AP Psychology Flashcards: Biological Bases of Behavior, Neurons, Brain, Neurotransmitters

A neuron is a nerve cell that transmits electrical and chemical signals throughout the nervous system. Its three main parts are the cell body, or soma, which contains the nucleus and maintains the cell's life functions; the dendrites, which are branching extensions that receive incoming signals from other neurons; and the axon, a long fiber that carries the electrical impulse away from the cell body toward other neurons, muscles, or glands. Many axons are covered by a myelin sheath, a fatty insulating layer that speeds up signal transmission.

An action potential is the brief electrical charge that travels down the axon of a neuron when the cell is stimulated beyond its threshold. At rest, the neuron has a negative internal charge of about negative 70 millivolts called the resting potential. When stimulated, sodium channels open and positively charged sodium ions rush in, depolarizing the membrane. This triggers a chain reaction down the axon. After firing, potassium channels open to restore the negative charge in a process called repolarization.

A synapse is the tiny gap between the axon terminal of one neuron and the dendrite of the next neuron. When an action potential reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters from synaptic vesicles into the synaptic cleft. These neurotransmitters cross the gap and bind to receptor sites on the receiving neuron, either exciting or inhibiting it. After transmission, neurotransmitters are cleared from the synapse through reuptake back into the sending neuron, enzymatic breakdown, or diffusion.

Key neurotransmitters include acetylcholine, which enables muscle action, learning, and memory and is depleted in Alzheimer's disease. Dopamine influences movement, motivation, reward, and pleasure and is implicated in Parkinson's disease and schizophrenia. Serotonin regulates mood, sleep, appetite, and is linked to depression when deficient. Norepinephrine affects alertness, arousal, and the stress response. GABA, or gamma-aminobutyric acid, is the main inhibitory neurotransmitter that reduces neural activity and is targeted by anti-anxiety medications.

The nervous system divides into the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord, serving as the command center. The peripheral nervous system connects the central nervous system to the rest of the body and divides into the somatic nervous system, which controls voluntary movements, and the autonomic nervous system, which controls involuntary functions.

The frontal lobe, located behind the forehead, controls executive functions like planning, decision-making, personality, and voluntary movement through the motor cortex. The parietal lobe, behind the frontal lobe, processes sensory information like touch, temperature, and pain through the somatosensory cortex. The temporal lobe, above the ears, processes auditory information and is involved in memory and language comprehension through Wernicke's area. The occipital lobe, at the back of the head, processes visual information.

Broca's area, located in the left frontal lobe, controls speech production and the motor movements needed to form words. Damage to Broca's area causes Broca's aphasia, where the person understands language but struggles to produce fluent speech, speaking in short effortful phrases. Wernicke's area, located in the left temporal lobe, is responsible for language comprehension. Damage to Wernicke's area causes Wernicke's aphasia, where the person speaks fluently but the speech is meaningless and they cannot understand spoken or written language. The arcuate fasciculus connects the two areas.

The limbic system is a group of brain structures involved in emotion, motivation, memory, and the stress response. Key structures include the amygdala, which processes emotions especially fear and aggression and attaches emotional significance to memories. The hippocampus is essential for forming new explicit memories and spatial navigation. The hypothalamus regulates homeostasis including hunger, thirst, body temperature, and the endocrine system by controlling the pituitary gland.

Neuroplasticity is the brain's ability to reorganize itself by forming new neural connections throughout life in response to learning, experience, or injury. When one brain area is damaged, other areas can sometimes compensate by taking over the lost function, especially in younger brains. Neuroplasticity explains how people recover function after strokes, how musicians develop enhanced auditory cortex regions, and how London taxi drivers show enlarged hippocampi from navigating complex routes. It demonstrates that the brain is not fixed after childhood but remains adaptable. ---