Chapter 2

Neurophilosophy

• No separation of mind and brain

• Mind, body and soul are not different things

• Monism

• W. Richie Russell (from Brain Memory Learning: A Neurologist's View, 1959)

Cell Theory

All tissue is composed of microscopic units called cells

• Theodor Schwann (1839)

Golgi Stain

cell body (soma)/perikaryon

Perikaryon

central region containing nucleus

Golgi’s Drawings

showed neurons in a reticulum (network), hence “Reticular Theory”

• rat hippocampus

The Neuron Doctrine

The principle that individual neurons are the elementary signalling elements of the nervous system

• Santiago Ramon y Cajal (1852-1926)

Cajal’s contribution:

• Neural circuitry

• Neurons communicate by contact, not continuity

Neuron Doctrine:

• Neurons adhere to cell theory

• Use of Golgi stain

Franz Nissl (~1885)

• Medicine

• Pathologist

Nissl Stain

• Fixation – alcohol

• Cresyl violet

• Nissl bodies - rER

Histology

The microscopic study of tissue structure

Advances in Fixation Procedures: The Nissl Stain (1800s)

• Stains rER in the cell body and dendrites

• Facilitates the study of cytoarchitecture in the CNS

• Does not produce much detail about the structure of the neuron

What is the relationship between Nissl bodies and the rough endoplasmic reticulum (rER)?

• Nissl bodies are the neuron-specific, visible form of rough endoplasmic reticulum + ribosomes

• They are crucial for producing the proteins neurons need to function

Cell Body (Soma)

Nucleus

• typically gives rise to a single axon

Neurites

• Axons

• Dendrites

Unipolar

• Single process (invertebrate)

• Specialized segments

Bipolar

• Dendrites carry info to the cell body

• Axon transmits it to other cells

Multipolar

Dominate vertebrate nervous system

Single Neurite

Unipolar

Two or More Neurites

• Bipolar - two neurites

• Multipolar- more than two

Microscopy

• Light microscope

• Electron microscope

• Fluorescence microscope

• Confocal microscope

• Two-photon excitation microscope (2P scope)

Classifying Neurons

Based on dendritic and somatic morphologies:

• can be spiny or aspinous

Further Classification:

By connections within the CNS (e.g.):

• Primary sensory neurons,

• Motor neurons,

• Interneurons

Based on neurotransmitter type:

• e.g., Cholinergic = Acetycholine at synapses

Stellate Cells

star-shaped

Pyramidal Cells

pyramid-shaped

Dendrites

• “Antennae” of neurons

• Dendritic tree Synapse—receptors

• Dendritic spines:

  • Small protrusions of membrane

  • Postsynaptic (receives signals from axon terminal)