Chapter 4.9-4.18 Neural Conduction And Synaptic Transmission

Question 1

What are axodendritic synapses?

Answer 1

Synapses of axon terminal buttons on dendrites

Question 2

Many axodendritic synapses terminate at what?

Answer 2

Dendritic spines

Question 3

What are dendritic spines?

Answer 3

Nodules of various shapes that are located on the surfaces of many dendrites

Question 4

What are axosomatic synapses?

Answer 4

Synapses of axon terminal buttons on somas (cell bodies)

Question 5

What are dendrodentric synapses?

Answer 5

Capable of transmission in either direction

Question 6

Why are axoaxonic synapses important?

Answer 6

Important because they can mediate presynaptic facilitation and inhibition
ie can selectively facilitate or inhibit the effects of that button on the postsynaptic neuron

Question 7

What are directed synapses?

Answer 7

Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity

Question 8

What are nondirected synapses?

Answer 8

Synapses at which the site of release is at some distance from the site of reception

• neurotransmitter molecules are released from a series of varicosities (bulges/swellings) along the axon and the branches are widely dispersed to surrounding targets
• often called string-of-Beads synapses due to their appearance

Question 9

There are two basic categories of neurotransmitter molecules: _____ and _____

Answer 9

Small neurotransmitters: several types

Large neurotransmitters: all neuropeptides

Question 10

What are neuropeptides? Where are they assembled? How do they get to terminal buttons?

Answer 10

Large neurotransmitters.

• short amino acid chains composed of between 3 and 36 amino acids ie short proteins
• assembled in the cytoplasm of the cell body on ribosomes - then packaged in vesicles by the Golgi complex and transported by microtubules to the terminal buttons at 40 cm a day

Question 11

where are small molecule neurotransmitters synthesized and how do they get to the terminal button?

Answer 11

Synthesized in the cytoplasm OF the Terminal Button

• packaged in synaptic vesicles by th button’s Golgi complex
• vesicles are stored in clusters next presynaptic membrane

Question 12

What is coexistence?

Answer 12

Term given to Neurons that contain two neurotransmitters

Question 13

What is exocytosis in reference to neurons?

Answer 13

The process of neurotransmitter release

Question 14

what are voltag activated calcium channels?

Answer 14

Channels in the presynaptic membrane

• when stimulated by action potentials, these channels open, and Ca2+ ions enter the button
• entry of Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane and empty their contents into the synaptic cleft

Question 15

How does exocytosis of small-molecule neurotransmitters differ from exocytosis of neuropeptides?

Answer 15

• Small-molecule neurotransmitters are typically released in a pulse each time n action potential triggers a momentary influx of Ca2+ through the presynaptic membrane
• Neuropeptides are released gradually in response to general increases in the even of intracellular Ca2+ ions

Question 16

What are receptors?

Answer 16

Proteins in postsynaptic membrane that contains binding sites for only particular neurotransmitters

Question 17

What are the patterns of release and the function of small-molecule neurotransmitters

Answer 17

Small molecule neurotransmitters
-released into directed synapses
-activate either ionotropic receptors or metabotropic receptors that act directly on ion channels
Function:
-transmission of rapid, brief excitatory or inhibitory signals to adjacent cells

Question 18

What are the patterns of release and the functions of neuropeptides?

Answer 18

Neuropeptides
-released diffusers and virtually all bind to metabotropic receptors that act through second messengers
Function:
-transmission of slow, diffuse, long lasting signals

Question 19

What is a ligand?

Answer 19

Any molecule that binds to another

Question 20

What are receptor subtypes?

Answer 20

Different types of receptors to which a particular neurotransmitter can bind
-typically located in different areas of the brain and respond to the neurotransmitter in different ways

Question 21

The influence the binding of a neurotransmitter to a receptor has on a postsynaptic neuron is dependent on what?

Answer 21

Depends on whether the receptor is ionotropic or metabotropic

Question 22

What are ionotropic receptors?

Answer 22

Associated with ligand-activated ion channels
-when a neurotransmitter binds, the associated ion channel opens or closes immediately - inducing an immediate postsynaptic potential

Question 23

What s a metabotropic receptor?

Answer 23

Associated with signal proteins and G proteins

• more prevalent hat ionotropic receptors
• effects are slow and long-lasting, more diffuse and more varied in comparison to ionotropic receptors

Question 24

When a neurotransmitter binds to a metabotropic receptor, what happens to the G protein?

Answer 24

A subunit of the G protein breaks away

Question 25

After the subunit of the G protein breaks away, there are two possible occurrences; what are they?

Answer 25

1. Subunit moves along inside surface of membrane and binds to an ion channel - induces an EPSP or IPSP
2. May trigger the synthesis of a chemical called the second-messenger.
   - second messenger diffuses through the cytoplasm and may influence the activity of the neuron in a variety of ways

Question 26

What are autoreceptors?

Answer 26

Metabotropic receptor that have two unconventional characteristics:

1. They bind to their neuron’s own neurotransmitter molecules
2. They are located on the presynaptic (rather than postsynaptic) membrane

Question 27

What is the usual function of autoreceptors?

Answer 27

To monitor the number of neurotransmitter molecules in the synapse - to reduce subsequent release when the levels are high and increases release when low

Question 28

What two mechanisms are in place to terminate synaptic messages? What would happen if they weren’t there?

Answer 28

1. Reuptake by transporters
2. Enzymatic degradation

If nothing happened, neurotransmitter molecule would remain active and clog that channel of communication

Question 29

What is reuptake?

Answer 29

Deactivation mechanism
-The majority of neurotransmitters, once released, are almost immediately drawn back into the presynaptic buttons by transporter mechanisms

Question 30

What is enzymatic degradation?

Answer 30

Deactivation mechanism

- eurotransmitters in the synapse are degraded by enzymes

Question 31

What are gap junctions?

Answer 31

Narrow spaces between adjacent cells that are bridged by fine, tubular, cytoplasm-filled protein channels called connexins
-connect the cytoplasm of two adjacent cells - allowing electrical signals and small molecules (2ndary messengers) to pass from be cell to the next

Question 32

What is tripartite synapse?

Answer 32

The hypothesis that each astrocyte may coordinate the activity of synapses in its domain

Question 33

What are four classes of small molecule neurotransmitters?

Answer 33

1. Amino acids (amino acid neurotransmitters)
2. Monoamines (monoamineneurotransmitters)
3. Acetylcholine
4. Unconventional neurotransmitters

Question 34

How many classes of large molecule neurotransmitters are there?

Answer 34

1: the Neuropeptides