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ASCENDING PATHWAYS

Alvin B. Vibar, M.D.


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CASE:

A 25 y/o male fell to the ground hitting his

lower back against the gutter when his

motorbike skidded on the wet road. When he

tried to get up, he was unable to move his right

leg. He was brought to the hospital and upon

examination, he could NOT FEEL PAINon

the left side up to the level of the umbilicus.He could NOT FEELthe VIBRATIONof

the tuning fork on his right foot.


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GENERAL SENSES Light Touch

Pressure

Pain

Temperature

Proprioception

-Vibration sense


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Tactile senseawareness and precise location of verydelicate mechanical stimuli

Includes:

Two point senseability to distinguish stimulation by one or two points applied to the skin

Fine touch / Stereognosisability to recognize objects by touchalone

Graphesthesia- abilityto recognize numbers or letters drawn on theskin


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Pressure= deep touch

Involves stimuli applied to

subcutaneous structures;firmly pressingon the skin

with a blunt object and by

squeezing subcutaneous

structures

Pain

Fast painsharp,pricking and well localized

Slow paindull, burningtype and diffuse

Temperature

Hot

Cold


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Proprioception

Position / Posture senseawareness of the positionof parts of the body; tested by passively moving a limb or oneof its parts to a certain position and having the subject movethe opposite limb to the same position

Motion senseawarenessof active or passivemovements of the parts of the body; tested by passivelyflexing and extending individual fingers and toes, hand and

foot, forearm and leg etc. with eyes closed, the subject shouldbe able to recognize the direction, speed and range of the

movement


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Sensory information is detected by specific receptors that aresensitive to stimuli arising from both outside and within ourbodies

EXTERORECEPTORS external world; respond to pain,

temperature, touch, vibration and pressure

ENTERORECEPTORS - within the body

PROPRIOCEPTORS within the body and signal awareness ofbody position and movement in space


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Receptors

Mechanoreceptors

touch, pressure and

proprioception

Nocireceptorspain

Thermoreceptorswarm

/ cold


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Review: General Sensation

Receptors

Touch

Meissners corpuscles , Merkels disc ,

Hair follicle endings , Golgi Mazzoni

PressurePacinian corpuscles

PainFree nerve endings

TemperatureCold - Krause end bulb

Hot Ruffinis corpuscles

ProprioceptionTendon and Muscle spindles


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Review: Spinal Cord


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3 Columns in the White Matter

Posterior funiculus

Lateral funiculus

Anterior funiculus

Each column is subdivided into tracts.

These tracts are:

Ascending tract

Descending tract

Intersegmental tracts


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Parts of the Gray Matter

Posterior horn

Lateral horn

Anterior horn

The cell bodies in the gray substance are grouped into

clusters of nuclei of laminae.


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Laminae of Rexed - groupings

Laminae I VI located in theposterior horn

Lamina VII located at thelateral horn

Laminae VIII and IX located at the

anterior horn Lamina X gray substance

surrounding the central canal


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Spinal cord with laminae of Rexed


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ASCENDING TRACTS

Location Origin DestinationANTERIOR COLUMN

Ventral Spinothalamic med. to ant. nerve roots Free nerve endings for Post-central gyruslight touch & pressure

Spino-olivary junction of ant. & lat. Cutaneous & proprio- Infr. Olivary nuclei

white columns ceptive organs LATERAL COLUMN

Dorsal Spinocerebellar periphery of lat. white Muscle spindles, tendon Cerebellar cortex

column organs, joint receptors

Ventral Spinocerebellar periphery of lat. white Muscle spindles, tendon Cerebellar cortex

column organs, joint receptors Lat. Spinothalamic med. to Ventral Spino- Free nerve endings for Post-central gyrus

cerebellar tract pain & temperature

Spinotectal ant. to Lat. Spinothalamic Midbrain TectumPOSTERIOR COLUMN

Fasciculus gracilis beside dorsomedian sulcus Meissners, Pacinian, Post-central gyrus

muscle spindles,

tendon organs

Fasciculus cuneatus between Fasc. Gracilis & Meissners, Pacinian, Post-central gyrus

post. gray column muscle spindles, tendon organs


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Review:Dermatomes Area of the skin supplied by the

somatosensory fibers from a singlespinal nerve ; useful in localizing thelevels of lesions

C2 back of head C5 tip of shoulder

C6 thumb C7 middle finger C8 small finger T4 T5 nipple T10 umbilicus L1 inguinal L4 L5 big toe S1 small toe S5 perineum


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REMEMBER: Rule number 1

Sensory information can either be

CONSCIOUS and make us aware of the

sensation or on a NONCONSCIOUS level

and serve to adjust the movement or

function of our body


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REMEMBER: Rule number 2

Sensory information is bundled according to MODALITY

MECHANICAL STIMULI discriminative touch,pressure, vibration and proprioception Posterior Column

Medial Lemniscus

NOCICEPTIVE STIMULI pain and temperatureAnterolateral System

PROPRIOCEPTION conveyed to the Cerebellum


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Ascending Tracts

Dorsal / Posterior Column

Position sense

2 pt discrimination

Fine, discriminative

Stereognosis

Vibration sense

Spinothalamic tract

ASTT touch / P

LSTT pain & temp


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REMEMBER:

Somatosensory pathwaysconsist of three neurons:

Number 1in the sensory ganglia

Number 2 in the spinal cord or brainstem

Number 3in the thalamus


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Pain and Temperature Pathway

using the LSTT

Free nerve endingsDorsal root ganglion

Postero-lateral funiculusPosterior horn

Laminae V VIILateral spinothalamic tract

VPLN of the thalamusPrimary somatosensory

area ( Broadmanns area 3,1,2)


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Medial Lemniscus Pathway

Axons enter the SC and pass directly

to ipsilateral posterior column (caudal fibers below T6 enterFasciculus gracilis and rostral fibersabove T6 enter Fasciculus cuneatusto ascend)

Terminate in Nucleus gracilis andNucleus cuneatus

Axons of secondary nuclei cross themidline as Internal arcuate fibersand form the Medial Lemniscus

Terminates in the VPLN of thalamus


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Discriminative Touch and Pressure

ReceptorsDorsal root ganglionCuneate

fasciculus and Gracile fasciculusCuneate andGracile nucleiMedial lemniscusVPLN of

the thalamusPrimary Somatosensory cortex

( BA 3, 1, 2 )


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Discriminative Touch and Pressure

Pathway


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Somatotopic

distribution of fibers

in the Posterior

Column Medial

Lemniscus system


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Slide 7.31

Sensory and Motor Areas of the

Cerebral Cortex

Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 7.14


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Proprioception Pathway

Receptors

Muscle spindles

Tendon spindles

Conscious proprioception

= fibers each the cerebrum

Unconscious proprioception= fibers each the cerebellum


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Receptors

Dorsal root ganglion

Posterior columnCuneate and gracile

fasciclesCuneate and gracile nuclei

Medial lemniscus

VPLN of the thalamus

BA 3, 1, 2

Conscious Proprioception Pathway


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CASE:

A 25 y/o male fell to the ground hitting his

lower back against the gutter when his

motorbike skidded on the wet road. When he

tried to get up, he was unable to move his rightleg. He was brought to the hospital and upon

examination, he could NOT FEEL PAINon

the left side up to the level of the umbilicus.He could NOT FEELthe VIBRATIONof

the tuning fork on his right foot.


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Brown-Sequard

s syndrome

Spinal Cord Hemisection

Features:

Contralateral loss of pain & temperature

Ipsilateral loss of proprioception

Ipsilateral manifestations of upper and

lower motor neuron lesions


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Dermatomes Area of the skin supplied by the

somatosensory fibers from a singlespinal nerve ; useful in localizing thelevels of lesions

C2 back of head C5 tip of shoulder C6 thumb C7 middle finger C8 small finger T4 T5 nipple T10 umbilicus L1 inguinal L4 L5 big toe S1 small toe S5 perineum


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Spinal Cord lesions:

Syringomyeliaprogressive cavitation around thecentral canal; loss of pain & temperature sensations inhands & forearm ( common in cervical)

Tabes Dorsaliscaused by neurosyphilis; dorsalroot involvement with secondary degeneration ofdorsal columns ( loss of vibration and position sense)


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Disorders of the Sensory System

Anesthesialoss of sensitivity to pain in all /part of the body

Hypoesthesiaan abnormally reduced

sensitivity to touch Hyperesthesiaan abnormally heightened

sensitivity of part of the body

Paresthesiaan abnormal or unexplainedtingling, pricking or burning sensation on theskin


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Somatic Sensory arising from Face

Trigeminal Gasserian or Semilunar

ganglion

3 divisions:

Opthalmic

Maxillary Mandibular


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Trigeminal Nerve

P i d T t P th


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Pain and Temperature Pathway -

Face

Receptors N1 ( Gasserian / Semilunar Ganglion)

N2 ( Nucleus of Trigemino Spinal tract )

N3 (Ventral Postero Medial nucleus of Thalamus)

- Post central gyrus ( B.A. 3,1,2)


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Touch and Pressure Pathway - Face

Receptors N1 ( Gasserian / Semilunar Ganglion)

N2 ( Main sensory nucleus )

N3 (Ventral Postero Medial nucleus of Thalamus)



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Proprioception Pathway - Face

Receptors N1 ( Mesencephalic nucleus)

N2 ( Main Sensory nucleus)

N3 (Ventral Postero Medial nucleus ofThalamus)



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Trigeminal Neuralgia (Tic Douloureux)

Episodes of sharp, stabbing painthat radiates over

the areas innervated by sensory branches of the

maxillary or mandibular divisions of CN V

Triggered by moving the mandible, smiling or

yawning, or by cutaneous stimulation

May becaused by pressure on or interruption of

the blood supply of the trigeminal ganglion


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THANK YOU.

in due time we

shall reap

.

if we don

t lose

heart .

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