Lect 1-09-CNS

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LECTURE 1 OUTLINE

CYTOLOGY OF NEURONS

CLASSIFICATION OF NEURONS

SYNAPSES

MYELINATION

NEURONAL CYTOSKELETON

SYNTHESIS AND TRAFFICKING OF NEURONAL PROTEINS

NEURONAL EXTENSION AND MIGRATION

NEURONAL CELL BIOLOGY

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Medical Physiology, Boron and Boulpaep, p. 259

Morphology of a Typical Neuron

Dendrites

Dendritic Spines

Soma (cell body)

Axon

Axon hillock

Initial segment

Myelin sheath

Node of Ranvier

Presynaptic terminal

Synaptic cleft

CYTOLOGY OF NEURONS

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CLASSIFICATION OF NEURONS

Basis for classification

Axonal projection

Dendritic pattern

Number of processes

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Goes to distant

CNS area

Stays in local

CNS areaIntrinsic neuron or

Interneuron

Retinal bipolar cell

Cortical inhibitory neuron

Basis for

classificationFunctional Implication Structure and Examples

Axonal projection

Affects different CNS

areas

Affects only nearby

neurons

Projection neuron or

Principal neuron

Dorsal root ganglion cell

Cortical motor neuron

Medical Physiology, Boron and Boulpaep, p.263

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Basis for


Dendritic pattern

Pyramid-

shaped spread

of dendrites

Radial-shapedspread of

dendrites

Large area for receiving

synaptic input; determines

the pattern of incoming

axons that can interact with

the cell -Pyramid shaped





the cell-Star-shaped

Hippocampal pyramidalneuron

Cortical stellate cell


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Basis for



Number of

processes

One process

exits the cell

body

Two processes

exit the cell

body

Many

processes exit

the cell body

Small area for receiving

synaptic input; highly

specialized function

Small area for receiving

synaptic input; highly

specialized function





the cell

Unipolar neuron

Dorsal root ganglion cell

Bipolar neuron

Retinal bipolar cell

Multipolar neuron

Spinal motor neuron

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Types of Synapses

Axospinous

Axodendritic

Axosomatic

Axoaxonic

SYNAPSES


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Typical anterior spinal motor neuron

A neuron receives multiple inputs and must

integrate the information

Textbook of Medical Physiology, 10th Ed. Guyton and Hall p,516

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MYELINATION

Principles of Neural Science, 4th Ed. Kandel, Schwartz and Jessell, p.81

1. Peripheral Nervous System

Sensory or motor neuron

Schwann cells

Nodes of Ranvier

Myelin composed of proteolipid, sphingomyelin, and myelin specific

proteins

Expression of mylein genes regulated by contact between axon and

Schwann cell

Mesaxon

Mature myelin sheath

SC

Axon

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2. Central Nervous System

Oligodendrocyte (glial cell)

A single oligodendrocyte typically ensheaths several axon processes

Expression of myelin genes appears to depend on astrocytes.


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NEURONAL CYTOSKELETON

Neuronal cytoskeleton is the major intrinsic determinant of the

shape of a neuron and is responsible for the asymmetric

distribution of organelles within the cytoplasm.

1. Microtubules

2. Neurofilaments

3. Microfilaments

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Characteristics of Microtubules

Extend full length

Diameter 25-28 nm

a- and - tubulinTubulin is GTPase

Involved in transport of organelles

Stabilized by microtubule associated

proteins (MAPs)

1. Microtubules


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2. Neurofilaments

Cytokeratin

Most abundant10 nm diameter

Polymerized

Important in neuronal cell structure

Characteristics of Neurofilaments


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3. Microfilaments

Characteristics of Microfilaments

3-5 nm diameter

and g actinInvolved in motility of growth cones and

formation of pre- and post-synapticmorphologic specializations

Dynamic changes in polymerization and

depolymerization

Often found in cell periphery under

plasmalemma


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SYNTHESIS AND TRAFFICKING OF NEURONAL PROTEINS

Proteins are synthesized in the cell body, but must be transported to

the axons and terminalsPrinciples of Neural Science, 4th Ed. Kandel, Schwartz and Jessell, p.93

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Ribosomal RNA is found in the cell body and

dendrites, but not in the axon


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Axoplasmic transport


The primary site of secretion,

the axon terminal, is

considerably distant from the

cell body and dendrites where

secretory proteins are

synthesized

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Movement of membranous organelles

Anterograde transport

Kinesin or kinesin-related proteins

Retrograde transport

Dynein

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Globular heads that bind microtubules

Fan-shaped tail that binds the organelle

Kinesin is a ATPase

Hinge region allows walking along the microtubules


Model for how kinesin may move organelles along microtubules

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Fast anterograde transport

Rate is 410 mm/day

Saltatory movement along microtubules

Disrupted by colchicine and vinblastine

Motor molecule is kinesin

ATP-dependent

Not effected by protein synthesis inhibitors (after incorporation)

Not dependent on the cell body

Mitochondria and vesicles transported

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Experiment establishing axoplasmic transport

[3H] Leucine injected into the dorsal root ganglia in the lumbar region of

the spinal cord and fragments of the sciatic nerve collected at specific

times after injection. Experiment performed by Ochs and colleagues.


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Fast retrograde transport

Rate is 200-300 mm/day

Saltatory movement along microtubules

Motor molecule is dynein

ATP-dependent

Degraded vesicular membrane and absorbed exogenous material

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Slow axoplasmic transport

Anterograde direction only

Rate is 0.2-5 mm/day

Cytoskeletal proteins and cytoplasmic proteins such as

intermediary metabolism enzymes

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NEURONAL EXTENSION AND MIGRATION


Growth cone

Filopodia extend

Cell-matrix

adhesion regulatedby integrins and their

ligands-laminins

Role for actin

microfilaments to

move filopodium

forward (protrusion)

Cell-cell adhesion

controlled by

cadherins, N-CAM

and others

Guidance -growthfactors from target

cells

Grow at rate of slow

axoplasmic transport

Lect 1-09-CNS

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