Synaptic Transmission

Question 1

Pre-synaptic bouton

Answer 1

• place where axon terminates, specialized for NT release
• contain active zones to convert electrical into chemical signals that are released into follower cells
• contain highly concentrated of NT packets (vesicles) that are released when bouton depolarizes

Question 2

dendritic spines

Answer 2

• RECEIVE chemical signals at the synapse, convert chemical signals to electrical signals, modulated in forms of plasticity

Question 3

Neurotransmitters

Answer 3

small molecules that transmit impulses at chemical synapses

Question 4

Two main NTs to make nervous system work

Answer 4

1. glutamate (main EXCITATORY)

2. GABA (main INHIBITORY)

Question 5

3 criteria for an NT

Answer 5

• present in nervous system in pre-synaptic terminals
• released in response to depolarization in (Ca2+ dependent manner)
• specific receptors exist for the NT on post-synaptic cells that generate a signal in post-synaptic cell

basically (present in PRE, can be RELEASED, can be RECEIVED to generate signal)

Question 6

When does synaptic release occur?

Answer 6

Triggered when an AP propagating down axon reaches pre-synaptic bouton containing Ca2+ channels that open in response to depolarization

Question 7

Describe a classic vesicle cycle

Answer 7

1. import of NT
2. movement of vesicle to active zone
3. docking at plasma zone
4. Ca2+ triggered exocytosis
5. endocytosis via clathrin coated vesicles (to be used again)

synaptic vesicles can be filled, exocytosed, and recycled within a minute

Question 8

Generally, how big of a change is needed to alter membrane potential and initiate AP?

Answer 8

Little change needed. Movement of as few as 6000 ions/um^2 needed to account for AP (compared to much much more ions needed in typical neuron)

exception: INTRACELLULAR CALCIUM

Question 9

What processes are regulated by calcium?

Answer 9

• synaptic release of NT
• plasticity
• gene regulation
• excitation-contraction coupling of muscle

Question 10

Where are Ca2+ channels located in the pre-synaptic bouton?

Answer 10

directly below active zone

Question 11

What is a target for bacterial toxins?

Answer 11

fusion machinery (around synapse)

Question 12

Do post synaptic NT receptors respond to voltage or ligand binding?

Answer 12

ligand binding

Question 13

Which receptors are found at EXCITATORY synapses and open to allow cations to pass through channel?

Answer 13

ionotrophic glutamate receptors

Question 14

What is the zero current potential of the Glu receptor channel?

Answer 14

Near 0mV. so opening it will drive membrane potential to depolarize

Question 15

At rest, describe glutamate receptors

Answer 15

Relaxed and closed….to open, a torqued conformation (energetically unfavorable) is required

Question 16

If glutamate receptor opening is energetically unfavorable, what keeps them open?

Answer 16

LIGAND BINDING. (when glutamate binds)

glutamate binds to stabilize active state

Question 17

How do antagonists work?

Answer 17

Antagonists bind to stabilize and favor inactive state…agonists are vice versa

Question 18

With regards to how neuron signals spread throughout dendrites to soma, what is the space constant?

Answer 18

increases with higher membrane resistance and lower axonal resistance (signal will decay exponentially is tube diameter stays constant)

Question 19

What factors complicate signal transmission in dendrites?

Answer 19

varying branch diameters, varying distance of inputs from soma, voltage gated channels (i.e. Ca and Na boost synaptic inputs)

Question 20

Why is synaptic summation needed?

Answer 20

many small synaptic events must sum together to reach a threshold and generate AP (each synapse is only capable of making a small change in somatic membrane potential)

Question 21

What are two types of synaptic summation?

Answer 21

spatial summation and temporal summation

Question 22

spatial summation

Answer 22

Two EPSP synaptic events…

A. occur together within overlapping compartment = sub-linear summation (competing for receptors)
B. occur in electrically distant compartments = linear summation to generate independent currents that work together to drive depolarization

Question 23

temporal summation

Answer 23

potentials occuring in brief succesion can add together to produce larger combined responses (depends on rate limiting step = usually elimination of NTs within synaptic clef i.e. reuptake)

Question 24

components of a typical glutamate excitatory synapse

Answer 24

glutamine, phosphate activated glutaminase in mitochondria (PAG), excitatory AA transporter (EAA), and vesicular proton driven transporter (VGlut)

Question 25

Which two receptors are activated by glutamate?

Answer 25

AMPA and NMDA (respond to Ca)

Question 26

components of typical GABA inhibitory synapse

Answer 26

GABA transaminase (GABA-T), Glu Acid Decarboxylase (GAD), Vesicular inhibitory AA transporter (VIAAT)

Question 27

How do excitatory and inhibitory synapses work together?

Answer 27

Feedback, feedforward, lateral inhibition (“winner take all”, silence other inhibitors)