S1B5 - Autonomic Physiology 1

Question 1

Each connection or pathway in the autonomic nervous system is composed of how many fibers?

Answer 1

The connections or pathways of the autonomic nervous system are composed of two fibers, a preganglionic and postganglionic fiber.

Question 2

What division of the autonomic nervous system can function independent of the central nervous system?

Answer 2

The enteric nervous system functions via a system of intramural ganglia and plexuses that can function independently of the central nervous system. Please note that the majority of the time, there is input from the central nervous system via the autonomic nervous system.

Question 3

Where do preganglionic neurons of the sympathetic nervous system originate from?

Answer 3

Preganglionic neurons of the sympathetic nervous system originate in the intermediolateral cell column (T1-L2) of the spinal cord.

Question 4

Are postganglionic fibers of the sympathetic nervous system short or long?

Answer 4

Postganglionic fibers of the sympathetic nervous system are long.

Question 5

What is the predominant neurotransmitter of postganglionic fibers of the parasympathetic nervous system?

Answer 5

Postganglionic fibers of the parasympathetic nervous system release acetylcholine (ACh).

Question 6

What innervation does the myenteric (Auerbach’s) plexus carry and to what layer of the gastrointestinal wall?

Answer 6

Two nerve plexuses within the gut coordinate gastrointestinal motility and secretions, respectively:

• Myenteric (Auerbach’s) plexus: provides sympathetic and parasympathetic innervation to the muscularis propria to coordinate motility
• Submucosal (Meissner’s) plexus: provides parasympathetic (secretomotor) innervation to the mucosa and muscularis mucosae to coordinate secretory function

Question 7

Are the preganglionic fibers of the sympathetic nervous system short or long?

Answer 7

Preganglionic fibers of the sympathetic nervous system are short.

Question 8

What is the predominant receptor type on target organs of the parasympathetic nervous system?

Answer 8

Target organs of the parasympathetic nervous system have muscarinic receptors (M1, M2, etc.).

Question 9

What is the major neurotransmitter of the enteric nervous system?

Answer 9

The major neurotransmitter of the enteric nervous system is serotonin (5-HT), which generally promotes motility.

Question 10

What is the only organ that is directly innervated by preganglionic neurons of the sympathetic nervous system?

Answer 10

There is one component of the sympathetic nervous system that does not follow the two neuron rule. Some preganglionic neurons directly innervate the adrenal medulla, which then releases epinephrine into the general circulation.

Question 11

What is the primary function of the enteric nervous system?

Answer 11

The enteric nervous system primarily serves to regulate gastrointestinal motility.

Question 12

What is the role of sensory neurons in the enteric nervous system?

Answer 12

Sensory neurons in the intestinal mucosa and muscularis propria layers sense acid, glucose, amino acids, osmotic changes, muscle stretch, and muscle tension. This information is relayed back to the central nervous system so that it can coordinate proper autonomic output to the enteric nervous system.

Question 13

What is the general function of the parasympathetic nervous system?

Answer 13

The parasympathetic nervous system is generally involved in “rest and digest” responses such as decreasing heart rate, bronchoconstriction, and increasing blood flow to the GI tract.

Question 14

What body system regulates visceral functions?

Answer 14

The autonomic nervous system serves to regulate visceral functions, including smooth muscle, cardiac muscle, and glandular tissue.

Question 15

Where do preganglionic fibers of the parasympathetic nervous system originate from?

Answer 15

Preganglionic fibers of the parasympathetic nervous system originate in the cranial and sacral regions of the CNS including:

• CNs III, VII, IX, and X
• S2, S3, S4

Question 16

What neurotransmitters are released by postganglionic fibers of the sympathetic nervous system that innervate sweat glands and renal blood vessels?

Answer 16

Two exceptions are postganglionic neurons that innervate sweat glands, which release acetylcholine (ACh), and postganglionic neurons that innervate renal blood vessels, which release dopamine.

Question 17

Where (2 locations) do postganglionic neurons of the sympathetic nervous system originate?

Answer 17

Postganglionic neurons originate in two locations, each with distinct targets which include:

• Sympathetic trunk, projecting to blood vessels, sweat glands, and arrector pili muscles
• Prevertebral ganglia, projecting to abdominal and pelvic viscera

Question 18

What division of the autonomic nervous system is responsible for the “fight or flight” response?

Answer 18

The sympathetic nervous system is generally involved in “fight or flight” responses. Its activity results in various changes including increased heart rate, bronchodilation, and increased blood flow to skeletal muscles.

Question 19

Are postganglionic fibers of the parasympathetic nervous system long or short?

Answer 19

Postganglionic fibers of the parasympathetic nervous system are short.

Question 20

Are preganglionic fibers of the parasympathetic nervous system long or short?

Answer 20

Preganglionic fibers of the parasympathetic nervous system are long.

Question 21

What target of the sympathetic nervous system has muscarinic acetylcholine receptors?

Answer 21

Sweat glands have muscarinic acetylcholine receptors. This is important because muscarinic antagonists, such as atropine that act specifically on M3 receptors, can affect the sweat glands.

Question 22

What type of receptor is found at the synapse between the preganglionic and postganglionic neurons in both the sympathetic and parasympathetic divisions of the autonomic nervous system?

Answer 22

For both the sympathetic and parasympathetic systems, the receptor type at the synapse between the preganglionic and postganglionic neurons (including between the preganglionic neuron and adrenal medulla) is a nicotinic cholinergic receptor.

Question 23

Which gastrointestinal nerve plexus provides only parasympathetic innervation to the mucosa and muscularis mucosae?

Answer 23

Two nerve plexuses within the gut coordinate gastrointestinal motility and secretions, respectively:

• Myenteric (Auerbach’s) plexus: provides sympathetic and parasympathetic innervation to the muscularis propria to coordinate motility
• Submucosal (Meissner’s) plexus: provides parasympathetic (secretomotor) innervation to the mucosa and muscularis mucosae to coordinate secretory function

Question 24

What is the predominant receptor type on target organs of the sympathetic nervous system?

Answer 24

Target organs of the sympathetic nervous system, except the sweat glands and renal vessels, have adrenergic receptors.

Question 25

What is the major neurotransmitter of postganglionic fibers of the sympathetic nervous system?

Answer 25

Most postganglionic fibers of the sympathetic nervous system release **norepinephrine (NE).**

Question 26

Preganglionic neurons of the autonomic nervous system secrete what neurotransmitter?

Answer 26

Each neuron secretes a specific neurotransmitter from its axon terminals. Preganglionic fibers for both the sympathetic and parasympathetic nervous system secrete **acetylcholine (ACh)** and thus are **cholinergic neurons**.

Question 27

What are the three divisions of the autonomic nervous system?

Answer 27

The autonomic nervous system has three divisions: **sympathetic, parasympathetic**, and **enteric**..

Question 28

What is the site of integration and control for many autonomic dunctions?

Answer 28

**Hypothalamus** – site of integration and control for many autonomic functions. It is also the origin of the neuroendocrine, hypothalamic-pituitary axis.

Question 29

Which type of receptor gives excitatory responses to EPI, NE and PE?

Answer 29

**α 1** - Excitatory responses of EPI, NE and phenylephrine (PE) - vasoconstriction, mydriasis, secretion of thick, mucoid saliva, sphincter contraction, ejaculation. Postjunctional α 1 effects are mediated through Gq and second messengers; either IP3 and DAG or Ca++.

Question 30

What kind of receptor gives inhibitory responses to EPI, NE and PE?

Answer 30

**α2** - Inhibitory responses of EPI, NE and PE - decreased motility and secretory activity in the gastrointestinal tract. Stimulation of α2 receptors inhibits adenylate cyclase hence it inhibits cAMP production thus making it less available as a 2nd messenger. Gi-mediated. (1) Prejunctional inhibition of adrenergic and cholinergic postganglionic neurons prevents further transmitter release. (Prejunctional α2 receptors are responsible.) (2) Postjunctional α2 receptors are found primarily in the CNS. Other sites are speculated.

Question 31

What kind of receptor gives excitatory responses to ISO, EPI or NE?

Answer 31

**β1** - Excitatory responses due to isoproterenol (ISO), EPI or NE on β1 receptors are positive chronotropic and inotropic effects on the myocardium, as well as renin release.

Question 32

What kind of receptor gives inhibatory responses to ISO, EPI or NE?

Answer 32

**β2** - Inhibitory responses due to ISO, EPI or NE include relaxation of smooth muscle (gastrointestinal, bronchiolar, urinary bladder detrusor muscle, and blood vessels in skeletal muscle). β2 receptors may be involved in some metabolic responses.

Question 33

What kind of receptor gives metabolic responses to ISO, EPI or NE? What is the metabolic response?

Answer 33

**β3** - Metabolic response due to ISO, EPI or NE is **lipolysis**

Question 34

How does activation of β receptors affect cAMP availability as a second messenger?

Answer 34

Stimulation of β receptors **activates adenylate cyclase** hence it **increases cAMP** production thus enhancing its availability as a 2nd messenger. This is Gs-mediated.

Question 35

How does β1-receptor stimulation effect Ca++ availability in cardiac muscle?

Answer 35

In cardiac muscle β1, effects **make more Ca++ available** for contraction and cardiac acceleration.

Question 36

Does stimulation of β2 receptors result in smooth muscle contraction or relaxation?

Answer 36

Where β2 receptors are involved, **increased uptake of Ca++ into the SR** and **phosphorylation of MLCK** result in **smooth muscle relaxation**.

Question 37

Where are α1 receptors located?

Answer 37

Smooth muscle

Question 38

Where are α2 receptors located?

Answer 38

Presynaptic nerves

Question 39

Where are β1 receptors located?

Answer 39

heart

Question 40

Where are β2 receptors located?

Answer 40

smooth muscle

Question 41

Where are β3 receptors located?

Answer 41

fat tissue

Question 42

What adrenergic receptor types are located in smooth muscle?

Answer 42

α1 and β2