injury and repair of the NS

Question 1

what happens to information when a nerve breaks?

Answer 1

info is blocked and cant be transmitted

Question 2

what is a primary lesion/injury?

Answer 2

where a nerve is cut

Question 3

where can nerve damage spread to?

Answer 3

• anterograde degeneration - moving forward to the next synaptic bouton
• retrograde degeneration - moving backwards
• to the cell body
• through transneuronal degeneration

Question 4

what is the endoneurium?

Answer 4

layer of c.t. around axons. Enclose and protect myelin and axons

Question 5

what is the perineurium?

Answer 5

axons organised into fascicles. Perineurium is c.t. around a fascicle.

Question 6

what is the epineurium?

Answer 6

outermost layer of dense c.t. Fasicles bundled together with blood supply and fatty acid tissue. These are surrounded by an epineural sheath.

Question 7

what does the success of nerve repair depend on?

Answer 7

o The severity of the initial injury (primary damage):
- What has been damaged
-How much has been damaged
o The extent of secondary damage.

Question 8

what is neurapraxia?

Answer 8

temporary loss of motor and sensory function due to blockage of nerve conduction

Question 9

when does neurapraxia occur?

Answer 9

during ischaemia

Question 10

what is damaged in neurapraxia?

Answer 10

myelin is disrupted

axon remains intact

Question 11

does nerve degeneration occur in neurapraxia?

Answer 11

no

Question 12

what is axonotmesis?

Answer 12

disruption of axons and myelin sheath damage resulting from severe crush or contusion.

Question 13

what is damaged and what remains intact in axonotmesis?

Answer 13

Epineurium sheath as well as Schwann cells remain intact

Myelin and axon are damaged

Question 14

is neurapraxia reversible?

Answer 14

yes

Question 15

is axonotmesis reversible?

Answer 15

yes

Question 16

why is axonotmesis reversible?

Answer 16

bc the epineurium is intact so the nerve still has a metabolic and blood supply

Question 17

what is neurotmesis?

Answer 17

when both the axons and nerve sheath are disrupted

Question 18

is neurotmesis reversible?

Answer 18

no

Question 19

what is the most severe form of nerve injury?

Answer 19

neurotmesis

Question 20

what is the least severe form of nerve injury?

Answer 20

neurapraxia

Question 21

when is neuron damage reversible?

Answer 21

when the epineurium is intact, even if the axon is damaged

Question 22

what are the 2 main things that happen after axon damage?

Answer 22

cell is alerted that damage has occurred

cells in the DRG change their phenotype

Question 23

how is a cell alerted that damage has occured

Answer 23

a burst of APs sent to the DRG of axon
disruption of retrograde transport flow of trophic support
positive injury signals

Question 24

what are neurotrophic factors?

Answer 24

factor that is associated with providing nourishment to allow for growth. Their expression (especially of the nerve growth factor) is increased when there is a nerve injury.

Question 25

give examples of neurotrophic factors

Answer 25

Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF), Glial cell-Derived Neurotrophic Factor (GDNF)

Question 26

what happens when cells in the DRG change their phenotype?

Answer 26

switch from transmission state to growth state decrease in all ion channels and proteins involved in neurotransmission upregulation in proteins involved in axonal growth to make new membranes

Question 27

what does afferent terminal atrophy lead to?

Answer 27

loss of input to spinal cord --> disinhibition of neurons in the spinal cord --> spontaneous activity --> cell death

Question 28

describe the process of nerve regeneration

Answer 28

* Schwann cells divide to make daughter cells in mitosis * They secrete trophic factors to attract axons (guided back to the reconnection) and allow growth to happen. * Daughter cells re-myelinate the axon after growth and make the new functional axon

Question 29

what is the growth rate in the pns?

Answer 29

1mm/day | can vary between 0.5-0.9mm/day

Question 30

why is it unusual for patients to regain normal functions?

Answer 30

the process of reconnecting various components is very complex

Question 31

why is the outcome better when repair occurs earlier?

Answer 31

* Prolong axotomy = reduces the number of motor neurons and axons that can regenerate. * After 1 month, Schwann cells down-regulate regeneration associated factors

Question 32

what does prolonged denervation of muscles lead to?

Answer 32

o Muscle atrophy and fibrosis | o Profound decrease in numbers of regenerating axons through deteriorating intra-muscular sheath.

Question 33

when is cns repair needed?

Answer 33

in spinal cord injury

Question 34

what is tetraplegia?

Answer 34

total loss of all use of all 4 limbs and torso

Question 35

what is paraplegia?

Answer 35

impairment in motor or sensory function of the lower extremities

Question 36

what are the types of spinal cord trauma?

Answer 36

laceration | concussion

Question 37

what does spinal cord trauma produce?

Answer 37

site of primary cell death - epicentre

Question 38

what does the epicentre spread into?

Answer 38

zone of secondary cell death

Question 39

how does a glial scar form?

Answer 39

after primary cns injury - macrophages and microglia engulf debris and the injury site becomes walled off by a glial scar

Question 40

why is a glial scar good?

Answer 40

o Engulfs debris o Seals the lesion site o Repairs the BBB

Question 41

how can a glial scar be a problem?

Answer 41

o Expresses chemicals that inhibit axon growth (chondroitin sulphate proteoglycans) – released by astrocytes --> acts as a physical and chemical barrier for neurodegeneration

Question 42

explain what a sprouting response is?

Answer 42

axons will try and grow through glial scar but cannot go anywhere. Distal tracts will undergo Wallerian degeneration which will lead to lots of myelin debris and chemicals which inhibits axonal growth.

Question 43

what are the two main barriers to cns repair?

Answer 43

hostile environment - glial scar and myelin-associated inhibitory proteins - poor regenerative response

Question 44

what is tinel's sign used for?

Answer 44

used to identify sensory recovery --> lightly tapping over nerve to elicit sensation of tingling.

Question 45

what procedures can be used to solve early problems with the cns?

Answer 45

neuroprotection - contains the effects of early trauma promotion of axonal regeneration guiding axonal regrowth