ascending neural pathways Flashcards
what are the three ascending ascending pathways of sensory information?
- dorsal column/medial lemniscus pathway
- spinothalamic pathway
- spinocerebellar pathway
which dorsal column/medial lemniscus pathway carries information from the upper limb?
fasciculus cuneatus
which dorsal column/medial lemniscus pathway carries information from the lower limb?
fasciculus gracilis
what type of modal information is carried by the dorsal column pathway? (4)
- conscious proprioception (i.e. where your limbs are when your walking etc)
- discriminative touch (two point discrimination)
- vibration
- pressure
what type of sensory fibres are the dorsal columns composed of?
AB fibres (fast, large diameter fibres) (30-70m/s conduction velocity, 5-12um diameter)
where does the primary afferent neurone of the medial lemniscus pathway enter from and synapse?
primary afferent neurone enters the dorsal column of spinal cord, synapses on second order neurone in the brain stem (either gracile or cuneate nuclei)
which vertebrae does the fasciculus cuneatus pathway start above?
T6
where does the second order neurone of the medial lemniscus pathway originate and synapse?
comes from the gracile or cuneate nuclei in the brain stem, ascends CONTRALETERALLY as the medial lemniscus and synapses in the ventral posterolateral lobe of the thalamus (VPL)
where does the third order neurone of the medial lemniscus pathway originate and synapse?
originates in the VPL region of the thalamus and projects to corresponding are of the somatosensory cortex
what pathological processes can develop from a lesion in the medial lemniscus pathway BELOW T6?
gait ataxia (brain is deprived of info about feet)
what symptoms does dorsal column disease cause and what is the cause of this disease?
causes paraesthesias in the extremities (i.e. tingling, crawling, numbness, deadness in fingers and toes)
caused by ectopic discharge in damaged dorsal column axons
how can dorsal column function be tested?
by testing proprioception in fingers and toes or testing vibration sense with tuning fork
what does the spinothalamic pathway detect primarily?
PAIN - nociception
what types of pain does the spinothalamic pathway detect? (3)
- mechanical pain (coarse pain and sharp pain)
- thermal pain (e.g. extreme cold or heat)
- chemical pain (e.g. histamine-sensitive fibres, noxious chemicals)
what type of sensation do Aδ fibres detect?
- non-descriminative touch (but is high pressure sensitive)
- hot/cold pain
- sharp pricking pain - precise location of pain
what do C fibres detect?
- dull aching pain (non-descrimitivae pain)
- itch sensitive (histamine sensitive)
where do the first order neurones of the spinothalmic pathway originate and synapse?
enter the dorsal horn of spinal cord where they synapse with the second order neurone
where do the second order neurons of the spinothalamic pathway originate and synapse?
organist in dorsal horn and cross immediately to contra-lateral side of spinal cord “QUICK TO CROSS”; ascend in either lateral spinothalmic route or anterior route depending on fibre type; and project to thalamus (VPL region)
where do the third order neurons of the spinothalamic pathway originate and synapse?
originate in VPL region of thalamus and project to somatosensory cortex of brain (Aδ project tp somatosensory cortex to give more precise info about location of pain whereas C fibres do not)
what is the lateral spinothalmic route made up of?
C and Aδ fibres:
pain
temperature
dull pain and itch
what is the ventral anterior spinothalmic rate made up of?
C fibres only:
corse, non discriminating touch
what happens when there is lesions in the spinothalamic tract?
patients have decreased perception of pain on the contraletral side of their body
what substance is used in peripheral nerve endings to modulate pain
substance P
which chemical do chilli peppers contain which mimic tissue damage?
capsaicin - stimulates Trp1 receptors
can be used to treat chronic pain
how does referred pain work?
signals of noxious signals from viscera synapse with normal cutaneous fibres in the dorsal horn on the same ascending nerve fibres.
information from the viscera is then mapped on the somatosensory cortex
what type of sensory information does the spinocerebellar pathway carry?
UNCONCSIOUS information from:
muscle spindles
golgi tendon organs
touch receptors
how many neurons is the spinocerebellar pathway composed of and where do these end up?
only 2 neurone pathway
end in the vermis of the cerebellum
how do dorsal tract neurons ascend and which peduncle of the cerebellum do they enter?
ipsilaterally and enter via the inferior peduncle
how do ventral tract neurone ascend and which peduncle do they enter the cerebellum?
contraleterally and via the superior peduncle
what is Friedrich’s ataxia cause by?
inherited disease where the spinocerebellar tract becomes increasingly ineffective
