Gastrointestinal System + Neurophysiology Flashcards
Why do we have a digestive system?
We need nutrients (chemical energy, building new body tissues, repair damaged tissues)
Foods need to be broken down into smaller molecules to be absorbed by cells
Digestive system optimised for processing food (extensive surface area, in contact with external environment)
What is the gastrointestinal tract (GI) tract?
A continuous tubular system
Extends from mouth to anus
5-7 metres long
Physiological barrier between the outside world and the body
Segmental heterogeneity (different parts adapted for different functions)
What are the 6 processes of the digestive system?
Ingestion
Secretion
Motility
Digestion
Absorption
Defecation
The mucosa layer of the GI Tract is a mucous membrane.
It is formed of 3 layers. What are they?
- Epithelial Layer - direct contact with contents of GI tract. Simple columnar epithelium with tight junctions to restrict leakage. Exocrine cells secrete mucus and fluid. Enteroendocrine cells secrete hormones
- Lamina Propria
Connective tissue. Blood and lymphatic vessels for nutrient absorption. Mucosa associated lymphatic tissue MALT - Muscularis mucosae
Smooth muscle fibres. Creates folds in the mucous membrane
What are the layers 2-4 of the GI Tract?
Submucosa
Muscularis
Serosa
What are the accessory organs of the GI tract?
Teeth
Tongue
Salivary glands
Liver
Gall bladder
Pancreas
Digestive system is composed of the … and …
GI tract
Accessory organs
What does the GI tract include?
Mouth, pharynx, oesophagus, stomach, small intestine, large intestine and anus
What 4 layers is the GI tract composed of?
Mucosa
Submucosa
Muscularis
Serosa
What are the functions of the stomach?
Mix saliva, food and gastric juice = CHYME
Act as a reservoir for food before release into small intestine
Secrete gastric juice
Digestion starts - protein, triglycerides…
Secrete gastrin into blood (peptide hormone, stimulates secretion of gastric juice)
What is gastric juice composed of?
HCL - kills bacteria and denatures protein
Pepsin - start protein digestion
Intrinsic factor - absorption of vitamin B12
Gastric lipase - digestion of triglycerides
What cells make up the gastric pits?
Surface mucous cell - secretes mucus
Mucous neck cell - secretes mucus
Parietal cell - secretes hydrochloric acid and intrinsic factor
Chief cell - secretes pepsinogen and gastric lipase
G cell - secretes the hormone gastrin
Movement through the stomach is driven by 3 processes. What are they?
Propulsion - peristaltic wave moves gastric contents from body to antrum
Retropulsin - food particles too large to fit through pyloric sphincters. Forced back into body of stomach
Gastric emptying - chyme passes through pyloric sphincter. 3ml chyme at a time.
What is the small intestine?
Adapted for digestion and absorption
Large surface area (circular folds, villi, microvilli)
Three regions (duodenum, jejunum, ileum)
What are the functions of the small intestine?
Segmentations - mix chyme with digestive juices. Bring food into contact with mucosa for absorption
Peristalsis - propels chyme through small intestine
Digestion’s - completes digestion of carbohydrates, proteins and lipids. Starts and ends nucleic acid digestion
Absorption - 90% nutrients and water passing through digestive system
Peyer’s patches in the ileum are located in the lamina propria layer of the mucosa.
What are their function?
GALT - gut associated lymphoid tissue
They catch microorganisms and other antigens entering the intestinal tract. Dendritic cells, B lymphocytes and T lymphocytes
Peyer’s patches are covered by a special epithelium that contains micro fold cells (M cells)
What do Brunner’s glands in the duodenum do?
Secrete alkaline mucus
Neutralises gastric acid in the chyme
Where does most of the digestion and absorption take place?
Small intestine
What are the Teniae Coli of the large intestine?
3 bands of thickened longitudinal muscle
Separated by portions of the wall with less or no longitudinal muscle
Tonic contractions gather the colon in pouches called HAUSTRA
What is the function of the large intestine?
Haustral churning and peristalsis
Drive contents into rectum
Bacteria are present in large intestine (micro biome). Convert proteins to amino acids. Breakdown amino acids. Produce some B vitamins and vitamin K
Absorption of some water, ions and vitamins
Formation of faeces
Chyme in the large intestine for 3-10 hours
Defecation
What are the 4 major regions of the large intestine?
Cecum, colon, rectum and anal canal
What cells make up the small intestine?
Absorptive cell - digests and absorbs nutrients
Goblet cell - secretes mucus
Enteroendocrine cell - secretes hormone secretin, cholecystokinin or GIP)
Paneth cell - secretes lysozyme abs is capable of phagocytosis
What cells make up the large intestine?
Absorptive cell - absorbs water
Goblet cell - secretes mucus
What does the mouth do / what does it contain?
Mechanical digestion - mastication. Food > bolus
Salivary glands - food dissolves. Amylase = digestion of starch
Swallowing - extrinsic and intrinsic tongue muscles
The pharynx is a funnel shape tube with skeletal muscle lined by a mucous membrane.
What does it consist of?
3 parts
Nasopharynx - respiratory function
Oropharynx + Laryngopharynx - respiratory and digestive function
Swallowed food goes from mouth to Oro and Laryngo
What is deglutition (swallowing)?
Movement of food from mouth to stomach (via pharynx and oesophagus)
3 stages of swallowing:
Voluntary - into oropharynx
Pharyngeal - into the oesophagus
Oesophageal - into the stomach
What is the central nervous system CNS?
Brain and spinal cord
What is the peripheral nervous system PNS?
Nerves and ganglia OUTSIDE the CNS. Connect the CNS to the limbs and organs
Somatic nervous system - voluntary muscular.
Autonomic nervous system - largely unconscious. Smooth muscle and glands
What is the autonomic nervous system?
Sympathetic ‘fight or flight’
Parasympathetic ‘feed and breed’ or ‘rest and digest’
Enteric nervous system - GI tract
What does the myenteric plexus regulate?
GI tract motility
What does the submucosal plexus regulate?
Regulates GI secretion
What do parasympathetic fibres of GI tract do?
Increase GI tract secretion and motility
Increase activity of ENS neurons
What do sympathetic fibres of GI tract do?
Decrease GI tract secretion and motility
Inhibit ENS neurons
Neural regulation is a gastric phase of digestion where food enters the stomach.
What else happens?
Stretch receptors stimulated by gastric distension
Chemoreceptors activated if pH increases with protein
Nerve impulses to the submucosal plexus (secretions)
Negative feedback loop
What are the stages of gastric phase of digestion?
- Food enters the stomach. Ph increases and activates chemoreceptors. Stomach walls are stretched and activates stretch receptors
- Nerve impulses sent to submucosal plexus. Parasympathetic neurons activated. OUTPUT: stomach (parietal cells, smooth muscle)
- Parietal cells secrete HCL. Smooth muscle contracts
- Increase in acidity of stomach chyme. Stomach contents are mixed. Stomach empties.
- Negative feedback loop. pH reduces. Stomach returns to pre eating state
Gastrin is released from the G cells of the gastric glands in response to:
Distension of the stomach by chyme
Partially digested proteins in chyme
High pH of chyme due to the presence of food in the stomach
Caffeine in gastric chyme
Acetylcholine released from parasympathetic neurons
Gastrin is released into bloodstream and stimulates gastric glands which:
Secrete large amounts of gastric juice
Strengthens the contraction of lower oesophageal sphincter
Prevents reflux of acid chyme into oesophagus
Increases motility of stomach
Relaxes the pyloric sphincter to promote gastric emptying
Gastrin secretion is inhibited when… and is stimulated when…
It ensures optimal low pH for…
pH of gastric juice drops below 2.0
pH rises
Functioning of pepsin, killing of microbes, denaturing of proteins in the stomach
Smooth muscle contractions are initiated at the Interstitial cells of Cajal (pacemaker).
What do they generate?
Spontaneous electrical slow waves
Slow waves differ between regions. What do slow waves generate?
Phasic contractions - Peristalsis
Peristaltic wave moves gastric contents from body to antrum (propulsion)
What is absorption?
What substances can be absorbed without undergoing digestion?
Movements of products via digestion from lumen of GI tract into blood or lymph
Water, vitamins, ions, cholesterol
The small intestine has less … so more …
Tight junctions
Paracellular movement
What is passive transport of molecules?
No energy required
Moving down the concentration gradient
Diffusion - simple / facilitated
Transmembrane proteins
What is active transport of molecules?
Energy required
Move against concentration gradient
ATP hydrolysis - ATPase Na+ / K+ exchange
Ion gradient - energy released during movement of inorganic ion down a gradient
Pump solutes against their gradient - anti Porter, symporter
What is the importance of sodium and potassium?
Two primary electrolytes
Important for maintaining fluid balance in the body
Blood pressure
Nerve and muscle function
What are the 3 mechanisms of sodium absorption from the lumen?
Co transport with nutrients (1 glucose: 2 Na+)
In exchange for H+
Specific sodium channels
What happens during sodium transport?
Na+ actively transported out of absorptive cells
Basolateral sodium potassium pumps (Na+ - K+ ATPases)
Most of Na+ ions in GI secretions are reclaimed (not lost in faeces)
What happens during potassium transport?
Small intestine absorbs potassium
Large intestine secretes potassium
Potassium balance regulated by aldosterone
Loss of potassium in faeces
What is aldosterone?
Mineralcorticoid
Secreted by adrenal cortex
Regulates homeostasis of Na+ and K+
Water is bi directional, moves due to osmosis, diffusion and through aquaporins.
What is the paracellular and trans cellular route?
Paracellular - between cells. Through tight junctions. SLOW
Transcellular - through cells. Water channels. Aquaporins increase trans cellular flux. FAST
Summary of Sodium:
Sodium absorption is efficient with only 0.5% of intake lost in faeces
Primary mechanism for absorption - coupled transport to movement of glucose, amino acids and fatty acids after a meal
Absorbed sodium rapidly leaves the basolateral side of the cell (sodium pumps)
Increases the osmolarity in the intracellular space
Summary of potassium:
Small intestine absorbs potassium
Large intestine secretes potassium
Potassium balance regulated by aldosterone
Summary of water:
Diffuses in response to osmotic gradient established by sodium
Most movement is trans cellular through aquaporins
What are the dietary carbohydrates?
Monosaccharide - glucose, fructose, galactose
Disaccharide - maltose, sucrose, lactose
Polysaccharide - starch
Most carbohydrates we eat are starches
Only monosaccharides can be absorbed into bloodstream
Ingested disaccharides and starch must be broken down into monosaccharides
Starch is a polysaccharide of glucose monomers joined by glycosidic bonds.
What are amylose and amylopectin?
Amylose - linear polymer. 200-1000 glucose units
Amylopectin - branched polymer. 2000-200 000 glucose units.
Increased surface area.
High in rice, potato and sweet potato.
Glycogen (storage in animal tissues) has same structure
What is the carbohydrate digestion pathway?
Mouth to stomach (not all starch is broken down in mouth, food swallowed too quickly)
Salivary glands
Salivary amylase continues to act on swallowed food for -1hr
Stomach acid (low pH) inhibits enzymatic activity
Breakdown of starch into:
Maltose - disaccharide
Maltotriose - trisaccharide
a dextrin - short chain glucose polymer
What bonds is a dextrin linked by?
D glucose units linked by a (1-4) or a (1-6) glycosidic bonds
What is the purpose of the liver in the carbohydrate digestion pathway?
Maintains normal blood glucose level
Low: breakdown glycogen to glucose. Convert certain amino acids, lactic acid, fructose and galactose to glucose
High: glucose to glycogen and triglycerides for storage
What is the purpose of the small intestine in the carbohydrate digestion pathway?
Intestinal juice
Absorptive cells synthesise several digestive enzymes:
Brush border enzymes, plasma membrane of microvilli, a dextrinase, maltase, sucrase, lactase
Absorption of monosaccharides:
120g/h of monosaccharides absorbed in the …
All dietary carbohydrates absorbed except … and …
Small intestine
Cellulose
Fibre
How is fructose absorbed?
How are glucose and galactose absorbed?
Facilitated diffusion
Secondary active transport
What is the purpose of the large intestine in the carbohydrate digestion pathway?
Bacteria - ferment any remaining carbohydrates. Hydrogen, carbon dioxide and methane gas
Mumps is inflammation and enlargement of the parotid glands.
What is cause, symptoms and treatment?
Cause: mumps virus (paramyxovirus)
Symptoms: moderate fever, extreme pain in the throat, swelling on side of face
Treatment: vaccine
Gastro oesophageal reflux disease GORD is where the stomach contents reflux into oesophagus.
What is cause, symptoms and treatment?
Cause: lower oesophageal sphincter fails to close properly after food enters stomach
Symptoms: burning sensation in oesophagus (heartburn)
Hydrochloric acid HCL
Treatment: avoid drinking alcohol and smoking. Antacids. Avoid foods that stimulate stomach acid secretion - coffee, chocolate, orange juice
What is the mechanism of vomiting?
Nerve impulses to medulla oblongata
Returning impulses result in squeezing the stomach between diaphragm and abdominal muscles
Contents expelled through open oesophageal sphincters
Prolonged vomiting can be serious. Why?
Loss of gastric acid juice = alkalosis (higher than normal blood pH). Dehydration. Damage to the oesophagus and teeth
Pancreatitis is inflammation of the pancreas.
What is cause, symptoms and treatment?
Cause: primary - alcohol abuse (70% of cases). Chronic gallstones.
Mechanism: heavy alcohol intake or biliary tract obstruction, pancreatic cells release trypsin. Trypsin begins to digest pancreatic cells.
Treatment: fluids, oxygen, painkillers. Long term avoid alcohol, diet, surgery
Hepatitis is inflammation of the liver.
What is cause, symptoms and treatment?
There is Hepatitis A, B, C, D, E
Causes: viruses, drugs, chemicals, alcohol
Treatment: Vaccines
Peptic ulcers are are lesion in the GI tract membrane.
What is cause, symptoms and treatment?
Cause: helicobacter pylori bacteria - urease enzyme splits urea into ammonia and CO2, ammonia shields bacterium from acidity and damages mucosal layer
NSAIDS
Hypersecretion of HCL
Treatment: avoid smoking, caffeine, alcohol, antibiotics. Proton pump inhibitors eg. Omeprazole blocks secretion of H+ from parietal cells (HCL hypersecretion)
Crohn’s disease is inflammation of the GI tract. A chronic condition.
What is cause, symptoms and treatment?
Symptoms: diarrhoea, stomach aches and cramps, blood in stool, fatigue, weight loss
Causes: autoimmune, smoking, genetics
Treatment: immunosuppressants eg steroids. Surgical procedures
Diarrhoea is increase in frequency, volume and fluid content of faeces
What is cause, symptoms and treatment?
Outcome: dehydration, electrolyte imbalances
Causes: lactose intolerance, stress, microbes irritating gastrointestinal mucosa
Constipation is infrequent or difficult defection.
What is cause, symptoms and treatment?
Mechanism: decreased motility of intestines, faeces remain in colon for prolonged periods, excessive water absorption leading to dry and hard faeces
Causes: poor habits, colon spasms, insufficient dietary fibre and fluid intake
Treatments: mild laxative eg milk of magnesia, increase dietary fibre and fluid intake
Why do we have biological clocks?
Anticipate and prepare for predictable environmental changes
Optically synchronised with the environment
Adapt to changing environments
What does circadian mean?
Circadian: drive 24hr rhythms in physiology and behaviour
What are rhythms in physiology?
Lung function
Cardiovascular
Muscle function
Metabolism
Sleep deprivation can be…
Acute - single night of sleep loss
Chronic - persistently short sleep episodes
Health risks in shift work? (Night shifts etc)
Obesity and weight gain
Type 2 diabetes
Coronary heart disease
Breast, prostate and colorectal cancer
Occupational accidents
Sleep restriction affects metabolism by:
Impairs glucose tolerance
Reduced acute insulin response
Risk factor: diabetes, obesity, hypertension
The appetite hormones:
What is ghrelin?
Leptin?
Ghrelin - produced by enteroendocrine cells of GI tract (stomach). Hunger hormone. Highest levels before meals
Leptin - adipose cells and enterocytes in small intestine. Inhibits food intake. Increases energy expenditure.
How does sleep restriction affect appetite?
Sleep restriction for 2 days: increases ghrelin, decreases leptin
Increased food intake
Decreased energy expenditure
Proteins are polymers of amino acids linked via peptide bonds.
Describe primary, secondary, Tertiary, quaternary structure.
Primary - linear (not branched) chain with defined amino acid sequence
Secondary - local folding of peptide chain (alpha helix,beta pleated sheet)
Tertiary - overall 3D structure
Quaternary - interaction of multiple proteins in complexes
What are the proteolytic enzymes, exopeptidase and endopeptidases?
Exopeptidase enzymes - carboxy or amino peptidases. Liberate free amino acids
Endopeptidases - liberate smaller peptide chains
The digestion of proteins involves the mechanical disruption by chewing and gastric motility. What else does it involve?
Protein denaturation by HCL
Combined effect of chemical and enzymatic digestion
Stomach is where enzymatic digestion of proteins begins. What is the role of pepsin there?
Secreted by chief cells. Most effective in the very acidic environment of the stomach (around pH2). Becomes inactive at higher pH
Cleaves certain peptide bonds between amino acids. Breaks peptide bonds adjacent to phe, try, tyr, aps, glu, leu, met
What prevents pepsin from digesting the protein in stomach cells?
- Pepsin is secreted in an inactive form = pepsinogen. Pepsinogen is converted into active pepsin when it comes into contact with HCL secreted by parietal cells + active pepsin molecules.
- Stomach epithelial cells protected from gastric juices. Later 1-3mm thick of alkaline mucus. Secreted by surface mucous cells and mucous neck cells
The small intestine contains pancreatic juice in an inactive form to protect the pancreas.
How?
Trypsin secreted in an inactive form called trypsinogen
Pancreatic acinar cells secrete trypsin inhibitor
Blocks enzyme activity of any trypsin formed accidentally in the pancreas or in pancreatic juice
How are proteins digested in the small intestine?
Trypsinogen reaches the lumen of the small intestine. Activates brush border enzyme = enterokinase. Splits off part of trypsinogen = trypsin
Trypsin acts on other inactive precursors:
Chymotrypsinogen = chymotrypsin
Procarboxypeptidase = carboxypeotidase
Proelastase = elastase
How is protein digestion completed by 2 peptidases in the brush border?
Aminopeptidase - cleaves off the amino acid at the amino end of a peptide
Dipeptidase - splits dipeptides (two amino acids joined by peptide bond) into single amino acids
Most proteins are absorbed as amino acids via active transport process in duodenum and jejunum.
Where are these absorbed AA found?
50% of absorbed AA are present in food
50% from the body - proteins in digestive juices + dead cells sloughed off mucosal surface
95-98% of the protein present in the small intestine is digested and absorbed
How are proteins absorbed?
Na+ dependant amino acid transport
H+ co transport with small peptides
Larger peptides moved by transcytosis
Amino acids are transported in blood to … (hepatic portal system)
Hepatocytes … (remove NH2) amino acids
Toxic ammonia NH3 converted to mixh less toxic … (excreted in the urine)
Hepatocytes … most plasma proteins - alpha and beta globulins, albumin, prothrombin and fibrinogen
Liver
Deaminate
Urea
Synthesise
How is the mouth involved in lipid digestion?
Lingual glands in the lamina propria of tongue
Secrete mucus and lingual lipase
Acts on 30% of dietary triglycerides (fats and oils)
Converts them to simpler fatty acids and diglycerides)
How is the stomach involved in lipid digestion?
Chief cells
Gastric lipase - operates best at pH 5-6
Splits triglycerides into fatty acids and monoglycerides.
Monoglyceride = glycerol molecule + one fatty acid molecule
How is the small intestine involved in lipid digestion?
Most lipid digestion occurs here
Pancreatic juice - pancreatic lipase
Bile salts - emulsification
Triglycerides broken down into fatty acids and monoglycerides
Short chain fatty acids = fewer than 10-12 carbons. Hydrophilic - more water soluble.
Long chain fatty acids - hydrophobic = not water soluble
Pancreatic lipase is made up of 3 different enzymes what are they?
Triglycerol hydrolase
Cholesterol ester hydrolase
Phospholipase A2
What is the action of pancreatic lipase?
(Triaglycerol hydrolase)
Specific for 1st and 3rd ester bonds
Maximal enzymatic efficiency requires:
Colipase - stabilises active catalytic site, prevents inactivation by bile salts
Alkaline pH
Bile acids for emulsification
Bile salts are sodium and potassium salts of bile acids.
They are amphipathic what does this mean?
What does emulsification mean?
Amphipathic - hydrophobic non polar region
Hydrophilic polar region
Emulsification - hydrophobic region interacts with large lipid globule
Hydrophilic region interacts with watery intestinal chyme
Large lipid globule broken apart into several small lipid globules (1um in diameter)
Emulsification is crucial for … the surface area for … action
Increasing
Lipase
What are micelles and what do they do?
Increase solubility
20-50 bile salt molecules
Hydrophobic regions of bile salts interact with fatty acids and monoglycerides
Hydrophilic regions interact with watery intestinal chyme
Summary of lipid digestion:
Emulsification by…
Formation of mixed …
Micelle breaks down close to … low pH of acid microclimate zone
Fatty acids are …
Bile salts
Micelles
Luminal surface
Released
Summary of lipid absorption :
All dietary lipids are absorbed via …
Adults absorb about … of lipids present in small intestine
Small short chain fatty acids pass through absorptive cells via …
Micelles move to … of absorptive cells
Long chain FA and monoglycerides diffuse out of cell into …
Micelles remain in …
Micelles continually repeat … function
- pick up more short chain, long chain FA and monoglycerides
Micelles also solubilise other large … molecules. Fat soluble vitamins (A,D,E,K) and cholesterol.
Simple diffusion
95%
Simple diffusion
Brush border
Absorptive cells
Chyme
Ferrying
Hydrophobic
What happens inside absorptive cells - lipid absorption?
Long chain FA and monoglycerides combine to = triglycerides
Aggregate into globules along with phospholipids and cholesterol to become coated with proteins
Chylomicrons - large spherical masses. Leave absorptive cells via exocytosis - cannot enter blood capillaries as too large!
What does the hydrophilic protein coat do in lipid absorption?
Keeps chylomicrons suspended in blood, prevents them from sticking to eachother
Within 10 minutes 50% chylomicrons have been removed from blood
2-3 hours after a meal few chylomicrons remain in the blood
What does lipoprotein lipase do?
Breaks down triglycerides in chylomicrons and other lipoproteins into fatty acids and glycerol
What is enterohepatic circulation?
What happens when there’s insufficient bile salts?
Most bile salts are reabsorbed by active transport in the iluem
Returned by the blood to the liver through hepatic portal system
Re secreted into bile
Insufficient bile salts - obstruction of bile ducts, removal of gall bladder, diminished lipid absorption, loss of up to 40% of dietary lipids in faeces
What happens during lipid metabolism in the liver?
Hepatocytes store some triglycerides
Break down fatty acids to generate ATP
Synthesise lipoproteins - transport FA, triglycerides and cholesterol to and from body cells
Synthesise cholesterol
Use cholesterol to make bile salts
What is the importance of healthy fats in the diet?
Delay gastric emptying - helps a person feel full
Enhance the feeling of fullness by triggering the release of CCK
Necessary for absorption of fat soluble vitamins
Amino acids are processed by the …
Liver
Dietary fat consists mainly of …
Triaglycerol
Majority of lipid digestion involves:
Pancreatic enzymes
Bile
Bile salts are critical for forming …
Micelles
Absorbed lipids form into … within the enterocyte are are released into the lacteals
Chylomicrons
What is cholecystokinin CCK and what is it released in response to?
Released from CCK cells of intestinal glands in small intestine
Released in response to chyme containing - amino acids (partially digested proteins) and fatty acid (partially digested triglycerides)!
What does cholecystokinin CCK simulate?
Satiety via hypothalamus
Slows gastric emptying - contraction of pyloric sphincter
Secretion of pancreatic juice (digestive enzymes)
Contraction of the wall of the gallbladder
Promotes normal growth and maintenance of the pancreas
Enhances the effects of secretin
Secretin is released from S cells of intestinal glands in small intestine.
What is it released in response to?
Acidic chyme entering the duodenum
What does secretin do?
Inhibits secretion of gastric juice
Increases flow of pancreatic juice - high in bicarbonate HCO3- ions to buffer acidic chyme
Promotes normal growth and maintenance of the pancreas
Enhances the effects of CCK
What are segmentations?
(Small intestinal motility)
Portions of intestine distended by chyme
Do NOT push contents along the tract
Localised, mixing contractions
Mix chyme with digestive juices
Bring food into contact with mucosa for absorption
Speed varies
Duodenum = 12 per minute
Iluem = 8 per minute
Peristaltic contractions are responsible for … in small intestine.
Forward movement
What are the phases of the migrating motor complex?
Phase 1: quiescence
Phase 2: intermittent and irregular activity
Phase 3: short period of intense activity
Phase 4: quiescence
What are the general principles of GI tract motility?
All segments have 2 forms of motility: mixing and propulsion
Main stimulus for contraction is distension: enteric nervous system
Distension in the region of GI tract immediately before a sphincter causes it to open - otherwise it’s toncially contracted
Distension and absorption in 1 segment will inhibit contraction and motility in preceding segment
Eg SI activity inhibits the stomach.
Makes the gut more energetically efficient
What are the 3 phases of secretion in the GI tract?
Cephalic Phase: pre ingestion and food in mouth
Gastric phase: food in stomach
Intestinal phase: food in small intestine
What is the cephalic phase?
Initiated when receptors in the head (cephalic) are stimulated - thought, sight, smell and taste of food
Involves parasympathetic nervous system
Prepares body for influx of food
‘Pavlov’s Dog’
What secretions are stimulated during cephalic phase?
FEED FORWARD MECHANISM
Salvia production
Gastric acid
Gallbladder contraction - releasing bile into SI
Exocrine pancreatic secretions - releasing HCO3 and enzymes into SI
What happens during the gastric phase?
Food now in the stomach
Secretion of HCL
Pepsinogen (protease enzyme)
Intrinsic factor - to allow ileal abosrption of vitamin B13
Production of the mucus bicarbonate layer
What is the purpose of HCO3 - and prostaglandins in the gastric phase?
HCO3 - creates a micro environment around surface cells to prevent damage
It is inhibited by sympathetic NS
Prostaglandins - increase mucus production. Inhibition of enzymes of prostaglandin production results in gastric damage eg NSAIDS
What is the intestinal phase?
Inhibition of gastric acid secretion
HCO3- secretions neutralise acidic chyme from stomach
Bicarbonate can come from pancreas and duodenal brunners gland
Secretion of digestive enzymes (pancreas) and bile (liver)
What does pancreatic exocrine secretion contain?
Acini clusters contain Zymogen granules with digestive enzymes
Pancreatic juice, watery solution of enzymes and HCO3-
Proteases secreted in an inactive form to prevent auto digestion
Amylase (starch) and lipases (Triaglycerol) secreted in ACTIVE form
What are primary bile salts?
What is bile fluid?
Synthesised from cholesterol in hepatocytes
Cholic acid
Chenodeoxycholic acid conjugated with glycine or taurine - secreted as Na+ salts which increase solubility
Bile fluid - watery secretion
Contains HCO3- from epithelial cells lining the bile canaliculi
What is enterohepatic circulation?
Bile salts released into small intestine
Little reabsorption from duodenum or jejunum
90-95% reabsorbed from ileum (passive + active)
Bile salts returned to liver via portal vein and taken up by hepatocytes and re secreted
Bile salt pool recycled up to 10 times per day, at least 3-8% lost in faeces per day
Secondary bile salts are formed by bacteria by dehydroxylation of primary bile salts.
Examples?
Deoxycholate from cholic acid
Lithocholate from chenodeoxycholic acid - poorly absorbed, TOXIC
3 reasons why the body needs nutrients
Energy
Building
Repair
Name 3 accessory organs to the GI tract
Salivary glands
Tongue
Teeth
Two functions of the stomach
Produce chyme, act as a reservoir, produce gastric juice, secrete gastrin
Four components of gastric juice
HCL
Pepsin
Gastric lipase
Intrinsic factor
What structures in small intestine increase surface area
Circular folds
Villi
Microvilli
What is function of segmentations
Mix chyme with digestive juices
Bring chyme into contact with mucosa for absorption
What is located in Peyer’s patches?
Gut associated lymphoid tissue
What are the 3 stages of swallowing?
Voluntary
Pharyngeal
Oesophageal
What does the myenteric plexus layer of the enteric nervous system control?
GI tract motility
What receptors are activated when food enters the stomach?
What are the 2 outcomes of this activation?
Stretch and chemoreceptors
Increased secretion of HCL and stomach wall contractions
What impact does gastrin have on sphincter muscles?
Lower oesophageal contraction strengthens, pyloric relaxes
Where are the spontaneous slow waves initiated in the stomach?
Interstitial cells of Cajal
What are the 2 actions of CCK?
Indicate satiety
Slows gastric emptying
Secretion of pancreatic juice
What is the function of the mucosal layer in the stomach?
Protect against damage - from HCL and pepsin
What does sensation mean?
The conscious or subs conscious awareness of changes in the external or internal environment
What does perception mean?
Conscious interpretation of sensations
Primarily a function of the cerebral cortex
What are the general senses?
Somatic - tactile (touch, pressure) , thermal, pain and proprioceptive sensations
Visceral - conditions within internal organs eg stretch, chemicals, nausea, hunger
What are the special senses?
Discrete specialised organs
Eg. Smell, taste, vision, hearing and balance
Describe the process of sensation
- Stimulation of sensory receptor
- Transduction of stimulus
- Generation of nerve impulses
- Integration of sensory input
What is the microscopic structure of sensory receptors?
- Free nerve endings of first order sensory neurons
Eg pain, temperature, tickle, itch - Encapsulated nerve endings of first order sensory neurons
Eg pressure, vibration - Separate cells that synapse with first order neurons
Eg hair cells for hearing, gustatory receptors in taste buds, photoreceptors in retina of eye for vision
Where are exteroreceptors, interoceptors and propioceptors located?
Extero - located at or near external surface of body
Intero - located in blood vessels, visceral organs, muscles and nervous system
Proprio - located in muscles, tendons, joints and inner ear
Mechanoreceptors
Sensitive to mechanical stimuli eg deformation, stretching or bending of cells
Thermo receptors
Detect changes in temperature
Nocieptors
Respond to painful stimuli from physical or chemical damage to tissue
High density in skin, low density in bone, muscle, joints, blood vessels
Photoreceptors
Detect light that strikes the retina of the eye
Chemoreceptors
Detect chemicals in the mouth, nose and body fluids
Osmoreceptors
Detect the osmotic pressure of body fluids
Properties of a sensory stimulus
Modality
Location
Intensity
Duration
Phasic receptors
Rapidly adapt
Specialised for signalling changes in a stimulus
Eg pressure touch smell
Tonic receptors
Slowly adapting receptors
Continue to trigger nerve impulses as long as stimulus persists
Eg pain body composition chemical composition of blood
What is the receptive field ?
Region where presence of a stimulus will alter firing of that neuron
IMPORTANT for the discrimination of 2 stimuli
Smaller receptive fields at higher density enhance discrimination between 2 stimuli
Proprioceptive receptors
Provide info about body position and movements (kinaesthesia)
Embedded in muscles and tendons
Hair cells of inner ear
Gustation means taste. What are the 5 primary tastes?
Sweet - sugars and artifical sweetness
Sour - H+ released when acids dissolved in water
Salty - Na+ ions eg from sodium chloride
Bitter - eg caffeine, quinine, morphine
Umami - Japanese for delicious - amino acids particularly glutamate. MSG = mono sodium glutamate
Taste receptors are located in taste buds. What are the 3 types of epithelial cells found in taste buds?
Supporting cells
Gustatory receptor cells
Basal cells
Individual gustatory cells only respond to 1 type of tastant.
What are tastants?
Chemicals that stimulate gustatory receptor cells
Dissolve in saliva and make contact with gustatory microvilli
Taste transduction - depolarising receptor potential
Exocytosis of synaptic vesicles from gustatory receptor cell
How are salt receptor potentials generated?
Na+ ions enter gustatory receptor cells via Na+ channels
How are acid receptor potentials generated?
H+ ions enter gustatory receptor cells via H+ channels - depolarisation and release of NT
How are sweet, bitter and umami receptor potentials generated?
Bind to G protein coupled receptor
Activate enzymes and produce IP3 (inositol trisohosphate) leading to depolarisation
Olfaction (smell)
Olfactory receptors (1st order neurons) are located in the … of the nose
Transduction occurs at the …
Olfactory epithelium
Olfactory cilia
What are odorants?
Chemicals that bind to and stimulate receptors in the cilia
What is the lifespan of olfactory receptor cells?
2 months
Summary of Olfaction
Olfactory receptor cells are first order neurons
Receptor cells respond to one odorant
-400 functional types
Receptor potentials generated: G protein coupled receptors
What is the function of the cornea of the eye?
Physical protection
Refracting (focusing) incoming light - fine tuning is provided by the lens
What happens to pupil of the eye in bright light?
Constricts as the circular muscles of the Iris CONTRACT (parasympathetic)
What happens to the pupil of the eye in dim light?
Pupil dilates as the radial muscles of the Iris contract (sympathetic)
The lens of the eyeball
Formed of proteins called crystallins
Transparent, connective tissue
No blood vessels
Enclosed by a clear connective tissue capsule
Held in position by encircling zonular fibres
Focus images on retina to facilitate clear vision
What is myopia?
(Image formation)
Focus in front of retina
See close objects clearly but NOT distant objects
What is hyperopic?
(Image formation)
Focus behind retina
See distant objects clearly but NOT close objects
What is astigmatism?
(Image formation)
Irregular curvature of lens or cornea
Blurred vision!
What are rods?
Dim light (scotopic? Vision
Human retina has -120 million rods
What are cones?
Bright light (photopic) vision
Trichromatic colour vision
Human retina has -6 million cones
What is the fovea centralis?
Contains only cones
Area of highest visual acuity (resolution)
Photopigments
Each type of photoreceptor contains a specific photo pigment:
Rhodopsin (rods)
Red / green / blue cone pigments
Photopigment:
Opsin (glycoprotein)
Retinal (derivative of vitamin A)
Describe the process of phototransduction
- Isomerisation - cis retinal absorbs photons of light. Isomerises to trans retinal
- Bleaching - trans retinal dissociates from opsin protein. Change in opsin protein
- Conversion - retinal isomerase converts trans to cis retinal
- Regeneration - cis retinal binds to opsin protein
What happens in the dark - phototransduction?
Dark = depolarising receptor potential
Cis retinal associated with opsin
High cGMP (guanylyl Cyclase)
cGMP gated Na+ channels are open
Dark current - depolarises (-40mv)
Voltage gated Ca+ channels open
Exocytosis of synaptic vesicles
Glutamate release (inhibitory NT)
Hyperpolarises bipolar cells
No signals to ganglion cells
What happens in the light - phototransduction?
Light = hyper polarising receptor potential
Cis retinal isomerised to trans retinal
Activation of G protein - transducin
Transducin activates enzyme cGMP phosphodiesterase
Breakdown of cGMP
cGMP gated Na+ channels close
Decreased Na+ flow
Membrane potential reduces (-65mv)
Hyper polarising receptor potential
Voltage gated Ca+ channels close
Decreased NT release
Excited bipolar cells
Ganglion cells are stimulated - action potentials
Visual processing in the retina
Rods and cones are connected to 2nd order retinal neurons, bipolar cells
Bipolar cells in turn connect to 3rd order retinal neurons, ganglion cells
At both of these levels, photic info is processed and integrated
If this retinal processing did NOT take place, handling the info from the photoreceptor would exceed the capacity of the Brain!
Visual pathway
The axons of the ganglion cells leave each retina via the optic nerve
A partial crossing over of the optic nerves takes place at the optic chiasm so that info from both eyes can enter both hemispheres
Most optic nerve fibres project to the lateral geniculate nucleus
The lateral geniculate nucleus projects to the visual cortex, the centre of subjective vision
Non visual effects of light - neurophysiological
Increase core body temp
Increase heart rate
Pupillary light reflex
Non visual effects of light - neurobehavioural
Increase alertness
Increase performance
Increase mood
What does synchronising the circadian clock mean?
Resetting the effects of light!
The ear can detect changes in balance.
Receptor organs are the vestibular apparatus. What are they?
Utricle
Saccule
Semi circular ducts
The ear and balance: Hair Cells
Sensory receptors
Stereocilia of graduated height
One kinocilium (tallest)
Hair bundle = stereocilia and kinocilium
What are the columnar supporting cells of the ear?
Secrete otolithic membrane
Thick, gelatinous, glycoprotein layer
What are the otoliths of the ear?
Dense calcium carbonate crystals
What does the utricle respond to?
Linear acceleration or deceleration in horizontal direction
Eg when body is being moved in a car that is speeding up or slowing down
What does the saccule respond to?
Linear acceleration or deceleration in vertical direction
Eg when body is being moved up or down in an elevator
What happens when head tilts forward?
Otolithic membrane and otoliths are pulled by gravity
Slide over hair cells in direction of tilt
Bend hair bundles
What happens when head jerks forward?
Otolithic membrane lags behind head movement (inertia)
Bends in other direction - opens cation channels / depolarising receptor potentials
Bending in opposite direction closes the cation channels - hyperpolarisation
Hair cells depolarise and hyper-polarise which…
Release NT at a faster or slower rate
Ampulla =
Dilated portion of the duct
The vestibular apparatus is involved in…
Balance
Utricle
Linear acceleration or deceleration in horizontal direction
Head tilts forward or backward
Saccule
Linear acceleration or deceleration in vertical direction
Semi circular ducts
Rotational acceleration and deceleration
Protein digestion begins in the …
HCL denatures …
Pepsin begins …. Digestion
Stomach
Proteins
Enzymatic
Pancreatic juice is secreted into the …
Pro enzymes are …
Peptidases in …
Small intestine
Activated
Brush border
Amino acid and peptides are absorbed by three mechanisms of …
Active transport
Amino acids are processed by the …
Liver
Dietary fat consists mainly of …
Triaglycerol
Lipid digestion begins in the …(lingual lipase) and continues in the … (gastric lipase)
Mouth
Stomach
Majority of lipid digestion occurs in the … (pancreatic lipase)
Small intestine
Bile salts are … for emulsification and forming …
Critical
Micelles
Small fatty acids diffuse into … and the capillaries
Absorptive cells
Large fatty acids form into …and are released into the …
Chylomicrons
Lacteals
What are the different causes of GI tract disturbance?
Viral
Bacteria
Inflammation
Disrupted processes
Medications
Behaviours
Transport of molecules
Water - osmosis
Sodium - cotransporters, H+ exchangers, sodium specific channels
Potassium - diffusion
Carbohydrates - facilitated diffusion, cotransporters
Proteins - cotransporters, transcytosis
Lipids - diffusion
Name 2 substances that can be directly absorbed WITHOUT undergoing digestion
Water, vitamins, ions and cholesterol
Name 1 mechanism by which sodium is absorbed from the lumen
Co transporter (glucose / amino acids), hydrogen exchange, sodium channels
Where is potassium secreted?
Large intestine
Where is aldosterone secreted from
Adrenal cortex
Name a monosaccharide
Glucose
Fructose
Galactose
Where does salivary amylase act on carbohydrates?
Mouth and stomach until it is denatured by acidic environment
Where is maltase located?
Brush border of absorptive cells in small intestine
How is fructose absorbed?
Facilitated diffusion by GLUT5 and GLUT2
Which class of enzymes creates short peptide chains
Endopeptidases
What format is pepsin secreted in
Pepsinogen - activated to pepsin when in contact with HCL
What do pancreatic acinar cells secrete?
Trypsin inhibitor
What does aminopeptidase do?
Cleaves off an amino acid at the amine end of a peptide chain
How do larger peptide chains get absorbed
Transcytosis
What is a triglyceride formed of
Glycerol + 3 fatty acids
What pH does gastric lipase operate best at
pH 5-6
What 2 actions do bile salts have in the process of lipid digestion
Emulsification and micelles
How are short chain fatty acids absorbed
Simple diffusion
What issues can vomiting cause
Dehydration, alkalosis, damage to oesophagus and teeth
What causes jaundice
Build up of bilirubin
What is the treatment for Crohn’s disease?
Immunosuppressants
What is movement?
When living organisms moves a body part without a change in the position of the organism
What is locomotion?
When the movement of a part of the body leads to a change in the position and location of the organism
Movement and locomotion are both brought about by the joint efforts of… systems
Neuronal, skeletal, muscular
What is smooth muscle?
Lines the digestive tract and arteries, innervated by the autonomic nervous system
What is striated muscle?
Cardiac (heart muscle innervated by ANS) and skeletal muscle
Skeletal muscle makes the bulk of muscle in the body
Controls ALL aspects of movements: eyes, breathing, speech, move bones around joints
Motor neurons control muscle
They collect signals that initiate movement
Signals travel down axon
Neuronal signal crosses to the muscle at neuromuscular junction (chemical synapse)
Muscle contracts
What is the resting membrane potential?
When a neuron is inactive ions are asymmetrically distributed across the membrane
Outside: Na is high, K is low, Ca high, Cl - is high
Inside: Na is low, K is high, Ca is low, Cl- is low
Ionic concentrations are different because of the … inside the neuronal membrane
Active transport mechanisms
The action potentials
We can record neuronal signals by entering a neuron with a small glass pipette
We can simultaneously enter the cell with a stimulating electrode to mimic activation by injecting current
Injecting current into the cell evokes distinct electrical signatures = ACTION POTENTIALS
Each action potential is characterised by 5 phases:
Resting potential, rising phase (depolarisation), overshoot, falling phase (repolarisation), undershoot (after hyperpolarisation)
Action potential conduction
The process of rest, depolarisation, repolarisarion is dependant on the spatial arrangement of ion channels
Action potentials travel along the axon as 1 region is depolarised by excitation in the neighbouring segment
Action potential conduction confers a … from the neuronal cell body via the … to the synapse
Signal
Axon
The chemical synapse
Action potentials travel down the axon
Axon terminal forms a synapse onto another neuron (or muscle)
Electrical excitation causes release of synaptic vesicles
Neurotransmitter is released into synaptic cleft
Neurotransmitter bind to post synaptic receptors to trigger activation = action potential
Neurotransmitter - excitation actions:
Excitatory transmitter binds to post synaptic ligand gated ion channel
Ion channel mainly conducts Na
Na influx causes rapid depolarisation (excitatory)
= Excitatory post synaptic potential EPSP
Neurotransmitter - inhibition actions:
Inhibitory transmitter binds to post synaptic ligand gated ion channel
Ion channel mainly conducts chloride
Chloride influx causes rapid hyperpolarisation (inhibition)
= Inhibitory post synaptic potential IPSP
Neuromuscular junction and muscle contraction
NJ is the axon terminal of the motor neuron
Acetylcholine is the excitatory NT of the NJ
Binding of ACh to nicotinic ACh receptors causes depolarisation of the muscle and calcium release inside post synaptic muscle fibres
Muscle contracts
Muscle spindle
Sits inside muscle fibres
Covered in fibrous capsule
A stretch receptor
Innervated by la sensory neurons that feedback muscle tension
Alpha, la and gamma neurons work together
After alpha motor neuron activation, extra fusal muscle fibres TENSE
Intra fusal fibres elongate, which inhibits la sensory neurons
Gamma motor neurons fire = intra fusal neurons shorten to balance tension
What is reflex?
The simplest control of movement
A reflex is a simple perception cycle:
Perceive aversive stimuli
Activate motor neuron
Move away from stimulus
The brain is NOT involved in…
Reflexes
Example of monosynaptic stretch reflex:
(Knee jerk reflex)
Tap the tendon under the knees cap
Tendon stretches the quadriceps muscle of thigh
Muscle contracts
Leg extends
During stretch reflex:
Elongate 1 muscle and antagonist muscles must be relaxed (flexor vs extensor)
Reciprocal inhibition of antagonistic muscles by inhibitory inter neurons
The flexor withdrawal reflex:
Polysynaptic reflex
Speed of withdrawal depends on amount of pain
Direction of withdrawal depends on location of pain stimulus
Flexor reflex is slower than stretch reflex
Activated by Nocieptor neurons
Nocieptor activate multiple excitatory inter neurons (IN) in the spinal cord
IN activate nociceptor
Nociceptor activate flexor muscles
When flexor reflex is activated there is a need to … movement on the other side of the body
Reciprocal inhibition causes … movement in the other half of the body
Compensate
Opposite
One main function of the brain is to…
Direct the purposeful intervention with its environment
Adaptive neural circuitry allows mammals to..
Interact in sophisticated ways
Voluntary movements differ from reflexes, they are…
Initiated by a deliberate internal decision
Motor cortices control …
Voluntary movement
What are lateral pathways
Voluntary movement of limbs
Direct cortical control
What are ventromedial pathways
Control of posture and locomotion
Controlled by the brain stem
What are the lateral pathways?
Corticospinal tract and rubrospinal tract
Multiple sclerosis incurs demyelination of spinal cord axons
Demyelination of axons leads to impaired signalling
Demyelination is visible as lesions in fMRI imaging
Lesions cause slow worsening of motor impairments in patients as it mainly affects corticospinal tracts
What are the ventromedial pathways?
Vestibuli spinal, tectospinal, reticulospinal, pontine and medullary tracts
Primary motor cortex
Electrical stimulation (during brain surgery) will elicit movements
Detailed application of stimulation revealed a somatotopic map
Important movements have bigger representation: hand, face, lips
Cortical motor neurons encode directions of …
Movement
Movement is NOT encoded by single neurons but collectively by a large number of neurons =
Population coding
Premotor area PMA
Has somatotopic organisation like M1
Part of motor planning network
Specific functions determined in monkey experiments
Mirror neurons help to …
Plan movements and learning of complex motor programs
Supplementary motor area SMA
Somatotopic map
Connected to pre frontal cortex
Involved in motor planning of complex movements
PFC, SMA for … and … motor planning
Deliberate
Abstract
Parietal , somatosensory and PMA for integrating sensory info with …
Motor planning
M1 executes … by activating appropriate muscles
Motor plan
The brain sends axons directly to .. in the spinal cord
Motor neurons
Descending pathways are separated by originating areas into …
Lateral and ventromedial pathways
Corticospinal tract essential for …
Voluntary movement
Multiple areas in the frontal cortex contribute to …
Voluntary movement
Motor areas are organised into…
Somatotopic maps
Deep layer pyramidal cells send axons to the spinal cord (forming the corticospinal tract) and contribute to movement in …
Multiple directions
PMA neurons signal preparation for ..
Movement
Mirror neurons in the PMA help to understand motor actions and support … motor planning and learning
Complex
Subcortical control of movement - key brain areas are…
Thalamus, cerebellum, basal ganglia, brain stem
2 loops influence motor function via the thalamus…
Cerebellar loop and basal glanglia loop
Cerebellar loop contributes to…
Motor function by processing additional sensory info
Basal ganglia loop is crucial for …
Action selection / inhibition via direct and indirect pathways
Brain stem controls many fundamental motor activities like …
Breathing, cardiovascular function and posture
Lesions to the thalamus have been used to reduce tremor in patients for …
Thalamotomy
The cerebellum
A large structure near the bottom of the brain (cerebellum = little brain)
Damage to the cerebellum cause ATAXIA = patients show inaccurate and crude movements
Effect of alcohol on movement largely due to inhibition of cerebellar function
Basal ganglia function
Control and regulate complex movement patterns
Supports action selection and habitual movements
NO projections to the spinal cord
What diseases are due to affected basal ganglia?
Parkinson’s disease
Huntington’s chorea
Tics
Dystonia = muscles contract uncontrollably
Basal ganglia support motor function through 2 main pathways:
Direct and indirect pathways
Parkinson’s disease
A complex neurodegenerative disorder
Main pathology is neurodegeneration in the SNc
Cells that produce the NT dopamine die
Balance between direct and indirect pathway disturbed = tremor
Deep brain stimulation in the STN reduces … Parkinson’s disease
Tremor
Brain stem
Control of respiration
Smooth muscle
Gastrointestinal function
Stereotyped movements of the body
Reticular and vestibular nuclei control whole body movement and posture
Anencephaly is a rare developmental disorder where the newborn is missing…
All the brain structures ABOVE the brain stem
What is perception?
Conscious interpretation of sensations
What do visceral senses detect?
Conditions within internal organs
Name the 4 modalities of somatic sensation
Tactile, thermal, pain, proprioceptive
What do we mean by a transduction of a signal?
Conversion of the energy into a stimulus into a graded potential
Name the micro structures of a receptor cell
Free nerve endings of 1st order sensory neurons
Encapsulated nerve endings of 1st order sensory neurons
Separate cells that synapse with 1st order sensory neurons
How is the intensity of a stimulus encoded?
Frequency of action potentials
What are phasic receptors specialised for?
Rapidly adapt and specialised for signalling changes in a stimulus
What is the ligand for a sour gustatory receptor?
Hydrogen ions
What type of cell is a olfactory receptor cell?
Bipolar neuron
What type of cell is involved in olfactory transduction?
G protein coupled receptor
What is the iris of the eye concerned with?
Regulation of pupil size
What structures are important for focussing light?
Cornea, lens, zonular fibres and ciliary muscles
Name the cell types in the retina
Photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells
What is the membrane potential of a rod in the dark?
Depolarised
Examples of a NON visual response to light
Pupil light reflex
Increased HR and temperature
Improved alertness and performance
Melatonin suppression
Resetting the clock
What does the amplitude of a sound wave describe?
How loud the sound is (decibels)
Name the structures of the middle ear
Malleus, incus and stapes
What are the key features of the hair cells in the inner ear that are involved in sound transduction?
Stereocilia with tip links and cation channels
What structures are involved in monitoring head tilt?
Utricle and saccule
What structures are involved in monitoring head rotation?
Semi circular ducts with ampulla
EEG allows to record changes in … due to electrical signalling in the …
Voltage
Brain
The brain shows … when recorded with EEG
Several rhythms
EEG rhythms are divided by their …
Frequency
Synchronisation and oscillations can be established through a … or feedback inhibition
Pacemaker
… manifests as episodes of hypersynchronous EEG activity
Epilepsy
Sleep is divided into different sleep …
Stages
Sleep stages are identified based on characteristic …and other physiological signatures
EEG
Spectral analysis allows … analysis of sleep EEG dynamics
Detailed
Neuromodulators control sleep through the change of …. Patterns
Neuronal firing
Sleep plays a crucial role in …
Memory consolidation
EEG amplitude depends on how … neuronal activation is
If synaptic inputs arrive at different times the sum of activity is … If arrive at the same time it is …
Synchronised
Small
Large
Brain rhythms exist in all …
Mammals
What are the 2 mechanisms of brain rhythms?
Central pacemaker (conductor)
Feedback inhibition (collective)
Epilepsy can be caused by mutations that cause an imbalance between excitation and inhibition, such as:
Mutant sodium channels with increased excitation
Mutant GABA channels with reduced inhibition
EEG is the routine diagnostic test for …
Epilepsy
What are the 3 main stages of sleep?
WAKE
Non REM
REM sleep
Spindle oscillations occur in EEG recordings during …
Sleep
Acetylcholine, serotonin and cortisol distinguish non REM from … sleep
REM
Emotions exist in … and …
Animals
Humans
Basic emotions can be described in …
Humans
Emotions evoke typical bodily …
Reactions
Subconscious emotions evoke … and brain …
ANS
Activation
Emotional processing is a distributed brain feature, key areas are:
Frontal cortex
Cingulate cortex
Amygdala
Hypothalamus
The amygdala is crucially involved in the processing of …
Eg during classical conditioning
Fear
The hypothalamus is a key brain area involved in the regulation of … behaviour
Aggressive
What are the 5 basic emotions?
Happiness
Sadness
Anger
Fear
Disgust
What is the Cannon Bard theory?
Emotional experience is generated by the brain first and may be independent of emotional expression
= physiological changes
What is the James Lang theory?
Emotional experience appears as a response to physiological changes in our body
What does the limbic system include?
Amygdala
Hippocampus
Cingulate gyrus
Pre frontal cortex
Thalamic nuclei
What was Antonio Damasio’s somatic marker hypothesis?
Somatic markers (SM) are signals from the body which are regulated in the emotion circuity of the brain - particularly pre frontal cortex
SM may influence info processing in may areas of brain - eg motor and sensory cortices
SM help to regulate decision making in situations of complexity and uncertainty
Sham rage only occurs if the posterior hypothalamus is left …
Intact
Affective aggression is due to the …
Medial hypothalamus
Predatory aggression is due to the …
Lateral hypothalamus
Mental health science links …mechanisms to pathological changes in behaviour
Genetic, molecular and brain
Developing novel treatments will rely on … approaches
Eg induced pluripotent stem cells
Molecular medicine
Anxiety disorders are characterised by constant and … anxiety and worry
Excessive
Anxiety can be due to activation of the …
HPA
Amygdala enhances / hippocampus reduces … activation
HPA
Psychotherapy and pharmacotherapy are used to treat …
Anxiety
Major depression occurs to about … of the general population
5-10%
Antidepressants include … and more recently …
SSRI
Ketamine
MD is a complex disorder caused by … factors
Genetic, developmental and environmental
Reduced serotonin signalling is a major cause of …
Depression
Most current antidepressants block re uptake of … at the synaptic cleft = increased serotonin
Serotonin
How does ketamine work?
Blocks NMDA receptors on inhibitory inter neurons
Activates other signalling pathways for protein translation and synaptogenesis
What are the 2 main types of muscle tissue in the body?
Striated and smooth
What is the name of the synapse between a motor neuron and a muscle?
Neuromuscular junction
What is the difference between EPSP and IPSP?
Excitation and inhibition
What is the post synaptic receptor of the neuromuscular junction?
Nicotinic acetylcholine receptor
Which neuron fires first during the stretch reflex?
La neuron
What are the main descending motor pathways in the spinal cord?
Lateral and ventromedial pathways
What is the function of the tectospinal tract?
Support eye movements
What is somatotopic representation?
The mapping of motor function to different parts of M1
What is a function of the premotor area?
Preparation for movement
When does a mirror neuron (MN) fire?
MN fire when observing movements in others
What brain structures form the 2 main sub cortical loops that support motor function?
Cerebellum + basal ganglia + thalamus
What is ataxia?
Impairments in movement
What are neurons that form a large part of cerebellum?
Purkinje cells
What is the net effect of the direct pathway on the motor cortex?
Excitation
What is the final effect of deep brain stimulation in PD patients?
Disinhibition of the thalamus
What is located in peyer’s patches of the ileum?
Gut associated lymphoid tissue GALT
During emulsification of large lipid globules, the … region of bile salts interacts with the lipid and the … region interacts with chyme
Hydrophobic
Hydrophilic
When blood pressure … this leads to … aldosterone secretion
Decreases
Increased
What is the mechanism by which dipeptides are absorbed in the small intestine?
Hydrogen co transporters
Enterokinase is a brush border enzyme .
If it was ABSENT which is the following processes would be inhibited?
The conversion of trypsinogen into trypsin
Increased pressure in which segment of the gastrointestinal tract results in ‘reverse’ peristalsis?
Rectum
The direction of a sound source is computed in the …
Cerebrum by comparing the signal from both ears
The … of a sound wave indicates the pitch and the … indicates the loudness
Frequency
Amplitude
An action potential is elicited in a sensory neuron during a reflex movement.
Order the events that occurs during
- Na+ channels open leading to
- Depolarisation
- K+ channels open leading to
- Repolarisation
- Returns to resting state potential
Which brain areas are part of the Papez circuit?
Amygdala
Cingulate gyrus
Hippocampus
What are the basic emotions?
Disgust
Anger
Fear
Happiness
Sadness
Which brain area is involved in deliberate and abstract motor planning?
Supplemental motor area SMA
What neurons form a large part of cerebellum?
Purkinje cells
What is the function of the tectospinal tract?
Support body orientation based on visual information
What is the name of the 1st brain rhythm described?
Alpha
What are the 2 mechanisms for generating synchronised activity in neuronal networks?
Pacemaker and feedback inhibition
What is a cause of epilepsy?
Mutant sodium channels that cause increased excitation
What is a sleep stage?
N3
What is a characteristic oscillation linked to NREM 2 sleep?
Spindle
Which neuromodulator concentration is increased during REM sleep?
Acetylcholine
What parts of the nervous system are involved in processing emotions?
Amygdala and ANS
Which part of the amygdala integrates sensory and aversive stimulus info during fear conditioning?
Basolateral nuclei
Which part of the brain mediates sham rage?
Hypothalamus
Which neural pathways is crucially involved in anxiety disorder?
HPA
What is the effect of the amygdala on the HPA?
Excitatory
What is the mechanism of action of anti depressants?
Blocking re uptake of serotonin
What are pre cursors for induced pluripotent stem cells?
Somatic cells
What is the effect of Benzodiazepine on GABA receptors?
Increase chloride influx
EEG amplitude depends on … inputs to cortical neurons
Synchronous
A clinical disorder which results in the autoimmune destruction of GASTRIC PARIETAL CELLS would prevent the absorption of what nutrient?
Vitamin B12
What enzyme is located at the brush border of the small intestine and plays a role in carbohydrate digestion?
Lactase
What nutrient in the diet would NOT be soluble in water?
Triaglycerol
Correct order of layers in the gastrointestinal wall
Mucosa
Submucosa
Muscularis externa
Serosa
What is FALSE about the peristaltic contractions in the GI wall?
Their main function is mixing of food bolus with digestive enzymes
What is true about gastric acid secretion?
The secretion is initiated in the cephalic phase before food enters the stomach
What are the main descending motor pathways in the spinal cord?
Lateral and ventromedial pathways
What is NOT an accessory organ to the GI tract?
Ileum
Which of the following cell types is essential for the digestion of proteins?
Parietal cell - secretes hydrochloric acid and intrinsic factor - denatures protein and activates pepsinogen
During the pharyngeal stage of swallowing, the medulla oblongata sends a signal to trigger the movement of what structures?
Uvula
Soft palate
What is true about gastrin?
Strengthens the contraction of the lower oesophageal sphincter muscle
Presence of chyme in the duodenum stimulates what?
Sympathetic nervous system
What can cause an increase in pH of the GI tract?
Secretin
Examples of active transport?
Sodium glucose co transporters in small intestine
Transcytosis of small peptide chains
What enzymes are located at the brush border?
Lactase
Aminopeptidase
Decreased blood pressure leads to increased aldosterone levels which leads to … absorption of sodium and … vasodilation
Increased
Decreased
Gastrin does NOT directly influence what enzyme?
Trypsin
Thermo receptors are …
Phasic receptors
Constant prolonged stimulus
What special sense has a receptor that is 1st order neuron?
Olfactory
Put the retinal layers in order that light passes through them
Ganglion cell layer
Inner synaptic layer
Bipolar cell layer
Outer synaptic layer
Photoreceptor cell layer
What would NOT apply to a touch receptor in the skin?
It is a visceroceptor
What special sense does NOT involve a G protein coupled receptor?
Detection of a sour gustant
In a cone photoreceptor, what is the consequence of a depolarising membrane potential?
Increase in NT release
Hyperpolarisation of bipolar cells
