Summary Full explanation of Nervous system

Introduction to Nervous Tissue Histology

 Nervous system includes cells that resemble stars and neurons branching like bare
trees.
 Purpose: Send and receive electrical signals, facilitating body communication.

Organization of the Nervous System
 Central Nervous System (CNS): Brain and spinal cord.
 Peripheral Nervous System (PNS): Nerves branching out from the CNS.

Anatomy of Nerves and Neurons
 Nerves are made of clusters of smaller neurons, similar to electrical cables.
o Transverse Cross-Section: Shows nerve as a "busy" cluster of cells.
o Longitudinal Section: Shows axons running along the nerve's length.
Connective Tissue Layers around Nerves
 Epineurium: Outermost layer; dense, irregular connective tissue.
 Perineurium: Wraps each bundle (fascicle) of neurons.
 Endoneurium: Surrounds individual neuron cells.

Neuron Structure
 Neuron Components:
o Cell Body (Soma): Contains nucleus and organelles.
o Dendrites: Branches that receive impulses from other cells.
o Axon Hillock: Starting point for impulses traveling down the axon.
o Axon: Long structure carrying electrical impulses; can be over a meter long.
o Axon Terminals: End branches that release neurotransmitters to communicate
with other cells.

Types of Neurons
 Myelinated vs. Unmyelinated Neurons:
o Myelinated: Have a myelin sheath (fatty layer) that speeds up signal
transmission.
o Unmyelinated: Lack myelin, resulting in slower signal transmission.
Neuron Types by Shape and Function
 Multipolar Neurons: Most common; one axon with multiple dendrites, found in
brain and spinal cord.
 Bipolar Neurons: One axon and one dendritic tree; found in sensory organs like the
retina.
 Unipolar Neurons: One axon, no dendrites; often found in sensory pathways.

Cell Types in Nervous Tissue
 Neurons: Main signaling cells.
 Glial Cells: Supportive cells; provide structure, protection, and metabolic support.
Types of Glial Cells

,  Astrocytes: Star-shaped; regulate the blood-brain barrier, support synapses, and clear
excess neurotransmitters.
 Oligodendrocytes: Produce myelin in the CNS (brain and spinal cord).
 Schwann Cells: Produce myelin in the PNS.

Myelin and Signal Transmission
 Myelin Sheath: Fatty layer around axons that increases signal speed.
o White Matter: Myelinated axons; faster signal transmission.
o Gray Matter: Unmyelinated fibers; slower transmission.
Types of Axons by Speed and Diameter
 Type 1a Fibers: 4-20 µm wide, myelinated, transmit signals at 70-120 m/s.
 Type B Fibers: 1-4 µm wide, myelinated, slower than Type 1a.
 Type C Fibers: 0.2-1.5 µm wide, unmyelinated, conduct at 0.5-2.5 m/s.

Central Nervous System (CNS) Histology
 Spinal Cord:
o White Matter: Made of myelinated fibers.
o Gray Matter: Dense, unmyelinated fibers arranged in horn-like structures
(anterior, lateral, dorsal horns).
 Brain:
o Meninges: Layers surrounding the brain.
 Dura Mater: Outer layer, dense connective tissue.
 Arachnoid Layer: Middle layer, spiderweb-like.
 Pia Mater: Innermost, delicate layer.
o Cerebrum Layers:
 Cerebral Cortex: Outer layer with six layers.
 Subcortical White Matter: Deep layer under the cortex.

Example Explanation of Histology Terminology
 Epineurium, Perineurium, Endoneurium: Similar to muscle layers (epimysium,
perimysium, endomysium) but named for nervous tissue.
 Myelinated vs. Unmyelinated: Like comparing insulated and bare electrical wires;
myelin acts as insulation for faster impulse travel.

Overview of Action Potential in Neurons
 Communication in Neurons:
o Dendrites: Receive incoming signals.
o Axon: Carries outgoing signals to the nerve terminal for communication with
other cells.
o Action Potential: Electrical signal that travels along the axon, allowing fast
communication across the neuron.

Resting Membrane Potential
 Definition: Electrical difference across the neuron membrane when at rest.