Ballyk's week 1 lectures

Question 1

In neurons information transfer is….

Answer 1

UNIdirectional

Question 2

What is involved in the electrical transfer of information in the neuron

Answer 2

1. Dendrites
2. Cell body
3. Axon
   NOT synaptic terminal

Question 3

Where are bipolar neurons found?

Answer 3

1. Inner ear cochlea

Question 4

Where are pseudouipolar neurons found?

Answer 4

ALL somatic and visceral sensory neurons

still unidirectional flow

Question 5

How does communication occur in the neurone?

Answer 5

Electrically, through a change in TM potential

Question 6

Where is Vm graded in amplitude?

Answer 6

In dendrites and cell body

Graded: Amplitude of signal is proportional to intensity

Question 7

Where is the Vm fixed in amplitude?

Answer 7

Action potential, in AXONS

Signal intensity is coded by AP frequency

Question 8

Synaptic input can vary - name 2 types

Answer 8

1. Sensory Ns generating a receptor potential

2. Synaptic input generating a synaptic potential

Question 9

Where is the spike initiation zone located

Answer 9

1. near cell body at axon hillock (multipolar Ns)

2. In periphery at dendrites (Pseudounipolar Ns)

Question 10

What cellular organelles are present and missing in the axon?

Answer 10

1. no ribosomes, but have mitochondria and CK proteins

Question 11

Anteretrograde transport is fast to move…400mm/day

Answer 11

Membrane-bound substances, precursors of NTs - towards synaptic terminals + mitochondria

Question 12

Anteretrograde transport is slow to move… 5mm/day

Answer 12

Cytosolic and cytoskeletal proteins synthesize in soma (axoplasmic flow)
(REMEMBER USES KINESIN)

Question 13

Retrograde transport - fast 50-200mm/day

Answer 13

transports vesicles, endosomes, mitochondria, NGF, viruses, along DYNEIN

Question 14

What are the conditions necessary for ions to move through a channel?

Answer 14

1. An external force must induce ionic movement (specific electrochemical gradient for that ion)
   a) Electrical gradient
   b) Concentration gradient
2. channel must be permeable to the ion
   a) nongated (RMP)
   b) gated - voltage, ligand, mechanically gated

Question 15

Ion flux =

Answer 15

Electrochemical gradient (FORCE) X Conductance (where channel is open or closed)

Question 16

DEPOLARIZATION IS

Answer 16

A decrease in transmembrane potential

Question 17

HYPERPOLARIZATION IS

Answer 17

An increase in Tm potential

Question 18

sensory Ns in muscle spindles respond to what type of receptors?

Answer 18

Mechanoreceptors

Question 19

Receptor potentials have 2 properties with respect to intensity of stimulus

Answer 19

1. Graded - code the strength

2. Are decremental (decrease in amplitude over space)

Question 20

describe key features of the AP

Answer 20

1. ALL or none - NOT decremental
2. Triggered at the spike initiation zone
3. UNIdirectional
4. Propagate regeneratively
5. Information is coded in FREQUENCY AND PATTERN

Question 21

How can you increase the frequency of the AP?

Answer 21

Allow greater depolarization

Question 22

What happens to VG Na channels and VG K+ channels with sustained depolarization? (OVERSHOOT phase)

Answer 22

VGNa channels close - inactivate

VGK+ channels remain open!

Question 23

What is the absolute refractory period?

Answer 23

Na+ channel inactivation prevents AP generation

Question 24

During the relative refractory period what happens to Na+ channels?

Answer 24

They are resting and their population increases with repolarization

Question 25

Where are VG Na+ channels most concentrated?

Answer 25

In axon in spike initiation zone

Question 26

What happens if the terminal end of the axon is artificially depolarized to its threshold?

Answer 26

ANTIDROMIC AP generated

Question 27

What does myelin do?

Answer 27

Decreases membrane capacitance (decreased ability to hold charge), promotes current flow along the axon core.

Question 28

At the nodes of ranvier you have a high concentration of….

Answer 28

Na+ channels - allow saltatory conduction

Question 29

With the loss of myelin what happens?

Answer 29

Increase membrane capacitance - conduction block

Question 30

What is the difference between the resistance across the membrane vs axial resistance along the axon?

Answer 30

HIGHER membrane resistance

Question 31

In MS where does demyelination occur?

In GBS where does it occur?

Answer 31

1. MS - Central axons

2. GBS - peripheral axons

Question 32

How does lidocaine work? and which axons is it selected for?

Answer 32

1. Blocks the Na+ channels from the inside, causes conduction block
2. Selects for axons with lots of Na+ channels that are open, so it can get in, those are small unmeylinated pain axons