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Course coordinators: Carl D. Hopkins |
LECTURE LINKS (2009)A page of LINKS to resources related to lectures, listed by lecture number and topic. This page will be especially useful for those engaged in active learning: the process of actively seeking, mining, organizing, and conceptualizing information presented in this course. Lecture 01. Introduction to Neurobiology (Hopkins). Many of the ideas in this lecture came from Foundations of the Neuron Doctrine, published by Gordon Shepherd in 1991 for the centenary of the formulation of Neuron Doctrine in 1891. To find out more about Camillo Golgi and Santiago Ramon y Cajal view the website for the the 1906 Nobel Prize for Physiology and Medicine. It is ironic that Cajal used Golgi's technique for staining nerve cells, but came to a different conclusion from Golgi about the neuron doctrine. Golgi was a "reticulist" and confronted Cajal, the "cellulist" at the Nobel ceremony in Stockholm. You can read how Golgi dismisses the neuron theory as unproven, even though Cajal's evidence was overwhelming at the time. The great book of Cajal (1909-1911), published in Spanish and translated into French as "Histologie du Systeme Nerveux de l'Homme et des Vertebretes, Vols. 1 and 2. A. Maloine. Paris." has been translated into English by Swanson and Swanson. Since Cajal and Golgi won the Nobel Prize, there have been many prizes awarded for the study of the nervous system. For a list of all Nobel Prizes awarded the the field of Neuroscience, see Dr. Eric Chudler's (U. Washington) Neuroscience website. The most recent awards were to Linda Buck and Richard Axel for their work on olfaction, and to Rod Mackinnon for his work on the structure of the Potassium Channel, and of course , , and Roger Tsien, who won the Prize in Chemistry in 2008 for developing Green Fluorescent Protein as a cell marker. The modern extension of the Golgi technique used by Cajal combines GFP with fancy molecular biology to produce Brainbow 2.1 (Livet et al., Lichtman lab, Harvard) a transgenic marking technique that shows neurons in a rainbow of cell-specific colors. Ramon y Cajal observed not just vertebrates, but also many insects. The Golgi method continues to be important in understanding the nervous systems of these animals. See the Drosophila Brain project for some incredible Golgi stains of the fruitfly. For a gallery of Golgi preparations, Cajal's method, and a modern Medical Research Institute in Spain, see Cajal Institute. Anyone interested in Cajal's life may wish to check out his autobiography, published in the 1930's, and translated into english: Ramon y Cajal, Santiago (1989 edition) Recollections of My Life., The MIT Press, Cambridge, Mass (see Resources). Lecture 02 (Fetcho) Basic Properties of Neurons and Membranes. 03. Resting Potential. Lecture 04 (Fetcho). Resting Potential, Action Potential. The importance of sodium ions in generation of action potentials was demonstrate in the famous experiments of Hodgkin and Katz discussed in lecture. These experiments show the effects of sodium ion concentrations on membrane potential of the squid axon. This and many (i.e. 1878-1997) historically important articles are now available for free from the Journal of Physiology, thanks to the Physiological Society of London. Lecture 05 (Fetcho). Action Potentials Tetrodotoxin. The drug Tetrodotoxin acts as a potent nerve toxin by selectively blocking sodium channels in the nerve membrane. It has a curious cage-like structure that is probably derived from either an adipose C5 sugar or iopentenyl-PP. The biosynthetic pathway is unknown for pufferfish. In Japan, the pufferfish Fugu, which produces Tetrodotoxin, is a delicacy that causes a tingling sensation on the mouth, mild facial paralysis, a "light headed" feeling and other symptoms, including death. As a poison, it is more than 1200 times more toxic than cyanide. Curiously, the pufferfish is itself highly resistant to poisoning itself. Its sodium channels have a single point mutation in the Na channel (a protein) which causes TTX to fail to bind to the pore. How clever of that pufferfish! Click here to see the original voltage clamp data under TTX conditions (from Hille, B. (1966) Nature 210:1220.) Animation of the Action potential with Na and K channels. To see the animation of the action potential with the timed events of opening and closing the Na channels, and opening and closing the K channels, see the web site for the the textbook, Neurobiology, by Gary Matthews. Lecture 06 (Fetcho). In lecture we learned of the effects of multiple-sclerosis, a disease that results in the damage of the myelin insulation on neuron axons and consequently the loss of timing precision in action potential propagation.The National Institute of Neurological Disorders and Stroke maintains an authoritative Multiple Sclerosis web site on this disease: its causes, prognosis, research, and clinical trials underway to search for treatment. 07. Ion Channels and Diseases of Ion Channels. (FETCHO) Potassium Channels. The first complete x-ray crystal structure of an ion channel was determined by Roderick MacKinnon's laboratory, and is available to download on a number of websites. Click here to see "Turning Thought into Action", a flash video showing the mechanism of ion channel selectivity and speed. View the structure of the protein using your web-browser on the PDB web site. There are several options for viewing this and other macromolecular structures. The quick PDB works with a simple java applet, others will require downloading a program such as CHIME or RASMOL. This is all described on the PDB website. Is it worth the trouble to take a look at these structures? Most definitely! It is amazing to see the structure, especially the pore through the membrane, and the precise nature of the selectivity filter. Once you get the display to work on your computer, you can use the mouse to move and position the molecule in any orientation you like. The best view of the KcsA K channel is an instructive web site from Carnegie Mellon University. As indicated for the previous lecture, you might need a copy of CHIME to see these molecular structures. Recently, the MacKinnon lab released a novel structure for a voltage-gated potassium channel. The mechanism of the voltage sensitivity depends on a large 'paddle-like charged subunits, that when subjected to an electric field changes the opening of the pore Check out the Nature paper about the voltage gated potassium channel. Called KvAP, this awesome molecule is also available on the membrane bound protein structure database. To see more animated ion channels, check out the rest of the membrane channels and pumps on the CM (Carnegie Mellon) site. To see the voltage-gated potassium channel (Rod MacKinnon's new K channel structure), see the CM site. We'll have more to show you later in the course about other interesting molecular models, including sensory transduction channels, so keep Chime around for a while. Ion channel evolution and diversity. Much has been written about the evolution of ion channels, as biologists have sought to trace the origin of some of the curious ion channel proteins back in time by searching for gene sequences in the comparative genomes of ancestral organisms. See the article by Anderson and Greenberg for more information on this topic. Bertil Hille's Ion Channels of Excitable membranes is a very readable book for advanced students that does a great job reviewing this exciting (no pun intended) field. The book is organized around the ion channel superfamilies. To gain an appreciation of the diversity of ion channels that are known, check out the Neuromuscular Disease Center's web site on ion channels, transmitters, receptors, and disease. There is a special segment just on ion channels. 08. Ionic Mechanisms of Synaptic Excitation. (JOHNSON)
The term synapse comes from the greek word 'syn' for union or association. A similar term, synapsis which is the pairing of homologous chromosomes during meiosis, was put forward by Slavin Moore independently. Neither Moore or Sherrington was aware of the other use of thse similar term for different structures. (see Shepherd and Erlukar, TINS, 1997) SYNAPSE is a tutorial developed by Jon Glase, Brendan Holt, and Bruce Johnson for use in teaching basic concepts of synaptic physiology and neurobiology. Developed at Cornell, it takes students through virtual experiments similar to that of a lab course environment. Check it out and send us feedback. The experimental work by A. Takeuchi and N. Takeuchi (1960) discussed in lecture was published in the Journal of Physiology (London) Volume 154, 52-67. It was the first demonstration that the nicotinic acetylcholine receptor in muscle was a non-selective cation channel. Takeuchi and Takeuchi used the voltage clamp method to hold the voltage of the muscle cell constant during these experiments. They were thus able to determine the "reversal potential" for the synaptic current. In lecture, you saw a hydraulic analogy for reversal potential in relationship to current flow through the membrane. Click here to see an animated version of the hydraulic analogy. It is useful to work through the discussion section problem set number 4 on reversal potentials if you do not yet understand these relationships.
09. Inhibition and Neuronal Integration (Johnson). In lecture we heard about the controversy that raged between physiologists of the early 20th centruy over the nature of synaptic transmission -- was it chemical or electrical?. This has been called the War between the Soups and Sparks -- with one side arguing that synaptic transmission was caused by release of a chemical (SOUPs) and the other side arguing that it was caused by electrical transmission (SPARKS). If you are interested in the history of this war, see these reviews. electric synapses and gap junctions.
Neuronal integration: The spike initiation typically occurs in the region of the neuron called the axon hillock. In lecture we discussed temporal and spatial integration of synaptic inputs, but also many other factors, including both spiking and non-spiking interactions. You can see an animation of neuronal integration on THE NEURON from Children's Hospital Boston. See the SYNAPSE tutorial for much more. Finishing on the topic of integration, we heard that dendrite sometimes fire action potentials of their own, changing the old view that dendrites passively integrate synaptic inputs without spiking. One important paper in this regard was Llinas and Sugimori (1980). We also learned how a combination of factors, including high membrane resistance in dendrites, presence of Persistent Sodium Currents (INa-p), and Calcium currents could lead to integration even from distal dendrites. 10. Release of Transmitter (Johnson). For an animation of the various events tied to synaptic release, see Matthews's textbook animation. Many of the critical factors involved in release of neurotransmitter trace to the work of Sir Bernard Katz whom we have already heard of in the context of the Hodgkin and Katz experiments, the Goldman, Hodgkin and Katz equation, and many other discoveries. Katz describes the evidence for Quantal release of neurotransmitter in his Nobel lecture. He and Miledi studied the Squid Giant Synapse which allowed them to record the "pre-synaptic" spike at the synapse and established the highly non-linear effect of Calcium ion concentration on the post synaptic potential. There is an excellent tutorial on the dissection and recording of giant synapse of squid in the Methods in Neuroscience page. Critical to our current understanding of synaptic function was the realization thatneurotransmitter is released in quantal "packets", not continuous streams. Here is a famous figure from the Fatt and Katz paper from Nature, 1950 showing miniature end plate potentials from frog muscle . Katz died in 2003 and is remembered as a pioneer in cellular electrophysiology. The use of sharp ultramicroelectrodes for recording intracellular potentials was essential to this and much subsequent electrophysiological work. The technique was invented by Ling and Gerard in 1949 (Journal of Cellular and Comparative Physiology 34, 383-396). The quantaized packet concept made perfect sense when J. D. Robertson made the first electron microscopic images of the synaptic terminals showing the synaptic vesicles. The evidence was even stronger when Heuser and Reese developed the freeze fracture technique for visualizing the syanptic vesicles making contact with the presynaptic membrane. Click on this link to see a reprint of the original paper: Membrane-bound vesicles: Fixed, fused.
The modern view of synaptic transmitter release has focused on all of the molecular machinery of the vesicle movement is well summarized in the text and in an excellent web site from the University of Colorado. The complex events leading to vesicle docking, membrane fusion, transmitter release, and eventual recormation of vesicle is best explained by an animation published in Science magazine. View the animation of the complexities of vesical fusion. One student asked in lecture how neurotransmitter is loaded into vesicles, saying that he had the impression that the vesicle membrane formed around the neurotransmitter. This impression may have been given by the Purves et al, 4th edition synaptic vesicle cycle animation which is quite misleading (last 10 seconds of the animation) as it shows the membrane forming around the neurotransmitter, whereas it should explicitly show the neurotransmitter being actively transported into the vesicle. Question -- where is the ATP binding site for these ATPase-transporters?. B. Gasnier, writing in Biochimie 82(4):327-37 wrote (in 2000) that neurotransmitters are loaded into vesicles by ATP-driven transporter molecules that are specific to this task. There are a number of different proteins involved in transporting classical non-peptide neurotransmitters into vesicles prior to release. For more on the synaptic vesicle cycle, see The Synaptic Vesicle Cycle from the Michael Nonet lab at Washington Univ. St. Louis. 11. Neuromodulators (Johnson). See Matthews Neurobiology animations for an illustration of direct and indirect (modulatory) effects of neurotransmitters. Here you will be able to visualize the various steps in the activation of ion channels via G-protein coupled receptors. A variety of neurotransmitters serve as neuromodulators including dopamine, serotonin, norepinephrine, peptides. For a reviews, see Harris-Warrick and Marder (1991) and Katz and Harris-Warrick 1990. Click here to see an animated G-protein coupled receptor being activated. 12. Neurochemistry (Johnson). The point of this lecture was to introduce you to the chemistry of neurotransmitters, and neurotransmitter receptors. A whirlwind tour, of course, but it gives you a sense of the origins, evolution, diversity, and functions of an array of chemical compounds of great biological importance. Since this is Darwin's birthday week, consider the importance of molecular evolution in all this chemistry. Recently the laboratories of Adam Siepel and Carlos Bustemante from Cornell's Department of Biological Statistics and Computational Biology have published a study showing how sensory and neurotransmitter genes are undergoing strong positive selection in humans and other primates. See PLOS GENETICS for the whole story. The NMDA receptor is a glutamate receptor of great importance in neurobiology. It is implicated in synaptic plasticity, and the whole idea that cells that fire together wire together. We will re-introduce this important receptor later under learning and memory.13. Just say know. Drugs and the Brain (Johnson). The National Institute on Drug Abuse (NIDA) provides reliable information about drugs, drug effects, and drug addiction, including most of the drugs mentioned in lecture. In addition, there are resources for research, clinical trials, and other activities building on the knowledge learned about drugs. This lecture emphasized the imporance of Knowing about drugs. The US Department of Health and Human Services also provides information about alcohol and drugs on their website. 14. Early Development of the Nervous System (BASS). For an excellent animation of the early stages of development of the human nervous system, see the University of Pennsylvania medical library. Click here to see an animation of neurulation in the mouse embryo. For more on the definition and composition of the peripheral nervous system, see wikipedia. Click here for a drawing of the cranial nerves divided into sensory and motor function. For definitions of homeobox and Hox genes consult wikipedia. See the pattern of Hox gene expression in vertebrate sound production by Bass et al. Science 2008. 16 & 17. Functional Organization of the Adult Nervous system I and II (BASS). These two lecture defined and illustrated many neuroanatomical terms and concepts that apply to all vertebrate nervous systems: fish, amphibians, reptiles, birds, and mammals. In addition to the slides for this lecture, there are many web-sites devoted to the anatomy of the nervous system (usually medical or veterinary sites). Your textbook comes with priviledges to use a neuroantomical website, called Sylvius 4 for Neuroscience. On this website you will find many useful tutorials and neuroanatomical images illustrating the anatomy covered in lecture. There are two main parts to the nervous system of all vertebrates: Peripheral Nervous System (PNS), Central Nervous System (CNS) Peripheral Nervous System (PNS): all parts of the nervous system except the brain and spinal cord. The PNS includes spinal and cranial nerves, sensory ganglia, motor ganglia, and sensory receptors. The sensory nerves bring information about the sense organs in the periphery to the central nervous system. Motor neurons carry signals from the central nervous system to the peripheral muscles, glands, and organs. Peripheral Nerves are bundles of axons or dendrites that run together along the same route between the CNS and some other organ system. Nerves are ensheathed in connective tissue. See peripheral nervous system on the Wikipedia web site. There are various links to the atlas for the nerves assocated with skeletal muscle. 18. Sensory Maps (Bass). The concept of a sensory map in the cortex traces to the work of Wilder Penfield who made the first sensory maps of human patients who were having surgery for epilepsy. The somatosensory system is mapped into the post-central gyrus in human. Penfield's drawing of the sensory map as a Homunculus (little man) has been repeatedly reprinted. The homunculus is animated here. Other sensory systems have sensory maps: the visual system has a map of the retina (retino-topy), and the auditory system has a map of the cochlea (tono-topic map). You heard about the work of Ken Catania and the star nose mole. The mole has a remarkable somatotopic map in its sensory cortex which shows a very large area devoted to its nose -- Those fleshy appendages around the nostrils are mechanosensory structures that give the mole great tactile discrimination ability. BRAIN LAB LINKS. In sections, students will be able to dissect an sheep's brain. To view a tutorial on the dissection see the University of Scranton's website on sheep brain dissections or this Tutorial on sheep brain. To print out a dissection guide before lab, see Barnard college's Neuroanatomy of the sheep brain guide. 19. Principles of Sensory Function: Touch. Touch and Principles of Sensory Function. (HOPKINS). For an excellent overview of sensory function, see the Howard Hughes Medical Institute web site on "Senses and Sensitivity" (Thank you Jane Austin) a Bioactive website of the Howard Hughes Medical Institute. See on that site two excellent interactive lectures on vision, and two on hearing, at the HHMI holiday lectures series with web-cast recorded lectures by Dr. James Hudspeth (Rockefeller Univ.) and Dr. Jeremy Nathans (Johns Hopkins Univ.).
The mechanosensory channel or channels of mammalian somatosensory systems remain elusive. See Raoux et al. for review (2007) for a current review of proposed channel proteins. To read Lowenstein's work on the mechanisms of adaptation in Pacinian corpuscle, see J. Physiol. 1965. For a summary of the dorsal-column medial lemniscal pathway see Wikipedia or see the Univ. Wisconsin medical neuroanatomy site. The Integrate and Fire model of sensory encoding is taken quite seriously by computational neuroscientists who are attempting to relate synaptic and sensory currents to neuronal firing patterns. Click here for a taste of the computational theory behind integrate and fire. The logarithm rule for sensory transduction and encoding is embodied in the famous Weber Fechner Law which postulates that the "perception" of a stimulus is proportional to the log of the stimulus magnitude. To understand the origin and derivation of this principle, read about Weber's experiments on the perception of weight. The principle of lateral inhibition were laid out for the visual system by Keffer Hartline who discovered it in the retina of frogs and horshoe crabs. Dorsal column nuclei are shown in this nissl stained series from the Rhesus macaque (see Cuneate nucleus, CN) and Gracille nucleus in the caudal medulla. Don't forget, these sections come from the website, Brainmaps.org and you can zoom in on the nucleus and see the collection of cell bodies. Next to the Cuneate nucleus is the Cuneate fasciculus or Cuneate Tract which brings fibers from the upper trunk and limbs to the caudal medulla. The apparent inversion of the face on the homonculus was noted by Servos et al. in 1999 using FMRI. Sensory processing of the somatic senses is recently summarized in Vernon B. Mountcastle's The Sensory Hand (Harvard Univ. Press) in 2005. 20. Sensory Transduction. (HOPKINS) For an excellent overview of sensory function, see the Howard Hughes Medical Institute web site on "Seeing Hearing and Smelling the World" a Publication of the Howard Hughes Medical Institute. For two excellent lectures on vision, and two on hearing, see the HHMI holiday lectures series with web-cast recorded lectures by Dr. James Hudspeth (Rockefeller Univ.) and Dr. Jeremy Nathans (Johns Hopkins Univ.). For topics covered in this overview lecture, we recommend Hudspeth's lecture #1 entitled :"Sensory Transduction -- Getting the Message". These lectures were given to HighSchool students back in 1997, but are still excellent for all introductory audiences. Gordon Fain has recently published an informative book on the topic of Sensory Transduction, (Sinauer Publisher) that may prove interesting to students seeking up in-depth coverage on this topic. Another well respected source is Bertil Hille's Ion Channels of Excitable Membranes (3rd ed), also published by Sinauer, which covers all aspects of ion channel physiology and molecular biology, including sensory mechanisms. To view an excellent animation of the light-induced shape change in retinal and rhodopsin, see blackwell's publishing page for Gary Matthews' Neurobiology. To read about Buck and Axel's research, see the original paper in Cell. See the description of their work on the Nobel Prize site. Richard Axel's Nobel lecture explains the molecular logic of smell on Video and PDF. His lecture was entitled "Scents and Sensibility" (another apology to Jane Austen). 21. Visual Periphery. (HOPKINS) In finishing up sensory transduction many of the review article cited in the references for this lecture came from a special review issue in Nature, Volume 413, 13-September 2001, focusing on advances in Molecular Sensing. To read about the solution to the structure of bovine rhodopsin, see Nature, 2000 view the structure of rhodopsin using any number of viewers, see Bovine Rhodopsin page on PDB (protein data bank). Some of the early chemical characterization of visual transduction was done by George Wald, who won the Nobel prize in 1967. To see the theoretical olfactory receptor structure mentioned in class, see Leffingwell and Associates (a software company for the food service industry) website. So far the crystal structure has not been determined, but instead is based on rhodopsin and models of protein folding. The original paper describing the crystal structure of Rhodopsin was Palczewski K et al Science (2000). See Matthews' animation of sensory transduction in the lateral line. The lecture on the visual periphery begins with the anatomy of the visiual system. Check out the Anatomy of the visual system web site put together by the department of anatomy at U. Penn. To demonstrate the "blind spot" on your retina, click here (HTML) or here (for printed .PDF version). Have you ever seen your own retina? If not, click here for a demo. 22. Vision in the CNS. (HOPKINS)The website, Serendip, has a nice demonstration of lateral inhibition with numerous examples. H. Keffer Hartline, who discovered lateral inhibition in the Limulus eye (horseshoe crab) won the Nobel Prize in 1967 for his pioneering work on vision. Read Hartline's Nobel Lecture for a fascinating account of the lateral inhibition phenomenon. To see the movies illustrating the technique of determining the receptive field of a cell, see the "on-center-off surround" cell recorded in the Lateral Geniculate nucleus (recorded by Hubel and Weisel) and the "off-center-on surround" cell also recorded in the Lateral Geniculate. Check out the page on the morphology of ganglion cells. To see the illustrated version of the retina-pretectum pupillary reflex pathway, see this link. For an introduction to visual cortex, see webvision. For more on the visual cortex, see this link by George Mather (Univ. Sussex). See Wikipedia's site for a definition and explanation of the Weber-Fechner Law (i.e. the relation between a stimulus and perception is logarithmic). A student asked if a sensory receptor were over-stimulated, would one 'feel' pain? A great question: according to the theory of 'labeled-lines', one senses pain when specific types of pain receptors are stimulated (i.e. nociceptors or thermal receptors, activated by noxious chemical, thermal, or mechanical stimuli). For example, if individual photoreceptors were over-stimulated with laser light, such that damage was done to only to the visual receptor cell -- this should not produce pain, but the sensation of bright light instead--this would be followed by a loss of sensation once the damage was done. The pain would come only if the light also stimulated pain receptors in the eye. Pain to the skin comes from stimulation of specific nociceptors or temperature located in the skin itself (Purves et al.2007)An alternative viewpoint is discussed in a recent article by A. D. Craig in the Annual Review of Neuroscience. Visual illusions illustrate the power of neuronal processing in our visual system. The lecture notes discuss the Hermann Grid illusion which is caused by neural processing in your retina. Another striking illusion, the "rotating mask illusion" (an MPEG1 video). This is another striking example of how perceptual experience shapes your interpretation of visual images such as faces. Your brain refuses to let you see a face as hollow, changing the direction of movement of a hollow mask which is rotating to compensate for the changes in perspectives. See Hollow Mask Illusion by Dr. Richard Gregory. Dr. Gregory (University of Bristol) has assembled a series of these illusions as videos. His book, "Eye and Brain" is highly recommended. To see many other visual illusions, check out the illusion works website. Check out the amazing checker shadow illusion. See the proof of the checker shadow stimulus. Visual Cortex. For more on the work of Hubel and Weisel, check out the Nobel Prize 1981. For more on the visual motion sense deficit after stoke, see the HHMI site. To see the movie of calcium imaging discussed in lecture, see activity of visual cortical neurons, published in Nature. See also Clay Reid's web site.
Visit the University of Sussex hearing group web page to see some excellent SEM photographs of the mouse cochlea. Promenade 'round the cochlea is a guided tour of the cochlea and the basilar membrane. The University of Wisconsin has an excellent site on the anatomy of the auditory system. C. Quentin Davis and Dennis M. Freeman have a nice site with video clips of sound-induced motion of the hair bundles, tectorial membrane, etc.
To see another video of basilar membrane motion in response to sound, see the Animated Cochlea from HHMI . To see more on the movement of outer hair cells, see this tutorial on hearing and hair cells. Also see the award winning Rockin' (Turn your sound on) Video of outer hair cell movement video from Jonathan Ashmore, Univ. College London. Click here for an animated movie that demonstrates the Jeffress model of sound localization. For an good overview of auditory processing, from cochlea to cortex. 24. Lower Motor Neurons and Central Pattern Generators (FETCHO). In this lecture Dr. Fetcho emphasized the anatomical arrangement of motor neurons to muscles, the physiological control of muscles according to task, as described by the size principle, and the role of central pattern generators in the production of movement. Click here to get a tutorial on human muscle names, actions, insertion points, and limb movement control on GetBodySmart.com. Motor Units. A motor unit is defined as the set of muscle fibers innervated by a single motor neuron in the spinal cord. In mammals, there is a single motor neuron innervating each muscle fiber, although any given motor neuron may innervate many fibers, all of which are the same type of muscle (i.e. Type I or slow twitch, Type IIA or fast twitch but fatigue resistant, or Type IIB - fast twitch easily fatigued). Each type of muscle fiber has its own physiological properties in terms of metabolism, blood supply, color, and size. Size Principle. The size principle in motor control is a basic set of rules governing how motor neurons are recruited during the generation of movement. Dr. Lorne M. Mendell has written a short essay in the Journal of Neurophysiology in 2005 describing the size principle and the key papers that elucidated it. This was largely the work of Elwood Henneman (1915-1995) of Harvard University who first demonstrated that motor units are recruited in a highly ordered sequence based of their size. The smallest motor neurons are recruited first and in response to the lowest threshold of afferent input, to produce the smallest possible force of contraction; intermediate sized motor neurons are recruited next at a higher threshold; the largest motor neurons are recruited last and generate the greatest force. As larger and larger motor neurons are recuited, there is a physiological transition from Type S motor units (slow twitch, small force, high resistance to fatigue) to Type FR (fast twitch, intermediate force, intermediateresistance to fatigue), to Type FF (fast twitch, highest force, fastest fatigue). The muscle types differ in biochemistry and metabolism. Central Pattern Generator. A central pattern generator is a set of neurons functioning as a unit that controls a motor pattern without the need for sensory input. Central pattern generators are a logical alternative to reflex chains in which actions which are completely controlled by fixed sensory inputs working as reflexes. CPGs are found in systems that control rhythmic action patterns - walking, swimming, chewing, flying. Some famous rhythmic CPG systems are found in the: stomatogastric ganglion of lobster which contains 30 neurons involved in the generation of the rhythm in the gastric mill of the lobster's stomach and the pylorus rhythm in the lobster gut;the ventral nerve cord of the leech, which controls swimming behavior. One of the best studied CPGs in a vertebrate is the Tadpole Swimming CPG described in lecture. For a review, see Roberts et al., (1998). Also see a recent review in Brain Research Reviews. Roberts, Li, and Soffe recently reviewed the role of inhibition in this circuit. 27. Eye Movements and other aspects of sensory-motor integration. The study of head stabilization in herons was done by Gadi Katzir and colleagues at the University of Haifa in Tivon Isreal. He spent a sabbatical at Cornell a number of years ago. The heron study was published in J. comp. Physiology. Here is a link to the movie shown in class. The eye tracking video was made by Dr. Mary Hayhoe at the University of Texas Austin. She studies the cognitive aspects of vision including planning, route taking, ball games, and reward. Her peanut butter and jelly sandwitch movie is available on line. Here is a nice review of eye tracking in natural behavior (Trends in Cognitive Sciences). Image stabilization on the retina is described in the Purves et al. textbook (pp. 487). Our course web site has instructions on how to see the "Purkinje Tree" -- the capillaries on your own retina (see See Retina). To see excellent images of the eye muscles and eye movements, see Wikipedia. It was Fuchs and Luschei who recorded from the abducens nerve during saccades; they described the spikes fromthe abducens nerve as producing sounds like musical notes, demonstrated in lecture, as the eyes rapidly switched from one position to the other. In lecture, we head only a few remarks about the neral control of saccades; the text has much more information about the complete pathway (pp. 501-509). By tracing the signal back, you can follow it to the sites in the cortex that control saccades (see Fig. 21.13 in the text). The Vestibular Occular Reflex is well described in the text (Chapter 14 on the Vestibular system, pp. 356-7 on the VOR). The plasticity of the VOR is reviewed in the text chapter 19 (see Fig. 19.14). Students may be especially interested in the recently discovered vestibulo-auricular reflex in the cat, where the cat can move its pinna to locate a sound, but then stabilizes the pinna by a reflex control of the pinna position from the vestibular sytem. 38. Memory (Hoy). The study of memory was forever changed by the patient HM who is described in this Wikipedia entry. Click here for more on HM's story. For a quick review of the cognitive science of memory, see the Memory definition in Wikipedia. Listen to the NRP interview of and about HM released February 2007. 39. Epilepsy (Hoy). Here are some links that will help you answer some/most of the questions that 42. Neuroethology (Hopkins). The field of Neuroethology developed out of a combination of cellular neurobiology and ethology. Ethology traces back to the pioneering work of Tinbergen, Lorenz, and Frisch who won the Nobel Prize in 1973. Krogh's Principle is explained in Wikipedia -- an entry written by Cornell Grad. Student, Jason Gallant. To learn about one of Neuroethology's founder's read about T.H. Bullock (Wikipedia) and J. Comp. Physiol. The discovery of Squid Axons. The giant axon of squid was discovered by J. Z. Young in 1936. Read an historic account by Richard Keynes. In these videos posted on Smith College's web site, you can see pictures of the dissection and identification of squid giant fibers by their discoverer. Electric fish. The diversity, electrogenesis, and neuroethology of electric fish is described on the Hopkins website. For a recent review, see the Encyclopedia for Neuroscience article on electrical perception and communication. For a nice review on sound localization in barn owls, see "Listening with Two Ears". To see more on the map of auditory space, see the original article by Knudsen and Konishi (1978). To read more about the circuit for sound localization in the barn owl, see Carr and Konishi (1990) Echolocation in Bats. Cynthia Moss at the Univ. Maryland has published much on the acoustics of bat echolocation (see movies on her website). To read more about Nobua Suga's work on the auditory cortex of bats, see Scientific American.
These notes are prepared by Carl D. Hopkins. |
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