Lecture 3

Audio recording started: 12:03 PM Wednesday, January 21, 2009

 
 

Neurons and Muscle Contraction

 
 

• If you monitor the membrane potential between two electrodes with one inside a cell and one outside the cell the potential will be 0
  
  • membrane potential only occurs at the membrane
    
  • caused by movement of ions across membrane
    
  • if the movement of ions stops then the membrane potential will be 0
    
• Potential caused Na/K pumps
  
  • Pumps 3 Na out and 2 K into the cell
    
  • ATP Powered
    
  • Na+ outside, K+ inside
    
  • Enhance potential
    
  • Na leaking in reduces potential
    
• K leak channels
  
  • Allow K to leak out of the cell
    
  • Creating + charge outside and leaving negative charge inside
    

   
   

• Ion Concentrations
  
  • K+
    
    • high [ ] inside the cell
      
    • K+ leak channels act as a major input into membrane potential
      
    • channels are 100x more permeable to K to leaving the cell
      
  • Na+
    
    • high [ ] outside the cell
      
    • Na+ voltage gated channels
      
    • there are some Na+ leak channels that allow for some Na to leak in, reducing potential slightly
      
• Charge
  
  • Outside (+)
    
  • Inside (-)
    
  • Charge inside and outside the membrane is due to concentration gradients
    

    10:1 for Na+
    

    35:1 for K+
    

   
   

• 
  Resting Potential
  
  • average resting potential of a neuron = -70mV (mostly due to K leaking out – there are more pluses going out than are coming in)
    
  • resting membrane potential can range from -40 to -90 mV
    
    • Measured inside vs. outside
      

   
   

• Voltage Gated Ion Channels
  
  • have voltage gated channels at specific voltage that open and allow for transmission of an AP
    
  • usually permeable to (+) ions which can alter the potential
    
  • Chemically gated channels DO exist
    

   
   

• Action Potential
  
  • neurons and muscles use AP as messages
    
  • an electrical stimulus causes hyperpolarization, depolarization (closer to 0) to create an AP
    
  • if reach threshold -55 mV an AP will occur
    
  • if threshold is reached slowly, this will allow the neuron to accommodate ionic changes and no AP will occur
    
  • if there is a rapid depolarization to -55 mV Na+ channels will open and raise the memebrane potential to +35mV
    

1. repolarization occurs when the Na channels close (two gates), K channels open (K channels only have one gate), K channels are slower to open
   
2. hyperpolarization occurs due to slow closing of K channels
   
3. when K channels finally close membrane potential is again achieved
   

 
 

1. 
   Threshold
   
   1. usually -55 mV, but not always
      
   2. a quick 15-30 mV change in membrane potential is needed to initiate an AP
      
   3. accommodation = gradual increase in membrane potential that reaches the threshold and passes it but does not initiate an AP
      

    
    

2. Refractory Periods
   
   1. absolute refractory period = period where where a neuron WILL NOT fire again no matter how big the electrical stimulus (measured in time, msec)
      
   2. relative refractory period = take a strong electrical stimuli to initiate an AP
      
   3. total refractory period = absolute + relative refractory period
      
   4. refractory period of cardiac muscle much longer than skeletal muscle, can keep a skeletal muscle contracted for a long period of time by continuing to supply a continuum of signals
      

       
       

3. Dendrite
   
   1. Don't work with wave propagation
      
   2. These have channels, but they don't have voltage gates, b/c they don't propogate AP
      
   3. These just allow charge to build at Hillock
      

       
       

4. Wave Propagation
   
   
   1. surface of skeletal and cardiac muscle
      
   2. only goes in one direction
      
   3. is the transfer of charge down the axon
      
   4. series of opening/closing Na/K channels
      
   5. slower, covers a longer distance
      
   6. muscles use this ONLY in unmyelinated neurons
      

       
       

5. 
   Axon
   
   1. messages are sent down the axon
      
   2. the start of the electrical signal is at the initial segment (axon hillock)
      
   3. These are what is mylinated
      

       
       

6. Sink Conduction/Electrotonic Conduction
   
   
   1. FASTER than wave propogation, dissipates quickly
      
   2. short distance
      
   3. a positive charge pulls on the negative charge inside the membrane and makes the end slightly positive
      
   4. amplified by the presence of Ca2+
      
   5. transfers the positive charge and causes a dissipation of charge
      
   6. have multiple dendrites feeding into soma and summing charge until hit threshold
      

       
       

7. Myelination – Saltatory Conduction
   
   1. if want to speed up wave propagation have myelination with Nodes of Ranvier
      
      1. Casued by schwann Cells
         
      2. Sodium channels concentrated at nodes of Ranvier
         
      3. Use Sink conduction
         
      4. JUMPING
         
   2. brain is myelinated at 1.5 years
      
   3. fast electrontonic conduction allows for jumping from node to node
      
   4. CNS  oligodendrocytes wrap many axons
      
   5. PNS  schwann cells wrap only ONE axon
      
   6. multipolar axons use the axon hillock to sum all the (+) and (-) input and elicit appropriate responses
      
   7. unipolar and bipolar summation takes place in the initial segment of the axon
      

    
    

8. Definitions
   
   1. tonal = firing all the time
      
   2. phasic = waiting to fire, can only "say" I fired
      

    
    

9. Muscle Contraction in Skeletal Muscle
   
   1. skeletal muscle = muscle fiber that has one motor neuron synapsing on it, this synapse is a chemical synapse
      
   2. acetylcholine (Ach) = neurotransmitter used at synapse to stimulate muscles
      
   3. AP moves 5m/s
      
   4. Ach comes out at synapse at synaptic cleft and causes the opening of gates and the AP travels in one direction
      
   5. Travels into T-Tubule
      
      1. Triggers dihydropyridine receptor
         
         1. Formed in units of 4 (tetrad)
            
         2. Open by Ca and closed by Ca
            
         3. All 4 Sit over EVERY OTHER ryanodine receptor in terminal cistern
            
         4. Electric event triggers increase in cytoplasm potential
            
         5. Triggers every
            
         6. Ca opens _________
            
            1. As it gets higher, the second receptor works only with
               
   6. motor end plate = location of the synapse, chemically gated channels here
      
   7. synapses located ONLY under end plate
      
   8. nicotinic receptor = imitate affects of nicotine
      
   9. Ach signals event across surface
      
   10. positive wave front
       

    
    

   Pasted from <file:///C:\Users\Derek\AppData\Local\Temp\OneNote\0-3\Lecture%202%20Neurons%20and%20Muscle%20Contraction.doc>
   

    
    

Lecture 2

Thinking Scientifically, continued…..

 
 

• Is vague terminology used,
  

  "empty calories,"
  

  Invented as scare tacktic term - means anything the speaker wants it to
  

  Taco chips…whole corn
  

  #1 corn best, #2 ave. #3 poor
  

  #2 = 9% protein, has carbs, fats, vitamins, minerals, h20
  

  NOT EMPTY
  

  "healthier," "Wellness"
  

  "unnecessary biopsies"
  

  Team of chineses researchers said that # of unnecessary biopsies could be reduced by NOT teaching women how t check for breasts
  

  Mamograms and ultrasound, when used together have resulted in a high number of unncessary biopsies
  

  "comes back negative"
  

  Better to just let them DIE???
  

  "eases the symptoms of NFD"
  

  Our clinical studies have shown….
  

  Marketing sugar pills for hypochondriacs
  

  "clinics" mean nothing
  

  Vague
  

  Clinical study = BS
  

  Clinical research = ok
  

  REAL drugs have side affects
  

  "ask dr. if its right for you"
  

   
   

• Does the statement use other words, "accompanied by," "significant" – probably not due to near chance, not really a quantity
  

  "significant" does not indicate a best result
  

  "Probably not due to mere chance"
  

   
   

• Is the statement irrational nonsense?
  

  "dr.'s don't want you to know about this natural cure"
  

  "this purges toxins from the body"
  

  Leads to being addictive
  

   
   

  Liberty University has Dino bones that are from only 3000 yrs. Ago
  

  ALL other accounts say 65 million yrs. Ago
  

  Like saying Mt. everest is 16 inches high
  

   
   

• Does statement refer to preliminary results?
  

  Means claim is not based on ANY research trial whatsoever
  

  "a study" or "one study"
  

  Usually non-repeatable research
  

  New scientific research doesn't go on tv before it gets published
  

   
   

• Is statement an untested hypothesis?
  

  Vets: the umbilical chord should stay attached as long as possible after foal delivery
  

  b/c the fold starts on the placental end of the cord and moves down - so it gets the blood inside
  

  WHY DOES IT NEED BLOOD if it hasn't had it for the entire time its been inside
  

  NEVER accept "it cant hurt"
  

   
   

• Only rely on textbooks that cite the references
  
  • Miner library - reserve for 204 - Medical Physiology, by vernon B mountcastle
    
  • 2 volume - considered Gray's anatomy of physiology
    
  • Used descriptions of experiments that lead to that statement
    
  • Every single statement made must be referenced
    

   
   

• SciAm stated that WE were just as liable to be taken in to false claims
  
  • Being taught FACTS, instead of how to think scientifically
    
  • **Reason for success in science in the last 200 years is due to the development of the Scientific Method**
    

     
     

• 2400 ago Hippocrates lived in IONIA
  
  • Declared diseases had causative method
    
    • Not a punishment from Gods, therefore there were preventative measures
      
  • Never found a single cause or cure for any disease, just that they COULD be
    

Lecture 1

10 questions on exam 1 on 1st 2 lectures

 
 

Lecture 1: January 14th, 2009

 
 

The Origins of Science and the Scientific Method

 
 

I. IONIA

-Science started in Ionia (Islands of western coast now known as Turkey) + thin strip of western coastland

Ionians: spoke Greek - most trace roots back to greece

Used the Phoenician alphabet – added vowels, very literate (greeks didn't add vowels)

Not just priests or upper echelon

No centralized government

No religion

Wouldve dictated a universal knowledge to all, but….

-Ionia was the crossroads for Greeks, Babylonians, Phonetians, Egyptians and was a center of trade between these people

-Each of these civilizations had their own set of gods

insisted that their gods were true and the others were false and made up by the priests by other civilizations

-Believed Nature was due to god's actions

Attributed nature to God

Volcanoes, earthquakes, harvest…etc.

-Ionians skeptical - why are all these different Gods used to explain the same thing??

DID NOT use the gods to explain Nature but instead used:

KNOWN AS FREE THINKING

1. Logic

2. Observation

3. Experimentation

 
 

Thales

From Amilitus - city on edege of turkey

1st to use free thinking, didn't use experimentation

Many ideas incorrect

Introduced this Free thinking method

 
 

 
 

II. PHILOSOPHERS

 
 

1. 1^st Century
   

    
    

• Anaximander (2600 years ago)
  
  • performed the first recorded experiment
    
  • proposed man evolved from lower animals
    

    Helpless newborns too helpless to survive on own - must have evolved from more ind. Species.
    

     
     

b. Democritus (2400 years ago) – proposed the atom and "the void"

• Greek "cut" = tom,
  
• atom = no more cuts
  
• Cut through a cone the 2 sides exposed were no longer a cone
  
• Determine volume of cone and stacking disks on top of one another
  
• Recorded area of each disk, and adding them up
  
  • Integral calculus
    
  • Did not always follow logic of day, but fundamentally correct
    

  -said if cut people apart into smaller and smaller pieces eventually reach something can't cut apart anymore
  

  -wrote 73 books
  

   
   

c. Science stopped for a short time b/c of:

-suppression by priests

Upset that Gods were being left out of everything

-poor communication

-no proof (not technology to pass on teachings, ideas)

-Democritus not directly attacked, but attack on free thinking began in his lifetime

-destruction of writing (by other philosophers, Plato ordered burning of all of Democritus' writings, some of his books remained at Alexandria Writing Library, and they burned, but eastern scholars recorded some and brought back to their homelands and this is why we know of his ideas today)

Plato was 58 when Democritus' books

 
 

1. 2^nd Century A.D.
   

    
    

2. Ptolemy (astronomer)
   
3. Galen (anatomist)
   

   -Ptolemy and Galen's teachings were held to be irrefutable laws and science until 1543 when entered Dark Ages
   

 
 

THESE guys were top in field and for 1400 years, their teachings were irrefutable evidence - dark ages

 

c. There was a reawakening of science with writings by:

1543

Copernicus (astronomer)

Vesalius (anatomist)

Based their ideas on own logic

d. an attempt was made to suppress writings

but technology did not allow this

-Gutenberg Press

-printing with movable type

-allowed copies and communication

-suppression no longer an option and there were too many texts to destroy

e. 1654

-Pascal and Fermat

-determined the probability of poker hands

-hired by elite Frenchmen to do this

-intro to probability calculations

 

f. Early 1800's

-normal distribution (bell-curve) of statistics recognized

-standardization of weights and measures improved calculations

 
 

g. William Gosset write under the anonymous name "Student"

-developed Student's T-test

-increased reliability of data extracted from small samples

 
 

Additions to Free Thinking

1. Data Collection

2. Statistical Analysis

 
 

1. Scientific Method
   

   1. Identify problem/phenomenon that one wants to explain
   

   -Problem = applied science
   

   -Phenomena = pure science
   

   2. Propose a hypothesis
   

   Use reason to determine an explanation
   

   3. Design a repeatable experiment and carry it out
   

   -must be able to be analyzed statistically to support hypothesis
   

   -95% to be statistically significant
   

   -1 in 20 false
   

   -null/void = NOT support the hypothesis
   

   -purported to be valid if results support hypothesis
   

   Must be tested over and o
   

   -Accepted hypothesis = reported to be valid hypothesis
   

   -theory = broad, viable explanation for a phenomenon supported by a hypothesis
   

   -NOT a blind guess
   

   -can be shown to be invalid (NEVER rejected completely), MUST be replaced by a new theory
   

   -accepted theory is only discarded if one can replace it
   

• Found by using scientific method
  

   
   

 
 

D. How to Rule out Skepticism

1. Throw out obvious garbage (ex. ESP, UFO, etc)

ESP has never been able to pass repeatable tests

Voyager 1 is 1/10000 speed of light - fastest object ever created by man

Voyager 1 was traveling at a speed of 17.1 kilometers per second relative to the sun (3.6 AU per year or 38,400 miles per hour or 61 600 km/h),

If going to nearest star system (40 light years away)

80,000 to get there and back

2 million yr trip to a star system 100 light yrs away

 
 

2. Consider:

anecdotal evidence or pseudoscience as FALSE

-person's story, story without statistics

Groups with an agenda

Merchandisers

Famous people in ads

Once they say "I've been asked to try this and this is what I think…" - they are telling an anecdotal story

-pseudoscience

preconceived ideas never give proof,

practiced by non-science groups,

consist of strange data, vague parameters, self-diluting logic

answering questions with questions

Never absolutely certain

Science NEVER deals with truths, only probabilities

 

-true science – never infallible or irrefutable

-clinical research = most amount of variables that can't be controlled (need very large groups)

-immunity studies carried out in-vitro to reduce # of variables

Might not reflect true results in vivo

Ideal experiment compares two groups, differing in one variable

1. Check for undefined terms
   
2. Was ex. Design true to hypothesis?
   
3. Was it analyzed correctly?
   
4. Contains ridiculous statements
   
5. Statement that refers to "preliminary results" or initial studies or based upon one study
   
6. Untested hypothesis
   
7. Question whether the experiment was a real test of the hypothesis
   
   1. All variables accounted for
      
   2. Does the data support the conclusions
      
   3. Data analyzed using appropriate statistics
      
   4. Researchers use reasonable logic
      
   5. Were they looking for what they found
      
      1. Researchers can use self-diluting logic, but rarely do
         

 
 

Pasted from <file:///C:\Users\Derek\Documents\College%20Work\Rochester\Classes\Senior%20Sem.%202\Physio\Lectures\Lecture%201%20Scienctific%20Method.doc>

 
 

Buddies