Introductory Neurobiology Week 7 Notes
Introductory Neurobiology Week 7 Notes Biol 3640
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This 6 page Class Notes was uploaded by lucy allen on Tuesday March 1, 2016. The Class Notes belongs to Biol 3640 at University of Denver taught by Dr. John C Kinnamon in Fall 2016. Since its upload, it has received 10 views. For similar materials see Introductory Neurobiology in Biology at University of Denver.
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Date Created: 03/01/16
Introduction To Sensory Systems -the lady and the unicorn: tapestries of a lady and a unicorn to her left, lion to her right, different versions describe the different senses -slide 3: holding the horn, touch -slide 4: holding a flower, smell -slide 5: playing an organ, assistant operating the bellows, sound -slide 6: plate of cookies, monkey stole one, taste -slide 7: unicorn with forepaws in lady's lap, looking at reflection, sight -slide 8: wider and more obscure, putting her necklace in a chest, meaning unknown History -go back to Aristotle -court case: in the 19th century -Johannes Muller called in as an expert witness for a trial -case: man was walking along a dark street at night and he was accosted by a mugger, who hit him on the head hard and robbed him -in the trial the victim said he could identify the mugger by virtue of the lights he saw when the mugger hit him on the head -he saw starts from getting hit on the head -Muller argued that by virtue of the law of specific nerve energies, the nerves carrying visual information to the brain were stimulated by the hit to the head, causing him to see stars -there was no light there! -he was seeing phosphenes -can also be seen if you apply pressure to the side of your eyes -we sense objects through our nerves, they mediate our sensation -if I stimulate the nerve that carries information for vision mechanically, you still sense it as vision -if I stimulate the nerve involved in hearing by applying pressure to the hear drum, it may be sensed as a sound despite the mechanical nature of the stimulus Features of Sensory Stimuli -quality -modality: hearing, seeing, touch, taste, smell submodality: vision: colors -intensity -how strong the stimulus is, how bright, loud, forceful, etc. the stimulus -perceived intensity can decrease over time as a result of sensory adaptation -duration -how long the stimulus is presented -location -different senses have different abilities to locate sensory stimuli -the ability to discriminate between two closely spaced stimuli -locating visual sources is easy -smells are more challenging -sounds -two pathways, depending on frequency of the sound -has to do with the sound waves (low frequency, long waves; high frequency, short waves) -lower frequency is hard to distinguish between two locations Sensory Modalities According to Aristotle -taste (chemoreceptors) -smell (chemoreceptors) -receptor cells are technically part of your CNS, the first synapse in the smell pathway is in the olfactory bulb (in your brain) -provides access for diseases to go from your nose into your brain -amoebas in hot springs -typically fatal -touch (mechanoreceptors, proprioceptors (determining position of limbs), nociceptors(pain receptors)) -hearing (mechanoreceptors) -whether TRP channels are involved or not is controversial -has been observed in drosophila -vision (photoreceptors) -photoreceptors respond to photons of light Submodalities -vision: colors -hearing: pitch -taste: sweet, sour, salt, bitter, umami (and maybe fat too) -small: bananas, rose, etc. -somatosensory (touch): pressure, vibration, temperature, length, tension, pain Components of Sensory Systems -sensory receptors -can be specialized like photoreceptors in your retina -can be primary afferent nerve fibers (pain fibers, unmyelinated c fibers) -many are either specialized cilia (visual system, photoreceptor cells; olfactory system: olfactory receptor neurons) or specialized microvilli -cilia: central doublet of microtubules, nine doublets of microtubules around the periphery of the cilia -photoreception, olfaction -microvilli: packed with actin fibers -gustation -certain number of action potentials based on location of the cilia on the cell -can also determine velocity -and can determine acceleration Activation -ligand-gated channels -consumption of acidic drink, acid bind to receptor on taste cell, opens up an ion channel -direct modulation of ion channels (e.g. taste) -sodium will go directly through the ion channel and you taste salt -stretch-activated ion channels (mechanoreceptors) -mechanoreceptive stretch activated ion channels opened by mechanical stimulation of cells (poking your skin) -G protein coupled receptors (taste, smell) -receptor potential -each sensory cell generates a receptor potential -large enough means it can generate an action potential -receptor potential itself is graded -electrotonically propagated -depolarizing or hyperpolarizing -similar to postsynaptic potential -dynamic range: a receptor has a threshold below which it does not detect anything, and it can be saturated with stimulation -in between threshold and saturation is the dynamic range -when the receptor functions best -specialized receptors can change the tension of the receptor so that you are always in your dynamic range -impulse generation: can be in either a primary afferent neuron or in a specialized receptor cell -slide 25: invertebrate muscle receptor connected to muscle -stimulus provided, receptor potential occurs, if strong enough a series of action potentials occur -sensory coding: generally by the frequency of action potentials -as the stimulation in creases in magnitude the number of action potentials from the sensory nerve will increase -coding intensity -frequency of action potentials -recruitment of receptors -when stimulus is strong, receptors are recruited -coding duration -adaptation -rapidly adapting "phasic" receptors -gives a response of a brief burst of action potentials, and then it ceases -an 'on' response and an 'off' response -slowly adapting "tonic" receptors -continues to fire as long as the stimulus is provided -range fractionation: series of joint receptors, some of which detect best when the arm is extended up all the way up to 20 degrees, another from 20 to 45, and another from 45 to 90, and so on -complete range of stimuli divided up into regions, and receptors are tuned optimally to each of those regions of ranges of stimuli -in the visual system: range fractionation occurs through the types of photoreceptors present, each tuned to a specific color for optimal efficacy in sensory processing -cones: color, blue, green, red -convergence -receptive field: all of the receptors that provide input for a given sensory neuron -some receive input from just a few receptors, little convergence -others receive input from many receptors, much convergence -divergence -occurs in the visual system -start with the retina, significant convergence -in visual cortex next, significant divergence -photoreceptor can respond to an individual neuron -you might not consciously perceive it but response is still there -hearing: 0.2 micrometers of movement -olfaction (pheromone): one molecule -taste: 1 Molar sucrose (sweet) -pH 1 coca cola -catfish: covered with gustatory receptors -have taste buds on sides of their faces and down the sides of their bodies, can detect a multitude of flavors -nanomolar concentrations Examples of Sensory Systems -types of neurons -short receptors: characterized by a specialized sensory receptor cell (taste bud or an auditory receptor cell) -long receptors: typically a neuron, the primary afferent neuron, also a receptor cell itself -temperature fibers, pain fibers, unmyelinated c fibers Cells which Mediate Hearing Balance and Acceleration -all short receptor cells with rows of microvilli -one kind of cilium at the end of the bundle -if it is deflected towards this cilium there is a depolarization -if it is deflected away from the cilium there is a hyperpolarization Vision -uses a specialized cilium for sensory transduction -dark current (in cone or rod cell): in the dark, the photoreceptors are depolarized, there is an electrical current (sodium entering and potassium leaving the cell) -when the cell is in the light, ion channels close and the current stops -become hyperpolarized -photoreceptor cells do the opposite of what you would think (depolarized in the dark and hyperpolarized in the light) Touch -involves many types of receptors, all go to dorsal route in spinal cord -each segment of the spinal cord has a dermatome, or a receptive field -different sized nerves for different parts of the system -group 1: (Aalpha) largest diameter, most myelination, fastest, 80-120 m/sec conduction velocity, in proprioceptors of skeletal muscle -group II: (Abeta) generic mechanoreceptors in skin, 6-12 micrometers in diameter, conduction velocity is fast but slower than group 1Aalphas -group III: (Adelta) pain, temperature -group IV: (C), unmyelinated C fibers, 0.5-2 m/sec conduction velocity -very slow -temperature, pain, itch, chili peppers -convergence in the human body -lips/fingers: little convergence -easy to distinguish closely placed stimuli as separate -back/thighs: lots of convergence -why don't we have little convergence everywhere? -it would take up too much space -all goes to the somatosensory cortex -it is mapped out -larger amount of space taken up on the somatosensory cortex means there is not very much convergence, indirect relationship -homunculus: the relative amount of brain that is used in the representation of mechanosensory stimuli -mapping of the brain is based on "use it or lose it" basis -use of the receptors increases the amount of sensory cortex devoted -if the receptors are not used, the amount of space devoted by the sensory cortex will decrease -experiment: monkeys -removal of a digit on the hand will show a resultant decrease in space devoted by the sensory cortex, and the 'real estate' goes to the other adjacent fingers -muscle spindle provides information about the length of the muscle -muscle spindle: specialized muscle in parallel with the muscle fibers -stretched muscle = stretched muscle spindle -1A sensory motor neuron (fastest) associated -when muscle spindle stretches, it causes activity of this neuron -muscle spindle and the main muscle have different neurons -gamma motor neuron stimulates the muscle spindle and causes contraction -alpha motor neuron stimulates the main muscle -if the main muscle contracts due to this activity, it takes all o the tension off of the muscle spindle, taking it out of its dynamic range so it can no longer sense the length of the muscle -by virtue of the gamma motor neuron, it stimulates the muscle spindle and causes in to shorten to retune itself and put it back into the center of its dynamic range Golgi Tendon Organ -monitors muscle tension -located in the tendon, between muscle and bone -nerve innervating this organ is the 1B afferent neuron -ramifies throughout the collagen fibrils inside the tendon -wired in an interesting way to protect you -reflex -1B afferent neuron signals the tension, goes into the spinal cord and synapses onto an inhibitory motor neuron -has an inhibitory synapse onto the alpha motor neuron Synesthesia -mixing of the senses -people who are common synesthetes commonly have a mixture of numbers and colors -when they see colors they'll have numbers -certain words will be colors -'contrasting sounds' Kandinsky (founder of abstract expressionism) -colors represent sounds -not just different sounds but different intensities of sounds -"composition x"
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