anatomyofascendinganddescendingtracts-100630161722-phpapp01.ppt

7/21/2019 anatomyofascendinganddescendingtracts-100630161722-phpapp01.ppt

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Ascending&

Descending tracts

Dr. Israa M. Sulaiman

Department of Anatomy

IMS/MSU


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The ascendingtracts


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By the end of the lecture, students should

be able to

define the ascending tract

enumerate the tracts according to their functional

components

explain general outline of neuronal chain of ascending

tracts

illustrate and trace the neuronal chain of each tract

apply anatomical knowledge to correlate with the

clinical condition in case of injury to these tracts


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contents

function of nervous system in general

sensory system overview

spinal cord and nerve tracts

ascending tracts

organization in general

ascending tracts

functional components


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nervous system

communication

receive information

transform it into impulses ( transduction

transmit impulses to the !"#

correlate $ coordinate

transmit impulses to the effector organs

response $ action


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CENTRAL NERVOUS SYSTEM

integration $ processing $ modulating

stimulus

receptor neurone

motor $ descending tracts

effector organ $ response

PNStransmission

lower motor neurone

sensory $ ascending tracts


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#ensory system

sensory information

three basic information

%xteroceptive information

&nteroceptive information

'roprioceptive information


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sensory information

are received and carried by ascending tracts

exteroceptive sensationorigin) outside the body

e*g* temp, touch, light, sound, chemicals, mechanical

receptors) surface layer of skin, mucosa

proprioceptive sensationorigin) within the body

e*g* muscles, joints, tendons

receptors deeper layer of skin, tendons, joints, +-, musclespindles, ligaments


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sensoryinformation

from the peripheral sensory endings

is conducted through the nervous systemby a series of neurones


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information conscious sensation reach the cerebral cortex

unconscious sensation

reach to the areas other than cortex


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spinal cord +rey matter

mostly made up of cell bodies of neurone

.hite matter

composed of nerve fibres ( ascending and descending tracts embedded in neuroglial cells


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nerve fibres

enter the spinal cord through posterior nerve root after entering the spinal cord

sorted out and segregated into nerve bundles, tracts

( origin, function, termination


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ascending tracts

bundles of nerve fibres

linking

spinal cord with higher centres of the brain

convey information

from

soma $ viscera to higher level of neuraxis


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ascending sensory pathwayare organized in

three neuronal chain

) /irst order neurone

) #econd order neurone

) hird order neurone


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dorsal rootdorsal rootganglion

spinalnervedorsalhorn

FIRST ORER NEURON


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#econd order neurone

cell body in posterior gra! "olumn o# spinal"or$

a%on "rosses t&e mi$line ' $e"ussate (

ascend 0 synapse with third order neuron in1'2 nucleus of thalamus


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SECON ORER NEURON

cross the mid line

in front of central canal

VPL

)st

*n$


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hird order neurone

cell body in the t&alamus

give rise to projection fibres to the cerebralcortex, postcentral gyrus ( sensory area


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ascending sensory pathway

( in general form )

from sensory endings

to

cerebral cortex

( note the three neurons chain )


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racts 0 their functional components

lateral spinothalamic tract

pain, temperature

anterior spinothalamic tract

touch, pressure


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posterior white column conscious proprioceptive sense,

discriminative touch, vibratory sense

spinocerebellar tract $ cuneocerebellar

tract

unconscious information from muscle,joints, skin, subcutaneous tissues


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sensation receptors pathways destination

Pain and temperature Free nerve endings Lateral STTSpinal lemniscus

Postcentralgyrus

Light touch and pressure Free nerve endings Anterior STTSpinal lemniscus

Postcentralgyrus

iscriminative touch!vibratory sense!conscious muscle "oint sense

#eissner$s corpuscle!pacinian corpuscles!muscle spindles!tendon organs

Fasciculus gracilis and cuneatus#edial lemniscus

Postcentralgyrus

3ain somatosensory pathways


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2ateral spinothalamic tractpain and thermal impulses

( input from free nerve endings, thermal receptors

transmitted to spinal cord in delta 4 and ! fibres

central process enters the spinal cord through

posterior nerve root, proceed to the tip of the dorsal

gray column


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the central process of 5st order neuron

synapse with cell body of 6ndorder neuron

in substantia gelatinosa of posterior gray column

of the spinal cord


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the axon of 6nd

order neuroncross to the opposite side

in the anterior gray and white commissure

and ascend in contralateral white column as

lateral spinothalamic tract

end by synapsing with 7rdorder neuron in the

ventral posterolateral nucleus of thalamus


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axon of the 7rd order neuron passes through

the posterior limb of internal capsule and

corona radiata to reach the postcentral gyrusof cerebral cortex ( area 7, 5 and 6


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pain and temperature pathways


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!linical application

destruction of 2# loss of

pain and thermal sensation

on the contralateral side

below the level of the lesion

patient will not

respond to pinprickrecognize hot and cold


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4nterior spinothalamic tract

light touch and pressure impulses( input from free nerve endings, 3erkel8s tactile disks

/irst order neuron dorsal root ganglion( all level

#econd order neuron in the dorsal horn, cross to the opposite side (decussate ascend in the contralateral ventral column as 4# end in 1'2 nucleus of thalamus

hird order neuron in the 1'2 nucleus of thalamus project to cerebral cortex ( area 7, 5 and 6


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touch and pressure pathways


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destruction of 4#

loss of touch and pressure sense

below the level of lesion

on the contralateral side of the body


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/asciculus gracilis and fasciculus cuneatus

discriminative touch, vibratory sense andconscious muscle joint sense( inputs from pacinian corpuscles, 3essiner8scorpuscles, joint receptors, muscle spindles and +olgitendon organs

axon of 5storder neuron enter the spinal cord

passes directly to the posterior white column ofthe same side ( without synapsing


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long ascending fibres travel upward in the

posterior column of the same side as fasciculusgracilis and fasciculus cuneatus ( /+ carrying fibres from lower thoracic, lumbar and sacral regions $

including lower limbs

( /! ) only in thoracic and cervical segments $ including upper limb

fibres

synapse on the 6ndorder neuron in the nucleusgracilis and cuneatus of me$ulla o+longata of

the same side*


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lower % thoracic segments

lumbar segments

sacral segments

cervical segments

upper % thoracic segments

fasciculus gracilis

fasciculus cuneatus

& nucleus ' *

in medulla

,C


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axons of 6ndorder neuron

9 internal arcuate fibres : cross the median plane

' sensor! $e"ussation (

ascend as medial lemniscus

through medulla oblongata, pons, and midbrain

synapse on the 7rdorder neuron in ventral posteriolateral nucleus of

thalamus

axon of 7rdorder neuron leaves and passes through the internal capsule,

corona radiata to reach the postcentral gyrus of cerebral cortex area 7, 5and 6


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pathways for

conscious proprioception

discriminative touch

vibratory sense


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destruction offasciculus gracilia and cuneatus

loss of muscle joint sense,position sense, vibration sense

and tactile discrimination on the same side below the level of the lesion

(extremely rare to have a lesion of the spinal cord tobe localized as to affect one sensory tract only


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'osterior 0 anterior spinocerebellar tract

transmit unconscious proprioceptive information to thecerebellum

receive input from muscle spindles, +-s and pressure

receptors

involved in coordination of posture and movement of

individual muscles of the lower limb


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/irst order neuron

in dorsal root ganglion

axons end in nucleus dorsalis of !larke

#econd order neuron cell body in nucleus dorsalis of !larke

give rise to axons ascending to the cerebellum of the

same side

' anterior - "rosse$ . un"rosse$ #i+res / posterior - un"rosse$ #i+res(


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muscle "oint sense pathways to cerebellum


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#pinotectal tract passes pain, thermal, tactile information to superior

colliculus for spinovisual reflexes cross the median plane synapse in the superior colliculus integrate visual and somatic sensory information

( it brings about the movement of eye and head towardsthe source of information

#pinoreticular tract uncrossed fibres, synapse with neurones of reticular

formation(important role in influencing level of consciousness

#pino)olivary tract


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spinotectal tract

spinoreticular tract

spino+oloivary tract


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clinical application

relief of painposterior rhizotomy (posterior root

cordotomy (lateral #

&njury

hemisection of spinal cord

diseases

tabes dorsalis $ syringomyelia $ vascular


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;emisection of the spinal cord

( Brown #e


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spinal cord hemisection


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below the level of lesion

on the side of lesion

lateral column damage

>3"2

dorsal column damage

loss of position sense

loss of vibratory sense

loss of tactile discrimination

anterolateral system damage

loss of sensation of pain and

temperature on the side opposite

the lesion

lo"al segment

si$e o# lesion

orsal Root irritate $estru"tion

Ventral root #la""i$ paral!sis


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2esions of central gray matter

seen in syringomyelia ( progressive cavitation around or nearthe central canal of spinal cord especially in cervical segments

interrupt fibres of lateral spinothalamic tract that passes

in front of the central canal

loss of pain and temperature sensibility on both sides

( proprioception and light touch is spared

sensory dissociation


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'osterior root lesionsseen in tabes dorsalis ( neurosyphilis

bilateral degeneration of posterior root andposterior funiculus ( particularly in lower segments ofspinal cord

!linically&nitial stage

&rritation ) paraesthesia &ntermittant of attack of sharp pain2ater decreased sensitivity to pain loss of muscle stretch reflexes

loss of position sense, posture senses positive ?omberg sign ( visual compensation walk with legs apart, high stepping gait


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blood supply of spinal cord

4nterior spinal artery

'osterior spinal arteries

#egmental spinal arteries

) radicular arteries

/eeder arteries

) 4damkiewicz


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posterior 7rdof spinal cord

dorsal column

penetrating branches

anterior and part of gray matter

circumferential branches

anterior white matter


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dorsal 5$7rd resulting from occlusion of the posterior spinal artery

ventral 6$7rd resulting from occlusion of the anterior spinal artery


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=escending tracts

By the end of this lecture, students shouldbe able to

define the tract

enumerate the tracts according to their

functional componentsillustrate and trace the neuronal chain of eachtract

apply their knowledge of anatomy to correlate

with the clinical condition in relation to the injuryto these tracts


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3otor system

areas of the nervous system that are

responsible for controlling movements

premotor cortex #34 '3! basal ganglia

&


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cerebellum

premotor cortex motor cortex

motor unit

muscle spindle

pyramidal tract

sp cd internreurons 0

central pattern generator

extrapyramidal tracts

premotor cortex #34 '3! basal ganglia

cortical

sensory area

3--? #@#%3

&

&&

&&&

&1

1


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2evel &

initiation, planning, programming of movements

in response to desire to move

( probably originate in the limbic system and posterior parietal cortex

desire is translated into movements( basal ganglia and their cortical projections in the frontal lobe)#34, '3!

2evel &&

coordination of movements

cerebellum( compare the intended movement $ actual movement


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2evel &&&

descending pathways

pyramidal tract ) !o#t originates in the motor, premotor and somatosensory

corticies

synapse direclty on 3" , &"

extrapyramidal tract 1e#t, ?e#t, e#t, ?u#t

originate from subcortical structures

receive inputs from motor cortex

complex distribution, synapse on 3", &"


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2evel &1 motor organization in spinal cord

alpha 0 gamma neurons ?enshaw8s cells interneurons $ !'+s descending tracts

!o#t, ?u#tdistal musculature fine skilled movement 1e#t) ?e#t) e#t

axial, proximal musculature balance, posture

2evel 1 final common pathway


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primary structure

responsible for translating

desire into a movement is

the basal ganglia


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&ntroduction

brain exerts powerful and subtle influences

upon the activity of the voluntary musculature

( modulate, regulate, bias the activities of23"

through the descending pathways


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descending tracts segregated bundles of nerve fibres in the white

matter of the spinal cord descending from the

supraspinal centres

referred to as upper motor neurons ( >3" are concerned with somatic and visceral motor

activity

cells of origin lie in cerebral cortex and brain stem regulate the 23" activity


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motor homunculus

cerebral cortex


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lower motor neurons ( 23"

motor neurons that innervate the voluntary muscles

in anterior gray column of spinal cord $

motor nuclei of brainstem

innervate skeletal musclesform #inal "ommon pat&wa!

23"


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23"

constantly bombarded by nerve impulses( excitatory or inhibitory

that descend from cerebral cortex,

pons,midbrain and

medulla

sensory inputs from the posterior root


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upper motor neurons ( >3"

the descending supraspinal pathways thatinfluence the activity of the 23"

e*g* !o#t, !oBt, ?u#t, e#t, ?e#t, 1e#t


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>3"

control voluntary motor activity maintenance of posture 0 e


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"ere+ral "orte% - mi$+rain 0 pons 0 me$ulla o+longata

descending tracts

23"

sensory inputs


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!orticospinal tract

arises from the pyramidal cells of cerebral cortex

fibres travel through

corona radiata posterior limb of the internal capsule

cerebral peduncle ( middle 7$ Ath

pons

medulla oblongata ( passed through the pyramids


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at the caudal partof medulla oblongata

most of the fibres C D cross the mid line(motor decussation descend in the lateral column as 2!#

terminate on 23" of anterior gray column at all spinal

level

remaining uncrossed fibres descend as 4!#

eventually fibres cross the mid line and terminate on23" of anterior gray column of respective spinal cord

segments


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motor decussation

medulla oblongata


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corticospinal tract

for fine skilled movements


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?ubrospinal tract nerve cells in red nucleus( tegmentum of midbrain at the level of superior colliculus

nerve fibres $ axons cross the mid line

descend as rubrospinal tract through pons and medulla oblongata

terminate anterior gray column of spinal

cord

( facilitate the activity of flexor muscles


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t i l t t


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ectospinal tract nerve cells in superior colliculus of

the midbrain

nerve fibres$ axons cross the mid line

descend close to medial longitudinal

fasciculus

terminate in the anterior graycolumn of upper cervical segmentsof spinal cord

' responsi+le #or re#le% mo1ement o#

&ea$ . ne"2 in response to 1isual stimuli (


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1estibulospinal tract


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1estibulospinal tract nerve cells in vestibular nucleus

(in the pons and medulla oblongata

received afferents from inner earand cerebellum

axons descend uncrossed through medulla and through the

length of spinal cord

synapse with neuron in the anteriorgray column of the spinal cord

' +alan"e +! #a"ilitate t&e a"ti1it! o#t&e e%tensor mus"les (


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?eticulospinal tract

nerve cells in reticular formation

fibres pass through

midbrain, pons, and medulla oblongata

end at the anterior gray column of spinal cord control activity of motor neurons

'in#luen"e 1oluntar! mo1ement an$ re#le% a"ti1it! (


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reticulospinal tract


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clinical application

pyramidal tract

refer to corticospinal tracts

extrapyramidal tract

other than corticospinal tract

( 1e#t, ?e#t, e#t, ?u#t


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upper motor neuron lesion

Babinski sign ( extensor plantar response

#uperficial abdominal reflexes ( absent

!remasteric reflex ( absent

2oss of performance of fine skilled voluntary movement


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lower motor neuron lesion

flaccid paralysis

atrophy of muscles loss of reflexes

muscular fasciculation

muscular contracture


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extrapyramidal tract lesions

severe paralysis with little or no atrophy

spasticity or hypertonicity exaggeration of deep muscular reflexes and clonus

clasp)knife reaction


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hese motor pathways are complex and

multisynaptic, and regulate

4xial muscles that maintain balance and

posture

3uscles controlling coarse movements of

the proximal portions of limbs

;ead, neck, and eye movement


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dorsal column

lateral #

anterior #

pyramidal tracts

extrapyramidal tracts

nerve roots

spinal cord hemisection


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thank you

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