Spinal Cord: Structure and Function Flashcards by Amin Bemanian

Spinal Cord : Structure

Invested by meninges: Dura, arachnoid, pia mater
Located in the vertebral canal within the bony vertebral column
Derived from embryonic neural tube

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Spinal Cord : Vasculature

Supplied by branches of the anterior spinal artery and the posterior spinal artery, arising from vertebral arteries
Supplied by multiple radicular arteries from segmental vessels

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Spinal Cord : Length

Extends from medulla at foramen magnum to lower border of L1

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Spinal Cord: Enlargements

Cervical and lumbar enlargements innervate upper and lower extremities

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Conus medullaris

L1 & L2 vertebrae, ending of spinal cord proper

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Lumbar puncture

L4-l5 vertebrae

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Filum terminale

Pia mater from conus medullaris to the coccygeal ligament

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Cauda equina

Lumbrosacral roots surrounding the filum terminale

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Spinal Cord : Segments

31 pairs of spinal nerves:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Each (except C1) innervates a single ipsilateral dermatome
Each innervates a single ipsi myotome

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Referred pain

Convergence of somatic and visceral afferents

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Spinal nerve exit

Vertebral canal via the intervertebral foramina (Location of DRG)

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Spinal cord - Indentations transverse

Anterior median fissure (anterior spinal artery and vein)
Posterior median sulcus/septum
Posterolateral sulcus (entry of dorsal roots)
Anterolateral sulcus (exit of ventral roots)
Posterior intermediate sulcus (cervical & upper thoracic only, separation between 2 major ascending tracts)

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Internal Structure of Spinal Cord

White matter (axons and glia) surround the roughly H-shaped gray matter (neuronal cell bodies and glia)
Cerebral canal (containing CSF) in the middle

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Size of Spinal Cord

Varies
Largest at cervical enlargement
Smallest at sacral level

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Amount of matter

White matter increases from the most caudal to most rostral

Gray matter varies, greatly expanded at the cervical and lumbar enlargements especially in the ventral horns

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White Matter Divisions

Posterior funiculus (Dorsal column)
Lateral funiculus (column)
Anterior funiculus (column)

Posterior funiculus subdivisions

Ascending somatosensory fibers

Fasciculus gracilis (sacral & lumbar)
Fasciculus cuneatus (thoracic & cervical)

Lateral funiculus subdivisions

Descending tracts to the spinal cord
-Lateral corticospinal tract
-Rubrospinal tract
Ascending tracts from the spinal cord
-Spinothalamic tracts = Anterolateral tract
-Posterior spinocerebellar tract
Anterior funiculus (column)
-Smaller ascending & descending tracts
-Crossing of spinothalamic tr

Gray Matter Divisons

Dorsal horn: Sensory
Ventral horn: Motor
Lateral horn

Dorsal Horn

Sensory input
Mediates synapses
Gives rise to ascending sensory pathways

Ventral horn

Houses alpha and gamma motoneurons
Houses interneurons
Neurons innervate, extrafusal & intrafusal muscle fibers

Lateral horn

Intermediolateral cell column (T1-L2-3)

Thoracolumbar sympathetic outflow

Internal structure of the spinal cord

Rexed’s lamination subdivideds the gray matter into 9 cellular laminae or groups (I-IX) plus an area X around the central gray

Rexed Lamination: Dorsal Horn

All sensory - I to VI
I: Marginal zone (mainly pain and temperature)
II: Substantia gelatinosa: interneurons
III-V: Processing of mechanical, visceral, and noxious stimuli
VI: Prominent only at enlargements
Neurons in I,V,and some of VII give rise to anterolateral tract

Rexed Lamination: Intermediate zone

Dorsal VII Medial: Clarke's nucleus (C8-L3) gives rise to dorsal spinocerebellar tract Lateral: Intermediolateral cell column (T1-L2/3): Preganglionic sympathetic Sacral autonomic nuclei (S2-4) Preganglionic parasympathetic

Rexed Lamination: Ventral horn

Ventral VII, VIII & IX | Motor neuronal groups in lamina IX: Innervate truncal & limb muscles

Spinal Cord : Functional Significance - DRG

Primary sensory afferent inputs from the DRG at each segmental level and relays them to the brain stem, cerebellum or the thalamus Inputs may or may not synapse first within the spinal cord

Spinal Cord : Functional Significance - Motoneurons

Houses alpha and gamma that innervate extrafual and intrafusal muscles respectively in body and extremities

Spinal Cord : Functional Significance - Spinal reflexes

Mediates them

Spinal Cord : Functional Significance - Intermediolateral cell column

T1 to L2-3 Preganglionic sympathetic fibers Synapse in the paravertebral and prevertebral ganglia

Spinal Cord : Functional Significance - S2-4

Preganglionic parasympathetic neurons

Spinal Cord : Major sensory and motor tracts

Ascending and descending tracts | Some synapse within spinal cord

Dorsal root lesions

Dorsal rhizotomy | Hypesthesia or anesthesia

Ventral root lesions

Weakness or flaccid paralysis and atrophy of muscles | Involvement of autonomic preganglionic fibers may result in autonomic dysfunction

Spinal cord hemisection

Brown-Sequard syndrome Loss of fine touch, vibration, proprioception ipsilateral to and below lesion Loss of pain and temperature contralateral to and below lesion Spastic paralysis ipsilateral to and below lesion

Spinal cord transection

Destruction of ascending and or descending tracts produce sensory, motor, or mixed deficts

Syringomyelia

Damage crossing fibers around the central canal