ascending & descending nerve tracts sanjaya adikari department of anatomy

Ascending &

Descending nerve tracts

Sanjaya AdikariDepartment of Anatomy

Control of the body by the brain

L

R

Contralateral representation

Contralateral = Opposite sideIpsilateral = Same side

Decussation = Crossing

Medulla

Sensory organs

LR Sensory

Medulla

Sensory organs

LR Sensory

Medulla

Effecter organs

LR Motor

Medulla

Effecter organs

MotorLR

Medulla

Sensory organs

Effecter organs

LR

Medulla

Thalamus

First order neuron

Second order neuron

Internal capsule

Third order neuron

Corona radiata

Ascending tracts

Medulla

Internal capsule

Sensory

Posterior surface

Upper medulla

Internal capsule

Upper motor neuron

Lower motor neuron(Final common pathway)

Descending tracts

Motor

Anterior surface

Lower medulla

Internal capsule

20%

Internal capsule

Corticobulbar

Corticospinal

L

Cranial nerves

Spinal nerves

LeftAscending tracts

White columns

Posterior white column

Lateral white column

Anterior white column

Anterior nerve root

Posterior nerve root

Lateral spinothalamic

Pain & temperature

Anterior spinothalamic

Crude touch & pressure

Medulla

Thalamus

First order neuron

Second order neuron

Internal capsule

Third order neuron

Pain & temperature

Crude touch & pressure

10

9

8

10

9

8

Crosses within one spinalsegment

Crosses within several spinalsegments

Fine touch, vibration,Conscious muscle & joint sense

Fasciculus gracilis

Fasciculus cuneatus

Medulla

Internal capsule

Muscle & joint sense to cerebellum

Anterior & posteriorspinocerebellar

Superior, middle & inferiorcerebellar peduncles

Left

Descending tracts

OlivospinalVestibulospinalTectospinal

RubrospinalLateral corticospinal

Anterior corticospinal

Left

Clinical Neuroanatomy by Richard S. Snell

Lemniscus

• This term is used for some ascending (sensory) nerve tracts in the upper part of

the medulla, pons and midbrain – Spinal lemniscus

combination of spinothalamic, spinotectal tracts

– Medial lemniscus

crossed posterior column fibers

– Lateral lemniscus

3rd neuron of auditory pathway

sensory motor

1 – All sensory and motor loss on contralateral side

1

R R

3

3 - Fine touch and vibration and motor weakness on the ipsilateral side, pain and

temperature loss on the contralateral side (Brown-Sequard)

2

2 – Fine touch and vibration loss on the ipsilateral side, pain and temperature and

motor weakness on the contralateral side

Thalamic

Mid-braintem

Unilateral cord lesion(Brown-Sequard)

Weakness (UMN)

Clinical Medicine by Kumar & Cleark’s

DA

B

Spinal cord lesions

C

Refer Clinical Medicine by Kumar & Cleark’s

A

A – Syringomyelia

A – Syringomyelia

Loss of pain and

temperature sense

without loss of fine touch.

Discontinuous sensory

loss

Loss of upper limb reflexes

Symptoms progress when

the cavity enlargesClinical Medicine by Kumar & Cleark’s

B

B – Poliomyelitis

C – Tabes dorsalis

C

Demyelination

C – Tabes dorsalis (of neurosyphilis)

Demyelination of dorsal roots

–Lightening pains, sensory ataxia,

reflex and sensory loss, muscle

wasting, charcot joints

–Argyll Robertson pupils

Sensory ataxia of tabes dorsalisThis is due to loss of proprioception

(position sense)

- stamping gait

- positive Romberg’s test

Argyll Robertson pupilsNo reaction to light. Constricts to

convergence

Lesion in the cerebral aqueduct

Anterior spinal artery occlusion

• Bilateral loss of motor function due to damage to corticospinal tracts and anterior gray horns

• Bilateral thermoanesthesia and analgesia due to damage to spinothalamic tracts

• Loss of bladder and bowel control due to damage to descending autonomic tracts

• Vibration, fine touch & position sense normal

Refer Clinical Medicine by Kumar & Cleark’s