neuroscience - chapter 7

Question 1

Define postsynaptic effects briefly/simply.

Answer 1

Postsynaptic effects refer to the changes that occur in the neuron receiving the signal (postsynaptic neuron) when a neurotransmitter binds to its receptors.

Question 2

What are the effects of the neurotransmitter on the postsynaptic cell?

Answer 2

-The transmitter diffuses across the cleft
-The transmitter binds to postsynaptic receptors
-The binding is highly specific
(The shape of the transmitter
and the receptor must match
Like a lock-and-key).

Question 3

What are the different types of receptors?

Answer 3

-Receptors that are channels (e.g., ACh receptor; ionotropic receptors)
-G-protein-coupled receptors (metabotropic receptors)

Question 4

What do G-proteins do?

Answer 4

Transmitter actions at G-protein-coupled receptors. The binding of neurotransmitter to the receptor leads to the activation of G-proteins. Activated G-proteins activate effector proteins, which may be (a) ion channels or (b) enzymes that generate intracellular second messengers.

Question 5

What is the Acetylcholine receptor made of?

Answer 5

It is made of 5 subunits, with 2 alpha subunits.

Question 6

How do we activate the acetylcholine receptor?

Answer 6

• ACh binds to the alpha subunits
• The channel opens
• Na+ enters the postsynaptic cell

Question 7

Describe the process of the excitatory post-synaptic potentials (EPSPs).

Answer 7

The generation of an EPSP. (a) An action potential arriving in the presynaptic terminal causes the release of neurotransmitter. (b) The molecules bind to transmitter-gated ion channels in the postsynaptic membrane. If Nat enters the postsynaptic cell through the open channels, the membrane will become depolarized. (c) The resulting change in membrane potential (Vm), as recorded by a microelectrode in the cell, is the EPSP.

Question 8

What can the excitatory post-synaptic potentials (EPSPs) be caused by?

Answer 8

1. Opening of channels permeable to Na+ and K+
   (Na+ enters the cell = Excitatory response)
2. Closing of K+ channels (K+ stops leaving the cell)

Question 9

What is the Quantal release? (Quantal analysis of EPSPs)

Answer 9

Quantal release refers to the idea that neurotransmitters are released in fixed “packets” or quanta from the presynaptic neuron. Each quantum represents the amount of neurotransmitter stored in one synaptic vesicle.

In quantal analysis of EPSPs (excitatory postsynaptic potentials), scientists study how each packet of neurotransmitter contributes to the strength of the EPSP in the postsynaptic neuron. By measuring EPSPs, they can estimate how many quanta (vesicles) are released and how much each contributes to the overall signal.

In short, quantal release is the way neurotransmitters are released in small, measurable packets, and quantal analysis helps us understand how these packets affect postsynaptic signaling.

Question 10

Describe the process of the inhibitory post-synaptic potentials (IPSPs).

Answer 10

The generation of an IPSP. (a) An action potential arriving in the presynaptic terminal causes the release of neurotransmitter. (b) The molecules bind to transmitter-gated ion channels in the postsynaptic membrane. If CI enters the postsynaptic cell through the open channels, the membrane will become hyper-polarized. (c) The resulting change in membrane potential (Vm), as recorded by a microelectrode in the cell, is the IPSP.

Question 11

What can the inhibitory post-synaptic potentials (IPSPs) be caused by?

Answer 11

1. Opening of channels permeable to Cl- (Cl- enters the cell (under certain conditions))
2. Opening of K+ channels (K+ leaves the cell)

Question 12

Define synaptic integration.

Answer 12

Synaptic integration refers to how a neuron combines multiple signals (EPSPs and IPSPs?) to decide whether to fire an action potential. Since a single EPSP is usually too small to trigger an action potential on its own, neurons rely on summation to reach the threshold for firing.

Question 13

How can EPSPs be summed?

Answer 13

-Over time (temporal summation)
-Across different synapses (spatial summation)

Question 14

Describe the process of EPSP summation, spatial summation and temporal summation.

Answer 14

EPSP summation. (a) A presynaptic action potential triggers a small EPSP in a postsynaptic neuron. (b) Spatial summation of EPSPs: When two or more presyn-aptic inputs are active at the same time, their individual EPSPs add together.
(c) Temporal summation of EPSPs: When the same presynaptic fiber fires action potentials in quick succession, the individual EPSPs add together.

Question 15

Are EPSPs graded events and explain why.

Answer 15

-EPSP decay with distance
-EPSPs are “graded” events because transmission is passive (in general), unlike action potentials, which are “all-or- none” events.

Question 16

What equation do we use to determine the strength of EPSP at a distance x from the synapse (origin)? (talk about variables.

Answer 16

Vx=Vo/(e^(x/wavelength))

• Vx: membrane depolarization at a distance x
• V0: depolarization at the origin
• e: base of natural logarithm
• x: distance from origin (synapse)
• λ: length constant
• When x = λ, Vx = V0/e = 0.37(V0)
• So, λ is the distance traveled by the time the EPSP has dropped to 37% of its original value V0.

Question 17

Do different dendrites have different length constants?

Answer 17

yes!

Question 18

What is the correlation between the wavelength and how excitable a neuron is?

Answer 18

The higher the wavelength, the more excitable the neuron is.

Question 19

Why is the excitability of a dendrite good?

Answer 19

• This can “boost” the EPSP on the way to the soma
• Very useful for synapses far from the soma

Question 20

What is a metabotropic receptor?

Answer 20

A metabotropic receptor is a type of receptor on the surface of a cell that, instead of directly opening ion channels when activated, triggers a series of internal chemical reactions through molecules called second messengers. (example, G-protein)

Question 21

How can metabotropic receptors modulate EPSPs?

Answer 21

Metabotropic receptors use “second messengers” The Norepinephrine β receptor closes K+ channels
* Closing K+ channels makes the membrane less leaky
* Length constant is increased, and EPSPs have a larger effect

Question 22

What is postsynaptic inhibition?

Answer 22

Postsynaptic inhibition occurs when inhibitory postsynaptic potentials (IPSPs) reduce or cancel out the effects of excitatory postsynaptic potentials (EPSPs), making it harder for the neuron to reach the threshold for firing an action potential.

Question 23

What is shunting inhibition?

Answer 23

Shunting inhibition refers to a form of inhibition that effectively reduces the strength of EPSPs before they can reach the neuron’s soma (cell body) and trigger an action potential. This happens when an inhibitory synapse is located close to the soma or along the dendrites, in the path of the incoming excitatory signals.