Chapter 3: The Synapse

Question 1

This is a unique junction that mediates the transfer of information from one neuron to another or from one neuron to an effector cell.

Answer 1

SYNAPSE

Question 2

Most synapses occur between axonal endings of one neuron and the dendrites or the cell bodies of other neurons. This is called:

Answer 2

axodendritic or axosomatic synapse

Question 3

The neuron conducting impulses toward the synapse is called:

Answer 3

presynaptic neuron

Question 4

The neuron that transmits the electrical signal away from the synapse is called:

Answer 4

postsynaptic neuron.

Question 5

True regarding Synapse. Except:

1. The postsynaptic neuron sends the information and the presynaptic neuron is the information recipient.
2. Most neurons function as both presynaptic and postsynaptic neurons, receiving information from one neuron and sending it to another neuron.
3. Neurons have between 1000 and 10 000 axonal terminals.
4. The postsynaptic cell may be either another neuron or an effector cell.

Answer 5

Except: number 1

Correct: 1. The presynaptic neuron sends the information and the postsynaptic neuron is the information recipient.

Question 6

Synapses between neurons and muscle cells are called:

Answer 6

neuromuscular junctions

Question 7

Synapses that between neurons and gland cells are called:

Answer 7

neuroglandular junctions

Question 8

___________ - Bridged junctions that correspond to the gap junctions found between certain other body cells. They contain protein channels that interconnect the cytoplasm of adjacent neurons and allow the current carrying ions to flow directly from one neuron to the next.

Answer 8

Electrical Synapses

Question 9

Communication may be ___________ or ___________ depending on the nature of the synapses.

Answer 9

uni-directional

bi-directional

Question 10

Electrical synapses are abundant in certain non-nervous tissues, such as ________ and _________.

Answer 10

cardiac

smooth muscles

Question 11

Specialized for release and reception of chemical neurotransmitters.

Answer 11

Chemical Synapses

Question 12

Typical chemical synapse has two parts:

Answer 12

1. Axonal terminal of the presynaptic neuron.
2. A receptor region on the membrane of a dendrite or the cell body of the postsynaptic neuron which have (several types of) neurotransmitter receptors.

Question 13

___________ - they are tiny membrane bound sacs, found in axonal terminals of the presynaptic neuron.

Answer 13

Synaptic vesicles

Question 14

___________ - they are fluid filled spaces, that separate pre and postsynaptic neurons.

Answer 14

Synaptic cleft

Question 15

______________________ is a chemical event that depends on the release, diffusion and receptor binding of neurotransmitter molecules and results in uni-directional communication between neurons.

Answer 15

The transmission of signals across chemical synapses

Question 16

Chemical synapses convert the ___________ into chemical signals (neurotransmitters) that travel across the ___________ to the postsynaptic cells, where they are converted back into electrical signals.

Answer 16

electrical signals

synapse

Question 17

There are a series of events that trigger neurotransmitter release. Once released the neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic membrane, causing changes in the postsynaptic membrane permeability. This process is called:

Answer 17

Information Transfer Across Chemical Synapses

Question 18

Series of events that trigger neurotransmitter release:

Answer 18

1. Calcium gates open in the presynaptic axonal terminal.
2. Neurotransmitter is released by exocytosis.
3. Neurotransmitters bind to postsynaptic receptors.
4. Ion channels open in the postsynaptic membrane.

Question 19

They are substances such as norepinephrine, acetylcholine and dopamine that are released when the terminal end of an axon is stimulated.

Answer 19

Neurotransmitters

Question 20

All statements are TRUE. Except:

1. The neurotransmitter then travels across the dendrite to another neuron or an effector cell to either stimulate or inhibit the effector.
2. There are over 50 different chemicals that are either known neurotransmitters or are candidates.
3. Neurotransmitters are classified as being present in the pre-synaptic terminal axon and are released when appropriately stimulated.

Answer 20

Except: 1

Question 21

Some neurotransmitters can be synthesized in different areas of the nervous system. This areas are:

Answer 21

1) cell body of the neuron
2) Pre-synaptic terminal

Question 22

What are the mechanisms in termination of neurotransmitter Effects?

Answer 22

1. Degradation by enzymes
2. Removal from the synapse by re-uptake into the presynaptic terminal where it is stored or destroyed by enzymes.
3. Diffusion of the neurotransmitter away from the synapse.

Question 23

Determine if the statements are True or False:

Neural transmission across a chemical synapse is slow and reflects the time required for neurotransmitter release, diffusion across the synapse and binding to receptors. This synaptic delay lasts 0.3 - 0.5 ms and is the rate-limiting step of neurotransmission; therefore transmission along short neural pathways occurs rapidly. Transmission along multi-synaptic pathways occurs more slowly.

Answer 23

True

Question 24

Classification of Neurotransmitters:

Answer 24

1. Acetylcholine
2. Biogenic Amines
3. Amino Acids
4. Peptides

Question 25

\_\_\_\_\_\_\_\_\_\_\_ - Types consist of dopamine, norepinephrine and serotonin. They are broadly distributed in the brain where they play a role in emotional behaviour and in the regulation of the biological clock.

Answer 25

Biogenic Amines

Question 26

\_\_\_\_\_\_\_\_\_\_\_\_ - This was the first neurotransmitter to be identified. It is the best understood because it is released at the neuromuscular junction. It is synthesized and enclosed in synaptic vesicles within axonal terminals.

Answer 26

Acetylcholine

Question 27

\_\_\_\_\_\_\_\_\_\_ - They are difficult to prove as neurotransmitters. They occur in all cells of the body and are important in many biochemical reactions. neurotransmitters have only been found in the CNS.

Answer 27

Amino Acids

Question 28

Neuropeptides include a broad spectrum of molecules with diverse effects. Neuropeptide called substance P is an important mediator of pain signals.

Answer 28

Peptides

Question 29

\_\_\_\_\_\_\_\_\_ - act as a natural euphoric and decrease our perception of pain, under certain stressful conditions.

Answer 29

Endorphins

Question 30

Receptors on postsynaptic membranes are specialized to open ion channels which convert chemical signals into electrical signals. These chemically gated channels are not as sensitive to changes in membrane potential, unlike voltage-gated ion channels.

Answer 30

Postsynaptic potentials and synaptic integration

Question 31

Two types of chemical synapses

Answer 31

1. Excitatory 2. Inhibitory

Question 32

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ , neurotransmitter binding causes depolarization of the postsynaptic membrane. Here only one type of channel opens allowing Na+ ions to diffuse through the membrane.

Answer 32

Excitatory Synapses

Question 33

If enough neurotransmitters bind, depolarization of the postsynaptic membrane can successfully cause local graded depolarization events called ___________ , which occur at excitatory postsynaptic membranes.

Answer 33

Excitatory Postsynaptic Potentials (EPSP)

Question 34

Each EPSP lasts a few milli-seconds then membrane returns to RMP; therefore, the function of EPSP is to help trigger an __________ at the axon hillock.

Answer 34

action potential

Question 35

All Statements are True regarding excitatory postsynaptic potentials (EPSP). Except: 1. If currents reaching the axon hillock are strong enough to depolarize the axon to threshold, axonal voltage gated channels open and an action potential, is generated. 2. A single EPSP cannot induce an action potential in the postsynaptic neuron. If thousands of excitatory axonal terminals fire on the same postsynaptic membrane, the probability of reaching threshold depolarization increases. 3. EPSPs added together (or summated) can influence the activity of a presynaptic neuron.

Answer 35

Except: number 3 ## Footnote Correct: EPSPs added together (or summated) can influence the activity of a postsynaptic neuron.

Question 36

Can result from the opening of Cl- or K+ channels. The ionic flow in either case, will cause the inside of the postsynaptic cell to hyperpolarize. Hyperpolarizing postsynaptic potential is called an __________________ .

Answer 36

inhibitory postsynaptic potential (IPSP)

Question 37

\_\_\_\_\_\_\_\_\_\_\_\_\_ occurs when the release of excitatory neurotransmitters by one neuron, is inhibited by the activity of another neuron, via an axo-axonic synapse.

Answer 37

Presynaptic inhibition

Question 38

Integration of input from synapses is called _________ and occurs at the trigger zone.

Answer 38

summation

Question 39

There are two types of summations:

Answer 39

Spatial summation Temporal summation

Question 40

\_\_\_\_\_\_\_\_\_\_\_\_\_\_ - results from a build up of neurotransmitters released by a single presynaptic end bulb, two or more times in rapid succession.

Answer 40

Temporal summation

Question 41

\_\_\_\_\_\_\_\_\_\_\_ - results from build up of neurotransmitters released simultaneous by several presynaptic end bulbs.

Answer 41

Spatial summation

Question 42

TRUE or FALSE Spatial and temporal summations are usually acting together to influence the chance of a nerve impulse occurring. The sum of all the excitatory and inhibitory effects at any given time determines the effect on the postsynaptic neuron.

Answer 42

TRUE