somatosensory pathway and cortex Flashcards
wat are the two basic ascending pathways from neurons to cortex?
-one is specialised for pain and temperature
-one is specialised for touch and joint sense
which receptors are responsible for touch and joint sense?
low threshold mechanoreceptors
what did vesalius do?
described the complete anatomy of the human body as far as the eye can see it
spinal nerves
axons that innervate each of your somatosensory receptors coalesce into large bundles called nerves
Where they exit or ender the spinal nerve
what does each spinal nerve do?
innervate a particular area of the body
how many spinal nerves do humans have??
31 pairs
the spinal nerve splits into two sections near teh spinal cord, what are these?
the dorsal root and the ventral root
ventral root contains
motor neuron efferents
dorsal root contains
sensory afferents
dorsal root ganglion
cell bodies of primary sensory fibres
swelling in the spinal nerve
grey matter
where the cells bodies are predominantly located
white matter
heavy concentration of myelinated axons
morphology of dorsal horn
granular- cell bodies are small
morphology of ventral horn
cell bodies are large
hypothesis for different cell bodies sizes in ventral and dorsal horn?
hypothesised that these differences are likely to have important functional correlates
so they divided the grey matter up into different local regions depending on cell morphology
two divisions of the grey matter
dorsal horn and ventral horn
rexed’s laminae
split grey matter into 9 regions based on cell morphology
rexed’s laminae dorsal horn divisions
lam 1-6
rexed’s laminae transition zone laminae
lam 7
rexed’s laminae ventral horn laminae
lam 8 and 9
rexed’s laminae temp/ nociception laminae
lam 1-2 (and 5)
rexed’s laminae skin-touch laminae
lam 3-5
rexed’s laminae joint position laminae
lam 6
what fibre types synapse in the spinal cord
all fibre types
touch/ proprioception fibres synapse in the spinal cord and…
send direct collaterals to the brain
what are tracts/ columns?
Neurons in the spinal cord send their axons towards the brain, and these axons coalesce into nerve bundles called tracts/columns
which column does touch and proprioception information go through?
dorsal column
what can the dorsal column be split into?
gracile facile and cuneate fasicle
gracile fascicle receive information from
the legs and lower trunk
cuneate fascicle receives information from
the upper trunk and arms
which column does the nociceptive and touch information run through?
the anterolateral columns
e.g., spinothalamic tract
what pathway is the anterolateral column a part of?
the anterolateral pathway
what pathway is the dorsal column a part of?
teh dorsal column medial lemniscus pathway
what is the dorsal column pathway?
axons in the dorsal column terminate in the medulla oblongata
what are the two constituent parts of the brainstem
medulla oblongata and pons
what is the trigeminal nuclei sensitive to?
touch on the face
what three nuclei do we have a complete representation
trigeminal nuclei
cuneate nuclei
gracile nuclei
where do the trigeminal, cuneate and gracile nuclei project their axons to?
ribbon like structure: medial lemniscus
what does the medial lemniscus do?
takes tactile stimulus to the thalamus
two divisions of the thalamus involved in somatosensation
ventroposterior lateral nucleus (VPL)
ventroposterior medial nucleus (VPM)
where do thalamic neurons project to?
the somatosensory cortex
where is the somatosensory cortex located?
on the post central gyrus
summary of the dorsal column medial lemniscus pathway
mechanoreceptors
dorsal root ganglion
dorsal columns
medial lemniscus
Ventroposterior lateral nucleus (VPL- thalamus)
primary somatosensory cortex
supragranular cortical layers
layers 1-3
granular cortical layers
4
infragranular cortical layers
5-6
cortical layer 4 projects to
cortical layer 2/3
cortical layer 2/3 projects to
cortical layer 5/6
cortex
cortical layer 5/6 projects to
subcortex
where do axons from the somatosensory thalamus terminate?
cortical layer 4
what did Brodmann do?
Brodmann noticed the layered staining pattern was different in different parts of the cerebral cortex
Noted these anatomical differences are have functional differences
Made brodmann’s map, based on cytoarchitecture
how many areas are there in Brodmann’s map?
around 40
how many Brodmann areas do the VPL and VPN project to?
about 4 areas
Area 1, 2 , 3a, 3b located in the postcentral gyrus
DR wilder penfield
Operating on people to treat epilepsy
Localised location in the brain from which the epiliectiform activity originates, aimed to treat by removing this focus
Electrically stimulated different parts of the surface in conscious patients, could see where the epilepsy was coming form, and also parts of the brain that controlled important functions, such as speech
He also made important discoveries about how the cortex is organised
what feeling was reported when parts of teh postcentral gyrus were stimulated?
typically reported a tingling sensation in some part of their body
what was the resolution of penfield’s data?
only 1mm
what was the resolution of penfield’s data?
only 1mm
what type of map is the homunculus?
topographic map
somatotopic map
method of electrophysiological recording on anesthetised animals
put in microelectrodes into different parts of the post central gyrus
Gently stimulate different parts of the body as you record response from the neuron
Receptive field of the neuron is the part of the body that field represents
how did body maps produced by animal experiments relate to penfield’s data?
on a coarse scale, penfields data seemed very accurate as the same sequence was observed
what did high resolution somatotopy reveal in the finger? what is this consistent with?
there is a second representation of the body in the postcentral gyrus
which coincides with brodmanns areas 3b and 1
what did fMRI bold responses show?
fMRI data is consistent with Brodmanns map
humans have 4 maps of the body in postcentral gyrus, corresponding to the 4 brodmanns areas
what did monkey electrophysiology studies show?
different parts of the body represented at different spatial resolutions (homunculus)
magnification factor
area of teh cortex devoted to given body part by its skin area
what are different magnification factors caused by?
Large differences in the number of neurons devoted to different parts of the body
magnification factor of vibrissae
high
behaviourally important parts of the body
lips for language
hands for object manipulation
relationship between magnification of body parts and receptive field size
inverse relationship
small receptive field = large magnification
discrimination threshold
determined by 2 point discrimination task
threshold is low where magnification factor is high and receptive fields are small
