Lecture 4

Audio recording started: 12:21 PM Friday, January 23, 2009

 
 

WENT OVER PAPER HANDOUT

 
 

• Action potential for a wave front traveling across skeletal muscle -90 – 0mV
  

   
   

• When goes down does not have hyperpolarization does not happen in muscle
  

   
   

• Depolarization due to influx of Na
  
• Repolarization due to efflux of K
  
  • Open Na channel and Na flows in bringing positive charge in, when open K positive charge goes outside and brings membrane potential back down to resting potential
    

  Wave of excitation goes over surface of the cell, sarcolema and heads down the T-tubule
  

  t-tubules have terminal cisterns
  

  AP travels down and hits a dihydropyridine receptor
  

  Dihidropyridine receptor made of four subunits and between subunits 2 and 3 you find a loop that goes down
  

  The loop goes down to ryanodine receptor between second/third subunit, loop is a physical link to ryanodine receptor
  

  http://en.wikipedia.org/wiki/Ryanodine_receptor#Physiology
  

  Terminal cistern is filled with Ca
  

  Ca is taken in by ER and went into terminal cistern and is waiting ot be released
  

  Dihydropyridine receptor has four loops/four subunits (this is one receptor)
  

  Four loops go down to ryanodine receptor, but only every other ryanodine receptor has a tetrad above it
  

  Every other ryanodine receptor has a physical link to open calcium, electrical event changes shape of tetrads and the loops go up and will open the ryanodine receptors and calcium will be effluxed and will open other ryanodine receptors (negative feedback system)
  

  Ryanodine receptor has a high affinity Ca receptor that will open if that is stimulated, it will bind Ca in low levels, when Ca comes out from ryanodine receptor and it will release Ca and this will increase Ca in the area and it will bind to low affinity Ca ryanodine receptors
  

  Troponin of the Thin filament (two rows of globular actin strung in a row)
  

  Tropomyosin covering active site
  

  Troponin keeps tropomyosin in place
  

  There are three troponin proteins:
  

  Tn-C
  

  Tn-T
  

  Tn-I
  

  Tn-C has two globular ends and one is called the C(carbon) end and the other is the N(nitrogen) end
  

  When making an amino acid you have a carboxyl and an amine end and you just stick these together to form a peptide chain
  

  Tn-C already bound to Tn-I
  

  N part of Tn-C not bound to anything
  

  If add Ca N end will bind to Tn-I
  

  When bind causes troponin to change shape and will break Tn-I off of actin molecule and will slide off of strip of tropomyosin and this will slide off of active site and expose
  

  Actin has an outer and an inner site, actin in the outer domain and it slips into inner site, exposing the active site
  

  Ca enters into cytoplasm bind to N part of globular Tn-C which will bind to Tn-I to cause shape change to expose the active site
  

  What does the active site do?
  

   
   

  Motor Unit = one neuron supplying several muscle fibers in a muscle
  

  If fine control muscle have as few as three fibers for one neuron
  

  Support/weight bearing muscle several hundred fibers per neuron
  

   
   

  During isometric contractions find that the lever arm is unmoving, ADP
  

  Lever arm in rigor state, but Pi has popped off and is in a great deal of tension, Z-disc can't move
  

  More tension want to put in that isometric contraction, the more subunits you initiate
  

   
   

  Isotonic contraction  the farther you want to go the more subunits you initiate and fire
  

   
   

  Can monitor the electrical activity in the muscles using an EMG (electro myogram)
  

  Have two electrodes, which attach to arm and will monitor electrical activity and will acquire a bipolar reading, sometimes you will see a plus associated with these
  

  Electrodes are attached to an amplifier which is attached to a pen, which will be making a recording on a piece of paper
  

  When one electrode sees a positive charge it tells the pen to move in one direction, when the other electrode sees the positive charge it tells the pen to move in the opposite direction (BIPOLAR RECORDING)
  

   
   

  If have muscles see positive on outside, but can't see negative on inside, have some excitation traveling across it, front of the wave is positive and back is negative therefore have positive wave front
  

  If have positive wave front traveling parallel to electrodes, pen doesn't move
  

  If have wavefront and doing a bipolar reading, if running parallel the wave front is imaginary and can use this idea to determine direction
  

  If have wavefront perpendicular to electrodes, get max deflection
  

  Able to rotate electrodes and observe raise/fall of deflection to determine direction of motor neuron
  

   
   

  Raw EMG = very rough, NOT smooth
  

   
   

  If not enough Ca, Mg will replace
  

   
   

  occurs on chain
  

  Neck changes shape and picks motor core up and puts it closer to active site - doesn't have to travel as far…quicker contraction time
  

  Ca stays for about 30ms
  

  1/2 life of phosphorolation = 1.3 seconds
  

   
   

  Cardiac muscle cannot sustain a contraction
  

   
   

  Myosin can only move in ONE direction
  

   
   

  2 types of contractions:
  

  Isotonic - same tension
  

  All sarcomeres are contracting in an all-or none fashion, however overall movement is SMOOTH
  

  Motor units are responsible for smoothness (primary cause for smooth movements)
  

  Group of muscle fiber cells that are innervated from many collateral axon fibers from a single axon
  

  …….3
  

  Fine control
  

  Fingers, eye muscle
  

  Or single nerve can innervate several hundred fiber
  

  When ONE nerve fiber fires, all motor units contract at once and smooth movement results
  

  Isometric - same length