Chapter 4.9-4.18 Neural Conduction And Synaptic Transmission Flashcards
What are axodendritic synapses?
Synapses of axon terminal buttons on dendrites
Many axodendritic synapses terminate at what?
Dendritic spines
What are dendritic spines?
Nodules of various shapes that are located on the surfaces of many dendrites
What are axosomatic synapses?
Synapses of axon terminal buttons on somas (cell bodies)
What are dendrodentric synapses?
Capable of transmission in either direction
Why are axoaxonic synapses important?
Important because they can mediate presynaptic facilitation and inhibition
ie can selectively facilitate or inhibit the effects of that button on the postsynaptic neuron
What are directed synapses?
Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity
What are nondirected synapses?
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
There are two basic categories of neurotransmitter molecules: _____ and _____
Small neurotransmitters: several types
Large neurotransmitters: all neuropeptides
What are neuropeptides? Where are they assembled? How do they get to terminal buttons?
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
where are small molecule neurotransmitters synthesized and how do they get to the terminal button?
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
What is coexistence?
Term given to Neurons that contain two neurotransmitters
What is exocytosis in reference to neurons?
The process of neurotransmitter release
what are voltag activated calcium channels?
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
How does exocytosis of small-molecule neurotransmitters differ from exocytosis of neuropeptides?
- 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
What are receptors?
Proteins in postsynaptic membrane that contains binding sites for only particular neurotransmitters
What are the patterns of release and the function of small-molecule neurotransmitters
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
What are the patterns of release and the functions of neuropeptides?
Neuropeptides
-released diffusers and virtually all bind to metabotropic receptors that act through second messengers
Function:
-transmission of slow, diffuse, long lasting signals
What is a ligand?
Any molecule that binds to another
What are receptor subtypes?
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
The influence the binding of a neurotransmitter to a receptor has on a postsynaptic neuron is dependent on what?
Depends on whether the receptor is ionotropic or metabotropic
What are ionotropic receptors?
Associated with ligand-activated ion channels
-when a neurotransmitter binds, the associated ion channel opens or closes immediately - inducing an immediate postsynaptic potential
What s a metabotropic receptor?
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
When a neurotransmitter binds to a metabotropic receptor, what happens to the G protein?
A subunit of the G protein breaks away
After the subunit of the G protein breaks away, there are two possible occurrences; what are they?
- Subunit moves along inside surface of membrane and binds to an ion channel - induces an EPSP or IPSP
- 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
What are autoreceptors?
Metabotropic receptor that have two unconventional characteristics:
- They bind to their neuron’s own neurotransmitter molecules
- They are located on the presynaptic (rather than postsynaptic) membrane
What is the usual function of autoreceptors?
To monitor the number of neurotransmitter molecules in the synapse - to reduce subsequent release when the levels are high and increases release when low
What two mechanisms are in place to terminate synaptic messages? What would happen if they weren’t there?
- Reuptake by transporters
- Enzymatic degradation
If nothing happened, neurotransmitter molecule would remain active and clog that channel of communication
What is reuptake?
Deactivation mechanism
-The majority of neurotransmitters, once released, are almost immediately drawn back into the presynaptic buttons by transporter mechanisms
What is enzymatic degradation?
Deactivation mechanism
- eurotransmitters in the synapse are degraded by enzymes
What are gap junctions?
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
What is tripartite synapse?
The hypothesis that each astrocyte may coordinate the activity of synapses in its domain
What are four classes of small molecule neurotransmitters?
- Amino acids (amino acid neurotransmitters)
- Monoamines (monoamineneurotransmitters)
- Acetylcholine
- Unconventional neurotransmitters
How many classes of large molecule neurotransmitters are there?
1: the Neuropeptides
