Synaptic Transmission Flashcards
What is the intermembrane structure that connects cells for gap junctions called?
connexons
in what direction does conduction flow through a gap junction?
both directions (gap junctions are bidirectional)
at what speed does conduction travel through the gap junction?
fast, there is no synaptic delay like that seen in chemical synapses that must undergo secretory process)
what is an important characteristic of gap junctions for electrical conduction?
allow large number of cells to contract simultaneously
in what ways does a gap junction differ from other membrane channels?
- the normal state of the channel is to be open.
- the gap junction channel spans two cell membranes.
- both ends of the gap junction channel are intracellular.
- both cations and anions can pass through the same channel.
can gap junctions close?
Gap junction channels can close so that cells are no longer electrically coupled. This may protect normal cells from neighboring cells that are damaged
what might make a gap junction close?
high Ca
high H (or low pH)
depolarization of one cell
what are the first two parts of synaptic transmission?
- Release of a chemical transmitter from the presynaptic nerve terminal.
- Diffusion of the transmitter to the postsynaptic membrane
what are chemical synapses?
Distinct cytoplasmic discontinuity that separate the presynaptic
and postsynaptic membranes, synaptic cleft.
Contains a high concentration of mitochondria and synaptic
vesicles
what is the third and fourth steps of synaptic transmission?
- Binding of the transmitter to the postsynaptic receptor and response.
- Inactivation or removal of the transmitter
what direction co chemical synapses flow?
only one direction
at what speed do chemical synapses work?
slightly slower than electrical due to the synaptic delay of 0.5 msec
what criteria’s needed in order for something to be considered a neurotransmitter?
- Synthesis of the neurotransmitter occurs in the neuron itself
- It can be found in the presynaptic membrane
- Its release into the synaptic cleft causes a change in the postsynaptic membrane
- Its effect on a neuron is the same whether released exogenously (i.e., from outside the organism as a drug) or endogenously (from the presynaptic terminal)
- Once released, the molecule is specifically removed from the synaptic cleft either by reuse or degradation
what are examples o neuroactive peptides?
a. Opioid peptides (enkephalins, endorphins, dynorphins)
b. Nonopioid peptides (Substance P, vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK)
what are examples of other neuromodulators?
a. Purine nucleotides (ATP)
b. Purines (adenosine)
Neuromuscular junctions as well as other chemically mediated synapses act as _____
amplifiers
what does amplification do for NMJ?
Amplification allows the relatively tiny currents in a 5 μm α-motoneuron axon to
elicit an action potential in a 100 μm muscle fiber
in humans the neuromuscular
synapse is ________
always excitatory, never inhibitory.
The presynaptic terminal of NMJ has large concentrations of _____
mitochondria
what is the active zone of the NMJ?
where synaptic vesicles containing transmitter accumulate around presynaptic dense bars.
what is the synaptic cleft?
The synaptic cleft is filled with an
amorphous network of connective tissue called the basal lamina
what is the steps of transmission at the NMJ?
-AP conducted
-VG Ca channels open
-Ca flows in causing release of Ach
-Ach diffuse across cleft
-activates Ach receptor, opens ligand gated Na/K channels
-Na depolarizes triggers AP
-muscle contracts
what is evoked transmitter release?
-nerve terminal depolarized by AP, VG Ca channel open and Ca enters
-Ca intracellular messenger allowing synaptic vesicles to exocytosis contents
-Ca removed
-amount NT released is proportional to amount of Ca
how does increase intracellular Mg change NT release?
increasing Mg decreases NT because Mg competes with Ca for entry to Ca channel
less Ca=less NT