spinal cord anatomy and injuries
TRANSCRIPT
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SPINAL CORD ANATOMYDR. UTKARSSH A W
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Gross Appearance• Cylindrical in shape• Foramen magnum L1/L2 (adult)• L3 (newborn)• Occupies upper ⅔ of vertebral canal• Surrounded by 3 layers of meniges:– dura mater– arachnoid mater– pia mater
• CSF in subarachnoid space
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31 pairs of spinal nerves:8 cervical12 thoracic 5 lumbar5 sacral1 coccygeal
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With increasing age, the vertebral column and dura lengthen more rapidly than the neural tube, and the terminal end of the spinal cord gradually shifts to a higher level.
At birth, this end is at the level of the third lumbar vertebra.
As a result of this disproportionate growth, spinal nerves run obliquely from their segment of origin in the spinal cord to the corresponding level of the vertebral column.
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• Dorsal root – sensory fibres
• Ventral root – motor fibres
• Dorsal and ventral roots join at intervertebral foramen to form the spinal nerve
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Structure Of The Spinal Cord
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Gray Matter• H-shaped pillar with anterior & posterior gray horns• United by gray commissure containing the central
canal• Lateral gray column (horn) present in thoracic & upper
lumbar segments• Amount of gray matter related to the amount of
muscle innervated• Consists of nerve cells, neuroglia, blood vessels
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Nerve cells in the anterior gray columns• Large & multipolar• Axons pass out in the anterior nerve roots as
α-efferents• Smaller nerve cells are multipolar• Axons pass out in anterior roots as ɣ-
efferents
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Nerve cells in the posterior gray columns• 4 nerve cell groups• Substantia gelatinosa– situated at the apex– throughout the length of spinal cord– composed mainly of Golgi Type II neurons– receives afferent fibres concerning with pain,
temperature & touch from posterior root
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• Nucleus proprius– anterior to substantia gelatinosa– present throughout the whole length of spinal
cord– main bulk of cells in posterior gray column– receives fibers from posterior white column that
are assoc with proprioception, 2-point discrimination & vibration
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• Nucleus dorsalis (Clark’s column)– base of posterior column– C8 – L3 / L4– associated with proprioceptive endings
(neuromuscular spindles & tendon spindles)• Visceral afferent nucleus– lateral to nucleus dorsalis– T1 – L3– receives visceral afferent info
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• Nerve cells in the lateral gray columns• Formed by the intermediolateral group of
cells• T1 – L2 / L3• Cells give rise to preganglionic sympathetic
fibres• In S2, S3, S4; they give rise to preganglionic
parasympathetic fibres
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The gray commissure & central canal◦ connects the gray on each side◦ central canal in the centre◦ posterior gray commissure◦ anterior gray commissure◦ central canal present throughout◦ superiorly continuous with the central canal of
medulla oblongata◦ inferiorly, expands as terminal ventricle◦ terminates within the root of filum terminale
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White Matter
• Divided into– anterior white column– lateral white column– posterior white column
• Consists of nerve fibres, neuroglia, blood vessels
• White due to myelinated fibres
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Tracts
• Ascending• Descending• Intersegmental
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Ascending Tracts
• Fibres that ascend from spinal cord to higher centres
• Conduct afferent information which may or may not reach consciousness
• Information may be– exteroceptive (pain, Tº, touch)– proprioceptive (from muscles & joints)
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Organization
• Ascending pathway that reach consciousness consists of 3 neurons:– 1st-order neuron– 2nd-order neuron– 3rd-order neuron
• Branch to reticular formation (wakefulness)• Branch to motor neurons (reflex activity)
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• Lateral spinothalamic tract– pain & Tº
• Anterior spinothalamic tract– light (crude) touch & pressure
• Fasciculus cuneatus• Fasciculus gracilis– discriminatory touch, vibration, info from muscles &
joints• Anterior spinocerebellar tract• Posterior spinocerebellar tract– unconscious info from muscles, joints, skin, subcut
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• Spinotectal tract– spinovisual reflexes
• Spinoreticular tract– info from muscles, joints & skin to reticular
formation• Spino-olivary tract– indirect pathway to cerebellum
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Lateral spinothalamic tract
• Pain & temp pathways• 1st-order neurons• Pain conducted by δ A-type fibres & C-type fibres• 2nd-order neurons– decussate to the opposite side– ends in thalamus (ventral posterolateral nucleus
• 3rd-order neurons– ends in sensory area in postcentral gyrus
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Anterior spinothalamic tracts
• Light (crude) touch & pressure pathways
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Posterior white column
• Discriminative touch, vibratory sense, conscious muscle joint sense (conscious proprioception)
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Posterior spinocerebellar tract
• Muscle joint sense pathways to cerebellum• Unconscious proprioception• Muscle joint info from muscle spindles, GTO,
joint receptors of the trunk & lower limbs• Info is used by the cerebellum in the
coordination of movements & maintenance of posture
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Anterior spinocerebellar tract
• Majority of 2nd-order neurons cross to the opposite side
• Enter cerebellum through superior cerebellar peduncle
• Info from trunk, upper & lower limbs• Also carries info from skin & subcut tissue
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Descending Tracts
• Lower motor neurons• Upper motor neurons• Corticospinal tracts– concerned with voluntary, discrete, skilled
movements
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• Reticulospinal tract– facilitates or inhibits voluntary movement or reflex
activity• Tectospinal tract– reflex postural movements in response to visual
stimuli• Rubrospinal tract– facilitates activity of flexor muscles & inhibits
activity of extensor muscles• Vestibulospinal tract– facilitates extensor muscles, inhibits flexor muscles
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Meninges
• Dura mater• Arachnoid mater• Pia mater
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Dura mater
• Dense, strong fibrous membrane• Encloses the spinal cord & cauda equina• Continuous above with meningeal layer of
dura covering the brain• Ends at the level of S2• Separated from wall of vertebral canal by the
extradural space• Contains loose areolar tissue & internal
vertebral venous space
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Arachnoid mater
• Delicate impermeable membrane• Lies between pia and dura mater• Separated from pia mater by subarachnoid
space• Continuous above with arachnoid mater
covering the brain• Ends on filum terminale at level of S2
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Pia mater
• Vascular membrane• Closely covers spinal cord• Thickened on either side between nerve
roots to form the ligamentum denticulatum
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Blood supply
Arteries of the spinal cord• Anterior spinal artery• Posterior spinal artery• Segmental spinal arteries
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Anterior spinal artery• Formed by the union of 2 arteries• From vertebral artery• Supply anterior ⅔ of spinal cord
Posterior spinal arteries• Arise from vertebral artery or posterior
inferior cerebellar arteries (PICA)• Descend close to the posterior roots• Supply posterior ⅓ of spinal cord
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Segmental spinal arteries• Branches of arteries outside the vertebral
column• Gives off the anterior & posterior radicular
arteries• Arise from lateral intercostal artery or
lumbar artery at any level from T8 – L3
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DERMATOMES
• Area of skin innervated by sensory axons within a particular segmental nerve root
• Knowledge is essential in determining level of injury
• Useful in assessing improvement or deterioration
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MYOTOMES• Segmental nerve root innervating a muscle• important in determining level of injury
• Upper limbs:C5 - Deltoid C 6 - Wrist extensorsC 7 - Elbow extensorsC 8 - Long finger flexors T 1 - Small hand muscles
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• Lower Limbs : L2 - Hip flexors
L3,4 - Knee extensors
L4,5 – S1 - Knee flexion
L5 - Ankle dorsiflexion
S1 - Ankle plantar flexion
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Sign Upper motor neurone Lower motor neurone
1) Weakness Voluntary movements are disturbed
Paralysis of muscles supplied by that segment or nerve
2) Tone Hypertonia (clasp- knife spasticity
Hypotonia
3) Reflex ( tendon) Increased,+- clonus Decreased or absent
4) Reflex ( superficial) Absent or decreased Absent or decreased
5) Plantar response Extensor Flexor or absent
6) Muscle nutrition Disuse atrophy Marked atrophy
7) Fasciculations Absent Present
8) Reaction of degeneration
Absent Present
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SPINAL CORD INJURIES CLASSIFICATION
• Quadriplegia :injury in cervical regionall 4 extremities affected
• Paraplegia :injury in thoracic, lumbar or sacral segments2 extremities affected
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Injury either:
1) Complete
2) Incomplete
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Complete: i) Loss of voluntary movement of parts
innervated by segment, this is irreversibleii) Loss of sensationiii) Spinal shock
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Incomplete:
i) Some function is present below site of injury
ii) More favourable prognosis overalliii) Are recognisable patterns of injury,
although they are rarely pure and variations occur
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Injury defined by ASIA Impairment Scale
ASIA – American Spinal Injury Association :
A – Complete: no sensory or motor function preserved in sacral segments S4 – S5
B – Incomplete: sensory, but no motor function in sacral segments
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C – Incomplete: motor function preserved below level and power graded < 3
D – Incomplete: motor function preserved below level and power graded 3 or more
E – Normal: sensory and motor function normal
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MUSCLE STRENGTH GRADING
• 5 – Normal strength• 4 – Full range of motion, but less than
normal strength against resistance
• 3 – Full range of motion against gravity • 2 – Movement with gravity eliminated • 1 – Flicker of movement• 0 – Total paralysis
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Spinal Shock : • Transient reflex depression of cord function
below level of injury• Initially hypertension due to release of
catecholamines• Followed by hypotension• Flaccid paralysis • Bowel and bladder involved• Sometimes priaprism develops • Persists for less than 24 hours (may be as
long as 1 – 4 weeks)
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Neurogenic shock: • Triad of i) hypotension
ii) bradycardia iii) hypothermia
• More commonly in injuries above T6
• Secondary to disruption of sympathetic outflow from T1 – L2
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• Loss of vasomotor tone – pooling of blood• Loss of cardiac sympathetic tone – bradycardia • Blood pressure will not be restored by fluid
infusion alone• Massive fluid administration may lead to
overload and pulmonary edema • Vasopressors may be indicated• Atropine used to treat bradycardia
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TYPES OF INCOMPLETE INJURIES
i) Central Cord Syndrome
ii) Anterior Cord Syndrome
iii) Posterior Cord Syndrome
iv) Brown – Sequard Syndrome
v) Cauda Equina Syndrome
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CENTRAL CORD SYNDROME
• Also associated with fracture dislocation and compression fractures
• More centrally situated cervical tracts tend to be more involved hence flaccid weakness of arms > legs
• Perianal sensation & some lower extremity movement and sensation may be preserved
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CENTRAL CORD SYNDROME
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ANTERIOR CORD SYNDROME
• Due to flexion / rotation• Anterior dislocation / compression fracture
of a vertebral body encroaching the ventral canal
• Corticospinal and spinothalamic tracts are damaged either by direct trauma or ischemia of blood supply (anterior spinal arteries)
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Clinically: • Loss of power• Decrease in pain and sensation below lesion• Dorsal columns remain intact
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ANTERIOR CORD SYNDROME
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POSTERIOR CORD SYNDROME
Hyperextension injuries with fractures of the posterior elements of the vertebrae
Clinically: • Proprioception affected – ataxia and
faltering gait • Usually good power and sensation
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POSTERIOR CORD SYNDROME
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Brown – Sequard Syndrome
• Hemi-section of the cord• Either due to penetrating injuries: i) stab wounds
ii) gunshot wounds• Fractures of lateral mass of vertebrae
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Clinically: • Paralysis on affected side (corticospinal)• Loss of proprioception and fine
discrimination (dorsal columns)• Pain and temperature loss on the opposite
side below the lesion (spinothalamic)
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Brown – Sequard Syndrome
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CAUDA EQUINA SYNDROME
• Due to bony compression or disc protrusions in lumbar or sacral region
Clinically • Non specific symptoms – back pain
- bowel and bladder dysfunction- leg numbness and weakness- saddle parasthesia
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Poliomyelitis• Acute viral infection of the neurones of
anterior gray column• Motor nuclei of cranial nerves• Death of motor neurone cells → paralysis &
wasting of muscles• Muscles of lower limb more often affected
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SPINAL TUMOURS
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• The first order sensory neurons are in the dorsal root ganglia or the sensory ganglia of cranial nerves. 2. The second order sensory neurons are in the dorsal gray column or various sensory nuclei of the brainstem. 3. The third order sensory neurons are in the thalamic nuclei. The long ascending sensory tracts found in the spinal cord or the brainstem are formed by either the first or the second order neurons.
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• EXAMPLE:
Typically, the perception of pain travels through three orders of neurons. The first-order neurons carry signals from the periphery to the spinal cord; the second-order neurons relay this information from the spinal cord to the thalamus; and the third-order neurons transmit the information from the thalamus to the primary sensory cortex, where the information is processed, resulting in the "feeling" of pain.
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