SPINAL CORD ANATOMYDR. UTKARSSH A W

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

31 pairs of spinal nerves:8 cervical12 thoracic 5 lumbar5 sacral1 coccygeal

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.

• Dorsal root – sensory fibres

• Ventral root – motor fibres

• Dorsal and ventral roots join at intervertebral foramen to form the spinal nerve

Structure Of The Spinal Cord

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

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

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

• 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

• 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

• 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

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

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

Tracts

• Ascending• Descending• Intersegmental

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)

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)

• 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

• Spinotectal tract– spinovisual reflexes

• Spinoreticular tract– info from muscles, joints & skin to reticular

formation• Spino-olivary tract– indirect pathway to cerebellum

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

Anterior spinothalamic tracts

• Light (crude) touch & pressure pathways

Posterior white column

• Discriminative touch, vibratory sense, conscious muscle joint sense (conscious proprioception)

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

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

Descending Tracts

• Lower motor neurons• Upper motor neurons• Corticospinal tracts– concerned with voluntary, discrete, skilled

movements

• 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

Meninges

• Dura mater• Arachnoid mater• Pia mater

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

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

Pia mater

• Vascular membrane• Closely covers spinal cord• Thickened on either side between nerve

roots to form the ligamentum denticulatum

Blood supply

Arteries of the spinal cord• Anterior spinal artery• Posterior spinal artery• Segmental spinal arteries

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

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

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

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

• Lower Limbs : L2 - Hip flexors

L3,4 - Knee extensors

L4,5 – S1 - Knee flexion

L5 - Ankle dorsiflexion

S1 - Ankle plantar flexion

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

SPINAL CORD INJURIES CLASSIFICATION

• Quadriplegia :injury in cervical regionall 4 extremities affected

• Paraplegia :injury in thoracic, lumbar or sacral segments2 extremities affected

Injury either:

1) Complete

2) Incomplete

Complete: i) Loss of voluntary movement of parts

innervated by segment, this is irreversibleii) Loss of sensationiii) Spinal shock

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

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

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

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

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)

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

• 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

TYPES OF INCOMPLETE INJURIES

i) Central Cord Syndrome

ii) Anterior Cord Syndrome

iii) Posterior Cord Syndrome

iv) Brown – Sequard Syndrome

v) Cauda Equina Syndrome

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

CENTRAL CORD SYNDROME

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)

Clinically: • Loss of power• Decrease in pain and sensation below lesion• Dorsal columns remain intact

ANTERIOR CORD SYNDROME

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

POSTERIOR CORD SYNDROME

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

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)

Brown – Sequard Syndrome

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

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

SPINAL TUMOURS

• 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.

• 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.