K1iv: Describe the major sensory and motor pathways (including anatomy)

  • Spinal cord from brainstem → L2
  • Part of CNS
  • Covered by 3 membranes of CNS: dura, arachnoid, pia
  • Protected by vertebral column

Ascending Tracts

Descending Tracts

  • SENSORY
  • Starts with ‘spino’
  • MOTOR
  • Ends in ‘spino’
  • CNS transmits motor commands in response to sensory info

3 tracts

  1. POSTERIOR COLUMN TRACT
  2. SPINOTHALAMIC TRACT
  3. SPINOCEREBELLAR TRACT

2 tracts

  1. CORTICOSPINAL TRACTS
  2. SUBCONSCIOUS TRACTS
  • Chain of neurons: 1st order, 2nd order, 3rd order

* via SNS (somatic) →  contraction of skeletal m.

UMN →  motor nuclei →  LMN →  skeletal m.

* via ANS (autonomic) →  glands, smooth m., cardiac m.

Neurons running up sensory tracts are arranged according to:

  • Sensory modality e. fine touch has own tract
  • Somatotropic e. arranged according to site of origin
  • Medial → lateral rule e. sensory n. that enters at a low level of SC are more medial
  • Sensory n. that enters at a higher level is more lateral

Preganglionic →  autonomic ganglia →  ganglionic n.

NOTE:

31 pairs of spinal nerves:

Nerves

Vertebral Level

8 cervical

C1 – C7

12 thoracic

T1 – T12

5 lumbar

L1 – L5

5 sacral

Sacrum

2 coccygeal

Coccyx

Ascending Tracts: Sensory

Posterior Column

  • Proprioception
  • Fine touch
  • Pressure
  • Vibration
  • Fasciculus gracilis (from below T6)
  • Fasciculus cutaneous (from T6 + up)
  • Carry to sensory cortex opposite stimulus

Spinothalamic Tract

  • Lateral Spinothalamic Tract
    • Pain & temperature
  • Anterior Spinothalamic Tract
    • Crude touch & pressure
  • To sensory cortex opposite side

Spinocerebellar Tracts

  • Posterior Spinocerebellar
    • Proprioception

To cerebellar cortex on same side as stimulus

  • Anterior Spinocerebellar
    • Proprioception

To cerebellar cortex primarily on same side as stimulus

Descending Tracts: Motor

Corticospinal Tracts

  • Corticobulbar tracts
    • Control of eye, jaw, face muscles via CN

Subconscious Motor Tracts

  • Vestibulospinal Tracts
    • Inner ear monitors head position
    • Alters muscle tone for posture/balance
  • Tectospinal Tracts
    • Response to sudden movement/loud noise
  • Reticulospinal Tracts
    • Eye movements
    • Respiratory muscle activation
  • Rubrospinal Tracts
    • Flexor & extensor muscles

Voluntary Command

  • Decision for movement from frontal lobes
  • Info to Motor Association Areas of Cortex
  • Info to BG & CEREBELLUM
  • Movement begins;
  • Motor Assoc. Areas send instructions to 1° motor cortex → movement modified by BG & Cerebellum →  involuntary adjustment of position & muscle tone

Spinal Cord Arterial Supply

Anterior Spinal Artery → anterior 2/3 of SC

  • Comes off vertebral arteries
  • Unites @ Foramen Magnum
  • Descends as single vessel
  • Penetrates medial sulcus

2 Posterior Spinal Arteries

  • Two from:
    1. Vertebral arteries
    2. Posterior inferior cerebellar arteries
  • Supply → posterior 1/3 of SC

Radicular Branches

  • Arises from local arteries
  • Supply local areas of SC

Venous Drainage: 2 median, 2 ant-lat, 2 post-lat VENOUS CHANNELS

Anterior Spinal Artery Syndrome

  • Sudden back/neck pain
  • Rapid progressive flaccid & areflexic paralysis
  • Loss pain + temp to sensory level
  • Preserved proprioception & vibration
  • Urinary incontinence

Posterior Spinal Artery Syndrome

  • Loss of proprioception & vibration
  • Preserved pain + temp
  • Loss reflexes below segment
  • No motor deficits