Chapter 12.5: Axon Regeneration

Regeneration is possible if

• neuron cell body is intact

• enough neurilemma remains

Regeneration success is more likely if

• damage is less extensive

• distance between site of damage and structure it innervates is shorter

Step 1 of regeneration

axon is severed by trauma

Step 2a of regeneration

proximal to cut, axon seals off and swells

Step 2b of regeneration

distal to cut, axon and sheath degenerate (Wallerian degeneration) but neurilemma survivies

Step 3 of regeneration

• neurilemma and endoneurium form regeneration tube

  • axon regenerates guided by nerve growth factors released by neurolemmocytes

  • axon reinnervates OG effector or sensory receptor

Why is regeneration extremely limited?

• oligodendrocytes secrete growth-inhibiting molecules; not growth factors

• large number axons crowd CNS

• regrowth obstructed by scars from astrocytes and CT

Three types of voltage-gated Na+ channels

• resting tate: activation gate closed; inactive gate open. entry of Na+ precented

• activation state: activation gate open (due to voltage change); inactivation gate open. Na+ moves through channel

• inactivation state: activation gate open; inactive gate closed. entry of Na+ prevented. This state last short time-channel resets to resting state

Functional segments in neuron

• receptive segment (dendrite and cell body)

  • chemically gated channels (Cl- channels)

• initial segment (axon hillock)

  • VG Na+ channels and VG K+ channels

• Conductive segment (axon and branches)

  • VG Na+ channels and VG K+ channels

• transmissive segment (synaptic knobs)

  • VG Ca2+ channels and Ca2+ pumps