3: Physiology - Excitatory and inhibitory neurotransmission in the CNS

Question 1

Given that nerve cells depolarise to cause an action potential, are their resting membrane potentials positive or negative?

Answer 1

Negative

Question 2

Which ion channels open to cause a depolarisation?

Answer 2

Na+

Ca²⁺

i.e positively charged ions

Question 3

Which ion channels open to cause a hyperpolarisation?

Answer 3

C- (flows inwards, makes cell more negative)

K+ (flows outwards, makes cell more negative)

Question 4

In which directions do

a) sodium

b) calcium

c) chloride

d) potassium

ions flow to cause a/b) depolarisation and c/d) hyperpolarisation?

Answer 4

a) Inwards

b) Inwards

c) Inwards

d) outwards

Question 5

What type of nerve transmission is triggered by a depolarisation?

Answer 5

Excitation

Question 6

What type of nerve transmission is triggered by a hyperpolarisation?

Answer 6

Inhibition

Question 7

Given that sodium influx causes a cell to depolarise, what effect do

a) sodium channel agonists
b) sodium channel antagonists

have on nerve cells?

Answer 7

a) Excitatory

b) Inhibitory

Question 8

Given that potassium efflux causes a cell to hyperpolarise, what effects do

a) K+ channel agonists
b) K+ channel antagonists

have on nerve cells?

Answer 8

a) Inhibition
b) Excitation

Question 9

What is the difference between an axon and a dendrite?

Answer 9

Both are projections of a neuron

Axons carry outputs to other neurons

Dendrites receive inputs from other neurons

Neurons have many dendrites but only one axon

Question 10

What is the space between a pre-synaptic cell and a post-synaptic cell called?

Answer 10

Synaptic cleft

Question 11

Which ion is essential in triggering the release of neurotransmitters across a synaptic cleft?

Answer 11

Ca²⁺

Question 12

What releases neurotransmitters into the synaptic cleft?

What transport process is this an example of?

Answer 12

Synaptic vesicle

Exocytosis

Question 13

By which three means are neurotransmitters cleared from the synaptic cleft?

Answer 13

1. Recycling into axon terminal or glial cell

2. Deactivation by enzymes

3. Diffusion out of synaptic cleft

Question 14

Which types of receptors

a) directly
b) indirectly

activate ion channels as a result of the binding of neurotransmitters?

Answer 14

a) Direct receptors for ligand-gated channels

b) G-protein coupled receptors

Question 15

What is faster, direct or indirect gating of ion channels?

Answer 15

direct gating

ligand binds to receptor, response

where as indirect gating involves proteins and metabolites which have to react and change confirmation etc etc

Question 16

What is the main excitatory neurotransmitter?

Answer 16

Glutamate

Question 17

What are the main inhibitory neurotransmitters?

Answer 17

GABA

Glycine

Question 18

Molecules called AMPA and NMDA are sometimes found bound to glutamate (excitatory) receptors.

What happens to the speed of the neurotransmision when NMDA is bound?

Answer 18

Slows down - “slow component”

Question 19

What happens to the speed of neurotransmission at a glutamate (excitatory) receptor when AMPA is bound?

Answer 19

Speeds up - rapid transmission

Question 20

What are the main inhibitory neurotransmitters?

Answer 20

GABA

Glycine

Question 21

What are ionotropic and metabotropic receptors?

Answer 21

Ionotropic - directly gated by ions which bind to them to cause a response e.g channel opening

Metabotropic - indirectly gated - binding by a ligand causes a chemical reaction / protein release etc. etc. which eventually opens the channel

Question 22

Which type of receptor is faster acting - ionotropic or metabotropic?

Answer 22

Ionotropic

Question 23

Ionotropic receptors are often responsible for ___ an action potential at the post-synaptic terminal.

Answer 23

triggering

Question 24

Because metabotropic receptors are slower acting than ionotropic receptors, which role do they have in a synapse?

Answer 24

Alter PROPERTIES of action potential e.g firing rate, amplitude

Alter neurotransmitter release

Question 25

In general, **ionotropic receptors** trigger **(fast / slow) action potentials**.

Answer 25

**ionotropic** - fast action potentials

Question 26

In general **metabotropic** **receptors** trigger **(fast / slow)** action potentials.

Answer 26

**metabotropic** - slow action potentials

Question 27

What is the name of the action potential triggered by neurotransmitters in the neuron FOLLOWING a synapse?

Answer 27

**Post-synaptic potential**

Question 28

What must the **post-synaptic potential** overcome to trigger an **action potential**?

Answer 28

**Threshold potential**

Question 29

In terms of **threshold potential**, what is meant by an **excitatory** or **inhibitory post-synaptic potential?**

Answer 29

**Excitatory** - depolarises the neuron and brings it closer to the threshold potential required for an AP **Inhibitory** - hyperpolarises the neuron and brings it further away from threshold

Question 30

What **variable** determines the **amplitude of an AP generated by sensory neurons?**

Answer 30

**Stimulus intensity**

Question 31

What is meant by the term **graded potential**?

Answer 31

**A gradual change in membrane potential rather than a sharp jump**

Question 32

Why does the **graded potential** of a neuron decrease?

Answer 32

**Time** - ion channels open and close **Distance** - charge leaks away

Question 33

If a **graded potential** overcomes threshold, what does it become?

Answer 33

**Action potential**

Question 34

What **neurotransmitters** cause **depolarisation** of the post-synaptic neuron?

Answer 34

**Glutamate** **-** excitatory neurotransmitter

Question 35

Which **neurotransmitters** cause **hyperpolarisation** of the post-synaptic neuron?

Answer 35

**GABA** **Glycine**

Question 36

What is an **interneuron**? Which neurotransmitter does it secrete?

Answer 36

**An independent neuron which processes local information** **GABA** (inhibitory)

Question 37

What is a **quanta** of neurotransmitter?

Answer 37

**The volume secreted from ONE synaptic vesicle**

Question 38

What influences the **number of quanta** of neurotransmitter secreted by a synaptic vesicle?

Answer 38

**Stimulus intensity**

Question 39

From other lectures, what is a) **spatial summation** b) **temporal summation**?

Answer 39

**a) Whether a neuron fires or not depends on all the excitatory and inhibitory synapses connected to it** **b) Whether a neuron fires or not depends on the number of excitatory / inhibitory signals and the sequence they're received in**