Synapses Flashcards
Chemical Synapses involve…
neurotransmitters (NT) that are released from the presynaptic cell and bind receptors to excite, inhibit, or modify post- synaptic cell.
how many NT have been identified
> 100
chemical synapse conduction
one way conduction
what determines function?
the receptor, not the NT
The — receptor subtypes are the largest known neurotransmitter-receptor family (– total receptor types).
serotonin
14
Three Morphological Types of Chemical Synapses
axosomatic
axodendritic
axoaxonal
Axosomatic synapses terminate on
neuronal cell bodies
Axosomatic synapses tend to be
inhibitory
axodendritic synapses terminate on
dendrites or dendritic spines
axodendritic synapses tend to be
excitatory
axoaxonal synapses terminate on
an axon, often close to synaptic terminals
axoaxonal synapses modulate
the release of NT
Presynaptic Events (4)
- AP arrival at the synaptic terminal causes membrane depolarization
- Voltage Gated Ca2+ channels open
- Ca2+ enters the synaptic terminal
- Exocytosis of vesicles filled with NT
The amount of Ca2+ that enters dictates
the amount of NT released
Synaptic delay of at least — between the pre-synaptic depolarization and post-synaptic response
0.5ms
synaptic delay is due to (4)
time for calcium entry for exocytosis,
presynaptic neurotransmitter release,
diffusion in the synaptic cleft,
and postsynaptic receptor activation.
Allows one to gauge the complexity of a reflex pathway (number of synapses) by looking at the
speed of the reflex
Small molecules, rapidly-acting (3)
– Elicit acute responses.
– Final processing occurs in the axon terminal. Vesicles
are docked & ready for release from presynaptic terminal
– Ex: Acetylcholine, Norepinephrine, Dopamine, Serotonin (5-HT), Histamine, Glycine, GABA, Glutamate, Nitric Oxide (NO).
Neuropeptides; larger molecules, slower (4)
– Effects are slower, more potent, & more prolonged.
– Produced in the cell body and transported down the
axon via axonal streaming.
– Fewer neuropeptides produced and released
– Ex: LH, ACTH, GH, vasopressin, oxytocin, angiotensin
II, substance P
NT action is terminated by: (3)
- Re-uptake by the pre-synaptic membrane
- Absorption by glial cells
- Inactivation by enzymes in the synapse
NT binds to receptor on
post-synaptic cell
Ionotropic Receptors:
directly affect ion channels
Binding of the ligand and the opening or closing the channel can: (4)
- Change a cell’s membrane potential
- Stimulate muscle contraction and/or relaxation
- Stimulate secretion
- Act as a second messenger to alter cellular activity
Metabotropic Receptors:
G-protein coupled receptors
GPCR
Nernst Potentials
Na+ =
Cl- =
K+ =
Na+ = +61 mV Cl- = -69 mV K+ = -86 mV
EPSPs due to (2)
- Opening Na+ channels
* Closing K+ and/or Cl- channels
IPSPs due to (2)
- Opening Cl- channels
* Increased K+ conductance
It is the — that determines the response produced
specific receptor, not the NT,
The 5-HT3 receptor
ligand-gated ion channel (Na+ and K+) that is proposed to be structurally
similar to the nicotinic
cholinergic receptor. The only 5-HT receptor that is not a GPCR.
5HT1A,B response (2)
increase K+ conductance
hyper polarization
(produce IPSPs)
5HT2A/5HT2C response
decrease K+ conductance due to channel closing (produce EPSP)
5HT3 response (2)
gating of Na+, K+ due to channel opening \fast depolarization
(produce EPSP)
5HT4 response (2)
decrease K+ conductance due to channel closing
slow depolarization
(produce EPSP)
Discharge of one pre-synaptic neuron cannot
reach threshold (+20 mV more positive than rest)
The diameter of the soma is large causing almost no resistance to electric current flow through the soma, which allows for — to occur
summation
— is almost always necessary to produce an AP
Summation
two types of summation
spatial
temporal
postsynaptic potentials last up to
15 ms
SPATIAL summaiton
Simultaneous EPSPs or IPSPs from multiple pre-synaptic neurons
(ex. Neuron 1 and Neuron 2).
Added in SPACE.
TEMPORAL summaiton
Successive EPSPs or IPSPs from a single presynaptic nerve terminal (ex. Neuron 1).
Added in TIME.
