Synaptic Transmission

Question 1

synapse

Answer 1

junction between two cells, often two neurons, but can be any 2 cells

can be electrical or chemical

Question 2

convergence

Answer 2

many pre-synaptic neurons affecting a single post-synaptic neuron.

can recieve signals from ~10,000 cells.

action potentials are often a result of the sum on all the connections

Question 3

Do we physically change when we learn?

Answer 3

We change the number and quality of our dendrites

There is no difference in the number of neurons, but there is a difference in the number of neuronal connections

Question 4

Electrical Synapses

Answer 4

• These are rare
• Are formed between 2 cells that are connected by gap junctions
• The junctions are big enough so that many types of molecules can be shared vetween the adjacent cells
• Signal passes extremely rapidly
• Signal can be bidirectional, or pore configurations can limit direction
• passage of signal is guaranteed and does not require amplification

Question 5

Chemical synapses

Answer 5

Includes a presynaptic neuron in which the AP triggers release of a chemical into the extracellular space. The chemical binds to chemically gated ion channels on post-synaptic neuron triggering a graded potential and potentially an action potential in the post-synaptic neuron

Question 6

Where are ribosomes located?

Answer 6

Just outside the nucleus

Question 7

Which protein does anterograde NT transport?

Answer 7

Kinesin

Question 8

Which protein does retrograde NT transport?

Answer 8

Dynein

Question 9

Anterograde transport

Answer 9

• Transport from the cell body to the axon terminal
• Transports nutrients, enzymes, mitochondria, neurotransmitters
• uses kinesin
• can moce up to 15 inches a day

Question 10

Retrograde transport

Answer 10

• transports from the axon terminal to the cel body
• moves recycled vesicles, and recycled NT
• uses Dynein

Question 11

Neurotransmitter release

Answer 11

The end product of AP in many neurons.

NT are encased in vesicles

Vesicle-cell membrane fusion is required for release

Question 12

Divergence

Answer 12

Then one presynaptic neuron has many acon terminals and forms many synapses

Question 13

What voltage gated ion channels are at the axon terminal?

Answer 13

Na, K, Ca

Question 14

What happens with Ca when the depolarization reaches the axon terminal

Answer 14

Voltage gated ion Ca channels open and Ca2+ rushes into the cell.

Ca then binds to receptors on the vesicle membrane, triggering a shape change that allows the vesicle membrane to fuse with the cell membrane.

Question 15

Explain the events in the synaptic cleft

Answer 15

NT moves throuhg the synapse by diffusion, and binds to the receptors on the post synaptic cell. (This occurs slowly ~0.2ms)

Question 16

What can change the efficiency of NT signalling in the synaptic cleft?

Answer 16

• The concentration of receptors on the post synaptic cell
• The concentration of NT in the synapse.
  *

Question 17

What happens when there is more NT in the synapse?

Answer 17

More NT=more receptors bound=Bigger Graded potential

Question 18

What are three methods for removing NT from the synapse?

Answer 18

• Re-uptake
• Diffusion
• Breakdown by enzymes in the presynaptic cleft

Question 19

Reuptake

Answer 19

NT is actively transported back into the presynaptic neuron or the surrounding glial cells

Question 20

Can presynaptic synapses release more than one NT?

Answer 20

Yes

Question 21

Which ion triggers synaptic vesicles to merge with the plasma membrane?

Answer 21

Ca

Question 22

What triggers Ca channls to open?

Answer 22

A + intracellular voltage

Question 23

What is true about a relative refractory period?

Answer 23

Some Na channels are inactivated, and some are closed.

An AP can occur if the stimuli is strong enough.

Question 24

Can graded potentials moce the cell closer to and further from threshold?

Answer 24

Yes

Question 25

Can action potentials moce the cell closer to and further from threshold?

Answer 25

No. They are all or nothing and always depolarize to the same amplitude.

Question 26

Excitatory post-synaptic potential (EPSP)

Answer 26

If the binding of an NT to a receptor on the post synaptic neuron results in depolarization

One EPSE changes the RMP 0.5mV (a 15mV change is needed to reach threshold)

Question 27

Inhibitory post synaptic potential (IPSP)

Answer 27

the binding of an T to a receptor on the post synaptic neuron results in hyperpolarization.

Can happen either by allowing + ions out of the cell(like K), or letting - ions into the cell (chloride)

Question 28

Summation

Answer 28

adding graded potentials together to reach threshold and spark an action potential

Question 29

Temporal Summation

Answer 29

Fires EPSP after EPSP within a short period of time, so the membrane does not have time to repolarize, and summation occurs to reach threshold.

Question 30

Spatial Summation

Answer 30

Multiple EPSPs from different presynaptic neurons, adding up to reach threshold

Question 31

Factors that effect synaptic strength/summation

Answer 31

• Availability of NT/NT precursor molecules
• Availability of Ca outside the presynaptic neuron
• Receptor concetration/sensitization on post synaptic neuron
• Enzymatic destruction of NT in synaptic cleft
• diffusion factors

Question 32

Synaptic plasticity

Answer 32

• Receptor expression can be up/down regulated.
• Another set of chemicals, neuromodulators can effect the availability og NT in eurons
• receptors can desensitise