UW BIOUNIT 1

LECTURE 5THE SYNAPSE & CELL COMMUNICATION

LECTURE 5 THE SYNAPSE LEARNING TARGETS

AFTER SUCCESSFULLY COMPLETING THIS LESSON YOU WILL BE ABLE TO:• TO UNDERSTAND HOW TWO ELECTRICAL CELLS COMMUNICATE

WITH EACH OTHER• TO UNDERSTAND WHAT A NEUROTRANSMITTER IS, AND HOW IT IS:

• PACKAGED, • RELEASED, • RECOGNIZED, • METABOLIZED, AND • RECYCLED

• TO DIFFERENTIATE BETWEEN EXCITATORY SYNAPTIC EVENTS AND INHIBITORY ONES

• TO PUT SYNAPSE FORMATION AND LOSS IN THE CONTEXT OF LEARNING

PRESYNAPTIC NEURON= 1ST NEURON IN A SERIES OF TWO COMMUNICATING NEURONS

• EXAMINE THE DIAGRAM TO THE RIGHT.

• WHICH PART OF THE PRESYNAPTIC NEURON IS INVOLVED IN COMMUNICATING TO THE POST-SYNAPTIC NEURON?

Presynaptic Neuron

Post synaptic Neuron

Synapse

PRESYNAPTIC NEURON= 1ST NEURON IN A SERIES OF TWO COMMUNICATING NEURONS

FEATURES & FUNCTIONS OF THE PRE-SYNAPTIC BULB• AXON WIDENS TO FORM PRE-

SYNAPTIC BULB• VESICLES FORM AROUND

NEUROTRANSMITTERS PACKAGED AND THEN RELEASED

• NEUROTRANSMITTERS FOUND HERE CHEMICAL MESSENGERS

• ACTION POTENTIAL TRIGGERS RELEASE OF NEUROTRANSMITTERS

• NEUROTRANSMITTERS RELEASED FROM PRE-SYNAPTIC BULB INTO SYNAPSE WHEN VESICLE FUSES TO MEMBRANE EXOCYTOSIS

Action Potential

Exocytosis

EXOCYTOSIS

Exocytosis= actively transporting molecules out the cell with the use of a vesicle to encase and transport molecules to the exterior membrane.

Vesicle• made of cell membrane/phospholipid • transports molecules from the interior of the cell

to the exterior and out the cell membrane.

PRESYNAPTIC NEURON= 1ST NEURON IN A SERIES OF TWO COMMUNICATING NEURONS

http://kvhs.nbed.nb.ca/gallant/biology/synapse.html.

NEUROTRANSMITTERSTHE NEUROTRANSMITTER NAMES NECESSARY TO KNOW IN THIS CLASS ARE REPRESENTED BY THE WORD SNAGGED

SNAGGED

=Serotonin= Norepinephrine= Acetylcholine= Glutamate= GABA= Epinephrine= Dopamine

NEUROTRANSMITTERS• LOOK AT THE

STRUCTURES OF DOPAMINE, SEROTONIN, EPINEPHRINE, & NOREPINEPHRINE.

NEUROTRANSMITTERS

• EPINEPHRINE AND NOREPINEPHRINE ARE RELATED AS THEIR NAMES SUGGEST.

• BUT ONLY ONE HAS AN NH2 GROUP.

Epinephrine Norepinephri

ne

NEUROTRANSMITTERS• BOTH DOPAMINE AND SEROTONIN HAVE AN NH2

GROUP (AMINE) AND ARE CHEMICALLY RELATED.• SO NOREPINEPHRINE, SEROTONIN, AND DOPAMINE ARE

IN A GROUP KNOWN AS THE “MONO AMINE” NEUROTRANSMITTERS.

DopamineSerotonin

NEUROTRANSMITTERS• NEUROTRANSMITTERS HAVE

STRUCTURAL AND CHEMICAL PROPERTIES THAT ALLOW THEM TO BIND TO RECEPTORS

• NEUROTRANSMITTERS FIT THE RECEPTOR LIKE A LOCK AND KEY

• ONCE A NEUROTRANSMITTER IS RELEASED IT DOES ONE OF THREE THINGS:• BOND TO A RECEPTOR• METABOLIZED BY ENZYMES• RECYCLED BACK INTO THE PRE-

SYNAPTIC BULB

POST SYNAPTIC NEURON• NEW SYNAPSES FORM

AND OTHERS ARE LOST DAILY.

• 1ST YEAR OF LIFE HUMANS DOUBLE THE NUMBER OF SYNAPSES THEY HAVE THEN AS WE AGE, SOME UNUSED SYNAPSES GET PRUNED AWAY.

EXAMPLE:• PRACTICING YOUR FLUTE, FOR

INSTANCE, IS THE ONLY WAY TO ENSURE THAT YOUR BODY KEEPS THE SYNAPSES AROUND THAT ARE NECESSARY TO GET THE RIGHT FINGER POSITIONS FOR THE NOTES YOU WANT TO PLAY.

• WITHOUT PRACTICE, THE BRAIN CONSERVE RESOURCES AND PUTS ITS ENERGY INTO SYNAPSES YOU DO USE (SUCH AS THOSE YOU USE TO PLAY VIDEO GAMES).

• EVERY DAY WE MAKE CHOICES THAT INFLUENCE HOW OUR BRAINS WILL WORK LATER. THESE CHOICES ARE NOT JUST ABOUT WHETHER TO USE DRUGS.

POST SYNAPTIC NEURON• ONCE THE

NEUROTRANSMITTER (NT) BINDS TO THE RECEPTOR, IT CHANGES SHAPE.

• ONE OF TWO THINGS CAN HAPPEN:• EVENT 1 - THE BINDING OF

THE NT CHANGES THE RECEPTOR SO THAT THE SODIUM CHANNEL OPENS UP

• EVENT 2 - THE BINDING OF THE NT CHANGES THE RECEPTORS IN A WAY THAT OPENS A CHLORIDE CHANNEL.

• FOR BOTH EVENTS THE ION WHOSE CHANNEL IS NOW OPEN AND IS MORE CONCENTRATED OUTSIDE THE CELL.

• ONCE THE GATES ON THE CHANNEL BECOME OPEN THE ION WILL FLOW INTO THE NEURON.

POST SYNAPTIC NEURONSO WHAT HAPPENS WHEN THE CHANNEL IS OPENED?• EVENT 1: SODIUM IONS

(NA+) ARE POSITIVELY CHARGED AND TYPICALLY INDICATE INITIATION OF AN ACTION POTENTIAL NEURON FIRES SIGNAL IS SENT TO THE NEXT CELL • EXCITATORY SIGNAL

FIRE!

POST SYNAPTIC NEURON• EVENT 2: CHLORIDE IONS

ARE NEGATIVELY CHARGED (CL-) SO WHEN CL- ENTERS A NEURON IT BECOMES EVEN MORE POLARIZED OR HYPERPOLARIZED. • ITS CHARGE IS NOW

SUPER NEGATIVE. • PUSHES THE RESTING

POTENTIAL OF THE NEURON FARTHER AWAY FROM THRESHOLD

• INHIBITORY SIGNAL NO FIRE

TEST OF CONTENTWHICH CRITERIA ARE NECESSARY TO CALL A MOLECULE A NEUROTRANSMITTER? NOTE ALL THAT ARE CORRECT.a. IT IS A CHEMICAL PRODUCED BY A NEURON.b. IT CAN ONLY BE FOUND IN THE SYNAPSE.c. AFTER RELEASE, IT CAN BE REMOVED BY

DEGRADATION OR RECYCLING.d. IT CAN ACT ON A NEURON TO EXCITE OR INHIBIT IT.e. IT CAN ACT ON A MUSCLE TO EXCITE IT.f. IT TRAVELS LONG DISTANCES TO ACHIEVE ITS GOAL.

TO FIRE OR NOT TO FIRE?POST SYNAPTIC NEURON GATHERS INFORMATION FROM ALL OF ITS VARIOUS INPUTS & DECIDES WHETHER OR NOT TO FIRE BASED ON THE BALANCE OF THOSE INPUTS • IF CL- ENTERING = THE

AMOUNT OF NA+ ENTERING NEURON WILL NOT FIRE.

• IF MORE NA+ ENTERS THAN CL- NEURON WILL FIRE BECAUSE THE INTERNAL CHARGE OF THE NEURON HAS CHANGED FROM NEGATIVE TO POSITIVE GENERATES THE ACTION POTENTIAL

HOW CAN WE PREDICT IF SODIUM OR CHLORIDE WILL ENTER? • DEPENDS ON THE

NEUROTRANSMITTER THAT’S BOUND

TO FIRE OR NOT TO FIRE?Neurotransmitters whose receptors are also sodium channels (therefore "excitatory")

Neurotransmitters whose receptors are also chloride channels (therefore "inhibitory")

Dopamine (for this class) GABA

Acetylcholine  

Norepinephrine  

Glutamate  Epinephrine

Serotonin is not in this table because it's receptors can either be sodium or chloride channels.

EXTRA VIDEO SUPPORT

• CHEMISTRY OF ADDICTION-HANK GREEN-

ERSREQUIREDLISKA- CHAPTER 5: DRUGS AT THE SYNAPSEINTERNET:• HTTP://FACULTY.WASHINGTON.EDU/CHUDLER/SYNAPSE.HTML• HTTP://FACULTY.WASHINGTON.EDU/CHUDLER/CHNT1.HTML • HTTP://WWW.YOUTUBE.COM/WATCH?V=HQWV0IEF4HO&FEATUR

E=RELATED (RECYCLING TRANSPORTER)

SUPPLEMENTAL FROM INTERNET HTTP://WWW.SCIENCEDAILY.COM/RELEASES/2007/03/070314134812.HTMHTTP://WWW.SCIENCEMAG.ORG/CGI/CONTENT/ABSTRACT/318/5847/103