White Matter
Association fibers
- Connects anteroposteriorly
- Different lobes in the same hemisphere.
Short Association Fibers | Connects two adjacent gyri |
Arcuate fasciculus | Broca's speech area (Area 44 and 45) ⇔ Wernicke's speech area (area 22) |
Long Association Fibers | ã…¤ |
Superior longitudinal fasciculus | Frontal lobe ⇔ occipital lobe |
Inferior longitudinal fasciculus | Temporal lobe ⇔ occipital lobe |
Cingulum | Surrounds Corpus callosum |
Uncinate fasciculus | Broca’s speech area (Area 44 and 45) ⇔ Auditory area (Area 41 and 42) |
Commissural fibers
- Made of white matter fibers.
- Connects the right and left half of the brain.
- Corpus callosum
- Largest
- Forms the roof of the lateral ventricle.
- Anterior commissure
- Posterior commissure
- Habenular commissure
- Hippocampal commissure
Projection Fibers
- Internal capsule
- Corona radiata
- Fimbria / Tracts
Corpus callosum
- RGB IS (rostrum, genu, body, Ischium, splenium) stored in brain
Parts | ã…¤ |
Rostrum (R) | Front part, beak-like. |
Genu (G) | Curved anterior part. |
Body (B) | Main middle section. |
Splenium (S) | Posterior rounded end |
Connections
- Largest commissural fiber
- Connects the two cerebral hemispheres
- Develops from lamina terminalis
- Point where anterior neuropore closes
- Formation: between 12th to 16–20th weeks of gestation
Â
ã…¤ | Forms |
Forceps minor | Anterior wall of anterior horn of lateral ventricle |
Forceps major | Superior wall of posterior horn of lateral ventricle |
Part | Connections | Named Fibers | Ventricular Relations |
Genu | Frontal lobe | Forceps minor | • Anterior bend of CC |
Body | Parietal / Temporal lobe | Tapetum fibers (laterally) | • Forms Roof of body of lateral ventricle • Connects Occipital to lower part of temporal lobe |
Splenium | Occipital lobe (striate cortex) | Forceps major | • Thickest part Fibers form: • Bulb of posterior horn • Elevation on medial wall of posterior horn |
- Tapetum fibers
- Tapetum fibers lie lateral to posterior horn
- Tapetum connects to occipital and lower temporal lobes
- Genu → Frontal → Forceps minor
- Body → Tapetum → Lateral wall/roof contribution
- Splenium → Occipital → Forceps major → Bulb of post. horn
Corpus callosum agenesis
- MRI head:
- Racing car appearance
- Prominent dilated posterior horns of lateral ventricles.
- Seen in
- Fetal warfarin syndrome → Disala syndrome
- Aicardi syndrome
- Neurodevelopmental disorder
- Triad
- Infantile spasms (early infancy)
- Agenesis of corpus callosum
- Eye
- Chorioretinal lacunae
- Well-circumscribed
- Pale retinal lesions
- Retinal colobomas
In Alcohol Abuse
- Marchiafava Bignami
- Widespread demyelination of Corpus callosum
- March il bigname call cheyth - Callosum
Striate cortex
- Primary visual cortex
- Area 17
- Located in posterior part of calcarine sulcus
- Lobe: Occipital
- Heavily myelinated
- Striate appearance:
- Striae of Gennasi (also known as striate cortex)
- Mnemonic: Genz vision brod anu → 17, 18, 19 yr olds
- Accessory visual areas
- Area 18 → Secondary visual cortex
- Area 19 → Tertiary visual cortex
Fornix
Marked structure
Mark B → Fornix
- Structure: White matter.
- Two fornices (one on each brain side).
- Origin:
- Hippocampus.
- Termination:
- Joins mammillary body and thalamus.
Fibers
- Contains all 3 fiber types:
- Association fibers >
- Commissural fibers >
- Projection fibers
- Right and left fornix connected by commissural fibers.
Blood Supply:
- Anterior Cerebral Artery
Location and Relations
- Forms:
- Medial wall of lateral ventricle (with septum pellucidum).
- Roof of 3rd ventricle (with choroid plexus).
- Position:
Papez Circuit – (Posterior to anterior)
- Present in both sides of the brain
- Connects memory & emotion of limbic system.
- Hippocampal formation
- Mammillary bodies
- Anterior nucleus of the thalamus
- Cingulate gyrus
- Entorhinal cortex
→ projects back to hippocampus
↓ via Fornix
↓ via Mammillothalamic tract
↓
↓ via Cingulum
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