Download Lower motor neuron

Motor Systems
三總神經科部
宋岳峰醫師
March 24, 2016
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Outlines
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Lower motor neuron and muscles
Lower motor neuron lesions
Descending pathways to the spinal cord
Descending pathways to motor nuclei of cranial nerves
Upper motor neuron lesions
Systems that control the descending pathways
Basal ganglia
Movement disorders
Upper motor neuron and cortical lesions
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Organization of the motor systems
supraspinal control
feedback circuits
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Lower motor neuron
• Alpha motor neurons
– Innervate extrafusal fibers
• Type I fibers (slower contraction, resistant to fatigue, little ATPase)
• Type II fibers (faster contraction, more rapidly fatigued, high ATPase)
• Gamma motor neurons
– Innervate intrafusal muscle fibers
– Control length and tension of neuromuscular spindles
– Control sensory nerve endings (receptors for the spinal stretch reflex)
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Gamma Loop
Provides additional control of alpha motor neurons and muscle contraction
Circuit: Gamma motor neuron →
intrafusal → muscle fiber → Ia
afferent axon → alpha
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Stretch reflex
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Lower motor neuron
• Graded control of muscle contraction by alpha motor neurons
– Varying firing rate of motor neurons (temporal summation)
– Recruit additional synergistic motor units
• More motor units in a muscle allow for finely controlled movement by the CNS
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Lower motor neuron lesions
• Injury of cell bodies or axons of the innervating neurons → muscle weakness
• Clinical features
– Reduced or absent muscle tone (flaccid paresis or paralysis)
– Decreased or absent deep tendon reflex (DTR)
– Muscle atrophy
– Fibrillation potentials (detected by electromyography), fasciculation (visible)
– Polyphasic waves, giant waves (due to reinnervation, detected by EMG)
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肌力測試
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Deep tendon reflex
Biceps jerk C5, C6 roots,
Musculocutaneous nerve
Supinator jerk C6, C7 roots,
Radial nerve
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Poliomyelitis 脊髓灰質炎(小兒麻痺症)
• Disease of the anterior horn motor neurons of the spinal cord and brain stem caused by poliovirus
• Flaccid asymmetric weakness and muscle atrophy, due to loss of motor neurons and denervation of their associated skeletal muscles
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Degenerative diseases
• Amyotrophic lateral sclerosis (ALS) 肌萎縮性
脊髓側索硬化症
• Spinal muscular atrophy
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Stephen Hawking suffers from amyotrophic lateral sclerosis Muscles wasting in a patient with ALS www.thelancet.com Vol 377 March 12, 2011 15
Electromyography
Fibrillation potentials
Tongue fasciculation
DOI:10.1056/NEJMicm1309849
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Hirayama Disease 平山病
Flexion MRI showing congested venous plexus appearing as a mass (due to anterior shift of posterior dura
OJHAS Vol. 12, Issue 3 : (Jul‐Sep 2013)
Non flexion MRI of spine showing hyperintensities
in cervical and upper thoracic spinal cord with no congestion of venous plexus
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Electromyography comparing normal, neurogenic, and myopathic features
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Signs similar to lower motor neuron lesion
• Disease of neuromuscular junction
– Myasthenia gravis
• Muscle disorders
– Dystrophy
– Myopathy
– Myositis
如何鑑別診斷？
NE, neurophysiological testing, biopsy
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Spinal cord
Descending pathways to the spinal cord
•Lateral Pathways
involved in voluntary of distal musculature movement under cortical control
•Ventromedial Pathways
involved in control of posture and locomotion, under brain stem control
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Corticospinal tracts
Cells in the primary motor and premotor areas of frontal lobe and in the parietal lobe, including the sensory area
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Posterior limb of the internal capsule
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Basis pedunculi of midbrain (some of the axons give off branches to red nucleus)
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ventral portion of pons
↓
pyramid of medulla ↓
caudal end of medulla
• 85% (cross, lateral corticospinal tract)
• 15% (ipsilateral, ventral corticospinal tract)
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The regions of the cerebral cortex that give rise to the corticospinal tract MI = primary motor cortex PMC = premotor cortex
SI = primary somatosensory
receiving area
SMA = supplementary motor area
The posterior parietal cortex (PPC) does not contribute to the corticospinal tract but does modulate its activity
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Corticospinal Tract (皮
質脊髓徑):
Carries motor commands from the brain
85% decussate to lateral corticospinal tract
15% continue ipsilaterally
as the medial corticospinal tract
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Lesions of the pyramidal tract
• Selective transection of monkey’s pyramidal tract ― weakness and reduced tone in the contralateral muscles and clumsiness in actions
• Impairment in controlling precision and speed
of skilled movements
• Babinski’s response: probably due to transection of corticospinal fibers
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Babinski’s sign
absent
present
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Rubrospinal tract 紅核脊髓徑
Arises from neurons in the red nucleus
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Cross the midline in the ventral midbrain (called the ventral tegmental decussation)
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Descend to the contralateral spinal cord
•Somatotopically arranged
– The cervical spinal segments receive fibers from the dorsal part of the red nucleus, which, in turn, receive inputs from the upper limb region of the sensorimotor cortex
– The lumbosacral spinal segments receive fibers from the ventral half
of the red nucleus, which in turn, receive inputs from the lower limb region of the sensorimotor cortex
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Rubrospinal tract
• The neurons in the red nucleus are activated monosynaptically by projections from the cortex
• In humans most of the efferent fibers emerging from the red nucleus terminate in the inferior olive
• Ends on interneurons that, in turn, project to the dorsal aspect of ventral (motor) horn cells
• Facilitates flexor motor neurons and inhibit extensor motor neurons
• Lesions of the midbrain tegmentum including the red nucleus are known to elicit contralateral motor disturbances (e.g., tremor, ataxia, and choreiform activity) 29
Rubrospinal tract
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Reticulospinal tracts 網狀脊髓徑
•Each half of the spinal cord contains two reticulospinal
tracts
•Axon來自於網狀
活化系統的cells
Pontine reticulospinal
tract
Medullary
reticulospinal
tract
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Ascending reticular activating system (ARAS)
• Receives input from all sensory systems, and projects widely to the thalamus, basal forebrain, and the cerebral hemispheres
• The crucial segment of the RAS for arousal is between the rostral midbrain and the midpons
Reticulospinal tract
• Pontine reticulospinal
tract
– arises ipsilaterally in the oral and caudal pontine
reticular nuclei
– Travels in the ventral funiculus
– Terminates bilaterally
• Medullary
reticulospinal tract
– Originates in the gigantocellular reticular nuclei on both sides of the medulla
– Descends in the ventral half of the lateral funiculus
– Ends bilaterally among spinal interneurons
(lamina VII)
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Reticulospinal tract
• Controls over most movements that do not require dexterity or the maintenance of balance
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Vestibulospinal tract 前庭脊髓徑
• Lateral vestibulospinal tract stays ipsilateral
and is not bilateral
– Innervates proximal and axial muscles
– Controls posture and balance
– Provides extensor tone to resist the pull of gravity
• Medial vestibulospinal tract is bilateral and limited to cervical spinal cord segments
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Lateral and medial vestibulospinal tracts
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Other descending tracts
• Tectospinal tract
– From the contralateral superior colliculus
• The descending component of medial longitudinal fasciculus 內側縱束 (also called “medial vestibulospinal tract”)
• Interstitiospinal tract
– Arises from the interstitial nucleus of Cajal and the Edinger‐Westphal nucleus
– Visuomotor coordination
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Tectospinal tract 頂蓋脊髓徑
• The neurons from which this tract arises are located in the superior colliculus 上丘
• The axons of these neurons terminate in upper cervical segments
• This tract is believed to aid in directing head movements in response to visual and auditory stimuli
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tectospinal tracts
Rubrospinal tracts
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Internuclear ophthalmoplegia (IOP)
lesions involving bilateral median longitudinal fasciculus (MLF)
Descending pathways to motor nuclei of cranial nerves
Frontal and occipital lobes, superior colliculus, and various nuclei in the brainstem
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Oculomotor, trochlear, and abducens nuclei
• Frontal eye fields → changing the direction of gaze voluntarily
• Occipital cortex → controls involuntary conjugate movements (tracking a moving object), looking at a near object (convergence)
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Corticobulbar
(corticonuclear) fibers
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Lower motor neuron lesion
Upper motor neuron lesion
Upper motor neuron lesions
Clinical features
• Voluntary movements of the affected muscles are absent or weak
• Profound atrophy dose not occur
• Increased muscle tone (spasticity), exaggerated deep tendon reflex, clasp knife phenomenon, clonus
• Abnormal plantar reflex
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Upper motor neuron lesions
• The superficial reflexes (abdominal reflex, cremasteric reflex) are suppressed or absent
• Pathological laughing or crying (laughter or crying on inappropriate occasions, pseudobulbar signs)
Systems that control the descending pathways
Cerebellar circuits
Contralateral neocortex
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Corticopontine and pontocerebellar fibers
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Cortex and central nuclei of the cerebellum
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Spinocerebellar tracts
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Ipsilateral proprioceptors in muscles, tendons and joints
Vestibular apparatus
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Cerebellar lesions
• Errors in the rate, range, force, and direction of willed movements
• Unilateral damage to cerebellar hemisphere lead to the symptoms that affect the same side of the body
• Ataxia, hypotonia, and intention tremor
Basal ganglia
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Basal ganglia
• Initiation, control, and cessation of all the components of regularly made movements
Parkinson’s disease
• Presence of Bradykinesia
• And at least one of the following: – Rigidity
– Resting tremor (4‐6 Hz)
– Postural instability
excitatory (glutamatergic) (blue arrows)
inhibitory, or GABAergic (black arrows)
Movement disorders
• Hypokinetic
– Parkinsonism
• Hyperkinetic
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Dystonia 肌張力不全症
Athetosis 手指徐動症
Chorea 舞蹈症
Stereotypy 刻板性行為
Dyskinesia 運動不良/運動不能
Tics 抽搐症
Tremor 顫抖症
Myoclonus 肌躍症
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Upper motor neuron and cortical lesions
Demyelinating
disease
Tumor
Vascular disease
Inflammatory disease
Infection
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Cortical lesions
• Primary motor area (MI)
– Contralateral flaccid paralysis • Premotor cortex (PMC)
– Contralateral weakness of shoulder and hip
• Supplementary motor area (SMA)
– Impairment of movements initiation, contralateral
limbs
CT
Infarction, Lt MCA territory
MRI, DWI
Infarction of right posterior limbs of internal capsule
Eye movements
眼球偏向左側
眼球偏向右側
左側肢體無力
右側額葉中風
右側橋腦中風
Frontal gaze
center
Pontine gaze
center
左側肢體無力
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Demyelinating diseases
• Multiple Sclerosis 多發
性硬化症
• Transverse Myelitis (TM) 横截性脊髓炎
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Tumor
• Astrocytoma: slowly progressive
• Ependymoma, hemangioblastoma
• Metastasis lesions (bone, spinal cord)
Spinal cord infarction
DWI
Lt
Rt
ADC Maps
T2‐Weighted MRI
Questions?
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