Chapter 2: Neurons and Glia Neuroscience: Exploring the Brain, 4e Chapter 2: Neurons and Glia

Introduction “Neurophilosophy” No separation of mind and brain Glia and neurons Glia insulate, support, and nourish neurons. Neurons Process information Sense environmental changes Communicate changes to other neurons Command body response

The Neuron Doctrine Histology Microscopic study of tissue structure Nissl stain Facilitates the study of cytoarchitecture in the CNS

The Neuron Doctrine—(cont.) Golgi stain (developed by Camillo Golgi) revealed two parts of neurons: Soma and perikaryon Neurites: axons and dendrites

Basic Parts of a Neuron

The Neuron Doctrine—(cont.) Cajal’s contribution Neural circuitry Neurons communicate by contact, not continuity. Neuron doctrine Neurons adhere to cell theory. Use of Golgi stain

Neurites in Contact, Not Continuity

The Prototypical Neuron The soma Cytosol: watery fluid inside the cell Organelles: membrane-enclosed structures within the soma Cytoplasm: contents within a cell membrane (e.g., organelles, excluding the nucleus)

The Prototypical Neuron—(cont.) The nucleus Gene expression Transcription RNA processing

Internal Structure of a Typical Neuron

The Prototypical Neuron—(cont.) Neuronal genes, genetic variation, and genetic engineering Neurons differ from other cells because of specific genes. Sequencing of human genome Genetic basis of many diseases of the nervous system Role of genetic engineering and gene targeting

The Prototypical Neuron—(cont.) The soma—(cont.) Ribosomes the major site for protein synthesis Rough endoplasmic reticulum

The Prototypical Neuron—(cont.) The soma—(cont.) Protein synthesis also on free ribosomes; polyribosomes

The Prototypical Neuron—(cont.) The soma—(cont.) Smooth ER and Golgi apparatus Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substances

The Prototypical Neuron—(cont.) The soma—(cont.) Mitochondria Site of cellular respiration (inhale and exhale) Krebs cycle ATP is cell’s energy source.

The Prototypical Neuron—(cont.) The neuronal membrane Barrier that encloses cytoplasm ~5 nm thick Protein concentration in membrane varies. Structure of discrete membrane regions influences neuronal function.

The Prototypical Neuron—(cont.) The cytoskeleton Not static Internal scaffolding of neuronal membrane Three structures Microtubules Microfilaments Neurofilaments

The Prototypical Neuron—(cont.) The axon Axon hillock (beginning) Axon proper (middle) Axon terminal (end) Differences between axon and soma ER does not extend into axon. Protein composition: unique

The Prototypical Neuron—(cont.) The axon terminal Differences between the cytoplasm of axon terminal and axon No microtubules in terminal Presence of synaptic vesicles Abundance of membrane proteins Large number of mitochondria

The Prototypical Neuron—(cont.) The synapse Synaptic transmission Electrical-to-chemical-to- electrical transformation Synaptic transmission dysfunction leads to mental disorders.

The Prototypical Neuron—(cont.) Axoplasmic transport Anterograde (soma to terminal) vs. retrograde (terminal to soma) transport

The Prototypical Neuron—(cont.) Dendrites “Antennae” of neurons Dendritic tree Synapse—receptors Dendritic spines Postsynaptic (receives signals from axon terminal)

Classifying Neurons Classification based on number of neurites Single neurite Unipolar Two or more neurites Bipolar: two Multipolar: more than two

Classifying Neurons—(cont.) Classification based on dendritic and somatic morphology Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped) Spiny or aspinous

Classifying Neurons—(cont.) Classification by connections within the CNS Primary sensory neurons, motor neurons, interneurons Classification based on axonal length Golgi type I Golgi type II

Classifying Neurons—(cont.) Classification based on gene expression Creation of transgenic mice Example of “ChAT-Cre mice” Green fluorescent protein Classification based on neurotransmitter type

Glia Function of glia Support neuronal functions Astrocytes Most numerous glia in the brain Fill spaces between neurons Influence neurite growth Regulate chemical content of extracellular space Astrocyte

Glia—(cont.) Myelinating glia Oligodendroglia (in CNS) Schwann cells (in PNS) Insulate axons Cross section of myelinated nerve fibers

Glia—(cont.) Myelinating glia—(cont.) Oligodendroglial cells Node of Ranvier Region where axonal membrane is exposed

Other Non-Neuronal Cells Ependymal cells Microglia as phagocytes (immune function) Vasculature

Concluding Remarks Structural characteristics of the neuron provide insight into how neurons and their different parts work. Structure correlates with function.