Spinal Cord and Tracts

Amadi O. Ihunwo, PhD

School of Anatomical Sciences

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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

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Function

Receive afferent fibres from sensory receptors of trunk & limbs

Control movements of trunk & limbs

Provide autonomic innervation for most viscera

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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

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Internal Structure

Dorsal median sulcus divides it into 2 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

◦ Contain Ascending & Descending fibres

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Dorsal Horn

Gray mater

Ventral Horn

Gray mater

Spinal Cord – internal structure

Cervical Thoracic

Lumbar Sacral

More white matter

More grey matter

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Ventral

Lateral Column

Dorsal Columns

Fasciculus Gracilis (FG) &

Fasciculus Cuneatus (FC)

LSTT – Lateral spinothalamic tract

PSCT - Posterior spino cerebellar Tract

FC FG

Lateral corticospinal tract (LCST)

ACST

Tectospinal T

VST Recticulospinal

Rubrospinal

Olivospinal Ant Spinocerebellar T

Ascending & Descending Tracts

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Ascending Descending

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

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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

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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)

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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

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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

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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 }

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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

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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

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Corticospinal tract…

Function

◦ voluntary control of discrete, skilled

movements especially neck & limb muscles

Lesion

◦ Hereditary spastic paraparesis (inherited

degenerative disorder)

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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

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Tectospinal

Origin

◦ Neurons in superior

colliculus

End

◦ Cervical segments

Function

◦ Reflex movement in

responses to visual stimuli

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Vestibulospinal tract

Origin

◦ Vestibular nuclei in pons &

medulla

End

◦ cervical & lower lumbar spinal

segments

Function

◦ mediates excitation of limb

extensor muscles

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Reticulospinal Tract

Origin

◦ Pons (medial) & medulla

(lateral)

End

◦ Cervical to sacral segments

Function

◦ control reflex activities, muscle

tone & vital functions

(respiratory & cardiovascular)

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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

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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

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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

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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

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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)

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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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