Unit 1: Biological Bases of Behavior

Biological psychology

The approach to psychology that explains thoughts, feelings, and behaviors in terms of underlying physical processes in the body, especially the nervous system.

Neuron

The basic unit of structure and function of the nervous system that transmits information via electrical signals within the cell and chemical signals between cells.

Glial cells (glia)

Support cells that help neurons function by guiding development, providing nutrients, cleaning waste, and forming myelin to speed neural conduction.

Myelin sheath

A fatty insulating layer formed by glial cells around many axons that increases the speed of neural conduction.

Soma (cell body/cyton)

The part of the neuron containing the cytoplasm and nucleus; integrates incoming signals and directs synthesis of substances such as neurotransmitters.

Dendrites

Branching tubular processes of a neuron that receive information from other neurons.

Axon

A single conducting fiber that carries impulses away from the neuron’s soma toward other cells.

Axon terminals (terminal buttons/synaptic knobs)

The branched endings of an axon that release chemical messengers to communicate with other neurons.

Neurotransmitter

A chemical messenger released from a sending neuron into the synapse that binds to receptors on a receiving neuron and changes its likelihood of firing.

Sensory (afferent) neuron

A neuron that carries information from sensory receptors (e.g., skin, eyes, ears) to the central nervous system; “afferent arrives” to the CNS.

Motor (efferent) neuron

A neuron that carries commands from the central nervous system to muscles and glands; “efferent exits” from the CNS.

Interneuron

A neuron located within the brain and spinal cord that connects other neurons and performs much of the CNS’s integration and interpretation.

Effector

A muscle cell or gland cell that carries out a response (muscles contract; glands secrete).

Neurogenesis

The growth of new neurons, which occurs throughout life.

Neural network

An interconnected group of neurons whose coordinated activity supports complex functions; damage can disrupt the network rather than one isolated ability.

Resting potential (polarization)

The neuron’s baseline electrical state in which the inside of the cell membrane is more negative than the outside, leaving the neuron ready to fire.

Action potential

A brief electrical impulse that travels down an axon when a neuron is sufficiently activated.

Threshold

The minimum level of activation needed to trigger an action potential.

All-or-none principle

If threshold is reached, a neuron fires fully; if not, it does not fire—action potentials do not vary in size.

Firing rate

How often a neuron fires action potentials; typically how stronger stimulation is coded (not by larger action potentials).

Depolarization

A rapid change in membrane potential during an action potential caused by a net flow of sodium ions into the neuron, beginning the impulse that travels down the axon.

Refractory period

A short recovery time after a neuron fires during which it cannot (or is less able to) fire again; helps limit firing rate and promotes one-way transmission.

Nodes of Ranvier

Gaps between segments of myelin sheath along an axon where the action potential can be regenerated.

Saltatory conduction

In myelinated axons, the “jumping” of depolarization from node to node, which speeds conduction.

Synapse

The junction where a neuron communicates with another neuron (or cell), typically via chemical signaling across a small gap.

Receptor sites

Specialized locations on a receiving neuron where neurotransmitters bind, changing the likelihood that the receiving neuron will fire.

Excitatory vs. inhibitory effects

Excitatory effects increase the likelihood a receiving neuron will fire, while inhibitory effects reduce or prevent neural impulses; balance is essential for stable control.

Reuptake

A process in which the sending neuron reabsorbs neurotransmitters from the synapse, reducing their activity there.

Agonist

A substance that increases a neurotransmitter’s action (e.g., by mimicking it at receptors or increasing its availability such as by blocking reuptake).

Antagonist

A substance that decreases a neurotransmitter’s action, often by blocking receptor sites and inhibiting the neurotransmitter’s effects.

Central nervous system (CNS)

The brain and spinal cord.

Peripheral nervous system (PNS)

The nerves outside the CNS that connect the CNS to the rest of the body via spinal and cranial nerves, carrying sensory info to and motor info away from the CNS.

Somatic nervous system

A subdivision of the PNS that carries sensory information to the CNS and controls voluntary movement via motor neurons that stimulate skeletal muscles.

Autonomic nervous system (ANS)

A subdivision of the PNS that controls involuntary functions by stimulating smooth and heart muscle and glands (e.g., heart rate and digestion).

Sympathetic nervous system

The ANS branch that mobilizes the body in stress (“fight-or-flight”), increasing arousal (e.g., faster heart rate, inhibited digestion).

Parasympathetic nervous system

The ANS branch that calms and restores the body after sympathetic activation (“rest-and-digest”), supporting digestion and returning the body toward baseline.

Reflex arc

The neural pathway underlying a reflex (often a few neurons): sensory/afferent neuron → interneuron(s) → motor/efferent neuron → effector.

Plasticity

The brain’s ability to reorganize after damage by changing connections or reallocating functions (more robust in younger brains but not limitless).

Thalamus

A structure that relays visual, auditory, taste, and somatosensory information to and from appropriate cortical areas and helps regulate attention (often described as routing sensory info except smell).

Hypothalamus

A structure that regulates basic drives and homeostasis (feeding, drinking, temperature, sex, rage threshold), influences the ANS, and controls endocrine function by regulating pituitary hormone secretion.

Hippocampus

A limbic structure essential for forming new long-term (explicit) memories.

Amygdala

A limbic structure involved in processing emotion, especially fear and threat detection, and tagging experiences as emotionally significant.

Broca’s area

A left frontal-lobe language area important for speech production; damage can cause expressive aphasia (difficulty producing fluent speech).

Wernicke’s area

A left temporal-lobe language area important for language comprehension; damage can cause receptive aphasia (difficulty understanding language).

Corpus callosum

A large band of nerve fibers connecting the two cerebral hemispheres, enabling communication between them.

EEG (electroencephalogram)

An amplified recording of the brain’s electrical activity (“brain waves”) from electrodes on the scalp; excellent for timing (e.g., sleep, seizures) but poor for pinpointing deep sources.

MRI (magnetic resonance imaging)

A structural brain-imaging method using a magnetic field and radio waves to produce detailed soft-tissue images of brain anatomy.

fMRI (functional MRI)

A functional brain-imaging method that infers activity by measuring changes in blood oxygenation (BOLD signal), typically with higher resolution than PET.

Hormone

A chemical messenger secreted by endocrine glands into the bloodstream that travels to target cells and binds to specific receptors, usually producing slower, longer-lasting effects than neurotransmitters.

Heritability

A population statistic: the proportion of variation among individuals in a group that is due to genetic causes (not the “percent genetic” for a person, and not the same as unchangeable).