L19 - Motor system 2 Flashcards
Structure and composition of spinal nerves?
- The dorsal and ventral rootlets form the dorsal and ventral spinal nerve roots, which join to form spinal nerves of the respective levels
- Dorsal rootlets/roots are primarily sensory (with dorsal root ganglion)
- Ventral rootlets/roots are primarily motor (carries LMN)
Spinal nerve organization in the spinal cord lower than T12 level.
- Spinal cord tapers and ends at T12-L1, called conus medullaris
- Residual extension of spinal cord pia mater running from the conus to the coccyx = filum terminale
- Lumbar 2-5, sacral, coccygeal nerve roots emerge as a bundle = cauda equina
> > descend and form spinal nerves and exit at respective levels of the spine lower down
Cervical nerve exits at the spinal cord?
C1 nerve exits above C1 vertebra; C8 nerve exits between C7 and T1 vertebrae
Thoracic nerve exits at the spinal cord?
T1 nerve exits below T1 vertebra and so on, all the way down; L5 nerve exits between L5 and S1 vertebrae etc.
Where is lumbar puncture performed? Why?
Performed at lower lumbar region to avoid the cord
Needle through skin»_space; subarachnoid space»_space; obtain cerebrospinal fluid for diagnosis
Cauda equina moves aside
Spinal level and vertebral level are identical with each other. T or F?
False
The lower the spinal nerve, the larger the gap between the spinal segment and vertebral level
i.e. Sacral and coccygeal regions: S1 to S5 + CX1 spinal segment s correlate to T12 to L1 vertebral level (6-10 levels above)
Relate the posterior horns of the spinal cord to its functions?
Posterior horn for sensory (exception: C1 does not have sensory root)
- Sensory receptor»_space; sensory neuron enter via dorsal root to posterior horn: 6 laminae:
i) Relay by interneuron to motor neuron to effector organ for reflex
ii) Ascending tracts at posterior funiculus to brain (i.e. spinothalamic tract or DCML)
Relate the anterior horns of spinal cord to its function? (remember Lateral and Medial motor systems)
Anterior horn for efferent motor (e.g. reflex):
- Brain > descending tract > motor neuron > effector organ
- Connection between upper and lower motor neurons:
i) Corticospinal = brain to s.c.
ii) Corticobulbar = brain to CN
Indirect pathway = brainstem to s.c.
- Lateral motor systems»_space; anterior horn cells for distal muscles (fine movement, e.g. piano)
- Medial motor systems»_space; anterior horn cells for proximal muscles (gross movement)
Relate the posterior white matter of the spinal cord to its function?
Sensory, ascending (afferent) pathways:
- Dorsal column medial lemniscus system:
a) Cuneate fasciculus (more lateral): cervical, thoracic (2nd order neuron, upper body)
b) Gracile fasciculus (more medial): lumbar, sacral (2nd order neuron, lower body)
Relate the lateral white matter of the spinal cord to its function?
- Pyramidal tracts: (motor)
i) Lateral corticospinal tract - Extrapyrimidal tracts (motor)
i) Rubospinal tract
ii) Reticulospinal tract - Spinocerebellar tract: (sensory)
i) Posterior spinocerebellar t.
ii) Anterior spinocerebellar t. - Anterolateral system: (sensory)
i) Lateral spinothalamic tract
Relate the anterior white matter of the spinal cord to its function?
Pyramidal tracts (medial): i) Anterior corticospinal tract (motor)
Extrapyramidal tracts: (motor)
i) Reticulospinal tract
ii) Olivospinal tract
iii) Vestibulospinal tract
Anterolateral system: (sensory)
i) Anterior spinothalamic tract
Spino-olivary fibers (sensory)
Trace the course and functional output of the corticospinal tract? (remember the 2 parts)
Part of pyramidal tracts:
- Mainly From Area 4 (precentral gyrus), 6 (premotor, supplemental motor)»_space; internal capsule
- Incompletely decussated at the medulla oblongata:
i) 75- 90% = cross at pyramids = lateral corticospinal tract**»_space; interneurons and alpha motor neurons at ventral horn»_space; Distal muscles voluntary movement
ii) 10-25% = uncrossed at pyramids = Anterior corticospinal tract»_space; (later cross by interneuron)»_space; neck, arm, proximal, paraxial muscles for balance and posture
** Lateral CST – cervical is medial segment at lateral s.c.; sacral is lateral segment
Trace the general course and functional output of the extrapyramidal tracts?
Found in lateral and anterior grey matter of the spinal cord
- Originate from brainstem nuclei
- Under influence of nigrostriatal system, cerebellum & sensory system
- Modulate reflexes, posture and CST activities
- Influence mainly axial and proximal muscles
List examples of extrapyramidal tracts?
– Rubrospinal tract – Tectospinal tract – Pontine (medial) reticulospinal tract – Medullary (lateral) reticulospinal tract – Lateral vestibulospinal tract
Trace the course and functional output of the Rubrospinal tracts?
(From interposed nuclei of cerebellum to red nucleus)
Magnocellular neurons of red nucleus in midbrain»_space; cross midline
> > contralateral medulla oblongata
> > cervical spinal cord, lateral descending system
UL flexion predom.
Trace the course and functional output of the Tectospinal tracts?
From superior colliculus (midbrain)
> > contralateral cervical segments
> > Tract in anterior white column of spinal cord
Reflex movement in response to visual, auditory stimuli
Trace the course and functional output of the Reticulospinal tracts?
From undefined nuclei in Pontine reticular formation
> > Split into 2 tracts in the medulla:
1) Pontine (medial) reticulospinal tract: excites extensors
2) Medullary (lateral) reticulospinal tract: inhibits extensor, flexor predom.
• Influence voluntary movement
Trace the course and functional output of the Lateral Vestibulospinal tracts?
From lateral vestibular nucleus + Input from cerebellum and vestibular apparatus
Innervates ipsilateral trunk muscle»_space; Extensor-predominant»_space; maintains posture, balance (e.g. stand)
What is the reflex used to test lateral vestibulospinal tract in infants?
Labyrinthine Righting Reflex
Tilting of infant triggers head movement to stay upright and maintain posture
Summarize the functions of the corticospinal tracts?
- Lateral CST (crossed) executes conscious voluntary movement at distal muscle
- Ventral CST (uncrossed) controls balance and posture at proximal, neck muscle
Summarize the functions of the extrapyramidal tracts?
– Provide background condition and ‘readiness’ for CSTs to act
– Execute ‘unconscious’ responses to external stimuli and sensory feedback from the body
– Maintains a balance between flexion and extension motor activities + posture and balance
Explain the clinical sequalae of lentico-striate arteries stroke. (think about the supplied structure, and what tracts go though)
Internal capsule infarction
> > Lateral CST has poor recovery (poor fine movement i.e. cannot write)
> > Extrapyramidal tracts has good recovery of proximal muscles and gross movements
> > Some imbalance of flexion, extension = gait change
Explain the mechanism of decorticate positioning and decerebrate posturing in unconscious patients with brain lesions exam
1) Decorticate positioning: Lesion cut off cortex
- Lesion above red nucleus = rubrospinal tract intact = upper limb flexion
- Lower limb plantar flexion + knee extension
2) Decerebrate position: Lesion at lower brainstem between red nucleus and vestibular nucleus
a) Rubrospinal tract destroyed = No UL flexion, Unopposed UL extension and pronation
b) Vestibulospinal and Reticulospinal tracts intact = UL Extension and pronation
c) Lower limb extension and plantar flexion
List 3 causes of spinal cord injury?
Spinal fracture
Spinal epidural haematoma
Penetrating injury
List 3 causes of Spinal Cord Dysfunction
Spinal tumour
Multiple sclerosis
Spinal spondylosis
Explain how Aortic dissection may cause CNS lesion? Clinical sequaelae?
Aortic dissection causes false lumen
> > obstruction of lumen cause cord ischaemia
> > UMN lesion occurs:
i) Lateral CST damage = no voluntary movement
ii) Extrapyramidal tract damage = no descending modulation = hyperactive reflex arc
Compare examples of causes and locations of UMN vs LMN lesions?
UMN = CNS only = cerebral infarction, spinal cord injury/ ischameia
LMN = CNS or PNS damage = Poliomyelitis, Cauda equina injury
Compare the effector muscle distribution between UMN and LMN lesion?
UMN = Groups of muscles affected
LMN = Segmental
Compare the structures involved between UMN and LMN lesion?
UMN = Cortex; Descending tracts, e.g.: Corticospinal, Corticobulbar, Extrapyramidal
LMN = α-motor neuron, motor fibres in spinal or cranial nerves
Compare the type of paralysis between UMN and LMN lesions?
UMN = Spastic paralysis (esp. anti-gravity muscle. Clasp-knife rigidity
LMN = FLACCID paralysis
Compare the reflexes between UMN and LMN lesions?
UMN = HYPERACTIVE reflexes
LMN = Decreased or absent reflexes
Compare the change in muscle bulk affected by UMN vs LMN lesions?
UMN = Mild disuse atrophy
LMN = pronounced atrophy
Compare some classical signs of UMN vs LMN lesions?
UMN = Babinski’s reflex, Clonus
LMN = none
Compare the type of motor neuron lesion between Myelopathy vs Radiculopathy?
Myelopathy = Spinal cord injury:
• LMN lesion at that level (anterior horn cells affected)
or UMN lesion below that level
Radiculopathy = damage to nerve root as it exits the spinal cord
• LMN lesion only
• Cord itself unaffected
Compare the general type of damage caused by central vs lateral IVD herniation?
Central = myelopathy = UMN +/- LMN lesion
Lateral = Radiculopathy = LMN lesion
Which has worse prognosis: Internal capsule infarction or spinal cord lesion at or above conus medullaris?
Spinal cord lesion has worse prognosis: UMN lesion at level of lesion + LMN lesion below that level:
- BOTH lateral CST and extrapyramidal tracts damaged»_space; no voluntary movement or modulation, hyperactive reflex arc
Whereas internal capsule infarction damages Lateral CST but extrapyramidal tract usually intact»_space; gross movement still possible (extrapyramidal tract take over)
Consequence of complete cord transaction?
Complete motor paralysis, sensory loss below
Sphincter dysfunction (e.g. bladder)
Consequence of Hemitransection, e.g. tumour (Brown-Sequard syndrome)?
- At the level: ipsilateral root/segmental signs
- Below the level:
1) Ipsilateral:
a) Pyramidal weakness (extensors weakened more than flexors in upper limbs, flexors including ankle dorsiflexion weakened more than extensors in lower limbs)
b) Impaired joint position sense, accurate touch localization (DCML)
2) Contralateral: impairment of pain, temperature sensation (spinothalamic)
Consequence of central cord syndrome?
1) Segmental loss:
a) Affect decussating secondary sensory neurons
b) Late involvement of anterior horn cells
c) Upper limb pain/numbness
2) Long tract sign:
a) First affect medial fibres with Sacral sparing
(From medial: lose cervical first; from lateral: lose lumbar first)
Consequence of anterior cord syndrome?
Paraplegia
Spinothalamic loss
Intact posterior column
Consequence of posterior cord syndrome?
Pain, paraesthesia (tingling / pricking) in upper limb, trunk
Mild upper limb paraparesis (partial paralysis)
Compare the extend of paralysis caused by injury to C4/ C6/ T6/ L1 levels.
1) C4: involves brachial plexus + everything below= quadriplegia (includes shoulder, breathing difficulties)
2) C6: C5 of brachial plexus may be spared = quadriplegia (below shoulder: can still lift arm, switch positions)
3) T6: brachial plexus spared = paraplegia (leg + trunk)
4) L1: brachial plexus spared = paraplegia (leg)
Peripheral nerve lesions distal to the spine have the same outcome as spinal nerve root lesion. T or F?
False
Peripheral nerve lesions distal to the spine are a different matter since they can involve several spinal nerve roots
Symptoms of Radiculopathy are general and MRI must be used to narrow down on the lesion location. T or F?
False
Disc hernitation at diff levels affect diff nerve roots»_space; different symptoms to locate lesion
Distinguish the type of motor neuron lesion above/ at/ below the conus medullaris? Clinical sequalae?
Above conus: UMN lesion
At conus medullaris = Mixed UMN and LMN lesion
At Cauda equina = LMN lesion
Both can lead to:
- Saddle anesthesia (S2-S5): sensory loss at peri-anal region
- Sphincter dysfunctions
Define cauda equina syndrome, type of motor neuron affected and symptoms?
- LMN lesions
- Affect lumbosacral nerves
Symptoms: • LL weakness • Sensory loss • Sphincter dysfunction (late) • Sexual dysfunction • Back pain
What type of sphincter dysfunction is associated with cauda equina syndrome?
(irreversible unless very early intervention):
i) Bladder: painless acute urinary retention (loss of sensory output but maintain sphincter contraction)
ii) Bowel: constipation, Lax anal tone
Case presentation:
RUL and RLL weakness + Speech deficit + Right Lower facial weakness
Where is the lesion?
Right sided limb affected = Left hemisphere
Speech deficit = Temporal region affected
Lower Facial weakness = ** lower face muscles have contralateral innervation
> > > Left cerebral hemisphere lesion
Case presentation
RUL + RLL weakness, Hyperactive right limb reflexes with normal left limb function + Normal CN
Where is the lesion?
RUL + RLL weakness but normal CN and left limb function = spinal cord likely affected instead of cerebral infarction/ brainstem infarction
hyperactive reflex = UMN lesion
> > Likely cervical spinal cord affected
Case presentation:
Weakness and numbness in proximal UL
Normal Distal UL
Where is the lesion?
Proximal muscles served by C5 or above
Likely C5/C6 spinal cord lesion
Case presentation:
Weakness in wrist extension with OK wrist flexion
Proximal UL OK
where is the lesion? check
Wrist extension served by C5 or above
Likely C5/C6 spinal cord lesion
