Neurotransmission

Synapses:
-Chemical synapses:
--About 20nm, wider than electrical synapse.
-Electrical synapses:
--2~3nm, forming gap junctions.
--When gap juntions exist problem, it might cause hereditary disease.

Synapses & Neuromuscular junctions:
-Synapse is used for integration for messages.
--Doesn't always have action when recieving stimulation.
--*Proteins accumulate at postsynaptic side -> Postsynaptic density.
-Neuromuscular junction is between motor neuron & skeletal muscle fibers.
--One stimulation results into on action or movement.
--*Juntional fold -> increasing the surface area.
--*Synaptic vesicles fuses with the presynaptic membrane -> electric capacity (++)

Neurotranmitter -> Synthesis, Storage, Release, Action, Termination.

Neurotransmission:
-Ca2+ - dependenct release.
--Determination step -> vesicle getting close to membrane.
--Quantal Release:
---Ca2+ open the channel in great amount, kicking out Mg2+.
---Mg2+ stucks the channel, while lack Mg2+ -> Quantal Release.
-Activation of neurotransmitter receptor.
--Including NMDA Receptor & GABA Receptor.
-Termination of neurotransmitter activation.
--Ach: G-protein couple receptor.
--Dopamine(DA):
---Dopamine increases -> raises emotion -> split personality.
---Medicine blockage of dopamine return to pre-synapse decreases melancholy.

Presynaptic & Postsynaptic inhibition.

Ionotropic receptors(ligand-gated ion channels)
Metabotropic receptors(G-protein coupled receptors)

Neurotransmitters:
-Acetylcholine:
--Nicotinic receptors & M1, M2, M3, M4, M5 receptors.
-Catcholamines:
--Dopamine -> D1, D2, D3, D4, D5 receptors.
--Norepinephrine -> alpha(1,2) & Beta(1,2,3) receptors.
--Epinephrine.
-Amino Acids:
--Excitatory Amino Acids(EAAs)
---Glutamate(Aspartate) -> NMDA, AMPA & kinate receptors, metabotropic receptors.
--Inhibitory Amino Acids(IAAs)
---GABA -> GABA(A) & GABA(B) receptors.

Satellite Cells - PNS Neuroglia

Also called "Ganglionic gliocytes"
-Appears only with peripheral ganlia.

Schwann Cells - PNS Neuroglia

Sometimes called "neurolemmocytes":
-Forming myelin sheath around nerve fibers.

One Schwann cell ensheathes ..
-One myelinated axon or several unmyelinated axons.

Both myelin sheath and nodes of Ranvier are covered by a basal lamina.

Nodes of Ranvier:
-Interruptions in myelin sheath, exposing the axon.
-Result in saltatory conduction.

Microglia - CNS Neuroglia

-Smallest.
-With scant cytoplasm.
-Oval to triangular nucleus.
-Irregular short process.

Possibly derived from mononuclear phagocytes.

Function as phagocytes in CNS:
-cleaning debris and damaged structures (like phagocytes in PNS).

Ependymal Cells - CNS Neuroglia

Cell type -> low columnar to cuboidal epithelial.

Lining ventricles of brain & central canal of spinal cords.

Most are ciliated -> facilitating movements of cerebrospinal fluid(CSF).

Choroidal ependyma & choroid plexus epithelium:
-Special ependymal cells on surface of choroid plexus.
-Producing the cerebrospinal fluid(CSF).

Tanycytes:
-Found in floor of the 3rd ventricle.
-Involved in endocrine control of enterior pituitary.

Oligodendrocytes - CNS Neuroglia

Present in both gray & white matter of CNS.

Smaller & contain lesser processes with sparse branches.

Nuclei smaller, rounder & denser.

Cytoplasm is denser and contain large quantities of..
-Free ribosomes, rER, mitochondra & microtubules.

Classification:
-Interfascicular Oligodendrocytes:
--Found in rows among myelinated axons.
-Satellite Oligodendrocytes:
--Surround cell body of some large neurons.

Astrocytes - CNS Neuroglia

Largest & most numerous & most elaborate of all glial elements

Distinct cytoplasmic bundles(intermediate filaments):
-Glial Fibrillar Acidic Protein (GFAP)

Form pervascular end feet by processes:
-Blood-Brain Barrier(BBB).
-External & internal limiting membranes lining ventricular system.

Scavenging ions and remnants of neuronal metabolism.

Contribute to energy metabolism by releasing glucose from stored glycogen.

Corpora amylacea:
-Clusters of glycoproteins and lipoproteins contained in processes.

Recruit cellular scar tissue to damaged areas.

Abnormal increase of astrocytes near trauma -> gliosis.

-Fibrous astrocyte:
--Mostly in white matter of CNS, with long unbranched proccesses.
-Protoplasmic astrocytes:
--In gray matter of CNS.
--Stellate-shaped cell body with large nucleus.
--Many short banching process.
--Some surrounds synapses and nodes of Ranvier.