Synapses and Plasticity One

Question 1

Describe the basic features of a neuron:

Answer 1

Soma (cell body)
Axon (Only, it carries output AP) (Mostly myelonated 50ms velocity vs 1ms)
Dendrites (many of these- incoming information)
Many synapses on the dendrites

Question 2

What is unique about a neuron?

Answer 2

Polarised cell.

Question 3

Where can synapses occur?

Answer 3

On the dendrite (neuron to neuron)
On glia
On muscle (neuromuscular junction)

10 trillion synapses in the brain

Question 4

What do synapses allow?

Answer 4

Rapid communication

Question 5

What do synapses allow the formation of?

Answer 5

Neural circuits

Question 6

How are neural circuits formed?

Answer 6

Synapses allow the transmission of APs by:

Converting an Electrical Information (AP) into Chemical Information (Neurotransmitter release) which crosses the synaptic cleft and activated a receptor (ligand gated ion channel), Post synaptic cleft receptors convert this chemical information back into the Electrical information which travels through dendrites and its processed with all other incoming information (as many dendrites and even more synapses)

Question 7

What are synapses thought as?

Answer 7

The basic information processing units in the brain

Question 8

Describe the structure of a synapse.

Answer 8

Presynaptic cleft: Contains vesicles packaging neurotransmitter, which are bound to cytoskeleton by Calcium sensitive vesicular proteins. The base of the presynaptic cleft is a dense zone (Lots of protiens, where neurotransmitter binds)

Synaptic cleft (Extracellular space where neurotransmitter crosses)

Postsynaptic cleft: Contains receptors for neurotransmitter that activate ligand gated ion channels. Followed internally a post synaptic density (protein dense)

Question 9

On the presynaptic cleft, what is the dense zone also referred to?

Answer 9

The active zone

Question 10

What is the role of the active zone?

Answer 10

It is the region where vesicles fuse to the presynaptic terminal and release their neurotransmitter. It is an active process because of the Ca dependent proteins that mediate this process.

Question 11

Why is the role of the post synaptic density?

Answer 11

It is protein rich area and its role is to get the receptors where they need to be to receive neurotransmitter release. Highly coordinated event to allow synaptic transmission to occur.

Question 12

How does disease influence synapses?

Answer 12

Every disease tends to involve changes in synapses i.e number of location of efficency

Question 13

What happens to the vesicles once they have fused with the presynaptic terminal?

Answer 13

They are recycled

Question 14

Describe neurotransmission

Answer 14

Neurotransmitter is synthesised and packaged into vesicles.
AP reaches the presynaptic cleft and activae voltage gated Ca channels.
Ca influxes.
This activates Ca sensitive proteins and causes vesicles to fuse with the presynaptic membrane.
Neurotransmitter is released and crosses the synhaptic cleft and binds to receptors on the post synaptic celft, activating the ligand gated ion channels influxing ions and causing an AP.

Question 15

How does the vesicles release neurotransmitter?

Answer 15

Snare proteins mediate exocytosis.

Ca dependant snare proteins on the membrane and vesicle wrap around each other, pulling the vesicle close to the membrane, once close enough exocytosis occurs

Question 16

What are some examples of snare proteins?

Answer 16

On the vesicle:
Synaptobrenin
Synaptotagmin

Membrane:
Syntaxin
SNAP25

Question 17

What are the main types of synpases?

Answer 17

Excitatory Synapses or Inhibitory Synapses

Question 18

What is the function of inhibitory synapses?

Answer 18

Allows balance between excitation and inhibition

Question 19

What does disease do to inhibitory synapses?

Answer 19

It leads to an off balance between excitation and inhibition which presents as symptoms

Question 20

Whats an example of a group of inhibitory synapses?

Answer 20

5% of interneurons are inhibitory.

Question 21

What makes interneurons inhibitory?

Answer 21

They are extremely polarised and contain many processes.

Releasing inhibitory neurotransmitter at their synapse.
e.g GABA and Glycine

Question 22

What are the affects of GABA and Glycine?

Answer 22

They bind to their receptors on excitatory neurons (and inhibitory neurons), these channels allow the influx of Cl ions therefore transiently hyperpolarising the resting membrane potential

Question 23

The affects of inhibitory neurotransmitter are called?

Answer 23

Inhibitory Post Synaptic Potential

Question 24

What is the main neurotransmitter for excitatory synapses?

Answer 24

90% of excitatory neurons are glutamanergic.

Question 25

What are the post synaptic receptors for gultamate?

Answer 25

The post synaptic receptors for glutamate are: Ion channels: 1) AMPA 2) NMDA GPCR's 3) Metabloic glutamate receptors

Question 26

Why are there multiple receptors?

Answer 26

The different receptors have different properties

Question 27

Is there a difference between AMPA and NMDA receptors?

Answer 27

Yes their properties are very different. AMPA receptors activate when glutamte binds and allows the passage of primariily Na and some K ions NMDA receptors allow the passage of primarily Ca and some Na, K

Question 28

When it comes to plasticity what kind of glutamate receptor is most important?

Answer 28

NMDA

Question 29

When it comes to activation what is the difference between NMDA and AMPA?

Answer 29

AMPA receptors are neurotransmitter dependent only. NMDA receptors require Neurotransmitter and are voltage gated.

Question 30

How are NMDA receptors voltage gated?

Answer 30

At RMP (-60mV) NMDA receptors have a Mg ion blocking off the channel. (So binding of neurotransmitter can occur but no Ca flux.) When the membrane potential depolarises (i.e AMPA receptors have being activated) the channel undergoes a conformational change causing Mg release and allowing the influx of Ca ions, providing neurotransmitter has bound. Requires lots of Na influx from AMPA

Question 31

Why do synapses have two types of receptors?

Answer 31

AS different properties change the strength of the synapse.

Question 32

What is a requirement for high levels of Ca influx with NMDA receptors?

Answer 32

High levels of Pre and Post synaptic activation will result in high levels of Ca influx.

Question 33

What is the high levels of pre and post synaptic activation called? in reference to NMDA receptors?

Answer 33

Co-incidence detectors

Question 34

What is meant by co-incident detectors?

Answer 34

NMDA receptors detect high levels of pre and post synaptic co-activation

Question 35

What is co-activation important in?

Answer 35

Synaptic plasticity