Ascending spinal tracts - Spinothalamic tract Flashcards
Where does the spinothalamic tract lie in the spinal cord white matter?
Lies lateral and ventral to the ventral horn of the spinal grey matter
What type of information does the spinothalamic tract carry?
Information relating to pain and thermal sensation and non-discriminative (course) touch and pressure
Some sources state that there are two tracts, what are they and what types of information do they carry?
- Anterior spinothalamic tract - carries the sensory modalities of crude touch and pressure
- Lateral spinothalamic tract - carries sensory modalities of pain and temperature
Where do the first order neurones arise and where do they synapse?
Arise from the sensory receptors in the periphery - enter the spinal cord
What is the spinothalamic tract also known as?
The anterolateral or ventrolateral system
Spinothalamic tract begins with neurones which extend from the skin to the dorsal horn of the spinal cord - these are of two types, what are they?
- A-delta fibres = large diameter axons that transmit fast immediate pain, which is rapidly localised and travels in the lateral spinothalamic tract (eg: stepping on a lego piece)
- C fibres = make several connections in the dorsal horn before ascending. They transmit slow, aching pain that may result from inflammation. The slow type of pain is poorly localised
Once the neurons enter the spinal cord, they ascend 1-2 vertebral levels, this is achieved by travelling via which tract?
Lissauer’s tract - collection of ascending and descending collaterals of the primary neurons
The first order neurons then synapse with the second order neurons - where does this happen?
- Substantia gelatinosa (Rexed laminae II)
OR - nucleus proprius (Rexed laminae III, IV)
What do the second order neurons do?
Carry the sensory information from the substantia gelatinosa or nucleus proprius to the thalamus
Where do the second order neurons decussate?
Within the spinal cord - axons cross to the opposite side of the cord by passing through the ventral white commissure and thus enter the contralateral spinothalamic tract
Once the second order neurons have crossed to the opposite side, they form two distinct tracts, what are they?
- Anterior spinothalamic tract - crude touch and pressure fibres
- Lateral spinothalamic tract - pain and temperature fibres
These tracts run alongside each other and travel superiorly within the spinal cord, synapsing in the thalamus
In the brainstem, the spinothalamic fibres run in close proximity to the medial lemniscus and are known as what?
spinal lemniscus
Where do the second order neurons terminate?
Majority terminate in the ventral posterior nucleus of the thalamus, contacting the third order neurons
What do the third order neurons do?
Travel further upwards, passing through the posterior limb of the internal capsule to reach the ipsilateral postcentral gyrus
Clinical link - outline syringomyelia
The central canal becomes enlarged to form a cavity compressing adjacent nerve fibres. The second order neurons subserving pain and temperature are damaged as the decussate in the ventral white commissure close to the central canal causing a selective loss of pain and temperature awareness in the upper limbs = dissociated sensory loss (slight touch and proprioceptive sensation are retained)
