Anatomy of the Myenteric Plexus

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Questions and Answers

What is the primary function of the Myenteric Plexus in the digestive system?

Detecting chemoreceptors and stretch receptors

Regulating secretions of the mucosal epithelium

Integrating CNS signals for extrinsic reflexes

Controlling the movement of the bowel (correct)

Where is the Myenteric Plexus located in the digestive system?

Outside the digestive system wall

Between the submucosa and mucosa layers

Between the longitudinal and circular smooth muscle layers (correct)

Within the submucosa

What type of neurons are involved in triggering reflexes in the digestive system?

Motor neurons

Sensory neurons (correct)

Pacemaker cells

Interneurons

What is the role of the Submucosal Plexus in the digestive system?

Regulating secretions of the mucosal epithelium Signup and view all the answers

What is the term for reflexes that are totally controlled by the Enteric Nervous System?

Short reflexes Signup and view all the answers

What is the role of the Autonomic Nervous System in the digestive system?

Providing regulatory input to the Enteric Nervous System Signup and view all the answers

What is the term for reflexes that involve the CNS as an integration center?

Long reflexes Signup and view all the answers

Can short and long reflexes occur simultaneously in the digestive system?

Yes, they can occur simultaneously Signup and view all the answers

What percentage of saliva is composed of water?

97-99.5% Signup and view all the answers

What type of enzymes are found in saliva?

Salivary amylase and lingual lipase Signup and view all the answers

What is the primary function of mucin in saliva?

To form a thick, lubricating mucus Signup and view all the answers

What division of the autonomic nervous system (ANS) controls salivation?

Parasympathetic (PS) division Signup and view all the answers

What stimulates the release of watery, enzyme-rich saliva?

Food ingestion Signup and view all the answers

What is a consequence of inhibited saliva secretion?

Increased dental cavities Signup and view all the answers

What is the result of anaerobic bacterial growth in the mouth?

Bad breath (halitosis) Signup and view all the answers

What is the function of lysozyme in saliva?

To kill bacteria Signup and view all the answers

What is the primary function of mixing contractions in the small intestine?

To mix food with intestinal secretions and bring it into repeated contact with the absorptive epithelium Signup and view all the answers

What is the frequency of segmentation contractions highest in?

Duodenum Signup and view all the answers

Which nervous system activity increases segmentation contractions?

Parasympathetic activity Signup and view all the answers

What is the primary function of propulsive movements in the small intestine?

To move chyme from the small to the large intestine Signup and view all the answers

What is the function of the ileocecal valve?

To prevent the return of fecal content into the small intestine Signup and view all the answers

What type of contractions are responsible for the majority of chyme movement in the small intestine?

Propulsive contractions Signup and view all the answers

What is the term for the slow passage of chyme in the small intestine?

Retention Signup and view all the answers

What regulates the frequency of segmentation contractions in the small intestine?

Pacemaker cells Signup and view all the answers

What is the major function of the muscularis mucosae?

Local movements of the mucosa Signup and view all the answers

What type of tissue is predominant in the submucosa layer?

Dense connective tissue Signup and view all the answers

Which structure helps prevent food backflow in the GI tract?

Sphincters Signup and view all the answers

Where is the serosa replaced by adventia formed of fibrous connective tissue?

Esophagus Signup and view all the answers

What is the function of the epithelium in the gum and hard palate?

Protection against abrasion Signup and view all the answers

What characterizes the red margin of the lips?

Poorly keratinized and translucent Signup and view all the answers

What is a key function of the hard palate?

Assist the tongue in chewing Signup and view all the answers

Which action prevents food from entering the nasal cavity during swallowing?

Soft palate is pulled upward Signup and view all the answers

What is the purpose of secondary peristalsis in the esophagus?

To empty the esophagus Signup and view all the answers

Which phase of swallowing is primarily involuntary and involves the esophagus?

Pharyngeal-esophageal phase Signup and view all the answers

Which structure relaxes to allow food to pass into the stomach?

Lower esophageal sphincter Signup and view all the answers

What triggers the second phase of esophageal motility?

Presence of saliva or food in the posterior pharynx Signup and view all the answers

Which statement best defines the motor functions of the stomach during digestion?

Storage of large quantities of food until it is accommodated in the duodenum Signup and view all the answers

Study Notes

Enteric Nervous System (ENS)

Located between longitudinal and circular smooth muscle layers
Provides major nerve supply to GI tract wall
Controls GI tract motility
Pattern control of segmentation and peristalsis is largely automatic
Involves pacemaker cells and local reflex arcs between enteric neurons in same or different plexuses (or organs)

Submucosal Plexus (Plexus of Meissner)

Found within the submucosa
Motor neurons supply secretory cells of the mucosal epithelium, controlling secretions of organs of the GI tract

Control of the Digestive System

Interneurons interconnect neurons of the myenteric and submucosal plexuses
Sensory neurons are chemoreceptors or stretch receptors that trigger reflexes
Neurons of the NS can function independently, but are subject to regulation by the autonomic nervous system
Reflexes can be intrinsic (short reflexes) or extrinsic (long reflexes), involving the CNS as an integration center
Short and long reflexes can occur simultaneously

GI Tract Anatomy

Composition of saliva:
- 97-99.5% water, hypoosmotic
- Slightly acidic to neutral pH
- Electrolytes: Na+, K+, Cl-, PO43-, and HCO3
- Digestive enzymes: salivary amylase and lingual lipase
- Proteins: mucin, lysozyme, defensins, and IgA
- Metabolic waste: urea and uric acid
Control of salivation:
- Intrinsic glands secrete saliva continuously
- Food ingestion activates extrinsic glands
- Salivation is mainly controlled by the parasympathetic division of the ANS
- Dehydration inhibits salivation

Movements of the Small Intestine

Mixing contractions: segmentation, important for mixing and absorption
Propulsive contractions: responsible for the majority of chyme movement
Migrating motility complexes: remaining amount of chyme is removed

Motility

Mixing contractions (segmentation):
- Localized contractions mix chyme with intestinal secretions and bring it into repeated contact with intestinal absorptive epithelium
- Under the control of slow waves and excitatory activity of the nervous system
Propulsive movements:
- Peristaltic waves propelled by enteric nervous system, autonomic nervous system, and hormones
- Arrival at the ileocecal valve prevents the return of fecal content into the small intestine
Migrating motility complexes (MMCs):
- Important for the removal of remaining chyme from the small intestine

GI Tract Layers

Mucosa: most inner, moist epithelial layer that lines the lumen of the alimentary canal
- Epithelium, lamina propria, muscularis mucosae
- Functions: secretion of mucus, absorption of end products of digestion, protection against infectious disease
Submucosa: dense connective tissue containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves
Muscularis externa: circular muscle and longitudinal muscle, plexus, responsible for segmentation and peristalsis
Serosa: outermost layer, protective, replaced by adventia in esophagus

Oral Cavity

Involves ingestion and initial digestion of food
Accessory organs: teeth, salivary glands, and tongue
Epithelium of gum and hard palate is slightly keratinized for protection against abrasion
Releases antimicrobial peptides: defensins

Pharyngeal-Esophageal Phase

Larynx pulled upward and respiration briefly inhibited
Epiglottis swings backward over the opening of the larynx
Tongue blocks off mouth to prevent passage of food into the trachea
Pharyngeal muscles contract and the upper esophageal sphincter relaxes
Rapid peristaltic wave to allow food processing into the esophagus

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Description

This quiz covers the structure and function of the myenteric plexus, also known as the plexus of Auerbach, including its role in peristaltic movement and GI tract motility. Learn about its location and importance in the digestive system.