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BIOL 373 L EXAM.docx

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Bruce Wolff

BIOL 373 L EXAM LAB #1 – Neural and Sensory Function Special Senses 1. Vision - Visual Acuity: the degree of detail the eye can distinguish o Snellen Chart used to determine visual acuity o Stand 6 metres (20 feet) from chart and cover one eye and read successively smaller lines of print until hard to distinguish o Last line without mistakes is the approximate visual acuity for the eye o Myopia: near-sighted  light focuses in front of the retina  Unable to see far – distant objects are out of focus o Hyperopia: far-sighted – difficult to focus objects near - Astigmatism: blurring or distortion of visual image caused by defective curvature of refractive surfaces of eye o Light rays not sharply focused but spread over broad area o PROCEDURE: view from 3 metres (10 feet) with one eye at a time  Focus on middle and bars SHOULD be sharp and evenly dark  Astigmatic eye will see some lines thick and dark while others are lighter and blurred - Colour Vision: diminished ability to sense colour accurately = colour blindness o Caused by deficiency in retina’s systems for converting red, blue or green light into receptor potentials (by sensory cells called cones) o Ichikawa colour vision test  Series of coloured plates to detect and identify colour blindness  Most common hereditary is red-green deficiency  Display plates for 3 seconds each from about 80 cm away and record subject’s responses on score sheet  Plates 1-4 for orientation and testing begins on plate 5  Subject concentrates on each plate and says number that he/she sees clearer  Normal vision: need to have at least 8 plates correct (plates 5-14), testing done  If more than 3 abnormal responses, test continues to classification plates (15-19) to determine which type of colour deficiency present 2. Taste - Taste buds consist of barrel-shaped groupings of sensory cells located on tongue and in epithelial lining of mouth o PROCEDURE: dry tongue and apply dab of 5% sucrose solution to tip, sides, and back of tongue  Repeat using 1% acetic acid, 5% NaCl, and 0.5% quinine sulphate  Rinse mouth and dry tongue between solutions o Taste buds are not uniformly distributed and not tasted equally well everywhere inside the mouth 3. Olfaction - PROCEDURE: Pinch nostrils together so unable to breathe through nose and pick up a peppermint candy and unwrap it and place it in mouth o Release nostrils and note change in flavour - Sensory cell with prolonged stimulation allows it to be classified as tonic or phasic o Tonic (slowly-adapting sensors): produce continuous sequence of action potential as long as stimulus lasts o Phasic (rapidly-adapting receptors): detect stimulus of constant strength  Sends stream of action potentials of steadily-decreasing frequency to CNS  Usually senses stimuli that are not important to survival - PROCEDURE: remove stopper on test tube containing crushed garlic 4. Hearing - Hearing normally involves vibration of oval window in response to sound waves conducted through air o Sound waves transmitted through skull bones also detected and ability used to diagnose hearing problems of inner and middle ear - Rinne’s Test: make tuning fork vibrate by striking arms against heel of hand o Place butt on handle against mastoid process of temporal bone with tuning fork pointed down and behind the ear o If there is no damage or blockage in middle ear, sound will reappear after removal o Ear is more efficient at detecting sound waves conducted through bone rather than air - Weber’s Test: hold vibrating fork on midline of top of skull; repeat with one ear plugged o Plugged ear will be louder o The external noise on the perceived loudness of the sound that originates from the tuning fork is not as loud - Auditory acuity: strike tuning fork and place it close to open ear and slowly move away until sound can no longer be heard o Lower frequency heard further away, but higher is only heard for short distance 5. Equilibrium: Romberg Test - Maintenance of upright posture while standing or moving depends on input from different senses o Information integrated in the brain, which responds by sending signals to muscles of legs, back and other locations o PROCEDURE: subject stands with back close to blackboard and arms hanging at sides – observe the swaying; repeat with left shoulder closer to blackboard - Proprioceptors send sensory information to brain regarding tension in skeletal muscles and positions of limbs - Ears also provide brain with information to help maintain balance Somatic Senses - Receptor cells of skin are widespread and not grouped into organs o Variety of sensory neurons in skin are sensitive to one type of stimulus: touch, pressure, pain, heat, or cold o Cell bodies located in dorsal root ganglia near the spinal cord o Single long axon extends in both directions from cell body – one end located in skin, and other enters spinal cord - Once stimulus detected by receptor endings in skin, neuron responds by initiating electrical impulses that are carried into spinal cord o Impulses relayed to other neurons in spinal cord then to thalamus of brain and are then transmitted to neurons in somatosensory cortex of cerebrum - Detection: occurs at receptor endings in skin - Perception: occurs only when appropriate neurons in somatosensory cortex of brain receive incoming sensory impulses - Each part of body has own portion of somatosensory cortex devoted to perceiving touch – some larger space in brain than others - Skin pressure sensors show rapid sensory adaptation to constant stimulus 1. Two-point Discrimination of Touch - For touches at two separate points on skin to be perceived and discriminated by brain as two distinct stimuli, need to meet requirements: a. Stimulation of at least 2 spatially separated touch-sensitive nerve endings (more likely to occur if widely spaced and if they occur in sensitive areas of skin) b. Nerve impulses triggered by two stimuli need to be carried in two separate pathways – activity in two separate locations in somatosensory cortex - Advantages of having different densities of touch receptors in different regions of the body: o More sensitive in certain areas therefore have less distance 2. Mapping Cold Receptors - Skin has thermosensory nerve cells with receptor endings specifically sensitive to temperature - Established from physiological and psychological testing that warm-sensitive neurons and cold-sensitive neurons o Warm receptors respond preferentially to warmth and cold receptors to cold o Branches of both kinds terminate as free receptor endings, beneath skin surface - Concentration of thermosensitive points varies in different body regions Reflexes - Are unconscious actions and not subject to voluntary control - Reflex arc – most fundamental pathway linking sensory input and motor output o Typically includes a receptor and an effector o Receptor is a sensory cell which converts stimulus to a sequence of action potentials that are passed along an afferent/sensory neuron to spinal cord o Monosynaptic reflex: Sensory transmits to motor pathway leading to an effector (muscle or gland) - Reflexes are either visceral or somatic 1. Spinal Reflexes: involved neurons within spinal cord that bring about stimulation and inhibition of muscle contraction without participation of higher centres - Knee Jerk: when tap patellar tendon, leg will pop upwards o When balancing a coin, it is easier to kick up because the mind isn’t thinking about the leg and the reflex - Achilles Jerk: kneels on stool and examiner strikes Achilles tendon at level of ankle - Triceps Jerk (Radial Nerve): tester holds subject’s arm so it is horizontal and hands downwards o Tester strikes tendon of triceps humoris 2. Cutaneous Reflex – The Babinski Reflex - Stimulation of cutaneous receptors in sole of foot – integrated in brain and not spinal cord - Response carried by pyramidal cells located in motor cortex – axons descend from brain to form synapses with motor neurons in spine - Normal response: flexion of great toe, while other toes flex and come together - Abnormal response: great toe extends (bends upwards) and other toes flex 3. Cranial Nerve Reflexes - Pupillary Light Reflex: hold hand vertically in front of face to prevent light originating on right side from shining into left eye o Reflex is consensual – stimulus on one side provides response on both sides o When one eye is covered, the pupil of other eye shrinks o The optic nerve is involved in these reflexes - Corneal Blink Reflex: blow quick small stream of air on partner’s cornea o Reflex is consensual - Menace Reflex: tell partner will strike him/her in the eye o Reflex is unable to be controlled by higher centres 4. Fine Motor Control - Single motor neuron and all of skeletal muscles that it controls form a motor unit - Number of muscle cells controlled by single motor neuron is variable o Low ratio of muscle cells to motor neurons give muscle ability to control motions precisely o Motor units may have many muscle cells connected to single nerve cell – predominant in muscles used for lifting heavy loads - When trying to write a name with heavy jug filled with sand, first letter isn’t as steady o Fine motor units try to correct itself later on Study Questions: 1. List the events, in sequence that occurs between the striking of the patellar tendon and the extension of the leg. Receptor converts stimulus to a sequence of action potential that are passed along an afferent (sensory) neuron to the spinal cord - Sensory neuron transmits signals directly to motor pathway (efferent neuron), leading to an effector 2. If a normal stimulus does not bring about the expected response in a stretch reflex, damage to a specific motor nerve or region of the spinal cord may be suspected. On the other hand, an abnormal Babinski response may indicate damage to the spinal cord at any level. Why? An abnormal Babinski response indicates damage to nerve paths that connect the spinal cord and the brain. This means it could mean there is damage at any level of the spinal cord. 3. Sensory signals from all regions of the body are sent to the somatosensory cortex, where they are perceived. Which parts of the body have the largest areas of the cortex? Which have the smallest? The largest area of the somatosensory cortex is the most sensitive (ex. hands, fingers, tongue). The smallest region would be the leg or arm. 4. How does the ear transduce sound waves into electrical nerve impulses? Vibrations cause sound waves and the ear picks up the vibrations via cilia. The vibrations become electrical nerve impulses. 5. If the subject has a severe middle ear infection (both ears), how will this affect the results of Rinne’s test? An ear infection in the middle ear means that there is blockage. This means that the sound will not reappear when the tuning fork is close to the external auditory opening. However, bone conduction is more efficient than air conduction. 6. What senses are affected by lateral inhibition? Briefly explain how the process functions. Touch, vision, and hearing are all affected by lateral inhibition. Lateral inhibition enhances contrast and improves stimulus localization. A stimulus is sent to the primary neuron response with the same strength. The pathway closest to the stimulus inhibits neighbours so that there is an increased perception of the stimulus. LAB #2 – Enzymatic Digestion I & II Digestion of Nutrient Molecules is accomplished by hydrolysis - Most nutrient molecules hydrolyzed from original polymeric form into monomeric subunits o Able to be absorbed across the wall of digestive tract o Enzymes accelerate hydrolytic reactions 1. Proteins - Stomach acid and pepsin make digestion of peptides in small intestine easier and faster o Acid denatures proteins  changes shapes from globular/fibrous to linear  exposes more peptide bonds o Pepsin breaks some peptide bonds o When encounters neutral/alkaline conditions, smaller peptides unable to resume original shapes  peptide bones exposed to peptidase enzymes - Natural Protein Molecule Denatured Protein Molecule Small Peptide Molecules 2. Carbohydrates - Starch is a polymer of glucose that is digested by two separate reactions o Amylases hydrolyze starch to maltose & small amounts of maltotriose and isomaltose o Maltose is broken down to glucose with aid of maltase - Starch Maltose Glucose 3. Lipids - Most dietary lipids are triacylglycerol molecules o Lipase enzymes hydrolyze each molecule to TWO free fatty acids and ONE monoacylglycerol - Triacylglycerold Monoacylclycerol + 2 Free Fatty Acids Human Digestive Enzymes 1. Proteinases  Pepsin (proteins peptides)  Trypsin (proteins peptides)  Chymotrypsin (proteins peptides)  Aminopeptidase (peptides  amino acids,  Carboxypeptidase (peptides  amino acids, dipeptides, tripeptides) dipeptides, tripeptides) 2. Carbohydrases  Amylase (starch  maltose, maltotriose,  Isomaltase (maltose, maltotriose  isomaltose) glucose)  Maltase (maltose, maltotriose  glucose)  Sucrase (sucrose  glucose, fructose)  Lactase (sucrose  glucose, fructose) 3. Lipases - Lipases (triacylglyceroles  monoacylglyceroles, fatty acids) - Phospholipases (aka lecithinases) – (phospholipids  phosphoglycerides, fatty acids) o - Lipid digestion is visible within 30 minutes of incubation at 37 C o Digestions of starch and protein require 24 hours of incubation Diagnostic Tests 1. Proteins - Small egg white diameters digested more quickly - ****** rate of digestion??? - Lead acetate test – tests positive for amino acids that contains sulphur o Add 2 mL of 10% NaOH and up to 2 mL of digestion mixture o Add 5 drops of 10% lead acetate and mix thoroughly o Heat in boiling water bath for 5 minutes o Black precipitate will form if positive 2. Carbohydrates - Iodine test – tests positive in presence of starch o Add one drop of testing solution to one drop of sample o Dark blue-black colour indicates positive - Benedict’s test – for reducing sugars o 2 mL sample mixed with 4 mL Benedict’s solution o Mixture placed in boiling water bath for 5 minutes o Appearance of bright red indicates very positive result o Slight positive will give cloudy green 3. Lipids - Digestion related to acidity of fatty acids that are produced when lipids are hydrolyzed - Litmus powder added to reaction mixture to make it pale blue o As digestion proceeds, pH falls and colour changes to pink o Progress of lipid digestion depends on change in pH - Lipidase enzymes dissolved in water but most lipid substrates have low aqueous solubilities and form micelles o Immiscibility limits degree of interaction between enzyme and substrate - Those that are more soluble in water will influence pH of digestion mixture to a greater extent Study Questions 1. What are the limitations of the lead acetate test in this experiment? How could it be used to produce meaningful information? The lead acetate test limits to testing amino acids that contain sulphur. However, it is meaningful since cysteine and methionine are the only amino acids that contain sulphur. It also ensures proteins are digested. 2. Describe the process, in the human digestive tract, that promotes maximum interaction between hydrophilic lipase enzymes and their substrate, hydrophobic lipid molecules. The process of promoting maximum interaction between hydrophilic lipase enzymes and substrates begin from the release of lipase from pancreas to duodenum. Lipase is used to digest lipids in the digestive tract. If the lipids or globs are too big and have low surface area to volume ration, bile and bile salts are secreted by the liver and break off the globs. Bile is amphipathic, with hydrophobic and hydrophilic regions. The arrangement allows the hydrophobic regions to associate with the lipids. Bile salts then form spherical structures around the fat in the gut, called a micelle. The formation of micelles allows bile salts to break up fat particles into smaller ones for absorption. 3. Where is each of the following enzymes synthesized in the human body, and where does it function? Pepsin: synthesized in chief cells in stomach; functions in stomach Chymotrypsin: synthesized in pancreas, functions in duodenum Lipase: synthesized primarily in pancreas but also mouth and stomach; functions in duodenum Aminopeptidase: synthesized and functions in glands of small intestine Maltase: synthesized in intestinal glands; functions in small intestine 4. List the digestive enzymes that are secreted in the form of zymogens, and for each, name it’s activating factor. Pepsinogen: activated by HCl Trypsinogen: activated by enteropeptidase Chymotrypsinogen: activated by trypsin 5. How are the inner linings of the stomach and intestine protected from damage by digestive enzymes? Mucous is secreted and lines the stomach and intestine so there is a physical and chemical barrier. Pepsin and other forms of enzymes are also secreted in an inactive form. This prevents the digestive enzymes from harming the linings. Tight junctions also seal each epithelial cell to its neighbours, confining the digestive juices to the lumen. A buffering layer of bicarbonate solution also covers the surface of epithelial cells. 6. Why does the hydrolysis of starch by amylase produce maltotriose m
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