Neuronal signaling- synaptic transmission

Question 1

What are the characteristics of an Electrical synapse?

Answer 1

No delay
good for fast transmission
Bidirectional- synchronisation
Gap junctions between interneurons important for oscillatory rhythms in the brain

Question 2

Describe what happens at an electrical synapse.

Answer 2

The presynaptic nerve is in direct contact with the Postsynaptic cell/nerve.
This is achieved via connexions.
This allows an ionic current to flow through the channels.

Question 3

Explain the elements of the chemical synapse

Answer 3

Synaptic cleft:
Gap between cells
filled with a matrix of fibrous protein

Presynaptic element:
synaptic vesicles-vesicles filled with neurotransmitters

Active zone:
presynaptic vesicle release sites

Postsynaptic density:
site of neurotransmitter receptors

Question 4

Explain the mechanics of synaptic transmission.

Answer 4

neurotransmitters are synthesized and stored
as AP moves down the presynaptic terminal
depolarizes- open voltage-gated Ca2+ channels
influx of Ca2+
Ca2+ causes vesicles to bind to the presynaptic membrane
Released into synaptic cleft- exocytosis
Binds to receptor molecules on post
opens or closes channels
Postsynaptic currents cause an excitatory or inhibitory postsynaptic potential.
The retrieval of vesicles from plasma membrane

Question 5

Describe vesicle loading.

Answer 5

Active hydrogen pump
Pumps hydrogen into the vesicle
Then exchanger pump exchanges Hydrogen for neurotransmitters

Question 6

What happens to vesicles when ca2+ enters the cells?

Answer 6

Release is quick
the V snares on the vesicle membrane bind to the T snares on the presynaptic terminal membrane

Question 7

Explain how Botox works.

Answer 7

It prevents neurotransmission
destroys members of the snare needed for exocytosis
Paralysis as no Ach is released

Question 8

Describe the levels of exocytosis in the neuromuscular junction and CNS synapses.

Answer 8

NJ- Ach more, huge EPSP
CNS- glutamate- less, low EPSP

Question 9

Describe the different neurotransmitter receptors.

Answer 9

Direct gating/ Inotropic:
Binds directly to the channel
faster response from channels

Indirect gating/Metabotropic:
Binds to the receptor that induces a secondary response
slower but allows for signal amplification

Question 10

Describe neurotransmitter reuptake.

Answer 10

ACh is broken down in the synaptic cleft by AChE, into choline and acetic acid
thus is then taken up by transporters and repackaged in vesicles.

Question 11

What inhibits AChE?

Answer 11

Organophosphate poisoning

Question 12

Explain presynaptic inhibition.

Answer 12

Action potential stimulates the influx of Ca2+ on an axon terminal.
however, another nerve can release a substance, for instance, GABA, which can inhibit the influx of calcium on the mutual nerve
hence the mutual nerve has less Ca2+ as a result fewer neurotransmitters are released.

Question 13

Which substance amplifies the influx of calcium?

Answer 13

serotonin

Question 14

What are the outcomes of a chemical synapse?

Answer 14

depolarization at excitatory synapses (an excitatory postsynaptic potential EPSP)
stabilization
hyperpolarization at inhibitory synapses (an IPSP).

Question 15

Explain the Ionic current in terms of EPSPs.

Answer 15

There would be an inward movement of Na+ into the axon.
as a result, there is a negative outward current
this is the same as a positive inward current
as a result depolarization

Question 16

Explain the Ionic current in terms of IPSP.

Answer 16

a result of the influx of negative ions such as cl-
this causes a positive outward current= a negative inward current
this leads to hyperpolarization

Question 17

What is synaptic integration?

Answer 17

The process by which synaptic inputs combine to generate neural output.

Question 18

At which site does the action potential initiate on a nerve?

Answer 18

Axon hillock

Question 19

Explain why the spatial location of a synapse is important for its effect on the output of a neuron.

Answer 19

Due to the length constant and time constant, there is a decrease in depolarization as a function of distance.
Hence, there is a higher velocity in the dendrites than in the cell body.
Also in order for the action potential to be produced the axon hillock must be depolarized to the threshold, via voltage-gated Na channels.
As a result inputs closer to the axon hillock will have a greater influence than inputs far away on the dendritic tree.

Question 20

Describe when an Epileptic Seizure would occur.

Answer 20

Imbalance between EXCITATION and inhibition of neurons