Lecture - MSK (Spinal Cord)

Question 1

Organisation of the nervous system:

1. What is the CNS?
2. What cell bodies of neutrons called in CNS?
3. What are dendrites and axons called in CNS?
4. What is in the PNS?
5. What cell bodies of neutrons called in PNS?
6. What are axons called in PNS?

Answer 1

1. Brain and spinal cord
2. Grey matter
3. White matter
4. Cranial nerve and spinal nerve
5. Ganglia
6. Spinal nerves/cranial nerve (extensions away from CNS)

Question 2

Spinal cord

1. Continuation of what?
2. Is the vertebral column longer or shorter?
3. There are two enlargements - where and what are they called?
4. Where is the conus medullar is?
5. Where is the end of subchondrial space?
6. What is the film terminale?

Answer 2

1. Continuation of medulla to
   L1/L2 level
2. Shorter than vertebral
   column
   -When born, vertebral and cord same size but as we grow, bone grows fast and NS grows slower so bone goes further down and finishes at L1/L2 level.

3. Two enlargements where
the cord has more neurons:
-cervical enlargement and
-lumbosacral enlargement 
(Bc plexus - more neurons there so looks larger)

4. Lower border of L1
5. S2
6. • thread of pia-like
     connective tissue
     connects spinal cord to
     coccyx
     -From conus medilaris, there is an extension of pia mater and goes all the way down and pierces arachnoid + dura mater at S2 level but goes all the way down to coccyx
     -It’s called () (pia CT extension) - fucntion is to anchor spinal cord to coccyx at the bottom

Question 3

Spinal cord (contd)

1. Floats in what?
2. Attached to?

Answer 3

1. CSF
2. Attached to:
   • brainstem above (to medulla)
   • dura mater laterally (via denticulate ligament*)
   • coccyx below (via filum terminale)

• = On the sides up to L1, there are sleeves of pia mater called denticulate ligaments (look like teeth) - also anchor spinal cord to the dura mater

Question 4

In both CNS and PNS there are 4 types of neurons and nerves, what are they?

Explain that grey matter in terms of the horns - dorsal, later and ventral

What is the white matter divided into?

Answer 4

Somatic
• Motor (efferents)
• Sensory (afferents)
Visceral
• Motor (efferents)
• Sensory (afferents)

There is grey matter in the middle in the shape of an H and the thin ends of that are facing posterior. In that grey matter:

• dorsal horn: somatic sensory
• laterla horn: visceral motor (deals with sympathetic nervous system so axons for symapthetic fibres will originate from lateral horn)
• ventral horn: somatic motor

Dorsal, ventral and lateral column - they contain ascending and descending nerve tracts

Question 5

Spinal cord: somatic nerves

1. What type of axons run in the anterior or ventral root?
2. What about posterior root?

Answer 5

1. Motor
2. Sensory

The spinal nerve is when the post and ant combine so there are both sensory and motor axons in that

Question 6

What does a segment of the spinal cord look like?

Answer 6

Slide 11

Question 7

Spinal segments in relation to levels of corresponding vertebrae:

1. How many spinal segments are there?
2. How many vertebrae are there?
3. Because of the discrepancy between level of spinal segments and corresponding vertebra…..

Answer 7

1. 31: C8, T12, L5, S5 and Co1
2. 32-33: C7, T12, L5, S5 and Co3-4

Roots will still come through at their respective intervertebral disc even though finish at L1

3. ……the lower spinal roots become increasingly oblique and emerge from their intervertebral foramen at increasingly lower levels. Form CAUDA EQUINA

=Roots of spinal nerves (not spinal nerves! They are v short - roots form spinal nerve)

Question 8

What forms the spinal nerve and then what does the spinal nerve divide into?

Answer 8

The posterior and anterior root form it and then it will divide into small posterior and large anterior rami. Posterior goes to intrinsic back muscles and anterior goes to all muscles except intrinsic back muscles

Question 9

What are you doing and testing when you do the patellar tendon reflex test?

Answer 9

Trying to test a specific level of spinal cord

Stimulate extensor muscles - spindles in muscle get sitmualted and mesages then go to dorsal root ganglion and then it excites the extensor muscles and inhbits the antagonist of that extensor group so they dont get activated

Question 10

Spinal cord (more)

So the anterior ramus is mixed aka contains motor and sensory fibres. What can you say about sympathetic fibres in this case?

Answer 10

They run with the spinal nerve; they use the spinal nerve to reach their targets

The sympathetic fibres originate from lateral horns of T1-L2. Sympathethic fibres originate from lateral horn and leave via the anterior horn and latch onto anterior root of spinal nerve and close to the vertebral coloum, there is a chain of symapthethic ganglia

There is sympathethic chain next to verterbra and made up of axons and clumped ganglia so referred to paraertebral ganglia. Linked to spinal cord via the communicans
-the sympathetic
axons use spinal nerve ramus to reach the
target after synapsing in the paravertebral
ganglion of the sympathetic trunk.

There is the white ramus communican (pre-ganglionic, myelinated) and grey ramus communican (axon unmyelinated after synapse)

Question 11

Slides 16-22

Answer 11

Go and review them and understand them. Perhaps integrate that info with last year’s stuff too

Question 12

Three layers of meninges in spinal cord - what are they?

Answer 12

1. DURA MATER:
   • Dura is tough outer most layer of the meninges. In the vertebral canal outside the dura is extradural/epidural space with extradural fat
   • (epidural anaesthesia is given in this space

Tough outer covering

Outside this is a layer of fat - extradural fat (region where epidural anaes given)

Only in vertebral canal do you find the fat bc dura firmly attached to endosteium in brain

Dura protects spinal cord

2. ARACHNOID MATER:
   • in contact with but not attached to dura, middle layer
   • subarachnoid space between the arachnoid and pia mater, which contains cerebrospinal fluid (CSF)
   • very fine tissue (like a spider’s web - arachnoid trabeculae)

After dura - in contact with dura and is the middle layer

3. PIA MATER:
   • thin, vascular, innermost
   • lies on surface of brain and spinal cord
   • lateral extensions - denticulate ligaments

Deep to arach

Delicate

Goes to sulki

Snuggly attached to nervous tissue

But also sends sleeve to arachnoid and anchors to dura mataer

Question 13

What can you say about denticulate ligament?

Answer 13

(part of pia)
fuses with arachnoid
and dura

Anchor the spinal cord in place

Also lie in bw the anterior and posterior roots and rootlets so dividing part bw dorsal and ventral roots of spinal nerve

Question 14

Spinal meninges: clinical implications - what can you say about the anasthesia?

Answer 14

Spinal anes given in subarachnoid space but epi dural (just before the dura) - same area to block pelvic strucutes and lower limb (both work). Spinal words faster and epi takes a little longer to go to sides where spinal nerves are

Subdural space not that large

Question 15

Lumbar puncture - tell me about it

What layers over the posterior intervertebral space must you pass to aspirate CSF?

Answer 15

Sometimes need to take CSF sample

Safer area is below L1/2 bc spinal cord finishes there

Subarach space finishes at S2 so cauda equina is floating in CSF below L1.

Safest area for lumbar punc is L4/5

To get there - find highest point of illiac crest, go towards vert coloumn, and that hits body of L4. You can get sample just above or below (L3 or L5)

Layers:

• skin
• superficial fascia
• (deep fascia)
• supraspinous lig.
• interspinous lig.
• ligamentum flava
• extra(epi)dural space
• dura
• (subdural space?)
• arachnoid mater
• subarachnoid space

Find it by finding the highest point of iliac crest - that’s L4

Question 16

What lies in the space between L1 and S2?

Answer 16

Cauda eqina (bundle of spinal nerve roots

• cluster of the roots of L/
  S/C nerves on their way
  to intervertebral
  foraminae

All the toots here are called cauda equina

There is CSF in this area so the nerve roots of spinal nerves floating aroud there

Question 17

What is the spinal cord blood supply like?

Answer 17

Supplied by single anterior artery and usually 2 posterior spinal art (one on right and one on left)

Ant spinal art lies in median fissure

Come from foramen magnum area - branches of vertebral artery and it supplies the ant part of the spinal cord

Post part of spinal cord supplies post region

Lateral parts of spinal cord also supplied by anterior artery too

As these BV come down, there are a number of anastomoses/communications bw different sections of vert coloumn……So if they are in the thoracic area, they will communicate/be helped by the post intercostals vessels

If go in lumbar area, there are lumbar arteries from abd aorta and they also anastomose with verterbral arteries

In pelvis, vessels from internal illiac (lateral sacral arteries) anastomose

So lots of communication = imp bc spinal cord imp so if one gets blocked, there are back ups

Veins:
The veins anastomose freely
Number of plexus ant and post form around spinal cord and they also communicate with diff sections of body

Like, in neck - these communicate with vertibral veins

In thoracic area, they communicate/anastomose with azygoous vein so all thoracic post drain into azygous veinous system etc