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BIO271_Lecture 01_Jan9.docx

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University of Toronto St. George

BIO 271, Jan. 9, 2013 BIO 271HIS: Neurobiology Prof. Melanie Woodin January 9, 2013 Introduction - BIO 271 is like the follow-on to BIO 270 - labs and lab reports will be similar to those last time - prof is in Cell and Systems Biology - team lead for course is Dr. Chris Garside and Peggy Sammon [sp?] is course coordinator - prof does not administer the lab - if you have lab questions, talk to Peggy, your TA or Dr. Garside - prof will lecture first ½ of this term; then there will be a midterm; then Dr. Garside lectures - office hours Mondays 11-12 in Ramsay Wright Room 303 - she welcomes and encourages you to come - sometimes students are nervous to come if they don’t have a specific question but it’s fine to come and ask her to go over some slides again - she usually lectures for about 45 minutes, takes 5-10 break, lectures for about 40 minutes, ends 10 minutes early - usually during break and after, students will gather and ask questions so you can come and chat - textbook is same as BIO 270 and there are required readings - prof will try to post readings one week before lecture - lectures will follow textbook quite closely - you also need Short Guide to Writing About Biology - [see slide for course schedule] - midterm is Feb. 13 About the Prof - prof took this course more than 20 years ago - then, neurophysiology was taught from a different perspective - they said brain was like black box with lots of things like electrical cables - prof will take a different approach, not so electrical - did her MSc in zoology department, studying diving ducks - did a PhD at U Calgary - interested in synaptic physiology, particularly synaptic elasticity (the cellular basis for learning) - did postdoc at Berkeley studying hippocampus - then came back to U of T as assistant professor; that was about 10 years ago - she’s taught this course quite a few times and hopes she has improved it over time Today - how nervous system is organized - there is a diversity of neuron types, but will look at how they’re generally structured - electrical signals in neurons and the membrane potential - this is important for later courses - graded and actual potentials - at the end of the class you should be able to answer: - Which ions can flow to depolarize the membrane? - Which ions can flow to hyperpolarize the membrane? Page 1 of 6 BIO 271, Jan. 9, 2013 - if you can’t answer them, go over the notes/textbook again; can also come to office hours Nervous System Organization - nervous system is very complex - includes brain and spinal cord; nerves come out of spinal cord - nervous system can be divided in 2 sub-divisions: central and peripheral - slide shows Purkinje neuron found in cerebellum (back of brain – important for things like riding bicycle and control) - this neuron has been filled with fluorescent dye; slide shows dendrites coming out of neuron - dendrite arbour – like branches coming out of tree - these receive 100s to 1000s of synaptic inputs at any time - they take the inputs and put them together to make a decision about whether to communicate further - membrane potential: many cells have voltage difference across their cell membranes - many other cell types have a voltage difference too - we can change neuron membrane potential rapidly; this is called the action potential - thus we call neurons excitable - (heart cells are also excitable) - neurons use this to transmit information, sometimes over long distances (like from brain to hand taking notes) - we’re often biased when talking about neurons and think they do everything - nervous system has other cell types as well (astrocytes, etc) and they’re critically important in how neurons function in nervous systems - 20 years ago, thought of glial cells as support network; now we know they’re much more active How Neurons are Structured - neurons can look very different - [see slide showing neurons from different parts of body] - though they may vary in structure, they use the same basic mechanisms to send signals - book defines 4 regions (slightly artificial) in a neuron: - signal reception area - composed of dendrites that receive information (like your TV antenna on the roof) - signal reception can happen in dendrites or cell body - there will be a change in the membrane potential (converting chemical signal to electrical signal) - signal integration - 100s or more signals are coming together at one time - strong signal is converted to an action potential (AP), usually in region called Axon hillock or signal/spike initiation zone - signal conduction - conducts action potential - AP travels down the axon - many are wrapped in myelin, allowing them to travel quickly - signal transmission - signal transmitted to another cell at the axon terminal - [see slide showing above regions in motor neuron, sensory neuron, and Purkinje cell] Page 2 of 6 BIO 271, Jan. 9, 2013 - because of this organization neurons have a specific polarity - neurons often communicate with neurons - they also communicate with other cells, e.g. muscles - [see slide showing neuromuscular junction, which used to be most heavily studied synapse point in body] - principles that apply in neuromuscular junction are pretty much the same in cortex of hippocampus in mammals - textbook schematics make things look simple – it isn’t as simple in real life - practicalities are challenging - currently only way to figure out where axon is vs. dendrite is to take a slice of tissue, fix it, put antibodies on, wash them off, wait, and see where antibody for specific protein on axon is - there are new techniques helping overcome challenges - dendritic spine (protrusions from dendrites) - identified about 15 years ago with high resolution images - enlargement at end is called spine head - dendrite spine is post-synaptic site of neurotransmission - [see slide] Electrical Signals in Neurons and the Membrane Potential - neurons, like all cells, have a resting membrane potential - this is because there are different concentrations of ions outside of cell vs. inside of cell - people discovered this by putting electrode in cell; recorded difference of about 70 millivolts - inside is more negative than outside - membrane potential is negative at rest - neurons are also excitable, meaning they can rapidly change their membrane potential - (like person moving from relaxing on couch to doing jumping jacks) - Depolarization – membrane potential becomes less negative (e.g. goes from -70 towards 0) - Hyperpolarization – membrane potential becomes more negative (e.g. goes from -70 to -100) - Repolarization – membrane potential returns to resting value (e.g. goes back to -70) - [see slide showing graph of changes in membrane potential] - changes in membrane potential act as electrical signals Membrane Potential - many factors contribute to membrane potential - most important factors are: - distribution of ions across the membrane (i.e. what concentration is) - relative permeability of the ions (permeability = ability of molecule to cross a barrier) - charges of the ions + + - 2+ - ions: primarily we’re talking about Na , K , Cl and Ca -
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