Enteric Nervous System I

Question 1

Where does the enteric nervous system start and end?

Answer 1

The ENS starts at the back of the mouth (upper esophageal sphincter) and ends at the internal anal sphincter.

Question 2

Roughly how long is the ENS in humans?

Answer 2

7 m.

Question 3

Most neurotransmitters and their receptors are found in the ENS. True or false?

Answer 3

True.

Question 4

There are a larger number of neuron cell bodies located in the ENS than in the spinal cord. True or false?

Answer 4

True.

Question 5

The ENS is fairly difficult to study as does not survive well after isolation from the body. True or false?

Answer 5

False.

Question 6

Which component of the gut makes it easier to study and why? Does this have any drawbacks?

Answer 6

The large amount of connective tissue. It protects the ENS from the effects of distortion but at the cost of making it harder to access the neurons.

Question 7

The ENS is the largest part of the autonomic nervous system. True or false?

Answer 7

True.

Question 8

The ENS includes the axons and terminals of _______ _______ ________, _________ neurons and __________ neurons that innervate the GI tract.

Answer 8

The ENS includes the axons and terminals of visceral sensory neurons, sympathetic neurons and parasympathetic neurons that innervate the GI tract.

Question 9

Do parasympathetic and sympathetic neurons innervate the muscle or secretory apparatus directly?

Answer 9

No. They target the enteric neurons and act indirectly through them to produce their effects.

Question 10

Roughly how many neuron cell bodies are located within the ENS?

Answer 10

300 000 000. (300 million).

Question 11

Name the 2 ganglionated plexuses within the ENS.

Answer 11

• Myenteric plexus

- Submucosal plexus

Question 12

In the small intestine, the mucosal epithelium is organised into villi. True or false?

Answer 12

True.

Question 13

Nutrients are absorbed at the base of the villi. At the tips of the villi, new epithelial cells are produced and secretion occurs. True or false.

Answer 13

False. Nutrients are absorbed at the tips of the villi (as is water). At the base of the villi new epithelial cells are produced and secretion occurs.

Question 14

Villi are not seen in the large intestine or in the stomach (the mucosa is much flatter). True or false?

Answer 14

True.

Question 15

Describe the submucosal plexus.

Answer 15

The SMP is a layer of blood vessels, connective tissue and groups of neurons clumped together and connected by internodal strands.

Question 16

Where does the GANGLIONATED submucosal plexus begin?

Answer 16

At the pylorus. (SMP present in stomach, but not ganglionated).

Question 17

The myenteric plexus contains roughly 5 times the number of neurons that are found in the submucosal plexus. True or false?

Answer 17

True.

Question 18

Within the ENS, where is motor control of the muscle predominantly located?

Answer 18

The myenteric plexus.

Question 19

Axons in the myenteric plexus run ____________ around the gut and represent the motor control system of the ENS.

Answer 19

circumferentially

Question 20

Where does the ganglionated myenteric plexus begin?

Answer 20

At the upper esophageal sphincter.

Question 21

Sympathetic nerves innervate the whole length of the GI tract. True or false?

Answer 21

True.

Question 22

How do sympathetic nerves modulate enteric nerve circuits?

Answer 22

By inhibiting transmission between enteric neurons (in effect, removing excitation from the system) rather than acting directly on the cell bodies to inhibit them.

Question 23

Parasympathetic nerves primarily innervate the upper and low GI tract. Where specifically are they less prominent?

Answer 23

In the jejunum and ileum.

Question 24

Extrinsic sensory neurons (visceral primary afferents) only innervate part of the GI tract. True or false?

Answer 24

False. They innervate the full length of the GI tract.