Signal Reception and Integration Flashcards
How do receptors on the dendrites/cell body transduce an electrical signal?
Membrane bound receptors bind to a neurotransmitter, receptors transduce the chemical signal to an electrical signal by changing the ion permeability of the membrane.
What is a graded potential?
A wave of depolarization through the cytoplasm
What is conduction with decrement?
Magnitude of graded potential decreases with increasing distance from opened ion channel.
What are the three causes of decrement?
leakage of charge ions across a membrane
electrical resistance of cytoplasm
electrical properties of membrane
An inhibitory graded potential causes…
Hyperpolarization; K+ and Cl-channels to open
An excitatory graded potential causes…
Na+ nd Ca2+ channels to open
What characterstic of the axon hillock is important in initiation of an action potential?
High density of voltage gate Na+ channels. An increased density lowers threshold and shortens relative refractory period.
Action potentials occur only when…
membrane potential at the axon hillock reaches the threshold.
What are the characteristics of action potentials?
- triggered by a net graded potential at axon hillock (trigger zone)
- do not degrade over time or distance
- travel long distances through a membrane
- all or none
- must reach threshold potential to fire
Define spatial summation
Graded potentials from different sites nfluence the net change.
Define temporal summation.
Graded potentials that occur at slight different times inlfluence net change
What does the strength of the graded potential depend on?
the amount of stimulation
What are the 3 resisters of the area of the axon?
Rm, Re, Ri
What is a capacitator?
stores electrical charge
How does an axon behave like an electrical circuit?
- ions moving through VGCs causse current across membrane
- current spread electrotonically along axon
- some current leaks out of the axon and flows backards along the outside of axon, completing the circuit
Higher resistance of intracellular and extracellular fluids cause…
greater decrease in voltage along the axon.
Lower resistance of the membrane causes…
greater decrease in the voltage of the axon
λ =
distance over which mebrane potential decreases to 37%
When λ is large…
the change in potential degrades less with distance
When λ is small…
the change in potential decreases more with distance
Increasing λ, _______ velocity of the action potential
increases
What three features affect capacitance?
- material properties
- area of two conducting surfaces
- larger area increases capacitance
- thickness of insulating layer
- increasing thickness decreases capacitance
τ =
time over which membrane potential will decay to 37% of its maximal value
What are the variables that affect τ?
- rm
- Cm
τ = rmcm
The higher τ is the ____ the conduction velocity.
the lower
Define conduction velocity.
Rate at which an impulse is conducted along an axon
How can you increase conduction velocity?
- increasing the diameter of the axon
- myelinating or insulating the axon
How does myelin increase membrane resistance?
Local currents cannot leak out through the internode, must flow through the Node of Ranvier.
How does myelin decrease membrane capacitance?
Capacitance is inversely relatied to the thickness of the insulating layer… decrease
Describe how oligodendrocytes myelinate an axon?
- oligodendrocytes select axons with less than 0.2um in diameter
- neurons with electrical activity are selected for ensheathment
- during the peak of myelination, oligodendrocytes elaborate about 3X their weight in membrane per day
- high energy requirements
- high ion requirements
What are the two types of damage to myelin?
- oxidative damage to oligodendrocytes and neurons - due to free radicals (ALS?)
- Immune-mediated damage
How do the nodes of ranvier save energy?
- Results in about 1000x less active membrane
- About 100 fold fewer Na+ entering the cell per impulse
- Translates into an energy savings of about 2 orders of magnitude
- Less need to restore post-impulse ionic balances
What is the optimal distance between Nodes of Ranvier? Why?
200um to 2mm
What is saltatory conduction?
Appears that electrical impulses jump fown the axon (APs only occuring at the nodes of ranvier)
