synapses Flashcards
where do neurons communicate?
- synapses
electrical synapses
– Pass electrical signals through gap junctions
- gap junctions = close communications
– Signal can be bi-directional
– Synchronizes the activity of a network of cells
chemical synapses
– Use neurotransmitters that cross synaptic clefts
neurocrines
– Neurotransmitters: messenger (ach, epi)
- neuromodulators: dopamine. reward system
- neurohormones: oxytocin, ADH, epi
what are ionotropic receptors also called?
- receptor channels
what are metabotropic receptors?
- G protein-coupled receptors for neuromodulators
what do neurotransmitters bind to?
- specific receptors except NO
nicotinic receptor
think skeletal muscles, autonomic neurons, CNS
muscarinic receptor
- smooth and cardiac muscle endocrine and exocrine glands, CNS
acetylcholine –> synthesis
- From choline (from membrane phospholipids) and acetyl CoA (from citric
acid cycle) - In axon terminals
acetylcholine –> binds cholingeric receptors
- Nicotinic receptors
- On skeletal muscles and in autonomic division of PNS and CNS
- Monovalent cation channels: Na+ and K+
acetylcholine –> muscarinic receptors
- In CNS and on target cells for autonomic parasympathetic division of PNS
- G protein–coupled receptors
amines
- Active in the CNS
- Derived from single amino acid
– Serotonin from tryptophan
– Histamine from histidine
– Dopamine, norepinephrine & epinephrine from tyrosine
*Adrenergic/noradrenergic neurons secrete norepinephrine - Adrenergic receptors bind norepinephrine & epinephrine
– G protein–coupled receptors- alpha and beta classes
glutamate
- excitatory –> CNS
- AMPA and NMDA receptors
aspartate
- excitatory –> brain
- depolarizes target cells
gamma-aminobutyric acid (GABA)
- inhibitory –> brain
- hyperpolarizes target cells by opening Cl- gates
glycine and D-serine
- enhance the excitatory effect of glutamate
peptides
- Substance P and opioid peptides (enkephalins & endorphins)
- Function as neurotransmitters, neuromodulators, neurohormones
- Cholystokinin, vasopressin, atrial natriuretic peptide
- Function as neurotransmitters and neurohormones
purines
- Adenosine, AMP and ATP bind to purinergic receptors (GPCRs)
gases diffuse in the cells
- NO, CO, H2S
lipids
- Eicosanoids, endogenous ligands for cannabinoid receptors
neurotransmitter release: classical model pathway
- Action Potential arrives at the axon terminal
- Voltage gated Ca2+ channels open in response to depolarization
- Ca2+ binds regulatory proteins and initiates exocytosis
- Neurotransmitter diffuses across synaptic cleft
- Neurotransmitter binds receptor on post-synaptic cell initiating a response
neurotransmitter release: kiss-and-run pathway
- Vesicles fuse with presynaptic membrane to form fusion pore
- Neurotransmitters pass through a channel
termination of neurotransmitter activity
- Diffusion away from the synaptic cleft
- Enzymatic breakdown
– Acetylcholinesterase (AChE) - Uptake into cells
– Presynaptic axon terminal
– Glial cells
single action potential
- results in the release of a constant amount of neurotransmitter
Action potentials code duration and magnitude in the frequency of action potentials produced
– Tonic activity: goes in one direction
– Burst activity: get the conduction going in all directions
chemical synapse
- the axon terminal contains mitochondria and synaptic vesicles filled with neurotransmitter
- the postsynaptic membrane has receptor for neurotransmitter that diffuses across the synaptic cleft
divergence
▪ One presynaptic neuron branches to affect a larger number of postsynaptic neurons
convergence
▪ Many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons
synaptic plasticity
– A change of activity at the synapses
– Occurs primarily in CNS
– May be short-term or long-term
– May be enhance or reduce synaptic activity
slow synaptic potentials
- involve G-protein coupled receptors and second messengers.
– Think neuromodulators
fast synaptic potentials
- involve opening of ion channels.
– An excitatory postsynaptic potential (EPSP) is depolarizing. (Na+)
– An inhibitory postsynaptic potential (IPSP) is hyperpolarizing. (K+)
spatial summation
– Two or more neurons simultaneously fire and have an additive effect
– Postsynaptic inhibition
▪ Release of neurotransmitter is inhibitory instead of excitatory
- inhibiting movement
- based on action potential
- 2 neurons firing at the same time and they cancel each other out
temporal summation
- based on graded potential
– Summation occurring when graded potentials overlap in time and having an additive effect
synaptic activity can be modified
– Modulatory neuron terminates on the presynaptic cell and modulates the release of neurotransmitter
– Presynaptic facilitation favors the release of neurotransmitter
– Presynaptic inhibition prevents the release of neurotransmitter
what is glutamate a key element in?
- potentiation
- AMPA receptors and NMDA receptors
long term potentiation is responsible for what?
acquired behavior
activity at a synapse induces sustained changes in quality or quantity of connections
– Potentiation similar to facilitation
– Depression similar to inhibition
- Disorders of synaptic transmission are responsible for many diseases
– Parkinson’s disease, schizophrenia, and some depressions
