Synapse Flashcards
Synapse
Where the axon terminal of one neuron touches another neuron and signals it
Presynaptic neuron (Pre-sN)
One neuron that does the signaling
Presynaptic neurons signals postsynaptic neuron when AP reaches the end of presynaptic neurons axon
Postsynaptic neuron (Post-sN)
neuron that gets signaled
* Presynaptic neurons signals postsynaptic neuron when AP reaches the end of presynaptic neurons axon
* That signal changes the membrane potential in post-synaptic neuron
Electrical Synapse
Gap junctions connecting neurons
Ions flow from one neuron to the next
Depolarizing postsynaptic neurons
Simpler & faster - only depolarize
Chemical Synapses
Pre synaptic neuron that releases chemicals, makes ion channels open or close on postsynaptic neurons
Much more common and complicated response
* Depolarize or hyperpolarize postsynaptic
* The response can be easily modified
Synaptic Cleft
space between pre + postsynaptic neurons
a type of chemical synapse
Neurotransmitters
Chemicals released by the pre to signal post
Released in response to AP on pre-s axon
a type of chemical synapse
Neurotransmitter Receptors
- Protein receptors for neurotransmitters on Post-sN
- Response to neurotransmitters open/close ion channels
- Changes the membrane potential of Post-sN
- Process is slow relative to AP
The more synapses in the pathway, the slower it is
a type of chemical synapse
Axon terminal
The end of the axon that releases neurotransmitter
Vesicles
Filled with neurotransmitters in the axon terminal - they release neurotransmitters by exocytosis
How do Neurotransmitters + Vesicles work together?
Neurotransmitters are mostly assembled in the soma (body) of neurons - Where the nucleus is
They’re transported down the axon in vesicles → pulled by motor proteins along microtubules in the axon
Neurotransmitter Release Process
- AP travels down the axon + reaches the axon terminal – Depolarizing the axon terminal
- Depolarization opens voltage-gated Ca++ channels – Ca++ flows into cell
- Ca++ activates Ca++ dependant proteins
- Activated proteins make vesicles bind with the membrane + exocytose neurotransmitters
How do neurotransmitters stop signaling PostsN once removed from the synaptic cleft?
3 ways
1. Diffusion: neurotransmitters diffuse out of a cleft
2. Degradation: enzymes in the cleft break down neurotransmitters
3. Reuptake: Pre-sN transports neurotransmitter back into the axon terminal – Can be repackaged in a vesicle or degraded
Postsynaptic Response
neurotransmitter leads to change in membrane potential in Post-sN
Neurotransmitter Receptors
Open & close ion channels - 2 Types
1. Ligand-gated ion channels: reception is an ion channel – Opens when it binds neurotransmitters
2. G-protein Coupled Receptors (GPCR): when they bind a neurotransmitter → activated g-protein – G-protein opens/closes ion channels
Graded potentials in a post synaptic response
- Depolarization or hyperpolarization - Big or small
- AP are all depolarization + all the same size
- More neurotransmitters released → bigger change
How does AP start in post-s neurons?
Changes in the membrane potential at synapse determine if post-s has AP
- Can increase or decrease the probability of an AP
- Depends on the neurotransmitter + its receptor
What causes an Excitatory Post Synaptic Potential (EPSP)?
Increases the chance of AP
Depolarizes membrane by:
- Opening Na+ or Ca++
- Closeing K+ or Cl-
Ions make it more positive in a post synaptic response.
What causes an Inhibitory Post Synaptic Potential (IPSP)?
Decreases chance of AP
Hyperpolarizes membrane:
- Open K+ or Cl-
- Close Na+ or Ca++
Ions make it more negative in a post synaptic response.
Axon Hillock
Spot at the beginning of an axon, right next to the soma
AP Activation Threshold
The minimum depolarization needed to start AP - open voltage gated Na+ channels
If neuron reaches threshold at AP Hillock → AP fires = AP starts + travels down the axon
Spacial + Temporal Summation
Ions flow through cell to axon hillock → all add up to effect membrane potential → if membrane potential reaching threshold → neuron fires AP
Each neuron makes a little calculation about whether to fire AP - based on inputs from other neurons at synapses
Acetyle Choline (ACh)
Made from AcetylCoA (important in cellular respiration) + choline
PNS
CNS
Acetylcholinesterase
Enzyme on membrane of post-s neuron
Degraded ACh into acetate + choline
- To remove from cleft
- Choline transported
Amine Neurotransmitters
Several different types
Have 6 carbon rings
NH2 group
Made from amino acids
Norepinephrine
A hormone released from the adrenal gland that initiates fight or flight response
Similar to epinephrine = adrenaline
PNS - sympathetic NS uses to signal organs
Efferent NS
CNS - ready for action
Inhibitory or excitory
Serotonin
Only inhibitory
Big role in signalling in digestive system
CNS - many things - not clear - signals recourse availability: Hunger, mood, sleep
SSRIs - antidepressants: Inhibit reuptake of serotonin + Increases serotonin in synapsys
Dopamine
Excitatory
Deals with decision making, planning reward
Has a big role in drug addiction - Not pleasure - reward based
Histamine
Inhibitory or Excitatory
CNS - wakefulness, appetite, memore
Important signal in immune system –> Stimulates inflammation + allergic reactions
Glutamate
Amino Acid Neurotransmitter
The most important excitatory neurotransmitter in CNS because it opens Na+ and Ca++ channels
GABA
Amino Acid Neurotransmitter that’s not found in proteins.
Most important inhibitory neurotransmitter in CNS –> Opened K+ and Cl- channels
Substance P
Primary (peptide) neurotransmitter of pain in PNS + CNS
- Many other cell types respond to
- Primary controller of response to noxious stimuli = things that hurt you
Endorphins
Peptide neurotransmitter that inhibit the transmission of pain.
- Hormone released from the pituitary too
- Not released onto dendrites → onto axon terminals of neurons that release Substance P → inhibit release of SubstanceP
Opiate Receptors
Receptors for endorphins
Opioids are agonists for opiate receptors
Gasotransmitters
Gasses (CO and NO) that act as neurotransmitters
Used for signalling between other cells too
Not stored in vesicles:
- Made on demand by enzymes
- Simple diffuse across the plasma membranes of both cells
- Receptors inside cells respond
Endocannabinoids
Lipid neurotransmitter found throughout PNS + CNS + lots of other systems
- Many cells use for signalling
- Memory, learning, hunger
Retrograde neurotransmitters
Lipid neurotransmitters that signal back from post-s neuron to pre-s neuron
- THC is an agonist to endocannabinoid reception
Neural Wiring
Organization of neurons in terms of ways they synapse together
Higher order decision-making is done by groups of neurons
Neural Circuit
A few neurons signal many:
Glands, efferent NS
Part of neural wiring
Converging Circuit
Many neurons signal a few:
- Afferent NS
- Eyes
Part of neural wiring
Reverberating circuit
- Neurons signal neurons that end up signally back to them
- Circular
- Lead to positive or negative feedback
Part of neural wiring
How do neurons end up synapsing on the correct neurons?
- Growth Cone with Neurotropic Factors
- Fire together - Wire together
- Synaptic Pruning
- Long Term Potentiation
Growth Cone
Tip of a growing axon that grows away from the cell body to the neurons it will synapse on. It follows neurotropic factors to make sure the cone follows the right neuron. Axon behind it is more stable
Neurotropic Factors
Chemicals that the growth cone follows to the correct neuron.
Fire together - Wire together
Neurons with AP at the same time become more strongly connected
AP at different times gets weaker
Synaptic Pruning
- Synapses are removed between neurons during development
- More important for learning than forming new synapses
- The number of synapses peaks at 2 years and then decreases after
Long Term Potentiation
- When synapse is used a lot becomes more sensitive and has a longer response
- Important for learning + memory
- Over a few days or your whole life
