Neurobio 2.1 (test 2, lec 1) Flashcards
Factors that affect action potential
MED
myelination
extracellular [K+]/ other electrolytes
diameter of axon
Lowest threshold for AP regeneration
Nodes of Ranvier
Why aren’t squid axons myelinated?
large diameter
T/F: Electrically coupled cells show a delay between the depolarization of one cell and another
False - virtually w/o delay
Term for any cell capable of firing AP
excitable
Gap junctions are also called
connexons
A single gap junction is composed of
two connexons
Each connexon is composed of
six connexins
A single connexon is also called
hemichannel
Gap junctions can be closed or open, and are usually _______
constitutively open
Benefits of electrical synapses
Sr. Dr. Synchronous activities of many cells Reliable Direct transfer of key small molecules Rapid signalling
Electrical synapses more prev during
development
Electrical synapses more prev in
vertebrates
Conditions under which gap junctions close
high intracellular [Ca2+] or [H+] (lower pH)
Conc. gets high within cell when cell is damaged
Ca2+ and H+
Capable of passing through gap junctions:
SAIGA
- Small, straight peptides
- ATP, cAMP, cGTP
- Ions
- Gluose
- Amino acids
Can calmodulin (CaM) pass through gap junctions?
no
Generally, molecules of this size or less can go through gap junctions
2,000 Da
chemical synaptic transmission involves conversion of ____ signal to _____ to _____
electrical, chemical, eletrical
Types of synaptic transmission
chemical and electrical
Synaptic plasticity is the result of _____ transmission because it has many _____
chemical, points for regulation
The double-edged sword of chemical synapses
complexity means many points for regulation, but also much can go wrong and a lot of neurological diseases are associated with abhorrent chem synaptic tsmission
neurons mainly receive synaptic input in ___
dendrites and cell body
synaptic input first generates ____ which propagates to
synaptic potential, passively to axon hillock
propagation of synaptic potential leads to
firing of action potential at axon hillock
axon hillock is also called
trigger zone or initial segment
How might propagation of synaptic potential be boosted?
many neurons have voltage-gated channels in dendrites and cell body which open in response to synaptic potential
myelination speeds up AP b/c why?
AP just jumps from node to node
saltatory conduction
Describe node of Ranvier
high density voltage-gated channels, only place current can flow across membrane of myelinated axon
Review: sodium flowing in is ______ current
inward
Diameter of squid axon
1mm
Diameter of mammalian axons
0.5-20 microns
Diameter of axon terminals?
1-2 microns (remember, they are not myelinated)
Increasing diameter of axon by one micron increases speed of AP firing by
about 5 meters/second
At body temp, in 20 micron diameter axon, AP firing can be as fast as
100 meters/s
multiple sclerosis results from
demyelination; you get weak and maybe cannot walk
Why is potassium loss more influential in muscle fatigue when you sweat?
The extracellular conc. is only 10-12 millimolar, that of sodium is higher
When extracellular potassium conc. goes down, RMP becomes more ____
negative
What happens if RMP is more negative in terms of stamina?
Depolarization is harder and you experience muscle fatigue
Typical distance between cells at chemical synapse
30-40nm
Example of electrically coupled cells
cardiac myocytes
Why is it advantageous for heart cells to be connected by gap junctions
Limit regulation so that there are not too many potential problems. Gap junctions are reliable and allow synchronous activity of many cells.
Describe topology of connexin
Four transmembrane domains, two extracellular loops, and intracellular N-terminal and C-terminal domains.
So basically an “M.”
Hint: “M” for myocyte junctions
Distance mentioned between two cells connected by gap junction
3.5nm
Why are gap junctions friendly?
Usually constitutively open
Diameter of gap junctional pore
10-20 Angstroms
“Ten to twenty is more than plenty (for various molecules to fit through such as ATP and linearlized polypetides lol)
Compare diameter of gap junction to that of selectivity filter of potassium channel
K+ channel is 3.2-3.3 Angstroms
Gap junctional pore is 10-20 Angstroms
These molecules cause gap junctions to close_____. This is a good idea because ___.
Ca2+ and H+. Cause cell death.
How to test if many cells are electrically coupled?
ucifer yellow dye - does it pervade all the cells?
Electrical synapses are seen more frequently during____. A plausible explanation is that _____.
Development. Neurons looking to reach same target may as well function as an electrical and biochemical unit.
In vertebrates, this type of synapse is more abundant than in invertebrates
electrical
Mechanisms for closing of gap junctions.
Phosphorylation and calcium or proton binding sites that induce conformational changes.
Diameter of unmyelinated human axon
1-2 micrometers
Speed of AP in unmyelinated human axon
1.8-2.2 m/s
Relationship between diameter of myelinated axon and speed of action potential
increase in 1 micrometer yields 5 m/s increase
Length of Node of Ranvier
2mm
To increase AP firing speed about 5 meters/second, increase diamter of axon by
1 micron
Significance of these numbers:
a) 1-2 microns
b) 2m/s
c) 10-20 Angstrom
d) 3.5nm
e) 30-40nm
a) diameter unmyelinated axon and axon terminals
b) speed of AP in unmyelinated axon
c) diameter gap junctional pore
d) length of electrical synapse
f) length of chemical synapse
