Spinal Cord function

Question 1

How many spinal segments and spinal nerves does a human have?

Answer 1

31
spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Discrepancy between spinal levels and vertebral levels (emerge from spinal cord vs vertebrae)

Question 2

where do spinal nerves exit the spinal cord

Answer 2

Through the intervertebral foramen

Question 3

Which spinal nerves are enlarged?

Answer 3

For the limbs - C3-T1

L1-S3

Question 4

How does the patterns of nerve exit changes at the cervical level?

Answer 4

8 nerves but 7 vertebrae
C1-C7, nerves exit above the corresponding vertebrae
BUT C8 comes out below
And from there on out, nerve exit under corresponding vertebrae

Question 5

Where do nerves L1 to S1 originate from in the cord?

Answer 5

The cord is much shorter than the vertebral column-the nerves descend from the chord (cauda equina) and the exit later-
The further down you go (even on thoracic levels), the more the distance between spinal chord and nerve-More discrepancy as you go down
(made use to administer anesthetics -underneath the cord)

Question 6

What is the organisation of meninges around the spinal chord? How does it differ from the brain and why does it matter?

Answer 6

Dura mater, arachnoid matter and pia matter (in brain as well)
in brain, no space between skull and dura
BUT in spine, epidural space between bone and dura (used to inject anesthetics-under the end of chord tho)
Still subarachnoid space (sample CSF) - between arachnoid and Pia (Pia ends with spinal chord)

Question 7

What anchors the spinal cord

Answer 7

Fillum terminale reaches out of end of chord down with cauda equina and anchors at the bottom

Question 8

What is the difference between an epidural and a spinal aneathetic

Answer 8

Epidurals are aimed between the Dura and the arachnoid

Spinal are aimed to bypass and aim for the subarachnoid space

Question 9

Describe the general look of a spinal cord section, inculing the immediate surroudings

Answer 9

Butterfly shape - grey matter in the center (cell bodies)-dorsal and ventral horns
Outside of the butterfly-white matter-towards brain (superior/rostral), and down (inferior/caudal)
generally says same all the way down-
Exiting from the horns, rootlets join to form the ventral and dorsal root respectively
Dorsal/posterior root has a ganglia
Roots join to form SPINAL NERVE (then ramus can exit)-this is where meninges end

Question 10

Explain myotomes and dermatomes

Answer 10

Dermatomes is an area of skin that is only serves by a single spinal nerve segment (eg: umbilicus is around T9/10)
Myotome-an area/collection of muscle that is only served by one spinal nerve segment

Question 11

Describe the splitting of spinal nerve as they exit the chord

Answer 11

Posterior ramus-small and innervates the back muscle of the spine
Anterior ramus-much larger and usually is what has the main role

Question 12

Describe the roots of pain versus touch on a single spinal level

Answer 12

Touch and proprioception enters via the dorsal horn and go straigt up
Temperature and pain enter the horn, then signals to another neuron which crosses to the other side of the chord and then run up

Question 13

Describe the location of the grey matter used in limb touch and motor

Answer 13

In the dorsal regions-sensory: fasciculatus gracilis (closer to median)-for ipsilateral lower limb. Fasciculatus cuneatus-upper limbs
Motor: Lateral region has spinocerebella region (to cerebellum)
And lateral corticospinal tract (ispsilatteral motor innervation of limbs
also lateral spinothalamic tract-pain and temperature
Frontal side also has area of motor innervation-anterior corticospinal tract

Question 14

Describe how motor fibres descend from the brain

Answer 14

Descending motor fibres can split-into the anterior corticospinal tract (IPSILATERAL) and split to the other side (15%) and 85% becomes the lateral corticospinal tract (CONTRALATERAL)

Question 15

Describe the principal pathway of sensory neurons

Answer 15

For touch-1st sensory neuron passes into the spinal cord and goes up immediately (no switching around)-and synapses around the medulla (WHERE THEY SWITCH SIDE) -the 2ndary neuron (which goes to thalamus)
For pain, synapse to 2ndary neuron crosses at the SAME LEVEL at which it enters
General rule- 2ndary neuron are always the ones that cross over
3rd sensory neuron are same for both pathway-up to cortex from hypothalamus

Question 16

What regions of the spinal cords do dorsal pathways pass by?

Answer 16

Touch passes by the fasciculus gracilis and cuneatus (on the same side its entered) till the medulla where it crosses
Pain arrives in the dorsal, and then switches to the anterilateral system of the spinothalamic tract, then goes up to thalamus

Question 17

Describe the organisation of a pathway reflex

Answer 17

sensory pathway to dorsal root, where directly synapses to a motor neuron on the same level
= a lot more happens too but not needed

Question 18

Describe the location of cell bodies in ANS outflow

Answer 18

PSNS-mostly brain and S24-cranial nerves cell bodies in brain
SNS-T1-L2. in these parts of the cord, lateral horns contain cell bodies of SNS

Question 19

What impacts the effects/severity of spinal lesions?

Answer 19

Directly related to how much tissue loss there is
Usually small with trauma, but can be worse with metastases, degenerative disease

The level is also important-the higher up, the greater the lesion

Also the transverse side-posterior affects sensory, anterior affects motor. and left vs right as well

Question 20

What are the main tracts involved in spinal lesions

Answer 20

The main ones-dorsal, lateral corticospinal and lateral spinothalamic

Question 21

What are the 2 stages of corticospinal tract injury

Answer 21

1) spinal shock-loss of reflex below lesion, flaccid paralysis
2) return of reflex, but stronger (hyperreflexia)-rigid paralysis