Internal structure of cerebral hemisphere (white matter & basal ganglia)

🖇 ANATOMY: CEREBRAL STRUCTURE OVERVIEW

📌 Two Main Structural Components

White Matter:

• Represents nerve fibers
• Appears white due to myelin sheath
• Organized into three main types (A, B, C)

Grey Matter:

• Represents nuclei (cell bodies)
• Appears spotted or grey
• Collections of neuronal soma

🖇 ANATOMY: WHITE MATTER CLASSIFICATION

📌 Three Main Types of Nerve Fibers

White matter organized into three categories:

1. Association Fibers
2. Commissural Fibers
3. Projection Fibers

🖇 ANATOMY: ASSOCIATION FIBERS (Type A)

📌 Definition & General Features

Definition: Connect different areas within SAME cerebral hemisphere (same side)

Characteristic: Do NOT cross midline

Organization: Based on distance traveled

🟠 Short Association Fibers

Function: Connect two adjacent gyri (centers)

Structural Note: Even if physically short but transition between different lobes (e.g., Frontal to Temporal), classified functionally as Long Association Fibers

Alternate Name: Arcuate Fibers (due to arch-like shape connecting adjacent gyri)

🟣 Long Association Fibers

Function: Connect two areas located far apart in different lobes within same hemisphere

Exam Importance: Highly relevant for exams (Exam Point)

Five Types (Examples):

1. Superior Longitudinal Fasciculus
2. • Course: Extends from frontal lobe back toward occipital lobe
   • Path: Passes through temporal lobe
   • Function: Long-range anterior-to-posterior connection
2. Frontopontine Fasciculus (Fronto-occipital Fasciculus)
3. • Connection: Connects frontal, occipital, and temporal lobes
   • Depth: Deeper than Superior Longitudinal Fasciculus
   • Positioning: Deep long-range tract
3. Cingulum
4. • Start: Cingulate Gyrus
   • Course: Runs to Parahippocampal Gyrus
   • Extension: Extends to Hippocampus and Middle Temporal Gyrus
   • Anatomy: Follows limbic lobe
4. Inferior Longitudinal Fasciculus
5. • Connection: Connects occipital lobe to temporal lobe
   • Position: Situated at lower level than Superior Longitudinal Fasciculus
   • Direction: Horizontal temporal-to-occipital pathway
5. Uncinate Fasciculus (Hooked Fasciculus)
6. • Connection: Connects frontal cortex (Broca's area) to temporal lobe
   • Shape: Hooked/curved appearance
   • Function: Speech-related language connection

🖇 ANATOMY: COMMISSURAL FIBERS (Type B)

📌 Definition & General Features

Definition: Connect corresponding or different areas in OPPOSITE hemispheres

Characteristic: Cross the midline (interhemispheric fibers)

Function: Enable cross-hemisphere communication

🟠 Five Main Types

1. Corpus Callosum

Significance: Largest and most famous commissural fiber bundle (Exam Point)

Exam Importance: Parts often tested (Exam Point)

Four Anatomical Parts:

1. Rostrum
2. • Position: Anterior
   • Description: Thin, fibrous anterior part
   • Function: Connects anterior structures
2. Genu (Knee)
3. • Position: Anterior-curved section
   • Description: Anterior curved, swollen part
   • Function: Curves anteriorly
3. Body (Trunk)
4. • Position: Central region
   • Description: Main central part
   • Largest portion: Contains most fibers
4. Splenium
5. • Position: Posterior
   • Description: Posterior enlarged part
   • Function: Posterior commissure section

Fiber Subdivisions (Visible in Transverse/Coronal Section):

Forceps Minor (Forceps Anterior):

• Origin: Extends forward from Genu
• Connection: Links two frontal lobes
• Function: Anterior commissural fibers

Forceps Major (Forceps Posterior):

• Origin: Extends backward from Splenium
• Connection: Links two occipital lobes
• Function: Posterior commissural fibers

Tapetum:

• Location: Runs through Trunk (Body)
• Connection: Connects parietal and temporal lobes bilaterally
• Specifics: Links parietal-temporal regions side-to-side

2. Anterior Commissure

• Position: Located anteriorly
• Connection: Links olfactory areas and posterior temporal lobe regions
• Function: Anterior cross-brain connection

3. Posterior Commissure

• Position: Located posteriorly
• Connection: Connects posterior area of diencephalon
• Contents: Contains fibers linking right and left superior colliculi
• Nuclei: Links certain nuclei bilaterally
• Function: Posterior diencephalic connection

4. Habenular Commissure

• Connection: Connects two Habenular Nuclei
• Location: Associated with epithalamus
• Function: Habenular cross-connection

5. Hippocampal Commissure (Fornix Commissure)

• Connection: Connects two Hippocampal Nuclei
• Associated structure: Part of fornix system
• Function: Hippocampal commissural connection

🖇 ANATOMY: PROJECTION FIBERS (Type C)

📌 Definition & General Features

Definition: Penetrate grey matter connecting Cortex (cortical areas) with Deep Centers (subcortical areas)

Deep Centers Include: Brainstem, spinal cord, subcortical nuclei

Direction: Can be Ascending or Descending

Ascending: From spinal cord/brainstem → to cortex (sensory)

Descending: From cortex → down to brainstem/spinal cord (motor)

🟠 Key Structures

1. Corona Radiata

• Definition: As fibers diverge upwards from deep centers
• Structure: Fan out formation
• Shape: Crown-like structure (radiata = radiating)
• Function: Divergence of projection fibers

2. Internal Capsule

• Definition: Primary collection point for projection fibers
• Structure: Fibers funnel down into this region
• Function: Crucial junction between cortical and subcortical areas
• Importance: Critical structure for motor/sensory function

🖇 ANATOMY: INTERNAL CAPSULE - DETAILED

📌 Definition & Location

Definition: Mass of white matter passing between surrounding masses of grey matter

Location: Separates:

• Medially: Caudate Nucleus and Thalamus
• Laterally: Lentiform Nucleus

Exam Importance: Critically important subject similar to Corpus Callosum (Exam Point)

🟠 Anatomical Parts (Five) - V-Shaped in Transverse Section

1. Anterior Limb

• Location: Between Head of Caudate Nucleus (medially) and Lentiform Nucleus (laterally)
• Function: Anterior fibers bundle
• Contents: Motor/sensory fibers to anterior structures

2. Genu (Knee)

• Location: Curvature connecting anterior and posterior limbs
• Function: Connection point between two limbs
• Contents: Fibers transitioning between anterior and posterior

3. Posterior Limb

• Location: Between Thalamus (medially) and Lentiform Nucleus (laterally)
• Function: Posterior fibers bundle
• Contents: Motor/sensory fibers to posterior/spinal structures

4. Retrolentiform Part

• Location: Runs BEHIND Lentiform Nucleus
• Description: Extension of posterior limb
• Contents: Visual pathway fibers (optic radiations)

5. Sublentiform Part

• Location: Runs BELOW Lentiform Nucleus
• Description: Inferior extension
• Contents: Auditory pathway fibers

🟣 Blood Supply - Highly Important (Exam Point)

Anterior Limb:

• Upper half: Supplied by Middle Cerebral Artery (MCA)
• Lower half: Supplied by Anterior Cerebral Artery (ACA)

Genu:

• Upper half: Supplied by Middle Cerebral Artery (MCA)
• Lower half: Supplied by Internal Carotid Artery (ICA)

Posterior Limb:

• Upper half: Supplied by Middle Cerebral Artery (MCA)
• Lower portion divided into sections:
• • One-third part: Supplied by Anterior Choroidal Artery
  • Two-thirds part: Supplied by Posterior Cerebral Artery (PCA)

Retrolentiform Part:

• Supplied by: Anterior Choroidal Artery

Sublentiform Part:

• Supplied by: Anterior Choroidal Artery

🖇 CLINICAL IMPORTANCE: INTERNAL CAPSULE LESIONS

📌 Spatial Anatomy - Closely Packed Structure

Critical Feature: Highly compacted area where all fibers representing entire body concentrated

Fiber Distribution:

• Legs fibers
• Trunk fibers
• Head fibers
• Face fibers
• ALL in close spatial relationship

🟠 Lesion Consequences

Clinical Severity: Even small hemorrhage or thrombosis causes severe deficit

Primary Clinical Manifestation: Contralateral Hemiplegia (paralysis of opposite half of body) (Exam Point)

Additional Deficits: Severe motor or sensory deficits affecting entire system

Why Severe: Due to close spatial relationship (closely packed) of all body representations

🟣 Pathology

Possible Lesion Types:

• Hemorrhage (bleeding)
• Thrombosis (clot/stroke)
• Traumatic damage
• Tumor compression

Result: Massive deficits due to fiber concentration

🖇 ANATOMY: BASAL NUCLEI (BASAL GANGLIA)

📌 Definition & Location

Definition: Collections of grey matter deep within cerebral hemispheres

Type: Subcortical nuclei

Function: Motor control, habit formation, reward processing

🟠 Primary Components

Three main components discussed:

1. Corpus Striatum (Striated Body)
2. Claustrum
3. Amygdaloid Nucleus (Amygdala)

🖇 ANATOMY: CORPUS STRIATUM

📌 Definition & Nomenclature

Definition: Named "Striated Body" because appears striped (grey, white, grey pattern)

Reason for Striations: White matter (Internal Capsule) passing through or separating grey matter components

Functional Classification: Often divided into:

• Neostriatum: Caudate + Putamen
• Paleostriatum: Globus Pallidus

🟠 Constituent Parts

Three Components:

1. Caudate Nucleus
2. • Position: Medial
   • Shape: C-shaped or comma-shaped
2. Anterior Limb of Internal Capsule
3. • Position: Central
   • Function: Creates the white matter stripe
3. Lentiform Nucleus
4. • Position: Lateral
   • Shape: Bi-convex lens-shaped

🖇 ANATOMY: CAUDATE NUCLEUS

📌 Shape & Organization

Shape: C-shaped or comma-shaped

Parts: Head, Body, Tail

Terminal Structure: Amygdaloid Nucleus located at terminal tip of tail

🟠 Anatomical Relationships

Medial to: Internal Capsule

Superior to: Thalamus

Related to: Lateral ventricle shape follows caudate

Tail Extension: Curves posteriorly following temporal horn of lateral ventricle

🖇 ANATOMY: LENTIFORM NUCLEUS

📌 Shape & Definition

Shape: Bi-convex lens-shaped structure (biconvex)

Position: Central grey matter nucleus

Layers: Contains two concentric zones

🟠 Boundary Relationships

Medial Border:

• Separated by: Internal Capsule
• From: Thalamus and Caudate Nucleus

Lateral Border:

• Separated by: External Capsule
• From: Claustrum

🟣 Two Concentric Zones (Internal Parts)

1. Globus Pallidus (G)

• Position: Inner, medial part
• Appearance: Pale/globular
• Function: Motor output nucleus

2. Putamen (P)

• Position: Outer, lateral part
• Description: Shell or covering layer
• Appearance: Striated appearance
• Function: Motor input region

🚨 Clinical Note on Lentiform Structure

Functional Significance:

• Globus Pallidus + Putamen functionally related
• Putamen receives input from cortex
• Globus Pallidus sends output to thalamus
• Sequential processing pathway

🖇 ANATOMY: CAPSULE SYSTEMS SURROUNDING LENTIFORM NUCLEUS

📌 Three Concentric Capsular Layers

Three layers of white matter surround or relate to Lentiform Nucleus

🟠 Internal Capsule (Medial)

Location: Medial to Lentiform Nucleus

Contents: Projection fibers (cortex to subcortical areas)

Clinical Importance: Critically important (as described earlier)

🟣 External Capsule (Lateral)

Location: Lateral to Lentiform Nucleus

Between: Lentiform Nucleus and Claustrum

Contents: Association and commissural fibers

🚨 Extreme Capsule (Outermost)

Location: Lateral to Claustrum

Between: Claustrum and Insular Cortex

Contents: White matter fibers

🖇 ANATOMY: CLAUSTRUM

📌 Anatomical Description

Shape: Thin, tooth-like layer of grey matter

Edge Characteristic: Serrated edges (saw-like)

Location: Situated outside External Capsule

Position Relative to Insular Cortex: Adjacent to insular cortex

🟠 Functional Significance

Function: Not fully understood; possibly involved in sensory integration

Connections: Receives input from multiple cortical areas

Size: Very thin layer structure

🖇 ANATOMY: AMYGDALOID NUCLEUS (AMYGDALA)

📌 Location & Relationship

Location: Located at tip (end) of tail of Caudate Nucleus

Position: In temporal lobe

Shape: Almond-shaped (amygdala = almond in Greek)

🟠 Anatomical Connections

Inferior to: Lateral ventricle inferior horn

Associated with: Hippocampus (nearby structure)

Part of: Limbic system

🟣 Functional Role

Function: Emotion processing, fear, reward

Input/Output: Extensive connectivity with cortex and other limbic structures

Significance: Important for emotional behavior and memory

🖇 EXAM FOCUS: KEY SUMMARY POINTS

📌 White Matter - Most Important Features

Association Fibers:

• SAME hemisphere, do NOT cross midline
• Short: Connect adjacent gyri (Arcuate fibers)
• Long: Five types tested (Exam Point)
• • Superior & Inferior Longitudinal Fasciculus
  • Frontopontine/Fronto-occipital Fasciculus
  • Cingulum
  • Uncinate Fasciculus

Commissural Fibers:

• OPPOSITE hemispheres, DO cross midline
• Five types (Corpus Callosum most important) (Exam Point)
• Corpus Callosum parts: Rostrum, Genu, Body, Splenium (Exam Point)
• Corpus Callosum subdivisions: Forceps Minor/Major, Tapetum

Projection Fibers:

• Cortex ↔ Deep centers (brainstem, spinal cord)
• Structures: Corona Radiata, Internal Capsule

🟠 Internal Capsule - Most Critical

Location: Separates Caudate/Thalamus (medial) from Lentiform Nucleus (lateral)

Exam Importance: Critically important (Exam Point) like Corpus Callosum (Exam Point)

V-Shaped Parts: Anterior limb, Genu, Posterior limb, Retrolentiform, Sublentiform

Blood Supply: Multiple arterial territories (MCA, ACA, PCA, Anterior Choroidal) (Exam Point)

Clinical: Even small lesion → Contralateral Hemiplegia (Exam Point)

Reason: All body representations closely packed

🟣 Basal Nuclei - Most Important Features

Corpus Striatum Components:

• Caudate Nucleus
• Internal Capsule (anterior limb)
• Lentiform Nucleus

Lentiform Nucleus Structure:

• Globus Pallidus (medial/inner)
• Putamen (lateral/outer)

Supporting Structures:

• Claustrum: Thin, serrated grey matter (lateral to external capsule)
• Amygdala: At tail tip of Caudate Nucleus (temporal lobe)

Capsule Systems:

• Internal Capsule: Medial to Lentiform (projection fibers)
• External Capsule: Lateral to Lentiform (between Lentiform and Claustrum)
• Extreme Capsule: Lateral to Claustrum (between Claustrum and Insular Cortex)