Structure and Function - Week 4 Neurotransmission Flashcards
What is neurotransmission? (2)
Communication within the nervous system and of the nervous system with other systems
Describe synaptic transmission (3)
AP arrives at pre synaptic terminal
Triggers entry of Ca2+ through voltage gated Ca2+ channel
Causes synaptic vesicles to release neurotransmitters across synaptic cleft
Neurotransmitter diffuse and bind to post synaptic receptors causing a post synaptic response
What could the post synaptic responses be? (4)
Depolarization
Hyperpolarization
Changes to biochemical cascade
Change to gene expression
What are the two types of transmission? (2)
Transmission can be extra-synaptic and non-synaptic too (volume transmission).
Describe electrical synapse (3)
Allow physical connection to exist between neurons through gap junctions
Gap junctions - made of connexin subunits (called connexon channels) - allow ions and other substances to transfer between 2 cells
Describe characteristics of chemical synapses (4)
Slow, has gain, diverse postsynaptic response, unidirectional release
Describe characteristics of electrical synapses (4)
Fast, lack gain, limited postsynaptic response, mostly bidirectional
Give examples of how could you assess electrical coupling between two neurons? (2)
Dual electrode recording
Cell traces
What are the 3 components of chemical synapses (3)
Presynaptic terminal
Synaptic cleft
Postsynaptic terminal
What is a bouton? (2)
Another name for axon terminals
Terminal enlargements on the axon where it forms a synapse
What are the different synapse locations (4)
Axon to soma
Axon to dendrite / spine
Axon to axon
Dendrite to dendrite
Describe axo-dendritic synapse (3)
Axon to dendritic shaft or spine
Spines are protrusions that increase surface area
Often excitatory
Describe Axo-Somatic synapse (3)
Axon to soma (cell body)
If synapse is at the axon hillock, large influence on firing
Often inhibitory
Describe Axo-Axonic synapse (3)
Modulatory - can be excitatory or inhibitory
Increased calcium current in presynaptic terminal = increase in transmitter release
Decreased calcium current in presynaptic terminal = decrease in transmitter release
What are the different types of vesicles? (2)
Small clear core vesicles
Large dense core vesicles
How do non-peptide neurotransmitters get inside synaptic vesicles at axon terminal? (1)
Use transporters - vesicle transporters
Describe how vesicle transporters work? (3)
H+ gradient is established by a V-type H+-ATPase. 2H+ exchanged for the positively charged neurotransmitter.
What are the methods of calcium clearance? (3)
Buffering
Removal
Active transport
Describe buffering as a method of calcium clearance (2)
Buffering by cytoplasmic Ca2+ binding proteins (Ca-B)
Describe buffering as a method of calcium clearance (2)
Removal from the presynaptic terminal (e.g. Na-Ca exchangers, Ca-ATPases).
Describe active transport as a method of calcium clearance (2)
Active transport to endoplasmic reticulum via Ca-ATPase pump.
Describe vesicle recycling (2)
Synaptic vesicles fuse to early endosomes (an organelle)
This is where new vesicles bud from after processing (e.g. clathrin coat)
Look at lecture
Describe dense core vesicles (2)
Dense core vesicles often released from extra-synaptic sites and slowly diffuse to their target
What can happen to neurotransmitters in synaptic cleft? (4)
Be taken back up by a neuron
Be taken up by a glial cell
Be broken down by an enzyme
Diffuse away from the cleft
Describe Botulinum Toxin (4)
Primarily affects neuromuscular junction, causing paralysis
Use in cosmetics and chronic pain
Cleaves SNARE proteins so SNARE complex does not form and neurotransmitter is not released at neuromuscular junction
Lead to muscle paralysis
Describe Tetatnus Toxin (3)
Primarily affects inhibitory interneurons of the spinal cord (GABA, glycine).
Loss of inhibition to motor neurons = muscle spasms (painful, constant contraction of muscles).
Describe post synaptic density (2)
Proteins for anchoring and trafficking neurotransmitter receptors, just below postsynaptic membrane
Describe the classifications of synapses (2)
Asymmetric (type I) synapses
Symmetric (type II) synapses
Describe Asymmetric (type I) synapses (2)
Thicker postsynaptic density (PSD). Typically excitatory
Describe Symmetric (type II) synapses (2)
PSD similar width to presynaptic component
Typically inhibitory
What are the two neurotransmitter receptors (2)
Ionotropic
Metabotropic
Describe metabotropic receptors (2)
May interact with G-protein-gated ion channels AND/OR enzymes which generate second messengers
What are EPSPs? (2)
Excitatory postsynaptic potential
A transient depolarisation
Net influx of positive ions depolarise and bring closer to firing threshold
What are IPSPs? (2)
Net influx of negative ions hyperpolarise and move further from firing threshold.
IPSP = inhibitory postsynaptic potential. A transient hyperpolarisation.
Describe PSPs (3)
Graded
Decay over distance
What is integration? (2)
Integration (decision making) occurs at the axon – to fire or not to fire.
What is temporal summation? (2)
Temporal summation as a result of one input receiving multiple stimuli close in time.
A single neuron can therefore exhibit temporal and spatial summation at the same time
What are neural circuits? (4)
Divergence
Convergence
Serial Processing
Parallel processing
Describe divergence (2)
Look at week 4 notes for structure and function
