NEUROPHYSIOLOGY...  Campbell reads:  7e: c48 pg 1011-102
                                                               
&    8e: c48 pg 1047-1061
, 1064-1069.
     ...Electrical Properties of Nerve cells
(neurons)
         
        electrophysiology of neurons lies in their... Membrane Physiology
                   the model organism is :   Squid  Giant
* Axon    [Loligo pealei]
                   there is a a great diversity* of Nervous Systems 
frog neuron SEM of a nerve cell on a microporcessor Aplaysia neurons
   FUNCTIONS of NERVOUS SYSTEM -
                                                 
[ akin to SIGNAL TRANSDUCTION : reception - transduction - response ]
                                             and a homeostatic regulator : receptor - controller - effector ]

           
   1.  gathers sensory input (sense organs via Peripheral NS) --> info in
                   2. 
integrates information (CNS - brain & spinal cord)  
   3. 
responds with motor output (effector organs via PNS - muscles)
 

 

 

 

 

 


STRUCTURAL PARTS of Nervous System - 
    central nervous system - brain and spinal cord...    
(neural stem cell = origin of brain)
    peripheral nervous system
- outside the CNS- carries signals in/out of CNS
       PNS = sensory  (affernet - in)     and    motor  (efferent - out)  neurons:
          - somatic nervous system
- carries signal to skeletal muscle - under conscious control
          - autonomic nervous system
- regulate homeostatic internal systems - involuntary control
 
                   2 complimentary    Parasympathetic (cranial & cholenergic) - calming: HR-, energy storage
          
             systems:    Sympathetic (spinal & noradrenaline) - energy & arousal: HR+, glycogen--> glu
  
   
    

FUNCTIONAL TERMINOLOGY of Neurons  -  
            Nerve
   -  bundle of individual neuron cells wrapped in connective tissue
            Ganglia
-  cluster of cell bodies of individual neurons      
            Sensory neurons... (afferent neurons)
- external stimuli from receptors toward CNS
            Interneurons... 
integrate & relay sensory input to motor neuron
            Motor Neurons... (efferent neurons) 
- convert signals to effector cells = response 
                                       

 

 

 

 
    
    common pathway through Nervous system*

 
        Reflex Arc - hard wired, unconscious rapid response to external stimulus
                                       involving spinal nerves & effector cell electrical impulses

                   knee-jerk reflex
*   or   another spinal reflex

                                 animation: by the Animated Brain

                                 narrated explanation of spinal reflex arc:  by Sumanas Multimedia, Inc.
                                                   
   
        a Model experimental system of reflex for the neurophysiologist is the...

                                                     neuro*muscular junction

 

 

 

 

 

 

 STRUCTURE  of an individual  NERVE  CELL              neuron
   Cell Body        - is main part of neuron cell with cytoplasm & organelles
   Dendrites
*     - short cylindrical outgrowths of cell Body  
                                           carry signals (electrical impulses) into cell body
   Axon
*             - long outgrowth of cell body - carry signals to next neuron
   Schwann cell
* - cells surrounding axon in vertebrates -
                                             produce myelin (sheath) membrane        
(components)
                                             protein + lipid-like membrane insulation surrounding axon 
   Nodes of Ranvier
*  - space between successive Schwann cells along axon... 
                                                                 the inter-node area is a non-myelinated area
                               
                       speed of conduction -  w/o myelin speed is less (5 m/sec)
                                                                                        w/myelin (100 m/sec or 200 mi/hr)
                                                       Multiple Sclerosis - degenerative disease of myelin sheaths

   Synaptic Knob
* - enlarged ends of neuron holds neurotransmitters in synaptic vesicles
   Glia cells* - (astrocytes) provide support, function as blood-brain barrier, etc...
                                   [
pic1 &  pic2 ]


           

  

 

 

 

 

 

 

 

 

 

 
 
The electrical properties of cells:    resting & action potentials

   RESTING POTENTIAL - the characteristic electric charge
                                             exhibited by a cell at rest...    most often negative (-)

             potential -
(in electrical terms) is amount of electrical charge
                                at one point in an electric circuit compared to some other 
                                point in the same circuit often measured with a volt-meter (multi-meters
*)

   How to measure membrane potentials
* in cells - microelectrode*   pic*
                                             inside  vs.  outside of cells    

SGA - 65 to - 70 mVi
Frog muscle fibers - 90 mVi
Nitella  (algae) - 150 mVi
Valonia  (algae) + 15 mVi
     
     

                                                   
                              
                                      
                                     
 

 

 

 

 

 
  Causes of Resting Potential...      of
-65 mV inside for SGA ... 
           ion distributions
* -   all of which make inside of cell negative (-)  But HOW ?
                                             How do these ions distribute themselves across a SGA?

  ENa    =  +62mVi      150/15  = 10      48.7b*
    Nernst   Emv  =  +/-  62 log10  [Co]/[Ci] EK      =  -90mVi       5/140   = 0.033  48.7a*
  ECl     =  -65mVi       120/10  = 12

    1.  active transport of Na & K*   high Na outside [3]  & high K inside [2] via NaK-ATPase
    2.  differential permeability
*  diffusion of  K (faster out)  &  Na (slower in) = inside (-)
    3.  lots of  protein anions
*  (-) at cell pH,  thus  inside more (-) then outside
    4.  normal  diffusion of
*  Cl- into the cell                     

                                                        Summary of SGA [ions] & resting potential*                                 
    


                           
                                                                                
                                                                                   
                
         
                                                                                                    

 

 

 

 

 

 

 

 

 ACTION POTENTIAL
              -
 self-propagating transient change in the RP voltage across membrane of nerve cells...
              -  name given to changes in electrical charges occurring during stimulation of a nerve cell, 
              -  usually visualized graphically from an oscilloscope
* recording [graph of AP*]

    PROPERTIES of an AP... 
              ... requires a living cell, i.e., requires O2 for metabolism 
     
                                                     is eliminated by metabolic poisons, such as cyanide
              ... is measured using microelectrodes impaled into cells 
              ... has a threshold - minimal amount of stimulus is needed to "fire" an AP
              ... is an "all-or-none" phenomena,  either yes or no, no in-between
              ... is very rapid - time course = 2-3 msec

 

 

 

 

 
EVENTS DURING an AP    oscilloscope trace
*     graph     [Gasser & Erlanger]     
   depolarization
* - cell goes from inside negative (-) to inside positive (+)
                                Na channel opens - Na diffusively floods in -->  -70mV toward +58mV
   repolarization
*  - Na channels close & K channels open [returns to inside (-)]
                                K follows its diffusive gradient & K diffuses out of cell
   hyperpolarization
 - "undershoot" of resting potential (-75mv)
   refractory period - time before another AP can 'fire'     
            current changes during an AP
*     and     overall mechanism*
                                                                                                AP animation (Blackwell Publishing)
*

CONDUCTION of an AP along an axon     

            local spreading of electric charge depolarizes
adjacent membranes 
            change in membrane permeability of adjacent non-myleinated region
            leads to an autocatalytic - "domino effect"....... figure
* [nonmylinated = 5 m/sec]

myleinated Saltatory Conduction*     node to node    [100 m/sec]  
Saltatory Conduction Animation - Blackwell Publ.                


                                     
          

                                           

 

 

 

 

 

 

  
 Synaptic Transmission...

        synapse - functional space connecting two neurons allowing transmission of
                                                        AP's between cells:   can be electrical or chemical
        synaptic cleft - open space between neurons
[ 10 to 20 nm across ]
                                                       across which a chemical neurotransmitter may diffuse
        synaptic knob - site of vesicles holding neurotransmitter at end of axon
        synaptic vesicle - holds neurotransmitters  (ex: acetylcholine)
                                                        
action potentials trigger release of neurotransmitters*
        pre-synaptic side - releases neurotransmitter
        post-synaptic side - has a receptor which binds transmitter and ...
        ... ion channels open - leads to change of potential charge 
                                                      on the post-synaptic membrane ----> new AP
        removal of stimulus - an enzyme destroys neurotransmitter:  ex. "ACH-ase"

Synaptic transmission animation*
Sumanas, Inc - chemical synapse transmission    [ <-- view for homework]  


                 

            

 

 

 

 


     
Post-synaptic responses:

  EPSP - excitatory post-synaptic potential  (from RP [-65mVi] to -15mVi)
             excitatory PSM neurons --> open Na channels --> inside + --may--> AP
  
  IPSP - inhibitory post-synaptic potential    (from RP to -75mVi)              figure
*
             inhibitory PSM neurons --> opens Cl channels -  Cl-in  ->  more
-  -->  no AP
                                                   -->  opens K channels - K-out ->  more 
-  -->  no AP   
 
  AP - all or none 120mv depolaorization/repolarization (-65  to  +62 mVi)
 
 

    integration of impulses*with multiple innervations      
    summation of impulses*    &   temporal/spatial summations*

  
           
 
           

 

 

 

 

  Neurotransmitters & Other stimulators and drugs ...
     Some common Neurotransmitters...
Table of transmitters*    Harvey Project    Dr. King's site

neuro-muscular junction acetylcholine... muscle contractions     [cholinergic neurons = Na+ influx]
biogenic amines (CNS) epinephrine & nor-epinepherine - [catecholamines]... increase heart rate 
   depression  =  reduced epinephrine/norepinephrine levels
                        serotonin & dopamine - affect mood, attention & learning
        Parkinson's = lack of dopamine   schizophrenia = too much dopamine
               Prozac and Paxil (antidepressants)...       animations
                             blocks reabsorption of serotonin from synaptic cleft
        LSD/mescaline - psycho-active drugs  
               function by binding to serotonin/dopamine brain cell receptors
amino acids     ASP & GLU    -  excitatory (CNS)    Chinese Restaurant Syndrome
GLY & GABA -  inhibitory  (Cl-)       
MSG &  taste & Umami  press release
peptides
    
 (small proteins)
endorphins - their role  &  [discovery]   is to decrease perception of pain
substance P - excitatory transmitter - signaling pain
          [immunoassay kit]
 Neurotransmitter actions on PSM




 



 


Stimulants/Depressants - chemicals that effect activities of neurons
  

    cocaine - blocks re-uptake of dopamine by synaptic vesicle -->  continual stimulation
                  
animation of cocaine action
 

    caffeine -
Caffeine's principal mode of action is as an antagonist of adenosine receptors in the
                   brain; reduced adenosine = increased dopamine = stimulation
of blood pressure,
                   breathing, HR
.    (caffeine archive)
   

    flea collars - fipronil - blocks GABA-gated Cl channels (normally inhibitory),
                    thus preventing hyperpolarization - results in excessive neural 
                    excitation,  hyper-excitation of CNS, of the fleas and death.

  

    barbiturates & valium - intensify the GABA (inhibitory) effects, thus are inhibitory

  

    poisons like strychnine - prevent loss of transmitter (Ach) = tetanus
                                                                                             a paradigm
Key Concepts*

        go to SENSORY PHYSIOLOGY*