#Week 5 - Animal energetics and thermal biology - Animal nervous system - Sensory system in animals - Lab - Computer- MetaNeuron- or Osmoconformers #12. Animal energetics and thermal biology - Review - Basic concepts on homeostasis and temperature - How does body size affects animal physiology? (Ch 42, pp 850-853). Body size has a pervasive effect on how animal function. This concept was introduced in the first lecture: Introduction to aquatic physiology - Surface area/volume relationship (refresh concepts on feeding and gas exchange structures) - Comparing mice and elephants: differences in mass specific metabolic rate - Changes during development - As animals gets larger, its volume increases much faster than its surface does - Case study: Newly hatched salmon can breathe through their skin and through their gills (Ch 42, pp 852, Fig. 42.11) - Specific heat capacity of water (see videos in link of interest) - Some basic concepts on thermal biology - Why temperature is important? - Temperature regulation is one of the most variable and noticeable form of homeostasis - There are enzymes within all cells that require optimal temperatures for them to remain functional - If the body temperature goes outside of the acceptable range, the cells will not be able to perform their chemical reactions - In addition, if the contents of a cell freeze, ice crystals can form inside the cell, which will damage the cellular structures - How do animals regulate their body temperature? (Ch 42, pp 854-858) - Heat flows “downhill”, from regions of higher temperature to regions of low temperature - If an individual is warmer than its surrounding, it will lose heat - If an individual is colder than its surrounding, it will gain heat - Mechanisms of heat exchange (Fig. 42.14) - Conduction - Convection - Radiation - Evaporation - Balanced equation: Heat storage = Total heat production ± Heat exchange by radiation ± Heat exchange by conduction and convection - Heat exchange by evaporation. Note: in aquatic environments, there is not evaporation and no significant radiation source (infrared radiation is rapidly absorbed in water). This leaves the equation: Heat storage = Total heat production ± Heat exchange by conduction and convection - Variation in thermoregulation (Ch 42, pp 855-858) - How animals obtain heat - Endotherm, produce adequate heat to warm its own tissues - Ectotherm, relies principally on heat gained from the environment - Whether body temperature is constant - Homeotherm, keep their body temperature constant - Heterotherm (or poikilotherm), allow their body temperature to rise or fall depending on the environment - Note: some authors refer to heterotherms as those animals which USUALLY keep a constant body temperature, but have specific periods where temperature is different (e.g., hibernation), while poikilotherms are those whose temperature changes according (and strictly) to the environment. Check this for terminology: https://books.google.com/books?id=Af7IwQWJoCMC&pg=PA222&lpg=PA222&dq=tolerate+dehydration+in+animals&source=bl&ots=T_n_TvYrGg&sig=o3CcSrI-jqcO1flcnZ-joOuG3Vg&hl=en&sa=X&ved=0CEkQ6AEwBmoVChMIx-ay99D8xwIVASmICh3VRAEm#v=onepage&q=tolerate%20dehydration%20in%20animals&f=false - - Range of temperature that tolerates - Eurytherm - Stenotherm (see The physiology of climate change, in links of interest) - Strict endotherm, ectotherm, homeotherm or heterotherm are extreme, many animals fall somewhere in between. Some examples: dessert-adapted mammals, naked moles, Japanese honeybees (see examples in pp 855-856. An extreme case is the Japanese honeybees which kill predators using heat, this is called facultative endothermy) - How animals survive to winter? - Strategy: torpor and hibernation vs. migration vs. adaptation - Ectotherms may become dormant. Dormancy is NOT hibernation. Fish are ectothermic, and so, by definition, cannot hibernate because they cannot actively down-regulate their body temperature or their metabolic rate. However, they can experience decreased metabolic rates associated with colder environments and/or low oxygen availability (hypoxia) and can experience dormancy - Contrasting adaptive strategies: endothermy vs. ectothermy (Ch 42, pp 856) - The major advantage of endothermy over ectothermy is decreased vulnerability to fluctuations in external temperature. Regardless of location (and hence external temperature), endothermy maintains a constant core temperature for optimum enzyme activity - Endotherms can warm themselves because their basal metabolic rates are extremely high. Mammals and birds retain this heat because they have elaborated insulate structures as feathers, fur or massive amounts of insulating fat (as we will explain later in marine mammals) - Ectotherms can also generate heat as a by-product of metabolism, but the amount of heat that they produce is small compared with the amount generated by endotherms - To fuel their high metabolic rates, endotherms have to obtain large amount of energy-rich food. The energy to produce heat is unavailable to other process such as reproduction or growth Food+O2=Heat+H2O+CO2 - In contrast, ectotherms can thrive with much lower intake of food, and because they are not oxidizing food to provide heat, they can use a higher proportion of their energy to support reproduction and growth - Downside of ectothermy: Chemical reaction rates are temperature-dependent, so muscle activity and digestion slow as the body temperature of an ectotherm drops. Q10 temperature coefficient - What happens in the aquatic environment? - Water is a “heat sink”: The high thermal conductivity and heat capacity of water compared with air promotes elevated rates of heat loss through conductive and convective pathways. This is due to the hydrogen bonding (Ch 2, pp 27-28) - Considering the balance equation, there is not evaporation and no significant radiation source (infrared radiation is rapidly absorbed in water). So for endotherms, either total heat production must be increased, or conductive loss must be minimized - Endothermy in aquatic animals (mammals) - Lower temperature differential: typical mammalian 36-38 C vs. cetaceans 35.5 C - Generally occur while diving - Lower body temp reduce O2 consumption (hypometabolism) - Promotes longer dives time - Increase body size (surface area /volume ratio)- Because of the high thermal conductivity and high heat capacity of water, a small animal loses heat rapidly and has no chance of attaining a body temperature very different form the medium - Increase metabolism heat (heat production) - Increase insulation (reduce conductance) - Blubber layer: sheet of adipose tissue reinforced by collagen and elastic fibers - Density or length of hair (sea other 125,000 hairs per cm2) - Hair = air = insulation, requires grooming - Vascular specialization - Countercurrent heat exchanger (see gray whale tongue in Ch 42, pp857-858) - Peripheral vasoconstriction - Locomotor activity - Behavioral thermoregulation - Clump together when cool to save heat - Haul out when warm in Polar Regions - Lie in water when warm - Sand flipping - Ectothermy in aquatic animals (fishes) - Fishes’ blood has almost direct contact with their heat-robbing environment—through the gills. So for fishes, this means that using your metabolism to keep warm would be very energetically expensive Heterothermy is primitive, in the fact that the first vertebrates were (and are) heterotherms - However, some species of fishes (fast-swimming fish e.g., tunas and sharks) achieve independent control of temperature in limited parts of the body. Therefore, they are endotherms. - These species use a counter-current circulatory system called the rete mirabile (Latin for “wonderful net”), which exchanges venous blood (going to the heart) and arterial blood (going from the heart)-- This minimizes the amount of heat that is lost between the fish’s warm, fast moving extremities and its cooler, slow-moving core. See Barbara Block’s paper on endothermy in fishes. - More recently, the deepwater opah (see links of interest) - Links of interest Specific heat capacity –very simple but instructive videos https://www.youtube.com/watch?v=UtyyUHJGsUY https://www.youtube.com/watch?v=Opitd0zQ9XY Q10-The temperature coeficient https://www.youtube.com/watch?v=UQWWSmGM0yQ Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus http://www.sciencemag.org/content/348/6236/786 More information about opah http://io9.com/behold-the-first-fully-warm-blooded-fish-known-to-scien-1704472418?utm_expid=66866090-48.Ej9760cOTJCPS_Bq4mjoww.0&utm_referrer=https%3A%2F%2Fwww.google.com Thermal biology of zebrafish http://www.sciencedirect.com/science/article/pii/S0306456510001440 The physiology of climate change: how potentials for acclimation and genetic adaptations will determine “winners” and “losers” http://jeb.biologists.org/content/213/6/912.full NOAA declares third ever global coral bleaching event Bleaching intensifies in Hawaii, high ocean temperatures threaten Caribbean corals http://www.noaanews.noaa.gov/stories2015/100815-noaa-declares-third-ever-global-coral-bleaching-event.html Thermoregulation in mammals (4 papers, very good for graphs): 1. The effects of water temperature on the energetic costs of juvenile and adult California sea lions (Zalophus californianus): the importance of skeletal muscle thermogenesis for thermal balance http://williams.eeb.ucsc.edu/publications/pdfs/Liwanag%20et%20al%202009.pdf 2. Energetic costs and thermoregulation in northern fur seal (Callorhinus ursinus) pups: the importance of behavioral strategies for thermal balance in furred marine mammals http://www.ncbi.nlm.nih.gov/pubmed/20950169 3. The fat and the furriest: morphological changes in harp seal fur with ontogeny http://www.ncbi.nlm.nih.gov/pubmed/25730271 4. Shifts in thermoregulation strategy during ontogeny in harp seals http://www.ncbi.nlm.nih.gov/pubmed/25086979 Endothermy in fishes: a phylogenetic analysis of constraints, predispositions and selection pressures http://link.springer.com/article/10.1007%2FBF00002518#page-1 Why do tunas maintain elevated slow muscle temperatures? Power output of muscle isolated from endothermic and ectothermic fish http://jeb.biologists.org/content/200/20/2617.long #13. Animal nervous system - Background - The ability to sense and react originated billions of years ago with prokaryotes that could detect changes in their environment and respond in ways that enhanced their survival and reproductive success - Such cells could locate food sources by chemotaxis - Later, modification of this simple process provided multicellular organisms with a mechanism for communication between cells of the body - By the time of the Cambrian explosion, systems of neurons that allowed animals to sense and move rapidly had evolved in essentially modern form - The nervous system among taxa - Nervous systems show diverse patterns of organization - All animals except sponges have some type of nervous system - What distinguishes nervous systems of different animal groups is how the neurons are organized into circuits - Cnidarians have radially symmetrical bodies organized around a gastrovascular cavity - In hydras, neurons controlling the contraction and expansion of the gastrovascular cavity are arranged in diffuse nerve nets - The nervous systems of more complex animals contain nerve nets, as well as nerves, which are bundles of fiberlike extensions of neurons - With cephalization come more complex nervous systems - Neurons are clustered in a brain near the anterior end in animals with elongated, bilaterally symmetrical bodies - In simple cephalized animals such as the planarian, a small brain and longitudinal nerve cords form a simple central nervous system (CNS) - In more complex invertebrates, such as annelids and arthropods, behavior is regulated by more complicated brains and ventral nerve cords containing segmentally arranged clusters of neurons called ganglia - Nerves that connect the CNS with the rest of the animal’s body make up the peripheral nervous system (PNS) - The nervous systems of mollusks correlate with lifestyle - Clams and chitons have little or no cephalization and simple sense organs. - Squids and octopuses have the most sophisticated nervous systems of any invertebrates, rivaling those of some vertebrates. - The large brain and image-forming eyes of cephalopods support an active, predatory lifestyle. - Principles of electrical signaling (Ch 46, pp 929-934) - Central nervous system vs. peripheral nervous system - Types of neurons in the nervous system - Sensory neurons - Interneurons - Motor neurons - The anatomy of a neuron (Ch. 46, pp 929-930) - Networks of neurons with intricate connections form nervous systems - The neuron is the structural and functional unit of the nervous system - The neuron’s nucleus is located in the cell body - Arising from the cell body are two types of extensions: numerous dendrites and a single axon - Dendrites are highly branched extensions that receive signals from other neurons - An axon is a longer extension that transmits signals to neurons or effector cells - Membrane potential (Ch 46, pp 930-938) - All cells have an electrical potential difference (voltage) across their plasma membrane. - This voltage is called the membrane potential - In neurons, the membrane potential is typically between −60 and −80 mV when the cell is not transmitting signals - The membrane potential of a neuron that is not transmitting signals is called the resting potential (ironically, the neurons invest lot of energy to keep that “resting potential stage”) - Resting membrane potential (Ch 46, pp 930-933, Fig. 46.3) - This concept is very well explained in the video by Ray Cinti (see links of interest), I think that we should follow that approach - In all neurons, the resting potential depends on the ionic gradients that exist across the plasma membrane. - A neuron at resting potential, the concentration of K+ is greater inside the cell while the concertation of Na+ is greater outside the cell - A neuron at resting potential contains many passive K+ channels and fewer passive Na+ channels; K+ diffuses out of the cell - Anions trapped inside the cell (e.g., proteins) contribute to the negative charge within the neuron - How the resting potential in maintained? The Na+/K+-ATPase - Membrane protein - 3 Na+ pumped out and 2 K+ pumped in - Against their electrochemical gradient - Actively transport: requires ATP –consumes energy- - Necessary to maintain K+ and Na+ gradients across the plasma membrane - Define action potential threshold - Sufficient to drive the interior potential from -70 mV up to -55 mV, the process continues - The action potential (Ch 46, pp 933-938) - Again, this concept is very well explained in the video by Ray Cinti (see links of interest), I think that we should follow that approach - An action potential is a rapid, temporary change in a membrane potential When stimulated, neurons mount action potential that allow them to communicate with other neurons, muscles or glands. This is a three-phase signal: - 1. Depolarization - Neurotransmitter stimulate ligated-gated Na+ channels (in dendrites) to open - Na+ comes inside the cell (due to electrochemical gradient: 1. Concertation of Na+ is greater outside the cell (chemical), 2. Negative charge within the neuron (electrical)) - The higher concentration of Na inside the cell activates voltage-gated Na+ channels which open quickly and more Na+ comes inside the cell (this happens at -55 mV aprox.), see Ch 46, pp 935, Fig. 46.6.- This is an example of POSITIVE feedback mechanism - The cell become more and more positive due to the accumulation of Na+ - At +40 mV, the equilibrium potential for Na+ is reached, voltage-gated Na+ channels close and the voltage-gated K+ channels open - The K+ leaves to the outside (massive movement of K out the neuron) through both voltage- and K+ leak channels (passive K+ channels) - 2. Repolarization - Due to the K+ leaving the neuron (electrochemical gradient), the inside of the neuron becomes less and less positive, until finally is negative compared to the outside - 3. Hyperpolarization - However, for K+, the chemical gradient is stronger than the electrical gradient so the efflux of K+ extends beyond electric neutral and even beyond -70mV to approx. -90mV, this is the hyperpolarization stage - Most K+ channels now close and Na+ channels remain closed and the Na/K ATP pump re-established concentration and therefore also electrical gradients across the membrane by pumping out 3 Na+ and taking in 2 K+ at the expense of ATP - Inactivated Na+ channels behind the zone of depolarization prevents the action potential from traveling backwards - Hyperpolarization prevents the neuron from receiving another stimulus during this time, or at least raises the threshold for any new stimulus - Part of the importance of hyperpolarization is in preventing any stimulus already sent up an axon from triggering another action potential in the opposite direction. In other words, hyperpolarization assures that the signal is proceeding in one direction: toward the synaptic terminals - Several factors affect the speed at which action potentials are conducted along an axon - One factor is the diameter of the axon: the larger the axon’s diameter, the faster the conduction - In the myelinated neurons of vertebrates, voltage-gated Na+ and K+ channels are concentrated at gaps in the myelin sheath called nodes of Ranvier - Only these unmyelinated regions of the axon depolarize - Thus, the impulse moves faster than in unmyelinated neurons - How’s the action potential propagated? Ch 46, pp. 936, Fig. 46.8. - The refractory state - The synapse (Ch 46, pp938-942) - The fact that the axon becomes positive temporarily (action potential) makes the voltage-gated Ca2+ to open at the end of the axon - The Ca2+ gets inside the cell massively - In response to the increase Ca2+ inside the axon, synaptic vesicles fuse with the membranes and release neurotransmitter into the synaptic cleft - In turn, neurotransmitters bind the ligated-gated Na+ channels in the dendrites of the next neuron (post-synaptic neuron), and makes them to open - Neurons integrate information from hundreds or thousands of synapses from other cells (Ch 46, pp 941, Fig. 46.14) - Excitatory popsynaptic potentials (EPSPs) - Inhibitory popsynaptic potentials (IPSPs) - Links of interest Lecture on resting membrane potential by Ray Cinti –Very good https://www.youtube.com/watch?v=RTRZNK9Aahc The action potential by Ray Cinti –Very good https://www.youtube.com/watch?v=fO5Xgnswl58 Invertebrate nervous system http://www2.le.ac.uk/departments/npb/people/matheson/matheson-neurobiology/images/publications/Matheson_ELS_2002.pdf Slides on nerve signaling http://www.slideshare.net/thelawofscience/nerve-signaling Series of educational animations on voltage-gated channels and the action potential http://highered.mheducation.com/olc/dl/120107/anim0013.swf http://www.sumanasinc.com/webcontent/animations/content/actionpotential.html http://www.sumanasinc.com/webcontent/animations/content/action_potential.html http://highered.mheducation.com/olc/dl/120107/bio_d.swf #14. Sensory system in animals - Background - Animals transform sound, smell, and other stimuli into signals that the brain can understand - Structures that make up sensory systems have been transformed by evolution into diverse mechanisms that sense various stimuli and generate the appropriate physical response - In most of cases, a specie’s sensory abilities correlate with the environment it lives in and its mode of life –how to find food and mates - Complex sensory system facilitates survival - How do organs convey information to the brain? (Ch. 47 pp 953) - Each type of sensory information (external and internal) is detected by a sensory neuron or by a specialized receptor cell that makes a synapse with a sensory neuron - Activation of sensory receptors results in depolarizations that trigger impulses to the CNS - The ability to sense a change in the environment depends on four processes (Ch 47, pp 953) - 1. Transduction, the conversion to a stimulus to energy /internal sign in the form of action of potential along sensory neurons - 2. Amplification, the strengthening of stimulus energy by cells sensory pathways - 3. Transmission of the signal to the central nervous system - 4. Integration of the sensory information, which occurs at the CNS - All action potential are exactly identical in shape and size. The difference is the frequency. The CNS integrates information of the frequency and where it comes from - Some receptor potential are integrated through summation - Some receptor potential are integrated by adaptation –decrease in responsiveness during continued stimulation- - If a sensory stimulus induces a large change in a sensory receptor’s membrane potential, there is a change in the ‘firing rate” of action potential sent to the brain - The amount of depolarization that occurs in a sound-receptor, for example, is proportional to the loudness of the sound. If the depolarization passes threshold, enough voltage-gated sodium channels open to trigger action potential that are relayed to the brain. - Note: All action potential have identical size and shape, the difference is the frequency (remember the “all or nothing”: amplitude of action potential is independent of stimulus strength once threshold is reached; amplitude of all action potential is constant) - In vertebrates, two keys to understand how the brain interprets sensory information: - Receptor cells are highly specialized - Each type of sensory neuron sends its signal to a specific portion of the brain - Sensory transduction (Ch 47 pp 953) - The first step in the sequence, transduction, requires a sensory receptor cell specialized for converting the stimuli into an electrical signal - Sensory receptors classification by location - Exteroreceptors - Respond to stimuli arising outside the body - Found near the body surface - Sensitive to touch, pressure, pain, and temperature - Include the special sense organs - Interoreceptors - Respond to stimuli arising within the body - Found in internal viscera and blood vessels - Sensitive to chemical changes, stretch, and temperature changes - Proprireceptors (mostly studied in human) - Nonvisual perception of body position - Found in joint receptors, muscles spindles and Golgi tendon organs (sense changes in muscle tension) - Constantly advise the brain of one’s movement - Sensory receptors classification by the energy they transduce - 1. Mechanoreceptor - 2. Photoreceptor - 3. Chemoreceptor - 4. Thermoreceptor - 5. Electroreceptor - 6. Magnetoreceptor - 7. Nociceptor - 1. Mechanoreception: sensing pressure changes - Animals have different mechanism for mechanoreception –the sensation of pressure changes- - The mammalian sense of hearing relies on mechanoreceptors that are hair cells in communication with an afferent neuron - The structure of hair cells (Ch 47, pp 954-955, Fig, 43.7) - Signal transduction in hair cells - Hair cells in aquatic organisms - Gravitational detectors - Statocyst - The Statocyst is a balance sensory receptor (pressure created by gravity) in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans - The statocyst consists of a sac-like structure containing a mineralized mass (statolith) and numerous innervated sensory hair cells. The statolith may be secreted by the statocyst or, as in lobsters, it may be formed of sand grains collected for the environment. - The statolith's inertia causes it to push against the sensory hair cells when the animal accelerates and when changes in orientation, allowing balance to be maintained - Because many echinoderms of this group have only simple nervous systems without a controlling "brain", they are limited in their actions and responses to stimuli. The statocyst is therefore useful for telling the animal whether it is upside down or not. An upside-down echinoderm is in danger since its belly is not protected by its spiny skin ![statolith](https://cloud.githubusercontent.com/assets/13633831/9692782/671566ec-5300-11e5-866c-98f80299ddae.JPG) - Otoliths - The vertebrate inner ear also operates like a statocyst. Otoliths, the equivalent of statoliths in vertebrates, move against hair cells called cristae inside fluid-filled ducts (ampullae) to detect gravity and acceleration. - The lateral line system (Ch 47, pp 958-959, and Fig. 47.8) - The lateral-line system is visible as a faint line running down each side of a fish’s body. In sharks, rays and many bony fishes, the neuromast receptors cells (hair-like clusters on the epidermal surface which are projected into a cupula) are located in a canal beneath the skin’s surface. The canal connects with the external environment through a series of pores - The lateral line is highly versatile, being employed in diverse tasks such as schooling (helping to explain the remarkable synchronous movements), tracking and detection of prey and predators and even sexual communication - The aquatic vertebrate’s mechanoreceptors have evolved to know the difference between water displacement caused by their own movement compared to the movement of other organisms, which could be potential predators, mates, or members of their own species. This type of mechanoreceptor allows the organism to sense other organisms before there is any physical contact taking place - The most striking analogy to the lateral line system of fish is found in cephalopods such as cuttlefish, squid and octopuses, where the head and arms bear similar lines of ciliated epidermal cells - A number of species in the shrimp families Sergestidae and Penaeidae have long trailing flagella on the second pair of antennae that are held parallel to the body at some distance. Their tips are equipped with curved setae that form tubes containing mechanoreceptors at regular intervals. Some mechanical properties of this system are remarkably similar to those of fish lateral lines - The electroreceptors of sharks and other electroreceptive fish are derived from the lateral line system. It is thus central to the sensory world of fish ![ll](https://cloud.githubusercontent.com/assets/13633831/9692791/723a6aae-5300-11e5-95f9-5bb6e540501b.JPG) - Echolocation (aka bisonar) - This strategy is valuable underwater, due to its favorable acoustic characteristics and where vision is extremely limited in range due to absorption or turbidity. - The case of toothed whales- see links of interest - 2. Photoreception: sensing light (Ch 47, pp 959-964) - Light is effectively parcels of energy called photons, which travel in a wave, the frequency (or wavelength) of which is proportional to the energy they contain - Most animas have a way to sense light. The organ involved in photoreception range from a simple light-sensitive eyespot in flatworms to the sophisticated, image-forming eyes of vertebrates, cephalopods, mollusk, and arthropods - The visual ability of an animal influences many aspects of its behavior, including feeding, defense and courtship ![electromagneticspectrum](https://cloud.githubusercontent.com/assets/13633831/9692813/99355e20-5300-11e5-8198-f45335edb5f3.JPG) - What is an eye? An eye is an organ that detects this light and translates it via nervous impulses to the brain, where the information is processed further. There is a wide variety of eyes in the animal kingdom, relating to the different types of environment that animal inhabit and the different behavioral takas they undertake - Compound eye - Insects, crustaceans, and certain arthropods have eyes formed form multiple units called ommatidia (Fig. 47.10) - Simple eye - Annelids, cephalopods (squid and octopuses) and vertebrates have single eyes, a structure with a single lens that focuses incoming light onto a layer of many receptor cells (Fig. 47.11) - Function and structure of rods and cones (Ch 47, pp 960-963) - Pineal gland in lower vertebrates - In ectotherms, the pineal gland displays adaptation to light perception. It is a vesicle located just below the skull in an area where the bone is thinner and the surrounding tissues are less pigmented thereby facilitating light entry –See blind fish see shadows in link of interest - see artcle on The energetic cost of vision and the evolution of eyeless Mexican cavefish, in links of interest - 3. Chemoreception: sensing chemicals (Ch 47, pp 964-967) - Chemoreceptors detect the presence of particular molecules by undergoing a change in membrane potential when a specific compound is present. In this way, information about the presence of a particular chemical is transduced to an electrical signal in the body - Taste and smell are important senses for many animals, helping them to find food and mates, communicate and navigate - Distant chemoreceptor: Smell is governed by olfactory receptors, which detect odor molecules from objects at a distance. The molecules can be carried in the air or in the water. On reaching an animal, the molecules bind to the membrane of olfactory hairs (cilia). Importance in que chemical/Pheromonal communication. There is evidence that fish and turtles can distinguish the smell of the area (stream or beach) they were born in and use this information as a navigational tool - Effect of current in olfaction ![currentandolfaction](https://cloud.githubusercontent.com/assets/13633831/9692806/8bead8f8-5300-11e5-99e6-101fc0b98593.JPG) - Direct chemoreceptor: Taste allows the animal to detect and identify molecules form objects that come in contact with its gustatory (taste) receptors. These sensory cells may be concentrated in different regions (e.g., mouth, skin or feet) - The sense of taste in aquatic organisms is probably very similar to the sense of taste in terrestrial organisms. In both cases, the chemicals which will be tasted must be dissolved in water - Peripheral chemoreceptors: sensory extensions of the peripheral nervous system into blood vessels where they detect changes in chemical concentrations - Quorum sensing in microbes (Ch 11, pp 216) -Quorum sensing is the regulation of gene expression in response to fluctuations in cell-population density - 4. Thermoreception: sensing temperature (Ch 47, pp 967) - Very important in animals that thermoregulate - Some thermoreceptors are located in CNS, while other are located in the skin and other outer surfaces of animals, so that changes in the environmental temperature can be sent. - 5. Electoreception: sensing electric fields (Ch 47, pp 967-968) - All animals give off weak electrical pulses that arise from the activity of their nerves and muscles. Since the water is a good conductor of these electrical impulses, many kind of fishes use electroreception, or sensation for electric field, to locate prey, detect predator and navigate. - Electroreceptors contain modified hair cells that reposnd to electric field - Sharks use electroreception to hunt and navigate: role of ampullae of Lorenzini (hair cells) - Electromagnetic fishes generate electric fields: electrocytes in electric eels - 6. Magnetoreception: sensing magnetic fields (Ch 47, pp 968) - The Earth produces a magnetic field as it rotates on it axis. Magnetoreception has been described in many groups of organisms including bacteria, fungi, invertebrate and vertebrates - Magnetotaxis in bacterias - Some contain little particles of minerals that orient with the planet’s magnetic fields to help the bacteria figure out whether they’re swimming up or down - Another less general type of magnetic sensing mechanism in animals that has been thoroughly described is the inductive sensing methods used by sharks, stingrays and chimaeras (cartilaginous fish). These species possess a unique electroreceptive organ known as ampullae of Lorenzini which can detect a slight variation in electric potential. These organs are made up of mucus-filled canals that connect from the skin's pores to small sacs within the animal's flesh that are also filled with mucus. The ampullae of Lorenzini are capable of detecting DC currents and have been proposed to be used in the sensing of the weak electric fields of prey and predators. These organs could also possibly sense magnetic fields, by means of Faraday's law: as a conductor moves through a magnetic field an electric potential is generated - Links of interest Low frequency sounds induce acoustic trauma in cephalopods http://www.esajournals.org/doi/pdf/10.1890/100124 Bottlenose dolphin: communication and echolocation http://seaworld.org/en/animal-info/animal-infobooks/bottlenose-dolphins/communication-and-echolocation/ For bats and dolphins, hearing gene prestin adapted for echolocation http://mbe.oxfordjournals.org/content/31/9/2552.full.pdf+html Adaptive features of aquatic mammals’ eye http://onlinelibrary.wiley.com/doi/10.1002/ar.20529/epdf Photoreception in marine invertebrates http://www.jstor.org/stable/3883142?seq=1#page_scan_tab_contents Structure and functional evolution of the pineal melatonin system in vertebrates http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.2009.04435.x/epdf Blind fish see shadows http://www.nature.com/news/2008/080124/full/news.2008.524.html The sensory world of aquatic organisms http://www.marietta.edu/~mcshaffd/aquatic/sextant/senses.htm Evidence that fin whales respond to the geomagnetic field during migration http://jeb.biologists.org/content/171/1/67.full.pdf+html Linea lateral in fish and other animals http://www.mapoflife.org/topics/topic_443_lateral-line-system-in-fish-and-other-animals/ Website about shark senses http://www.sharkproject.org/haiothek/index_e.php?site=funktion The energetic cost of vision and the evolution of eyeless Mexican cavefish http://advances.sciencemag.org/content/1/8/e1500363.full #LAB WORK 5 - Option 1: Metaneuron - MetaNeuron is a free computer program that models the basic electrical properties of neurons - The program is intended for the beginning neuroscience student and requires no prior experience with computer simulations - Different aspects of neuronal behavior are highlighted in the six lessons presented in MetaNeuron - We can download the software and teh manual for free at http://www.metaneuron.org/ - Although the software is very user-friendly, might be a little too adavanced of this course - Option 2: Salinity and volume regulation - As we explained, most of marine invertebraets are osmoconformers - Determine effect of different salinities and sacarose on changes on body weight and survival in a marine worm - Characerize the effect of NaCl (animal is permeable) vs. sacarose (impermeable) - Stablish differences in wet vs. dry weight