What are the two main types of adrenergic receptors?

Answer 37

Alpha (α) receptors and beta (β) receptors.

Question 38

What are the subtypes of adrenergic receptors, and what are their general effects?

Answer 38

The subtypes are α1, α2, β1, β2, and β3. Activation of α1 and β1 generally causes excitation, while α2 and β2 generally cause inhibition. β3 receptors are involved in thermogenesis in brown adipose tissue.

Question 39

How do adrenergic receptors differ in their sensitivity to NE and epinephrine?

Answer 39

NE stimulates alpha receptors more strongly than beta receptors, while epinephrine strongly stimulates both alpha and beta receptors.

Question 40

How is the action of NE terminated?

Answer 40

By reuptake into the releasing neuron or enzymatic inactivation by catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO).

Question 41

What is an agonist in the context of receptor activity?

Answer 41

A substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone.

Question 42

What is an antagonist in the context of receptor activity?

Answer 42

A substance that binds to and blocks a receptor, preventing the natural neurotransmitter or hormone from exerting its effect.

Question 43

What is a common use for the adrenergic agonist phenylephrine?

Answer 43

In cold and sinus medications to reduce nasal congestion by constricting blood vessels in the nasal mucosa.

Question 44

How is atropine used in medicine?

Answer 44

Blocks muscarinic ACh receptors, dilates the pupils, reduces glandular secretions, relaxes smooth muscle in the GI tract, and is used in treatments such as eye examinations and smooth muscle disorders, and as an antidote for chemical warfare agents.

Question 45

What is autonomic tone?

Answer 45

The balance between sympathetic and parasympathetic activity, regulated by the hypothalamus, which adjusts the levels of activity in each division to maintain balance in the body.

Question 46

How do the sympathetic and parasympathetic divisions typically affect body organs?

Answer 46

Most body organs receive innervation from both divisions, which typically work in opposition to one another. The sympathetic division generally prepares the body for action, while the parasympathetic division conserves energy and promotes restful activities.

Question 47

What structures receive only sympathetic innervation?

Answer 47

Sweat glands, arrector pili muscles, kidneys, spleen, most blood vessels, and the adrenal medullae receive only sympathetic innervation.

Question 48

What physiological responses are triggered during the sympathetic “fight-or-flight” response?

Answer 48

Pupils dilate
Heart rate, force of contraction, and blood pressure increase
Airway dilation for faster breathing
Blood vessels to non-essential organs (kidneys, GI tract) constrict
Blood vessels to essential organs (muscles, heart, liver) dilate
Liver performs glycogenolysis and adipose tissue performs lipolysis
Glucose release from the liver increases blood glucose
Non-essential functions (like digestion) are inhibited

Question 49

Why do sympathetic responses last longer and have more widespread effects than parasympathetic responses?

Answer 49

1. Sympathetic postganglionic axons diverge more, activating many tissues simultaneously.
2. NE lingers in the synaptic cleft longer than ACh, which is quickly inactivated.
3. Epinephrine and NE secreted by the adrenal medullae prolong the effects of sympathetic stimulation by circulating through the body.

Question 50

What are the main physiological effects of the parasympathetic division?

Answer 50

The parasympathetic division enhances rest-and-digest activities, supporting body functions that conserve and restore energy during rest. It promotes digestion, absorption of food, and energy conservation, while reducing functions that support physical activity.

Question 51

What does the acronym SLUDD stand for in relation to parasympathetic responses?

Answer 51

SLUDD stands for Salivation, Lacrimation, Urination, Digestion, and Defecation, which are activities primarily stimulated by the parasympathetic division.

Question 52

What are the “three decreases” of parasympathetic responses?

Answer 52

Refer to decreased heart rate, decreased airway diameter (bronchoconstriction), and decreased pupil diameter (pupillary constriction).