Spinal Cord: External Features

Question 1

Site and length

Answer 1

Occupies upper 2/3 of vertebral canal
45 cm long in males
42 cm long in females

Question 2

Beginning

Answer 2

Lower border of foramen magnum at level 1st cervical nerve as continuation of medulla oblongata

Question 3

End

Answer 3

Lower end tapers forming conus medullaris at following levels:
1. 3rd month intrauterine life
2. Birth
3. Adults

Question 4

3rd month intrauterine life

Answer 4

Occupies whole vertebral canal

Question 5

Birth

Answer 5

Ends at L3 vertebra level

Question 6

Adults

Answer 6

Ends at level of disc between L1 and L2 vertebrae

Question 7

What is the reason behind the changes in the spinal cord?

Answer 7

Due to differential growth between spinal cord (slower) and vertebral column (faster)

Question 8

Shape

Answer 8

Cylindrical
Shows 2 enlargements
1. Cervical enlargement
2. Lumbar enlargement

Question 9

Cervical enlargement

Answer 9

C5-T1 spinal segments
Spinal cord gives origin to brachial plexus of the upper limb

Question 10

Lumbar enlargement

Answer 10

From L1-S3
Spinal cord gives origin to lumbar and sacral plexus of lower limb

Question 11

Sulci (grooves) (6)

Answer 11

Shows 6 external longitudinal sulci
1. Anterior median fissure
2. Posterior median sulcus
3. Two antero-lateral sulci
4. Two postero-lateral sulci

Question 12

Anterior median fissure

Answer 12

Deepest

Question 13

Two antero-lateral sulci

Answer 13

For exit of ventral (motor) roots of spinal nerves

Question 14

Two postero-lateral sulci

Answer 14

For entry of dorsal (sensory) roots of spinal nerves

Question 15

Spinal segments and nerves

Answer 15

1. 31 segments
2. Each segment gives attachment to a pair of spinal nerves
3. Each nerve is attached to its corresponding spinal segment by 2 roots

Question 16

Roots

Answer 16

1. Trunk
2. Ventral (motor) root
3. Dorsal (sensory) root

Question 17

Ventro (motor) root origin

Answer 17

Emerges from anterior-lateral sulcus

Question 18

Ventro (motor) root contents

Answer 18

1. Somatic efferent motor fibers
2. Sympathetic and parasympathetic fibers in certain spinal segments

Question 19

Dorsal (sensory) root origin

Answer 19

Enters through posterolateral sulcus

Question 20

Dorsal (sensory) root content

Answer 20

General somatic Afferent
Sensory fibers from body below head

Question 21

1st order neuron formation

Answer 21

Each root carries oval swelling called dorsal root (spinal) ganglion representing 1st order neuron in pathways of general somatic sensations from body below head

Question 22

Trunk origin

Answer 22

Both roots unite at corresponding intervertebral foramen forming spinal nerve trunk which is mixed (motor and sensory)

Question 23

Trunk course

Answer 23

Trunk is very short
Once it emerges from the foramen, it divides into anterior and posterior ramifications which are mixed and supply anterior and posterior aspects of the body