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Lecture 2

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McMaster University
Life Sciences
Ramesh Balasubramaniam

Lecture 2 September-10-12 3:24 PM  Review from thurs o Coordination  Motions vary with objects and events o 3 Fundamental problems  Dof  Redundant number of joints and muscles  Infinite paths to a soloution  Yet we choose a specific path  Motor equivalence  Multiple effector sets to accomplish a goal  Serial order problem  How does the brain figure out in which order to do things  Its not one stimulus leads to one response, one stimulus leads to one response  Can prepare for one response before the stimulus o Da Brain  100 billion neurons in brain  10 synapses 100 billion x 10   Tools:Directions o Coronal - study lateral aspects o Horizontal - good for studying layers of brain (top to bottom) o Sagittal - focus on specific areas in certain areas on left and/or right area (side to side)  Four lobes o Frontal lobe - at front of brain o Central sulcus - divides brain from from back o Parietal - top middle o Temporal - above ear o Occipatal - towards back o Cerebellum - toward back an bottom of temporal lobe o Cerebral cortex: brains outer bark layer o Gyri = folds o Sulcus = crevices (indents)  The Evolved Brain o The brain envolved from invertebrate systems (primative) o Most invertebrate animals have input/output charaterizations despite that they don't have a spine o Vertebrates begin to develop a spinal cord o Paleo-mammalian brain: subcortical structures (midbrain, hindbrain, nether brain) o Neomammalian brain: cortex o Cortex makes inmportant decisions o Brain and spinal cord = CNS  Hierarchy o Spinal Cord - reflexes  Primitive responses are handled in the spine  "Spinal reflexes" o Brain stem (subcortical/supraspinal areas)  Arousal, tuning, emotions etc. o Cerebral cortex  The big cheese o Cerebellum talks to brain stem AND cortex (connected to both) o In 1912 Charles Sherington  Reflex  Was not aware of 3 fundamental problems  Thought all brain structure developed to maximize processing of reflexes  Discovered reflex arc  Connects outer surface of body to spinal cord  Info not being sent up to cortex  Cortex connects through tracts down through spinal cord to surface of muscles  Ventral corticospinal tract  Connect left side of brain to left side of body  Why would you want to wire facial muscles,eyes etc. By going through spine?  You wouldn't!  Corticobulbar tract contains nerves for those areas  Lateral corticospinal tract  Distal limbs  Ventral corticospinal tract  Trunk and leg muscles Unit of Action  Pavlolv  Doensn’t need a physical stimulus  Sherrington  What happens when you are poked  Receptors process disturbance and send to NS  Decision is made regarding what youa re going to do about this  Many discoveries occurred when observing his dog scratch  Is chaining of reflexes the way movements are organized?  If ask you to touch nose, are you using your previous movement to determine what you should do next?  Until 1950’s that’s what people though behaviour was organized that way  Now we know that reflex is important aspect but is not the way movement is organized  Reflex requirements 1. Outside agent required to activate movement 2. What happens when there is no stimulus 3. Fast movements where this no feedback like typing a. Have to start making movements before the last one has finished *Why we have a QWERTY keyboard Typewriter described so letters that don’t normally occur together are put beside each other and vice versa 1. You can overwrite reflexes depending on context a. If make you more and more aware of heat, you can train yourself to overcome the heat 2. Production of novel movements a. How would you know how to correct for it reflexively?  Spinal Cord Damage  Typically happens when traumatic event to cells within spinal cord and severs nerve tract  Two reasons we can't patch up spinal cord 1. SO many nerve fibres in tract 2. WE wouldn't knwo where they could go  Christopher Reeve  Lost all function  No voluntary mvmt capability below neck  Needed lot of support with daily living  Extreme paralysis  Point of laceration = paralysis below  Extremely difficult to fix in this case  Nerve tracts have such dense fibres that it is impossible to determine where they are supposed to go – there’s a 100 billion neurons converging!  Supported Canadian Science because Americans had a ban on embryonic stem cell research  Deafferentation and Neuropathy  D
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