Spinal Cord Flashcards
How many spinal nerves are there?
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.
What is Conus medullaris?
Caudal end of the spinal cord (S3–S5). In adult, ends at the L2 vertebra
What is the Filum terminale?
Slender pial extension that tethers the spinal cord to the bottom of the vertebral column
What does proximal-distal gradient mean relative to spinal cord?
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
How does CST pass?
Cortex (UMN body) -> crossing in the medullospinal junction -> Lateral corticospinal tract -> Anterior Horn of SC (LMN body) -> ventral roots -> muscle
What are the muscle stretch reflexes and Golgi tendon reflexes?
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
Which spinal cord segments and muscles are tested by knee (patellar) reflex?
L2 - L4 (femoral nerve), quadriceps muscle
Which spinal cord segments and muscles are tested by ankle reflex?
S1 (tibial nerve), gastrocnemius muscle
Which spinal cord segments and muscles are tested by elbow reflex?
- C5 - C6 (musculocutaneus nerve), biceps
- C6 - C7 (radial narve), triceps
Which spinal cord segments and muscles are tested by forearm reflex?
C5 - C6 (radial nerve), brachioradialis
What are the spastic and flaccid paralysis?
Spastic - lesion to UMN
Flaccid - lesion to LMN
What are the differences between UMN and LMN lesions?
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
What are the general principles of Sensory pathways in SC?
3-neuron system:
1˚ neuron: cell body in DRG
2˚ neuron: decussates
3˚ neuron: thalamus
How does dorsal columns - medial lemniscus pathway pass?
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
How does anterolateral (spinothalamic tract) pathway pass?
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)
How does Spinocerebellar Tracts for upper and lower limbs pass?
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)
What are the components of Brown-Séquard Syndrome?
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
How to distinguish different levels of spinal cords?
- there are both dorsal columns => C1 - T5
- there are lateral horns => T1 - L1
- there are large ventral horns => C5 - T1 or L2 - S3
Which structures does polio virus affect? What are the features?
Lower motoneurons in the ventral horn
Features:
a. Flaccid paralysis
b. Muscle atrophy
c. Fasciculations
d. Areflexia
e. Common at lumbar levels
Which structures does Amyotrophic Lateral Sclerosis affect? What are the features?
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
Which structures does Tabes Dorsalis affect? What are the features?
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
Which structures does Anterior Spinal Artery (ASA) Occlusion affect? What are the features?
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
Which structures does Subacute combined degeneration affect? What are the features?
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
Which structures does Syringomyelia affect? What are the features?
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
