Spinal cord

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Surface anatomy

i) General anatomy

Approx. 45cm long - 1 - 1.5cm in diameter

Begins at Foramen Magnum

Continuous with Medulla Oblongata

Occupies upper 2/3 of vertebral canal - Cervical, Thoracic & some Lumbar

Ends at level L1-L2 in adults - near L-3 in children

Anterior median fissure

Remember parts of the vertebral column! - 7, 12, 5, 5, 4

SC enlarged at 2 places

Cervical enlargement - origin of Brachial plexus (C3-T2)

Lumbar enlargement - origin of Lumbosacral plexus (L1-S3)

(Link to 2. Internal anatomy i) Gray matter - gray matter density in SC)

ii) Meninges

3 meningeal layers (like brain!)

Dura - outermost layer

Arachnoid

Pia - innermost layer

Denticulate ligament = continuation of pia that runs between dorsal & ventral roots

iii) Tail of SC

Conus Medullaris = most inferior point of SC

Cauda Equina = extension of bundle of nerve roots beyond SC (horses's tail)

Filum Terminale = prolongation of pia mater - descends from Conus Medullaris & attaches to coccyx - acts as an anchor - thin small strand

iv) Spinal nerves

31 pairs

8 cervical - pass over their respective vertebrae (except C8)

12 thoracic - pass under

5 lumbar - pass under

5 sacral - pass under

1 coccygeal

Part of PNS

Emerge from vertebral canal via intervertebral foramina

Attach to SC by:

ventral roots at ventrolateral aspect - ** Motor ** - efferent fibres sending info from SC to muscles/organs

dorsal roots at dorsolateral aspect - ** Sensory ** - afferent fibres sending info to SC & up to brain

Dorsal root ganglion

Each root attaches cord with rootlets

Spinal nerve branches into:

Dorsal ramus

Ventral ramus

Spinal nerves contain following fibres:

somatic efferent

visceral efferent

somatic afferent

visceral afferent

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Internal Anatomy

i) Gray Matter

Spinal cord composed inner core of gray matter - nerve cell bodies, glia, blood vessels

Divided into:

Dorsal column/horn

Ventral column/horn

Lateral column (intermediate zone)

Rexed's laminae (10 zones)

Dorsal gray column nerve cell groups

Extra info about dorsal nuclei!

Substantia gelatinosa contains large amount of opiate responsive neurons (morphine & heroin) (Link to Pain lecture)

Nucleus dorsalis most prominent at C8-L2 level

Sympathetic & parasympathetic autonomic NS have pre-ganglionic neurons in Nucleus dorsalis

Ventral gray column nerve cell groups

Extra info about ventral nuclei!

Neurons in Lamina 9 topographically organised based on:

Muscle they control (flexor or extensor)

Where in body that muscle located (axial or peripheral)

Medially located neurons control axial muscles

Laterally located neurons control limbs

Anteriorly located neurons control extensors

Posteriorly located neurons control flexors

Gray matter density varies at diff. levels of SC

Largest conc. at cervical & lumbosacral enlargements (Link to Surface anatomy i) General anatomy - enlargements)

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ii) White matter

Divided into 3 regions on each side:

Ventral funiculus - between anterior median fissure & anterolateral sulcus

Lateral funiculus - between anterolateral sulcus & posterolateral sulcus

Dorsal funiculus - between posterolateral sulcus & dorsal median sulcus

WM contains 3 types of tracts:

Ascending tracts - carry impulses from pain, tactile, thermal & muscle + joint receptors to brain

Intersegmental tracts - carry info from one segment of SC to another - spinal reflexes

Descending tracts - carry info from cerebral cortex & brainstem to muscles - movement, posture, muscle tone

Fibres passing in both directions surround outside of gray matter & project from dorsal horns

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Blood supply

i) Arteries

3 arteries

Anterior spinal

Posterior spinal arteries (2!)

Radicular arteries

ii) Veins

Blood drains from 6 longitudinal channels located around SC (outside dura mater)

Into anterior & posterior radicular veins (inside dura mater)

Which join together & drain into the intervertebral venous plexus

Which drains into the Ant. & Post. spinal veins

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Spinal Cord injury

V little nerve regeneration in CNS

Loss of sensory & motor control below level of injury

Resp stop when lesion above Phrenic nerve origin (C3,4,5) - intercostal & diaphragmatic paralysis

Possible injuries that can occur to the SC include:

Complete transection - SC is completely torn - usually leads to Lower Motor neuron paralysis @ level of injury & Upper Motor neuron paralysis below LOI

Hemisection - Aka Brown-Sequard syndrome - damage occurs on one side of SC - causes weakness or paralysis on one side of body & loss of sensation on opposite side

Contusion - 'bruising' of the spinal cord - can result in oedema & compression damage occurring to nerves - common

C4 injury = tetraplegia (including shoulders)

C6 = tetraplegia (not including shoulders)

T6 = paraplegia (above level of pubic symphisis)

L1 = paraplegia (below level of PS)

Image 1 = SC T-1 transection due to stab wound - http://www.onlinejets.org/article.asp?issn=0974-2700;year=2012;volume=5;issue=2;spage=204;epage=204;aulast=Yeung

Image 3 = Spinal cord odema due to hyperflexion sprain - http://www.radiologyassistant.nl/en/p49021535146c5/spine-cervical-injury.html

Some treatments for spinal cord injuries include:

Spinal alignment & stabilisation

Decompression

Drugs such as Methylprednisolone (corticosteriod that reduce inflammation & such any 2ndary damage to SC)

Some clinical presentations of SC injury:

Paralysis

Flaccid limbs

No tendon reflexes upon testing

Loss of sensation

Incontinence

Babinski sign:

Medial aspect sole of foot is 'stroked' from heel towards little toe

Normal rxn = Plantar flexion (toes point down & foot flexes)

Abnormal rxn = Extensor plantar response (toes point up & fan outward) - this is normal rxn in children under age 2