CTR - 8 - Synapses Flashcards
What is a benefit and negative of electrical synapses?
Very rapid response
Cannot be modulated easily (cannot be timed well)
What are the two types of synapses?
Chemical and electrical
Channels at the axon terminal of the pre-synaptic neuron are _________ gated.
Voltage
Channels at the dendrite of the post-synaptic neuron are _________ gated.
Ligand / chemically
What is the role of Ca2+ in a synapse?
Causes vesicles to release their contents via exocytosis into the synaptic cleft
How can a neurotransmitter response be terminated?
Diffusion away from the synapse
Enzymatic degradation
Re-uptake through transport proteins
How do anti-depressants work
Block re-uptake of neurotransmitter at a synapse
During exocytosis in a synapse, what happens?
v-SNARE proteins on vesicle surface bind with t-SNARE proteins on surface –> open a pore –> vesicle releases contents to exterior
What can block exocytosis? What effect does this have?
Botulin and tetanus toxins
Cut the proteins (t-snare and v-snare) so that exocytosis cannot occur.
Therefore, no NT released even with AP reaching the synapse
No muscle contraction –> muscles relax
What determines how much neurotransmitter is released?
How doe this affect GP size?
Frequency of AP
= high freq –> more calcium released –> more vesicles released –> more neurotransmitter released
Amount of neurotransmitter in vesicles
Increased amount of NT –> opens more Na+ channels on postsynaptic neurone –> increased GP size
What are EPSPs and IPSPs? What ions are involved?
Excitatory post-synaptic potentials
- NT binding increases chance of postsynaptic neuron generating AP
- Na+ into cell
- More positive inside = depolarisation
Inhibitory post-synaptic potentials
- Nt binding decreases chance of postsynaptic neuron generating AP
- K+ out, Cl- into cell
- More negative inside = hyperpolarisation
What is an example of divergence in the same pathway?
Walking (leg curl = hamstring) - in the same muscle group
What is an example of divergence in multiple pathways?
Walking (swing arms and legs) - different muscle groups
What is an example of convergence from multiple sources?
Appetite (smell and look nice)
What is an example of a reverberating circuit?
repetetive / rhythmic activities (sleep wake, breathing)
What is released at the neuromuscular junction? What does it cause?
ACh. Generates GP (if threshold) –> AP –> causes Ca2+ to flow in –> initiate protein filaments to contract
What does acetylcholine-esterase do at the NMJ? Purpose?
Breaks down excess ACh in synaptic cleft./
Which stops contraction of muscle (otherwise, ACh would stay there –> continous APs)
What is an agonist at the NMJ?
Nicotine - causes same effect when binding to NMJ.
What is the cause of myasthenia gravis? Symptoms? Treatment?
Auto-immune = antibodies destroy ACh receptors (less ACh receptors at NMJ)
Symptoms: diminished motor response at NMJ (muscle weakness, fatigue)
Treatment : ACh esterase inhibitors limit breakdown of ACh - more ACh available (maximises effect on remaining receptors)
What are the effects of the curare toxin? Treatment
ACh competitive antognist - occupies ACh receptor (prevents ACh binding postsynaptically –> no opening of ion channels –> no AP –> paralysis of skeletal muscle)
ACh inhibitors - limit breakdown of released ACh - leaving more available for the available receptors.
What do organophosphates do? Treatment
Inactivates ACh-esterase –> ACh not broken down –> high levels of ACh in synaptic cleft –> desensitise ACh receptors –> ACh receptor-channels close even in presence of ACh –> neuromuscular transmission fails
Treatment - atropine - ACh receptor blocker in parasymapthethic NS
Also - acetylcholine esterase reactivator
What causes botulism? Treatment?
Botulin - prevents ACh release (by cutting t-snares and v-snares) –> no binding of ACh –> ion channels remains closed –> no depolarisation –> no AP –> muscle remains relaxed
Treatment –> ventilator, surgery, stomach pump
What is learning?
Process by which knowledge is acquired about the world
What is memory?
Process by which knowledge is encoded, stored and later retrieved
What is consolidation? How long does it take?
Process of converting short term memory to long term memory (takes seconds to minutes)
What is declarative memory. One location. HM
Storage abut facts and events (places, people, objects)
- medial temporal lobe (HM had this removed)
What is non declarative memory?
Procedural, automatic, skills, habits, emotional responses
What is habituation. A form of _________
Learning to ignore meaningless stimuli
Form of non-assosciative learning
What happens to neurons during habituation?
GP becomes smaller and smaller
Presynaptic votage-gated channels become progressively and persistently less effective when opened repetitively
Therefore, not producing an AP
