Cells of the Nervous System

Neurons:
-Cytology:
--Cell body(=perikaryon) + Neurites(axon + dendrites).
-Classification:
--Golgi type I & Golgi type II
-Myelin sheath on nerve fiber.
-Forming synapses between neurons.
-Small neurons reaches proximal parts where large neurons reaches distal part.

Neuroglia:
-CNS:
--Astrocytes, oligodendrocytes, ependymal cells & microglia.
-PNS:
--Schwann cells + satellite cells

Neuron cytology:
-Cell surface:
--Plasma membrane embedded with proteins -> channels, pumps & receptor.
-Cytoplasm:
--rER, Nissl body(large neurons), mitochondria, golgi apparatus.
--Filamentous organelles: microfilaments, microtubules & neurofilaments.
--lysosomes, lipofuscin, neuromelanin.( remnant of neurotrasmitter )
-Nucleus with prominent nucleolus.

Neurites:
-Axon:
--Surface -> axolemma
--Cytoplasm -> axoplasm
--Collateral branch -> 90 degree branch in middle.
--Terminal branch (Telodendria) -> ends as synaptic turminals. (100 degree)
-Dendrites:
--Dendritic spines -> increasing surface area.

Neurons:
-Cell bodies:
--CNS -> Nuclei
--PNS -> Ganglia
--*Nuclei & ganglia -> Gathering of neurons with same function.
--Spinal cord -> Laminae
--*Board like partition in the spinal cord.
-Axons:
--CNS -> Tract
--CNS -> Fasciculi
--*Pathway -> named by function, Tract -> named by destination.
--*Fasciculi has more than to functional component, can't name by destination.
--PNS -> Nerves

Classification of Neurons:
-Golgi type I (Principal) neurons:
--Projection neurons -> with distal destination.
-Golgi type II neurons:
--Interneurons -> with proximal destination.

Neurohistological techniques:
-Cation stain(Nissl stain), reduce silver methods, myelin stain(Weigert's stain).
-Golgi stain, filling techniques, histochemical stain.
-Electron & confocal microscopy.

Neuroanatomical Research Methods:
-Metabolic marking:
--Radioactively labeled 2-deoxy-D-glucose
--Neurons can only use glucose as the source of energy.
-Axonal transport:
--Anterograde -> from nuclei to fibers.
--Retrograde -> from fibers to nuclei.
-Transynaptic transport -> passes from on neuron to another.

Myelin sheath:
-CNS -> oligodendrocyte ( one to many ) - unmyelinated fibers
-PNS -> Schwann cells ( one to one ) - myelinated fibers
-Node of Ranvier -> saltatory conduction.

Nerve fiber -> axon & myelin surrounding it.

Size & Conduction Velocity of Nerve Fibers:
-Radius increase -> myelin sheath increase -> conduction velocity increase.
-In order of radius ( large -> small ):
--IA:motor to skeletal muscle + sensory from muscle spindle proprioceptive endings.
--IB:Sensory from tendons(tension), Ruffini endings in skin.
--II:Sensory from Meissner's(touch) & pacinian(press) corpuscles & similar endings.
--III:Sensory from small hair follicles and free nerve endings for temp & pain.

Synapes:
-Chemical synapes:
--Neurotransmitters released from synaptic vesicles(presynaptic terminals)
--Diffuse across synaptic cleft, bind on postsynaptic receptor.
--Receptors:
---Ionotropic receptor -> fast transmission.
---Metabotropic receptors -> slow transmission.
-Electrical synapes:
--Common in invertebrates & lower vertebrates (Ex. gap junction)