Ballyk's week 1 lectures Flashcards
In neurons information transfer is….
UNIdirectional
What is involved in the electrical transfer of information in the neuron
- Dendrites
- Cell body
- Axon
NOT synaptic terminal
Where are bipolar neurons found?
- Inner ear cochlea
Where are pseudouipolar neurons found?
ALL somatic and visceral sensory neurons
still unidirectional flow
How does communication occur in the neurone?
Electrically, through a change in TM potential
Where is Vm graded in amplitude?
In dendrites and cell body
Graded: Amplitude of signal is proportional to intensity
Where is the Vm fixed in amplitude?
Action potential, in AXONS
Signal intensity is coded by AP frequency
Synaptic input can vary - name 2 types
- Sensory Ns generating a receptor potential
2. Synaptic input generating a synaptic potential
Where is the spike initiation zone located
- near cell body at axon hillock (multipolar Ns)
2. In periphery at dendrites (Pseudounipolar Ns)
What cellular organelles are present and missing in the axon?
- no ribosomes, but have mitochondria and CK proteins
Anteretrograde transport is fast to move…400mm/day
Membrane-bound substances, precursors of NTs - towards synaptic terminals + mitochondria
Anteretrograde transport is slow to move… 5mm/day
Cytosolic and cytoskeletal proteins synthesize in soma (axoplasmic flow)
(REMEMBER USES KINESIN)
Retrograde transport - fast 50-200mm/day
transports vesicles, endosomes, mitochondria, NGF, viruses, along DYNEIN
What are the conditions necessary for ions to move through a channel?
- An external force must induce ionic movement (specific electrochemical gradient for that ion)
a) Electrical gradient
b) Concentration gradient - channel must be permeable to the ion
a) nongated (RMP)
b) gated - voltage, ligand, mechanically gated
Ion flux =
Electrochemical gradient (FORCE) X Conductance (where channel is open or closed)
DEPOLARIZATION IS
A decrease in transmembrane potential
HYPERPOLARIZATION IS
An increase in Tm potential
sensory Ns in muscle spindles respond to what type of receptors?
Mechanoreceptors
Receptor potentials have 2 properties with respect to intensity of stimulus
- Graded - code the strength
2. Are decremental (decrease in amplitude over space)
describe key features of the AP
- ALL or none - NOT decremental
- Triggered at the spike initiation zone
- UNIdirectional
- Propagate regeneratively
- Information is coded in FREQUENCY AND PATTERN
How can you increase the frequency of the AP?
Allow greater depolarization
What happens to VG Na channels and VG K+ channels with sustained depolarization? (OVERSHOOT phase)
VGNa channels close - inactivate
VGK+ channels remain open!
What is the absolute refractory period?
Na+ channel inactivation prevents AP generation
During the relative refractory period what happens to Na+ channels?
They are resting and their population increases with repolarization
Where are VG Na+ channels most concentrated?
In axon in spike initiation zone
What happens if the terminal end of the axon is artificially depolarized to its threshold?
ANTIDROMIC AP generated
What does myelin do?
Decreases membrane capacitance (decreased ability to hold charge), promotes current flow along the axon core.
At the nodes of ranvier you have a high concentration of….
Na+ channels - allow saltatory conduction
With the loss of myelin what happens?
Increase membrane capacitance - conduction block
What is the difference between the resistance across the membrane vs axial resistance along the axon?
HIGHER membrane resistance
In MS where does demyelination occur?
In GBS where does it occur?
- MS - Central axons
2. GBS - peripheral axons
How does lidocaine work? and which axons is it selected for?
- Blocks the Na+ channels from the inside, causes conduction block
- Selects for axons with lots of Na+ channels that are open, so it can get in, those are small unmeylinated pain axons
