Sanders Enteric Nervous System Flashcards by Danielle Hayes

What are the 2 components of the enteric nervous system and what are they controlled by?

myenteric-> parasympathetics (motility)

submucousal->sympathetics (BV)

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The gut has the ability of (blank) motor and secretory activity (i.e it could be transplanted and work fine)

INTRINISIC

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What are the sensory neurons of the enteric?

chemoreceptors
mechanoreceptors
thermoreceptors

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What are the interneurons of the enteric?

reflex circuits and motor neurons

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What are the motor neurons of the enteric?

excitatory and inhibitory

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What are the effectors of the enteric?

epithelium (mucosa)
muscles
BVs

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(blank) are the final common pathway controlling the motility of the GI tract

motor neurons

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motor neurons on largely located in the (blank) and the outer (blank) close to circular muscle layer

myenteric plexus

submucous plexus

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Explain the layers of the small intestine from the mucosa inwards

mucosa, submucosa w/ BVs, submucous plexus circular muscle, myenteric plexus, longitudinal muscle, mesentary

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The mesenteric membrane has what 2 things

BVs and extrinsic nerves

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What is in between the longitudinal and circular muscle?

myenteric plexus

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Within the circular muscle layer is the non-ganglionated (blank) which contains the axons of motor neurons

deep muscular plexus

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THe (blank) is split into layers that giverise to the mucosal plexus on the back of the mucosa.

submucous plexus

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(blank) cells transduce luminal mechanical and/or chemical stimuli into the release of signaling molecules including peptides and amines. There are at least 14 different populations of these cells scattered throughout GI epithelia

enteroendocrine

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(blank), which contain and secrete serotonin (5-HT), are the largest population of enteroendocrine cells and have the most widespread distribution. These cells have both chemosensitive and mechanosensitive capabilities

enterchromaffin cells

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(blank) cells are the primary sensory organ affecting GI motility.

enterchromaffin cells (EC)

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(blank) cells contain 90% of the body’s 5-HT.They respond to mechanical stimulation and luminal chemicals including bacterial toxins.

Enterochromaffin

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5-HT released from these cells activates (blank) which trigger the emetic response, secretion and diarrhoea to expel potentially harmful substances from the body.

vagal afferents

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Once 5-HT is released, how do you get rid of it?

with SERT (seritonin reuptake transporter) or put into the blood to be placed in platelets for later use

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Following inflammation what happens to EC cells and SERT?

EC cells increase and SERT decreases which may explain IBS

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What does TPH1 (tryptophan hydroxylase) do?

converts tryptophan into seritonin

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What does L-AADC (aromatic L amino acid decarboxylase)

converts 5HTP to 5HT

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At rest, 5‑HT is synthesized by enterochromaffin cells. Upon mechanical or chemical stimulation,what happens?

5‑HT is released into the interstitial space of the lamina propria and binds to receptors on nearby nerve fibers

5‑HT signalling is terminated during the recovery phase: 5‑HT is transported by (blank) into epithelial cells where it is enzymatically degraded, or it enters the (blank) where it is transported into platelets and stored for future use.

SERT

blood stream

Most of the intrinsic and extrinsic primary afferent neurons that innervate the gut extend processes into the (blank) of the mucosal layer where they can become exposed to 5‑HT released by enterochromaffin cells.

lamina propria

Where do you homeostatic and digestion reflexes come from?

vagal affarents

Were do your pain and discomfort reflexes come from?

spinal affarents

Intrinsic and extrinsic affarent neurons that extend into the LP of the mucosal layer include (blank) afferent fibres arising from the nodose ganglion, spinal afferent fibres arising from (blank) ganglia, and intrinsic (blank) neurons located in submucosal and myenteric ganglia. There is also a class of mechanosensitive (blank) neurons in the myenteric ganglia that do not project to the mucosal layer.

vagal dorsal root AH S

What are the 5 ways to classify enteric neurons?

``` morphological electrophysiological neurochemical pharmacological retrogade labelling ```

What did FITC show us? | What did Calretinin show us?

NO synthase in inhibitory motor neurons | Longitudinal muscle motor neurons

One of the major excitatory transmitters of enteric neurons is (blank). Neurons that synthesize acetylcholine contain the enzyme (blank).

``` acetylcholine choline acetyltransferase (ChAT) ```

(blank) have large smooth cell bodies, are multipolar, have filamentous dendrites and are intrinsic afferent neurons. 20-30% of all enteric neurons are this.

AH neurons or Type II neurons

By looking at an action potential, how can you tell you are dealing with an AH cell?

You will see either 1 or 2 spikes followed by a long-lasting hyperpolarizing after-potential. Even increasing the injected current does not alter this response. ie. spike then latency

What type of cells are AH/type II neurons?

intrinsic primary afferent neurons (IPANs)

Explain what causes the action potential and latent period of an AH cell

Ca channels open and cell depolarizes=AP Ca activate K+ channels are opened and potassium moves down gradient out of neuron=repolarization continually movement of K+ out=hyperpolarization After hyperpolarization finally ends after Ca is pushed out of cell or sequestered into intracellular stores

Generation of excitatory post-synaptic potentials (EPSPs) in AH neurons causes them to become more (blank).

excitable

(blank) controls peristaltic propulsion of luminal contents. This neural control requires gating mechanisms to determine distance and direction of propagaion.

neural regulation

(blank) increase gating of sensory inputs to enhance responses.

Excitatory post-synaptic potentials (EPSPs)

AH neurons synapse with each other and other (blank) neurons by releasing (blank) forming a self-reinforcing network.

S neurons | tachykinins

AH neurons communicate with each other and other S neurons via (blank ). Because of these synaptic interactions, mucosal stimulation of one AH neuron could lead to the excitation of other AH neurons. In this way, the activity of AH neurons in a region of intestine is coordinated, potentially leading to synchronous activation of many neurons in response to stimulation.

slow excitatory postsynaptic potentials (SEPSPs

The sensory info in the gut is very distributed (due to connecting neurons) to produce a (blank) , this is why it is difficult to pin point where your pain in your gut stems from.

field effect

Networks of interconnected intrinsic sensory neurons (IPANs) or (blank) cells detect mechanical distortion and lumenal chemistry. These synapse with descending and ascending (blank), (blank) and (blank)

AH interneurons excitatory muscle neurons inhibitory muscle neurons

(blank) neurons have rough cell bodies with short lamellar dendrites, with a single long axon and are motor and interneurons.

Type 1 neurons/ S neurons

How can you tell you are dealing with an S neuron by looking at an action potential induced by a current?

S neuons fire action potentials throughout the duration of a depolarization current. They frequency of the repetitive spikes discharge in proportion to the amplitude of the injected current.

(blank) typically have very fast action potentials, whereas those of (blank) are distinguished by an inflection or “hump” on their falling phase, which tends to prolong the duration and which has been shown to be due to influx of Ca2+ ions. This then triggers after-hyperpolarisation via calcium-activated potassium channels

S cells | AH cells

Which have longer action potential, AH or S cells? Which have steeper APs? Which have more frequent APs?

AH AH S

S cells/ Type I neurons (which contain VIP or NO) in the myenteric plexus send projections in an aboral direction, traveling for only a few millimeters before entering the circular muscle layer. These neurons are considered (blank)

inhibitory motor neurons

Dogiel type I neurons (which contain ACh or Substance P) in the myenteric plexus send projections in an oral direction, traveling for only a few millimeters before entering the circular muscle layer. These neurons are (blank) motor neurons that lead to contraction of the circular layer.

excitatory

Dogiel type I neurons in the submucosal plexus containing VIP are excitatory motor neurons to the intestinal crypts and are called (blank) , they stimulate the crypts to secrete water, electrolytes and mucus

secretomotor neurons

If you have type 1 cells sending projections in the oral direction what are they? If you have type 1 cells sending projections in the aboral direction then what are they?

excitatory | inhibitory

If you have type 1 neurons in the submucosal plexus what are they?

excitatory secretomotor neurons

The main motor output that the myenteric plexus produces is (blank)

peristaltic reflex

Neurons above the site of stimulation are (blank) , below the site of stimulation are (blank) (hyperpolarization).

excitatory | inhibitory

Neurons above the site of stimulation are excitatory, below the site of stimulation are inhibitory (hyperpolarization). This is called the (blank) reflex

receptive reflex

(blank) occurs after the stimulus has been turned off, there is an excitatory effect that helps give an extra push.

Rebound excitation

Explain the pathway before the stimulus:

stimulus is transduced by enterchromaffin cells which stimulate affarents which stimulate ascending interneurons which stimulate excitatory motor neurons which stimulate contraction via AcH or neurokinins

Explain the pathway after the stimulus

stimulus-> EC cells-> intrinsic primary affarent-> descending interneuron-> inhibitory motor neuron->relax