NEURONS AND GLIA
CELLS IN THE NERVOUS SYSTEM
Glia
Insulates, supports,
and nourishes
neurons
Neurons
Process information
Sense environmental changes
Communicate changes to other neurons
Command body response
THE NEURON DOCTRINE
Cells are in the range of 0.01 – 0.05 mm of diameter
Need for techniques that allow to see such small structures
Histology
Microscopic study of tissue structure
The Nissl Stain (late XIX century)
Colors selectively only part of the cell (Nissl body)
Facilitates the study of cytoarchitecture in the CNS
Differentiation between neuron and glia
The Golgi Stain (1873)
Revealed the entire structure of the neuron
THE NEURON DOCTRINE
THE NEURON DOCTRINE
Camillo Golgi’s reticular theory
Neurites of different cells are fused together to form a continuous reticulum, a
network (like blood circulation)
Santiago Ramon y Cajal’s neuron doctrine
Neuron are not continuous one another but communicate by contact
Shared the 1906 Nobel Prize in
Physiology or Medicine
THE NEURON
Neuronal membrane
separate the inside from the outside
The Soma
Cytosol: Watery fluid inside the cell
Organelles: Membrane-enclosed
structures within the soma
Nucleus
Rough Endoplasmatic Reticulum,
Smooth Endoplasmatic Reticulum,
Golgi Apparatus
Mitochondria
Cytoplasm: Contents within a cell
membrane (e.g., organelles, excluding
the nucleus)
THE NUCLEUS
Contains chromosomes that have the
genetic material (DNA)
Genes: segment of DNA
Gene expression: reading of DNA in order
to synthesize proteins
Protein synthesis happen in the cytoplasm
RNA is the messenger that carry the
information contained in the DNA to the
cytoplasm
THE NUCLEUS
The enzyme RNA polymerase binds to the promoter of the gene in order to initiate
transcription
Exons: coding regions
Introns: non –coding regions
In the cytoplasm mRNA transcript
is used to assemble proteins
from amino acids
DNA
transcription
mRNA
translation
Proteins
ROUGH ENDOPLASMATIC RETICULUM
Major site for protein synthesis
Contains ribosomes attached to the
ER and free ribosomes
Cytosol
Membrane
SMOOTH ER and GOLGI APPARATUS
Sites for preparing/sorting proteins for delivery to different cell regions (trafficking)
and regulating substances
THE MITOCHONDRION
Site of cellular respiration (inhale and
exhale)
Pyruvic acid and O2, trough the Krebs
cycle are transformed in ATP and CO2
1 Pyruvic acid = 17 ATP
ATP- cell’s energy source (by breakdown
of ATP in ADP)
THE NEURONAL MEMBRANE
Barrier that encloses cytoplasm
~5 nm thick
Protein concentration in membrane varies
Structure of discrete membrane regions influences neuronal
function
THE CYTOSKELETON
Not static
Internal scaffolding of neuronal membrane
Three “bones”
Microtubules
Microfilaments
Neurofilaments
Microtubules
Big and run longitudinally along the neuron.
Microfilaments
Same size of the membrane. Role in changing cell
shape
Neurofilaments
Mediam size. Structurally very strong
THE AXON
The Axon is specialized for the transfer
information over long distances
Axon hillock (beginning)
Axon proper (middle)
Axon terminal (end)
Differences between axon and soma
ER does not extend into axon
(This means no protein synthesis there)
Protein composition: Unique
Variable diameter and length
THE SYNAPSE
The axon terminal is the site of contact with
another neuron or cell (synapse) and
transfer of information (synaptic
transmission)
In the Axon Terminal there are no
microtubules
Presence of synaptic vesicles (contain
neurotransmitter)
Abundance of membrane proteins post
synapsis)
Large number of mitochondria
THE AXOPLASMIC TRANSPORT
Allows the transport of the proteins
synthesized in the soma to the axon
terminal
Anterograde (soma to terminal):
could be fast (1000mm per day) or
slow (1-10 mm per day). Legs are
Kinesin
Retrograde (terminal to soma)
transport: feedback information.
Legs are dynein
THE DENDRITE
“Antennae” of neurons
All the dendrites of a neuron are called dendritic tree
Dendritic spines
Postsynaptic: receives signals from axon terminal by using protein
molecules called receptors that detect neurotransmitters in the synaptic
cleft
CLASSIFICATION OF NEURONS
Classification Based on the Number of Neurites
Single neurite
Unipolar
Two or more neurites
Bipolar- two
Multipolar- more than two
Classification Based on Dendritic and Somatic Morphologies
Stellate cells (star-shaped) and pyramidal cells (pyramidshaped)
Spiny or aspinous
CLASSIFICATION OF NEURONS
Further Classification
By connections within the CNS
Primary sensory neurons, motor neurons, interneurons
Based on axonal length
Golgi Type I - long axon, projection neurons
Golgi Type II - short axon, local circuit neurons
Based on neurotransmitter type
e.g., – Cholinergic = Acetycholine at synapses
GLIA
Mainly supports neuronal functions
Astrocytes
Most numerous glia in the brain
Fill spaces between neurons (Influence
neurite growth)
Regulate the chemical context of the
external environment of the neurons
Myelinating Glia
Oligodendroglia (in CNS) and Schwann
cells (in PNS) insulate axons
Node of Ranvier: region where the
axonal membrane is exposed