GI 1 - Mastication and Deglutition.doc

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McMaster University
Health Sciences
Cale Zavitz

G.I. 1: Mastication and Deglutition Mastication: the process of chewing your food. Deglutition: the process of swallowing. Peristalsis: alternating waves of muscle contraction and relaxation used to move food through the GI tract. Partly a property of smooth muscle. Contractions are partly regulated by the enteric nervous system (another branch of the peripheral nervous system). The Food Disassembly Line • Begin breaking down food in mouth mechanically (chewing) and chemically (breaking down complex sugars, adding other enzymes like lingual lipase- starts break down of fats) Our Journey Begins • Lower and upper lips (labia)- help keep food within oral cavity while chewing. Connected to the gums by tissue appendages- frenula • Frenula- superior and inferior labal- limit amount of mobility lips have. Horses and giraffes do not have well-developed frenula, so their lips are hyper mobile. • Lingual frenulum- on inferior surface of tongue, limits its posterior movement. Two little openings at base for submandibular gland. • Submandibular gland- under bone of mandible, produces saliva, controlled by CN VII- Facial nerve (also conveys sensations from anterior 2/3 of tongue) • Soft palate in back • Uvula- "grape"- part of soft palate, responsible for closing off nasal cavity while swallowing • Palatoglossal arch- from palate above to tongue • Palatopharyngeal arch- behind palatoglossal- in between two arches find mucosal associated lymphoid tissue (MALT)- these are the tonsils • Tonsils- modified lymphoid organ sitting in mucous membrane or oral cavity- good place for immediate pathogen response Gustation: to taste • Taste is provided by taste buds sprinkled throughout tongue- found in raised projections on the tongue- papilla- named for shape of raised projection • Vallate papilla- largest ones- formed in "V" fashion- 12 each will have 100-300 taste buds • Fungiform papilla- raised projections that look like mushrooms- scattered over tongue, each containing 5 taste buds • Filliform papilla- look like flames- makes a rough surface on tongue to create friction with food- cats have well pronounced filliform papilla- no taste buds • Foliate papilla- degenerate as we get older (around puberty)- well developed in childhood- accounts for changes in taste as you get older- in lateral margins of tongue • Taste receptors or gustatory receptor cells- specialized sensory cells that provide taste- modified neuronal cells that constantly renew themselves- cycle takes about 10 days- synapse with a sensory neuron (e.g. tip of tongue with CN VII) to send their signal up to primary gustatory cortex in temporal lobe • Most sensations pass through the thalamus (all but smell), so there is a relay for CN VII going through thalamus and on to primary gustatory complex • There are 5 primary tastes: sweet, bitter, salty, sour, and umami (savoury) • Most of approximately 10,000 taste buds are found on the tongue • 3 Cranial Nerves involved • Facial (VII)- anterior 2/3 of tongue • Glossopharyngeal (IX)- posterior 1/3 • Vagus (X)- throat and epiglottis- additional taste receptors associated with superior surface of epiglottis and throat Olfaction as well! • Taste is combined with smell • CN I- Olfactory Nerve- example of Central Nervous system escaping boney confines of skull (retina was other example)- cell bodies of neurons are sitting in mucous membrane of nasal cavity-they are specialized to detect odourant molecules- only way to do this is if the molecules get dissolved in liquid medium- this is why it's very important to have cells associated with this (mucous gland and cells) to produce a liquid barrier so that we can sense molecules- smoking will dry out nasal membrane and you will lose sense of smell for a few days until neurons regenerate • Smell will go through Olfactory tract- one sensation that does not relay through the thalamus- goes through another relay to help produce smell memory- mamillary bodies Then We Chew • Incisors- cutting (8) • Canines- tearing (particularly meat) (4) • Premolars- crushing (8) • Molars- grinding (12) • 32 teeth, including wisdom teeth • Deciduous- lose early on • Permanent- migrate and push out deciduous teeth • Wisdom teeth- In the past, we would have probably lost a few teeth, so when wisdom teeth grew in, there was room for them- Nowadays, mandible or maxilla cannot accommodate wisdom teeth and they cause problems- tooth could impact (erupt halfway through gums and stop)- leaves flappy gum on top of tooth, perfect place for food to accumulate and bacteria to grow- potential for abscess-why dentists remove wisdom teeth A Closer Look (at teeth) • Crown- top of tooth that we can see • Neck- region where tooth gets smaller (like other bones) • Root- embedded in bone of mandible and maxilla- held in place by dental ligaments • Dentin- contains a lot of calcium, more than bones supporting weight- 75% calcium cells (calcium phosphate, calcium carbonate)- makes it very strong • Enamel- 95% calcium- hardest substance in body, can almost cut glass (not encouraged) • Living part is inside (like red marrow) • Each tooth serviced by a neurovascular bundle- artery, vein, nerve • Trigeminal nerve (CN V)- conveys sensation of toothache- trigeminal has three branches- opthalmic up to eye (sensations from cornea), maxillary, and mandibular branch • Ligaments holding teeth will loosen as permanent dentition comes in- also loosen up in scurvy- pirates (gummy sailors)- because collagen in dental ligaments requires vitamin c to reproduce- if you don't have sufficient vitamin C through diet, ligaments will weaken and tooth will pop out Mastication: to chew • Mastication requires: ⁃ Teeth, tongue, cheek- muscles within cheek and tongue to keep food on small working surface of teeth while chewing ⁃ Saliva- helps to moisten food to make going down esophagus easier (less friction)- contains enzymes that help chemical digestion ⁃ Muscles of Mastication- muscles associated with moving mandible up toward maxilla- skeletal muscle • Partly voluntary and partly reflex (stretch receptors in cheeks)- muscles of mastication are skeletal muscle- but there are a lot of patterns stored in basal ganglia that help coordinate muscles of mastication • Swallowing- only a third of that response is voluntary, the rest is taken care of by deglutition centre in brain stem Tongue: Intrinsic Muscles • Muscles connect to connective tissue of tongue • Help change the shape of tongue • Cannot help stick tongue out • Longitudinal Muscles- run the length of the tongue- Superior and Inferior group- when they contract, tongue gets shorter • Transverse muscles- from side to side- Superior and Inferior group- when they contract together, tongue gets skinnier- if Superior act alone, tongue curls • Vertical Muscles- flatten tongue out Tongue: Extrinsic Muscles • Insert on tongue and connect to bone- named after attachments • Hyoglossus- inserts on tongue, attaches to hyoid bone (free floating bone in front of larynx- attached by ligaments to cartilage of larynx)- when it contracts, allows you to pull base of tongue down towards floor of mouth • Styloglossus- attaches to styloid process (pen shaped process in front of mastoid process)- attached to base of tongue- when it contracts, elevates tongue towards upper palate- useful in swallowing • Genioglossus- attaches to base of tongue and anterior aspect of mandible- when contracted, allows you to stick out (protract) tongue • All controlled by CN XII- Hypoglossal nerve • Hyoid bone- useful for
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