3.1 Spinal Cord Anatomy

Question 1

What is in the epidural space of the spinal cord?

Answer 1

Mostly fat

Question 2

At what vertebral level does doe the spinal cord/pia mater end? What procedure is this important for?

Answer 2

L1/L2; important for lumbar puncture (lumbar cistern)

Question 3

Which vertebrae do the dura and the arachnoid mater extend down to?

Answer 3

Second sacral vertebrae

Question 4

Where is the cauda equina located? What is it inferior to?

Answer 4

• Located in lumbar cistern
• Inferior to conus medullaris (base of spinal cord)

Question 5

What are two enlargements of the spinal cord?

Answer 5

Cervical: Origin of brachial plexus

Lumbar: Origin of lumbosacral plexus

Question 6

At what vertebral levels are the lumbar and cervical enlargements?

Answer 6

Cervical: C3-T2

Lumbar: L1-S3

Question 7

Why does the spinal cord not fill the whole vertebral column?

Answer 7

• Spinal cord stops growing at 4
• Vertebral column grows until adulthood

Question 8

In terms of fissures/sulci, how do you tell whether you’re looking at the A/P surface of the spinal cord?

Answer 8

Anterior: deeper, anterior median fissure

Posterior: shallower, posterior median sulcus

Question 9

The spinal nerve is formed by the joining of…

Answer 9

The dorsal root and the ventral root

Question 10

How many pairs of spinal nerves are in each of the vertebral sections (e.g. cervical, thoracic etc.)

Answer 10

Cervical: 8
Thoracic: 12
Lumbar: 5
Sacral: 5
Coccygeal: 1

Question 11

What is the area between the dorsal/ventral horns of the spinal cord called?

Answer 11

The intermediate zone

Question 12

The lateral horns of the spinal cord are important for _____ function

Answer 12

Autonomic

Question 13

What are the three pairs of columns in the spinal cord?

Answer 13

• Dorsal
• Ventral
• Lateral

Question 14

What changes grey matter/white matter proportions in different cross sections of the spinal cord?

Answer 14

More innervation -> more myelinated axons -> more white matter

More muscles -> more grey matter

Question 15

What modalities does the DCML tract carry?

Answer 15

• Proprioception
• Vibration
• Fine touch

Question 16

What are the two fascicului of the DCML pathway? Which is medial/lateral?

Answer 16

Medial: Fasciulus cuneatus (upper limb)
Lateral Fasciculus gracilis (lower limb)

Question 17

Which modalities does the anterior vs lateral spinothalamic tract carry?

Answer 17

Lateral: pain/temp
Anterior: Crude touch and pressure

Question 18

What is the function of the spinocerebellar tract? Where are they found in a lateral cross-section?

Answer 18

• Carry unconscious proprioceptive info ipsilaterally
• Found on lateral aspect of spinal cord

Question 19

Which of the anterior/lateral corticospinal tract decussates at the level of the pyramids?

Answer 19

Lateral decussates. Anterior does not.

Question 20

Corticospinal tract function

Answer 20

Voluntary control of musculature

Question 21

What is the function of extrapyramidal motor tracts?

Answer 21

• Involuntary muscle movement
• Posture, balance, tone etc.

Question 22

What are the four extrapyramidal tracts and their functions?

Answer 22

• Rubrospinal (flexion/inhibition of extension)
• Vestibulospinal (balance, head and neck position)
• Reticulospinal (posture and gait)
• Tectospinal (head and eye movement)

Question 23

Golgi tendon organ vs muscle spindle (location and sensation)

Answer 23

GTO: In tendon, detects changes in muscle length

Muscle spindle: In muscle belly, detects changes in muscle stretch/stretch velocity

Question 24

Which of GTO/muscle spindles have mono/polysynaptic afferent pathways to alpha motor neurons?

Answer 24

GTO: Poly
Muscle spindle: Mono

Question 25

What are the two types of nerve fibres that provide afferent information from muscle spindles?

Answer 25

• 1a fibres
• II fibres

Question 26

Give an example of how muscle spindles are used to regulate posture

Answer 26

-body begins to fall forward
- Muscle spindle detects decreased stretch/stretch velocity in back muscles
- Causes alpha motor neurons to contract muscle
- Upright again

Question 27

Do golgi tendon organs have efferent innervation? What about muscle spindles?

Answer 27

GTOs are located in tendons, so they don’t need to be contracted to maintain sensitivity.

Muscle spindles DO need to be kept at an optimum tension, though, so they do have efferent innervation via gamma motor neurons.

Question 28

Define “spinal reflex”

Answer 28

Rapid, involuntary, predicatable movements in response to specific stimuli. Mediated entirely by the spinal cord; no brain involvement.

Question 29

What are the different types of spinal reflexes?

Answer 29

• Stretch
• Golgi tendon reflex
• Crossed extensor
• Withdrawal reflex

(Two pairs: GTO/MS, and Crossed extensor/withdrawal)

Question 30

Describe stretch reflex

Answer 30

In response to stretching of muscle, intrafusal muscle spindles are activated, causing alpha motor neuron activation and contraction.

Question 31

Describe golgi tendon reflex

Answer 31

• Tendon tension increases
• Golgi tendon organs detect, and send afferent signal to inhibit alpha neurons

Question 32

What are crossed extensor reflexes (use an example)

Answer 32

Contralateral extensor activation in response to a withdrawal reflex (i.e. stepping on glass, ipsilateral flexor, contralateral extensor)

Question 33

What is a withdrawal reflex?

Answer 33

Automatic reflex that moves the body away from painful stimulus