Ascending Tracts Kassia Hitchcock and Katy Davidson

Note sensory fibres synapse in the thalamus Sensory tracts form a 3 neurone chain to the primary cortex 3 rd order neurons Ascend to cortex via internal capsule ARM 2 nd order neurons Decussate and ascend to thalamus via a lemniscus 1 st order neurons Ascend ipsilaterally to nuclei in the medulla Sensory fibres ascend to the thalamus and then pass to the cortex Leg Arm Head Face EXCEPTION: Spinocerebellar, only ascend as far as the cerebellum

 Dorsal columns  Spinothalamic  Spinocerebellar  Dorsal  Ventral Ascending Tracts

Dorsal columns SenseDiscriminative touch Vibration Conscious proprioception PartsFasciculus cuneatus - above T6 Fasciculus gracilis – below T6 InputsPacinian corpuscle (tactile and vibration) Meissner corpuscle (discriminative touch) Merkels receptor (light touch) Joint proprioceptors (position and movement) 1 st order neuronsAscend ipsilaterally 1 st synapseLower medulla at: nucleus cuneatus nucleus gracillis DECUSSATE HERE 2 nd order neuronAscend contralaterally 2 nd synapseVentral posterior nucleus of thalamus 3 rd order neuronTravels to primary sensory cortex

Cortex Brainstem Spinal Cord 2 nd order neurons ascend to ventral posterior nucleus of thalamus & synapse with 3 rd order neurons 1 st order neurons passes into dorsal cord and ascends ipsilaterally to lower medulla 1 st order neurons synapse with 2 nd order neuron at nucleus cuneatus or gracilis in lower medulla Leg Arm 2 nd order neurons decussate and ascend to thalamus 3 rd order neurons travel to primary sensory cortex Dorsal columns

Damage results in: Loss of fine touch, vibration, conscious proprioception, below level of lesion Ipsilateral symptoms (remember where the neurons travel) Sensory ataxia Pseudoathetosis Causes Tabes dorsalis in tertiary syphilis

Balance – Romberg Test Balance uses 3 inputs Vision Proprioception Vestibular If we lose 2 then we lose our balance Romberg test removes one (vision) temporarily to test the other 2 Ask the patient to close their eyes….but be ready for them to be unsteady!

Spinothalamic Tract SensePain Temperature Simple tactile sensation Parts InputsFree nerve endings (pain and temperature) 1 st order neuronsAscend ipsilaterally in dorsal grey for 1-2 vertebral levels 1 st synapse1 – 2 levels above entry DECCUSATE here via the anterior white commissure 2 nd order neuronAscend contralaterally in spinothalamic tract 2 nd synapseVentral posterior lateral thalamic nucleus 3 rd order neuronTravel to the primary sensory cortex

Cortex Brainstem Spinal Cord 2 nd order neurons synapse with 3 rd order in ventral posterior lateral thalamic nucleus 1 st order neurons ascend 1-2 vertebral level in dorsal grey matter before synapsing with 2 nd order neurons 2 nd order neurons ascend spinothalamic tract to ventral posterior lateral nucleus of thalamus 2 nd order neurons decussate via the anterior white commissure 3 rd order neurons travel to primary sensory cortex Spinothalamic Tract

Head Arm Leg & sacrum Spinothalamic tract is somatotopically organised An expanding ventral grey matter tumour can knock out all contralateral pain & temperature sensation except sacral region = Sacral sparing

Spinal lemniscus and trigeminal lemniscus These are the names for the spinothalamic tract as it passes through the brainstem – SPINAL LEMNISCUS And for the sensation from the face (pain and temperature) – TRIGEMINAL LEMNISCUS

Spinothalamic Tract Damage results in: Contralateral loss of pain and temperature sensation 1- 2 levels below the level of the lesion Causes Syringomyelia Expansion of the central canal in the cervical region of the spinal cord – compresses neurons where they decussate across the anterior white commissure Bilateral loss of pain and temperature sensation Affects neurons decussating from both sides at this point

Spinocerebellar Tract SenseUnconscious proprioception PartsDorsal Ventral InputsDorsal – muscle spindles; Golgi tendon organs Ventral – Golgi tendon organs Lesions RARELY seen in isolation, but symptoms would be: Ataxia Wide-based gait Normally masked by motor weakness/paralysis For the DORSAL spinocerebellar tract 1 st order neurons synapse at Clarke’s dorsal nucleus Damaged in Friedrich’s ataxia Clarke’s dorsal nucleus Sits between C8-T2 1 st order dorsal column neurons synapse in here

Cortex Brainstem Spinal Cord Lower limb Upper limb Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract Cortex Brainstem Spinal Cord Lower limb Upper limb

Remember there’s overlap in dermatomes

Pain and temperature loss Fine touch & conscious proprioception loss Where’s the lesion?  Pain and temperature lost around T8  SPINOTHALAMIC TRACT  Fine touch and conscious proprioception lost around T6  DORSAL COLUMNS Damage at T6 on the left hand side REMEMBER TO PUT THE SIDE!!!! (left or right)

Where’s the lesion? Brainstem – left hand side Neurons from the body have already decussated but those from the face haven’t so damage is: Contralateral to the lesion for the body Ipsilateral to the lesion for the face Sensory loss of pain and temperature

Glossary Decussate – crossing over of nerve fibres from one side of the CNS to the other Contralateral – relating to the opposite side Ipsilateral – relating to the same side Afferent – carrying towards Efferent – carrying away from Ataxia – loss of ability to coordinate voluntary movements Pseudoathetosis – abnormal writhing movements, usually of the fingers caused by loss of proprioception NB – athetosis is the same movements caused by degeneration of basal ganglia Proprioception – detection of position and movement of body parts Somatotopically – orderly representation of body parts in the CNS Dermatomes – area of skin innervated by a single spinal nerve