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What is a synapse?
Functional association of a neuron with another neuron or with effector organs.
What are the types of Synapses?
What are electrical synapses?
Two neurons linked together by gap junctions, some are between neurons and glial cells.
What is the function of electrical synapses?
- Rapid communication
- Bidirectional communication
- Excitation and inhibition at same synapses
What are the components of a Synapses
- Presynaptic neuron
- Postsynaptic neuron
- Synaptic cleft
What are the different neron-to-neuron synapses?
What are the anatomical parts of a Synapse?
- Axon terminal
- Synaptic vesicles carrying neurotransmitter
- Voltage-gated Ca ion channel
- Synaptic cleft
- Re-uptake molecule
What are the functions (in order) of a synapse?
- 1. Action Potential
- 2. Voltage-gated Ca channels open
- 3. Ca binds to docking proteins and stimulates exocytosis
- 4. NT diffuses and binds to receptor
- 5. Response in cell (terminated by removing neurotransmitter from cleft)
- 6. Degradation
- 7. Re-uptake
- 8. Diffusion
What is synaptic delay and what is it caused by?
- 0.5 - 5 msec btwn arrival of AP and change in postsynaptic Vm
- Caused by changes in [Ca] and release of neurotransmitter
What are the 2 forms of signal transduction at synapses?
Channel-linked receptors - fast and direct-acting
G-protein-linked receptors - slow acting, require metabolite
What is postsynaptic potential (PSP)?
Change in membrane potential in response to receptor-neurotransmitter binding.
- Some excitatory (EPSP)
- Some inhibitory (IPSP)
What are the differences between excitatory and inhibitory synapses?
Excitatory - more likely to produce AP, depolarization
Inhibitory - less likely to produce AP, hyperpolarization, membrane stabilization
What are the 2 ions associated with IPSP?
K+ and Cl-
Why are IPSPs graded potentials?
- Higher frequency of APs
- More NT released
- More NT binds to receptors to opn/close channels
- Greater increase/decrease in ion permeability
- Greater/lesser ion flux
- Greater hyperpolarization
What is Neural Integration?
The summing of input from various synapses at the axon hillock of the postsynaptic neuron to determine whether the neuron will generate APs
What are some examples of neurotransmitters?
- Biogenic amines
- Amino acid neurotransmitters
- Other NTs
What is the most abundant NT in the PNS?
What is the chemical reactoin of Acetylcholine synthesis? Where does it happen and what enz is involved?
Acetyl CoA + choline --> acetylcholine + CoA
- Synthesized in cytosol of axon terminal
- Enz for synth = choline acetyl transferase (CAT)
What is the chemical reaction for Acetylcholine breakdown? Where does it happen and what enz is involved?
Acetylcholine --> acetate + choline
- Degraded in synaptic cleft
- Enz of deg = acetylcholinesterase (AChE)
What is a cholinergic synapse?
Synapse utilizing acetylcholine
"-ergic" means bind; cholinergic binds choline
What are the 2 types of Cholinergic Receptors?
1. Nicotinic - ionotropic
2. Muscarinic - metabotropic
What are biogenic amines derived from and what are some examples?
- Catecholamines - derived from tyrosine (dopamine, norepinephrine, epinephrine)
- Serotonin - derived from tryptophan
- Histamine - derived from histidine
What are the enzymes responsible for degrading biogenic amines?
- Monoamine oxidase (MAO)
How are biogenic amines synthesized and where are they released?
Synthesis: cytosol of terminal, packaged into synaptic vesicles, released
Release: Dopamine & Norepinephrine CNS, Norepinephrine also in PNS, Epinephrine from CNS but more commonly released as hormone from adrenal medulla
What are the 2 different adrenergic receptors and waht are their subunits?
- Alpha adrenergic receptors
- Beta adrenergic receptors
Which adrenergic receptor has the greatest affinity for epinephrine? ... norepinephrine?
Alpha and Beta 1
What is the speed of adrenergic receptor responses?
- G-protein coupled
- Linked to second messengers
What are the properties of Serotonin?
- CNS NT
- Regulates sleep
What are the properties of Histamine?
- CNS NT
- More commonly known for paracrine actions
Which AA NT are at excitatory synapses?
Which AA NT are at inhibitory synapses?
What are Neuropeptides?
- Short chains of AAs
- Co-located with other NTs
- Modulate response caused by other NT
- Ex. Endogenous opioids (enkephalins, endorphins). TRH, ADH, Oxytocin, Substance P