Exam 1 Flashcards
Sensory Transduction
Converting physical stimuli to electrical impulses
Glial Cell Functions
- Maintenance of extracellular ionic concentrations
- Generation of blood brain barrier
- Trophic support
- Immunological regulation
- Degradation/uptake of neurotransmitters
- Synapse development
Astrocytes
- Regulating ion concentration in extracellular space
- Form tribartite synapse (involved in regulation and modulation of excitatory neurotransmission between neurons)
Oligodendrocytes
- CNS
- Create multiple myelin sheaths originating from single “multi-polar” cell body
Schwann Cells
- PNS
- Single Schwann cell forms singular myelin envelopment
- Trophic support to axon
- Electrical insulation of axons (increase action potential speed)
Microglia
- Resident immune cells of CNS
- Highly plastic
What is the shape of mitochondria in dendrites?
Elongated
What is the shape of mitochondria in axons?
Punctate
Kinesin Motors
Move towards the plus end of microtubules
Dynein Motors
Move towards the negative end of microtubules
Microtubules
- Forms from alpha and beta tubulin dimers (create asymmetric filament)
- Plus end undergoes polymerization and negative end is stable
How are microtubules oriented in axons?
Plus end away from soma
How are microtubules oriented in dendrites?
Mixed orientation
F-Actin
- Filamentous
- Forms dendritic outgrowths
Periodic Actin
Forms rings to generate structural support of axons and dendrites (often cross-linked with spectrin proteins to maintain rigidity)
Longitudinal Actin
Myosin mediated protein transport via myosin proteins
Presynaptic Cell
Releases chemical message via fusion of synaptic vessel with the membrane (releases chemical neurotransmitters)
Postsynaptic Cell
Expresses specialized receptors to detect released NT (translate signal to electrical or biochemical response)
Synaptic Cleft
Space between presynaptic cell and postsynaptic cell
Mechanotransduction
Convert pressure in skin to electrical voltage
Advantages of Electrical Signaling
- Operates at high speeds across long distances
- Requires little instantaneous energy expenditure
Disadvantages of Electrical Signaling
- Energetically expensive to maintain ion concentration gradients
- Requires transduction mechanisms to convert signals to/from chemical/mechanical signals to electrical signals
Charge (Q)
- elementary physical property of subatomic particles (electrons/protons) defining electrostatic interactions
- Uneven distribution of charges across atoms due to ions
Current (I)
- Movement of charges as a function of time
- I= delta Q/delta t
- Inward or outward with respect to the neuron
Inward Current
- Positive ions moving into the cell
- Negative ions moving out of the cell
- Depolarization
Outward Current
- Positive ions moving out of the cell
- Negative ions moving into the cell
- Hyperpolarization
Voltage (V)
- potential energy resulting from the separation of charges (ions) across a non-permeable membrane
- All cells have a resting transmembrane voltage that results from the uneven distribution of charges in the intracellular and extracellular compartments
- Relative to outside of the cell
Hyperpolarization
- Increase the membrane potential difference relative to the outside
- Vm becomes more negative
- Results from the net accumulation of negative charge in the cell
- Outward current
Depolarization
- Decreases the membrane potential difference relative to the outside
- Vm becomes more positive
- Results from a net accumulation of positive charge in the cell
- Inward current
Capacitor (C)
- Any device that separates (and stores) charges
- Plasma membrane
What is the amount of charge that can be stored on the capacitor proportional to?
Surface area of the cell
What is voltage directly proportional to?
The number of separated charges
What is voltage inversely proportional to?
The size of the capacitor separating an identical number of charges
Resistance (R)
- Measure of how difficult it is for current to flow
- More channels = lower resistance
Conductance (G)
- Measure of how easy it is for current to flow
- More channels= higher conductance
Ohm’s Law
- States that the change in voltage across a membrane is equal to the product of the charge and resistance across the membrane
- Opening/closing of channels creates current
- Movement of ions produces change in voltage
- Change in voltage allows neuron signaling
Electrical Gradient
Uneven distribution of ions created by the concentration gradient results in the development of an electrical gradient in the opposite direction
Nernst Equation
- Relates the chemical and electrical driving forces
- Mathematically defines the equilibrium potential (E(ion))
Equilibrium Potential
Voltage at which the concentration gradient and electrical gradient are equal and opposite
Permeability
Relative ability of each ion to move
GHK Equation
- Used to calculate the resting membrane potential in case of multiple permeant ions
What determines the resting membrane potential?
- Concentration of each permeant ion inside/outside the membrane
- Relative permeability of each ion across the membrane
Why is the resting membrane potential highly dependent on K+ concentration?
- Membrane at rest is highly permeable to K+
- Leak channels
What does distance depend on?
Relative resistances of the intracellular space and the membrane
What does time depend on?
The resistance and capacitance of the neuron (ability to hold charge)
Threshold
Membrane voltage at which sodium channel activation becomes negative (not a fixed number)
What does threshold depend upon?
- K+ currents in the cell
- Number of availability of sodium ions
Trigger Zone
- Axon initial segment (AID)
- Site of action potential generation
- Highest density of sodium channels and is the locus of action potential generation
Explain the upstroke of action potential.
- Voltage dependent sodium channels open in response to membrane depolarization
- Peak: Vm approaches E(Na) (driving force for sodium decreases)
Explain the downstroke of action potentials.
- Delayed activation of K+ channels
- When K+ channels open, large driving force at peak of AP - K+ efflux drives hyperpolarization towards E(K)
