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Karnes 7303- Lecture 1.6
Synapses & Neurotransmission
Terms in this set (48)
How do neurons interact with one another?
What type of synapses are mostly seen in CNS?
What ion is presynaptic membrane impermeable to at rest?
What happens once the AP reaches membrane?
Extracellular Ca+2 rushes in, causing vesicles to move and fuse with membrane and release NT into synaptic cleft, NT binds with receptors on post synaptic membrane and opens chemically regulated Na+ channels to open
What does inflow of Na+ cause on post synaptic cell?
Initiation of excitatory response -> local depolarization
What happens at an excitatory synapse?
A local depolarization of post synaptic membrane upon binding of transmitter substance
What happens at inhibitory synapse?
A local hyper polarization
What does the overall excitatory or inhibitory effect of post synaptic neuron depend on?
Summation of postsynaptic responses
How are synapses named?
According to their locations
What are the 3 most prominent synapses in CNS?
Axoaxonic, axosomatic, axodendritic
What is axoaxonic synapse?
axon to axon
What is a axosomatic synapse?
axon terminal ends on cell body
What is an axodendritic synapse?
synapse between axon and dendrite
What is the resting membrane potential?
potential across the membrane of an excitatory cell at rest
What happens if the post synaptic cell is excited?
AP is generated
What happens if the post synaptic cell is inhibited?
AP is not generated
Is inhibition an active process?
YES*, it's not simply an absence of activity
What is an excitatory postsynaptic potential? (ESPS)
depolarizing event, graded potential (membrane potential goes from -70 to -68)
What is an AP a result of?
spatial/ temporal summation of many EPSPs
What is summation?
Cumulative effect from the firing of synapses
-if firings are EPSPs, then net effect may produce an action potential
What is spatial summation?
Cumulative effect from the firing of many synapses at approximately the same time
What is temporal summation?
Cumulative effect from the rapid, repeated firing of a single synapse
What is an IPSP (inhibitory postsynaptic potential)?
hyper polarizing, graded potential
-exact opposite of EPSP cuz it makes potential more negative
What is excitation?
depolarization leading to an AP
What is facilitation?
Bringing membrane potential closer to threshold, but not producing AP
-result of successive firing of EPSPs, but only summing it to get a new resting potential (bw -60 and -70)
What is inhibition?
exact opp of facilitation (<-70)
-results from successive firing of IPSPs
What is disfacilitation?
removal of facilitation
-relative hyper polarization, resulting in net inhibition (further away from "potential" than during facilitation)
What is disinhibition?
"Inhibiting an inhibitor" with the net effect being facilitation (potential moves closer to firing threshold)
What is recurrent inhibition?
Collateral axon excites an inhibitory interneuron, that in turn inhibits the same &/or neighboring neurons
What's the significance of recurrent inhibition?
feedback inhibition to control transmission or inhibit competing impulses
What is autogenous inhibition?
Inhibitory interneuron makes synapse connection and inhibit motor units going out to the same mm (homonymous) and other motor nn that are going out to synergistic mm
-feedback system for Golgi tendon organs
-milk gallon example
What is reciprocal inhibition?
impulses activating agonists muscles send collateral to inhibitory interneurons to inhibit antagonists
-inhibition is relative: relaxed but not flaccid
-limited to action of alpha motor neurons
What is presynaptic inhibition?
Action of an axoaxonic synapse at a synaptic terminal that decreases the neurotransmitter released by presynaptic membrane
-release inhibitory NT: GABA -> binds to Ca+2 channels so Less Ca+2 enters cell -> less vesicles move -> less NT released
What is integration a result of?
spatial and temporal summation
Where does integration occur?
What is neuronal integration?
impulses synapsing on neurons are integrated at cellular level to determine wherever or not to fire
What is a discharge zone?
With discrete populations of neurons, certain ones fire as a result of incoming excitatory impulses
What are the firing neurons known as?
What affects the neuron firing?
-neuron size (easier to excite/ inhibit smaller ones)
-location of synapse: located closer to axon hillock are more effective
-number of competing EPSPs and IPSPs
-relative excitability of the membrane
What is subliminal fringe?
neurons that don't fire
What is inhibition referred to as?
increase in the subliminal fringe
What is post-tetanic potentiation?
-After a rapid sequence of Pre-synaptic APs, graded potentials in the Post-synaptic neuron are higher than normal
-Prolonged facilitation period of synaptic transmutation following repetitive titanic stimulation of the presynaptic neuron
What is post titanic potentiation related to?
increased release of transmitter rather than change in postsynaptic excitability
what is accomodation in a neuron?
-reduction in neuronal in response to maintained stimulation
-allows the neuron to be more responsive to change in stimulation
What is interneuronal integration?
much of the integrative action of the NS is dependent upon complex interactions among populations of neurons
What is convergence?
inputs from several interneurons may converge onto one neuron to increase its chances of firing or to provide it with info from diff neural systems
What is divergence?
input from one area may spread to a larger area
What is a reverberating circuit?
It is when one neuron in the circuit receives feedback from another neuron in the circuit
-continue the discharge long after the original stimulus occurred
THIS SET IS OFTEN IN FOLDERS WITH...
Karnes 7303- Lecture 1.1
Karnes 7303- Lecture 1.2
Karnes 7303- Lecture 1.3
Karnes 7303- Lecture 1.4
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