Biology, Behavior, Mind — Neurons, Structure, and Neural Signaling

The brain is organized such that various regions have particular functions (localization of function).
Biological psychology studies the links between biology (genetic, neural, hormonal factors) and psychological processes.
The mind/brain are involved in processing and constructing experiences through integrated information across brain systems.
Our adaptive brain is wired by experience, meaning learning and environment shape neural connections and functions.
Examples in everyday experience include how brain systems process sensory experiences like color; information is integrated to form coherent perceptions.

Neurons are the basic building blocks of the nervous system.
A neuron is a cell body with branching fibers.
Dendrites: bushy, branching extensions that receive messages from other neurons; they listen to incoming signals.
Axons: long extensions that pass messages to other neurons, muscles, or glands; they speak by sending signals away from the cell body.
Dendrites listen; axons speak.
Some axons are long; dendrites are often shorter.

Dendrites receive information via their branches.
Axons transmit information to other neurons, muscles, or glands.
The basic communication pattern is from dendrites to the cell body, then along the axon to the terminal endings.

Myelin sheath: a fatty layer segmentally encasing the axon.
Myelinated axons enable vastly faster transmission of neural impulses.
Conduction occurs more quickly because the impulse hops from node to node along the axon (saltatory conduction).
The presence of myelin increases neural efficiency, supporting faster judgment and control.
Degeneration of myelin can lead to Multiple Sclerosis, which disrupts neural communication and can cause loss of muscle control.
Nodes of Ranvier are the gaps between myelin segments where the impulse jumps.

Axons carry messages away from the cell body toward other neurons, muscles, or glands.
The axon membrane contains a selective barrier that regulates which ions can cross, influencing electrical transmission.

The neuron’s resting potential is established by ions distributed inside and outside the axon.
Outside the axon: positively charged ions; inside the axon: negatively charged ions.
The interior of the axon is negatively charged relative to the exterior during resting potential.
The axon's surface is selectively permeable, allowing certain ions to pass while restricting others.

When a neuron fires, a neural impulse travels down the axon as an action potential.
During this process, ions are exchanged across the membrane.
Sodium ions (Na+) flow into the membrane, contributing to depolarization.
The refractory period is the period of inactivity after a neuron has fired.
During recovery, sodium ions are pumped back out (and other ions are redistributed) to restore the resting state.
Positive ions outside and negative ions inside help drive the electrical change across the membrane.

Signals can be excitatory (pushing toward firing) or inhibitory (pushing toward stopping).
The threshold is the level of stimulation required to trigger an action potential.
If excitatory signals exceed inhibitory signals, an action potential is triggered; otherwise, the neuron does not fire.
This creates a discrete all-or-none response: a neuron fires fully or not at all.
The rate of firing (frequency) conveys information about stimulus intensity, within the constraints of neuronal mechanisms.

Action potentials are all-or-none; a neuron either fires a full impulse or none.
When firing occurs, the frequency of action potentials can encode the strength or intensity of the stimulus.

Myelin integrity is crucial for rapid and reliable neural communication; demyelinating diseases (e.g., Multiple Sclerosis) impair muscle control and other functions.
Understanding synaptic transmission and action potentials underpins medical treatments that affect neural signaling (pharmacology, neuroprosthetics, rehabilitation).
The brain’s plasticity (its ability to rewire in response to experience) has practical implications for education, therapy, and recovery after injury.