Chapter 3B: Neuropsychology: The Generation, Transmission, and Integration of Neural Signals

Question 1

Action potential

Answer 1

Originate in the axon hillock and propagate along the axon

“Firing” is how one cell sends a message to another cell

Question 2

Action potential triggers

Answer 2

LESS LIKELY: Hyperpolarization: making the membrane potential of a neuron more negative by increasing the negative charge on the inside
Ex: -65mV → 70 mV

MORE LIKELY: Depolarization: making the membrane potential of a neuron more positive on the inside
Ex: -65 mV → -55mV

Question 3

Hyperpolarization

Answer 3

Spreads passively from the point of stimulation

Response diminishes the further you get from the source

Response is graded: the stronger the stimulus, the stronger the response

Question 4

Depolarization

Answer 4

If enough stimulation is applied, the threshold of activation (-40mV) is reached and an action potential occurs

Response is NOT graded: it’s all or nothing (it doesn’t vary in size, it fires fully or not at all)

Doesn’t diminish (full strength all the way down the axon)

Question 5

What events explain the action potential?

Answer 5

Once activation is triggered, an action potential begins

Voltage-gated Na+ channels open and Na+ ions rush into the cell

This continues until the membrane potential reaches +40mV (the Na+ equilibrium potential)

Once this trigger point of +40 is reached, voltage-gated K+ channels open

K+ rushes out and the resting potential is restored

K+ channels close slowly, causing too many K+ ions to leave

Makes the cell more negative for a brief period

Then, membrane potential returns to resting

Happens all the way down the axon

Question 6

Refractory periods

Answer 6

Absolute refractory phase: the point where you can’t fire any more action potential; the channels are already open

Relative refractory phase: right after the channels close; CAN fire an AP at this period but requires extra stimulation

Question 7

How is the AP propagated along the axon?

Answer 7

The AP is a spike of depolarizing activity, so it strongly depolarizes the next adjacent axon segment

The next segment has voltage-gated Na+ channels, so the depolarization there causes them to open and produce another electrical spike

Occurs at Nodes of Ranvier all the way down the axon

Myelin insulates signal and pushes it from node to node

Question 8

Conduction velocity

Answer 8

The speed of the action potential

Question 9

Nodes of Ranvier

Answer 9

Small gaps in the insulating myelin sheath
Where the Na+ channels that propagate the AP are located

Question 10

Saltatory conduction

Answer 10

The action potential travels inside the axon and jumps from node to node

Question 11

Demyelinating disorder

Answer 11

Multiple sclerosis (MS) is a disorder that occurs when a body’s immune system produces antibodies that attack myelin

Question 12

Action potentials cause release of…

Answer 12

Neurotransmitters

The point of firing an AP is to cause release of neurotransmitters from the presynaptic cell across the synapse to the postsynaptic cell

Question 13

Steps for transmission at the synapse

Answer 13

1) The AP travels down the axon to the axon terminals

2) This opens voltage-gated calcium (Ca2+) channels at the terminal and causes influx of Ca2+

3) Calcium comes into the cell, which causes the vesicles to fuse with the presynaptic membrane (exocytosis)

4) Neurotransmitters spill into synaptic cleft

Question 14

Blocking neural transmission

Answer 14

Animal toxins selectively block certain channels
Tetrodotoxin and saxitoxin block voltage-gated Na+ channels

Batrachotoxin forces Na+ channels to stay open

Botulinum toxin and tetanus toxin inhibit neural transmission by cutting up SNARE proteins and stopping exocytosis

Question 15

Postsynaptic potentials

Answer 15

Neurotransmitters released into the synaptic cleft bind to receptors on the postsynaptic cell and briefly alter the membrane potential of the postsynaptic cell

They either depolarize or hyperpolarize it, making it more or less likely to fire an action potential

Question 16

Excitatory postsynaptic potentials (EPSPs)

Answer 16

Some neurotransmitters cause an electrical change that make the membrane potential less negative

Depolarization

Makes it more likely that neuron will fire by bringing it closer to threshold of activation

Question 17

Inhibitory postsynaptic potentials

Answer 17

Some neurotransmitters cause an electrical change that make the membrane potential more negative

Hyperpolarization

Makes it less likely that neuron will fire by bringing it further from threshold of activation

Question 18

PSPs are local and graded

Answer 18

Local: the change in membrane potential spreads passively over the neuron and degrades in strength over time and distance

Graded: a big stimulus generates a big response, while a small stimulus makes a small response

Question 19

Spatial summation

Answer 19

Inputs vary across space

Question 20

Temporal summation

Answer 20

Inputs vary in timing

Question 21

Question: How will the effect be different if a PSP is received at a far away dendrite versus one on the cell body? Which one will have a stronger effect and why?

Answer 21

Immediate action at the synapse might be the exact same, but the closer one yields a stronger change because it has less far to travel

Further away the input is, the less strong effect it has on the postsynaptic cell because the message diminishes as it spreads

Question 22

Ligands

Answer 22

Fit receptors exactly and activate or block them

Question 23

Endogenous ligands

Answer 23

Neurotransmitters and hormones

Inner origin

Question 24

Exogenous ligands

Answer 24

Drugs and toxins from outside the body

Outer origin

Question 25

Transmitters binding to receptors can control the opening of ion channels in two ways

Answer 25

Ionotropic and metabotropic

Question 26

Ionotropic receptors

Answer 26

Ligand-gated ion channels

When a neurotransmitter binds to the receptor, it causes the receptor to change shape and allows ions to enter the cell

Quick

Question 27

Metabotropic receptors

Answer 27

G protein-coupled receptors

When the transmitter binds, it activates G-protein molecules that open nearby channels or trigger other reactions

Utilizes second-messenger system: first the transmitter binds, then chemical signal activated by G protein that amplifies its effect

Slow

Question 28

Autoreceptors

Answer 28

Located on the presynaptic membrane

Neurotransmitters can bind here to inform presynaptic cell about how much neurotransmitter is in the synapse, regulate future NT release with exocytosis, and can act as a shut-off mechanism

Question 29

Axo-axonic synapses

Answer 29

Form near axon terminals, allowing the presynaptic neurons to regulate how much neurotransmitter will be released from that terminal

Question 30

Dendro-dendritic synapses

Answer 30

Allow coordination of activities

Question 31

Retrograde synapses

Answer 31

Use gas to signal from the dendrite of a postsynaptic cell to the axon terminal of the presynaptic cell to release more neurotransmitter