...          material from Chapter 48 & 49.

Cell Communication...
  at the molecular levell --> SIgnal Transduction Mechanism.

Electrical Properties of Nerve cells
                            the electrophysiology of neurons lies in their...
Membrane Physiology

   there is a
great diversity
of Nervous Systems  [mouse gut & mouse retinal ganglia]
      a neurophysiology model organism is :   
Squid*Giant Axon   
[Doryteuthis pealeii] 
                              cell on chipAplaysia neurons

               is akin to SIGNAL TRANSDUCTION        : reception - transduction - response 
               and a HOMEOSTATIC REGULATOR       : receptor - controller - effector

        1.  sense organs via Peripheral NS gathers sensory input  --> signals info in
integration (transduces) information (within CNS - brain & spinal cord 
responds via motor output (effector organs & PNS - muscles : )







a common pathway in a Nervous System*

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


narrated explanation of spinal reflex arc.*

                                  knee-jerk reflex*   or   another spinal reflex

                      To study the actions and functions of nerves and muscles    
                                    a good model experimental system is the...

                                             neuro muscular*junction









STRUCTURE of an individual NERVE CELL [a NEURON*]
the term neuron was coined by the German anatomist Heinrich von Walder-Hartz
        in 1891 to describe an individual cell in the brain.
   Cell Body*     - is main part of neuron cell with cytoplasm & organelles
*     - short cylindrical outgrowths of Cell Body  
                                            carry signals (electrical impulses) into cell body

* (pic)             - long outgrowth of cell body - carry signals to next neuron
   &  Schwann cell     
- cells surrounding peripheral neuron axons in vertebrates -
                                             produce myelin (sheath) membrane
     (mylein origins?
                                             protein + lipid-like membrane insulating material surrounding axon 
    Nodes of Ranvier
*  - space between successive Schwann cells along axon... 
                                             node area is a non-myelinated area that regulates the
             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...













What is the informational content of neurons???
                    it's in the ELECTRICAL PROPERTIES of neuronal cells...

  What is the the electrical charge across a cell's membrane...
                    what is a
  RESTING & ACTION potentials

             exhibited by cells at rest...  most often inside NEGATIVE (
-) in animal cells
             which is due to the existing distribution of ions across the cell membrane.

  electrical 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

   How to measure membrane potentials
* in cells - microelectrode*   recording equipment* 

                                                  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...      what is cause of
inside  -65 to -70 mVi  for SGA ? 
                       homeostatic distribution of  
ions in neurons & surroundings
                       all of which result in the inside of cell being negative (-65mVBut HOW ?
                       how are these ions distributed across a SGA - passively or

   ENa    =  +62mVi     150/15  = lg 10   = values*
Nernst Eq.* Emv= +/-62 lg10[Co]/[Ci]  EK     =  -90mVi      5/140 = lg 0.035  
   ECl     =  -67mVi       120/10  = lg 12  

   Ion transport through channel proteins establishes the Resting Membrane Potential include:
    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                      

              animation*view             Summary of SGA [ions]  &  resting potential*










ACTION POTENTIAL...  change resting potential charge due to passive ion transport
                      image of AP           axon AP  

9e: c4
   name given to changes in electrical charges occurring during stimulation of a nerve cell,
              -   transient change in the RP voltage at one point along membrane of nerve cells...
change in charge is self-propagating along an axon
usually visualized graphically from an oscilloscope* recording [ graph*of AP*]
              ... requires a living cell, i.e., requires O2 for metabolism 
                                        is eliminated by metabolic poisons, including cyanide
              ... requires Na/K pump and
ion channels for Na & K  (fig*) to produce ion distributions
              ... is measured at local point using
* impaled in cells or a nerve chamber* 
              ... has a threshold - a minimal amount of stimulus is needed to open channels & "fire" an AP
              ... is an "all-or-none" phenomena,  either yes or no,  but is always of same magnitude
              ... is very rapid - time course = 2-3 msec to elicit change in polarity








  EVENTS DURING an AP    oscilloscope trace
*     graph of AP   
   Voltage changes the  permeability of axonal membranes and elicit an Action Potential.

* -  cell goes from inside negative (-) to inside positive (+)
                                Na channel opens - Na diffusively floods in -->  -70mV toward +62mV

*  -  Na channels close & K channels open outward [returns to inside (-)]
                                K follows its diffusive gradient & K diffuses out of cell (returns -)

 - "undershoot or overshoot" of resting potential (-75mv)
   refractory period   - time before another AP can "fire" again (about 2-3 mSec)   
overall mechanism***   &      AP animation (Pearson)*     Current changes during an AP     

CONDUCTION of an AP along an axon     
            local spreading of electric charge
adjacent membranes 
            changes the membrane permeability of adjacent non-myleinated region
            leading to continuous propagation in an autocatalytic - "domino effect"...  figure

                     AP Conduction is continuous in  non-mylinated axons        =    2-3 m/sec
                     Saltatory Conduction* in mylinated axons  [node to node]  =   100 m/sec

   animation of conduction*           animation of conduction*long version - view@home 









 Synaptic Transmission...   
synapse animation*                     .

        synapse - functional space connecting two neurons allowing transmission of
                                              AP's between cells:   may be electrical or chemical
        synaptic cleft -
[20 to 30 nm across] open space between neurons
across which a chemical neurotransmitter may diffuse
        synaptic knob - site of vesicles holding neurotransmitter at end of axon
        synaptic vesicle - holds neurotransmitters  (ex: acetylcholine in neuromuscular junctions)

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. "








Post-synaptic membrane potential responses...
      depends upon post-synaptic receptor type and how it responds.

  EPSP - excitatory post-synaptic potential  [goes positive from RP [-65mVi] to -55mVi]
              excitatory PSM neurons --> open Na channels --> inside + --if threshold--> AP

  IPSP - inhibitory post-synaptic potential    [goes negative from RP to -80mVi]             
             inhibitory PSM neurons --> opens Cl channels -  Cl-in  ->   more
-  -->  no AP
                                                   -->  opens K channels - K-out  ->  more 
  -->  no AP   
  AP - all or none 120mv depolarization/repolarization (from -65  to  +55 mVi)  

    multiple innervations  and  integration of EPSP & IPSP impulses*   
    temporal/spatial summations*    and   summary of neural impulses* 
    How is Sensory Information encoded*

                        Review of Action potentials & Synaptic Transmission
* [<-- view @ homework ]  







Neurotransmitters...   some stimulators and drugs.

neuro-muscular junction acetylcholine... muscle contractions     [cholinergic neurons = Na+ influx]
biogenic amines
epinephrine & nor-epinepherine - [catecholamines]... increase heart rate
serotonin &
dopamine - affect mood, attention, & learning
   depression  =  often from reduced epinephrine/norepinephrine levels
                           or an imbalance of serotonin.

amino acids     ASP & GLU   -    excitatory (CNS)
Chinese Restaurant Syndrome  +  MSG  
GLY & GABA -    inhibitory  (Cl-)    
(small proteins)
endorphins    -    their role [discovery]  is to decrease perception of pain
substance-P  -    excitatory transmitter - signaling pain

                  Some common Neurotransmitters...     Table of transmitters










Stimulants/Depressants - are chemicals that effect the activities of neurons...
  cocaine - blocks re-uptake of* dopamine by synaptic vesicles -->  continual stimulation
of reward-motivated behavior           animation of cocaine action
  flea collars - fipronil - blocks GABA-gated* Cl channels (normally inhibitory),
                   thus preventing hyperpolarization = results in excessive neural excitation, 
a hyper-excitation of CNS of the fleas and death.

  strychnine (a poison) - antagonist of inhibitory GLY & ACH receptors in spinal cord,
                   resulting in increase muscular convulsion & asphyxia.

  Sarin (a nerve agent) blocks action of acetylcholinesterase, thus overloading body's
                   nervous system in toto, ultimately paralyzing the diaphragm = suffocation.
               a paradigmKey Concepts*    synaptic cleft - the Glut-Tang Clan video 


     copyright c2024  Charles Mallery,      Biology 150, Department of Biology,   U. of Miami,  Coral Gables, FL 33124































           copyright c2024      Charles Mallery,      Biology 150, Department of Biology,   U. of Miami,  Coral Gables, FL 33124















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

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

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

                  Prozac and Paxil (antidepressants)...       animation
                  blocks reabsorption of serotonin from synaptic cleft
                  & boost synthesis of serotonin, epinepherine, & norepinepherine
        Parkinson's = lack of dopamine   schizophrenia = too much dopamine
- psycho-active drugs
                    function by binding to serotonin/dopamine brain cell receptors

   facilitates juvenile brain plasticity

Campbell reads:      10e: c48 (pg 1061-1077) c49 (pg 1079-1083)
                                     11e: c48 (pg 1065-1079) c49 (pg 1083-1088)