L11 & 12: Neurobiology V & VI Flashcards
neuron signal information by
graded potentials and action potentials
graded potentials
are membrane potential changes of variable amplitude and duration that are conducted decremental.
graded potentials have no
threshold or refractory period
___ is required to initiate action potentials
summation of graded potentials
action potential
rapid change in the membrane potential during which the membrane rapidly depolarizes and repolarizes
action potentials provide
long-distance transmission of information through the nervous system
action potentials occur in
excitable membranes (neuronal and muscle cells) because there membranes contain many voltage-gated Na+ and K+ channels
depolarization of excitable membranes triggers an action potential only when
the membrane potential exceeds a threshold potential
regardless of the size of the stimulus, if the membrane reaches threshold,
the action potential generated is always the same size
a membrane is refractory
for a brief time following an action potential
action potential propagation is faster in
myelinated axons
a synapse
a structure that permits a neuron to pass an electrical or chemical signal to another cell
two types of synapses
electrical and chemical synapses
electrical synapses
pass electrical signals directly from cell-to-cell through gap junctions
chemical synapses
the vast majority of synapses, use neurotransmitters to pass information to the target cell
all gap junctions channels consists of a pair of
hemichannels
one hemichannel is in ____, and the other in ____
the presynaptic, the postsynaptic cell
these hemichannels make ___
contact in the gap between the two cell membranes, forming a continuous bridge between the cytoplasm of the two cells
the pore of the hemichannel has a diameter of
1.5 nm
the pore size permits small intracellular metabolites to pass
directly between the cytoplasm of the two cells
each hemichannel is called
connexon
connexon is made up of
six identical protein subunits, called connexins
electrical synapses occur
mainly in neurons of the CNS
information by electrical synapses can flow
in both direction
electrical synapses are also found in
glial cells, cardiac and smooth muscle, in non excitable cells that use electrical signals, such as the pancreatic beta cell
the primary advantage of electrical synapses is
the rapid conduction of signals from cell to cell that synchronies activity within a network of cells
neurotransmitters must cross
the synaptic cleft, 10 to 20 nm extracellular space that separates neurons
the physical separation of presynaptic and postsynaptic cells results in
one-way conduction along multi-neuronal pathways
aonx of the presynaptic neuron ends in a slight swelling
axon terminal
within the presynaptic active zone
synaptic vesicles contain neurotransmitter
post-synaptic density (PSD)
protein-dense region in the postsynaptic membrane in close apposition to the presynaptic active zone
post synaptic density ensures that
receptor are in close proximity to presynaptic neurotransmitter release sites
neurotransmitter release step 1:
action potential reaches the terminal of the presynaptic membrane
neurotransmitter release step 2:
terminals possess voltage-gated Ca2+ channels, in addition to Na+ and K+ channel; depolarization during action potential opens Ca2+ channels allowing Ca2+ to flow into the axon terminal
neurotransmitter release step 3:
Ca2+ activate processes that lead to the fusion of docked vesicles with the synaptic terminal membrane
neurotransmitter release step 4:
Ca2+ binds to synaptotagmin proteins associated with SNARE proteins; SNAREs anchor vesicles to the plasma membrane and undergo Ca2+ dependent conformational changes to stimulate vesicle fusion with the plasma membrane
__ proteins associated with SNARE proteins
synaptotagmin
synaptotagmin proteins associated with
SNARE proteins
unbound neurotransmitters are removed from the synaptic cleft in
three ways: diffusion, enzymatic transformation, or reuptake
in myelinated axons, action potentials are regenerated at
the Nodes of Ranvier in saltatory conduction
