Set 2- Neurons & Glia

Neurons

- Individual cells in the nervous system that receive, integrate, and transmit information.

- ~85 billion neurons in the human brain

- each neuron receives >1,000 synaptic inputs

Glia

cells in the nervous system that support, nourish, and protect neurons

1. Oligodendrocytes & Schwann cells

2. Astrocytes

3. Microglia

What are the major types of Glia?

Oligodendrocytes (CNS) & Schwann cells (PNS)

wrap around the axon to provide insulation in the form of myelin.

Astrocytes

provide supporting functions for neurons; they buffer potassium ions, take up glutamate released by neurons, and provide metabolic fuel

Microglia

are the resident immune cells of the brain; become activated to help fight off infection and clear cellular debris via phagocytosis

- Excitable cells

- process info

- sense environmental changes

- communicate changes to other neurons

- command body response

Neuron functions

Histology

microscopic study of tissue structure

Nissl Stain

- stains cell bodies

- facilitates the study of cytoarchitecture in the CNS

Golgi stain

- sparsely stains whole cells

- allows imaging of a whole neuron (cell body and neurites)

- Soma (cell body)

- Neurites: axons and dendrites

What did the Golgi Stain reveal?

Golgi stain (reticular theory)

described nervous system as a continuous network

Ramón y Cajal

used Golgi Stain to illustrate Neuron doctrine

Neuron Doctrine (Cajal)

- the nervous system is made up of discrete individual cells

- neurons communicate by contact, not continuity

Transmission Electron Microscope & Images

takes block of tissue and will recreate that neuron & its surrounding neuron

Pyramidal Neuron

Pyramid shaped excitatory glutamate containing neurons located in the cortex and hippocampus.

1. Soma

2. Nucleus

3. Dendrites

4. Axon Hillock

5. Axon

6. Myelin

7. Node of Ranvier

8. Axon Collateral

9. Presynaptic Terminal

10. Synaptic Vesicles

11. Synaptic Cleft

12. Postsynaptic Density

Parts of the neuron

classification and functions within the CNS:

- ex. primary sensory neurons, motor neurons

- Brain region specific neurons

- based on axonal length

- gene expression

- neurotransmitter

- number of neurites

- dendritic and somatic morphology

How to classify neurons?

Golgi type I

long axons, extend from one brain region to another (projection neurons)

Golgi type II

Short axons. Do not extend beyond their immediate brain region. Local circuit neurons

Glia- Astrocytes

most numerous glia in the brain, fill spaces between neurons, influence neurite growth, regulate chemical content of extracellular

Glia- Myelinating

Functional purpose to insulate and protect axons, increase action potential conduction (saltatory conduction)

Glia- Myelinating (Node of Ranvier)

Region where axonal membrane is exposed between adjacent myelinating cells

Glia- Microglia

-specialized form of glia, functions as phagocytes, resident immune cells in the brain

- involved in regulating synapse numbers

- pruning/elimination of synapses

Neurofilaments

What is the structural element made up of largest protein subunit?

microtubule > neurofilament > microfilament

Cell structural element from large to smallest

neuronal membrane

- Phospholipid membrane barrier that encloses cytoplasm

- ~5nm thick

- Protein concentration in membrane varies

- structure of discrete membrane regions influences neuronal function

cytoplasm

contents within a cell membrane (ex. cytosol, organelles, etc.) excluding the nucleus.

Cytosol

watery fluid inside the cell

Organelles

membrane enclosed structures within the soma

- gene expression

- transcription

- RNA processing

Components of a nucleus

Expression of specific genes

How do neurons differ from other cells

Made possible b/c of evolution of DNA & mRNA sequencing advances

How to understand the neuronal-specific genes?

in model organisms, contain detailed specific gene functions in neurons

Influence of genetic engineering & gene targeting technologies

ribosomes

Major spot for protein synthesis

Rough endoplasmic reticulum

proteins synthesized here are destined to be inserted into the membrane

Polyribosomes

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

Cytosolic patterns

What do free ribosomes produce?

Rough ER & Golgi apparatus

Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substances

Mitochondria

- site of cellular respiration (inhale & exhale)

- krebs cycle

- ATP is cell's energy source

Cytoskeleton

- A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement

- internal scaffolding or neuronal membrane

- microtubules

- microfilaments

- neurofilaments

3 structures of cytoskeleton

Microtubules

composed of individual tubulin molecules

- 20nm

Microfilaments

composed of individual actin molecules

- 5nm

Neurofilaments

long polypeptide molecules

- 10nm

Dendrites

Branchlike parts of a neuron that are specialized to receive information.

Postsynaptic

receives signals from axon terminal

axon

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands (length could be less than a millimeter to over a meter long)

Axon hillock

Cone shaped region of an axon where it joins the cell body (beginning)

Axon proper

middle of axon

Axon collaterals

side branches of the main axon

axon terminal

site of synaptic transmission to another neuron

- ER does not extend into axon

- few free ribosomes (no protein synthesis)

- protein composition of axonal membrane is unique

difference between axon and soma

axoplasmic transport

an active process by which substances are propelled along microtubules that run the length of the axon

anterograde

soma to terminal

retrograde

terminal to soma transport

Kinesin

motor proteins in anterograde transport

dynein

motor proteins in retrograde transport

Axon terminal

- no microtubules in terminal

- presence of synaptic vesicles

- abundance of membrane proteins

- large number of mitochondria

Synapse

A junction where information is transmitted from one neuron to the next.

leads to mental disorders

What happens if a synaptic transmission dysfunctions?