Wk_2___1_Histology_of_the_Nervous_System
Histology of the Nervous System Neuroanatomy 1
Readings
The Human Brain: Chapter 1 (all)
Optional: Clinically Oriented Anatomy: Chapter 1, section on nervous system.
Histology Textbook Material: Any relevant content on the nervous system.
Objectives
Identify the cell types of the nervous system.
Understand the basic parts of a neuron and their functions.
Recognize the organelles found in neurons and their unique aspects.
Explain the axonal transport system: its components and importance.
Describe the major components of synapses.
Classify the major types of neurons and glia, their locations, and functions.
Review Question: Cell Types
What are the 2 basic types of cells of the nervous system?
Neurons – transmit electrical and chemical signals.
Neuroglia (glia) – supportive cells with various functions.
Neuronal Parts
Review Question: Neuronal Parts
What are the 3 basic parts of a neuron?
Cell body: Central portion with organelles, metabolism and information processing.
Axon: Long cylindrical structure that transmits information.
Dendrites: Thin, tapering processes that receive information from other neurons.
Characteristics of the Cell Body
Also known as soma or perikaryon.
Shape: round/polygon.
Size: 5-100 μm.
Contents: nucleus, organelles, cytoplasm.
Function: Carries out metabolism, synthesis, and information processing.
Characteristics of Dendrites
Structure: Thin, branching processes, thicker proximally and tapering distally.
Contents: Most organelles found in dendrites except nucleus; abundant at proximal end.
Function: Receive information from other neurons; surrounded by synapses and glial cells.
More on Dendrites
Longitudinal Section: Features include Nissl bodies, mitochondria, and cytoskeleton for support.
Cross-section: Extensively branched with presence of microtubules and Nissl bodies.
Dendritic Spines
Small projections from the end of dendritic branches.
Function: Increase surface area for synapses; essential for memory and intellect.
Axons
Characteristics: Long cylindrical processes, typically one per neuron, less branching than dendrites.
Parts:
Axon hillock: Site where the axon attaches to the cell body.
Initial segment: Most excitable area of the axon.
Collateral branches: Side branches of the axon.
Terminal branches: End branches leading to synapses.
Bouton: Expanded distal end of the terminal branch; forms synapse, releases neurotransmitters.
Characteristics of Axons
Longitudinal section: Includes mitochondria, microtubules, but no Nissl bodies.
Cross-section: Mainly mitochondria, cytoskeleton, and myelin, which acts as electrical insulation.
Organelles
Review Question: Organelles
What cellular organelles do we know?
Functions: Nucleus, Golgi apparatus, mitochondria, Nissl bodies, nucleolus providing insight into the neuron’s secretory roles.
##What are Nissl Bodies?
Stained ribosomes that appear blue/purple under Nissl dye.
High concentrations indicate active synthesis processes in neurons relevant for identification.
Review Question: Cytoskeleton
Components: Microtubules, neurofilaments, intermediate filaments.
Functions: Provide structural support, shape, and transportation within the neuron.
Function of Microtubules
Hollow cylinders made of tubulin; integrated with microtubule-associated proteins (MAPs).
Role: Act as "railroad tracks" for axonal transportation.
Neurofilaments
Intermediate filaments consisting of cytokeratin proteins for structural support within neurons.
Microfilaments in Neurons
Composed of actin protein.
**Functions:**Movement of substances to cell membrane, axonal growth, and molecule attachment.
Axonal Transport System
Essential for axonal survival; classified into fast (anterograde and retrograde) and slow types.
Fast transport moves organelles, vesicles, and growth factors at high speeds; poorly understood mechanisms.
Fast Axonal Transport
Involves motor proteins like kinesin (anterograde) and dynein (retrograde) that traverse microtubules.
Parts: Head (ATPase) and tail (cargo-attached).
Synapses
Definition: Connections between neurons or neurons and muscles/glands.
Most common type occurs between axon and dendrite.
Structural Components of Synapses
Presynaptic Element: Typically axon releasing neurotransmitters.
Postsynaptic Element: Receives neurotransmitters and responds variably.
Synaptic Cleft: Gap between presynaptic and postsynaptic elements where neurotransmitters diffuse.
Characteristics of Neurons
Dendrites collect information, soma synthesizes macromolecules, and axons conduct information to other neurons.
Neuronal Classification
By Function: Sensory, motor, interneurons.
By Control: Somatic vs autonomic.
By Structure: Multipolar, bipolar, pseudounipolar, unipolar.
Types of Neurons by Shape
Multipolar: Many dendrites; most common.
Bipolar: Two processes; found in special senses.
Pseudounipolar: One process; involved in somatosensory functions.
Unipolar: Rare in humans; single process.
Types of Glia in PNS
Schwann Cells: Myelinate axons; support injury response and metabolic functions.
Satellite Cells: Surround peripheral neuron cell bodies; provide structural and metabolic support.
Types of Glia in CNS
Oligodendrocytes: Myelination support and protection.
Astrocytes: Regulation of ions and neurotransmitters; control blood flow and structural support.
Microglia: Immune function, debris removal, respond to injury.
Ependymal Cells: Line CNS ventricles, CSF circulation, and hormone transport.
Summary of CNS Components
Cell Types: Neurons, macroglia, microglia.
Functions and Locations: Specific roles in processing, support, and injury response within gray and white matter regions of the CNS.
References
Dalley AF, Agur AMR (2022). Clinically Oriented Anatomy, 9th Ed., Wolters Kluwer.
Vanderah TW, Gould DJ (2021). Nolte’s The Human Brain: An Introduction to its Functional Anatomy, 8th Ed. Elsevier.