SPINAL CORD

PROF DR NASARUDDIN ABDUL AZIZ

Management & Science University

dr_nasaruddin@msu.edu.my

OBJECTIVES• describe the external structure of the spinal

cord,

• draw and describe the internal structure of the spinal cord,

• draw and describe the ascending and descending tracts within the spinal cord,

• describe the meninges surrounding the spinal cord,

• describe the blood supply of the spinal cord,

• explain the clinical correlations of & applications related to the spinal cord

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

• Enlargements: cervical & lumbar

• Conus medullaris

• Filum termniale

• Anterior median fissure

• Posterior median sulcus

• 31 pairs of spinal nerves attached to it by the anterior roots & posterior roots

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

• Great anterior medullary artery of Adamkiewicz

• Arise from lateral intercostal artery or lumbar artery at any level from T8 – L3

Clinical correlations

Spinal shock

• Follows acute severe damage to the spinal cord

• All cord functions below the level of the lesion become depressed or lost

• Sensory impairment and flaccid paralysis occur

• Segmental spinal reflexes are depressed

• Persists for less than 24 hours (may be as long as 1 – 4 weeks)

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 anaesthesia

• Extradural anaesthesia