Degeneration, Regeneration and Plasticity

Question 1

WHICH NEURONS ARE CAPABLE OF NEUROGENESIS INTO ADULT LIFE

Answer 1

OLFACTORY NERVE
GRANULES OF DENTATE GYRUS
GRANULES OF CEREBELLUM

Question 2

WHY ARE CERTAIN NEURONS CAPABLE OF NEUROGENESIS IN ADULT LIFE

Answer 2

VERY SHORT AXONS

Question 3

HOW DOES RAPID REGENERATION OCCUR IN PNS

Answer 3

• schwann cells upregulate and multiply
• they secrete glial growth factors and stimulators
• they remove myelin debris
• resident macrophages in peripheral nerve are activated, proliferate, migrate and phagocytose myelin debris
• massive monocyte-derived phagocytes migrate from blood (blood nerve barrier is disrupted)

Question 4

WHY DOES MYELIN DEBRIS NEED TO BE REMOVED

Answer 4

BECAUSE IT HOLDS SOME SUBSTANCES THAT MAY INHIBIT GROWTH

Question 5

WHY DOES DEGENERATION OCCUR IN CNS

Answer 5

LOSS OF CONTACT BETWEEN OLIGODENDROCYTES AND AXON INITIATES APOPTOSIS
- inefficient myelin clearance –> BBB

Question 6

LACK OF REGENERATION IN CNS BECAUSE

Answer 6

GROWTH FACTORS AND STIMULATORS USUALLY NOT SECRETES BY CNS NEURONS
INABILITY OF MICROGLIA TO REMOVE MYELIN DEBRIS
BBB RESTRICTS MACROPHAGE ACCESS
ASTROCYTES CAN PRODUCE SCAR TISSUE

Question 7

HOW DO ASTROCYTES PRODUCE SCAR TISSUE

Answer 7

RELEASE CHEMICALS THAT BLOCK AXON REGROWTH

Question 8

AFTER EXTENSIVE OR SEVERE INJURY TO NEURON?

Answer 8

MAY NOT RECOVER DAMAGE

Question 9

WHAT FUNCTIONAL RECOVERY OCCURS IN MODERATE INJURIES (NEURONAL PLASTICITY)

Answer 9

• axon grows out sprouts to make contact with target (PNS)
• adjacent neurons take up the function of damaged neuron (CSN)
• neuron can grow collaterals to establish contact and restore functionality

Question 10

WHAT IS THE RESULT WITH DAMAGE TO THE SOMA

Answer 10

CELL DEATH

Question 11

WHAT OCCURS WHEN A NEURON IS DAMAGED

Answer 11

COMPLEX SERIES OF EVENTS INVOLVING NEURONAL DEGENERATION AND REGENERATION OCCUR

Question 12

WHAT OCCURS IF A NEURON IS CUT PROXIMAL TO CELL BODY

Answer 12

APOPTOSIS

Question 13

WHAT OCCURS IF NEURON IS CUT DISTAL TO THE CELL BODY

Answer 13

CHROMATOLYSIS OCCURS

• first soma takes in water and swells
• nucleus will be displace and become eccentric
• nissl substance become peripheral
• cell becomes larger

Question 14

WHAT OCCURS PROXIMAL TO THE SITE OF INJURY ON A NEURON

Answer 14

DEGENERATION UP TO THE FIRST NODE OF RANVIER

• retrograde degeneration
• may extend to a few more internodes if severe

Question 15

WHAT OCCURS DISTAL TO SITE OF DAMAGE OF NEURON

Answer 15

AXON SWELLS, DETERIORATES AND DISINTEGRATES

• disruption of axoplasmic transport
• disassembling axonal cytoskeleton
• myelin disintegrates
• phagocytes remove this myelin
• anterograde degeneration
• schwann cells multiple (for endoneural tube and guide growth of new neuron)

Question 16

WHAT OCCURS AS THE SOMA RECOVERS

Answer 16

IF NO SCAR, AXON SENDS OUT SPROUTS OR NEURITES ACROSS THE GAP, ONE ENTERS SCHWANN TUBE TO MAKE CONTACT WITH TARGET

Question 17

NEUROMA IS

Answer 17

WHAT OCCURS WHEN SPROUTS ARE DISORGANIZED AND CROWDED AND FORM A MASS OF TANGLED AXON AT NODE OF RANVIER