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129 Cards in this Set
- Front
- Back
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ethology
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the study of the natural history of behavior
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evolution of perception
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- how animals adapt to deal with tuning to environmental cues
- human taste - color vision in bees - in order to understand the complexities of human as an organism it is necessary to study organisms with simpler systems |
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nature vs. nurture controversy
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is behavior genetically inherited or is it learned?
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levels of analysis of behavior
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- alternatively instead of dichotomy between the two
- it is necessary to look at "levels of analysis of behavior" - proximate = how - ultimate= why, causation |
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instinct theory and mechanisms of behavior
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- communication and cognition
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why study behavior?
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- it bridges biology, social sciences, and humanities
- understanding behavior is central to medicine -psychiatry and pharmacology |
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behavior is...
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a "window in the brain"
- regardless of what type of brain, it still functions via chemicals, neurons ect. - we can understand our brian by and how it is organized by evaluating our behavior |
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themes and approaches to behavior
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- behavior is interdisciplinary it includes the concepts of genetics of behavior, neurobiology and ecology
- biologists use different animlas as models for research - behavior evolves |
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models
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- a model provides comparisons across clades
- helps to obtain understanding of more complex behaviors and systems based on simpler ones - common models are Fruit flies, C.elegans and sea slugs - they exhibit simple behaviors and have simple or no brains with simple neuron networks |
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evolution of behavior
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- it is adaptive and therefore can be acted on by natural selection
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what is ethology?
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- the natural history of behavior
- emphasizes field research - deals with perception and information processing - information processing- interpretation of environmental info or cues that allow organisms to respond to their to environment adaptively |
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perception
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- beahvior (mating, foraging, orientation, predator avoidance) is guided by information in the environment
- animals make "decisions" based on their sensory perception - what animals can percieve and how they respond depends on their ecology and evolution |
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human taste and food choice
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- eating a chip tastes good, but why?
-process of human evolution and adaptation - OB gene controls leptin - senory processing - mechanisms that induce brain - spatial memory - all of this has evolved in humans |
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process of human evolution and adaptation
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- human health improved after agriculture
- ex: enamel on teeth sows less wear among post agriculutral groups - a diet shift produced a decrease in stress on teeth and increase in nutrition - agriculture was an adaptive benefit - diet drives genetic change - pokot in Kenya live on dairy diet and have 3 gene mutations for lactose tolerance |
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OB gene
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- controls leptin
- leptin is a hormone produced in fat cells that controls appetite - leptin decreases appetite and controls how the brain responds to/ percieves food - those who are leptin deficient are fat because have nothing decreasing their appetite |
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sensory processing
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- taste buds are sensory receptors that can sense fatty foods and savory molecules
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mechanisms induce brain
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- mechanisms that induce the brain to send signals to continue eating or stop eating a certain food
- dopamine is related to pleasure centers in the brain and stimulates the desire to continue in the activity the organism is engaged in |
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spatial memory
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- the ability to map and locate high calorie food sources
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evolution of preference for fatty food in humans
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- sodium is important in physiological processes and fat is rich in calories
- both fat and sodium were rare in natural hominid environment - we evolved to desire and acquire these foods - today we are no longer restrained by those same limitations yet we still have the receptors stimulate this desire which results in obesity |
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ethology and Honeybee: can they percieve color?
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- to understand need to establish tests: 2 scientists and 2 approaches
- Carl von Hess - Carl Von Frisch |
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Carl von Hess
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- a vision physiologist inerested in the evolution of color
- he theorized that all invertebrates and fish were colorblind - he did lab based research - well known as a scientist |
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Car von Frisch
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- a "younger" (newer to the field) ecologist who thought that color blindness was absurd
- he did field based research - he was new and not well known |
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Von Hess's experiment
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- called the black box of bees
- his bioassay (test used to quantify behavior) - he shinied different color lights into the black box from its corners to see which color bees go for it --- in attempt to determine color preference - the bees showed "none" but did show a preference for the intensity of ligtht - this proved only that bees percieved more light as a potential way out |
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Von Frisch's experiment
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- he found it hard to believe that nature would make such an absurd mistake in not producing color seeing bees in a color filled environment
- his bioassay included marking bees and training them to associate a reward (sugar water) with the color blue - to exclude the issue of "handedness" he switched the position of the colored card, tested for gray scale variance and controlled odor and other potentially indentifiable variances - the critical test came when he removed food from teh card and allowed the bees to choose between the cards of varying color and the test color which was blue - the bees showed a preference for the specific color blue |
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sensory ranges for vision
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- bees can see in the UV range
- some snakes can see in the far red (infrared) - we see in the middle ranges of light wavelengths |
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rods and cones- us vs. bees
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- we have rods and cones in the eye that interact to capture light
- we have tri-chromatic vision that percieves blue, green and red wavelengths the best - bees have tri-chromatic vision as well but the pigments in their eyes all percieve UV, yellow and blue the best - they cannot percieve light in the red wavelengths and above - bees cannot see red and therefore do not pollinate red flowers - other pollinators get to those like hummingbirds |
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Stomatopods
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- mantis shrimps
- have eyes that contain 16 total pigments - scientists aren't clear how these pigments are used but it may have to do with increasing contrast detection rather than broader color indentification - an important ability on colorful reef systems |
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fathers of behavioral biology
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- Von Frisch was considered to be the 1st sensory physiologist as well as the first individual to study non-human communication
- Konrad Lorenz - Niko Tinbergen |
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Konrad Lorenz
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- in behavioral dept. he studied imprinting behavior among ones species of goose
- he was the first to look at development and behavior as well as the first to study the phylogeny of behavior - behavior is just like any other biological trait, and can be classed like animals in phylogenies |
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Niko Tinbergen
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- adaptive benefits of behavior
- he spent most of his time in the field asking why? questions - he studied egg shell removal among bird species and determines that because predators use the white insides of egg shells as an indicator that chicks have recently been hatched, parents will remove the shells to reduce the attraction of predators to their young - this is anti-predatory behavior |
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1933 nobel peace prize
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- Von Frisch, Lorenz and Tinbergen all shared nobel- peace prize for their discoveries in field of behavioral biology
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founding mothers
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- Sarah Hardy
- Jeanne Altmann - Jane Goodall |
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Sarah Hardy
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- studies infanticide among langurs
- careful study showed that it was about reproductive adaptation |
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Jeanne Altman
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- studies female non-human primatology
- up until her time it was a male centered study, done by men - she studied baboons |
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Jane Goodall
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-studied chimpanzees
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anti-thesis of ethologist
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- B.F Skinner and his box
- he was a "lab" guy who studied reinforcement training - he believed that the brain is completely "blank" at birth and that by the process of learning, animals develop their brains and behaviors - i.e behavior is learned |
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The Nature vs. nurture debate
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- ethologists: nature, hardwired, genetic, evolutionary, adaptive
- nurture: behavior is learned from context of environment by individuals - ultimately it is both - instead of maintaining this dichotomy it is more useful to evalute different levels of analysis of behavior |
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levels of analysis of behavior
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- physiological
- ontogeny -phylogeny - adaptive significance |
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physiological
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- mechanistically speaking, what activates sexual behavior?
- hormones like estrogen and testosterone |
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ontogeny
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- which is synonymous with development
- imprinting and following behavior |
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phylogeny
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- ancestral forms of behavior that can be traced through a process or evolution of new behavioral traits
- you can map behavior similiarly to physical traits to determine when traits developed along the evolutionary chain |
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adaptive significance
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- survival value
- environmental pressures can lead to adaptive behavioral changes |
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proximate causation
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- answers the question how does it work
-mechanistic - physiological and ontogeny |
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ultimate causation
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- answers question- why did it develop
- phylogeny and adaptive significance |
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how does behavior work? what are it's mechanisms?
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- instinct theory: key stimuli (KS) in the environment are percieved by the innate releasing mechanism (IRM) found in the nervous system
- this triggers a fixed action pattern (FAP) that induces a behavior - these are hardwired innate responses- the terminology implies a neural circuitry |
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species typical behavior
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- egg retrival in geese
- gulls and beak spots - egg incubation |
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egg retrival in geese
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- egg retrival in geese: the bird will automatically retrieve an egg that has been seperated from its nest
- if the egg is removed mid-retrieval the goose will continue with the retrival motions as if a button has been pushed and the bird must run its "operating program" in full before it can reset and try again |
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gulls and beak spots
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- gapping mouths and pecking at beaks to induce food regurigation among birds species
- the releaser is a visual signal and the chick responds due to an innate releasing mechanism (i.e sees the dot and innately knows to peck at it to recieve food) - dot color doesnt matter, contrast is the key here - since behavior can be quanitified here a bioassay could be developed which allowed biologists to develop models and then compare the responses to each model - responses where highest to long sticks with contrasting tip than to non contrasting beaks, partial parental head shapes and even to full model gull heads |
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egg incubation
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- supernormal responses
- gulls will attempt to incubate eggs that are unnaturally enormous compared to typical egg size they are capable of producing - this behavior shows a preference toward a larger (ie. fitter) eggs - it may be that they are programmed to prefer larger eggs, but because such abnormal sizes do not naturally occure they have not developed an upper limit on egg size and therefore fail to discriminate between their own species eggs and anothers |
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instict and animal communication
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- stimulus and response chains (stickleback)
- olfactory (chemical) communication 1. sex attractants 2. trail and alarm pheromones - ecology and communication - cognition |
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social releasers
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- stiumuli recived by social interaction: sending and recieving signals which influence behavior in both individuals involved
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the case of the 3-spined Sticklback in territory defense
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- males are the primary care parent
- they build algal nests in stream bed gravel - they must defend their territories (ie. resources) from other males of the same species - how do they recognize them? - males undergo a color change during breeding season, displaying brighter colors than at non- breeding times during the year - this coloration (a red underside) is a key visual cue - when tested a stimulus was introduced that mimicked the red underbelly of the stickleback males: there was an aggressive response to any shaped model that correctly displayed red underbellies |
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stickleback and courtship
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- when males see a femlae they dont display aggression
- instead they court her - how do they determine she is not another competitor? - male shows high degree of preference for body shape that shows high egg content - pear shaped feamles are Very good, they drive males crazy - they are typically high out-put females - in order to attract female the male does a zig-zag dance to attract the female and get her to deposit her eggs in his nest - she sizes him up to determine his fitness |
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firefly courtship
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- both male and female fireflies produce biological light through mixing of chemicals in their abodomen
- the flash patterns produced are species specific; i.e each species produces its own pattern in order to attract the correct mate of the same species - this type of behavior is significant as a pre-reproductive isolation mechanism - ethological (behavioral) isolation of sympatric firefly species is necessary to prevent mistakes in mating - selection is favored a strong divergence in firefly flash patterns therefore each species has a subtly unique pattern - allopatric species have no porblem in identifying mates therefore there was no selection for reproductive isolation |
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silk moth phermone
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- bombykol
- reproductive isolation through the use of chemicals - female silk moths- have glands on abdomen that release the sex pheromones to the air - male silk moths have larger feather like antennae that detect female pheromones - the sex pheromones are specific to species and present in very small quanities yet are very effective - Budtenandt- studied silk moths and researched biologically active molecules -500,000 female silk moths yielded 12mg bombykol - bombykol has high degree of species specificity inside its molecular structure |
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social insects --- ants
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- ants respond to simple chemcials following a trait; used for orientation and recruitment behavior
- ants secrete many chemicals that have a low molecular weight, are volatile and are transient- very important for alarm signalling |
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social insects--- bees
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- bee dance is used to tell of location of food sources; close to hive is a round dance
- far from hive is a waggle dance - waggle dance- the angle of the dance is relative to gravity and is equal to the angle of position of food sources from sun on horizon - vigorousness determines the distance of food source from the hive |
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human language
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- similar to bee dance in that it uses symbolism and abstraction to convey messages
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Vervet Monkeys
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- located in Eastern Africa and live in groups of 8-12 individuals
- produce predator specific alarm calls for leopards, marshal eagles and snakes - this type of communication is called a language of semantics (words with meaning) - the alarm calls differ acoustically and therefore produce different responses from the monkeys so that they can escape the predator effectively - ex: monkeys hide and get under cover when an eagle call is heard - vervet monkeys also lie to each other - ex: subordinate males give off false alarm call that distracts the dominant male so that the subordinate can improve his social situation |
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sensory systems and information processing
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- transduction
- neural circut - chameleon - rhodopsin |
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transduction
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conversion of energy of stimulus ( photons of light, mechanical sound) to chemical energy
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neural circut
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connects sensory apparatus to motor apparatus through neural tissue
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Chameleon
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sensory apparatus is large steroscopic eyes that detect prey and the motor apparatus is the stick tongue flying out to capture the prey
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rhodopsin
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- g protein
- visual pigments- rentinal and opsin - when light comes into eye, rhodopsin changes form the cis conformation to the trans conformation |
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Lecture 2 : Nerve cells and behavior
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1. environment to action- stimulus transduction
2. routing nerve implulses: sensory neutrons, interneurons and motor neurons, how neural circuts are designed 3. neuroethology of escape beahvior and other examples of specialized neural circuts |
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environment to action
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- stimulus perception to behavior
- two steps 1. transduction- conversion of energy of stimulus to electrical energy of nerve impulse 2. neural circuitry- neural organization from senses to muscles |
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transduction
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- energy of light, sound or chemical is transduced to nerve impulse energy
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how does transduction work?
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1. Rhodopsin is the visual pigment, made of teinal and a protein (opsin)
2. retinal has cis and trans forms 3. cis-retinal is converted to trans-retinal by light 4. this triggers a molecular cascade that opens sodium channels, causing a nerve cell depolarization (i.e neuron fires) |
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taste receptors
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- bitter, sour, salty, sweet
- decode composition of food - Gustducin (a G- protein in taste receptor cells) transduces bitter and sweet tastes |
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neurobiology: 2 components
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- neuroanatomy: microscopic level ex: looking at cell anatomy
- neural systems: macroscopic level, ex: which nerve innervates a certain muscle - environment favors neural systems to increase the fitness of the organism |
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sensory cells
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- detect changes in environment
- communicate to motor neurons |
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dendrites
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- recieve information
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action potential
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- an electrical current that moves down the axon of a neuron
- neurons communicate with each other via neurotransmitter release |
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afferent neurons
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- sensory neurons
- recives information and sends it to motor neurons |
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efferent neurons
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- motor neurons
- synpase onto muscles or glands |
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interneurons
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- in between afferent and efferent neurons
- intervening neurons - not found in monosynaptic reflexive arcs - ex: patellar reflex |
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sea slugs
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- Tritonia and Aplysia
- good model because they have simple behaviors, responses and nervous systems - stimulus: predators; starfish - response: escape behavior, sensory info (such as smells starfish odor or physical contact) is processed and used to control muscle movement - can record the activity of nerve cells when animal is moving upon probing an electrode |
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sea slug model
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-injection of dyed starfish scent into sea slug's environment results in alternating firing patterns of 2 neurons called coupled oscillators
1. DFN(dorsal flexion neuron) 2. VFN(ventral flexion neuron) - alternating firing pattern corresponds to alternating contraction of muscle - thus this simple rhythmic behavior of sea slugs can provide a good model for simple rhthymic behavior of humans such as walking, chewing, ect. |
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two generalizations from this model
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1. there is a command neuron which governs everything: takes sensory info and translates it to other neurons
2. central pattern generators- CPG- called couple oscillators which means that when one neuron is turning on it turns the other neuron off - sensory (olfaction, touch)--command neuron--- CPG--- motor neuron--- muscle - voltage comes out of neuron, produce color change in dye and therefore can read multiply and simulateously so you dont have to record one at a time |
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Cockroaches
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- microcurrents of air generated from the predator causes deflection of mechanorecptor hairs located on 2 appendages on the rear end of the cockroach
- these ahirs are connected to a nerve cell such that nerve cell fires when the hair has been deflected - these nerve cells firsts tells us that there is a stimulus (predator) in the environment and tells the direction that the air was coming from so the cockroach can escape the other way - doesnt involve brain, reflexive action - selection favors nervous sytem to facilitate escape in sea slugs and cockroaches |
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trap jaw ant
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- fastest known predatory response
- when prey comes, hairs detect change and there is a rapid closure of mandibles - mandibular motor neuron activates large neuron (thicker diameter of axon, less resistance) which facilitates rapid communication between hars and jaws |
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C. elegans
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- about 19,000 genes, 1/2 are homologous with other organisms
- 250 with neural function, 302 neurons compared with the millions in humans - 5000 neuromuscular junctions - common model for muscular dystrophy because of the small number of genes, neurons and neuronmuscular junctions |
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Phinnaeus Gage
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- survived after accident by personality changed due to first ever frontal lobotomy
- CAT scanes, fMRI, PET: methods to pinpoint what is going on in a live person's brain - fMRI and PET uses metabolism of glucose to mesaure brain activity - ex: eye gaze: there is a distinct portion of the brain which responds to eye gaze, thus you can tell if a person is being honest |
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Prosopagnosia
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- disorder primarily a result from trauma
- affects the face detector region of the brain - people with this condition cannot recognize other people they ahve known for years |
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Lecture 3 behavioral genetics
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- interested in the connection between genes which affect the neural response to ultimately affect behavior
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Contrasts
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- difference in body size between dogs is due to ONE gene
- contrasting behavior of indentical twins - ex: twins, Oscar and Jack are identifcal twins reared in 2 different enviornments: one in Nazi Germany and the other in Carribean - even with environmental differences, Oscar and Jack share same idosyncratic behavior - ex: both put rubber bands on their left wrists |
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CNS
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-central nervous system
-consists of the brain and a nerve cord which in vertebrates extends from brain through the vertebral column called spinal cord |
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PNS
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- peripheral nervous system
- consists of all neurons and projections of their plasma membranes that are outside of and connect with the CNS - such as projections of their plasma membranes that are outside of and connect with the CNS, such as projections that end on muscle and gland cells |
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evolution of nervous systems
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- allowed animals to recieve info about environment via PNS
- interpret that info in CNS - and if necessary initiate a behavioral response via their PNS |
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Peripheral nervous system example
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- neurons in the nose detect a stimulus (odor) and send signal to brain
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Central nervous system example
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- neurons in the brain interpret the odor as food
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Peripheral nervous system
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- the brain sends a signal to neurons in the PNS that stimulate the salvation response
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neurons
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- cells in the nervous system that send and recieve electrical and chemical signals to and from other neurons in the body
- number of neurons in the nervous system of different species varies widely, partly as a function of the size of animal's head and brain but also as a function of the complexity of it's behavior - ex: C. elegans has only 302 neurons in its nervous system , compared with 100 billion in human - regardless of total number, neurons in one animal species look and act much like neurons from any other species |
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cell body
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- also called soma
- neuron composed of cell body that contains the cell nucleus and other oraganelles - two types of extensions or projections that arise from cell body |
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two types of extensions arising from cell body
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- dendrites
- axon |
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dendrites
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- may be single projections of the plasma membrane but they are more commonly elaborate tree-like structures with numerous branching extensions
-chemical and electical messages from other neurons are recieved by dendrites and electrical signals move toward cell body |
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axon
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- extension of plasma membrane that is involved in sending signals from neuron to neighboring cells
- may be less than a millimeter long in insect or as long as 2 meters in girafee - typical neuron has a single axon which may have branches - part of axon closest to cell body is called axon hillock |
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axon hillock
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- part of axon closest to cell body
- important in nerve cell communication |
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terminal branches
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- also known as nerve terminals
- located at other end of axon and are terminal branches or nerve terminals that send electrical or chemical messages to other cells such as neurons or muscle cells |
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formation of nerves
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- many axons tend to run parallel in bundles to form nerves
- each axon within a nerve is surrounded by glial cells and the entire bundle is covered by protective layer of connective tissue - nerves enter and leave the CNS and they make contacts with structures outside the CNS - nerves transmit signals between the CNS and PNS |
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Glia
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- cells surrounding the neurons
- perform various functions and are many times more numerous than neurons depnding on species - human brain outnumber 50-1 - in vertebrates specialized glial cells wrap around the axons to form an insulating layer called myelin sheath |
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oligodendrocytes
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- specialized glial cells that wrap around axons to form insulating layer (myelin sheath)
- in brain and spinal cord |
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Schwann cells
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- glial cells that form myelin on axons that travel outside brain and spinal cord
- myelin increases speed with which electrical signals pass down axon |
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astrocytes
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- glial cell that provides metabolic support for neurons and also involved in forming blood- brain barrier
- blood- brain barrier is physical barrier between blood vessels and most parts of the CNS - barrier protects the CNS by preventing passage of toxins and other damanging chemicals from blood into CNS - also help maintain a constant concentration of ions in extracellular fluids |
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microglia & ect.
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- remove cellular debris produced by damaging or dying cells
- in developing embryos glia form tracks along with neurons mitigate to form nervous system - some glia function as stem cells to produce more glial cells and neurons |
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3 main types of neurons
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1. sensory neurons
2. motor neurons 3. interneurons |
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sensory neurons
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- detect or sense info form outside world such as light, sound touch and heat
- also detect internal body conditions such as blood pressure and body temp - also called afferent neurons because they transmit info to CNS - often have very long axon which is involved in rapidly communicating signals - they are unusual because axon bypasses cell body and goes directly to CNS - this arrangement allows for rapid transmission of sensory signal to CNS |
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motor neurons
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- send signals away from CNS and elicit some type of response
- one type is they cause movement - may cause other effects such as secretion of hormones from endocrine galnds - because send signals away from brain they are efferent neurons - like sensory they tend to have long axons but they originate from an axon hillcock at the cell body |
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interneurons
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- forms interconnections between other neurons in CNS
- greatest complexity of nervous system occurs among interneurons such as those found in the brain -signals that are sent between interneurons are critical in the interpretation of information that the CNS recieves as well as teh response that it may elicit - tend to have many dendrites and axons are typicall short and highly branches - arrangement allows interneurons to form complex connections with other cells |
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reflex circuts
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- types of neurons form interconnections with each other
- neurons transmit info to each other through series of connections that form a circut - simple circut is reflex arc- allows organism to respond rapidly to inputs from sensory neurons and consists of only a few neurons - stimulus from sensory neurons is sent to CNS but there is little or no interpretation of signal - few interneurons involved - signal is then transmitted to motor neurons which elicit a response such as knee jerk - response is quick and automatic - allow animals to respond quickly to potentially dangerous events - take flight in response to loud noise which could represent sudden danger - exists in simple animals such as flatworks and complex animals such as humans |
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Galvani
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- postulated that electric current could somehow be generated by tissue itself
- "animal electricity" - his animal eletricity comes from neurosn which use electrical signals to communiate with other neurons, muscles or glands - these signals or nerve impulses involve changes in amount of electrical charge across cell's plasma membrane |
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plasma membrane
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- a cell's plasma membrane of a neuron acts as a barrier that separates charges
- ion concentrations differ between interior and exterior of cell - such differences in charge act as electrical force measured in volts - there are positive and negative poles, these are outside and inside membrane - for this reason a neuron is said to be polarized |
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membrane potential
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- difference between electrical charges inside and outside the cell
- also called potential difference |
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resting potential
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- refers to membrane potential of a cell that is not sending nerve impulses
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squid giant axon
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- impale with microelectrode
- within microelectrode is salt solution that can conduct ions - neuron dissected from squid and placed in solution that has similar ionic concentration as normal extracellular fluid - microelectrode pushed through axon membrane to record from inside cell and another microelectrode is placed within solution bathing the neuron outside the cell -voltmeter records voltage difference between two microelectrodes which is mesaure of membrane potential |
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selectively permeable membrane
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- membrane is selectively permeable to cations and anions so it separates charge by keeping differnt ions largely inside or outside the cell
- interior of cell had a more negative charge than exterior which turns out to be true of all animal cells in resting state - tiny difference in charge across membrane of neuron is sufficient to generate a nerve impluse that can travel from one end of a neuron to the other - resting potential is determined by ions located along inner and outer surfaces of plasma mebrane |
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ions of opposite charges
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- align on either side of membrane because they are draw to each other due to electrical forces
- negative ions within cell are drawn to positive ions arrayed on outer surface of plasma membrane -actual number of ions that contribute resting membrane potential is extremely small compared with rest of ions within and outside cell |
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ions most critical for establishing resting potential
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- Na+, K +
- intracellular anions such as negatively charged proteins and Cl- |
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3 factors responsible for resting membrane potential
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- sodium potassium pump
- plasma membrane contains ion specific channels - negatively charged molecules more abundant inside cell |
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sodium potassium pump
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- Na+/ K+ - ATPase within plasma membrane continually moves sodium ions out of cell and potassium ions into cytosol
- sodium potassium pump uses ATP to transport 3 NA+ out of cell for ever 2 K+ it moves into cell - thus pump contributes to charge difference across plasma membrane and establishes gradients for Na+ and K+ |
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ion specific channels
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- affect permeability of ions across the membrane
- channels that are specific for Na+ or K+ influence the resting potential by allowing passive movement of ions - K+ channels tend to be open more frequently at the resting potential - there are about 50 times more potassium channels than sodium channels so the membrane is more permeable to potassium than sodium |
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negatively charged molecules more abundant inside cell
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- negatively charged molecules such as proteins are more abundant inside the cell
- these anions do not readily move through the plasma membrane so they contribute more negative electric charge to the interior of the cell |
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electrochemical gradient
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- membrane potential and the chemical concentration of ions influence the direction of ion movement across a membrane
- direction that an ion will move depends on it's electrochemical gradient - it is the combined effect of both an electrical and chemical gradient |
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example of gradient
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- a chemical gradient in which K+ concentration is higher on one side compared to the other
- in this scenario K+ will move from a region of high to low concentration |
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example 2 of gradient
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- chemical concentration of K+ is equal on both sides of the membrane but the concentrations of other ions such as Na+ and Cl- are unequal on both sides of the membrane and thereby produce an electrical gradient
- because K+ is positively charged it will be attracted to the side of the membrane with more negative charge - chemical gradient is balanced by an electrical gradient - electrical gradient would favor movement of K+ from left to right while the chemical gradient would favor movement from right to left -these opposiing forces can create an equilibrium in which there is no nent movement of K+ in either direction |
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Nernst equation
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- by measuring the membrane potential of isolated neurons in the presence of changing concentrations of extracellular ions, scientists have deduced a mathematical formula that relates chemical and electrical gradients to each other
- this gives the equilibrium potential for an ion at any given concentration gradient |
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chemical and electrical gradients
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- right compartment contains a higher chemical concentration of K+ while the left side has a higher amount of positive charge
- these gradients balance each other so that no net movement of K+ occurs |
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electrical current
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-movement of a charged ion down it's gradient results in electric current
- smaller an amplitude than those that run through our wires - provides electrical signal that neurons use to communicate with one another |
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acetylcholine
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- one of most widespread neurotransmitters in animals
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