3.21 Spinal Region Lecture 2 Flashcards
What do radicular arteries arise from?
thoracic and abdominal aortae
Each radicular artery gives rise to
one spinal artery (anterior spinal artery)
What happens to the 2 anterior spinal arteries?
- fuse and run in anterior median fissure
- run the entire length of SC
What supplies the anterior 2/3 of the SC?
branches of anterior spinal arteries
What supplies the posterior 1/3 of SC?
PICA
What happens to the PICA to supply the SC?
PICA
» 2 posterior spinal arteries
» proceed along dorsal rootlet attachments
Where are the dorsal rootlet attachments?
in posterolateral sulci
Does fusion occur with posterior blood supply?
nope
T12 significance with SC blood supply
- great radicular artery
- supplies lumbosacral in addition to everything else
How does venous drainage occur?
- via radicular veins
- drains into epidural venous plexus
functions of SC
- exchanging info from other segments via columns
- exchanging info from periphery
What is the “key” to SC that helps with modulation?
interneurons
3 things interneurons help with
- stepping pattern generators
- reflexes
- inhibitory circuits
function of inhibitory circuits
modulation of fine motor activity
What is a stepping pattern generator a subtype of?
central pattern generator
What do stepping pattern generators do?
help keep normal cadence/rhythm when you walk
stepping pattern generators in lower thoracic/lumbar regions
help with locomotion
stepping pattern: external stimulation
electrically stimulating LMNs
- no cortical input necessary
What produces stepping pattern generators?
SC
initial decision to move comes from
motor cortex
motor planning regions
adaptability of stepping pattern generators to different scenarios (ex.)
think feet on treadmills going different directions
Are stepping pattern generators sufficient for walking? Why or why not?
- no
- higher neural control for purposeful movements
What is necessary for activation of interneuron circuits for stepping pattern?
UMN activation
overall action of UMN with step pattern
fires to both flexor and extensor motor neurons
- extensors contract
- flexors inhibited
reciprocal inhibition
Interneuron activity in stepping pattern
- causes reciprocal inhibition
- get a refractory period
- cycle repetition
refractory period of interneurons: implication
- flexors now free to contract because they aren’t getting inhibition
- inhibition of extensors happen now as well
UMN contribution to walking
- doesn’t have to act much
- initial firing due to decision made
How does sensory input come into play with stepping pattern gen?
GTO helps with proprioception and appropriate level of firing of LMN to muscles
- inhibition of antagonist
- activation of agonist
reciprocal inhibition
- inhibition of agonist
- activation of antagonist
recurrent inhibition
When might reciprocal inhibition fail to occur?
when anxious (makes you really tired!)
What cells allow recurrent inhibition?
Renshaw cells
What are Renshaw cells?
- branches of alpha motor neurons
- feed back and inhibit themselves
Renshaw cells and inhibition: example
- playing piano and fine motor control
- keeps from overshooting notes
reciprocal and recurrent inhibition work _______
simultaneously
