10) The events involved in the transmission of signals at a synapse

Question 1

What are the 7 steps that consist of the transmission of signals at a chemical synapse?

Answer 1

1) nerve impulse arrives at synaptic end bulb (varicosity) of a presynaptic axon
2) depolarizing phase of NP opens voltage-gated Ca2+ channels in membrane of synaptic end bulbs. Ca2+ flows inward through open channels
3) Exocytosis of synaptic vsicles, which merge with PM and release NTs into the synaptic cleft
4) NTs diffuse across synaptic cleft and bind to neurotransmitter receptors (either ionotropic, or metabotropic) that are part of a ligand-gated channel in postsynaptic neuron’s plasma membrane
5) bindings of receptors on ligand-gated channels opens the channels and allows particular ions to flow across membrane
6) flow of ions causes voltage to change across membranes, resulting in a postsynpatic potential. Can be depolarizing (excitatory) or hyperpolarizing (inhibitory)
7) When a depolarizing potential reaches threshold, it triggers an action potential in the axon of the post-synaptic neuron

Question 2

Calcium ions (in neuron) are more concentrated in:

a) intracellular fluid, so the opening of voltage-gated Ca2+ channels causes calcium ions to flow inward
b) intracellular fluid, so the opening of voltage-gated Ca2+ channels causes calcium ions to flow outward
c) extracellular fluid, so the opening of voltage-gated Ca2+ channels causes calcium ions to flow outward
d) extracellular fluid, so the opening of Ca2+ channels causes calcium ions to flow outward

Answer 2

d

Question 3

A _____ is a depolarizing postsynaptic potential

Answer 3

EPSP

Question 4

A _____ is a hyperpolarizing postsynaptic potential

Answer 4

IPSP

Question 5

A _____ brings the membrane of a neuron closer to threshold.

a) excitatory postsynaptic potential
b) inhibitory postsynaptic potential
c) graded potential
d) action potential
e) synaptic potential

Answer 5

a

Question 6

T/F

A single EPSP can initiate a nerve impulse

Answer 6

False.
A single EPSP causes the postsynaptic cell to become more excitable; it is partially depolarized so it is more likely to reach threshold with the next EPSP

Question 7

Why is the generation of an action more difficult than usual with an inhibitory postsynaptic potential?

Answer 7

Because it causes the membrane potential to become more negative, and farther from the threshold than its resting state.

Question 8

Match the following to the correct definition:

1) axosomatic
2) axoaxonic
3) axodendritic

a) from axon to cell body
b) from cell body to axon
c) from axon to dendrite
d) presynaptic neuron synapses on axon of postsynaptic neuron
e) presynaptic neuron synapses on cell body of postsynaptic neuron
f) presynaptic neuron synapses on dendrite of postsynaptic neuron

Answer 8

Axoaxonic - (a) and (d)

Axosomatic - (b) and (e)

Axodendritic - (c) and (f)

Question 9

A postsynaptic neuron is a:

a) cell that responds to the impulse at the synapse
b) the nerve that is activated by the release of a neurotransmitter from another neuron and carries the nerve impulse away from the synapse
c) a neuron that propagates nerve impulses toward a synapse
d) the cell receives a signal

Answer 9

c

Question 10

A postsynaptic cell can be one of two things….?

Answer 10

1) postsynaptic neuron

2) effector cell

Question 11

An effector cell is a:

a) cell that responds to the impulse at the synapse
b) a neuron that propagates nerve impulses toward a synapse
c) a cell that is activated by the release of a neurotransmitter from a neuron
d) a cell that carries nerve impulses away from the synapse
e) more than one of the above

Answer 11

e - both a and c are true

Question 12

There are two types of synapses. What are they?

Answer 12

1) electrical synapses - action potentials conduct directly between the PM of adjacentneurons through gap junctions
2) Chemical synapses - plasma membranes are close in pre and post synaptic cell, but do not touch. they are separated by a synpatic cleft

Question 13

T/F

In chemical synapses, nerve impulses cannot conduct across a synaptic cleft

Answer 13

true - NPs cause NTs to be released, which diffuse across the synaptic cleft and stimulate the postsynaptic cell

Question 14

T/F

In electrical synapses, nerve impulses cannot conduct across a synaptic cleft

Answer 14

True

There is no synaptic cleft involved. Instead, APs conduct directly b/w PM of adjacent neurons throguh gap junctiosn

Question 15

How do electrical synapses conduct APs between adjacent neurons?

Answer 15

Gap junctions - contain tubular connexons through which ions flow, spreading APs from cell to cell

Question 16

What are the benefits of electrical synapses?

Answer 16

1) faster communication (APs conduct directly through gap junctions)
2) synchronization (of a group of neurons of muscle fibers)

Question 17

Why may electrical synapses work in two directions, but chemical synapses can transmit a signal only in one direction?

Answer 17

Electrical synapses - ions may flow in either direction, so either neuron can be the presynaptic one.

At a chemical synapse, one neuron releases NT and the other neuron has receptors that bind this chemical. Thus, the signal can only be proceeded in one direction

Question 18

What is a postsynaptic potential?

Answer 18

the chemical signal resposne of a postsynaptic cell. a type of graded potential

Question 19

A postsynaptic potential is a type of _____ potential.

Answer 19

graded

Question 20

Neurotransmitters are located in:

a) the synaptic cleft between the pre- and post-syanptic cells
b) gap junctions
c) the plasma membrane of the postsynaptic cell
d) the plasma membrane of the presynaptic cell

Answer 20

d

Question 21

T/F

Each neurotransmitter has 1 or more binding sites where its specific neurotransmitter binds

Answer 21

True!

Question 22

What are two types of neurotransmitter receptors?

Answer 22

ionotropic receptors - contains NT binding site and an ion channel that are part of teh same protein

metabotropic receptor - contains NT binding site but lack and ion channel (they’re components of different proteins

Question 23

Metabotropic receptors contain an:

a) ion channel
b) binding site
c) synaptic vesicles
d) both a and c
e) both a and b

Answer 23

b

they don’t contain ion channels

Question 24

How do metabotropic receptors differ from ionotropic receptors?

Answer 24

the binding site and ion channel are components of different proteins in metabotropic receptors

Question 25

Most excitatory neurotransmitters bind to:

a) ionotropic receptors that contain chloride channels
b) ionotropic receptors that contain cation channels
c) metabotropic receptors lined with potassium ion channels

Answer 25

b) - answer (results in depolarization)
a) - inhibitory NTs bind to these(results in hyperpolarization
c) inhibitory NTs bind to these (results in IPSP)

Question 26

An IPSP will occur when:

a) inhibitory neurotransmitters bind to ionotropic receptors lined with potassium ion channels
b) inhibitory neurotransmitters bind to ionotropic receptors that contain cation channels
c) inhibitory neurotransmitters bind to ionotropic receptors that contain chloride channels
d) more than one is right

Answer 26

Only c is right

A would be right if it said “inhibitory neurotransmitters bind to METABOTROPIC receptors lined with potassium ion channels”

Question 27

ionotropic and metabotropic receptors are

a) mechanically-gated ion channels
b) leak channels
c) ligand-gated ion channels
d) voltage-gated ion channels

Answer 27

c

Question 28

Are are metabotropic receptors activated?

Answer 28

metabotropic receptors are coupled to a separate ion channel by a type of membrane protein called a G protein. When the NT binds to a metabotropic receptor, the G protein either directly opens (or clsoes) the ion channel, or it may act indirectly by activating another molecule “second messenger” int he cytosol, which in turn opens or closes the ion channel

Question 29

Which of the following are true of metabotropic receptors (more than one may be true):

a) metabotropic receptors are coupled to a separate ion channels by G proteins
b) G proteins directly open/close ion channels
c) G proteins indirectly activate ion channels
d) the binding site and ion chaennel are components of the same protein

Answer 29

a, b, c are true

c - G proteins may indirectly activate another molecule “second messenger” in cytosol, which in turn opens or closes the ion channel

d - NT binding site and ion channel are components of DIFFERENT proteins

Question 30

T/F

The same neurotransmitter can be excitatory at some synapses and inhibitory at others

Answer 30

True! This depends on the structure of teh NT receptor to which it binds.

For example, ACh when it binds to ionotropic receptors containing cation channels, it is excitatory, but when it binds to metabotropic receptors coupled to G proteins that open K+ channels, it is inhbitory (IPSP)

Question 31

Why is the removal of neurotransmitters essential for normal synaptic function?

Answer 31

If NTs lingered in the synaptic cleft, they could influence the postsynaptic neuron, muscle fiber, or gland cell indefinitely

Question 32

Name 3 methods of neurotransmitter removal from the synapse.

Answer 32

1) Diffusion
2) enzymatic degradation
3) uptake/reuptake by cells

Question 33

In the removal of neurotransmitters from the synapse, _____ is when neurotransmitters are transported into neighboring neuroglia.

a) diffusion
b) reuptake
c) enzymatic degradation
d) uptake

Answer 33

d