Lec 12 Flashcards
Chemical transmission Steps: What is the first step of chemical transmission?
neurotransmitter molecules are packages into the synaptic vesicles. Specific transport proteins in the vesicle membrane use the energy of H+ gradient to energize uptake of the neurotransmitter in the vesicle
Chemical transmission Steps: What happens following the release of quanta of neurotransmitter molecules into the synaptic cleft?
the neurotransmitter molecules diffuse across the synaptic cleft and bind to the specific receptors on the membrane of the post synaptic cell.
What type of synapse can be reciprocal ?
electrical synapse (connexon)
Where, in a neuron, is the Action potential threshold the lowest?
axon hillock - so that an AP can take place
An instantaneous transmission time with no delay occurs with what type of protein?
connexon
The length constant is useful in measuring what?
how far a passive signal can travel
the decay of a passive response is due to what term?
cable properties
consequences of demyelination Total blockade is described as…
no action potentials or spikes are propagated as a result of demyelination.
Most ion channels consist of what range of subunits?
4-6 in rosette
Linked chemically or electrically? cardiac cells
electrically
What type of neuron has a slowly accumulating K+ current ?
small pyramidal neuron
“saltatory” transmission is permitted by…
intermittent myelination or nodes of ranvier between myelin sheath
the high density of current in the nodes of ranvier results in…
generation of an action potential.
Linked chemically or electrically? glia
electrically
Cells can be linked through what two types of synapses ?
chemical and electrical
Ca2+ activated K+ currents underlying the sAHP is an example of what type of neuron?
small pyramidal neuron
in a dendrogram, the various subtypes of connexins are named according to their….
molecular mass. Cx32 = ~32 kDa
an active zone is defined as…
the currents flow at one instant in time, as a result of an action potential.
The termination of a chemical transmission can occur by what 3 processes?
- enzymatic destruction of neurotransmitter 2. uptake of transmitter into the presynaptic nerve terminal or into other cells by Na-dependent transport systems 3. diffusion of the transmitter molecules away from the synapse
What type of neuron displays spike frequency adaptation?
small pyramidal neuron
What are the 2 types of potentials associated with a graded response?
receptor potential, synaptic potential
If a membrane is less leaky, what will happen to the length constant?
increase in length constant
Active zones or nodes between myelinated areas of an axon jump from node to node. This is known as a _______ manner.
“saltatory”
What happens to the current density of the membrane of an axon when partial myelination or demyelination occurs?
current density is greatly reduced
A chemical metabotropic synapse contains what type of membrane protein?
receptor/Gprotein
In a dendrogram, what two connexin gene subunits are similar in rats and humans?
cx32 and cx43
Which type of synapse has second messengers?
metabotropic (gprotein) chemical synapse
Chemical transmission Steps: What happens following the influx of Ca into the presynaptic terminal?
Increase in Ca concentration triggers the fusion of synaptic vesicles with the presynaptic membrane. As a result , quanta of transmitter molecules are released into the synaptic cleft
consequences of demyelination Ectopic impulse generation is described as..
even though there is no input in the proximal portion of the axon, action potentials arise spontaneously beyond the lesion. Causing unwanted AP
Where are Na channels most concentrated in a neuron?
axon hillock and nodes of ranvier
consequences of demyelination: decreased velocity is due to…
decreased velocity is due to progressively longer delays in train action potential spikes as a result of demyelination
If an excitatory cell is hyperpolarized by a large amount , the result is…
a corresponding negative current that decays with time.
Chemical synapses should be considered a ________ pathway for signal propagation that can be modulated by ______________ chemical communication between two interacting cells.
unidirectional, bidirectional
How many connexin in a full function gap junction?
12 connexin = 2 connexon= 1 gap junction
There is no delay in propagation of action potentials when what is present in the neuron?
Myelin sheath
Nicotinic ACh receptor channels are oligomeric and are known as a ….
hetero-oligomer Pentamer (5 subunits)
inactive zones are …
neighbours to active zones, and can be depolarized by outward currents
time constant is equal to what?
Membrane Resistance * membrane capacitance
electrical synapse contain what membrane protein?
connexon
What type of neuron exploits the interplay between depolarizing and hyperpolarizing currents?
large pyramidal neuron
What happens after the binding of receptors in the postsynaptic cell?
The process is terminated by neurotransmitter breaks down and its subunits are taken up by the presynaptic terminal or by other cells OR diffuse away from the synapse.
Electrical synapse proteins contain how many subunits?
Connexon –> Hexamer (6 connexin or subunits)
A decrease in internal resistance of an axon, would cause the length constant to …
increase in length constant
What type of response decays with distance and time?
passive or graded response
A full functioning gap junction consists of how many connexon?
2 connexon = 1 gap junction
If there was a sequence of recording sites, and an action potential was initiated in the first site, what would the final action potential look like? (the axon is not myelinated)
it would be identical in amplitude and duration, however there would be an increasing delay. the passive portion of the action potential will still decay over time.
By nature, what type of synapses are inherently rectifying or polarized?
chemical synapses
A connexon is an oligomer, and is known as..
homo-oligomer Hexamer (6 connexin or subunits)
When two cells are clamped and connected by a gap junction, what will be the comparison between the current in each cell?
the sum of the current through the gap junction and the membrane in cell 1 will be the mirror image of the current through the gap junction and the membrane in cell 2. (ohmic)
Which type of neuron has only fast Na+ currents and delayed rectifier K+ curents?
inhibitory interneuron
Connexon’s transmission speed is…
instantaneous
What type of response does not decay with distance and time?
active response
Chemical transmission Steps: What occurs after the vesicles have been filled with neurotransmitters?
An AP arrives at the presynaptic nerve terminal (due to Na and K voltage gated)
How will our length constant be affected if we have an increase in the resistance of the internal conductor?
smaller length constant and greater loss of signal
If the demyelination affects two adjacent axons, what can occur?
action potentials in one can cause action potentials to propagate in both directions in the adjacent axon. (crosstalk)
Because of myelination, the current flowing down the axon is __________. (conserved or dissipating.)
conserved
if an axon were to increase in its radius, what would happen to the corresponding length constant?
decrease length constant
The agonist for Chemical synapse is ..
Acetylcholine (ACh)
What disease is the result of impaired conduction of action potentials in nerve axons?
MS - Multiple sclerosis
What is crosstalk?
When demyelination affects two adjacent axons, action potentials in one can cause actions potentials to propagate in both directions in the adjacent axon.
What type of neuron can exhibit “rhythmetic bursting behaviour”?
large pyramidal neuron
How will our length constant be affected if there is a greater membrane resistance or cable radius?
a greater length constant and less loss of signal
Of the three types of neurons, which has the fastest firing rate?
inhibitory interneuron
The two types of chemical synapse are:
ionotropic and metabotropic
An instantaneous transmission time occurs in what type of synapse?
electrical
Electrical synapse transmission speed is ..
instantaneous
What kind of channel is formed by pores in each membrane that are 2.5 nm apart?
gap junction
Individual Connexon hemichannels could be involved in what..
allowing the secretion of substances such as ATP and glutamate from glia to act on neighbouring neurons.
What causes a gap junction to close?
increase in intracellular Ca
What type of response dissipates over long distances?
graded response
Voltage gated Na, K, Ca, and Ca release channels are oligomeric and are known as a …
pseudo-oligomer Tetramer (4 subunits)
membrane capacitance is defined as ..
“distance between charges”
an increase in membrane capacitance will cause the length constant to…
decrease in length constant
What happens to the capacitance of the membrane of an axon when partial myelination or demyelination occurs?
capacitance increases
Myelination of Neurons in the CNS is completed by what type of cells ?
oligodendrocytes
Electrotonic current can exists in the presence of what type of membrane protein?
Connexon channels, create gap junctions for the easy passage of small ions and molecules
In a myelinated axon, current only flows where?
the nodes of ranvier
if an excitatory cell is depolarized by a large amount the result is..
if the threshold is reach or surpassed, an all or nothing action potential will initiate and there will be no decay with time.
In a receptor activated by ACh and contains Gprotein receptors, what is the transmission time?
seconds to minutes
Where is the most likely trigger point in a neuron?
Highest concentration of Na channel - axon hillock or initial segment.
What happens to the resistance of the membrane of an axon when partial myelination or demyelination occurs?
decreased resistance
The size and shape of a “passive response” due to what 2 things?
is due to: 1. Ohm’s law (V= IR or current amplitude * resistance) 2. and the size of cell capacitance.
Which is more efficient? Myelinated or unmyelinated axon?
Myelinated.
A half gap junction channel, or a Connexon is made up of how many connexins?
6 connexin = 1 connexon (half channel)
A decrease in membrane capacitance will cause the length constant to…
increase in length constant
If an axon were to get small or have a decrease in radius, what would happen to the corresponding length constant?
increase in length constant
A synapse that contains connexon can be reciprocal (equally efficient in both directions) or efficient in only a single direction. The second scenario is known as ..
rectifying (one direction only)
Which type of neuron is star shaped?
inhibitory interneuron
Chemical transmission Steps: What happens following the arrival of an AP in the presynaptic terminal?
depolarization opens the voltage-gated Ca2+ channels which allows Ca to enter the presynaptic terminal.
What is the speed of transmission in a chemical ionotropic synapse?
~1ms delay
In a dendrogram, the degree of difference between two connexins is determined by what?
the summed length of the horizontal line segments connecting two connexins.
Myelination of Neurons in the PNS is completed by what type of cells?
Schwann cells
What is the speed of transmission in a chemical metabotropic synapse?
seconds to minutes
Under what 2 conditions can an inactive zone fire its own action potential after being activated by an adjacent active zone?
- If the unactivated zone is not in absolute refractory period 2. if the stimulus (current) is great enough to overcome the threshold
consequences of demyelination Increased mechanosensitivity-ectopic action potentials are described as..
arise by mechanical stimulation, causing unwanted firing of AP.
Ion channels that are made up of identical distinct subunits are called..
homo-oligomers
A neuron with a longer length constant (lambda) will have what degree of voltage-change spread?
a longer length constant = farther down the axon a voltage change can spread. (greater)
What disease is the result of demyelinated axons ?
MS - Multiple sclerosis
Why doesn’t current flow through the inter-nodal (myelinated) membrane ?
high resistance of myelin
What are the 5 consequences of demyelination?
1.decreased velocity 2. frequency-related block 3. total blockade 4. ectopic pulse generation 5. increased mechanosensitivity-ectopic action potentials
What are three neuron types?
inhibitory interneuron small pyramidal large pyramidal
Where , in a neuron, is the Action potential threshold the highest? - dendrites - soma -axon hillock
dendrites (-35mV)
can cells connected by a gap junction propagate an AP?
not identically, there is dissipation of current density and amplitude drops.
Define “the greater the stimulus, the greater the voltage response”
graded response
what is the length constant? (lambda )
determines how far the electronic spread of a local change in membrane potential is able to influence neighbouring regions of membrane.
What type of neuron has its firing rate regulated by A-type K+ currents?
inhibitory interneuron
Ion channel that are made up of distinct subunits that are homologous but not identical are called..
hetero-oligomers
How does Myelination affect the speed of a neuron transmission ?
by increasing membrane resistance and decreasing the membrane capacitance.
Ion channels that are made up of distinct subunits that are repetitive sub-unit like domains within a single polypeptide are called …
pseudo-oligomers
If a membrane is less leaky, what will happen to the membrane resistance?
increase in membrane resistance
A chemical ionotropic synapse contains what type of membrane protein?
receptor/channel protein
What happens to the length constant (lambda) of the membrane of an axon when partial myelination or demyelination occurs?
length constant decreases.
Electrical synapse cells can function as a network known as :
syncytium
The generation of unwanted action potentials in demyelination are called? (2 consequences)
- ectopic pulse generation 2. increased mechanosensitivity-ectopic action potentials
Fast Na currents and delayed rectifier K+ currents have their firing rate regulated by what type of current?
A-type K+ current
Because axon current is conserved by myelinated portions, the current density in nodes is …
very high current density in nodes
What type of synapse can be reciprocal or rectifying? which is Ohmic? (linear relationship)
reciprocal and reciprocal is ohmic
consequences of demyelination frequency-related block is described as…
does not pass high frequency trains, as a result some of the spikes are missing distally.
If an excitatory cell is depolarized by a small amount the result is…
a corresponding small positive current that decays with time
