Lecture 5 - The Vertebral Column and Spinal Cord

Question 1

what surrounds the spinal cord and what is its function, what is the vertebral column composed of and what does it form

Answer 1

• the spinal cord is surrounded by the vertebral column, a bony structure that protects the nervous tissue while allowing movement
  -its composed of individual bony elements called vertebrae whose central cavities, when lined up form the spinal or vertebral canal

Question 2

regions of the vertebral column, specifics for canine

Answer 2

divided into regions: cervical, thoracic, lumbar, sacral, coccygeal

minor species differences exist in number and shape of vertebrae in each region. for the dog its: C-7, T-13, L-7, S-3, Cg~20

Question 3

what are vertebrae separated by? what is their function
exception?

Answer 3

adjacent vertebrae are separated by intervertebral discs (except sacral and coccygeal)

these act as shock absorbers and points of flexion/extension which help allow the spine to move uniformly without compromising the spinal cord

Question 4

what is a major clinical syndrome in dogs? what is it called? what is the challenge with it

Answer 4

prolapse of intervertebral discs and subsequent neurological signs is a major clinical syndrome in dogs

called intervertebral disc disease (IVDD)

localizing and treating/managing these diseases is often a significant clinical challenge…. therefore making a diagnosis can be hard

Question 5

atlas and axis - why did they evolve, discs?

Answer 5

1st (atlas) and 2nd (axis) cervical vertebrae have evolved modified structure to support skull and allow enhanced movement compared to the rest of the vertebral column

no intervertebral disc is present between C1 and the skull, or C1 and C2

Question 6

the sacrum - how many and why are they fused species variation

Answer 6

3 sacral vertebrae are fused to form a single boney structure with defined foramina through which nerves pass

species variation in numbers fused: 3 dog and cat, 5 horse and cow

Question 7

meninges - a set of what? function?

Answer 7

a set of 3 tissue membranes surrounding brain and spinal cord

provide protection, support for blood vessels and containment of CSF

we cant just have nervous tissue hitting bone which is why we have membranes

Question 8

what are the membranes/layers of the meninges? and where are they in proximity to each other

Answer 8

-dura mater: outermost layer, strongest

-pia mater: bound tightly to surface of brain and spinal cord (shrinkwrapped), most blood vessels present in this layer

arachnoid mater: thin, “spiderweb” of membranes between pia and dura

Question 9

wjat are the spaces of the meninges and what do they contain/do

Answer 9

epidural: external to the dura (local anesthetics injected here)

subdural space: serous fluid

subarachnoid: between pia and arachnoid - filled with CSF (part of shock absorption)

Question 10

spinal cord - what is it a continuation of, where does it run, regions, what does it give rise to, what is special about the cervical region

Answer 10

a column shaped continuation of the brainstem (medulla), extending from the foramen magnum (base of the skull) to the lumbar region of the vertebral column

runs through the vertebral canal

regions: cervical (C1-8 but still only 7 vertebrae), thoracic, lumbar, sacral, caudal

gives rise to spinal nerves - all spinal nerves are MIXED nerves (sensory and both)

Question 11

spinal nerves - where do they form, what defines a spinal segment (+example), where do the spinal nerves extend from

Answer 11

spinal nerves are paired strucutres formed from the fusion of the dorsal and ventral roots at each level of the spinal cord

the region of the spinal cord where they originate defines a spinal segment (i.e. C6 segment is the source of C6 spinal nerves)

extend out of the vertebral column via the intervertebral foramina between adjacent vertebrae

Question 12

is sensory dorsal or ventral? what about motor?

Answer 12

sensory is always dorsal and motor is always ventral!

Question 13

what are dermatomes and myotome
clinical relevance

Answer 13

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

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

pricking dermatomes can help get a sense of where a lesion is. the animal wouldnt feel pain at any point caudal to lesions because the infor isnt going to brain

Question 14

spinal cord anatomical features - correspondance with vertebrae, results of that?

Answer 14

spinal segments DO NOT correspond with equivalent vertebrae. there is an additional cerivcal spinal segmnt relative to number of vertebrae

as a result the spinal nerves exit the vertebral canal via the intervertebral foramen cranial to the vertebrae which they are named between C1 and C7

then C8 exits caudal to the 7th vertebrae

then all subsequent spinal nerves exit CAUDAL to the vertebrae after which they are named

Question 15

spinal cord anatomical features - size of segments and result of that (terminal spinal segments)

what is the cauda equina

Answer 15

the caudal spinal segments are smaller than the cranial segments

this results in the spinal cord end ing cranial to the end of the vertebral column, with the terminal spinal segments found clustered in a short stretch of the spinal canal area of L4-L6

the spinal nerves from the terminal segments course caudally and form the structure called the cauda equina which occupies the canal caudal to L6

Question 16

enlargements - what are they called, what do they supply and what nerves are involved

Answer 16

cervical (cerviothoracic) enlargement: spinal segments that supply nerves to forelimbs (segments C6-T2)

lumbosacral enlargement: spinal segments that supply nerves to the hind limb (segments L4-S2)

Question 17

spinal cord - grey matter; what is it composed of, divided into

white matter; what is it composed of, divided into

Answer 17

any given cross section of the spinal cord contains a central area of grey matter and an outer area of white matter

grey matter = primarily composed of neuron cell bodies. divided into grey matter horns (dorsal horn (sensory neurons), ventral horn (motor neurons), lateral horn (autonomic neurons - in thoracic and first few lumbar and sacral segments only))

white matter = primarily composed of axons. divided into white matter columns which contain individual tracts (axons carrying specific types of info like sensory or motor) - dorsal column (sensory tracts), lateral column (mix of sensory or motor tracts), ventral column (mix of sensory and motor tracts)

Question 18

grey matter horns - neurons and their relationship, dorsal root, ventral root

Answer 18

types of neurons in different grey matter horns is consistent with their relationship to the dorsal and ventral roots

the dorsal root is where axons from sensory neurons ENTER the spinal cord, so the first neurons that they usually synapse upon (called a secondary neuron) are the first neurons encountered

the ventral root is where axons EXIT the spinal cord and the nerve cell bodies where these axons originate are physically close to this root

Question 19

white matter tracts - what are they, how are they organized
what analogy can you think of to remember organization

Answer 19

specific neuronal pathways in white matter through which action potentials relaying specific types of information (sensory, motor) pass

organized somatotopically meaning there is a strict relationship between where the tract/neuron is and the kind of information it conducts or mediates. this extends to other areas of the CNS where there is specific regional distribution of the function of neurons

this is why when a specific area of spinal cord is injured, there are specific signs that can be explained by the damage to specific neuron types (both in tracts and in grey matter)

401 - where it exits is hwere it goes into grey matter and synapses

Question 20

what is the importance of understanding the white matter tracts

Answer 20

understanding the significance of somatotopic structure of tracts will help to understand why regional injuries/diseases lead to specific signs, to localize lesions based on those signs and sometimes, to predict the course/progress of a particular disease based on the tracts affected

Question 21

general features of white matter tracts (5)

Answer 21

tracts are anatomically and functionally distinct from each other - each carries a specific type of sensory or motor information

most consist of a chain of two or three neurons

tracts are often named according to where they originate and terminate (e.g. spinothalamic tract contains axons relaying info FROM the spinal cord TO the thalamus)

neurons in tracts often decussate (cross over) at some point in the pathway between the spinal cord and the brain

all pathways are paired: one tract on left and right sides of the spinal cord

Question 22

spinal cord blood supply

Answer 22

spinal cord is segmentally supplied by branches that arise from the vertebral artery (in cervical and anterior thoracic regions), the intercostal artery (in thoracic region) and the aorta (lumbar region) that feed into three arteries that run the length of the cord:
1) a single ventral spinal artery - follows ventral surface of cord
2) paired dorsolateral spinal arteries - run along base of dorsal roots of spinal nerves

radial branches split off these arteries, supplying the core of the spinal cord

Question 23

what are the three names of blood vessels that are important to know

Answer 23

ventral spinal artery, dorsolateral spinal arteries, radial branches

Question 24

blood supple damage - disease name, what causes it

Answer 24

fibrocartilagenous embolic myelopathy (FCEM): disruption of the blood supply to a segment or segments of the spinal cord due to vascular obstruction by cartilage fragments, usually from the intervertebral disc