Synaptic Transmission Flashcards
1
Q
neurons
A
- specialized to rapidly send and receive information to maintain homeostasis and adapt to change
- dendrites, cell soma, axon with myelin, presynaptic terminals
2
Q
dendrites
A
- tapered processes arising from the cell body that greatly increases the receptive surface
- contain receptors for transmitters and voltage gated ion channels that can amplify the graded synaptic signal
- primary area for receiving and integrating complex information from thousands of synapses
- arbors can be simple or complex
3
Q
cell soma
A
- surrounds nucleus and contains the ER and golgi
- performs housekeeping functions-portein synthesis, degradation, processing
- membrane contains receptors that bind chemical transmitters released by afferent neurons
4
Q
axon
A
- single thin process arising from the cell body at the axon hillock
- all or none APs to the terminals after integrating transmitter mediated bioelectrical changes received in the dendrites and cell body
- some can be a meter long, containing 1000 times cyto-called axoplasm as a cell body
- many axons surrounded by myelin sheath
5
Q
presynaptic terminals
A
- specialized structures that concert electrical signals propagated down the axon into chemical signals (APs to neurotransmitter)
- neurotransmitters are released from presynaptic vesicles and transmitted to target cell at synapse
- post synaptic potentials are small graded changes
6
Q
axoplams
A
- contains parallel arrays of MTs and neurofilaments that provide structural stability and a means to transport materials back and forth between the cell body and presynaptic terminals
- fast transport both forward (kinesin) and backward (dyenin)
- cancer patients receiving MT disrupters may have peripheral neuropathies due to gradual vesicle depletion
7
Q
electrical synapses
A
- speed and synchrony
- bidirectional
- gap junctions and connexins
- connexons are hemi channels combine to form gap junction
- current flow changes the postsynaptic membrane potential, which can lead to generation of AP
- pores are much bigger-unselective diffusion of ions and ATP/metabolites
- less common in nervous system- regulation of breathing
8
Q
chemical synapses
A
- directionality, amplification, excitation and inhibition, plasticity, integration in space and time
- neurotransmitters in synaptic vesicles- clear and small with small molecules or large and dense with peptides
9
Q
criteria for chemical neurotransmitters
A
- present in presynaptic terminal
- released in a voltage and calcium dependent manner (calcium high outside cells
- specific receptors present in post synaptic target cell
- means to inactivate the transmitter
10
Q
chemical synapse
A
- neurotransmitter molecule sysnthesized and packaged in vesicles
- an action potential arrives and depolarizes the terminal membrane of the pre-synaptic terminal
- voltage gated Ca channels open and Ca comes in
- rise in Ca triggers fusion of synaptic vesicles with the presynaptic membrane
- transmitter molecules diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic cell
- bound receptors activate the postsynaptic cells- causes IPSP or EPSP
- neurotransmitter breaks down, is taken up, or diffuses away
- extreme activation all the time can lead to de-sensitization
11
Q
synapses
A
- presynaptic terminals have mitochondria and synaptic vesicles
- subset of vesicles docked at active zones- preferentially released
- post synaptic target cell has electron dense area with many receptors- post synaptic density
- glucose used in brain for pre-synaptic terminals
- fMRI can measure regional blood flow associated with changes in local cerebral glucose metabolism
12
Q
exocytosis of vesicles
A
- vesicle has synaptotagmin and synaptobrevin (vSNARE)
- membrane has SNAP 25, syntaxin and n-sec 1 on syntaxin (t SNAREs)
- n-sec dissociates and syntaxin and SNAP 25 form complex
- synaptobrevin winds around the complex
- draws vesicle in
- synaptotagmin interacts with calcium to fuse vesicle
- complex dissociated with alpha SNAP and NSF (ATPase)
- botulinum cleaves SNAP 25 or synaptobrevin- no EPSP
13
Q
chemical transmitters and time courses
A
- 1 msec to 10 days
- Ach (nicotinic) is fast, peptides are slow
14
Q
ionotropic
A
-contain an ion channel as part of their structure and binding triggers a rapid response
15
Q
metabotropic
A
-linked to G proteins that transduce a slower signal
16
Q
Ach
A
- common in periphery and CNS
- choline and acetate
- rapid with nAchR
- slower is mAchR
- AchE terminates
- also pump that puts it back into presynaptic
17
Q
post synaptic potentials
A
- conductance changes due to ion channel openings, leads to ionic flow through the channels that lead to changes in membrane potential
- excitatory makes the membrane potential more likely to fire AP
- inhibitory makes it less likely to fire AP
18
Q
glutamate
A
- major excitatory neurotransmitter and binds to ionotropic and metabotropic receptors
- AMPA receptors are selectively activated by AMPA and mediate a fast EPSP (ionotrppic) with Na and K
- NMDA activated by NMDA and mediate a slower EPSP via Na, K and Ca- only open if membrane is pretty depolarized because they are blocked in a voltage dependent manner by Mg (also ionotropic)
- metabotropic linked to G protein and slower
19
Q
GABA
A
- major inhibitory transmitter
- binds to ionotropic and metabotropic receptors
- hyperpolarizing responses- IPSP
- GABA A receptor channels mediate fast IPSP by Cl ions down gradient
- pentobarbital elicits larger IPSP when GABA is present because it increases channel open time/ single channel current
- GABA B receptors are slower because G linked
20
Q
neuronal integration
A
- brains contain 100 billion neurons, and each one integrates info from numerous synapses
- EPSP can be only a fraction of a milivolt, below threshold
- neurons innervated by thousands of synapses so summation occurs
21
Q
morphology of synapses
A
- AP in one neuron transmitted to another at synapse
- terminal regions of axons branch and form synaptic boutons
- myelination lost when bouton in close contact with dendrite or other cell body
- vesicles from the synaptic bouton (end of the axon) fuse with presynaptic membrane
22
Q
distance and potential
A
-potential changes decrease with increased distance from the stimulus
23
Q
passive events
A
- dendrites don’t transmit APs because not many Na channels and thresholds high
- small depol or hyperpol are passive events
- spread only a few mm and become smaller at greater distances from stim
- temporal and spatial effects-cable theory-capacitance, resistance, and longitudinal cytoplasmic resistance
- dendrites and long and membranes are thin and leaky to electric current
- before EPSPs reach soma, potential is lost- decremental conduction
24
Q
temporal summation
A
- firing of two APs quickly enough to reach threshold at axonal hillock
- membrane has longer time constant (holds potential longer)
25
Q
spatial summation
A
- firing of APs from multiple places with enough of the same effect to reach threshold
- need bigger space constant-holds EPSP for longer distance
26
Q
temporal and spatial summation
A
- determine the probability that and AP with fire
- neurons integrate lots of information
- axon hillock has high density of voltage gated Na channels
