Cytology Nikon ©

DENT/OBHS 131Neuroscience

reticular theory1886: Golgi-techniques

1888: Ramon y Cajal1897: Sherrington

Building blocks

Learning Objectives

Compare and contrast the morphology & function of neurons and glial cells

Explain neuronal polarization in terms of information signaling

Be able to give reasons for the energetic demands of neurons

Discuss the different roles of different categories of glial cells

Describe the relationship of neurons and glia with respect to synaptic signaling and action potential propagation

What are the most important types of cells in the brain?

1. Neurons

2. Glia

3. Neither neurons nor glia

4. Other cells

Types of cell

Neurons - nerve cells 100 billion

Glial cells ≈ 10 X neurons

50:50 volumeCNS vs PNS

autonomic (week 10) motor & sensory (weeks 5-8)

Learning Objective #2

Explain neuronal polarization in terms of information signaling

Basic function of a neuron

Transmit information from here to there

Parts of a neuron

Dendrites receive information

Soma synthesize stuff electrical integration

Axon information conduction

Axon terminal transmit information

En masse

Segregationwhitegray

Gross lab(week 2)

Same but different

Multipolar (typical)single axonmultiple dendrites

BipolarPseudo-unipolar

What type of cell is the large neuron?

1. Purkinje

2. Pyramidal

3. Granule

4. Motor

10

Pseudounipolar neurons….

single axon - bifurcatesclassical example - sensory fibers

Classes of neurons

SensoryMotorInterneuronsProjection

somatosensory (weeks 5-6) sensory-motor integration (week 6)

motor (weeks 7-8)

Synapses

Dendritic shafts / spinesinhibitory / excitatory(weeks 3-4)

synaptotagmin

MAP2

Axons are long

≈ 5ft motor neuron (e.g. Sciatic nerve)

≈99% cytoplasmHow to accomplish fast signaling (week 3)?

How to maintain structure?How to communicate between distant parts?

Cytoskeleton

axon growth cone

(Ken Balazovich)

Cross section of dendrite

Neurofilaments filamentous actin

Microtubules Tubulin (10% brain protein)

substrate for axonal transport

MAPs e.g. Tau (weeks 10-

11)

Active transport

Slow:few mm / day

Fast< 400 mm /day

RetroAntero

kinesin dynein

molecular motors

Ribosomes: Nissl substance

In dendrites (not largely in axons)may offset long transport distances in axons

Local protein synthesis at the base of spines - plasticity (weeks 10-11)

Leaching Objective #3

Be able to give reasons for the energetic demands of neurons

High energy use

30-40 % total energy consumption at rest Maintain ionic gradients (ion-exchange pumps) Protein synthesis Axonal transport

Mitochondria Site of oxidative metabolism - ATP Brain exclusively dependent on glucose

Found throughout the perikaryon, dendrites, spines, axons and in synaptic terminals

Other organelles

Similar to other cells

Nucleus: only a few 1000 CNS specific genes - encode CNS proteins

extensive RNA splicing

Golgi: post-translational modification

Relationship to other cells

Brain Glue

Special properties of glia?

Compared to neurons: (Astrocytes) star-shaped & largely lack polarity

No synapses - cells communicate through gap-junctions

Relatively low energy requirement; function well under anaerobic conditions

phalloidintubulinDAPI

Learning Objective #4

Discuss the different roles of different categories of glial cells

Key roles of glia

Remove glutamate and other amino-acids from extracellular space: de-toxify the brain

Form myelin to insulate axonsServe numerous homeostatic functions

Can and do proliferate postnatally

Classification

Radial glia - development (next session)

Astrocyte protoplasmic astrocyte (Type 1) fibrous astrocyte (Type 2)

Schwann cell Oligodendrocyte

Macroglia <=> Microglia

Microglia

engulfing a dying oligodendrocyte:

phagocytotic cells in the nervous system

blood derived cells comparable to macrophages

remove debris from the brain following injury and constitute an important defense system against pathogens.

Radial glia

Development (week 1)

neuronal guidance

Learning Objective #5

Describe the relationship of neurons and glia with respect to synaptic signaling and action potential propagation

Schwann cell

Myelination in the PNS

Myelin sheet

One-to-one

Gap junctions and disease

Charcot-Marie-Tooth diseaseprogressive loss of PNS axons - weakness, atrophy

Nodes of Ranvier

fast AP propagation (week 3)

Oligodendrocytes

1:10 to 1:50

Unmyelinated CNS fibers

CNS vs. PNS summary

Astrocytic end feet……

contact blood vessels

Astrocytic endfoot

Induce the blood-brain-barrier

Active transport

From here to there…..

Buffering of extracellular ions

Extracellular space is very narrow=> small ionic fluxes cause large concentration changes

Astrocytes are not really star-shaped

non-overlapping

space-filling

(Bushong et al., 2002)

Transmitter “shuttle”

Nervous system regeneration

The CNS does not regenerate while the PNS does

This is NOT due to differences in central

and peripheral neurons but due to differences in their glia

CNS oligodendrocytes actively suppress regeneration reactive gliosis

PNS Schwann cells promote it

Glia versus neuron - difference?excitability

(Bergles et al., 1997)