Somatosensory cortex Flashcards
Where do sensory nerve fibres entering dorsal root synapse?
One of 6 layers (rexed laminae) or dorsal horn
Where do touch afferents synapse?
lamina III and IV`
Where do proprioceptors synapse?
lamina V and VI
Where do nociceptors synapse
lamina I and II
What do you call the cells in the dorsal horn
Second order afferents
Where do axons of second order afferents travel?
Cross spinal cord within 1 segment of cell body and project up contralateral spinal cord in spinothalamic tract
What are the 2 components of spinothalamic tract?
Older lateral (paleo) part and newer medial (neo) part
What forms of cutaneous sensation does spinothalamic tract transmit
Heavy pressure, crude touch, temp and pain
What 2 places do touch and proprioceptive nerve fibres synapse/ branch to?
Cells in dorsal horn
Dorsal funiculi
What are the dorsal funiculi
Large tracts of white matter in dorsal spinal cord
What side of the spinal cord do fibres of dorsal columns ascend?
Same side they enter
Are fibres in dorsal columns post synaptic
No- they are actual extensions of afferent fibres in peripheral nerves with cell bodies in dorsal root ganglia
Where does dorsal fasciculi project to
The dorsal column nuclei in the lower medulla
What are the fibres leaving the base of the cuneate and gracile nuclei called
The start of the medial lemniscus
Where do medial lemniscal fibres leaving dorsal column nuclei send their axons?
Across the midline as internal arcuate fibres, and ascend to the VPL nucleus of contralateral thalamus. VPL cells project to somatosensory cortex
Where are medial lemniscal fibres known as internal arcuate fibres
At the region they cross the midline- the lower closed medulla
Where do cutaneous afferents from the face come from?
Contralateral trigeminal nucleus
Where do fibres from the trigeminal nucleus terminate
In the ventro-postero-medial nucleus
Where is the somatosensory cortex?
Runs medio-laterally just posterior to central sulcus
In the sensory homunculus, where are legs and face relativelly?
Legs- medial
Face- lateral
Why are the legs medial on the sensory homunculus?
Because the nerve fibres from the thalamus to the somatosensory cortex rotate 180 degrees
What does the somatosensory cortex tell us?
Where something is on your body, its touch and temperature
What types of areas occupy largest areas of map?
Areas with highest density of touch and proprioceptive receptors
Why do we have 2 pathways to the somatosensory cortex?
Spinothalamic tract conveys crude touch
Dorsal columns conveys discriminate touch
What does Rombergs test check?
Proprioception from muscles and joints
What is sensory ataxia?
Inability to balance with eyes closed
What are nocicepors and where are they found?
Receptors specific to tissue damage
Found at end of A delta and C nerve fibres
What is the function of nociceptor activity
Protective- minimises injury
How does inflammation promote pain?
Free nerve endings have TTX resistant sodium channels
Inflammation opens these channels leading to tonic depolarisation and nerve activity
Where do nociceptor afferents end
Lamina I and II
Where do cells from lamina I and II send their axons
across contralateral spinothalamic tract to form lateral part of spinothalamic tract
What receptors does a painful stimulus stimulate?
Touch receptors and nociceptors
Where do touch receptors project to?
Neospinothalamic which ends in VPL nuclei of thalamus
Why is the paleospinothalamic tract poor at localising pain?
Receptive fields of fibres are very large
What does paleospinothalamic tract register in terms of pain
Degree and chaacter
What mediates paleospinothalamic detection of pain
Cingulate and insula cortex of the limbic system
