Iowa State University



BIOL 212 SI Section 1Exam 4 ReviewSensory Systems Subdivisions of the nervous systemThe central nervous system is made up of the brain and spinal cordThe peripheral nervous system is made up of all of the nervesThe afferent nervous system transmits sensory information to the CNS via sensory neuronsThe efferent nervous system transmits motor information from the CAN via motor neuronsThe somatic nervous system is responsible for voluntary movement and responseThe autonomic nervous system is responsible for involuntary responsesThe parasympathetic division is responsible for relaxation and digestionThe sympathetic division is responsible for responses associated with the fight or flight responseThe human brainThe cerebellum is responsible for coordination of complex motor patternsThe diencephalon is responsible for relay of information to the cerebellumThe brain stem is responsible for relay of information to the spinal cord and autonomic control of the heart, lungs, and digestive systemThe cerebrum is responsible for conscious thought and processing of sensory information.Made up of four lobes: the parietal, occipital, temporal, and frontal lobesHow do animals transform stimuli into signals?Each type of sensory information has a specific type of receptor that makes a synapse with a sensory neuron. This process is called transduction. Mechanoreceptors respond to changes in pressureChemoreceptors respond to specific moleculesPhotoreceptors respond to wavelengths of lightElectroreceptors detect electrical fieldsMagnetoreceptors detect magnetic fieldsThermoreceptors detect changes in temperatureNocireceptors sense harmful stimuli like injuryThe signal must be amplified. The stronger the stimulus, the stronger the greater response from the receptor, the more action potentials produced.The final step is transmission of the signal to the central nervous system. The brain can interpret sensory information because receptor cells are highly specific, and each sensory neuron sends information to a different part of the brain. For example: different sensors are used to detect different pitches of soundMechanoreception Land animals use hearing organs to detect pressure changes in air, or sound. Aquatic animals detect pressure changes in water through a lateral line system.Both land and animals use structures called hair cells for mechanoreception.They have stiff outgrowths called stereocilia that are reinforced by actin filaments.Many also have a kinocilium, which is an arrangement of microtubules.Pressure on these cells results in depolarization or hyperpolarization.If the stereocilia are bent in the direction of the kinocilium, K+ channels open, causing ions to rush in and depolarize the membrane.Hair cells are covered by an extracellular fluid with a high concentration of K+, so it is still moving down the concentration gradient. Depolarization causes calcium ion channels to open, increasing the amount of neurotransmitter released between the hair cell and sensory neuron. Because of this, more action potentials are fired.If the stereocilia are bent in the other direction, ion channels close, hyperpolarizing the hair cell.The mammalian ear is made up of three sections:The outer ear: the ear canal funnels sound into the ear, vibrating the tympanic membrane. The middle ear: the tympanic membrane vibrates against the three ear ossicles. The last one vibrates against the oval window to produce waves of fluid inside the inner ear.The size of the oval window is very important. If it is too big, it doesn’t vibrate correctly. If it is too small, it can’t vibrate enough to produce strong waves in the cochlea. The inner ear: The cochlea is a coiled tube with three chambers. One of those holds the hair cells sandwiched between the basilar and tectorial membrane. Each segment of the basilar membrane vibrates in response to different frequencies.Bats and elephantsBats can detect high ultrasounds needed in order to echolocate. A large area of their basilar membrane is specialized for detecting high frequencies of the returning echoes.Elephants can detect low infrasounds needed for long-distance communication. Wild elephants can communicate even when they are miles apart!The lateral line system in aquatic amphibians and fish is made up of hair cells embedded in gel-like structures called cupulae inside a canal running along the length of the body. Some nocturnal predatory catfish were experimented on to see if they relied on their lateral line system for foraging. One group had the lateral line system removed and the other removed their chemoreceptors. The latter saw little change in hunting success, but the former had much less success.PhotoreceptionPupil shape and eye type correlates to the environment and behavior of the animal.Vertical pupils are usually used by small ambush predatorsRound pupils are usually used by large predatorsHorizontal pupils are usually used by prey animals living in open habitatMany insects have compound dyes made up of thousands of ommatidiam, each with a lens and four receptor cells. These are good for detecting movement. Simple eye structureThe outermost layer of the eye is the scleraThe front of the sclera forms a transparent sheet of connective tissue called the corneaThe iris is a pigmented, round muscle that controls how much light enters the eyeLight enters the pupil and passes through a curved, clear lensThe retina contains the photoreceptors, bipolar cells, and ganglion cells. Rods are sensitive to dim light and only detect black and white. Cones can detect different wavelengths of light, or colors.Rods and cones have membranous discs with large amounts of the transmembrane protein opsin.Each opsin is associated with a molecule called retinal. In rods these two form a complex called rhodopsin.When exposed to light, retinal changes from the cis conformation to the trans conformation, activating the opsin. In rods, the membrane is depolarized when in the dark. The molecule cGMP opens the ligand-gated sodium channels. When exposed to light, rhodopsin is activated, leading in a reduction of cGMP concentration. With less cGMP, sodium channels close and the membrane hyperpolarizes. Color vision and color blindnessHumans have three different types of cones, each with a different type of opsin that respond to different wavelengths: S, M, and L.Red-green color blindness occurs when there is a defect in M/L opsin. The L allele is functional, but the M allele is defective, so the green-sensitive cones are not present. This is more common in males because the gene for M opsin is located on the X chromosome. If females have a defective M, another M can compensate for it. Males only have one X chromosome, so they do not have another to compensate for a defective M. The types of opsin present depends on the behavior and habitat.ChemoreceptionThe senses of gustation and olfaction originate in the chemoreceptors.A taste bud is made up of 100 spindle-shaped taste cells that make a synapse with sensory neurons.Saltiness is detected when an excess of sodium ions depolarizes the cell membrane of certain taste cells.Sourness is detected when hydrogen ions from citric acid depolarize the membrane of certain taste cells. Bitterness is detected by a suite of transmembrane receptor proteins. Bitterness is extremely important because it usually indicates toxicity.Sweetness is detected by three closely related transmembrane receptor proteins. One detects umami while the other two taste for sweetness. One sweet receptor has binding sites for multiple types of sweet compounds. For olfaction, odor molecules must diffuse into a mucosal layer of the nasal cavity and bind to membrane-bound receptors, activating olfactory neurons. Each olfactory neuron has a different receptor and goes to a distinct region of the olfactory bulb. Many animals use thermoreceptors to detect changes in temperatures and relay that information to the hypothalamus.Pit vipers have extremely sensitive thermoreceptors in pits under their nostrils that are used for hunting small mammals. All animals give off electrical impulses, so many fish like sharks use electroreception to detect predators or prey.Sharks have pores called the ampullae of lorenzini.Bacteria, fungi, invertebrates, and many vertebrates have been found to be able to detect magnetic fields.Birds use magnetoreceptors in their beaks and eyes for navigation.A pheromone is a chemical that is secreted and affects the behavior and physiology of others of the same species.Bombyx mori females secrete BOMBYKOL to attract male moths.Bees will use them to alert others of an intruder.Female rodents will signal to a male when they are ovulating.Tetrapods have the vomeronasal organ on the roof of their nasal cavity to detect pheromones.Animal MovementLocomotion is the movement of an entire animal in relation to its environmentThere are three types of muscles in vertebratesSkeletal muscle is attached to bone or exoskeleton for voluntary control. Smooth muscle surrounds hollow tubes and cavities, under involuntary control.Cardiac muscle is found only in the heart and under involuntary control.Muscle structureSkeletal and cardiac muscle is made up of long, slender cells called muscle fibers.The muscle fiber is made up of many contractile strands called myofibrils.Myofibrils are striated, having dark and light bands. These areas are called sarcomeres.The light bands are made up of actinThe dark bands are made up of myosinThe muscle contracts when that sarcomere gets shorter. How do muscles contract?The shortening of sarcomeres occurs because myosin pulls actin towards the middle. The actin and myosin do NOT get shorter. This is called the sliding filament model. The actin-myosin interaction has 4 steps. This is also called the cross-bridge cycleWe start with myosin bound to actin. ATP binds to the myosin head, releasing it from the actinATP is hydrolyzed, causing the myosin head to change shape and bind to a different spot on the actin.The Pi is released, causing the myosin head to change shape again, moving the actin filament.The ADP is released, and the cycle repeats as long as Ca+ is presentRegulation of muscle activityWhen muscles are relaxed, tropomyosin and troponin work together to block the myosin binding sites on actinContraction begins when calcium ions bind to troponin, moving the complex and exposing the binding sites.How do neurons initiate contraction?The brain receives the signal, integrates it, and triggers an AP to the motor neurons. When action potential reaches the end of the motor neuron, Ca+ channels open and trigger the release of the neurotransmitter acetylcholine Acetylcholine binds to the ligand-gated channels on the cell membrane of the muscle fiber, propagating an action potential.That action potential travels to the T tubules.The Ca+ channels in the sarcoplasmic reticulum open, releasing Ca+ into the muscle. During relaxation, Ca+ is pumped back into the sarcoplasmic reticulum.Rigor MortisAfter death, the sarcoplasmic reticulum deteriorates, and cellular respiration stops. How does this cause rigor mortis?The sarcoplasmic reticulum stores calcium, so if it deteriorates, Ca+ is dumped into the muscle cell, causing troponin to expose the binding sites on actin. ATP is already present on the myosin, so the myosin goes through the cross-bridge cycle. However, without ATP, myosin cannot detach from actin. The muscle thus stiffens and cannot relax until the actin and myosin break down. Characteristics of muscle typesSmooth MuscleSingle nucleusUnstriated and has no sarcomeresUnbranchedInnervated by autonomic motor neuronsActivated by acetylcholine and inhibited by norepinephrine and epinephrineCardiac Muscle1 or 2 nucleiStriated and has sarcomeresBranched with intercalated disks between cellsInnervated by autonomic motor neuronsActivated by norepinephrine and epinephrine and relaxed by acetylcholineSkeletal MuscleMultinucleatedStriated and has sarcomeresUnbranchedInnervated by somatic motor neuronsStimulated by acetylcholine What factors affect force output of skeletal muscle?The relative proportion of different fiber typesThe organization of fibers within the muscleHow the muscle is usedSkeletal fiber typesAll fibers are present but in different amountsMyoglobin is an iron-containing pigment that binds to oxygenSlow Fibers (Red)High myoglobin concentrationDerive ATP from aerobic respirationMany mitochondriaStart slow but take long to fatigueFast Fibers (White)Low myoglobin concentrationDerive ATP from glycolysisFew mitochondriaStart fast but fatigue quicklyIntermediate FibersHigh myoglobin concentrationDerive ATP from glycolysis and aerobic respirationMany mitochondriaIntermediateMuscle fiber organizationLength and cross-section of a fiber influences its contractile propertiesParallel fibers: long chains of sarcomeres along the length. Have a long length but a large cross section, so they are fast but not strong.Pennate fibers: sarcomeres are lined up diagonally to a tendon. They have a large cross section but are shorter, so they are strong but not as fast.Hydrostatic SkeletonsHydrostatic skeletons use pressure of internal fluids to support the body.Found in sea anemones, jellyfish, mollusks, worms. Hydrostats is also used in tongues, penises, and tube feet of starfish.Earthworms use their hydrostatic skeleton for locomotionThey have two types of muscles: longitudinal muscles that run down the side of the body and circumferential muscles that run around the body like rings. The circumferential muscles contract, increasing the pressure of the fluid, extending the relaxed longitudinal muscles.The longitudinal muscles then contract, increasing the pressure of the fluid, extending the relaxed circumferential muscles.These two are an example of an antagonistic muscle group.EndoskeletonsA series of rigid structures inside the bodyThe vertebrate endoskeleton is a system of rigid levers and articulations that allow limbs to swivel, hinge, or pivot. Bone is made up of cells embedded in an extracellular matrix made up of calcium phosphate with calcium carbonate and collogen.Cartilage is made up of cells scattered in an extracellular matrix of polysaccharides and proteinsLigaments are bands of connective tissue like collagen that binds bones together and stabilizes jointsTendons are bands of connective tissue that attach bones to skeletal muscleAntagonistic muscles groups work together but opposite in order to perform movement.The flexors decrease the angle between bones, pulling them closer together. The extensors increase the angle of the joint, pull them further away from each other.Its important to know that muscles do not extend on their own, they need another muscle to pull them back into place. Bone is living tissue that is used to maintain blood calcium levels.Ostoblasts build the calcium matrix in bone, decreasing blood calcium levels.Osteoclasts break down the calcium matrix of bone, increasing blood calcium levels. ExoskeletonsEncloses and protects the body of animalsFound in arthropodsInsects have chitinous ingrowths of their exoskeleton called apodemes where muscles attach.Exoskeletons do not grow with the animal, so it must be occasionally moltedChemical Signals in AnimalsA hormone is a chemical signal that originates in a cell and circulates through the body fluids to reach and affect a distant target cellHow are electrical signals and chemical signals different functionally?Action potentials have short-term effects on a set of cellsChemical signals are produced in low concentrations but have enormous and lasting effects on target cells.They are used together to coordinate activities throughout the body. Categories of chemical signals in animalsAutocrine signals act on the same cell that secretes them Example: interleukin2Paracrine signals diffuse locally and act on nearby cellsExample: insulin, glucagon, cytokines Endocrine signals are carried between cells by blood or other body fluidsExample: hormonesNeural signals diffuse a short distance between neuronsExample: neurotransmittersNeuroendocrine signals are released from neurons and travel through the blood to target cellsExample: neurohormones like anti-diuretic hormoneHormone signaling pathwaysAll hormone pathways are regulated via negative feedback, meaning that the end response inhibits the production of the chemical signal.The endocrine pathway sends hormones directly from endocrine cells to effector cellsThe neuroendocrine pathway releases neuroendocrine signals that act directly on effector cellsIn the neuroendocrine-to-endocrine pathway, the neuroendocrine signals stimulate cells in the endocrine system, which produce an endocrine signal that acts on effector cellsHormones of the human endocrine systemThe hypothalamusThe pineal glandThe pituitary gland with an anterior and posterior region. Located right below the hypothalamusThe thyroid gland is in the neckThe four parathyroid glands are ebedded in the thyroid glandThe adrenal glands sit on the kidneysThe pancreas is located in the abdominal cavityThe testes and ovariesThe exocrine glands deliver their secretions through ducts into a space other than the circulatory system.Examples include salivary glands, digestive glands in the pancreasThere are three different types of hormonesPolypeptides are chains of amino acids. They bind to receptors on the surface of the cellAmino acid derivatives bind to receptors on the surface of the cellSteroids bind to receptors on the inside of the cellSteroid hormones travel throughout the body and enter the cells to bind to receptors inside the cell. The receptor-hormone complex then binds to DNA to trigger transcription.Lipid insoluble hormones like epinephrine trigger a signal transduction cascadeWhen the hormone binds to the receptor, it activates the G protein to split and activate adenylyl cyclase, which converts ATP to cyclic AMP.This cAMP then triggers a phosphorylation cascade, further amplifying a signal.When activated by epinephrine, the response is the breakdown of glycogen into glucose. Hormones coordinate activities in development, growth, and reproductionMetamorphosis in amphibians is driven by the hormone T3, or thyroxineMetamorphosis in insects is driven by two hormones: juvenile hormone and ecdysone. In the larval stage, both are in equal levels. When JH decreases in levels, the body goes through complete remodeling.In vertebrates, genes on the sex chromosomes are the primary determinate factor on sex. The male and female gonads produce testosterone and estradiol respectively.The surges of sex hormones associated with puberty are signaled by growth hormone Hormones respond to environmental changesIn mammals, photoreceptors in the eye send signals to the pineal gland, which releases melatonin to relay information to the hypothalamus.Changes in photoperiod (seasons) are associated with changes in sex hormone releases in species with breeding seasons.Many day-active lizard species have a parietal eye, or a small hole covered by membrane at the top of the skull containing photoreceptorsHormones are involved in the maintenance of homeostasis Homeostasis is the maintenance of relatively constant physical and chemical conditions inside the bodyHomeostatic systems depend on three componentsA sensory receptor that monitors a conditionAn integrator that processes information and compares it to a set pointEffector cells that return conditions to that set pointExamples: Insulin and glucagon regulate blood glucoseandidiuretic hormone and aldosterone regulate water and electrolyte balanceerythropoietin regulates oxygen availability by stimulating red blood cell productionHypothalamic-pituitary axisThe pituitary is directly connected to the hypothalamus. This connection is the basis of the connection of the central nervous system and endocrine system.To get the adrenal cortex to release cortisol in response to stress, the hypothalamus releases corticotropin releasing hormone (CRH) to stimulate the pituitary to release adrenocorticotropic hormone (ACTH), which triggers the adrenal cortex to release cortisol. Cortisol in turn inhibits those original signals.Circulation and Gas ExchangeFive essential steps for gas exchangeVentilation occurs when air or water moves through a gas exchange organ like gills or lungsDiffusion takes place when CO2 and O2 diffuse between the air or water and the ventilatory surfaceCirculation occurs, and CO2 and O2 are circulated through the body dissolved in bloodDiffusion takes place when CO2 and O2 diffuse between the blood and the cellsIn cellular respiration, O2 is used to produce ATP while CO2 is released as a byproductHow do O2 and CO2 behave in air?Partial pressure is the pressure of a particular gas in a mixture of gasesAccording to Dalton’s law, the partial pressure of a gas is the sum of partial pressures of all gases in the mixtureGasses diffuse from areas of high partial pressure to areas of low partial pressureTo calculate partial pressure, multiply the fraction of air that gas comprises by the total atmospheric pressure.Oxygen comprises 21% of air, what is the partial pressure at 760 mmHg?PO2 = 0.21 x 760 mmHg = 160 mmHgWhat is the partial pressure at 250 mmHg?PO2 = 0.21 x 250 = 53 mmHgAs you increase in elevation, it becomes harder to breath because the external partial pressure of oxygen is lowerHow do O2 and CO2 behave in water?There is less oxygen available in water than in air and water is much more dense and thus flows less easilyFactors that affect the amount of O2 and CO2 in waterSolublity of a gas in waterTemperature of gas in water: cold water contains more oxygenPresence of other solutes: more oxygen in fresh waterPartial pressure of gas in contact with waterThe activity of inhabiting organisms: photosynthetic organisms increase oxygen, decomposers decrease oxygenSurface area and mixing increases oxygenFick’s Law of DiffusionThere are three parameters that allow animals to maximize rate of diffusionA – a large surface area for gas exchangeP2-P1 – A high gradient of partial pressuersD – a low thickness of the surfaceSolubility of the gas and the temperature are in the constant KInsect tracheal systemSpiracles on the body surface lead to tracheae that branch into trachioles that terminate near the body cells.These are very efficient, being able to support insect flight muscles with a high metabolismThe tracheae are compressed and dilated for ventilation, similar to how we use our diaphragm Gills are outgrowths of the body surface or throat used for gas exchange in aquatic animalsGills allow for an extremely large surface area and have an extremely thin epitheliumGill structure is very diverse, being either internal or external depending on the speciesFish gills work via a countercurrent systemThe flow of the capillaries is opposite to the flow of water over the gillsThis exchange system creates a large partial pressure difference and keeps them from reaching equilibrium.Very efficient for exchange of both oxygen and carbon dioxideLung structuresAir enters through the mouth and nose, into the trachea and bronchi, and into the alveoliAlveoli are thin-walled structures with capillaries. They facilitate gas exchange by having a thin barrier and a large surface area.Negative Pressure ventilationThe air pressure inside the body cavity is slightly lower than the atmospheric pressure. This keeps the lungs from collapsing when we breath out.To inhale, the diaphragm flexes and increases volume in the body cavity. This decreases pressure in the lungs, pulling in air.To exhale, the diaphragm relaxes and decreases volume in the body cavity. This increases pressure in the lungs, forcing air out. Only seen in mammalsPositive pressure ventilationFrogs draw in air by increasing the volume of the oral cavity. The nasal passages are closed, and the air is pushed into the lungs by decreasing the volume of the oral cavity.How is ventilation used to maintain homeostasis?When exercising, O2 is used and CO2 is produced. When CO2 enters the blood, it is converted into bicarbonic acid, decreasing the pH of blood.CO2 + H2O H2CO3 H+ + HCO3The brain senses this change in pH and sends a signal to the respiratory system to increase breath rate. Blood is a connective tissue made up of mostly liquid plasma and the rest is made up of formed elementsThe formed parts are platelets, white blood cells, and red blood cellsHemoglobin is a tetramer, or made up of four polypeptide chains, each with a heme group.These heme groups contain one Fe++ atom each, which can bind to an oxygen moleculeOxygen diffuses from blood to tissues due to the partial pressure gradientOxygen dissociation curve/hemoglobin saturation curveThis graph plots the percent saturation of O2 in hemoglobin, or the affinity of hemoglobin to O2, versus the partial pressure of oxygen within the tissues.Low partial pressure in tissue, low affinity of hemoglobinHigh partial pressure in the tissue, high affinity of hemoglobinHemoglobin exhibits cooperative binding, meaning that the binding of oxygen increases the affinity of it to bind to more oxygen. This is why the graph is a sigmoidal curve.If this did not occur, the change of O2 release between rest and exercise would not be as great.During exercise, the change in pH causes the graph to shift to the right, causing oxygen to unload faster. This is called the Bohr shift.Fetal hemoglobin has a higher affinity, shifting the graph to the left. This allows the fetus to get oxygen from the mother. When CO2 enters the red blood cell, the enzyme carbonic anhydrase converts it to bicarbonate. The excess proton is taken up by hemoglobin to decrease pH. ................
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