Ascending & Descending nerve tracts Sanjaya Adikari Department of Anatomy

Control of the body by the brain Contralateral representation Decussation = Crossing R Contralateral = Opposite side Ipsilateral = Same side

L R Medulla Sensory Sensory organs

L R Medulla Sensory Sensory organs

L R Medulla Motor Effecter organs

L R Medulla Motor Effecter organs

L R Medulla Sensory organs Effecter organs

Ascending tracts Third order neuron Internal capsule Thalamus Medulla Thalamus Corona radiata Second order neuron Ascending tracts First order neuron

Medulla Internal capsule Sensory Posterior surface Upper medulla

Descending tracts Internal capsule Upper motor neuron Anterior surface Lower medulla Descending tracts Lower motor neuron (Final common pathway)

Internal capsule 20%

L Corticobulbar Corticospinal Internal capsule Cranial nerves Spinal nerves

Left Ascending tracts

White columns Posterior white column Posterior nerve root Lateral white column Anterior white column Anterior nerve root Posterior nerve root

Lateral spinothalamic Pain & temperature Lateral spinothalamic

Crude touch & pressure Anterior spinothalamic

Internal capsule Third order neuron Medulla Thalamus Second order neuron First order neuron

8 8 9 9 10 10 Pain & temperature Crude touch & pressure Crosses within one spinal segment Crosses within several spinal segments

Fine touch, vibration, Conscious muscle & joint sense Fasciculus gracilis Fasciculus cuneatus

Medulla Internal capsule

Muscle & joint sense to cerebellum Anterior & posterior spinocerebellar

Superior, middle & inferior cerebellar peduncles

Left

Descending tracts Lateral corticospinal Olivospinal Rubrospinal Vestibulospinal Tectospinal Rubrospinal 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 R R 1 – All sensory and motor loss on contralateral side 2 2 – Fine touch and vibration loss on the ipsilateral side, pain and temperature and motor weakness on the contralateral side 3 3 - Fine touch and vibration and motor weakness on the ipsilateral side, pain and temperature loss on the contralateral side (Brown-Sequard)

Unilateral cord lesion Thalamic Mid-braintem Unilateral cord lesion (Brown-Sequard) Weakness (UMN) Clinical Medicine by Kumar & Cleark’s

1 – All sensory and motor loss on contralateral side 2 – Fine touch and vibration loss on the ipsilateral side, pain and temperature and motor weakness on the contralateral side 3 - Fine touch and vibration and motor weakness on the ipsilateral side, pain and temperature loss on the contralateral side

Spinal cord lesions C D A B Refer Clinical Medicine by Kumar & Cleark’s

A – Syringomyelia A

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 enlarges Clinical Medicine by Kumar & Cleark’s

B – Poliomyelitis B

C – Tabes dorsalis Demyelination C

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 dorsalis This is due to loss of proprioception (position sense) - stamping gait - positive Romberg’s test Argyll Robertson pupils No 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