Encapsulated receptor > DRG >fasciculus gracilis or cuneatus > nucleus gracilis or cuneatus > Decussate in medulla internal arcuate fibers > medial lemniscus in medulla and pons > VPL > Brodmann 3,2,1 (postcentral and paracentral gyri)

Cord

-Leg: Medial

-Arm: Lateral

Medial lemniscus

Medulla (Man standing)

-Leg: Anterior

-Arm: Posterior

Pons/midbrain

-Leg: Lateral

-Arm: Medial

In medulla: feet are ventral

In pons and midbrain: feet are medial

Give the pathway of the spinothalamic tract

(6 steps including receptor and end point)

Free nerve endings > DRG > ascend 2-3 levels to Decussate in the anterior commissure > ascend in lateral&anterior spinothalamic tract > lateral medulla > VPL > Brodmann 3,2,1 (postcentral and paracentral gyri)

-Proprioception

-Vibration

-Fine touch/2 point discrimination

What is the rule regarding projections/cell bodies in the somatosensory pathway?

What is the exception to this rule?

Receptor -> body of first neuron in the dorsal root ganglia -> body of second neuron (changes)-> thalamus

Olfactory is an exception to this rule (does not project to the thalamus)

Stimulus intensity-> proportional to receptor potential->proportional to firing frequency of afferent axon

All sensory pathways use ___ as a neurotransmitter

- What this neurotransmitter does

Use Glutamate

Glutamate makes GABA (using the enzyme GAD and it's cofactor of Vit B6)

o   Dorsal stream: Posterior parietal cortex- visuospatial orientation (“where” system)

o   Ventral stream: Lateral temporal cortex- identification of objects (“what” system)

integrates different sensory stimuli to:

- coordinate movements (premotor cortex),

- emotions and memories (paralimbic cortex)

- thoughts (prefrontal cortex) via projections to these areas

Face blindness

Caused by lesion to the fusiform gyrus

Meissner corpuscle (fine touch), merkel disk (touch, texture), ruffini end organ (proprioception), pacini corpuscle (vibration), golgi tendon organ, muscle spindle

What type of axonal fibers are used in the dorsal column/medial lemniscus system?

How is damage to these evaluated?

o   A alpha and A beta, are large fibers with myelination

- Carry proprioception, touch, vibration

-  Damage to these evaluated by EMG

What type of axonal fibers are used in the spinothalamic system?

How is damage to these evaluated?

o   A delta (myelinated) and C fibers (unmyelinated) project to the Antereolateral spinothalamic system

§  Are small fibers

§  touch, pain and temperature

§  Damage to these evaluated by skin biopsy

Borders of the thalamus:

-inferior

-medial

-lateral

Inferior: hypothalamic sulcus

Medial: 3rd ventricle

Lateral: posterior limb of internal capsule

PCA

- P1 and P2 segments give off thalamo-perforating arteries

OR

Artery of Percheron (anatomic variant supplying bilateral thalami)

Mediodorsal nucleus (MD)- limbic, olfactory

Middle thalamic nuclei- limbic 

Ventral anterior (VA) and ventral lateral (VL)

·         Motor

·         Basal ganglia

·         Cerebellum

VPL

·         Somatosensory (dorsal column medial lemniscus and spinothalamic)

VPM

·         Somatosensory cranial nerves

Pulvinar

·         Superior colliculis (connects to tectospinal tract), visual information

§  ONLY thalamic nucleus that does not project directly to the cortex (does receive some cortical projections to the reticular nucleus)

§  Inhibits thalami-cortical neurons (controls what gets to the cortex) via inhibitory interneurons (GABA)

§  Generator of the Sleep Spindles on the EEG

§  Contralateral Pain and temperature loss 2 levels below the level of the lesion

o   Fibers decussate while rising in Lissauer’s tract two levels prior to synapsing at the anterolateral system on the contralateral side

§  Ipsilateral paralysis, numbness, and loss of proprioception and vibration below the level of the lesion

§  Band of hyperalgesia ipsilateral to lesion at the level of the lesion (knock out peripheral incoming ipsilateral spinothalamics)

What symptoms are seen in a central cord lesion?

What are two potential causes?

§  Loss of pain and temperature sensation bilaterally below the level of the crossing of the spinothalamic tract. If larger will cause loss of sensation and proprioception in the legs, if even larger can cause lower motor neuron signs followed by upper motor neuron.

§  Usually due to a syrinx (think chiari malformation) or an ependymoma tumor in the central cord

What is subacute combined degeneration?

What can cause this? (3)

-  Degeneration of bilateral corticospinal tracts

- B12 deficiency or nitrous oxide or copper deficiency

What symptoms are seen in an anterior cord syndrome?

What usually causes this?

§  Loss of pain and temperature (spinothalamics) and motor (corticospinal) below the level of the lesion

§  Usually due to anterior spinal artery infarct

o   Serotonergic neurons of raphe nuclei

o   Neuropeptide substance P (facilitates pain) to the locus ceruleus

§  Sends noradrenergic (NE) projections to modulate pain in the spinal cord dorsal horn

o   Histamine also modulate pain through H3 receptors

o   Endogenous opiate peptides aka endorphins, found widespread throughout the nervous system

§  Enkephalin

§  Beta-endophrine

§  Dynorphin

Inherited Erythromelalgia

- What it is

- Genetics

- Etiology

o   AD SCN9A

o   Voltage gated Na 1.7 channel (in the nociceptors)

o   Attacks of burning pain and redness in distal extremities, triggered by mild warmth or exercise

§  Block presynaptic voltage gated calcium channels, increases GABA

§  Lidocaine

§  PHT

§  CBZ

§  LTG