L8 Synaptic Transmission

Question 1

Synaptic transmission

Answer 1

Interaction between neuron and another neuron, muscle, or gland

Question 2

Motorneurons

Answer 2

Nerves that innervate muscle fibers

Question 3

Synapses

Answer 3

Junction between presynaptic neuron and a postsynaptic neuron

Question 4

What are two types of synaptic transmission? And what is their flow direction?

Answer 4

Electrical (gap junctions)
Chemical

Unidirectional
Always from presynaptic neuron to postsynaptic neuron

Question 5

Electrical synapse / gap junctions

Answer 5

Ions flow directly through gap junctions channels

direct current flows faster

Mainly seen in the heart

Question 6

Chemical synapse

Answer 6

Presynaptic neuron releases neurotransmitters

Ions winter synaptic cleft and then flow through postsynaptic channels

Question 7

Presynaptic neuron

Answer 7

Neuron that conducts action potential toward the synapse

Question 8

Postsynaptic neuron

Answer 8

Neuron whose action potential are propagated away from the synapse

Question 9

Synaptic knob

Answer 9

Contains synaptic vesicles

Question 10

Synaptic vesicles

Answer 10

Stores neurotransmitter (carries signal across membrane)

Question 11

Synaptic cleft

Answer 11

Space between pre and post synaptic neurons

Question 12

Synaptic delay

Answer 12

Time needed for conversion of the electrical signal from the presynaptic neuron (action potential) to an electrical signal in the postsynaptic neuron (EPSP or ISPS) by chemical means

0.5-1msec

Question 13

What’s Excitation -secretion coupling in chemical synapses?

Answer 13

Process of converting chemical signal back to electrical signal

Question 14

What’s are the steps in excitation-secretion coupling?

Answer 14

1. An action potential depolarizes the axon terminal
2. Depolarization opens voltage-gated Ca2+ channels and Ca2+ enters the cell
3. Calcium entry triggers exocytosis of synaptic vesicle contains
4. Neurotransmitter differs across the synaptic cleft and binds with receptors on the postsynaptic Cell
5. Neurotransmitter binding initiates a response in the postsynaptic cell

Question 15

Post synaptic sensory affects response how?

Answer 15

More receptors, more response

Less receptors, less response

Question 16

What are two types of receptors?

Answer 16

For fastest neurotransmission ligand-gated ion channels AKA Ionotrophic

Slow transmission - G protein-coupled receptors AKA metabotropic

Question 17

What’s the result at the post synaptic membrane ?

Answer 17

Graded synaptic potential

Excitatory or inhibitory

Question 18

What ends the signal?

Answer 18

Diffusion -slow
Enzymatic degradation -in synaptic cleft
Reuptake - recycled or destroyed in synaptic knob

Question 19

Cholinergic synapse

Answer 19

Employs ACh as its neurotransmitter

Action potential travels down axon opens voltage gate Ca2+ channels in synaptic knob

Triggers exocytosis of synaptic vesicles and the release of ACh which crosses the synapse

Reserve synaptic vesicles move up to the active sites and release their ACh

ACh diffuses across the synaptic cleft to bind to ACh receptors

ACh receptors trigger opening of ligand gated Na+ channels producing local potential (postsynaptic potential)

When reaches -55mV, triggers action potential to begin

Question 20

Cholinergic synaptic vesicle fusion and exocytosis

Answer 20

Vesicle that contains ACh has 2 proteins attached- synaptotagmin and synaptonrevin

2 proteins on plasma membrane- SNAP25 and syntaxin

Proteins automatically dock when they get close enough= SNAREs complex

Won’t release ACh until Ca2+ binds to synaptotagmin

Question 21

Removal of acetylcholine

Answer 21

Enzyme breaks down ACh to choline and acetic acid

Choline is recycled back into presynaptic knob

Acetic acid diffuses away

Question 22

Excitatory adrenergic synapse

Answer 22

Neurotransmitter = norepinephrine (NE)

Receptor is not an ion gate but a transmembrane protein associate with a G protein

Unstimulated NE receptor is bound to a G protein

Binding of NE to the site cause G protein to be released

The G protein binds to adenylate cyclase which activates the enzyme and concerts ATP to cAMP

cAMP produces an internal chemical that binds to a ligand-gated sodium channel depolarizing the cell

Causes EPSP

Question 23

Inhibitory GABA-ergic synapse

Answer 23

Neurotransmitter = GABA (gamma aminobutyric acid)

Binds to ion gates and causes a change in membrane potential

However the gate in this case is a Cl- channel and makes the RMP even more negative which then inhibits neuron firing (IPSP)