Spinal Cord and Tracts

Amadi O. Ihunwo, PhD School of Anatomical Sciences

1 Introduction

 Long cylindrical soft gelatinous structure  Av. length in adults – 45 cm; wt - 30 g  Extent: ◦ continuation of medulla at foramen magnum to conus medullaris at lower border of L1 vertebra ◦ Filum terminalis (pia mater) to S1  Diameter varies at different levels (av. 1.5 cm)  2 enlargements ◦ Cervical (C3 to T2) innervates upper limb via brachial plexus ◦ Lumbar (L1 to S3) innervates lower limb via lumbosacral plexus

40th Ed. Gray’s Anatomy

2 Function

 Receive afferent fibres from sensory receptors of trunk & limbs

 Control movements of trunk & limbs

 Provide autonomic innervation for most viscera

3 Relationship of spinal segment to vertebral column

Rule of thumb  Cervical cord segments ~ 1 spine higher than corresponding vertebra (C7 segment = C6 vertebra)  Thoracic cord segment ~ 2 spines higher  Lumbar cord segment ~ 3- 4 spines higher  Damage to bone at a particular level e.g. T6 vertebra does not necessarily mean damage to T6 spinal nerve level

4 Internal Structure

Dorsal Horn  Dorsal median sulcus divides it into 2 Gray mater symmetrical halves  Grey Matter – H-shape horns ◦ Anterior ◦ Posterior ◦ Intermediolateral (Thoracic segments only) ◦ Contain nerve cell bodies, dendrites, synapses ◦ Small central canal

 White mater ◦ Anterior ◦ Lateral ◦ Posterior Ventral Horn ◦ Contain Ascending & Descending fibres Gray mater

5 Spinal Cord – internal structure

Cervical More white matter Thoracic

More grey matter Lumbar Sacral

6 Ascending & Descending Tracts

Descending Ascending

Dorsal Columns Fasciculus Gracilis (FG) & Fasciculus Cuneatus (FC) FC FG PSCT - Posterior spino cerebellar Tract

Lateral corticospinal tract (LCST) Lateral Column Rubrospinal LSTT – Lateral spinothalamic tract

Recticulospinal VST ACST Ant Spinocerebellar T Olivospinal Tectospinal T Ventral

7 Ascending Tracts

 Carry impulses from pain, thermal tactile, muscle & joint receptors to cerebral cortex for conscious level & cerebellum for subconscious interpretations  Named tracts ◦ Dorsal column ◦ Spinothalamic tract ◦ Spinocerebellar tract ◦ Fasciculus proprius – intersegmental co-ordination

8 Dorsal Column

 Cell bodies of 1st order neurons in DRG just outside cord  3 different types of sensation: ◦ Proprioception (movement & joint position sense ◦ Vibratory sense ◦ Discriminative (fine) touch

9 Dorsal column …

 Termination ◦ Nucleus Gracilis & Cuneatus (second order neuron)  Internal arcuate fibres ◦ Decussate & become medial lemniscus  End ◦ contralateral VPL nucleus of thalamus ◦ 3rd order neurons via post. limb of internal capsule end in 1º & 2 somatosensory cortex (postcentral gyrus)  Lesion ◦ Tables dorsalis & Multiple sclerosis (Fasiculus cuneatus)

10 Spinocerebellar Tract (SCT)

 Anterior SCT & Posterior SCT  Origin ◦ Nucleus dorsalis of Clarke ◦ C8 to L2 ◦ Muscle spindle, Golgi tendon organs, tactile receptors ◦ to cerebellum for control of posture & co- ordination of movement  PSCT ◦ Non conscious sensation of muscle position & tone from lower limb  ASCT ◦ relays impulses about status of descending influences over spinal cord motor neurons

11 Lateral Spinothalamic Tract

 Origin ◦ Smaller unipolar neurons in DRG ◦ Fibrs cross to opposite side  Brainstem: spinal lemniscus which end in in Ventral Posterolateral (VPL) nucleus of Thalamus  3rd order neuron to somatosensory cortex  Function: pain and temperature; non- discriminative crude touch & pressure  Ant. STT ◦ light touch impulses; when lesioned, little or no disturbance in function  Selectively damaged in syringomyelia

 Selective surgical destruction to relieve intractable pain from a variety of causes

12 Descending Tracts

 Control movement, muscle tone, spinal reflexes, spinal autonomic functions & modulation of sensory transmissions  Named tracts ◦ Corticospinal tract (Pyramidal pathway) ◦ Rubrospinal tract } ◦ Tectospinal tract } Extrapyramidal ◦ Vestibulospinal tract } ◦ Reticulospinal tract }

13 Corticospinal Tract (CST)

 Origin ◦ precentral gyrus, premotor area, postcentral gyrus adjacent parietal cortex  Corona radiata & internal capsule to crus cerebri & pons  In medulla, form pyramids at junction of medulla & spinal cord

14 Corticospinal Tract…

 CST decussates (75-90%), forming large lateral CST  Anterior CST (uncrossed), but eventually crossed

 Termination in anterior horn & intermediate gray matter as follows: ◦ 55% in cervical ◦ 20% in thoracic ◦ 25% in lumbosacral levels

15 Corticospinal tract…

 Function ◦ voluntary control of discrete, skilled movements especially neck & limb muscles  Lesion ◦ Hereditary spastic paraparesis (inherited degenerative disorder)

16 Rubrospinal Tract

 Non pyramidal route by which motor cortex & cerebellum influence spinal motor activity  Origin ◦ Red nucleus  End ◦ cervical levels of spinal cord  Function ◦ control tone of limb flexor muscles; excitatory

17 Tectospinal

 Origin ◦ Neurons in superior colliculus  End ◦ Cervical segments  Function ◦ Reflex movement in responses to visual stimuli

18 Vestibulospinal tract

 Origin ◦ Vestibular nuclei in pons & medulla  End ◦ cervical & lower lumbar spinal segments  Function ◦ mediates excitation of limb extensor muscles

19 Reticulospinal Tract

 Origin ◦ Pons (medial) & medulla (lateral)  End ◦ Cervical to sacral segments  Function ◦ control reflex activities, muscle tone & vital functions (respiratory & cardiovascular)

20 Formation of Spinal Nerve

 Connect CNS (spinal cord) to sensory receptors, muscles & glands.  31 pairs; ◦ 8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 1 coccygeal  Each spinal nerve has 2 points of attachment to spinal cord; ◦ Posterior (dorsal ) root –sensory ◦ Anterior (ventral) root - motor  Both roots unite to form a spinal nerve (mixed nerve)  Plexuses formed from ventral rami except T2 –T11 (intercostals nerves) ◦ Cervical Plexus – C1 - C 5 ◦ Brachial plexus – C5 – T1 ◦ Lumbar Plexus – T12, L1 – L4 ◦ Sacral Plexus – L4, L5 S1, 2, 3, 4 ◦ Coccygeal Plexus – S4, S5, Co1

21 Functions of Spinal nerves

 Determined by their location in spinal cord  Control everything from body functions such as ◦ Breathing ◦ Sweating ◦ Digestion & elimination ◦ Gross & fine motor skills ◦ Sensations in arms & legs

22 Lesion of spinal cord

 Focal lesion of cord & nerves produce clinical manifestation in 2 ways ◦ Destroys function at segmental level ◦ Interrupts descending motor & ascending sensory tracts

 Damage to different parts is accompanied by distinct clinical syndromes

23 Result of spinal cord injury

 Extent of paralysis or weakness in legs, movement in torso, arms & hands will depend on where spinal cord was damaged

 Paraplegia – substantial or total loss of function in lower part of body ◦ Paraplegic is generally someone with an injury to back, between T1 - T12 or L1 - L5; has full use of arms & hands

 Quadriplegia - substantial or total loss of function in all four limbs ◦ Quadriplegic (or Tetraplegic) is generally one who has sustained an injury to neck, between C1 - C7; has weakness or paralysis in all four limbs

24 Spinal cord injury

 Dorsal column disease (1)  Cord hemisection, i,e Brown- Sequard syndrome (2) ◦ Ipsilateral loss of proprioception, UMN signs (hemiplegia, contralateral loss of pain & temperature sensation  Anterior cord lesion, e.g. anterior spinal artery occlusion (3)  Central cord damage (4)

25 Questions

 Indicate on a diagram of a cross-section of the spinal cord, the ascending and descending tracts.  List any three of each of the following: ◦ ascending tracts ◦ descending tracts ◦ characteristics of conscious ascending tracts.  Describe the origin, course, termination and functions of the corticospinal tract ( OR Dorsal column OR Spinothalamic tract).

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