Somatosensory Systems

What is proprioception?

Sense of body’s position in space

_ _ act as _ receptors, play a major role in proprioception

Muscle spindles, stretch

Spindles are innervated by type - afferents

• Tendon tap → _ _ → _ _ → _ _ → Extrafusal contraction

Ia

• Intrafusal stretch → Ia → AMN

Muscle stretch= CNR _

Extrafusal contraction= CNR _ _

Intrafusal contraction= CNR _

• Stretched

• Decreases tension

• Stretched

What is the somatotopic organization of the anterior horn?

Medial is trunk/neck, lateral is distal UE/LE, anterior is extensors, posterior is flexors

What neuron shortens intrafusal fibers during extrafusal contraction to maintain proprioception?

Gamma motor neurons

What do GTOs do?

Sense change in muscle tension (Ib) for smooth movement

Mechanoreceptors are - or -, which is important for 2 point discrimination?

Superficial or deep (superficial)

What are the two pain receptors and their characteristics?

Adelta for fast/sharp, C for slow/dull

Define…

• Allodynia

• Hyperalgesia

• Lower pain threshold

• Excessive pain response

What are the DCML and STT pathways for?

DCML for proprioception/vibration/light touch, STT for pain/temperature

List the DCML pathway out!

Cutaneous nerves → Large, thick peripheral nerves → DRG (1) → Dorsal columns → synapse at Cuneate + Gracile nuclei (2) → Decussation in caudal medulla → Medial lemniscus → synapse at VPL of Thalamus (3) → Internal Capsule → S1

Gracile fasciculus for _ and below, Cuneate for _ and above

T7, T6

Lesions of DCML below medulla is -, above is - effects

Ipsilateral, contralateral

VPM of thalamus for -/- somatosensory input from the - nerve (-)

Face/head, trigeminal (contralateral)

List the STT pathway out!

Cutaneous nerve → Small, thin peripheral nerves → DRG (1) → synapse on dorsal horn of STT (2) → Decussation in spinal cord at anterior white commissure → spinothalamic tract (lateral) → synapse at VPL of thalamus (3) → Internal capsule → S1

Sometimes, STT activation can cause - - deficits

Muscle activation

What is referred pain?

Pain pattern in one area of the body means a different system is affected

STT also projects to the - - -, which elicits release of endogenous opiates

Periaqueductal Gray (PAG)

What is syringomyelia/central cord syndrome?

Fluid-filled cyst in central canal obstructs STT bilaterally and AMN (LMN signs) at a certain level

• UE most affected