Cells of Nervous system

Huge Number of Cells:
- Composed of numerous separate but interconnected cells.

Neuron:
- Primary function as interconnected information processors essential for all tasks of the nervous system.
- Specialized for the reception, conduction, and transmission of electrochemical signals.
- Human brain has approximately 86 billion neurons.
Glial Cells (Neuroglial Cells):
- Supportive role to neurons.
- Provide scaffolding for the nervous system.
- Help neurons align for communication, provide insulation, transport nutrients and waste products, mediate immune responses, etc.

Historical Background:
- Earliest microscopes were developed in the late 1500s.
- In 1837, Johann Purkinje identified brain cells known as Purkinje cells.
- Delays in discovery were not due to the minuteness of cells.
Golgi Stain:
- Discovered in 1872 by Camillo Golgi through trial and error.
- Enabled visibility of individual neurons in silhouette but no internal details.
- Described as a fortunate mistake, notable for its influence on neuroscience.
Ramon y Cajal's Insight:
- Cajal noted the surprising effectiveness of the chrome-silver reaction.
- His observations remained largely unrecognized by the broader scientific community.

Pioneering Neuroscience:
- Spanish physician and artist known for his detailed drawings of the nervous system.
- Utilized Golgi’s methods on infant brains for clarity of neuron structure.
- Faced a rough childhood and strict academic upbringing.

Recognition of Contributions:
- Shared between Golgi and Cajal for their significant contributions to understanding nervous system structure.
- Acceptance speeches revealed a fundamental disagreement.
- Cajal supported the Neuron Doctrine (individual cells), while Golgi argued the Reticular Theory (a mesh-like structure).

Developed in the 1980s by Franz Nissl.
- Effective in binding only to structures in neuron cell bodies.
- Commonly used to estimate cell body counts via staining.

Technique involving thin slices of neural tissue treated with electron-absorbing substances.
Produces detailed 3D structures of neurons (example: a single neuron with 5,600 connections).

Plasma Membrane:
- Separates cell interior from the external environment and controls movement of substances.
Nucleus:
- Enclosed by a nuclear envelope, containing DNA for hereditary control.
Endoplasmic Reticulum (ER):
- Smooth ER: Synthesizes lipids, detoxifies.
- Rough ER: Modifies and transports proteins.
Ribosomes:
- Sites of protein synthesis, located in the cytoplasm or on the ER.
Mitochondria:
- Responsible for aerobic metabolism and ATP production.
Cytoplasm:
- The fluid interior where cellular processes occur.

Diversity in Neuron Types:
- All neurons include soma (cell body); most have dendrites, axons, and presynaptic terminals.
Function-Related Structure:
- Purkinje Cells: Highly branched dendrites, receiving input from up to 200,000 neurons.
- Bipolar Neurons: Short dendritic branches receiving input from two other cells.

Soma (Cell Body):
- Metabolic center of the neuron containing organelles.
Dendrites:
- Short, branched structures serving as input sites to collect information.
- Surface lined with synaptic receptors.
Axons:
- Transmit information from cell body to other neurons or muscles.
- Can be long, extending several feet.
Axon Terminals:
- Branches forming presynaptic terminals that release neurotransmitters at synapses.
Myelin Sheath:
- Insulatory material that increases communication speed.
Nodes of Ranvier:
- Interruptions in the myelin sheath facilitating faster transmission.

External Features:
- Cell Membrane: Encloses the neuron.
- Synapses: Gaps for chemical signal transmission.
- Axon Hillock: Cone-shaped region where axon meets cell body.

Afferent Neurons:
- Bring information into a structure (e.g., sensory neurons).
Efferent Neurons:
- Carry information away (e.g., motor neurons).
Interneurons/Intrinsic Neurons:
- Contained within a single brain structure, integrating neuronal activity.

Afferent Example:
- Sensory neurons report touch from a hot stove to the brain.
Efferent Example:
- Motor neurons relay signals from the brain to hand muscles.
Interneuron Example:
- Thalamus, integral in sensory processing.

Unipolar Neurons: One process, not in humans; mostly in invertebrates.
Pseudo Unipolar Neurons: One neurite dividing into two. Found in sensory neurons.
Bipolar Neurons: Two processes; found in retina and olfactory epithelium.
Multipolar Neurons: More than two processes; most common type (e.g., Purkinje cells).
Interneurons: Short axon or no axon, integrating activity within a structure.

Known as “Nerve Glue,” making up 50% of the nervous system’s volume.
Support neurons by buffering them, providing nutrients and oxygen, acting as housekeepers for damaged cells, and forming myelin sheaths.
Glial tumors (gliomas) are the most prevalent form of brain tumors.

Oligodendrocytes: Myelin-forming cells in CNS.
Schwann Cells: Myelin-forming cells in PNS.
Microglia: Scavenger cells that respond to injury.
Astrocytes: Star-shaped cells that maintain homeostasis and structural support.

Guide migrating neurons and axons/dendrites during embryonic development; become other glial types post-development.

Largest glial cells with structural and regulatory roles, including nutrient delivery, ionic balance, neurotransmitter reuptake, and blood-brain barrier maintenance.

Neurons mainly depend on glucose and require a steady oxygen supply for metabolism.
Thiamine (Vitamin B1) is necessary for glucose utilization; deficiency can lead to Korsakoff’s syndrome.