Neuro 101: Spinal Cord • LITFL • Neurology library

In this section, we will cover the anatomical structure of the spinal cord and vertebral column, spinal nerve organisation, blood supply, motor and sensory pathways, clinical examination principles, myotomes and dermatomes, localisation of spinal cord lesions, and common spinal cord syndromes.

Function

The spinal column encases and protects the spinal cord, which serves as a conduit for motor, sensory, and autonomic signals between the brain and the body.

Conducts ascending sensory information from the periphery to the brain
Conducts descending motor commands from the brain to the periphery
Mediates reflex activity independently of the brain

Testing

Clinical examination of spinal cord function involves assessing motor, sensory, and autonomic pathways.

Identify segmental level by examining myotomes and dermatomes
Assess for patterns of weakness or sensory loss that respect spinal levels
Evaluate reflexes for hyperreflexia (upper motor neuron signs) or hyporeflexia (lower motor neuron signs)
Observe for bladder, bowel, and sexual dysfunction in suspected cord lesions
Neuroimaging (MRI) is the investigation of choice for suspected spinal cord pathology

Pathology

Anatomy

Vertebrae:
- 7 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
Spinal nerves:
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
The spinal cord terminates at the L2 vertebral body (conus medullaris). Nerve roots below this level travel as the cauda equina.

Discrepancy exists between spinal segments and vertebral levels:

C1–C4 → C1–C4 vertebrae
C5–C8, T1–T4 → C4–T3 vertebrae
T5–T8 → T3–T6 vertebrae
T9–T12 → T6–T9 vertebrae
L1–L5 → T10–T12 vertebrae
S1–S5, Co1 → L1 vertebra

Afferent (or sensory) input to the nervous system arrives in the spinal cord via the dorsal root.

Efferents (or motor output) exit via the ventral root.

Grey matter

Central location within the cord
Anterior horn: motor neurons
Lateral horn: autonomic neurons
Posterior horn: sensory interneurons

White matter tracts

Descending tracts:

Corticospinal tract:
- motor control; crosses in medulla (pyramidal decussation); Left brain controls right body and right brain controls left body
Vestibulospinal tracts:
- Carry information from vestibular nuclei in brainstem to spinal cord
- Important for rapid correction of neck movement and posture (in response to changing body position)
Rubrospinal tract:
- Carries information from red nucleus to anterior horn cells
- Modulates voluntary motor movements
- Fibers cross before descending in lateral columns

Ascending tracts:

Posterior columns:
- Proprioception, vibration, fine touch, two-point discrimination
- Fibers cross at spinal cord then ascend
- Somatotopic organization: fasciculus gracilis and cuneatus
Spinothalamic tract:
- Carries sensory information from periphery to cortex
  - pain and temperature (lateral spinothalamic tract)
  - light touch (anterior spinothalamic tract)
- Somatotopic organization

Posterior column Ascending white matter tracts — **Posterior column**

Blood supply

Anterior spinal artery: anterior two-thirds of cord
Posterior spinal arteries: posterior third of cord
Radicular arteries: reinforcements from the thoracic aorta and the abdominal aorta, which supply the ventral and dorsal roots as well as the cord.
- largest radicular artery is the spinal artery of Adamkiewicz; important in the thoracic and lumbar regions; can be damaged during surgery on the aorta.

Myotomes

A myotome refers to all the muscles or groups of muscles innervated by the motor horn cells within a segment of the cord.

Upper limb:
- C5: shoulder control
- C6: elbow flexion/extension
- C7: wrist movement
- C8: finger flexion/extension
- T1: intrinsic hand muscles
Lower limb:
- L1–L2: hip flexion
- L3–L4: knee extension
- L5–S2: knee flexion
- L4: ankle dorsiflexion
- L5: great toe extension
- S1–S2: plantarflexion
- S2–S3: toe adduction

Dermatomes

A dermatome is a region of skin or a structure, which has somatic afferent sensory innervation provided by a single spinal cord segment and a single nerve root.

Localising spinal cord lesions

Exclude cranial nerve involvement to confirm spinal origin
Define level by identifying sensory or motor loss pattern
Crossed signs suggest brainstem lesion
Same-sided head and body signs suggest cerebral lesion

During and after your examination you should seek answers to the following questions.

Which tracts are involved?
Which side is involved?
What level is involved?
Are upper motor neurons or lower motor neurons involved?

Spinal cord syndromes

Small central lesion:

Affects crossing spinothalamic tract fibers
Bilateral loss of pain and temperature
Proprioception and vibration preserved
Causes: syrinx, expanded central canal

Large central cord lesion:

Bilateral pain/temperature loss
Lower motor neuron signs at level, upper motor neuron signs below
Sacral sparing possible (external compression produces sacral anaesthesia)
Causes: multiple sclerosis, tumours, astrocytoma

Brown-Séquard syndrome (hemisection):

Ipsilateral proprioception, vibration loss and and two-point discrimination below lesion
Ipsilateral loss of pain and temperature sensation at level of lesion
Contralateral pain/temperature loss 1–2 levels below lesion
Lower motor neuron signs at level, upper motor neuron signs below
Causes: penetrating injury, tumour, haemorrhage

Complete transection:

Bilateral motor and sensory loss below lesion
Lower motor neuron signs at level, upper motor neuron signs below
Spinal shock initially; total flaccidity early after injury
Autonomic dysfunction (bladder, bowel, respiration if above C5)
Causes: trauma, transverse myelitis, tumour, penetrating injury, haemorrhage

Combined degeneration of the cord:

Bilateral proprioception and vibration loss
Bilateral motor loss
Pain and temperature preserved
Causes: B12 deficiency, nitrous oxide abuse, copper deficiency

Tabes dorsalis:

Most often bilateral damage (affecting legs)
Loss of proprioception, sensory ataxia, lightning pains
Loss of reflexes, hypotonia
Cause: tertiary syphilis

Anterior spinal artery syndrome:

Bilateral pain/temperature loss
Proprioception and vibration sense remain intact
Bilateral loss of motor activity below lesion
Lower motor neuron signs at level, upper motor neuron signs below
Causes: aortic surgery, hypotension, atherosclerosis, Adamkiewicz injury

Posterior spinal artery syndrome:

Ipsilateral total sensory loss at level
Loss of segmental reflexes at level of lesion
Ipsilateral loss of proprioception and vibration sense below lesion

Clinical Neurology Essentials

Coni R. Neuro 101: Neurological Examination. LITFL
Coni R. Neuro 101: Cerebral Hemispheres. LITFL
Coni R. Neuro 101: Cerebellum and Basal Ganglia. LITFL
Coni R. Neuro 101: Brainstem. LITFL
Coni R. Neuro 101: Cranial Nerves. LITFL
Coni R. Neuro 101: Spinal Cord. LITFL
Coni R. Neuro 101: Peripheral Nervous System. LITFL

References

Robert Coni

Robert Coni, DO, EdS, FAAN. Vascular neurologist and neurohospitalist and Neurology Subspecialty Coordinator at the Grand Strand Medical Center in South Carolina. Former neuroscience curriculum coordinator at St. Luke’s / Temple Medical School and fellow of the American Academy of Neurology. In my spare time, I like to play guitar and go fly fishing. | Medmastery | Linkedin |