Lecture 5: Electrochemical Signals To Communicate

Question 1

What are the four steps to neurotransmission?

Answer 1

1. Synthesis: neurotransmitter either brought down from cell nucleus or released from storage vesicles
2. Release: in response to an action potential, NT is released at the presynaptic membrane
3. Receptor action: target receptors receive NT on post synaptic membrane
4. Inactivation: NT is either taken back into terminal or inactivated at synaptic cleft

Question 2

Describe synaptic transmission

Answer 2

1. Electrical signal arrives. Triggers release of NT into synaptic cleft
2. NT binds to receptors on post synaptic neuron and triggers next action potential
3. NT is recycled back into presynaptic membrane and/or via glial uptake, enzymatic degradation, or diffusion

Question 3

How are NTs synthesized?

Answer 3

1. DNA - synthesis on cell body, packaged at Golgi bodies, then transported down axon via microtubules
2. mRNA - synthesis at axon terminal by transporter proteins obtaining direction from blood supply, and energy from mitochondria

Question 4

How are NTs stored?

Answer 4

In vesicles bound to snare proteins in axon terminal

Question 5

How does release of NTs occur in presynaptic neuron?

Answer 5

1. Incoming Action potential opens voltage gated calcium channels, influx of calcium
2. Calcium binds to calmodulin to form calcium-calmodulin-complex.
3. Complex interacts with snare proteins and draws vesicles towards synaptic cleft
4. Vesicles empty contents into synaptic cleft via exocytosis

Question 6

How does receptor activation work?

Answer 6

Receptors are specific to neurotransmitter, and depending on the receptor it will either:

1. Depolarize (EPSP)
2. Hyper polarize (IPSP)
3. Initiate another chemical process

Question 7

List four ways inactivation occurs

Answer 7

1. Glial cells collect and breakdown, return the building blocks to presynaptic cell
2. Enzymatic degradation in the synaptic cleft
3. Simple, passive diffusion
4. Transporter proteins reuptake NTs back into presynaptic cell

Question 8

List different types of synapses

Answer 8

Dendrodendritic: to other dendrites
Axodendritic: axon onto dendritic spine
Axoextracellular: onto nothing but extrac space
Axosomatic: axon to cell body
Axosynaptic: onto another terminal
Axoaxonic: onto another axon
Axosecretory: directly into blood vessel.

Question 9

What are the only two types of messages a cell will send?

Answer 9

Excitatory or inhibitatory

Question 10

What is the criteria for a chemical to be a neurotransmitter?

Answer 10

1. Synthesized or present in neuron
2. Releases upon stimulation and must produce a response
3. Response must be replicable by experimental administration
4. There must be a mode to inactivate it when finished

Question 11

List some small molecule NTs synthesized from dietary nutrients

Answer 11

Acetylcholine
Histamine
Amines: dopamine, norepinephrine, epinephrine, serotonin
Amino acids: glutamate, GABA, glycine

Question 12

What is the main excitatory NT

Answer 12

Glutamate

Question 13

What is the main inhibitory NT

Answer 13

GABA

Question 14

What are neuropeptides

Answer 14

Chains of amino acids that act as NTs. Activate receptors that indirectly influence cell structure and function

Question 15

What are transmitter gases?

Answer 15

Nitric oxide and carbon monoxide. Water soluble gases which diffuse across the membrane and are immediately active

Question 16

What are the two classes of receptors?

Answer 16

1. Ionotropic: changes electrical potential of post synaptic membrane, has binding site and an ion pore, rapid change in voltage
2. Metabotropic: indirectly influence cellular changes, has only a binding site, causes activation of G protein which can open ion channels or bind to an enzyme

Question 17

Describe amplification cascade in metabotric receptors

Answer 17

An activation enzyme can in turn activate 100 molecules of a target zymogen, exponentially increasing molecules (enzyme #4 can activate 1,000,000 molecules)

Question 18

What is an excitatory NT in the somatic nervous system

Answer 18

Acetylcholine.

Question 19

What does the cholinergic system do in the CNS?

Answer 19

Maintains attention and awake patterns
Plays role in memory and attention
Decrease in acetylcholine related to Alzheimer’s

Question 20

Describe the dopaminergic system

Answer 20

Maintains normal motor behaviour
Decreases related to muscle rigidity, Parkinson’s
Causes feelings of reward and pleasure
Most effected by addictive drugs and behavioural addictions
Decreases related to attention deficit
Increases related to schizophrenia

Question 21

Describe noradrenergic system (norepinephrine)

Answer 21

Implicated in learning
Maintains emotional tone
Decreases related to depression
Facilitates brain development
Decreases related to ADHD
Increases related to mania

Question 22

Describe the serotonergic system

Answer 22

Maintains waking EEG pattern
Has role in learning
Decreases related to depression
Increases related to OCD

Question 23

What is hebbian learning

Answer 23

Permanent behaviour changes that occur when synapses undergo change in structure and function as a consequence of being repeatedly fired together. Neurons that fire together wire together

Question 24

Describe habituation and sensitization

Answer 24

Habituation: response becomes weak because of repeated stimulation
Sensitization: response becomes enhanced because of repeated stimulation