lectures - nervous tissue part 3

do we know much about dendrites

no

do dendrites have growth cones

they have mini growth cones, they can form throughout our lives

describe dendrite growth cone behavior

variable, sometimes responds to signals in reverse to axon growth cone

sometimes when synapsing with axon, responds identically to axon growth cone

describe the complexity of dendrites

branching depending on amount of incoming innervation and innervation activity levels

give an example of how dendrites can be very dynamic

in mice some dendrites in visual system can appear and disappear within minutes when exposed to stimuli

what do purkinje cells do

help drive limb movement and hand-eye coordination

oligodendrocytes are glial cells of the

CNS

schwann cells are glial cells of the

PNS

oligodendrocytes can make

multiple sheaths per cell

schwann cells can make

1 sheath per cell

in the CNS white matter is

myelinated

in the CNS gray matter is

not myelinated

what does myelin allow for

fast electrical conductance along axons

how does myelin help conductance

acts as electrical insulator

localizes Na channels at short gaps between adjacent myelin sheaths

is myelination dynamic

yes, oligos and schwann cells become worse with age

does CNS and PNS myelin plasticity differ

yes

why does CNS and PNS myelin plasticity differ

CNS has no axon repair

PNS has help in axon repair

in rodents, oligodendrocyte precursor cells (OPC) can

under go symmetric div. to make more oligo precursor

and/or diff into a post-mitotic pre-myelinating oligo (PO)

what happens when a OPC diffs into a PO

loses cell potency and can only express oligo genes

describe the PO cells after creation

80% attrition rate due to making more than needed

remaining 20% migrate to axon and become oligos producing myelin

describe CNS myelin plasticity

oligogenesis occurs throughout life, OPCs active in adulthood

numbers peak during middle age

rate of new oligo production ↓ with age

what are the 2 types of schwann cells (SCs)

myelinating and remak

very generally describe myelinating SCs

symbiotic relationship with axon

produce and wrap axons in myelin sheath

nourish axon

very generally describe remak SCs

non-myelinating

nourish axons

how are schwan cell precursors (SCP) formed

neural crest cells contact with peripheral neuron triggers det and diff into SCP

SC precursors are bound by

associated axons, dependent on them for survival

without feedback from the axon, what happens to SCs

they undergo apoptosis

where on the neuron does the SCP bind

more towards the axon

how are immature SCs (ISCs) formed

SCPs stop migrating up axon and det into ISC while axon is still growing

what is the function of ISCs

figure out which axons to myelinate through radial sorting

Describe radial sorting

based on diameter, the thicker the axon, the more insulation is needed so ISC targets these

when are mature myelinating SCs formed

after ISCs undergo radial sorting

are mature myelinating SCs "self-supporting"

yes

can peripheral nerves undergo regeneration

yes

why can peripheral nerves undergo regeneration

because of remak SCs

what are the caveats of peripheral nerve regeneration

1. effective only on minor injuries that are at single axon level and not too large

2. SCs competence diminishes with age

Describe the process of SC mediated PNS regeneration

1. myelinating and remak SCs undergo reprogramming

2. repair SCs remove damaged part of axon

3. damaged tissue is cleared out

4. repair SCs form scaffold to guide regrowing axon to target

5. repair SCs prolif and turn back on myelinating genes

6. newly reprogrammed myelinating SCs make myelin

describe how myelinating and remak SCs reprogram

myelinating SCs de-myelinate

remaks activate immediately

both become repair SCs

how do repair SCs work

pull away and break down edges of axon

produce trophic factors to nourish regrowing axons

do all repair SCs turn back on myelinating genes

no, some proliferate and form remak SCs

does Wallerian degeneration occur in the CNS

yes to a lesser extent, but its not as understood