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Neurocytology

There are 5 types of Neurons:

- Bipolaro Have a single dendrite and single axon leaving the cell body from opposite

sideso Very rare in humans, only found in eye, ear, and olfactory epithelium

- Unipolaro One process leaves cell body and splits into dendrite (central branch) and

axon (peripheral branch) going in opposite direction

- Multipolaro Dendrites protruding from cell body and single axon extending from cell

body

o Most common type of neuron in human body

- Pyramidalo Combination of bipolar and multipolaro Dendrites protruding from cell body as well as an extended stalk of

dendrites, with just a single axon from opposite side of cell body

- Purkinjeo Formed like a tree with the trunk and roots being the axon and the many

branches of the tree being the dendrites extending from a central point, the

cell body

o Found mostly in the cerebellum

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Neuroglia support neurons physically and metabolically.

4 Types of Neuroglia

- Astrocytes- Maintain the blood-brain barrier by covering the blood vessels in the CNS

- Have glycogen storages that they can release for neurons to metabolize

- Collect stray ions and neurotransmitters in extracellular space for recycling- Most common glial cell in the body

- Have many cytoplasmic processes, foot-like extensions, which terminate on

blood vessels, neuronal cells bodies, and axons, and surround synaptic terminals

and clefts. Functions include biochemical and physical support for neurons,insulation, guidance of migrating neurons during development, and repair

following injury. Astrocytes are commonly subdivided into two subclasses:

protoplasmic and fibrous. Fibrous astrocytes contain many filaments in long thinprocesses and are found predominantly in white matter. The protoplasmic form

has frequently branched processes and occurs mostly in gray matter.

- Ependymalcells- Line the ventricles of the brain and the central canal of the spinal cord

- Microglia

- Act as macrophages of CNS

- Originate from blood monocytes

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- Oligodendrocytes

- Produce myelin to insulate AP propagation through neurons of CNS- In the gray matterare called satellite cells and function in fluid and respiratory

exchange. Oligodendrocytes in the white matterform myelin sheaths in the CNS

(Schwann cells form myelin sheaths in the PNS). Each oligodendrocyte suppliesmyelin sheath segments to many axons while each Schwann cell supplies only

one myelin segment.

The Central Nervous System is composed of Gray and White MatterGray Matter

- Contains mostly nerve cell bodies and dendrites

- Also contains axons and supporting glial cells

- Only site in CNS where synapses occur- Makes up the cerebellar cortex of the brain

- In the Cerebellum it has 3 layers:

o Molecular layer

Purkinje cell dendrites fill this layer

o Purkinje cell layer

Contains the purkinje cell bodieso Granular layer

Purkinje cell axons and supporting glial cells

White Matter

- Contains only axons and their supporting glial cells- No synapses in white matter

Neurons are made up of:- Cell body

- Nucleus and nucleolus- Golgi, mitochondria and lysosomes

- Nissl substance

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- Composed of RER cisternae (sheets of RER) alternating with free

polyribosomes

- Found also in dendrites but not in axon or axon hillock- Neurofibrils

- Cytoskeleton of neurons

- Extend throughout neuron- Run through dendrites and extend through axon to terminus

- Are used to carry organelles and other things down axon to terminal for

use in regulating AP at terminus- Axon Hillock

- Start of axon from cell body

- No Nissl substance found here

- Myelin sheath starts here as well- Dendrites

- Receive signals from other neurons for propagation of AP

- Axon

- Microtubules and neurofilaments make up the internal cytoskeleton of axons- Myelin and Schwann cells make up the insulation layer of axons

- Microtubules are used for transport of organelles up and down axons- Organelles attach to microtubules and in an energy dependent process

are transported up or down axon