UW BIO UNIT 1 LECTURE 4 THE MEMBRANE, THE NEURON & ACTION POTENTIAL

LECTURE 4: LEARNING TARGETS AFTER SUCCESSFULLY COMPLETING THIS LESSON YOU WILL BE ABLE TO: TO UNDERSTAND BIOLOGICAL MEMBRANES – COMPOSITION AND FUNCTION TO UNDERSTAND HOW PUMPS AND CHANNELS ALLOW REGULATED AND SPECIFIC TRANSPORT TO LEARN THE CELL TYPES OF THE NERVOUS SYSTEM TO LEARN HOW NEURONS ARE STRUCTURED AND HOW THEY FUNCTION – AT REST AND IN ACTION

MEMBRANE COMPOSITION PLASMA MEMBRANE FUNCTION: SEPARATES THE INSIDE OF THE CELL FROM THE OUTSIDE MOVES MATERIAL FROM THE INSIDE OF THE CELL OUT ALLOWS NUTRIENTS FROM THE OUTSIDE OF CELL INSIDE

MEMBRANE COMPOSITION MADE OF A DOUBLE LAYER OF PHOSPHOLIPIDS (BILAYER) THE HEADS OF THE PHOSPHOLIPIDS ARE HYDROPHILIC ENSURE WATER SOLUBLE MOLECULES OUTSIDE THE CELL CAN’T PASS INTO THE CELL AND VICE VERSA THE TAILS OF THE PHOSPHOLIPIDS ARE HYDROPHOBIC head tail Hydrophilic= water loving Hydrophobic= water loathing

MEMBRANE COMPOSITION MEMBRANE PROTEINS ARE KEY TWO TYPES OF MEMBRANE PROTEINS: CHANNELS & PUMPS EMBEDDED IN THE PHOSPHOLIPID BILAYER ENABLE MATERIALS TO BE TRANSPORTED THROUGH THE PROTEIN INTO OR OUT OF THE CELL. ALLOWS MOVEMENT OF MATERIALS WITH OR AGAINST THE CONCENTRATION GRADIENT

CONCENTRATION GRADIENTS CONCENTRATION GRADIENT= MOVEMENT OF MATERIALS INTO AND OUT OF THE CELL THROUGH MEMBRANE PROTEINS DEPENDS ON THE RELATIVE CONCENTRATION OF THE MOLECULES COMPARED TO WHERE ITS MOVING TO  MOLECULES WANT TO MOVE FROM HIGH CONCENTRATION TO LOW GRADIENTS HAVE HIGH AND LOW SIDES (HERE HIGH CONCENTRATION SIDE IS OUTSIDE) MOLECULES CAN MOVE DOWN THEIR CONCENTRATION GRADIENT (WITH) OR UP THEIR CONCENTRATION GRADIENT (AGAINST)

CONCENTRATION GRADIENTS EX> GLUCOSE CONCENTRATION OF GLUCOSE IS GENERALLY HIGHER OUTSIDE THE CELL COMPARED TO INSIDE LITTLE TO NO ENERGY USED  PASSIVE TRANSPORT FACILITATED DIFFUSION  CARRIER PROTEINS INVOLVED GLUCOSE MOLECULES GET USED RAPIDLY ONCE THEY HAVE ARRIVED IN THE INSIDE OF THE CELL IF A MOLECULE NEEDS TO MOVE AGAINST THE CONCENTRATION GRADIENT THEN ENERGY (ATP) IS REQUIRED ACTIVE TRANSPORT

CONCENTRATION GRADIENTS & PROTEIN TRANSPORTERS DEPENDING UPON THE DIRECTION THAT MATERIALS ARE MOVING (WITH OR AGAINST THEIR CONCENTRATION GRADIENT)  THE TYPE OF TRANSPORT PROTEIN NEEDED IS DIFFERENT ION CHANNELS  PASSIVE TRANSPORT  DIFFUSION/ NO ENERGY SODIUM (NA + ), POTASSIUM (K + ) AND CHLORIDE (CL - ) NA+/K+ PUMP  ACTIVE TRANSPORT  REQUIRE ENERGY (Na + ) Ion Channel Na+/K+ Pump Membrane Proteins Lipid Layer

TEST OF CONTENT WHEN THE GATE ON A CHLORIDE CHANNEL OPENS, CHLORIDE FLOWS INTO A NEURON (A CELL OF THE NERVOUS SYSTEM). WHAT DOES THIS MEAN ABOUT THE CONCENTRATION GRADIENT OF CHLORIDE? a.CHLORIDE CONCENTRATION IS EQUAL INSIDE AND OUTSIDE THE NEURON. b.CHLORIDE CONCENTRATION IS HIGHER ON THE INSIDE OF THE NEURON. c.CHLORIDE CONCENTRATION IS HIGHER ON THE OUTSIDE OF THE NEURON. d.WE HAVE INSUFFICIENT INFORMATION TO DETERMINE ANYTHING ABOUT THE CHLORIDE CONCENTRATION GRADIENT.

CONCENTRATION GRADIENTS & PROTEIN TRANSPORTERS BOTH PUMPS AND CHANNELS ARE ‘SPECIALISTS’ NA+ ION CHANNEL ONLY ALLOWS NA +THROUGH, ETC NA+/K+ PUMP ALLOWS ONLY NA & K THROUGH. HOW CAN THERE EVEN BE CONCENTRATION GRADIENTS IF THERE ARE CHANNELS WHICH ALLOW MATERIALS TO DIFFUSE DOWN THEIR CONCENTRATION GRADIENTS? THE EXPLANATION IS THAT CHANNELS ARE FREQUENTLY GATED THE “GATE” ON THE CHANNEL COULD BE OPEN OR CLOSED. MANY CELL PROCESSES ARE DIRECTED BY THE REGULATED OPENING OR CLOSING OF GATES ON CHANNELS.

NEURONS & NEUROGLIAL CELLS- P. 7 IN NERVOUS SYSTEM REFERENCE BOOK (NSRB) TYPES OF NERVE CELLS NEURON= NERVE CELL; MAKES UP NEURAL TISSUE ELECTRICALLY ACTIVE CELLS SPECIALIZED SHAPES THAT ALLOWS THEIR ELECTRICAL MESSAGES TO BE TRANSPORTED FOR LONG DISTANCES A SINGLE NEURON CAN ME A METER LONG NEUROGLIAL CELL=NON-NEURAL BRAIN CELLS THAT PROVIDE STRUCTURE, SUPPORT AND NUTRITION TO THE BRAIN AND ITS CELLS ALSO REFERRED TO AS “GLIAL” CELLS

NEURONS & NEUROGLIAL CELLS- P. 7 IN NERVOUS SYSTEM REFERENCE BOOK (NSRB) TYPES OF NERVE CELLS ASTROCYTE= STAR SHAPED GLIAL CELLS IN THE CNS, PERFORM SEVERAL SUPPORT FUNCTIONS  OXYGEN, ANCHOR NEURONS TO BLOOD SUPPLY OLIGODENDROCYTE= CREATES MYELIN SHEATH TO SUPPORT AND INSULATE THE AXONS FOR THE CNS SCHWANN CELL= CREATES MYELIN SHEATH TO SUPPORT AND INSULATE THE AXONS OF THE PNS

NEURONS Dendrites Soma/ Cell Body Synaptic Bulb Node of Ranvier Schwann Cell or Oligodendrocyte Axon Nucleus Myelin Sheath

NEURONS & NEUROGLIAL CELLS- P. 7 IN NSRB PARTS OF THE NEURON AXON= SINGLE EXTENSION FROM THE NERVE CELL THAT CARRIES NERVE IMPULSES FROM THE CELL BODY TO OTHER NEURONS MAY OR MAY NOT BE WRAPPED IN MYELIN DENDRITE= EXTENSIONS FROM THE CELL BODY OF A NEURON THAT ARE THE “RECEIVING ENDS” OF A NEURON MYELIN (SHEATH)= FATTY INSULATION PRODUCED BY EITHER THE SCHWANN CELL (PNS) OR OLIGODENDROCYTE (CNS) WHICH ARE WRAPPED AROUND THE AXON OF MANY NEURONS; ASSISTS IN TRANSMISSION OF NERVE IMPULSE

NEURONS & NEUROGLIAL CELLS- P. 7 IN NSRB PARTS OF THE NEURON CONT. CELL BODY (SOMA)= PART OF THE NEURON THAT CONTAINS THE NUCLEUS AND OTHER ORGANELLES TO ALLOW THE CELL TO GROW AND REPRODUCE SYNAPTIC BULB= THE PRE-SYNAPTIC SWELLING OF THE AXON TERMINAL IS THE TRANSMITTING END OF NEURON; CONTAINS VESICLES WHICH CONTAIN NEUROTRANSMITTERS INVOLVED IN CHEMICAL TRANSMISSION OF THE NERVE IMPULSE ACROSS THE SYNAPSE NODE OF RANVIER= GAPS BETWEEN THE MYELIN SHEATH THAT ALLOW FOR FASTER NERVE IMPULSE TRANSMISSION DR. LINDA MARITIN-MORRIS ON NEURONS

NEURONS & NEUROGLIAL CELLS- BLOOD BRAIN BARRIER DIFFERENCES IN THE CIRCULATORY SYSTEM THAT NOURISHES THE BRAIN EXIST TO PROMOTE PROTECTION BY THE BBB. 1.CAPILLARY VESSELS ARE VERY CLOSE AND POROUS ALLOWS MATERIALS TO ENTER AND LEAVE THE CIRCULATORY SYSTEM ARE MUCH MORE RESTRICTIVE IN THE BRAIN. o CELLS CLOSER TOGETHER  LESS POROUS; MORE RESTRICTIVE 2.CAPILLARIES COMING INTO THE BRAIN ARE COVERED WITH GLIAL CELLS GLIAL CELLS ARE COVERED IN MYELIN AND WRAP AROUND THE CAPILLARY VESSELS AND INSULATE THEM  RESTRICTS THE FLOW OF MATERIALS INTO AND OUT OF THESE CAPILLARIES.

NEURONS & REST: RESTING POTENTIAL RESTING POTENTIAL= A DIFFERENCE IN ELECTRICAL POTENTIAL ACROSS THE MEMBRANE OF A NERVE CELL DURING AN INACTIVE PERIOD POTENTIAL TO ACT  ITS RESTING POTENTIAL NEURON IS POLARIZED LIKE A BATTERY, HAVING A (+) & (-) END A NEURON AT REST IS NEGATIVELY CHARGED ON THE INSIDE COMPARED TO THE OUTSIDE. -70MV

NEURONS &RESTING POTENTIAL NEURONS HAVE BOTH CHEMICAL AND ELECTRICAL GRADIENTS FOR MOLECULES (=CHEMICAL GRADIENT) OR CHARGE (=ELECTRICAL GRADIENT) THE INSIDE OF A NEURON HAS RELATIVELY MORE K+ THAN THE OUTSIDE AND LESS NA+ DOES IT SEEM WEIRD THAT BOTH NA+ AND K+ ARE POSITIVELY CHARGED, YET THE INSIDE OF THE NEURON IS NEGATIVELY CHARGED? TWO REASONS WHY: 1. THERE ARE OTHER IONS WE WILL NOT ASK YOU TO LEARN ABOUT 2. THE IMBALANCE OF SODIUM IS NOT EXACTLY EQUAL TO THE IMBALANCE OF POTASSIUM.

CHANNELS AND A PUMP HELP MAKE THE RESTING POTENTIAL THE NEURON AT REST IS MORE NEGATIVE ON THE INSIDE HAS MORE (NA+) ON THE OUTSIDE HAS MORE (K+) ON THE INSIDE NA+/K+ PUMP PUSHES ONE NET POSITIVE CHARGE OUT OF THE NEURON EACH CYCLE  3 NA+ OUT FOR EVERY 2 K+ INSIDE CELL. How the Sodium Potassium Pump Works d.mcgraw- hill.com/sites/ /st udent_view0/c hapter2/anima tion__how_the_ sodium_potassi um_pump_wor ks.html d.mcgraw- hill.com/sites/ /st udent_view0/c hapter2/anima tion__how_the_ sodium_potassi um_pump_wor ks.html

RESTING POTENTIAL & LEAKY GATES ONE CLASS OF POTASSIUM (K+) CHANNELS HAS VERY LEAKY GATES MEANS THAT K+ IS MORE CONCENTRATED ON THE INSIDE OF NEURONS  SMALL AMOUNT OF POSITIVE CHARGE ESCAPES THROUGH THESE LEAKY K+ CHANNELS. THE NA+ CHANNELS ARE NOT LEAKY. OVER TIME, THERE IS A BUILD-UP OF POSITIVE CHARGE ON THE OUTSIDE DUE TO ONE-DIRECTIONAL LEAKINESS.

ACTION POTENTIAL 1-THRESHOLD=THE STIMULUS INTENSITY THAT’S JUST ENOUGH TO CAUSE THE NERVE IMPULSE TO FIRE 2-DEPOLARIZATION=REDUCTION IN A MEMBRANE POTENTIAL--> INNER MEMBRANE SURFACE BECOMES LESS NEGATIVE AS NA+ GATES OPEN ALLOWING AN INCREASE IN INTERNAL NEURON CHARGE

ACTION POTENTIAL P. 9 IN NSR 3-ACTION POTENTIAL= PROPAGATED ELECTRICAL MESSAGE FROM A NEURON THAT TRAVELS ALONG THE AXON TO NEIGHBORING NEURONS OCCURS WHEN THE INTERNAL CHARGE INCREASE FROM -55MV TO + 30MV 4. REPOLARIZATION= WHEN THE NEURON GOES BACK TO A NEGATIVE INTERNAL CHARGE AS K+ MOVES FROM THE INSIDE OUT OF THE NEURON NA+/K+ PUMP ACTIVATED RE-ESTABLISHES THE CONCENTRATION GRADIENT  NEURON GOES BACK TO NEGATIVE ON THE INSIDE The reestablishment of Na+ and K+ gradients happens more slowly and requires more effort from the Na+/K+pump

ACTION POTENTIAL P. 9 IN NSR 5-HYPERPOLARIZATION=CHANGE IN MEMBRANE POTENTIAL MAKING IT MORE (SUPER) NEGATIVE INSIDE 6-RESTING POTENTIAL= A DIFFERENCE IN ELECTRICAL POTENTIAL ACROSS THE MEMBRANE OF A NERVE CELL DURING AN INACTIVE PERIOD NA+ AND K+ GATED CHANNELS ARE CLOSED NEURON RETURNS TO ORIGINAL CHARGE OF -70MV

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