Chapter 12- Synaptic transmission

Question 1

What is a synapse?

Answer 1

Where electrical impulses are transferred from one neuron to another.

Question 2

Generally, where does a synapse occur between?

Answer 2

Between the axon of neuron A and the dendrite of neuron B.

Question 3

What are electrical synapses?

Answer 3

A form of direct cell-cell to electrical coupling.

Question 4

Do ions pass directly through gap junctions?

Answer 4

Yes

Question 5

What are the pros and cons of electrical synapses?

Answer 5

Pro- extremely fast signal transmission. Ideal for defensive reflexes.

Con- Inflexible

Question 6

What does the chemical synapse contain?

Answer 6

1- Synaptic cleft

2- Synaptic end bulb

3- Voltage gated calcium channels

4- Ionotropic receptors

5- Neurotransmitter molecules

6- Synaptic vesicles

7- Mitochondria

Question 7

What is the synaptic cleft?

Answer 7

The gap between the pre and post synaptic neuron.

Question 8

Where is the synaptic end bulb found?

Answer 8

Found towards the end of the axon which has a big surface area.

Question 9

What is the presynaptic end bulb studded with?

Answer 9

Calcium channels

Question 10

What is the postsynaptic neuron studded with?

Answer 10

Ion channels gated by the binding of a specific neurotransmitter.

Question 11

What are neurotransmitter molecules?

Answer 11

Chemical messengers

Question 12

What do synaptic vesicles do?

Answer 12

Pack neurotransmitters into vesicles

Question 13

What does the mitochondria do?

Answer 13

Regulate voltage gated calcium channels and provide ATP for vesicle loading and transport.

Question 14

What are the key stages of chemical neurotransmission? (Good luck)

Answer 14

1- Action potentials arrives at axon terminal

2- Voltage- gated calcium channels in the synaptic end bulb open to allow ions to enter.

3- Calcium enters the presynaptic cell- calcium ions travel down their electrochemical gradient from the extracellular fluid into the bulb’s cytoplasm.

4- Vesicles containing neurotransmitter are transported to the synapse by motor proteins (kinesin).

5- The vesicle docks with the release site on the plasma membrane and undergoes exocytosis

6- Calcium is then quickly removed by the mitochondria by active ejection by pumps in the membrane.

7- Neurotransmitter diffuses across the synaptic cleft and binds to receptors.

8- Binding of neurotransmitter opens ion channels, creating graded potentials.

9- Removal of neurotransmitter- by terminating the neurotransmitter, it allows the receptor to return to its resting state. This occurs through a combination of:

1- Reuptake- by astrocytes or the presynaptic neuron

2- Degradation- by enzymes in the synaptic cleft

3- Diffusion- away from the synapse

Question 15

What is the difference between graded potentials and action potentials?

Answer 15

Graded potentials are the variable strength signals that can be transmitted over short distances whereas action potentials are large depolarizations that can be transmitted over long distances.

Question 16

Each muscle fibre receives input from how many neurons?

Answer 16

One neuron

Question 17

At the neuromuscular junction, how do the sodium channels open?

Answer 17

Acetylcholine (Ach) binds to the receptors on the sarcolemma

Question 18

What does the opening of sodium channels at the neuromuscular junction lead to? If the threshold is reached, what happens?

Answer 18

This leads to the influx of sodium ions and an end plate potential (EPP)(same as graded potential).

If the threshold is reached, an action potential is triggered.

Question 19

Explain what a excitatory post synaptic potential (EPSP’s) is

Answer 19

Some gates allow sodium and potassium to flow.

These don’t cancel out as the concentration gradient for sodium is greater.

The net result is a small, short-term increase in the number of positively charged ions inside the post synaptic neuron.

Question 20

Explain what an inhibitory post synaptic potential (IPSP’s) is?

Answer 20

Other channels either allow potassium to selectively leave the cell or chlorine to selectively enter the cell.

The net result is a small, short term decrease in the number of positively charged ions inside the post synaptic neuron.

Question 21

A single EPSP is unlikely to depolarise the cell enough to trigger an AP. So how would an AP be triggered?

Answer 21

1- If multiple EPSP’s are triggered closely in time (temporal summation)

2- If multiple EPSP’s are triggered in nearby locations on the postsynaptic membrane (spatial summation)

Question 22

Acetylcholine can either be excitatory or inhibitory. There are two types of acetylcholine:

Answer 22

1- Nicotinic- occur at neuromuscular junction and open sodium channels which means they are therefore excitatory.

2- Muscarinic- occur in the heart and open potassium and chlorine channels which means they therefore inhibitory.

Question 23

What causes Parkinson’s disease?

Answer 23

Defects in synaptic transmission

Question 24

What are agonists and antagonists?

Answer 24

Agonists are drugs that enhance the effectiveness of a receptor

Antagonists supress specific receptors