Dr. Karius' Synapse lecture Flashcards
Cell to Cell communication achieved by
Gap junctions
Gap Junctions are made from
connexons
Where might you find connexons?
in the heart because it creates rapid synchronicity
Endocrine means the chemical messengers are
released into the blood
Paracrine means the chemical messengers are
released via diffusion through Extracellular fluid (ECF) to neighboring cell
Autocrine means the chemical messengers are
released nito ECF, and the chemical binds to receptos on the cell that released it.
Which forms of chemical transmission uses the ECF as the route of transmission?
autocrine and paracrine
Membrane specificity: receptors INSIDE the cell will be utilized by chemical messengers sent via _______
endocrine
Neurotransmission may be classified as a specialized form of
paracrine communication
Synaptic Cleft
1) is an actual Gap
2) has actual ECF in between the pre-and post sides
3) anatomically isolated
Post-synaptic characteristics
1) densities = NT receptors
2) electron rich
3) contains receptors for neurotransmitter
4) Extensive surface area
Pre-synaptic characteristics
1) mitochondria
2) Vesicles for storage
3) increased surfaced area
Definition of neurotransmitter
a chemical mediator released from one neuron that acts on another neuron/excitable tissue at a synapse
Cholinergic =
acetycholine
Adrenergic =
dopamine norepinephrine epinephrine serotonin histamine
Excitatory amino acids =
glutamate/aspartate
Inhibitory amino acids =
glycine (spinal cord, brainstem)
GABA, CNS
Order of events leading up to NT release
1) synthesis in soma or axon
2) transport to pre-synaptic terminal
3) packaging in vesicles
4) congregation of vesicles in “active zone” (docking and priming)
NT release
: Axonal AP (Na influx, propagation) –> Presynaptic terminal influx of Ca through voltage gated Ca channels, depolarization opens channels
What does Calcium do for the NT release between a pre and post synaptic terminal junction?
Calcium binds to a protein complex that draws the pre and post synaptic membrane terminals (between two axons) together to form a pore so NT can diffuse across
Pre synaptic events (8)
1) depolarization of pre-syn terminal
2) opening of voltage gated calcium channels
3) influx of calcium into terminal
4) binding of calcium to appropriate proteins
5) conformational change in proteins brings docked vesicles to membrane
6) fusion of vesicular membrane with cell membrane
7) creation of fusion “pore”
8) diffusion of neurotransmitter into synaptic through/cleft
What proteins make up the “protein” complex between terminals?
VAMPS/SNAPs
Methods of ACh removal: the most basic is
diffusion, but limited by anatomy of synapse, can still have affects
Least favored form of ACh removal
diffusion
Method of ACh removal method 2
degradation or binding to proteins: only works for a few neurotransmitters
Method of NT removal 3
Enzymatic destruction of ACh by AChE in synaptic cleft
Method of NT removal 4
re-uptake (epinephrine): transporter protein will take NT back into presynaptic terminal
mechanisms by which a nueurotransmitter’s action is limited (3)
Enzymatic degradation (ACh) Natural degradation (NO) Re-uptake (Epinephrine/norepinephrine)
How many ACh are needed to activated a voltage gated ion channel?
2
What happens if the ACh opens a sodium or calcium channel (EAA) ?
Na/Ca enters the dendrite and causes depolarization to initiate an excitatory POST SYNAPTIC POTENTIAL (EPSP)
EPSP
excitatory post synaptic potential
produced by Na or Ca on a dendrite
Local, graded, die away w/distance and time
(~5 mV depolarization)
Some of the dendrite does not have
voltage gated ion channels
does have ligand gated ion channels
no way to make an action potential
If the soma does not have voltage gated ion channels, what does the axon hillock possess at its INITIAL SEGMENT
NO ligand gated channels
voltage gated channels
AP generation here
Chloride channels
glycine and GABA
cause HYPERPOLARIZATION
initiate an inhibitory post-synaptic potential
Glycine and GABA
NT’s that act to allow Cl- into SOMA of the neuron causing an inhibitory post-synaptic potentials
What’s the spacial difference between Na/Ca channels and Cl- channels?
the Na/Ca are on the dendrites further from the cell body, the Cl- channels are closer to the body of the neuron
IPSPs and EPSPs can
add together (summation)
Two kinds of summation
Temporal and Spatial
Temporal summation
multiple APs within a sec/msec (these would occur on the dendrite, not the cell body)
Spatial summation
multiple synapses (+ or -) acting simultaneously
synapses on both dendrites and soma
SS: What will happen if both signals are positive?
little hump up + big hump up
SS: What will happen if one signal is positive and one is negative
little hump down + big hump down
SS: What will happen if one signal is positive and one is negative?
one round hump up and one slope down
Ligand: GABA
receptor, channel type, response type
ligand gated Chlorine channel
IPSP
Ligand: Glycine
receptor, channel type, response type
ligand gated chlorine channel
IPSP
Ligand: NMDA (amino acid)
receptor, channel type, response type
ligand gated Ca channel
EPSP
Ligand: amino acids
receptor, channel type, response type
ligand gated Ca channel
EPSP
Ligand: ACh
receptor, channel type, response type
Ligand gated Na channel
EPSP
Ligand: EAA Response: Ions Electrical response Effect on excitability
EPSP
Na/Ca
Depolarization
Increased (more action potentials)
Ligand: ACh Response: Ions Electrical response Effect on excitability
EPSP
Na/Ca
Depolarization
Increased (more action potentials)
Ligand: GABA, glycine Response: Ions Electrical response Effect on excitability
IPSP
Chloride
hyperpolarization
Decreased (fewer aps)
Spatial summation
multiple synapses
IPSP or EPSP
Vm effects depend on synapses
Temporal summation
single synapse
all EPSP or IPSP
+ summation if sum is positive (depolarization)
- summation if sum is negative (hyperpolarization)
