Spinal Cord Flashcards
What are the investing membranes of the spinal cord?
Dura Mater
Tough, fibrous tubular sheath
Extends from foramen magnum to level of S2 vertebra & is continuous with cranial dura
Epidural/Extradural Space
Separates dura from vertebral column.
Contains loose areolar tissue & internal venous plexus.
Subdural Space
Narrow space between dura & underlying arachnoid mater.
Arachnoid Mater
Thin transparent sheath
Separated from underlying pia by subarachnoid space
Subarachnoid Space
Contains cerebrospinal fluid (CSF)
Pia Mater
Closely surrounds spinal cord
Sends septa into its substance
What is arachnoiditis?
Arachnoiditis is a disorder caused by the inflammation of the arachnoid.
What is the Filum Terminale?
Stabilises cord and dura lengthways
Filum Terminale Internum
Filament formed by pia mater tip of dural sac
Surrounded by cauda equina, bathed in CSF
Filum Terminale Externum
Extradural continuation
Attaches at tip of dural sac & extends to coccyx and ends as the coccygeal ligament
Filum is formed by pia mater
Terminale stabilises the cord distally
Spinal cord terminates around T12-L1- L2
Pointy bit = conus medullaris
What is the dentate ligament?
Formed by pia mater
Runs along both lateral margins of spinal cord between dorsal and ventral rootlets
Medial edge is continuous with pia at side of spinal cord
Lateral edge pierces arachnoid at intervals to attach to inside of dura
Helps stabilise cord from side to side
What is the anatomy of the spinal cord?
Occupies upper 2/3’s of adult spinal canal
42-45cm long in adults
Divided into 30 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and a few small coccygeal)
Continuous with medulla superiorly
Widens laterally as cervical & lumbosacral enlargements
Lumbosacral enlargement tapers off to form conus medullaris, which ends at L1/ L2 level of vertebral column in adults
Filum terminale consists of pia & glial fibres & often contains a vein
What is the grey matter in the internal divisions of the spinal cord?
H-shaped mass of grey matter surrounded by white matter
Made up of two symmetric portions joined across midline by a transverse connection of grey matter
Contains central canal or its remnants
CC = central canal – contains
small amount of CSF (very small amount)
Motor at the front – bottom of H
Sensory at the back = top of H
Autonomic - Side of H
What is the ventral/anterior horn in the internal divisions of the spinal cord?
Anterior to central canal
Contains cell bodies alpha & gamma motor neurons
Origin of the lower motor neurons (LMN), the efferent neuron of the peripheral nervous system (PNS) that connects the central nervous system (CNS) with the muscle to be innervated.
Also, location of anterior horn cell diseases.
Blood supply – anterior spinal artery.
Polio is an anterior horn disease – not as common now as vaccine
Anterior horn = origin of lower motor neuron – target is the muscle that it reaches
What is the lateral horn in the internal divisions of the spinal cord?
between dorsal & ventral horns
Prominent lateral triangular projection in thoracic & upper lumbar regions
Contains preganglionic cells for autonomic nervous system
Distal expansion of the H shape sideways is seen only in thoracic
What is the dorsal horn in the internal divisions of the spinal cord?
Posterior to central canal
Contains many layers (laminas) of nerve cells: lamina I, II, III, IV, V, and VI
Lamina II contains substantia gelatinosa of Rolando (important part of pain gate theory)
Other lamina contain neurons that respond to noxious stimuli, position & touch sense, & mechanical signals from skin & joints.
Many lamina are in the circle - on powerpoint
Sensory
Where is the white matter located in the internal divisions of spinal cord?
Dorsal/posterior White Column (PC)
Between posterior median sulcus & posterolateral sulcus
Lateral White Column
Between posterolateral sulcus & anterolateral sulcus
Ventral White Column
Lies between anterolateral sulcus and anteromedian fissure
Proprioception/ light touch / vibration / conscious joint position/ determining two points when applied to skin = PCon slide
What are the regional characteristics of the spinal cord?
Cervical Levels
Oval
Larger than other spinal levels
Large amount of white matter
Thoracic Levels
Round
Small posterior & anterior horns
Progressive decrease in white matter from upper to lower levels
Dorsal nucleus (of Clark)
Intermediate (unconcious proprioception, spinocerebellar a continuation)
Lateral horn - Autonomics
Lumbar Levels
Round
Quite large posterior & anterior horns
Less white matter than higher levels
Sacral Levels
Round
Smaller than lumbar levels
Consists mainly of gray matter
Thin shell of white matter
Intermediate/lateral horn (S2/S3/S4)
What are the Pathways in White Matter: Descending Fibre Systems?
Lateral corticospinal tract - Lateral is key one for movements of the limbs = reflex testing
Anterior corticospinal tract
Bottom 4 are tracts that are working in the background – don’t have clinical significance or testability of the other 2
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal
What is the lateral corticospinal tract?
Largest descending motor pathway
Function - Fine motor function, modulation of sensory functions
Course - Motor & premotor cortex > internal capsule > crus cerebri >basis pontis > medullary pyramid > 75-90% decussate in decussation of pyramids > contralateral lateral white column of spinal cord > ventral gray horn > contralateral anterior horn cells
Upper motor neuron
If something is going wrong in upper motor neuron something is going wrong within the lateral corticospinal tract
Decussation point is in the medullary pyramid
Upper motor neuron symptoms include weakness/paralysis/hyperactive reflexes/
What is the decussation point of the lateral corticospinal tract?
medullary pyramid
What is the Anterior Corticospinal Tract?
Small descending motor pathway
Function
Gross and postural motor function (proximal & axial musculature)
Course
Motor & premotor cortex > crus cerebri > basis pontis >medullary pyramid > 10-25% do NOT decussate > ipsilateral anterior white column of spinal cord > many decussate via anterior white commissure > ventral gray horn > interneurons > contralateral anterior horn cells
Anterior white commissure where they cross/ decussate
What is the decussation point of the Anterior Corticospinal Tract?
ipsilateral anterior white column of spinal cord many decussate via anterior white commissure
What is the vestibular tract and its function?
Vestibular nuclei receive afferents from vestibular apparatus (semicircular canals, utricle & saccule)
Function
Postural reflexes, quick movements in reaction to sudden changes in body position (e.g. falling), essential control of antigravity muscles
What is the course Lateral Vestibulospinal Tract?
Lateral vestibular nucleus > medulla (anterior to rubrospinal tract) > ipsilateral anterior white column of spinal cord > ipsilateral gamma & alpha motor neurons > postural control (especially related to movements of head) by inhibiting axial flexor muscles, & stimulating axial extensor muscles
What is the course Medial Vestibulospinal Tract?
Medial vestibular nucleus > mainly to ipsilateral cervical cord > ipsilateral gamma & alpha motor neurons
What is the course of the medial longitudinal faciculus?
Contains medial vestibulospinal, tectospinal & reticulospinal fibers co-ordination of head & eye movements
What is the function and course of the Rubrospinal Tract?
Facilitate flexor & inhibit extensor muscles
Course
Contralateral deep cerebellar nuclei (via superior cerebellar peduncle) & motor cortex bilaterally > red nucleus > contralateral lateral white column > ventral gray horn > alpha & gamma motor neurons
Decorticate vs. Decerebrate
A UMN lesion above the level of the red nucleus will result in decorticate posture (thumb tucked under flexed fingers in fisted position, pronation of forearm, flexion at elbow with the lower extremity in extension with foot inversion) while a lesion below the level of the red nucleus but above the level of the vestibulospinal and reticulospinal nuclei will result in decerebrate posture (upper extremity in pronation and extension and the lower extremity in extension). The reason for this is that the red nucleus output reinforces antigravity flexion of the upper extremity. When its output is eliminated then the unregulated reticulospinal and vestibulospinal tracts reinforce extension tone of both upper and lower extremities. If there is a lesion in the medulla then all the brainstem motor nuclei as well as the direct corticospinal tract would be out and the patient would be flaccid acutely. If the patient were to survive, tone would return because of interneuronal activity at the spinal cord level.
What is the function and course of the tectospinal tract?
Mediates contralateral movements of head in response to auditory, visual and somatic stimuli (protective reflex)
Course
Superior colliculus in tectum of midbrain > decussate soon after origin > descend through brainstem close to medial longitudinal fasciculus > contralateral anterior white column of spinal cord > ventral gray horn of upper cervical segments > alpha & gamma motor neurons
What is the function and course of Reticulospinal Tract?
Modulation of sensory transmission (especially pain), modulation of spinal reflexes, affect muscle tone & posture
Course
Scattered throughout midbrain, pons & medulla are cells known as reticular formation
What are the Descending Autonomics Function?
Modulation of autonomic functions (e.g. blood pressure, pulse, respiratory rates & sweating)
Cerebral cortex, hypothalamus, amygdaloid complex & reticular formation decussate in brainstem > contralateral lateral white column > autonomic motor cells in lateral gray horns in thoracic and upper lumbar (sympathetic outflow) & midsacral (parasympathetic) levels of spinal cord
