CHAPTER 3: THE BIOLOGICAL BASES OF BEHAVIOR
Empiricism
Multifactorial Causation
Heredity & Environment
Key parts of the neuron
Soma: Cell body
Dendrites: Branching structures that receive signals from other cells
Axon: Fiber that carries signals away from soma to other cells
Myelin sheath: Insulating material that encases some axons
Terminal buttons: Small knobs (at ends of axons) that release neurotransmitters at synapses
Glia
Glia are cells that provide support for neurons and contribute to signaling in the nervous system.
The neural impulse
Resting potential: Neuron’s stable, negative charge when inactive
Action potential: Voltage spike that travels along an axon
Absolute regractory period: Brief time after an action potential, before another action potential can begin
All-or-none law: A neuron either fires or doesn’t fire
Synaptic transmission
Synthesis and storage of neurotransmitters in synaptic vesicles
Release of neurotransmitters into synaptic cleft
Binding of neurotransmitters at receptor sites leads to excitatory and inhibitary PSPs
Inactivation or removal (drifting away) of neurotrans- mitters
Reuptake of Neurotrans- mitters by presynaptic neuron
Neurotransmitters and behavior
Acetylcholine: Released by neurons that control skeletal muscles
Serotonin: Involved in the regulation of sleep and arousal, and aggression; abnormal levels linked to depression
Dopamine: Abnormal levels linked to schizophrenia; dopamine circuits activated by cocaine and amphetamines
Norepinephrine: Abnormal levels linked to depression; norepinephrine circuits can be activated by cocaine and amphetamines
GABA: Inhibitory transmitter that contributes to regulation of anxiety
Endorphins: Opiate-like chemicals involved in modulation of pain
CENTRAL NERVOUS SYSTEM
Brain
Spinal cord
PERIPHERAL NERVOUS SYSTEM
Somatic nervous system Nerves to voluntary muscles, sensory receptors
Autonomic nervous system
Nerves to heart, blood vessels, smooth muscles, glands
Afferent Incoming nerves
Efferent Outgoing nerves
Sympathetic division Mobilizes bodily resources
Parasympathetic division
Conserves bodily resources
HINDBRAIN
Medulla
Regulates unconscious functions such as breathing and circulation
Cerebellum
Coordinates fine muscle movement, balance
Pons
Involved in sleep and arousal
MIDBRAIN
Involved in locating things in space; dopamine synthesis
FOREBRAIN
Cerebellum
Handles complex mental activities, such as sensing, learning, thinking, planning
Frontal lobes Primary motor cortex
Prefrontal cortex
May house executive control system crucial to planning and organization
Occipital lobes
Primary visual cortex
Parietal lobes
Primary somato-sensory cortex
Temporal lobes
Primary auditory cortex
Hypothalamus
Regulates basic biological needs, such as hunger, thirst, sex
Thalamus
Relay center for cortex; distributes incoming sensory signals, except smell
Limbic system
Loosely connected network that contributes to emotion, memory, motivation
Hippocampus Contributes to memory
Pleasure centers
Concentrated in the limbic system
Amygdala
Involved in learning of fear responses
Research methods for studying brain-behavior relations include lesioning; electrical stimulation; and CT, MRI, PET, and fMRI scans.
Plasticity of the brain The anatomical structure and functional organization of the brain is somewhat malleable.
Methods of study of lateralization
Split brain surgery: Bundle of fibers (corpus callosum) that connects two hemispheres is severed.
Perceptual asymmetries: Left-right imbalances in speed of processing are studied in normal subjects.
Left hemisphere
Usually handles verbal processing, including language, speech, reading, writing
Right hemisphere
Usually handles nonverbal processing, including spatial and musical processing, and visual recognition tasks
Basic concepts
- Chromosomes are threadlike strands of DNA that carry information.
- Genes are DNA segments that are the key functional units in hereditary transmission.
- Closer relatives share greater genetic overlap.
- Most behavioral traits appear to involve polygenic inheritance.
Research methods
Family studies assess trait resemblance among blood relatives.
Twin studies compare trait resemblance of identical and fraternal twins.
Adoption studies compare adopted children to their adoptive parents and to their biological parents.
Genetic mapping facilitates efforts to link specific genes to specific traits.
Interactions
- Research indicates that most behavioral qualities are influenced jointly by heredity and environment, which play off of each other in complex interactions.
- New work in epigenetics has further demonstrated that genetic and environmental factors are deeply intertwined.
Darwin’s insights
- Organisms vary in endless ways.
- Some traits are heritable.
- Variations in hereditary traits might affect organisms’ survival and reproductive success.
- Heritable traits that provide a survival or reproductive advantage will become more prevalent over generations (natural selection will change the gene pool of the population).
Key concepts
Fitness refers to the reproductive success of an organism relative to the population.
Adaptations are inherited characteristics sculpted through natural selection because they helped solve a problem of survival or reproduction when they emerged.
Behavior as adaptive traits
- Species’ typical patterns of behavior often reflect evolutionary solutions to adaptive problems.
- For example, behavioral strategies that help organisms avoid predators have obvious adaptive value.
- Many behavioral adaptations improve organisms’ chances of reproductive success.
- System consists of glands that secrete hormones into the bloodstream in a pulsatile fashion.
- Governed by the hypothalamus and pituitary gland, the endocrine system regulates our response to stress.
- Recent research suggests that the hormone oxytocin fosters bonding, and influences social behavior.
- It is widely believed that the cerebral hemispheres are specialized to handle specific cognitive tasks, that people are right- or left-brained, and that each hemisphere has its own cognitive style.
- However, task specialization is a matter of degree, evidence does not support the idea that people are right- or left-brained, and the data on hemispheres’ cognitive style are inconclusive.
- Efforts to use brain science to justify various education initiatives have shown that people often overextrapolate the implications of research findings.