Spinal Cord Vocabulary

u Foramen magnum

u Segments of cord

u Conus medullaris

u Cauda equina

u Filum terminale

u Cervical and lumbar enlargements

u Spinal reflexes

u White matter “columns”

u Long “tracts” of cord

u Gray matter “dorsal, ventral & lateral horns”

u Dorsal and ventral roots

u Dorsal root ganglia

u Vertebrae & intervertebral disks

u Intervertebral foramina

Spinal MRI

Spinal Vertebrae

u Spinal cord protected by same meninges and layer of cerebrospinal fluid as the brain

Meninges of Cord

Spinal Roots and Nerve

Ascending Tracts or Pathways

“Afferent" tracts bringing sensory input from body to brain

Basic Organization of Ascending Somatosensory Pathways

u A series of 3 neurons is needed to get the message from body surface to cortex:

u First-order neuron: carries input from periphery to CNS (dendrites are sensitive to external stimulus, soma is in dorsal root ganglia, axon enters CNS & synapses on 2nd neuron)

u Other axon branches may also participate in spinal reflexes.

Basic Organization of Ascending Somatosensory Pathways

u Second-order neuron: axon crosses the midline to the opposite side of CNS & carries input up to the thalamus. Also sends a branch to the reticular formation to arouse us.

u Third order neuron: Thalamus neuron relays input to the cortex.

Key Pathways Mediating Conscious Sensations

u Dorsal column pathway – discriminative (detailed, fine) touch, proprioception (limb position/motion sense), & vibration. This tract is needed for us to feel & precisely locate light touch, 2 point discrimination, stereognosis & graphesthesia.

u Spinothalamic pathways – pain, temperature and gross touch

White Matter Columns of Cord

Location of Spinal Tracts

Pain Chemicals Released When Tissue is Injured

The “Gate” of Gate Control Theory

What will happen if an individual suffers damage to or deterioration

of his/her dorsal column pathway?

Sensory Ataxia

u Gait (walking) problems related to loss of proprioception following degeneration of dorsal columns and/or dorsal roots.

u Can be caused by:

– Syphilis – “Tabes dorsalis”

– Vitamin B-12 deficiency

– Peripheral neuropathy (e.g. as seen in diabetics and alcoholics)

– Multiple sclerosis

u Watches feet while walking, feet tend to slap down; shows a “positive Romberg’s sign” (person sways and is unsteady if asked to stand with eyes closed)

Tabes Dorsalis

Irritation of Sensory Receptors

u As sensory receptors deteriorate, they may malfunction before they stop functioning causing paresthesia or dysesthesia.

u E.g. in tabes dorsalis shooting, lancinating, electrical-like or cramp-like pains occur, and in peripheral neuropathy unpleasant, abnormal tingling, burning, tightness, & “pins & needles” paresthesias occur.

Astereognosis

u Another symptom of dorsal column damage

u Without fine discriminative touch person cannot identify objects or textures by touch

u Can happen in MS if dorsal column loses its myelin

What will happen to an individual who has irritation of
or damage to the lateral spinothalamic pathway?

Have you had chicken pox?

If so, about 20% of you are likely to develop Shingles sometime later in your life.

Shingles (aka Herpes Zoster)

u After chicken pox the virus (Varicella zoster) lies dormant in your dorsal root ganglia.

u It may “re-activate” if your immune system is wakened or stressed, or as you get older (most common after 50).

u The first sign is tingling, burning or shooting pains, usually in a single unilateral dermatome.

u A few days later a pox-like painful rash develops in that dermatome, lasting a few weeks.

Treatment

u Antiviral drugs like acyclovir can shorten the attack & decrease complications.

u Antiinflammatory pain relievers may be necessary.

u Zostrix (capsaicin) cream applied to unbroken skin also relieves pain by decreasing the supply of Substance P in pain receptors.

Herpes Zoster or Shingles Rash

Herpetic Neuralgia – aftereffect of Herpes Zoster or Shingles

Syringomyelia

u Enlarged CSF filled cavity within cervical spinal cord, most often associated with Chiari malformation (cerebellum bulging thru foramen magnum)

u Cavity compresses and damages nearby tissue (like hydrocephalus of cord)

u “Cape anesthesia”, loss of pain & temp sensation from hands, weakness if ventral horns damaged

u If severe, operate on malformation or shunt.

Referred Pain – we experience pain from organs as if it were coming from the surface of body