Chapters 2 and 3
Structure and Function of the Nervous System
Chemical Signaling by Neurotransmitters and Hormones

Neuron Structure
Three main features of every neuron
Dendrites
Treelike projections from the soma that receive information from other cells
Constantly modified and change shape rapidly in response to changes in synaptic transmission
Soma
Cell boy
Contains the nucleus and other organelles that maintain metabolic function
Axon
Single tubular extension that conducts the electrical signal from the cell body to the terminal buttons on the axon terminals
Other structures
Semipermeable Membrane
Encloses each neuron cell
Cytoplasm
Fills the cells
Salty, gelatinous fluid
Extracellular Fluid
Salty fluid
Neurons take oxygen, nutrients, and drugs from this fluid and secrete waste products into it
These waste products ultimately reach the blood and are filtered out by the kidneys
Mitochondria
Generate energy from glucose in the form of ATP
Found particularly where energy needs are great
Neurons use large quantities of ATP
Components of Dendrites
Synapse
The gap between two cells where transmission takes place
Convergence
The act of a neuron receiving and integrating a vast amount of information from many cells
Divergence
Information being transmitted to a few neurons, or thousands
Dendritic Spines
Increase the receiving surface area
Constantly modified and change shape rapidly in response to changes in synaptic transmission
Long-lasting changes in synaptic activity change the number and shape of dendritic spines
Thin  Mushroom-shaped
Relationships Between Spines and Learning
Mental Retardation
Individuals with mental retardation have dendritic spines that are unusually small and immature-looking
Results from either:
Failure of maturation of small spines into larger spines
Inability to maintain spine structure
It is impossible to retain knowledge acquired during development without the large spines
Thus, small spines result in intellectual deficiencies
Schizophrenia
Have normally sized dendritic spines, but reduced spine density in the prefrontal cortex
They have normal intelligence, but there is still poor connectivity between neurons
Symptoms
Poor working memory, lack of attention, poor episodic memory, low motivation
Axons and Terminal Buttons
Axons are tubular structures filled with axoplasm
Vary in both length and diameter
Function
Transmit the electrical signal (action potential) that is generated at the axon hillock down the length of the axon to its terminals
Axon Collaterals
The branches of an axon
There is only one axon per neuron, but they branch
Terminal Buttons
Enlargements at the end of axons
Contain synaptic vesicles or neurotransmitters that allow for chemical transmission in the synaptic cleft to adjacent neurons
Myelin
A fatty insulating coating
Not a continuous sheath
Thicker myelin indicates faster conduction
Created by concentric layers of glial cells
Two types of glial cells
Schwann Cells
Myelinate peripheral nerves
Serve muscles, organs, glands
Oligodendrocytes
Myelinate nerves within the brain and spinal cord
Nodes of Ranvier
Breaks in the myelin sheath where action potentials are regenerated during conduction along the axon
Soma
Cell body is responsible for the metabolic care of the neuron
Functions
Synthesizes proteins that are needed throughout the cell for growth and maintenance
Axoplasmic Transport
How proteins are moved to their destinations in neurons
Depends on the structure of the cytoskeleton
Microtubules provide a stationary track along which small packets of newly synthesized proteins are carried by motor proteins
Anterograde
Direction toward the axon terminal
“Forward”
Retrograde
Direction toward the soma
“Backward”
Protein Synthesis
Chromosomes reside in the nucleus
Long strands of DNA that contain small portions, genes, that code for the manufacture of a specific protein
“Coding Region”
Region that provides the “recipe” for a specific protein, such as a receptor or an enzyme
Each