C11 15-19

Question 1

Synapse

Answer 1

A junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell .

Question 2

Axodendritic

Answer 2

synapse between axon endings of a neuron to dendrites of another

Question 3

Axosomatic

Answer 3

synapse between axon endings of a neuron to soma of another

Question 4

Presynaptic Cells

Answer 4

Neuron conducting impulses towards the synapse

Question 5

Postsynaptic Cells

Answer 5

Neuron conducting impulses away from the synapse

Question 6

Synaptic cleft

Answer 6

Fluid filled space that separates presynaptic/postsynaptic cells (chemical synapses)

Question 7

Chemical synapses

Answer 7

Structure: synaptic cleft/vesicles, ps receptor,
Synaptic delay .3 .5 ms
Common
Unidirectional
Size varies - amount of neurotransmitters
Neurotransmitters

Question 8

How are neurotransmitter effects terminated?

Answer 8

Degradation by enzymes associated with the postsynaptic cell membrane or in the synaptic cleft, Reuptake by astrocytes or the presynaptic terminal, diffusion away from the synapse

Question 9

Synaptic delay

Answer 9

The time required for a neurotransmitter to be released, diffuse across the synaptic cleft and bind to receptors. It is the slowest step of neural transmission.

Question 10

Postsynaptic potential

Answer 10

A graded potential in the postsynaptic neuron (caused by the presynaptic neuron releasing a neurotransmitter that crosses the synaptic cleft and binds to receptors on the postynaptic neuron)

Question 11

EPSP
What does this stand for?
What is it?
How does it happen?

Answer 11

• Excitatory Postsynaptic Potential
• Local GP depolarization event that occurs at excitatory postsynaptic membranes and function to help trigger an AP distally at the axon hillock.
• excitatory neurotransmitter opens Na+ channels (actually cation which allow flow of both K+ and Na+, but Na+ gradient is steeper) and depolarizes the membrane.

Question 12

IPSP
What does this stand for?
What is it?
How does it happen?

Answer 12

• Inhibitory Postsynaptic Potential
• GP that reduces a postsynaptic membranes ability to generate an AP.
• inhibitory neurotransmitter opens either K+ or Cl- channels and hyperpolarizes the membrane.

Question 13

6 steps in chemical synapse

Answer 13

1. AP arrives at axon terminal 2. Volt-gated Ca2+ channels open, Ca2+ enters axon terminal 3. Ca2+ entry causes syanaptic vesicles to release neurotranmitters by exocytosis 4. Neurotransmitter diffuses across SC and binds to specific receptors on the postsynaptic membrane. 5. binding of neurotransmitters opens ion channels creating GP. 6. Neurotransmitter effects are terminated.

Question 14

What step? Action potential arrives at axon terminal

Answer 14

1 Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal

Question 15

What step? Voltage gated Ca2+ channels open and Ca2+ enters the axon terminal

Answer 15

2 Depolarization of the membrane by the action potential opens not only Na+ channels but voltage gated Ca2+ as well. During the brief time the Ca2+ are open, Ca2+ floods down its electrochemical gradient from the extracellular fluid into the terminal.

Question 16

What step? Ca2+ entry causes synaptic vesicles to release neurotransmitters by exocytosis

Answer 16

3 The surge of Ca2+ into the axon terminal acts as a messenger. A Ca2+ sensing protein binds Ca2+ and interacts with SNARE proteins that control membrane fusion. As a result, synaptic vessels fuse with the axon membrane and empty their contents by exocytosis. Ca2+ is then removed from the terminal (taken up by mitochondria or ejected by Ca2+ pump)

Question 17

What step? Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.

Answer 17

4

Question 18

What step? Binding neurotransmitter opens ion channels, creating graded potentials.

Answer 18

5 The receptor changes the 3D shape of the protein channel and opens it. Often Ligand channels. May also be inhibitory.

Question 19

What step? Neurotransmitter effects are terminated.

Answer 19

6 As long as the neurotransmitter is bound to the receptor, it continues to affect the membrane permeability. It must be terminated (reuptake/degradation/diffusion)

Question 20

19. Describe how synaptic events are integrated..

Answer 20

Events are integrated by temporal and spatial summation of both IPSPs and EPSPs. The axon hillock keeps a tally of both - their potential reflects the sum of incoming neural info.

Question 21

19. Describe how synaptic events are modified.

Answer 21

By synaptic potentiation, presynaptic inhibition and neuromodulation.

• -Synaptic potentiation increases the excitability of the postsynaptic neuron
• -presynaptic inhibition decreases the excitatory stimulation of the postsynaptic neuron
• -Neuromodulation affects the strength of synaptic transmission.

Question 22

Synaptic potentiation

Answer 22

• A learning process that increases the efficiency of neurotransmission along a particular pathway.
• Repeated or continuous use of a synapse enhances the presynaptic neuron to produce larger than expected EPSPs.
• i.e. Signals being sent repeatedly along a circuit, circuit lead to the circuit being modified to be more efficient/useful (more receptors, more axon terminals, more neurotransmitters), changes in neuron.

Question 23

Presynaptic Inhibition

Answer 23

Occurs when the release of excitatory neurotransmitter by one neuron is inhibited the activity of another neuron.
The result is that less neurotransmitter is released and bound forming smaller EPSPs.

Question 24

What are neuromodulators, how does neuromodulation work?

Answer 24

• -Neuromodulators are chemical messengers released by a neuron that do not directly cause EPSPs or IPSPs, but instead affect the strength of synaptic transmission.
• -Neuromods may act presynaptically to influence synthesis/release/degradation or reuptake of a neurotransmitter OR they may act postsynaptically by altering the sensitivity of the postsynaptic membrane to neurotransmitters.

Question 25

Ca2+ plays a role in?

Answer 25

Nerve conduction, blood clotting, muscle contraction, hormonal mechanism, co-factor in enzymatic reactions

Question 26

Electrical synapse

Answer 26

Gap junctions, fast, rare, bidirectional, same signal size, ions (NA+, K+)