Neuroanatomy: Cerebral Connections Quiz

Medullary Substance (White Matter)

• Medullary substance refers to the white matter of the brain
• White matter consists of myelinated axons forming tracts and pathways
• These structures facilitate communication between different brain regions

Components of Cerebral White Matter

• Projection fibers: These fibers interconnect the cortex to lower brain centers (thalamus, brainstem, spinal cord)
  • Ascending (afferent) projection fibers carry sensory information from lower centers to the cortex
  • Descending (efferent) projection fibers carry motor commands from the cortex to lower centers
  • corona radiata refers to a collection of projection fibers
• Association fibers: These fibers interconnect various cortical regions within the same hemisphere
  • Short association fibers connect adjacent gyri
  • Long association fibers connect distant gyri
• Commisural fibers: These fibers interconnect corresponding cortical regions across the two hemispheres
  • Corpus callosum
  • Anterior commissure
  • Posterior commissure
  • Habenular commissure
  • Commisure of hippocampus (fornix)

Fibers of Cerebral White Matter

• Corpus callosum: The largest white matter structure connecting the left and right hemispheres
• Internal capsule: A major pathway of projection fibers
  • Anterior limb
  • Genu
  • Posterior limb
• Superior longitudinal fasciculus: A major association pathway connecting frontal, parietal, and occipital lobes

Types of Projection Fibers

• A. Ascending Fibers (Afferent):
  • Thalamic radiation: Fibers connecting various thalamic nuclei with different cortical regions of the brain
  • Optic radiation: Fibers originating from the thalamus and projecting to the visual cortex
  • Auditory radiation: Fibers conducting auditory information from the thalamus to the auditory cortex
  • Visceral pathway: Fibers transmitting visceral sensory information
  • To medial geniculate: transmitting auditory sensory information
• B. Descending Fibers (Efferent):
  • Pyramidal: (corticospinal and corticobulbar) transmitting motor commands
  • Corticopontine: relaying motor information to the cerebellum
  • Corticoreticular: controlling reflexes and muscle tone
  • Corticorubral: transmitting motor commands to the red nucleus; involved with motor control, particularly for limbs

Association Fibers (detailed)

• Short association fibers: Connect adjacent gyri within the same cerebral hemisphere
• Long association fibers: Connect distant gyri within the same hemisphere
  • Superior longitudinal fasciculus: Connects frontal lobe to parietal and occipital lobes; involved in language function
  • Inferior longitudinal fasciculus: Connects occipital and temporal lobes; contributes to visual recognition
  • Uncinate fasciculus: Connects frontal and temporal lobes; important for behavioral regulation
  • Cingulum: A fiber bundle in the cingulate gyrus; part of the limbic system
• Fronto-occipital fibers (connect frontal to occipital lobe) and ventral occipital fibers (connect parietal and occipital to temporal lobes)

Commissural Fibers (detailed)

• Corpus callosum: Largest commissural fiber bundle; connects homologous areas of the brain
• Anterior commissure: Connects temporal lobes and olfactory bulbs
• Posterior commissure: Involved in pupillary light reflex

Hippocampal Commissure (detailed)

• Composed of transverse fibers
• Interconnects posterior columns of the fornix

Additional terms

• Genu of the internal capsule: Area containing corticobulbar and parts of sensory thalamic radiation fibers
• Anterior limb of the internal capsule: Area containing anterior thalamic radiation and frontopontine fibers
• Posterior limb of the internal capsule: Area containing corticospinal, corticothalamic and geniculate nuclei fibers
• Sublentiform part: Area between thalamus and lentiform nucleus
• Retrolentiform part: Area that includes Posterior thalamic radiation
• Arcuate fasciculus: A subsidiary bundle of the superior longitudinal fasciculus; connects frontal and temporal lobes, crucial for language understanding.