Neurophysiology Lecture 5

The vertebral column and spinal cord

Bony Formula for Vertebral Column in Canines

Cervical: 7

Thoracic: 13

Lumbar: 7

Sacral: 3

Coccygeal: ~20

More thoracic, lumbar, sacral in larger animals

Coccygeal very species/breed dependent 

Between which vertebral segments are intervertebral discs NOT found? (3 areas along spine)

1) Sacral - fused

2) Coccygeal - fused

2) Between skull and C2

• Skull and C1, and between C1 and C2 - no IVDs

• Atlas and axis form a joint together

What is the purpose of intervertebral discs?

Shock absorbers

• Viscous, fibrous ring on outside AKA annulus fibrosis

• Points of flexion/extension which allow spine to move without compromising the cord

Name the condition: a prolapse of intervertebral discs with subsequent neurological signs 

IVDD

• Intervertebral disc disease 

• Annulus fibrosis ruptures

  • disc gets pushed into the spinal cord (neurologic symptoms)

What is the tissue that surrounds the spinal cord called?

the Meninges

Name the 3 layers of the meninges

1) Pia mater

• Closest to spinal cord

2) Arachnoid mater

• Middle, very thin

3) Dura mater 

• Outside, very thick

Name the three spaces between the meninges

1) Subarachnoid space

• Between Pia mater and Arachnoid mater

  • Filled with CSF

2) Subdural space

• Between Dura mater and Arachnoid mater

  • Filled with serous fluid

3) Epidural space

• External to the Dura mater

  • Anesthetics injected here

Name the regions of the spinal cord

• Cervical

• Thoracic

• Lumbar

• Sacral

• Caudal 

Do the spinal cord segments line up with the vertebral column segments?

i.e. the nerve for T3 leaves the T3 segment of the vertebral column

Yes, 

EXCEPT for an extra cervical segment

• The exit for the first 7 vertebrae happen in front of the vertebrae it is named for 

  • Nerve and spinal root for C1 exit in front of C1

• At C7, the spinal root exits in front of C7 and then a root also exits from behind it, which is called C8

  • From there on out they exit from behind the vertebrae they are named for 

Vertebral column

• C7

Spinal cord

• C8

Term meaning:

The area of skin innervated by the sensory fibers from an individual spinal nerve/spinal segment

Dermatome

Term meaning:

The muscles innervated by the motor fibers from an individual spinal nerve/segment

Myotome

The spinal cord terminates shorter than the vertebral column.

In which region (with correlating numbers) does the spinal cord terminate?

Lumbar; L4 - L6 (vertebrae)

What is the distal lumbar region called where the spinal cord is absent but vertebral column still continues?

Cauda equina

How many enlargements are there along the spinal cord?

Name them

2

Cervical (cervicothoracic) enlargement

Lumbosacral enlargement 

Why are the cervicothoracic and lumbosacral sections of the SC enlarged?

These are specific places where the nerves that innervate the fore and hind limbs come off of

What are the segments of the SC that encompass the forelimb nerve innervation (cervicothoracic)?

C6, C7, C8, T1, (T2)

What are the segments of the SC that encompass the hindlimb nerve innervation (lumbosacral)?

L4, L5, L6, L7, S1 (S2)

List the FOUR zones of spinal cord relevance when localizing a lesion

1) Above cervical enlargement

• C1 - C5

2) Within cervicothoracic enlargement

• C6 - (T2)

3) Between upper and lower enlargements

• T3 - L3

4) In lumbosacral enlargement

• L4 - S4

• Never localize past lumbosacral enlargement 

What are the two gross physical divisions within the spinal cord?

Gray matter and white matter

What is the white matter of the spinal cord made up of?

What pathways does it it contain?

• Made up of axons

  • makes it white due to myelin which doesn’t stain well

• Composed of funiculi/columns which have tracts that carry sensory or motor information

  • Dorsal column - sensory tracts

  • Lateral column - sensory and motor

  • Ventral column - sensory and motor

What is the gray matter of the spinal cord made up of?

What pathways does it it contain?

• Made up of neuron cell bodies

• Composed of gray matter horns

  • Dorsal horn - sensory neurons (2°)

  • Ventral horn - motor neurons (1°)

    • All lower motor neurons

    • Contract or relax somewhere on the outside

  • Lateral horn - autonomic neurons

    • Only in thoracic and first few lumbar/sacral segments

    • Interneurons found here, involved in relay pathways

In the gray matter, what is the difference between the neurons found in the dorsal root and ventral root specifically?

1) Dorsal root - 2° neurons

• Axons from the sensory neuron enter the SC here

  • The first neurons that they usually synapse on (2°) are the first neurons encountered

• Synapse ALWAYS enters through dorsal horn - sensory

  • Spinal nerve always in ganglion

2) Ventral root

• Axons of motor neuron exit the spinal cord here

  • Nerve cell bodies where these axons originate are physically close to this root

• Synapse ALWAYS leaves through ventral root - motor

  • LMNs in central gray matter horn

In regard to white matter tracts and gray matter in general, what does it mean if they are organized somatotopically?

There is a strict relationship between where the tract/neuron is and the kind of information it conducts/mediates

• With SC injuries, specific signs can be explained by the damage to specific neuron types

• Tracts relay ONE type of information

How are white matter tracts typically named?

According to where they originate and terminate

Ex: spinothalamic

• Contains axons that relay APs from SC to thalamus

How many neurons are in a tract?

Do they always ascend and descend from the spinal cord on the same side?

A tract is a chain of two or three neurons

• sensory comes in through DR, synapses in GM and then axon leaves and ascends through brain 

No! Some tracts stay on the same side, but most cross over at some point in the pathway

• All pathways are paired too; one tract on left and right sides of SC

What are the two primary arteries that supply the spinal cord with blood?

1) The ventral spinal artery

• Follows ventral surface of cord

2) Paired dorsolateral spinal arteries

• Along base of dorsal roots of spinal nerves 

Depending on the region, what are the three arteries that feed into the ventral spinal artery and the dorsolateral spinal arteries?

1) Vertebral artery

• Cervical/anterior thoracic

2) Intercostal artery

• Thoracic

3) Aorta

• Lumbar

What supplies the core of the spinal cord?

Radial branches splitting off of these arteries

What is the term for when fibrocartilage from an IVD gets in the vascular supply, causing a myocardial infarction?

Fibrocartilagenous embolic myelopathy (FCEM)