PSYC 304 MT2

Neural Communnication pt.2, Neural Communication pt.3

When a NT molecule bind to a postsynaptic receptor, how great are the voltage effects?

Very miniscule fluctuations

What does an EPSP do to the membrane potential?

Depolarizes it (closer to 0)

What effect does an EPSP have on generating AP?

It increases the chance of generating an AP

What does an IPSP do to the membrane potential?

Hyperpolarizes it (makes it more negative)

What does post synaptic mean?

The receiving cell (dendrites), responds to NT which are released from a pre synaptic neuron

What are 3 key properties of PSP?

• Graded

• Rapid

• Decremental

What are spatial summations of EPSP and IPSP like?

When 2 PSP at different synapses simultaneously sum/combine to produce a greater PSP (taller hill or bigger divot)

What are temporal summations of PSP like?

When 2 PSP in rapid succession synergize to make a larger PSP

How is an action potential generated?

When the sum of EPSP and IPSP depolarize membrane above the threshold of excitation to generate the AP

What 2 protein is responsible for AP generations?

• Voltage activated sodium ion

• Voltage activated potassium ion channels

What happens to voltage activated sodium ion channels when the membrane is depolarized enough?

1. Sodium travels through to increase the membrane potential to positive

2. Inactivation gate shuts off the channel, with the peak of the AP being the moment no more sodium flows in and the gate inactivates

3. No more action potentials during absolute refractory period —> must restore to resting membrane before another AP

What happens to voltage activated sodium ion channels when the membrane is depolarized enough?

1. Opens during AP

2. Fully opens at peak but closes slowly

3. Leads to hyperpolarization and relative refractory period (can have AP, but need lots of potential to push to resting)

Why do AP barely decay?

They constantly regenerate across axon sodium channels gates and is thus slower across axon

Where are the Na+ channel for myelinated axns?

Nodes of Ranvier (tiny gaps between myelination)

Why is AP faster with myelination?

Less sodium channels and time spent regenerating AP, more time travelling passively via electrical speed

Why do AP only travel one direction?

All or nothing and Na+ channels have inactivation gate which shuts and prevents AP from reverse direction

What is a terminal bouton?

A vesicle/bubble filled with NT at the end of the axon, presynaptic terminal

How is an AP (electrical signal) converted into a NT release (chemical signal)?

1. When AP reaches terminal bouton, the depolarization triggers NT release

2. Synaptic vesicles in terminal bouton has NT → AP arrival makes bouton potential briefly positive

3. Change in voltage rapidly opens voltage gated calcium proteins in the terminal membrane

4. The Ca++ is a release signal, and binds to a protein on the vesicle

5. The vesicle is linked to the SNARE complex (set of proteins bridging the vesicle membrane and presynaptic terminal membrane)

   1. SNARE protein pulls the two membranes together, fusing them which releases NT into synapse

How is PSP strength modulated?

Amplitude modulated, strength dpeends on amplitude

How is AP strength modulated?

Frequency modulated, more AP means stronger signal