Spinal Cord - Tracts (p79-89)

Spinal Cord - Tracts (p79-89)

1. White Matter of the Spinal Cord

   • Nerve fibres sharing common origins, terminations and functions
     • TRACTS/ FASCICULI
   • The intersegmental or PROPRISPINAL fibers occupy a narrow band immediately peripheral to grey matter
     • FASCICULUS PROPRIUS
   • Nerve fibres running between spinal cord and brain constitute
     • ASCENDING AND DESCENDING TRACTS

2. Descending Spinal Tracts

   • CONTROL OF MOVEMENT, MUSCLE TONE, SPINAL REFLEXES, SPINAL AUTONOMIC FUNCTIONS and the MODULATION OF SENSORY TRANSMISION to higher centres
   • Rubrospinal Tract
     • originates from
       • RED NUCLEUS (of midbrain tegmentum)
         • cross midline at level of nucleus and descend as rubrospinal tract
           • through pons and medulla to enter lateral funiculus
             • Descend to spinal cord and lie ventrolateral to and partly intermingled with lateral corticospinal tract
               • fibres terminate by synapsing on interneurons in anterior horn
         • receives afferent fibres from motor cortex and from cerebellum
           • represents a non-pyramidal route by which motor cortex and cerebellum can influence spinal motor activity
     • Exerts control over TONE OF LIMB FLEXOR MUSCLES
       • important intergrator and relay in cerebellar connections
         • facilitating activity of flexor muscles and inhibiting extensory
           • with loss of corticospinal tract, rubro influences on upper limb flexors become easily apparent
             • SPASTIC PALSY - flexion of elbow, wrist and fingers
   • Tectospinal Tract
     • Arise from
       • SUPERIOR COLLICULUS of midbrain
         • pass ventromedially around periaqueductal grey matter and cross in the
           • Decussation in Dorsal tegmental
             • descend through brainstem close to medial longitudinal fasicullus
               • SUPERIOR COLLICLUS receives
                 • VISUAL INPUT
               • descends in anterior funiculus close to anterior median fissure
                 • majority terminate in anterior horn in upper Cx by synapsing on interneurons innervating LMN
     • CONVEYS FIBRES ORIENTATING HEAD AND NECK DURING EYE MOVEMENTS
   • Vestibulospinal Tract
     • arise from
       • VESTIBULAR NUCLEI
         • in pons and medulla, in and near 4th ventricle floor
         • Receives input from labyrinthine system by way of vestibular nerve and cerebellum
         • Efferent fibres from LATERAL VESTIBULAR NUCLEUS
           • Descend ipsilat as the
             • LATERAL VESTIBULOSPINAL TRACT
               • Located in anterior funiculus
               • terminate at all levels of ipsilat spinal cord
                 • to facilitate excitatory influences upon EXTENSOR MOTOR NEURONS
                   • Serve to CONTROL EXTENSOR MUSCLE TONE in anti-gravity maintenance of posture
                     • mediate postural adjustments to compensate for movements or changes in position of body and coordinate position of the head and body in space
                   • inhibit flexor muscles
         • MEDIAL VESTIBULAR NUCLEUS
           • contributes descending fibres to ipsilateral MEDIAL LONGITUDINAL FASCICULUS also known as MEDIAL VESTIBULOSPINAL TRACT
             • inhibit motor neurons innervating axial muscles of neck and upper part of back
               • may also establish connections with nuclei of III, IV and VI for coordination of head and eye movements
             • responsible for stabilising head as we move our bodies or as our head moves in space
   • Reticulospinal Tract
     • Originate from reticular formation of pons and medulla
       • those from the pons descend ipsilat as
         • Medial Reticulospinal Tract
           • both in anterior funiculus
       • from medulla descend as crossed and uncrossed fibres in
         • Lateral Reticulospinal Tract
     • Primitive motor behaviours such as orientation of body towards or away from stimulus and motor behaviours that don't require dexterity
       • by controlling activity of both alpha and gamma motor neurons - muscle tone
       • Also mediate pressor and depressor effects upon circulatory system and are involved in control of breathing

3. Damage to the Spinal Cord at Specific Levels

   • Upper Cervical Cord Lesion
     • Spastic quadriplegia
     • Hyperreflexia
     • Extensor plantar responses (UMNL)
     • Incontinence
     • Sensory loss below level of lesion
     • Sensory ataxia
   • Lower Cervical Cord Lesions
     • Weakness, wasting and fasciculation of muscles
     • Areflexia in upper limbs (LMNU)
     • Spastic paraparesis
     • Paraparesis
     • Extensor plantar responses in lower limb (UMNL)
   • Thoracic Cord Lesion
     • Hyperreflexia
     • Incontinence
     • Sensory loss of below level of lesion
     • Sensory ataxia
   • Lumbar Cord Lesion
     • Weakness and fasciculation of muscle and areflexia of LOWER LIMB
   • Hemisection of Cord (BROWN-SEQUARD SYNDROME)
     • Ipsilat loss of general sensation
       • proprioception, vibration, touch
     • Upper motor neuron signs
     • Contralat loss of pain and temp sensations

4. Voluntary Movement Pathway for Limbs and Body - Corticospinal Tract

   • UMN in primary cortex of frontal lobe
     • through internal capsule, cerebral peduncles and pons as corticospinal fibres
       • at the top of medulla corticospinal axons are found ventral and medial grouped in pyramids
         • axons decussate in medulla at apex of pyramids
           • 75-95% pass contralat into LATERAL CORTICOSPINAL TRACT
             • runs length of spinal cord
             • synapse with LMN
               • in anterior horn
           • 5% remain ipsilat as ANTERIOR CORTICOSPINAL TRACT
             • runs to around T6 level
             • axons decussate in spinal cord at the level they exit
               • synapse with LMN
                 • in anterior horn

5. Voulntary Movement Pathway for the Face Via Facial Nerve

   • UMN are in primary cortex of frontal lobe
     • pass through internal capsule and cerebellar peduncles as corticonuclear fibres
       • most decussate in pons
         • axons pass both ipsulat and contralat to facial motor nuclei in lower pons
   • LMN in facial motor nucleus are grouped such that those innervating muscles in the scalp and upper face are dorsal
     • and believed to receive only contralat corticonuclear fibres
       • Clinically important
         • unilat UMNL = complete ipsilat paraylsis
     • motor axons pass with sensory part of VII to form CN VII