·         Spinal Cord Vocabulary

·         Foramen magnum

·         Segments of cord

·         Conus medullaris

·         Cauda equina

·         Filum terminale

·         Cervical and lumbar enlargements

·         Spinal reflexes

 

·         White matter “columns”

·         Long “tracts” of cord

·         Gray matter “dorsal, ventral & lateral horns”

·         Dorsal and ventral roots

·         Dorsal root ganglia

·         Vertebrae & intervertebral disks

·         Intervertebral foramina

 

 

·         Meninges of Cord

·         Spinal Roots and Nerve

·         How Sensory Input Enters Cord

 

·         Dermatomes

 

·         Ascending Tracts or Pathways

·         “Afferent" tracts carrying sensory input up cord from body to brain

 

·         Basic Organization of Ascending Somatosensory Pathways

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

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

·         Second-order neuron:  axon of 2nd cell crosses to the opposite side of CNS & carries input up to the thalamus.  Also sends a branch to the reticular formation to arouse us.

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

 

 

·         Key Pathways Mediating Conscious Sensations

·         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 & do 2 point discrimination, stereognosis & graphesthesia.

·         Spinothalamic pathways – pain, temperature and gross touch

·        The Sensory Exam

 

·         White Matter Columns in Cord (see Fig. 8.13)

·         Dorsal Column Pathway (Fig. 8.14)

·         Spinal Tracts

 

 

·         What happens if you suffer damage to or deterioration of the  dorsal column pathway?

·         Irritation of Sensory Receptors

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

·         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.

·         You’ve experienced temporary paresthesias when your arm or leg “falls asleep”; also one of the early signs of carpal tunnel syndrome

 

·         Sensory Ataxia

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

·         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)

·         Some of the causes:

·         Syphilis – “Tabes dorsalis”

·         Vitamin B-12 deficiency

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

·         Multiple sclerosis

·         Romberg Test

·         Tabes Dorsalis (see study guide)

 

·         Astereognosis

·         Another symptom of dorsal column damage

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

·         Example: Can happen in MS if dorsal column loses its myelin

 

·         Spinothalamic Pathway (Fig 8.15)

·         Pain, temperature and gross touch

 

·         Pain Chemicals

 

·         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)
(1 million cases/yr in US)

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

·         It may “re-activate” if your immune system is weakened or stressed, or as you get older (most common after 50-60).

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

·         A few days later a pox-like painful rash develops in that dermatome, lasting 4-5 weeks.

 

 

·         Herpes Zoster or Shingles

·         Treatment

·         Antiviral drugs like acyclovir can shorten the attack & decrease complications if taken when the first signs appear.

·         Antiinflammatory pain relievers may be necessary.

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

·         Now experimenting with boosting immunity with chicken pox vaccination.

 

·         Pain Perception

·         Recall the woman whose pain responses were being tested in the video

·         Electrode implanted in her calf, stimulating nerve of spinothalamic pathway

·         She perceived the pain as coming from her foot, not her calf

 

 

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

 

·         The “Gate Control” for Pain

 

·         Ramachandran’s
Mirror Box Therapy for Phantom Limb Pain

 

·         Descending Pain
 Suppression Pathway

 

·         Another disorder affecting the spinothalamic pathway: Syringomyelia

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

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

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

·         If severe, operate on malformation or shunt.

 

·         Syringomyelia

·         MRI of Cavity