BMS11004 - WEEK 3 - TUESDAY Flashcards

neuronal propagations, factors affecting neuronal conductions, saltatory conduction, demyleinating disease

1
Q

speed of AP propagation is determined by how fast next segment of membrane gets depolarised to thresold. which 2 factors determine this:

A
  1. space constant (length constant)
  2. time constant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is space constant (also known as length constant)

A

how far current can spread passively along axons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

why is current spread down axon passive

A

AP very brief and only affects small segment of membrane at at a time
passive due to laws of physics “like charges repel”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

explain mathematical cable theory

A

weakening of signal as spread along axon, axon like water hose and electricity is water electrical charge = water sitting still
electric current = charge in motion, water flow
voltage (forces pushing charges) = water pressure
resistance = what stops water flowing
capacitor = 2 plates with gap inbetween allowing charge to build up on 1 side creating voltage
axon like leaky hose, current can flow down but also leaks out via channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

give the formula for calculating space constant (using membrane resistance, internal resistance)

A

λ = √Rm/Ri
space constant = square root of membrane resistance divided by internal resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

explain membrane resistance

A

inversely proportional to surface area of membrane (more area = more leaks)
depends on axon circumference (c=2πr)
more membrane resistance = more space constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

explain internal resistance

A

inversely proportional to cross-sectional area of axon (wider hose = water travels more easily)
depend on area (rA=πr²)
wider axon = longer space constant
“how hard is it for current (water) to pass along axon (hose pipe)”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is time constant

A

how long it takes membrane to charge up (how long it takes for pressure to build up across wall)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

give equation for time constant

A

T = RmCm
membrane resistance = how unleaky hose wall is
membrane capacitance = how stretchy hose wall is

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

explain how membrane can be both resistor and capacitor

A

resistor = current can pass through but not very well
capacitor = charge can build up on one side

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

myelin insulation increases membrane resistance, what impact does this have for membrane capacitance

A

longer space constant so current can spread further down axon, so decreases membrane capacitance meaning it counteract effect of increased membrane resistance on time constant, allowing membrane to charge upa s quickly as usual

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

explain how saltatory conduction work

A
  1. charge enter via Na Channel inbetween myelin
  2. spreads passively through insulated axon part, then charge can enter again at next NoR/Na channel
  3. charge decays slow enough that by time reaches next NoR still above threshold (myelin insulation)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

explain how saltatory conductions saves energy

A

only Na+ etner at NoR not all along axon, so less work for Na/K pump to restore Na+ gradient, as less Na+ to be pumped in, so less energy wasted for removing excess Na+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

explain how myelination can save space in brain

A

without myelin, can only increase speed of conduction by widening axon following the rule =
to increase speed 10x, need increase radius 100x, so axon volume increased 10,000x

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

explain how demyelination diseases impairs neuronal conduction

A

distribution of ion channels are designed for use alongside myelin. if myelin disappear, signal can’t travel correctly - not insulated
cause ectopic spike in impulse conduction, due to maladaptive homeostatic compensation (neurons trying to fix problem without new myelin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what causes multiple sclerosis (affects CNS)

A

auto-immune disorder
attacks myelin
worsen when stressed/high temp = neuronal conduction “safer” at low temp due to Na+ channels inactivate slowly

17
Q

give symptoms of multiple sclerosis

A

episodic (symptoms worsen/better)
vision problem, numbness, muscle spasms

18
Q

whats Guillain-Barre syndrome - affects PNS

A

auto-immune disorder impacting PNS myelin
numbness, tingling, weakness
usually recover via PNS myelin regeneration