Lecture 4 Flashcards
T or F? Conduction is faster if the time constant is shorter.
T
T or F? Conduction is faster if the time length constant is shorter.
F. longer
How do the neurons of vertebrates and invertebrates differ?
invertebrates have a few very large neurons - escape response
The human body has about ___ neurons.
100 million
What is MS:
loss of myelin, debilitating loss of conduction in the NS
T or F? Graded synaptic potential decay exponentially with distance.
T, due to leakage of positive charge
Will a graded potential decay faster in a cell with a high or low membrane resistance?
low
What does the decline of the voltage of the graded synaptic potential depend on?
is the resistance of the membrane high or is the resistance of the internal cytoplasm high?
T or F? High membrane resistance reduces the decline of a graded synaptic potential?
T
T or F? High internal resistance reduces the decline of a graded synaptic potential.
F. Low internal…
Do GPs increase or decrease slowly with time?
increase
Do GP’s amplitude decrease or increase with distance?
decrease
How much time it takes for a graded potential to reach 63% of its maximum value:
time constant
How far a graded potential travels before it has decreased in amplitude to 37% of its initial value:
Space constant
What will happen to the voltage signals within an axon if the gated channels are blocked?
the signals decay with distance in an exponential manner
When is delta Vm measured?
after Vm reaches a steady state
math symbol for space constant
lambda
The space constant is AKA:
length constant
the distance along the nerve fiber where the voltage falls to 37% of the original voltage:
space constant (or length constant)
The likelihood of AP going down vs out is related to:
space constant
The space/length constant is related to:
membrane and internal resistance
How is the membrane resistance determined?
by the # of open channels
What is one space/length constant?
When a signals voltage has decreased to 37% of what it started out to be, how far how it traveled - that distance is one space/length constant
Internal res is determined by:
diameter of the fiber
Will a small diameter fiber have a high or low internal resistance?
high
T or F? The smaller the membrane resistance the further the charge will travel.
F. The BIGGER the..
T or F? Shorter space constants result in faster conduction.
F. Longer space…
What changes with the axon radius?
the internal resistance
Length constant is related to:
the radius of the cell
The larger the radius, the (bigger/smaller) the length constant.
bigger
PM resistance is inversely proportional to:
the radius of the nerve fiber
internal resistance is inversely proportional to:
(radius)^2 of the nerve fiber
As the nerve fiber radius increases, the space constant _______
increases
As the nerve fiber radius increases, electrical signals travel ______.
faster
If more channels open on the membrane, the space constant will _______.
decrease (check)
What does the time constant describe?
how fast membrane voltage changes at one location
What is capacitance?
A measure of how many charges are needed to change cell voltage
Explain time constant
look at one spot and ask how quickly that one spot changes its voltage
Why is a slow depolarization less likely to produce an AP?
bc Na channels are closing
Will a cell depolarize slowly or quickly at a short time constant?
quickly
What 2 factors influence the time constant?
membrane resistance and membrane capacitance
To get a fast response you want a ___ length constant and a ___ time constant.
long, short
What affect would open channels have on the length constant?
slow down the length constant
What is the time constant related to?
capacitance and resistance
What determines the speed of a response?
membrane time constant
T or F? A fast time constant reaches threshold much sooner
T
The time required for the voltage to increase or decrease to 63% of the peak:
time constant
Do neurons with high me capacitance have long or short time constants?
long
T or F? Myelin increases the capacitance and shortens the time constant.
F. lowers capacitance and shortens the time constant
Which curve will be higher on the graph, short time constant or long time constant?
short
What type of circuit is the membrane?
RC circuit
What is capacitance determined by?
thickness of lipid membrane
T or F? C for cells varies greatly.
F. bc the thickness of most cell membranes is about the same
What does a capacitor do?
absorbs charges
Will the voltage of a cell change slowly or quickly if you only have a resistor?
quickly
How does adding a capacitor to a cell effect the voltage change?
voltage will change slowly
This influences graded potential amplitude and speed of response:
resistance
This controls the speed of electrical response:
capacitance
Would you need to decrease or increase the capacitance to get a faster response?
decrease
How can you decrease capacitance of a cell?
add myelin, separates opposite charges, not as hard to keep them apart
T or F? Myelin increase capacitance.
F. Decreases
This separated charges across a membrane:
capacitor
Would you make a membrane thicker or thinner to lower capacitance?
thicker
Myelin is wrappings of:
glial cell membranes
Where are the channels concentrated on a nerve fiber?
bw myelin
T or F? Negative charge travels underneath the myelin until it gets to the next node.
F. Positive
Space immediately adjacent to the Node of Ranvier:
paranode (myelin attachment)
This is the myelin attachment:
paranode
Space adjacent to the paranode:
juxtaparanode
T or F? K+ channels are located at the Nodes of Ranvier.
F. in internodal regions
What is the internodal conduction time?
less than 0.1 msec
When does conduction through an internal region slow?
when you are producing another AP at the node
Through how many nodes can an AP travel through an unmyelinated axon before it can not produce another?
a couple
Why does the AP decay w/out myelin?
Current leaks out through PM (Na+ leaks out)
Which has higher conduction speeds, small diameter non0myelinated axon or large myelinated axon?
large myelinated
Local circuit current in myelinated axons is sufficient to depolarize how many downstream nodes beyond a block node?
1 or more
How is resistance affected if the diameter is increased?
resistance is lowered
Do squids have myelinated or unmyelinated axons?
un
What does conduction velocity depend upon?
Axon diameter and myelination
Synchronized activity by a large number of neurons:
field potential
How must neurons be oriented in field potentials?
same direction
the measure of voltage of many neurons:
field potential
Why do the neurons have to be oriented in the same direction for a field potential?
to generate a magnetic field
T or F? The extracellular potentials produced by field potentials can summate.
T
What is an ERG?
Electroretinogram
T or F? The field potential remains the same for the retina no matter how intense of dim light a light flash is.
F.
How can you determine if photo receptors are functional in the eye?
Electrode on retina, flash a light, get various wave forms similar to an EKG
