White matter of cerebrum

• White matter of telencephalon

  • Myelinated axons that form various pathways for communication between different regions of brain.
  • These pathways are critical for integration of sensory, motor and cognitive function.
  • Primarily located beneath grey matter of cerebral cortex and surrounds the deeper grey matter structures (basal ganglia)
• White matter of telencephalon is organised into 3 main types of fibers systems

  1. Association fibers
  2. Commissural fibers
  3. Projection fibers
• Association fibers

  • connect different areas within same hemisphere
  • enable communication between adjacent/nearby areas facilitating functions like perception, integration of sensory info, higher-order processing, memory function
• Types of association fibers

  1. Long association fibers: connects cortical regions in different lobes of same hemisphere.
  2. Short association fibers: connect adjacent gyri within same lobe
• Example of long association fibers

  1. Superior longitudinal fasciculus: connects frontal, occipitl and temporal lobes
  2. Inferior longitudinal fasciculus: connects temporal and occipital lobes
  3. Uncinate fasciculus: connects orbital part of frontal lobe with anterior temporal love involved in emotional processing and memory.
  4. Cingulum: runs within cingulate gyrus and connects parts of limbic system, involved in emotional regulation and cognition
• Example of short association fibers

  Arcuate fasciculus: connects broca’s area in frontal lobe with wernicke’s area in temporal lobe playing role in language processing.
• White fiber system of telencephalon

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• Commissural fibers

  • Connects homologous (corresponding) regions of the 2 hemispheres, facilitating intrahemispheric communication. They form the commissures of cerebrum.
• Example of commissural fibers

  • Anterior commissure: connecting archipallia( olphactory bulb, piriform area and parts of temporal lobe of the 2 sides)
  • posterior commissure: connects superior colliculus, pretectsl areas involved in light reflex + other visual reflexes
  • Habenular commissure: connects habenular nuclei
  • Hypothalamic commissure: including anterior hypothalamic commisure of gonser, ventral supraoptic commissure of guden and doral supraoptic sommissure of meyneit
• Projection fibers

  • Bundle of nerve fibers connecting cerebrum with lower brain regions (brainstem) and spinal cord
  • Facilitates bidirectional communication btw cerebrum and other parts of cns
• Example of projection fibers

  • Corona radiata
  • Internal capsule
• Internal capsule

  • Located deep within cerebrum, situated laterally to thalamus and medially to lentiform nucleus.
  • Contains concentration of ascending and descending fibers that connect cerebral cortex with brainstem, as well as fibers interconnecting different parts of cerebral cortex.

  
• Anatomical parts of internal capsule

  Appears as V-shaped in horizontal section with its concavity directed laterally and being occupied by lentiform nucleus

  • Anterior limb; lies btw head of caudate and lentiform nucleus.
  • Genu: the bend btw anterior snd posterior limbs
  • Posterior limb: lies btw thalamus and lentiform nucleus
  • retrolentiform part: lies behind lentiform nucleus
  • Sublentiform part: lies bellow lentiform nucleus and can not be seen in horizontal section

  
• Internal capsule fibers constituents

  • fibers can be categorized into motor, sensory and association fibers
• • Anterior limb: frontopontine + thalamocortical fibers
  • Genu: corticobulbar fibers
  • Posterior limb: corticospinal+ thalamocortical sensory + corticopontine fibers
  • Retrolentiform part: optic radiations ( visual info from lat geniculate body to primary visual cortex in occiptal lobe)
  • Sublentiform par: auditory radiations( auditory info from med geniculate body to primary auditory area in temporal lobe
• Corpus callosum

  • Largest commisural fiber bundle in brain, consisting of 200million axonal fibers.
  • Connects left and right cerebral hemisphere expect lower and anterior part of temporal lobes which are coomected by anterior commissure
• Corpus callosum is divided into 4 anatomical parts

  • Rostrum: most anterior part connecting orbital fissures of frontal lobes
  • Genu: the anterior bend, connects anterior frontal lobes of both hemispheres.
  • Body: largest, widest central part, conmects mid-frontal and parietal lobes
  • Splenium: posteior, rounded end. Connects posterior temporal and occipital lobes
• Function of corpus callosum

  • Enables communication btw the 2 cerebral hemispheres which is essential for: integration of sensory info, coordinating motor functions, facilitating cognitive processes and emotional and behaviour integration
• Split-brain syndrome


  Damage or removal of corpus collosum can cause split brain syndrome where each hemisphere operates independentl, affecting coordination and communication btw them. Patients may feel difficulties in task that require intrahemispheric coordination
• parts of corpus callosum