Synapses 1 Flashcards
synaptic transmission
the process of information transfer at a synapse
electrical synapses
synaptic transmission that’s an electrical current flowing from one neuron to the next
common in mammal brain
chemical synapses
the idea that chemical neurotransmitters transfer information from one neuron to another at the synapse
CNS
majority of synapses in brain = chemical
presynaptic v postsynaptic
first neuron is pre, target cell is post
gap junction
specialized sites where electrical synapses occur
membranes of cells separated by narrow narrow gap
narrow gap spanned by clusters of connexins
connexin
special proteins that cluster together and span the narrow gap between cell membranes
connexon
six connexins combined
gap junction channel
two connexons (one from each cell) combine to form this
electrically coupled
cells connected by gap junctions
because electrical current in the form of ions can pass through channels
postsynaptic potential (PSP)
caused by current that flows across gap junction channels
when second neuron generates action potential, will induce PSP in first neuron
several occurring at same time may strongly excite a neuron
synaptic cleft
separates pre and post synaptic membranes at chemical synapses
presynaptic element
presynaptic side of the synapse
synaptic vesicles
dozens of small membrane enclosed spheres
in axon terminal
store neurotransmitter
secretory granules
larger vesicles
contain soluble protein that appears dark in the electron microscope
sometimes called large dense-core vesicles
membrane differentiation
dense accumulations of protein adjacent to and within the membranes on either side of the synaptic cleft
presynaptic membrane differentiation
proteins jutting into the cytoplasm of the terminal along the intracellular face of the membrane (tiny pyramids)
active zones
pyramids and membrane associated with them
actual sites of neurotransmitter release
synaptic vesicles clustered in cytoplasm adjacent to active zones
postsynaptic density
protein thickly accumulated in and just under postsynaptic membrane
contains neurotransmitter receptors which convert intercellular chemical signal (neurotransmitter) into intracellular signal (change in membrane potential or chemical change) in postsynaptic cell
axodendritic
if postsynaptic membrane is on a dendrite, synapse is axodendritic
axosomatic
if postsynaptic membrane is on cell body, synapse is axosomatic
axoaxonic
if postsynaptic membrane is on another axon, synapse is axoaxonic
dendrodendritic
when dendrites form synapses with one another
gray’s type I vs gray’s type II
type I: membrane differentiation is thicker on postsynaptic side, asymmetrical
type II: membrane differentiations are of similar thickness, symmetrical
neuromuscular junction
chemical synapses that occur between the axons of motor neurons of the spinal cord and skeletal muscle
has many structural features of chemical synapses in CNS
motor end-plate
postsynaptic membrane
contains series of shallow folds
three kinds of chemical categories of neurotransmitters
amino acids, amines, peptides
major amino acids
GABA
glutamate
glycine
major amines
ACh dopamine epinephrine histamine norepinephrine serotonin
major peptides
CCK dynorphin Enk NAAG neuropeptide Y somatostatin substance P VIP
amino acids
small organic molecules containing at least one nitrogen atom
stored in and released from synaptic vesicles
amines
small organic molecules containing at least one nitrogen atom
stored in and released from synaptic vesicles
peptides
large molecules stored in and released from secretory granules
often exist in same axon terminals that contain amine or amino acid neurotransmitters
glutamate, gamma aminobutyric acid, glycine
mediate fast synaptic transmission at most CNS synapses
acetylcholine (ACh)
mediates fast synaptic transmission at all neuromuscular junctions
transporters
special proteins embedded in the vesicle membrane
concentrate neurotransmitters inside the vesicle
