General structure of nervous tissue

🖇 General Organization & Terminology

• Nervous tissue = neurons + intercellular components.
• Functional unit = Neuron (nerve cell).
• Divisions:
• • CNS: Brain + Spinal Cord.
  • PNS: Any nervous tissue outside CNS.
• Key Terms:
• • Nucleus (CNS): Group of neuron cell bodies inside CNS.
  • Ganglion (PNS): Group of neuron cell bodies outside CNS.
  • Nerve fiber = Axon.

📌 Neuron Structure
Parts: Cell Body, Dendrites, Axon.

🟠 Cell Body (Soma / Perikaryon)

• LM:
• • Nucleus round & central.
  • Cytoplasm basophilic due to RER → forms Nissl granules.
• Nissl Granules:
• • Clumps of RER → protein synthesis (neurotransmitters, memory proteins).
• Inclusions:
• • Lipofuscin: Waste material, ↑ with age ("stool of cell").
  • Melanin: Found in substantia nigra, iris, skin, hair.
  • Small amounts of lipids.
• Cytoskeleton:
• • Neurofilaments → Neurofibrils (structural support).
• Division:
• • Neurons don’t divide (no centrioles).

🟣 Dendrites

• Multiple, short, thin, highly branched.
• Have spines (gemmules) on branches.
• Contain same cytoplasmic contents as cell body except nucleus.

🟠 Axon (Nerve Fiber)

• Single, long, thicker than dendrites.
• Axon Hillock: Starting point of axon.
• Branching: Only at terminal → Telodendria.
• Axoplasm: Cytoplasm of axon.
• • No RER (Nissl granules) or Golgi → smooth signal conduction.
  • Contains mitochondria.
• Axonal Transport:
• • Anterograde: Cell body → axon terminal (e.g., neurotransmitters).
  • Retrograde: Axon terminal → cell body (e.g., waste products).

📌 Neuron Classification

🟣 By Polarity (Shape / Processes)

1. Unipolar / Pseudounipolar:
2. • Single process → T-shaped split.
   • Found in spinal ganglia.
   • True unipolar → Mesencephalic nucleus of CN V.
2. Bipolar:
3. • Two processes (one dendrite + one axon).
   • Found in special senses (retina, olfactory epithelium, inner ear).
3. Multipolar:
4. • Many dendrites + one axon.
   • Most common type → brain & spinal cord.
   • Types by shape:
   • • Pyramidal: Cerebral cortex.
     • Purkinje (Pyriform): Cerebellum.
     • Stellate: Autonomic ganglia.

🟠 By Axon Length

• Golgi Type I: Long axon.
• Golgi Type II: Short axon.

🟣 By Function

• Sensory (Afferent): Posterior horn of spinal cord.
• Motor (Efferent): Anterior horn of spinal cord.
• Interneurons: Connect neurons (e.g., reflex arcs).

📌 Ganglia

FeatureSpinal Ganglia (Dorsal Root)Sympathetic / Autonomic Ganglia

Cell Type

Pseudounipolar

Stellate multipolar

Arrangement

Grouped in clusters

Scattered individually

Cell Size

Uniform

Variable

Capsule

Thick connective tissue

Thin connective tissue

Satellite Cells

Present & surround groups

Present

Axons

Myelinated

Unmyelinated

🚨 Key Clinical Points

• Lipofuscin ↑ with age → sign of neuronal aging.
• Lack of centrioles → neurons don’t regenerate → injury permanent.
• Axonal transport disruption → linked to neurodegenerative diseases (e.g., Alzheimer's).
• Pseudounipolar neurons → sensory ganglia (dorsal root ganglia).

الدكتورة قالت الأسئلة دي وحليتها

Q) Explain the the light microscope and electron microscopeffeature of soma

Q) describe the structure and the content of the dendrites

Q) classification of the Neurons according to number of process

Q) differentiate between spinal ganglion and autonomic ganglion

Q) write a note on inclusions of neurons