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Introduction to Neurons
Fundamental Units: Neurons are the fundamental units of the nervous system, forming the basis for its powerful information processing capabilities.
Specialized Functions:
Specialized for transmitting and receiving information.
Communicate with each other.
Communicate with other cell types and tissues, such as muscles or glands.
Carry sensory information from the rest of the body to the brain.
Prevalence and Complexity:
Current estimates suggest approximately neurons in a typical human brain.
Neurons create complex circuitry, with each neuron forming many connections (typically thousands) with other neurons.
This results in hundreds of trillions to potentially more than a quadrillion areas in the human brain where neurons communicate.
Diversity in Form: While a common neuron image is used for discussion, neurons come in over a thousand different types, shapes, and sizes, though most share the same general components.
Basic Principles of Neuron Communication
Signaling Mechanisms: Most neurons use electrical and chemical signals to send messages throughout the brain.
Electrical Signals (Action Potentials):
Main type of electrical signal.
Created when charged particles called ions flow into neurons.
Generate an electrical impulse that travels from one end of a neuron to another.
Chemical Signals (Neurotransmitters):
Action potentials can cause the release of neurotransmitters.
Neurotransmitters travel from one neuron to the next, either generating or inhibiting a response in the postsynaptic neuron.
Speed: Neurons can spread signals throughout the brain in a fraction of a second using these mechanisms.
Electrical-Only Communication: Some rare neurons, particularly in the adult nervous system, rely solely on electrical signals without neurotransmitters for communication. These are not a primary focus here.
Anatomy of a Neuron
Dendrites:
Branch-like extensions typically jutting from the cell body.
The name comes from the Greek word meaning