Histological structure of Cerebrumcerebellum

🧠 Histology of the Cerebrum

🟣 1. General Organization of the CNS

🖇 Gray and White Matter arrangement:

• In the Spinal Cord: Gray matter is central, White matter is peripheral.
• In the Brain (Cerebrum): Gray matter is peripheral (outer), White matter is internal (inner).

🖇 Cerebrum Structure:

• Composed of right and left hemispheres.
• The two hemispheres are connected by the Corpus Callosum.
• The lower part continues as the Brainstem.

🟠 2. Cerebral Cortex Overview

📌 Definition:
The Cerebral Cortex is the outer gray matter layer of the cerebrum.

📌 Structure:

• The surface shows folds (gyri) and grooves (sulci) to increase surface area for information processing.
• Thickness: about 2–4 mm.

📌 Composition:

• Gray matter (outer): Contains neuron cell bodies, astrocytes, and capillaries.
• White matter (inner): Contains the axons of neurons from the gray matter.

📌 Functions:
Responsible for motor control, sensory perception, memory, attention, and awareness.

🟣 3. Six Layers of the Gray Matter

🖇 The cerebral cortex has six histological layers, arranged from superficial to deep.
Each layer differs in neuron type, size, and density.

📌 Layer 1 – Molecular (Plexiform) Layer:

• Contains mainly dendritic extensions from deeper pyramidal cells.
• Also contains Horizontal Cells of Cajal, which run parallel to the surface.

📌 Layer 2 – External Granular Layer:

• Contains many small stellate (granular) cells.
• Mainly sensory in function.

📌 Layer 3 – External Pyramidal Layer:

• Composed of medium-sized pyramidal neurons.
• Mainly motor in function.
• It is one of the largest layers of the cortex.

📌 Layer 4 – Internal Granular Layer:

• Contains small stellate cells, similar to layer 2.
• Another sensory layer, receiving input from the thalamus.

📌 Layer 5 – Internal Pyramidal (Ganglionic) Layer:

• Contains large pyramidal neurons, including the Betz cells (up to 120 µm).
• Strongly motor; the origin of the Corticospinal tract.

📌 Layer 6 – Multiform (Polymorphic) Layer:

• Contains fusiform and polymorphic neurons of various shapes.
• Deepest layer, connects to subcortical structures.

🟠 4. The Five Principal Neurons of the Cerebral Cortex

📌 1. Pyramidal Cells:

• The main (principal) neurons of the cortex.
• Found mainly in layers 3 and 5.
• Multipolar and responsible for motor function.
• Have long axons that leave the cortex and form tracts such as the Corticospinal tract.

📌 2. Stellate (Granular) Cells:

• Found mainly in layers 2 and 4.
• Involved in sensory functions.
• Small neurons with short axons that remain within the cortex (interneurons).

📌 3. Horizontal Cells of Cajal:

• Found in the outermost layer (Layer 1).
• Small, spindle-shaped neurons running horizontally parallel to the surface.

📌 4. Cells of Martinotti:

• Multipolar interneurons found throughout deeper layers.
• Their axons ascend toward Layer 1, forming synapses with pyramidal cells.

📌 5. Fusiform (Spindle-shaped) Cells:

• Found mainly in Layer 6.
• Vertically oriented neurons connecting cortex to subcortical regions.

🟣 5. Functional Classification of Cortical Layers

🖇 Motor Layers: Layers 3 and 5 (contain pyramidal and Betz cells).
🖇 Sensory Layers: Layers 2 and 4 (contain stellate cells).
🖇 Association Layers: Layers 1 and 6 (interneuronal communication).

🚨 6. Key Exam-Focused Questions

1. ⚡ What is the difference in gray and white matter arrangement between brain and spinal cord?
2. ⚡ Why does the cerebral cortex have folds? → To increase surface area.
3. ⚡ Which layers are motor (3 & 5) and which are sensory (2 & 4)?
4. ⚡ Describe Betz cells – location (Layer 5), size (~120 µm), and motor function.
5. ⚡ Compare Pyramidal vs. Stellate cells:
6. • Pyramidal → long axon, leaves cortex (motor).
   • Stellate → short axon, stays inside cortex (sensory).
6. ⚡ List the five neuron types in the gray matter of the cerebral cortex.

🧠 Histology of the Cerebellum

🟣 1. General Anatomy and Function

🖇 Definition:
The Cerebellum (the "little brain") lies below the cerebrum and behind the brainstem.

📌 Main Function:

• Responsible for coordination of voluntary movement
• Ensures musculoskeletal and neurological alignment

📌 Other Roles:

• Helps in attention, speech, and emotional regulation (happiness, fear).

📌 Structure:

• Two hemispheres connected by the vermis (midline part).
• Surface folded into many folia
• each folium = white core + gray covering.

📌 Gray & White Matter Arrangement:

• Gray matter (outer) = cortex.
• White matter (inner) = medulla.

🟠 2. Components of White Matter

🖇 Location: Inner region beneath the cerebellar cortex.

📌 Main Structures:

• Four deep nuclei: Dentate, Emboliform, Globose, and Fastigial (mainly anatomical importance).
• Two main fiber types:
• 1. Mossy fibers
  2. Climbing fibers

🟣 3. Layers of the Cerebellar Cortex

🖇 The Cerebellar Cortex has three layers (outer → inner):

📌 a. Molecular Layer

• Also called the Plexiform Layer.
• Contains:
• • Dendrites of Purkinje cells.
  • Stellate cells and Basket cells.
  • Axons coming from Granule cells below.
• Function: Integrative layer — connects input and output neurons.

📌 b. Purkinje Cell Layer

• A single row of large Purkinje cells
• Their dendrites extend upward into the Molecular Layer.
• These are the only output neurons of the cerebellar cortex.
• Axons go to the deep cerebellar nuclei.

📌 c. Granular Layer

• Innermost and thickest layer.
• Contains:
• • Granule cells → excitatory neurons.
  • Golgi type II cells → inhibitory interneurons.
• Input:
• • Mossy fibers → excitatory to Granule cells.
  • Golgi cells → inhibitory feedback to Granule cells.

🟠 4. Fiber Pathways

🖇 The cerebellum receives two types of afferent (input) fibers:

📌 Mossy Fibers

• Enter the Granular Layer.
• Synapse with Granule cells.
• Function: Indirectly activate Purkinje cells through Granule cell axons.

📌 Climbing Fibers

• Pass through white and granular layers.
• “Climb” up to the Molecular Layer.
• Synapse directly on Purkinje cell dendrites.
• Function: Provide strong excitatory input to Purkinje cells.

🟣 5. Summary of Neuronal Types

📌 Neurons of the Cerebellar Cortex:

• Stellate cells → Molecular layer.
• Basket cells → Molecular layer.
• Purkinje cells → Purkinje layer.
• Granule cells → Granular layer.
• Golgi type II cells → Granular layer.

📌 Fibers in White Matter:

• Mossy fibers.
• Climbing fibers.

🚨 6. Key Exam-Focused Questions

1. List the cell types in the cerebellar cortex and white matter.
   → Stellate, Basket, Purkinje, Granule, Golgi (cortex) + Mossy & Climbing (white matter).
2. What are the components of cerebellar white matter?
   → Deep nuclei + Mossy fibers + Climbing fibers.
3. Name and describe the three layers of the cerebellar cortex.
   → Molecular, Purkinje, Granular — with their characteristic cells.
4. Differentiate between Mossy and Climbing fibers.
   → Mossy → Granule cells (indirect path).
   → Climbing → Purkinje cells (direct path).
5. What is the main output neuron of the cerebellar cortex?
   → Purkinje cell.