Lecture 19

Question 1

What is the absolute refractory period?

Answer 1

Period during which no action potential is possible due to the inactivation gate of voltage-gated Na+ channels being closed

Occurs after depolarization to +30mV

Question 2

What is the relative refractory period?

Answer 2

Period during which a large stimulus can generate an action potential, but the membrane potential is more negative due to K+ efflux

Inactivation gates are in the process of opening

Question 3

Describe the movement of an action potential down the axon of a neuron.

Answer 3

An action potential activates adjacent segments of the axon by opening voltage-gated Na+ channels, propagating the signal along the axon

This process is known as active propagation

Question 4

What is synaptic transmission?

Answer 4

The process where neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, causing local potentials

This process occurs at the axon terminal

Question 5

Fill in the blank: Na+ = _______

Answer 5

Sodium

Question 6

Fill in the blank: K+ = _______

Answer 6

Potassium

Question 7

Fill in the blank: Cl- = _______

Answer 7

Chloride

Question 8

Fill in the blank: Ca2+ = _______

Answer 8

Calcium

Question 9

What types of channels are found on dendrites of some sensory neurons?

Answer 9

Mechanically-gated ion channels

More detail is provided in Lecture 23

Question 10

What are chemically gated channels?

Answer 10

Channels that open when a chemical molecule, such as a neurotransmitter, binds to a receptor, allowing ions to flow down their electrochemical gradient

Question 11

Define excitatory post-synaptic potential (EPSP).

Answer 11

A local potential that results in depolarization, making the membrane potential more positive, often due to Na+ influx

Question 12

Define inhibitory post-synaptic potential (IPSP).

Answer 12

A local potential that results in hyperpolarization, making the membrane potential more negative, often due to K+ efflux or Cl- influx

Question 13

What is temporal summation?

Answer 13

The process where local potentials arrive close together in time, allowing their effects to add together

Question 14

What is spatial summation?

Answer 14

The process where local potentials occur close together spatially, allowing their effects to combine

Question 15

At resting membrane potential (RMP), what is the state of the activation and inactivation gates of voltage-gated Na+ channels?

Answer 15

Activation gate closed, inactivation gate open

Question 16

What occurs during depolarization to threshold?

Answer 16

Activation gates of voltage-gated Na+ channels open, allowing Na+ to flow into the cell

Question 17

Describe the rapid depolarization phase of an action potential.

Answer 17

Na+ flows into the cell, causing a rapid increase in membrane potential to +30mV

Question 18

What happens during the inactivation phase of voltage-gated Na+ channels?

Answer 18

The inactivation gate closes, preventing further Na+ flow into the cell

Question 19

What initiates the repolarization phase of an action potential?

Answer 19

Opening of voltage-gated K+ channels, allowing K+ to leave the cell

Question 20

What causes hyperpolarization during an action potential?

Answer 20

Efflux of K+ as voltage-gated K+ channels close slowly

Question 21

What is the role of myelination in action potential propagation?

Answer 21

Myelin acts as insulation, preventing ion movement across the membrane except at Nodes of Ranvier, speeding up signal propagation

Question 22

What is the function of Nodes of Ranvier?

Answer 22

Gaps in the myelin sheath that contain concentrated numbers of voltage-gated Na+ and K+ channels, facilitating rapid regeneration of action potentials

Question 23

What is the unidirectional flow of information in synaptic transmission?

Answer 23

The flow of information is from the presynaptic neuron to the postsynaptic neuron

Question 24

What is the role of calcium ions (Ca2+) in synaptic transmission?

Answer 24

Ca2+ influx triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft

Question 25

What happens to neurotransmitters after they bind to receptors on the postsynaptic membrane?

Answer 25

They cause local potentials, such as EPSPs or IPSPs, depending on the type of neurotransmitter

Question 26

How is synaptic transmission turned off?

Answer 26

Neurotransmitters are removed from the synaptic cleft, often by enzymatic breakdown or reuptake

Question 27

What enzyme breaks down acetylcholine (ACh) in the synaptic cleft?

Answer 27

Acetylcholinesterase (AChE)

Question 28

What happens to choline after ACh is broken down?

Answer 28

Choline is taken back up by the presynaptic terminal and recycled to produce new ACh

Question 29

What are the main types of synaptic potentials?

Answer 29

* Excitatory Post-Synaptic Potentials (EPSPs) * Inhibitory Post-Synaptic Potentials (IPSPs)

Question 30

What is the threshold potential needed to trigger an action potential?

Answer 30

-60mV at the axon hillock

Question 31

What is the primary neurotransmitter involved in cholinergic synapses?

Answer 31

Acetylcholine (ACh)

Question 32

Which type of synapse uses GABA as a neurotransmitter?

Answer 32

Inhibitory synapses

Question 33

What is the effect of EPSPs on the postsynaptic neuron?

Answer 33

They can bring the neuron to threshold, initiating an action potential if sufficient in number

Question 34

What is the effect of IPSPs on the postsynaptic neuron?

Answer 34

They move the membrane potential further from threshold, preventing action potential firing

Question 35

What is the significance of action potential propagation in unmyelinated axons?

Answer 35

Each segment of the axon must generate an action potential, leading to slower propagation speed

Question 36

What is the significance of action potential propagation in myelinated axons?

Answer 36

Action potentials jump from node to node, increasing conduction speed due to reduced ion leakage

Question 37

The site of initiation of the action potential is the:

Answer 37

C) Initial segment ## Footnote The initial segment of the axon is where the action potential is generated.

Question 38

Which of the following statements regarding action potentials is NOT true?

Answer 38

D) A large stimulus may initiate an action potential during the absolute refractory period ## Footnote During the absolute refractory period, no action potential can be initiated regardless of stimulus size.

Question 39

At a typical nerve-nerve chemical synapse, an action potential in a presynaptic neuron commonly results in a:

Answer 39

A) post synaptic action potential ## Footnote Presynaptic action potentials typically lead to the release of neurotransmitters that can generate postsynaptic action potentials.

Question 40

What causes neurotransmitter release at a synapse?

Answer 40

D) Entry of Ca2+ into the presynaptic terminal ## Footnote The influx of calcium ions triggers the release of neurotransmitters from synaptic vesicles.

Question 41

True or False: EPSPs and IPSPs normally arise at different times.

Answer 41

False ## Footnote EPSPs (excitatory postsynaptic potentials) and IPSPs (inhibitory postsynaptic potentials) can occur simultaneously and affect the postsynaptic neuron.

Question 42

Fill in the blank: Myelin _______ the speed of action potential conductance.

Answer 42

increases ## Footnote Myelin acts as an insulator on axons, facilitating faster signal transmission.

Question 43

The repolarization phase of the action potential is due to _______ exiting from the axon.

Answer 43

potassium ## Footnote The outflow of potassium ions helps restore the resting membrane potential after depolarization.

Question 44

Action potentials normally propagate in only one _______.

Answer 44

direction ## Footnote This unidirectional flow is due to the refractory periods of the axon segments.