uoft psl300 term test 1 – membrane Questions With
Complete Solutions
how do you calculate length constant
square root of membrane resistance divided by internal
resistance
what creates internal resistance
things like organelles and stuff inside the cytoplasm
what is myelination
,specialized glial cells called Schwann cells of the PNS or
oligodendrocytes of the CNS wrap around sections of the axon
many times (50-100 layers)
how does myelination increase conduction velocity
myelination increases membrane resistance
how much of axons are myelinated
~20% are myelinated because it makes the axon very bulky
schwann cell vs oligodendrocyte
schwann cell: wraps a single portion of one axon
oligodendrocyte: has processes that streak out and wrap a bunch
of axons individually
what is the node of ranvier
- the small gaps between adjacent portions of the myelin sheath
(between adjacent glial cells)
- only place where action potentials can be generated (where you
can find the voltage gated Na+ channels)
what is multiple sclerosis
- nervous system disease affecting brain and spinal cords
- myelin sheaths are damaged
- leads to slowing down or blocking of signals & various
symptoms
what is saltatory conduction
- AP will jump from one node to the next and AP will not be
generated in between but rather spread passively
, - if AP strong enough, can depolarize and bring next 5-10 nodes
to threshold potential
how does saltatory conduction have a safety factor built into it
- if a node is poisoned then the depolarizing current will just
skip over it and move to the next healthy patch of membrane
are most axons myelinated or unmyelinated
- most axons are unmyelinated
- get a lot of current leakage and slowed down conductance
velocity
- Na+ and K+ voltage gated channels are intermixed
how do unmyelinated axons still have insulation
- schwann cell and oligodendrocyte still engulf the axon
(multiple 5-30) but without winding
- called a remak bundle
conduction velocity of myelinated vs unmyelinated axons in
humans
yes: 80m/s
no: 2m/s
why can an AP not go backwards
- an AP can not go backwards and re-propagate because of the
refractory period (Na+ channels are inactivated)
- AP dies out at the end of the axon
what is a synapse
Complete Solutions
how do you calculate length constant
square root of membrane resistance divided by internal
resistance
what creates internal resistance
things like organelles and stuff inside the cytoplasm
what is myelination
,specialized glial cells called Schwann cells of the PNS or
oligodendrocytes of the CNS wrap around sections of the axon
many times (50-100 layers)
how does myelination increase conduction velocity
myelination increases membrane resistance
how much of axons are myelinated
~20% are myelinated because it makes the axon very bulky
schwann cell vs oligodendrocyte
schwann cell: wraps a single portion of one axon
oligodendrocyte: has processes that streak out and wrap a bunch
of axons individually
what is the node of ranvier
- the small gaps between adjacent portions of the myelin sheath
(between adjacent glial cells)
- only place where action potentials can be generated (where you
can find the voltage gated Na+ channels)
what is multiple sclerosis
- nervous system disease affecting brain and spinal cords
- myelin sheaths are damaged
- leads to slowing down or blocking of signals & various
symptoms
what is saltatory conduction
- AP will jump from one node to the next and AP will not be
generated in between but rather spread passively
, - if AP strong enough, can depolarize and bring next 5-10 nodes
to threshold potential
how does saltatory conduction have a safety factor built into it
- if a node is poisoned then the depolarizing current will just
skip over it and move to the next healthy patch of membrane
are most axons myelinated or unmyelinated
- most axons are unmyelinated
- get a lot of current leakage and slowed down conductance
velocity
- Na+ and K+ voltage gated channels are intermixed
how do unmyelinated axons still have insulation
- schwann cell and oligodendrocyte still engulf the axon
(multiple 5-30) but without winding
- called a remak bundle
conduction velocity of myelinated vs unmyelinated axons in
humans
yes: 80m/s
no: 2m/s
why can an AP not go backwards
- an AP can not go backwards and re-propagate because of the
refractory period (Na+ channels are inactivated)
- AP dies out at the end of the axon
what is a synapse
