Spinal Cord

Question 1

How many spinal nerves are there?

Answer 1

31 pairs

• 8 cervical pairs of spinal nerves (C1 through C8). The cervical enlargement (C5 through T1) gives rise to the rootlets that form the brachial plexus, which innervates the upper limbs.
• 12 thoracic pairs of spinal nerves (T1 through T12). Spinal nerves emanating from thoracic levels innervate most of the trunk.
• 5 lumbar pairs of spinal nerves (L1 through L5). The lumbar enlargement (L2 through S3) gives rise to rootlets that form the lumbar and sacral plexuses, which innervate the lower limbs.
• 5 sacral pairs of spinal nerves (S1 through S5). Spinal nerves at the sacral level innervate part of the lower limbs and the pelvis.
• 1 coccygeal pair of spinal nerves.

The cauda equina consists of the dorsal and ventral roots of the lumbar, sacral, and coccygeal spinal nerves.

Question 2

What is Conus medullaris?

Answer 2

Caudal end of the spinal cord (S3–S5). In adult, ends at the L2 vertebra

Question 3

What is the Filum terminale?

Answer 3

Slender pial extension that tethers the spinal cord to the bottom of the vertebral column

Question 4

What does proximal-distal gradient mean relative to spinal cord?

Answer 4

Medial part of Anterior horns of SC has bodies of LMN which innervate proximal part of limbs, lateral part of Anterior horns of SC has bodies of LMN which innervate distal part of limbs

Question 5

How does CST pass?

Answer 5

Cortex (UMN body) -> crossing in the medullospinal junction -> Lateral corticospinal tract -> Anterior Horn of SC (LMN body) -> ventral roots -> muscle

Question 6

What are the muscle stretch reflexes and Golgi tendon reflexes?

Answer 6

Muscle stretch reflex - stretching of muscle provides its contraction
Golgi tendon reflex - too much muscle work provides muscle relaxation
BOTH REFLEXES ARE INHIBITED BY CORTEX (UMN) =>
=> lesion of UMN (spastic paresis) -> high muscle stretch reflex and clasp-knife when providing Golgi tendon reflex

Question 7

Which spinal cord segments and muscles are tested by knee (patellar) reflex?

Answer 7

L2 - L4 (femoral nerve), quadriceps muscle

Question 8

Which spinal cord segments and muscles are tested by ankle reflex?

Answer 8

S1 (tibial nerve), gastrocnemius muscle

Question 9

Which spinal cord segments and muscles are tested by elbow reflex?

Answer 9

• C5 - C6 (musculocutaneus nerve), biceps

- C6 - C7 (radial narve), triceps

Question 10

Which spinal cord segments and muscles are tested by forearm reflex?

Answer 10

C5 - C6 (radial nerve), brachioradialis

Question 11

What are the spastic and flaccid paralysis?

Answer 11

Spastic - lesion to UMN

Flaccid - lesion to LMN

Question 12

What are the differences between UMN and LMN lesions?

Answer 12

1) Upper Motor Neuron Lesion
- Spastic paresis
- Hyperreflexia
- Babinski sign present
- Increased muscle tone
- Clasp knife reflex
- Disuse atrophy of muscles
- Decreased speed of voluntary movements
- Large area of the body involved

2) Lower Motor Neuron Lesion
- Flaccid paralysis
- Areflexia
- No Babinski
- Fasciculations
- Decreased muscle tone or atonia
- Atrophy of muscle(s)
- Loss of voluntary movements
- Small area of the body affected

Question 13

What are the general principles of Sensory pathways in SC?

Answer 13

3-neuron system:
1˚ neuron: cell body in DRG
2˚ neuron: decussates
3˚ neuron: thalamus

Question 14

How does dorsal columns - medial lemniscus pathway pass?

Answer 14

Proprioceptors (vibration, proprioception, deep touch) -> DRG (1st neuron body) -> ipsilateral dorsal columns (gracilis (medial, from lower limbs) and cuneatus (lateral, from upper limbs)) -> gracilis and cuneatus nuclei in medulla (2nd neuron body) -> crossing (medial lemniscus) -> thalamus (3d neuron body) -> cortex

Question 15

How does anterolateral (spinothalamic tract) pathway pass?

Answer 15

Pain and temperature receptors -> DRG (1t neuron body) -> dorsal horns of SC (2nd neuron body) -> crossing 2 segments higher -> anterior columns -> thalamus (3d neuron body)

Question 16

How does Spinocerebellar Tracts for upper and lower limbs pass?

Answer 16

From Upper Limbs: Muscle spindles receptors -> DRG (1 neuron body) -> dorsal tract -> external cuneate nucleus (2 neuron body) -> cortex of cerebellum

From Lower Limbs: Muscle spindles receptors -> DRG (1 neuron body) -> Clarke’s nucleus (intermediate zone of SC horns, 2nd neuron body) -> dorsal tract -> cortex of cerebellum

Cerebellar tracts are ipsilateral (do not cross)

Question 17

What are the components of Brown-Séquard Syndrome?

Answer 17

On the side of lesion and below:

• loss of proprioception, vibratory sense, deep touch
• spastic paresis

On the other side (2 segments below):
- loss of pain ant temperature sensation

Question 18

How to distinguish different levels of spinal cords?

Answer 18

• there are both dorsal columns => C1 - T5
• there are lateral horns => T1 - L1
• there are large ventral horns => C5 - T1 or L2 - S3

Question 19

Which structures does polio virus affect? What are the features?

Answer 19

Lower motoneurons in the ventral horn

Features:

a. Flaccid paralysis
b. Muscle atrophy
c. Fasciculations
d. Areflexia
e. Common at lumbar levels

Question 20

Which structures does Amyotrophic Lateral Sclerosis affect? What are the features?

Answer 20

UMN and LMN

Features:
a. Progressive spinal muscular atrophy (ventral horn)
b. Primary lateral sclerosis (corticospinal tract)
• Spastic paralysis in lower limbs
• Increased tone and reflexes
• Flaccid paralysis in upper limbs
c. Common in cervical enlargement

Question 21

Which structures does Tabes Dorsalis affect? What are the features?

Answer 21

Dorsal roots (!) and Dorsal Columns

Features:
a. “Paresthesias, pain, polyuria”
b. Associated with late-stage syphilis, sensory
ataxia, positive Romberg sign: sways with eyes
closed, Argyll Robertson pupils, suppressed
reflexes
c. Common at lumbar cord levels

Question 22

Which structures does Anterior Spinal Artery (ASA) Occlusion affect? What are the features?

Answer 22

Ventrolateral parts of the cord: corticospinal tracts and spinothalamic tracts

Features:

a. DC spared
b. All else bilateral signs
c. Common at mid thoracic levels
d. Spastic bladder

Question 23

Which structures does Subacute combined degeneration affect? What are the features?

Answer 23

Dorsal columns and corticospinal tracts

Features:
a. Vitamin B12, pernicious anemia
b. Demyelination of the:
• Dorsal columns (central and peripheral myelin)
• Spinocerebellar tracts
• Corticospinal tracts (CST)
c. Upper thoracic or lower cervical cord

Question 24

Which structures does Syringomyelia affect? What are the features?

Answer 24

Cavitation of the central canal => lesion in crossing of spinothalamic tract (loss of pain and t) -> Ventral horns (LMN) (flaccid paralysis) -> descending hypothalamic fibers (Horner’s syndrome)

Features:
a. Vitamin B12, pernicious anemia
b. Demyelination of the:
• Dorsal columns (central and peripheral
myelin)
• Spinocerebellar tracts
• Corticospinal tracts (CST)
c. Upper thoracic or lower cervical cord