White matter tracts

What are white matter tracts

myelinated axons that connect different regions of the CNS enabling communicatin between cortical and subcortical structures.

What are the different types of white matter tracts

Commissural fibres, projection fibres and association fibres

What are commissural fibres

crossing the midline connecting cortical areas in one hemisphere to the other

what re projection fibres

connects the cortex to subcortical nuclei such as the brainstem and spinal cord

What are association fibres

connect cortical areas within the same hemisphere

What is the largest commisure and what are its parts

The corpus callosum. it has four parts. Rostrum and genu, body, isthmus and splenium. It ensures bilateral coordination. it connects the ipsilateral hemisphere with the contralateral hemisphere 

Name another commissure fibre

Anterior commissure connects the olfactory bulbs, amygdala and the anterior temporal lobes 

Name another commissure fibre 2

Hippocampal commissure located under the splenium it interconnects the ipsilateral hippocampal formation with the contralateral hippocampal formation and provides bilateral communication between medial and temporal structures 

Name another commissure fibre 3

posterior commissure is a small midbrain commissure connecting pretecal nuclei and coordinating pupillary light

Example of a projection fibre

internal capsule. V-shaped structure betweeen basal ganglia and thalamus with five parts; anterior limb, genu, posterior limb, rerolenticular part, sublenticular part

internal capsule anterior limb

between caudate and lentiform nucleus

genu of the internal capsule 

carries corticobulbar fibres to cranial nerve nuclei 

posterior limb of the internal capsule

between thalamus and lentiform nucleus; contains corticospinal tracts and thalaamocortical sensory fibres

retorolenticular part of the internal capsule

carries optic radiations to the occipital lobe

sublenticular part of the internal capsule 

carries auditory radiations to the superior temporal gyrus 

Name another projection fibre

corona radiata. fan-shaped arangement of fibres above the internal capusle connecting the thalamus to the cortex and the cortex to the brain stem

name and association fibre

short U-fibres. shallow tracts linking adjacent gyri, supporting local cortical processing

name another association fibre 

cingulum bundle runs deep to the cingulate gyrus arching around the corpus callosum and continuing into the parahippocampal gyrus. It links the cingulate cortex to the parahippocampal to the entorhinal cortex to the hippocampus forming part of papez circuit, important in memory and emotion

name another association fibre 3

superior longitudal fasciculus a long bidirectional tract running from the frontal to parietal, temporal and occipital lobes. functions: spatial attention and higher motor planning

What connects the cortex and the striatum

the corticostriatal fibres carry excitatory information from the motor and premotor cortex to the striatum. they travel through the corona radiata and internal capsule. this tells the basal ganglia what movement is being planned so it can be refined

What are nigrostriatal fibres

fibres from the substantia nigra pars compacta release dopamine into the striatum. loss of this pathways causes parkinson’s disease

Striatal output fibres

Striatum sends GABAergic inhibitory signals to GPi and SNr

medial forebrain bundle 

connects limbic structures with the ventral striatum (nucleus accumbens) relevant for motivation and reward-driven behaviour

What are the two types of association fibres

homotopic - connect corresponding areas

heterotopic - connect non-corresponding areas