White Matter- classification
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TractsAscending Tracts
Descending Tracts
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Clinical Correlates
Mixture of:
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1. Nerve fibers,2. Neuroglia,
3. Blood vessels.
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surrounds the grey matter
white colour
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myelinated nerve fibres.Sensory
Motor
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Association
Anterior white column
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(or funiculus)Lateral white column
(or funiculi)
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Posterior whitecolumn (or funiculus)
Anterior white
commissure.
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Collection of nerve fibres
with same
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Origin,Course,
Termination
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Spinotectal tract
Spinoreticular tract
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Descending autonomic tractSpino-olivary tract
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Lateral Spinothalamic Tract
Pain,
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Thermal sensationAnterior Spinothalamic Tract
Crude (Light) touch, (non-discriminative touch)
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PressureTickle, Itch
Dorsal Column
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Fine touch (discriminative touch)Fasciculus gracilis
Two point discrimination
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Fasciculus cuneatus
Vibration
Conscious Proprioception
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Anterior Spinocerebellar Tract
Unconscious Proprioception
Gross movements
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Posterior Spinocerebellar Tract
Unconscious Proprioception
Fine movements
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Spinotectal tract
Spinoreticular tract
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Descending autonomic tractSpino-olivary tract
Lateral spinothalamic tract
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Destination
Posterior central gyrus
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3rd Order NeuronVentral posterolateral
nucleus of Thalamus
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PathwaysLateral spinothalamic,
Spinal lemniscus? Spinotectal
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2nd Order Neuron? Substantia
gelatinosa/
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Rexed III-VII1st Order Neuron
Posterior root ganglion
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Decussation
Receptor
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Free nerve endingsAnterior spinothalamic tract
Destination
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Posterior central gyrus
3rd Order Neuron Ventral posterolateral
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nucleus of ThalamusPathways
Anterior spinothalamic,
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Medial lemniscus2nd Order
? Substantia gelatinosa/
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Neuron
Rexed III-VII
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1st Order NeuronPosterior root ganglion
Decussation
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Receptors
Pacinian Corpuscle
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Posterolateral tract of Lissauer
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1st order neuron enters posterior horn & divides into ascending anddescending branches that travel for 1-2 segments, then terminate
synapsing with 2nd order neurons in substantia gelatinosa.
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Antero-
Spinotectal tract
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Spinoreticular tractDescending autonomic tract
Spino-olivary tract
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Dorsal Column
Destination
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Posterior central gyrus3rd Order Neuron
Ventral posterolateral
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nucleus of Thalamus2nd Order Neuron
Nuclei gracilis and cuneatus in
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medulla oblagataFew IV-VI
FC
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FGPathways
Ipsilateral Fasciculi gracilis & cuneatus
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Medial lemniscusT 1-6, C
1st Order Neuron
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Posterior root ganglion
Receptors
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Meissner's corpuscles, Pacinian corpuscles,muscle spindles & tendon organs
T 7-12, L, S
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Axons of the second-order neuronsCalled Internal arcuate fibres cross the
median plane.
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Decussate with the corresponding fibres of
the opposite side in the medulla as sensory
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FCFG
Decussation
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Fibres ascend as a single compact bundle
T 1-6, C
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called medial lemniscus through thebrainstem.
T 7-12, L, S
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Spinotectal tract
Spinoreticular tract
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Descending autonomic tract
Spino-olivary tract
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Spinocerebellar TractsDestination
Cerebellar Cortex
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Through Superior & Inferior Cerebellar peduncles
Pathways
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Anterior Spinocerebellar tracts (Superior)Posterior Spinocerebellar tracts (Inferior)
2nd Order Neuron
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Nucleus Dorsalis/ Clarke's column C8-L3/4V-VII
1st Order Neuron
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Collateral branches of Ascending tracts of Dorsal Columnfrom dorsal root ganglion
Receptors
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muscle spindles & tendon organs, joint receptorsSpinotectal tract
Spinovisual reflexes
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Movements of the eyes & head in response tothe source of the stimulation
Spinoreticular tract
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Reticular formation,Levels of consciousness
Pain perception
Spino-olivary tract
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Conveys cutaneous and proprioceptive
information to cerebellum
Spino-cervicothalamic
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Hair movement, pinch, pressure,
pathway
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thermal stimuli, noxious stimuliOrigin
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Primary motor cortex (area 4),secondary motor cortex (area 6),
parietal lobe (areas 3, 1, and 2)
Pass through
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Corona radiata,
posterior limb of Internal Capsule
middle 3/5 of basis pedunculi of midbrain
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Site of crossoverpyramids of medulla
Pathway
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Corticospinal tracts
Termination
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98% on contralateral alpha and gamma motor neuronsin grey matter or interneurons.
also known as pyramidal tracts.
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Controls rapid, skilled, non-postural, voluntary movements,especially distal ends of limbs
gives branches to cerebral cortex,
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? basal nuclei,
? red nucleus,
? olivary nuclei,
? reticular formation.
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These branches keep the subcortical regions aware about the
cortical motor activity.
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Origin
Red nucleus of midbrain
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Site ofImmediately in midbrain
crossover
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Pathway
Rubrospinal tract
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DestinationMotor neurons in grey matter
Function
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Facilitates activity of flexor muscles and
inhibits activity of extensor muscles in
the upper limb
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? Red nucleus receive afferent impulses through connections with the :? 1. cerebral cortex
? 2. cerebellum.
? 3. Globus Pallidus
? Extends as far as corticospinal tract
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? Cortico-rubral connections from ipsilateral red nucleus? indirect pathway by which the cerebral cortex and the cerebellum
can influence the activity of motor neurons of the spinal cord.
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Extrapyramidal TractsReticulospinal tract
Inhibit or facilitate voluntary movement, reflex activity,
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assist hypothalamus controls sympathetic,parasympathetic outflows.
Tectospinal tract
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Reflex postural movements of head concerning visualstimuli
Vestibulospinal tract
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Unconscious maintenance of posture and balance; actson extensors
mediates head & neck movements in response to
vestibular sensory input
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Descending autonomic Control sympathetic and parasympatheticfibers
systems
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Anterior Spinothalamic Tract
contralateral loss of light touch sensations below the level of the
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lesioncontralateral loss of pressure sensations below the level of the lesion
The patient will
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not feel the light touch of a piece of cotton placed against the skin
and cant feel pressure from a blunt object placed against the skin.
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is caused by syphilis.a selective destruction of nerve fibres at the
point of entrance of the posterior root into the
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spinal cord,
specially in the lower thoracic and lumbosacral
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regions.Results in loss of some sensation &
hypersensitivity of others.
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Upper Motor Neuron (UMN) Lesions:
Lesions of corticospinal tracts (Pyramidal Tracts)
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Lesions of Extrapyramidal Tracts
Lesions of corticospinal tracts (Pyramidal Tracts)
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Babinski sign is present.superficial abdominal reflexes are absent.
cremasteric reflex is absent.
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There is loss of performance of fine-skilled,
voluntary movements, especially at the distal
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end, of the limbs.Lesions of Extrapyramidal Tracts lesions:
Spastic paralysis, (lower limb extended, and the upper limb flexed),
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Exaggerated deep muscle reflexes in some flexors,
Clasp-knife reaction -the muscles, after resistance on stretching,
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suddenly give way.By any lesion ( ex. Poliomyelitis) destroying neurons in the anterior grey
column or its axon in the anterior root or spinal nerve.
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Clinical signs:
1.
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Flaccid paralysis2.
Muscular Atrophy
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3.
Loss of muscular reflexes
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4. Muscular fasciculation5. Muscular contracture and degeneration .
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Following a spinal cord injury there will be :a short term loss of all neurological activity below the level of injury.
loss of motor, sensory reflex & autonomic function.
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due to temporary physiologic disorganisation of spinal cord function,
may last 30-60 minutes or up to 6 weeks.
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It can be caused by fracture dislocation of the vertebral column,Clinical features :
1. Bilateral LMN paralysis
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2. Bilateral spastic paralysis below the level of the lesion
3. Bilateral loss of all sensations below the level of the lesion.
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4. Bladder and bowel functions are no longer under voluntary control1. Bilateral LMN paralysis in the segment of lesion,
2. Bilateral spastic paralysis below level of the lesion,
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3. Bilateral loss of pain, temprature & light touch
below the level of the lesion,
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4. Two point discrimination & vibratory andproprioception sensations are preserved.
1. Bilateral LMN paralysis in the segment of lesion,
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2. Bilateral spastic paralysis below the level of the
lesion with characteristic sacral sparing,
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3. Bilateral loss of pain, temperature & light touch andpressure sensations below the level of the lesion with
characteristic sacral sparing.
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A 36 year old male is observed to have difficulty in walking during a clinic visit.
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Testing indicates that his joint position sense is intact. However, his reflexes in his
lower limbs are diminished. Based on the findings in this patient, which of the
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following pathways most likely have been damaged?A.
Lateral spinothalamic
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B.
Ventral spinothalamic
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C.Dorsal spinocerebellar
D.
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Cuneocerebellar
A 19 year old gang member presented in the ER with a stab wound of the neck.
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Neurological examination revealed left hemiparesis with complete loss of vibratoryand joint position sense below C6 on the same side as the weakness. Loss of pain
and temperature sensation was elicited on the left at C6 only and on the right
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below C6. An MRI of the cervical spinal cord will reveal which of these findings?
A.
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Hemisection of the left spinal cordB.
Complete transection of the spinal cord
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C. Lesion of the left anterolateral white mater only of the spinal cord
D. Damage to the cervical dorsal roots at C6 on the left side only
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A patient has an injury that results in damage to the lower motor neurons. Which ofthe following would you expect to see in the patient?
A.
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Spastic paralysis
B.
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HyperreflexiaC.
Increased muscle tone
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D.
Flaccid paralysis
A pain researcher wants to make a lesion to the Spinothalamic tract so that his
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subjects feel no pain and temperature sensation from the right leg, but leaves pain
and temperature sensation rostral to the arm. Where would you advise this
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researcher to make his lesion?A.
Lesion the most lateral aspect of the left spinothalamic tract
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B.
Lesion the most medial aspect of the left spinothalamic tract
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C.Lesion the most lateral aspect of the right spinothalamic tract
D.
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Lesion the most medial aspect of the right spinothalamic tract
During a play-off game, a college hockey player is struck hard on the back of his
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neck with a hockey stick. A CT scan reveals a bone fragment lodged into themedial aspect of his dorsal columns in the cervical spinal cord. Which of the
following functions will most likely be affected given this patient's presentation?
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A.
Touch, pressure, vibratory sense from ipsilateral leg
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B.Pain and temperature sense from contralateral leg
C.
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Pain from ipsilateral face
D.
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Pain and temperature sense from contralateral arm