Chapter 2: The Biology of Behavior
Chapter 2: The Biology of Behavior Psych 101
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Date Created: 01/31/16
Psych 101 The Biology of Behavior Your every idea, every mood, every urge is a biological happening Biological psychology: the scientific study of the links between biological (genetic, neural, hormonal) and psychological processes. (Some biological psychologists call themselves behavioral neuroscientists, neuropsychologists, behavior geneticists, physiological psychologists, or biopsychologists) Neurons: (nerve cells) The basic building blocks of the nervous system Each has a cell body and its branching dendrite fibers Dendrite fibers receive information and conduct it toward the cell body (dendrites listen)—short The cell’s lengthy axon fiber passes the message through its terminal branches to other neurons or to muscles or glands (axons speak)—axons may be very long, projecting several feet through the body Some axons are in cased in a myelin sheath, a layer of fatty tissue that insulates them and speeds their impulses Glial cells (glia) (glue cells): cells in the nervous system that support, nourish, and protect neurons; they may also play a role in learning and thinking—they provide nutrients and insulating myelin, guide neural connections, and clean up after neurons send messages to one another—may also play a role in learning and thinking, and in information transmission and memory The Neural Impulse - Neurons transmit messages when stimulated by signals from our senses or when triggered by chemical by chemical signals from neighboring neurons - In response, a neuron fires an impulse—the action potential: a brief electrical charge that travels down its axon (travels at speeds ranging from 2 miles per hour to 180 miles per hour) - Neurons generate electricity from chemical events—in the neuron’s chemistry-to-electricity process, ions (electrically charged atoms) are exchanged - The fluid outside an axon’s membrane has mostly + charged ions; a resting axon’s fluid interior has mostly - charged ions - When a neuron fires, the first section of the axon opens its gates and + charged sodium ions flood in through the cell membrane - This depolarizes that axon section, causing the next axon channel to open and then the next - During a resting pause, the neuron pumps the + charged ions back outside, then it can fire again - This electrochemical process repeats up to 100 or 1000 times a second - Each neuron is a miniature-decision making device performing complex calculations as it receives signals from hundreds, thousands, of other neurons - Most signals are excitatory (like pushing a neuron’s accelerator) - Some signals are inhibitory (like pushing a neuron’s brake) - If excitatory signals minus inhibitory signals exceed a minimum intensity, or threshold, the combined signals trigger an action potential - The action potential then travels down the axon, which branches into junctions with hundreds, thousands, of other neurons or with the body’s muscles and glands - Increasing the level of stimulation above the threshold will NOT increase the neural impulse’s intensity (neuron’s reaction is an all-or-none response, either fire or they don’t)—a strong stimulus can trigger more neurons to fire, and to fire more often, but does not affect the action potential’s strength or speed How Neurons Communicate - Neurons interweave very intricately - Scientists once believed that the axon of one cell fused with the dendrites of another in an uninterrupted fabric - British physiologist Sir Charles Sherrington noticed that neural impulses were taking an unexpectedly long time to travel a neural pathway, inferring there must be a brief interruption in the transmission—he called the meeting point between neurons a synapse - We now know that the axon terminal of one neuron is in fact separated from the receiving neuron by a synaptic gap (or cleft)—Santiago Ramón y Cajal called them “protoplasmic kisses” - When an action potential reaches the knob-like terminals at an axon’s end, it triggers the release of chemical messengers, called neurotransmitters - The neurotransmitter molecules cross the synaptic gap and bind to receptor sites on the receiving neuron - The neurotransmitter unlocks tiny channels at the receiving site, and electrically charged atoms flow in, exciting or inhibiting the receiving neuron’s readiness to fire - Then in a process called reuptake, the sending neuron reabsorbs the excess neurotransmitters from the synapse The Nervous System - The body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems - Central nervous system (CNS): the brain and spinal cord—it is the body’s decision maker o Brain Enables our humanity—thinking, feeling, acting 400 trillion synapses—places where neurons meet each other brain’s neurons cluster into work groups called neural networks o Spinal cord Connects the peripheral nervous system and the brain Ascending neural fibers send up sensory information and descending neural fibers send back motor-control information Includes the neural pathways governing our reflexes and automatic responses to stimuli A simple spinal reflex pathway is composed of a single sensory neuron and a single motor neuron—these often communicate through an interneuron Another neural circuit enables the pain reflex—example: when finger touches flame, neural activity travels via sensory neurons to interneurons in your spinal cord…the interneurons respond by activating motor neurons leading to the muscles in your arm… the simple pain-reflex circuit runs through the spinal cord and right back out so your hand jerks away before your brain receives and responds to the information causing you to feel pain Information travels to and from the brain by way of the spinal cord—to produce bodily pain or pleasure, the sensory info must reach the brain - Peripheral nervous system (PNS): the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body— responsible for gathering information and for transmitting CN decisions to other body parts (somatic and autonomic) o Somatic nervous system (skeletal nervous system): enables voluntary control of our skeletal muscles o Autonomic nervous system (ANS) (self-regulating): controls our glands and the muscles of our internal organs, influencing such functions as glandular activity, heartbeat, and digestion (may be consciously overridden, but usually operates on its own) Sympathetic nervous system: arouses and expends energy— if something alarms you, it will accelerate your heartbeat, raise your blood pressure, slow your digestion, raise your blood sugar, cool you with perspiration, all to make you alert and ready for action (fight or flight response) Parasympathetic nervous system: conserves energy as it calms you by decreasing your heartbeat, lowering your blood sugar, etc. In everyday situations the sympathetic and parasympathetic nervous systems work together to keep you in a steady internal state (homeostasis) - Nerves: bundled axons that form neural “cables” connecting the central nervous system with muscles, glands, and sense organs (optic nerve) - Information travels in the nervous system through 3 types of neurons o Sensory (afferent) neurons: carry messages from the body’s tissues and sensory receptors inward to the brain and spinal cord for processing (INPUT) o Motor (efferent) neurons: carry instructions from the central nervous system (brain and spinal cord) out to the body’s muscles and glands (OUTPUT) o Interneurons: within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs —information is processed via the brain’s interneurons—where our complexity resides The Endocrine System - The body’s “slow” chemical communication system; a set of glands that secrete hormones into the bloodstream - Hormones: chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues—when they hit the brain they influence our interest in sex, food, and aggression - Endocrine messages trudge along in the bloodstream taking several seconds or more to travel from the gland to target tissue and tend to outlast the effects of neural messages - EX. In a moment of danger ANS orders the adrenal glands on top of kidneys to release epinephrine (adrenaline) and norepinephrine (nonadrenaline), which increase heart rate, blood pressure, blood sugar, etc., providing surge of energy just like in the sympathetic nervous system BUT when emergency passes, hormones (and feelings of excitement) linger for a while - Most influential endocrine gland is the pituitary gland: under the influence of hypothalamus, the pituitary regulates growth and controls other endocrine glands (located in core of the brain) - Hormones released by the pituitary gland: o A growth hormone that stimulates physical development o Oxytocin: enables contractions associated with birthing, milk flow during nursing, and orgasm. Also promotes pair bonding, group cohesion, and social trust. o Influences the release of hormones by other endocrine glands making it a master gland—the pituitary triggers your sex glands to release sex hormones The BRAIN - The body’s right side is wired to the brain’s left side, and vice versa - Lesion: tissue destruction—a brain lesion is destruction of brain tissue caused naturally or experimentally Brainstem Oldest and innermost region Begins where the spinal cord swells slightly after entering the skull (medulla) —controls for your heartbeat and breathing lies here Above the medulla are the pons—they help coordinate movement Reticular formation Finger-shaped network of neurons extending from the spinal cord right up through the thalamus Filters incoming stimuli, relays important info to other brain areas, and controls arousal Thalamus Egg shaped structure that sits atop the brainstem Receive information from all the sense except smell, and routes that info to higher brain regions that deal with seeing, hearing, tasting, and touching— brains sensory router Transmits the replies to the cerebellum and medulla Cerebellum Extends from the rear of the brainstem (baseball-sized) Processes sensory input Enables non-verbal learning and memory Helps us judge time, modulate our emotions, and discriminate sounds and textures Coordinates voluntary movement and balance The Limbic System Lies between the newest (the cerebral hemispheres) and the oldest halves of the brain Contains the amygdala, the hypothalamus, the hippocampus o The Amygdala Two lima-bean-sized neural clusters Linked to aggression and fear o The hypothalamus Neural structure just below the thalamus (hypo) Directs several maintenance activities (eating, drinking, body temperature)—influences hunger and regulates thirst, body temperature, and sexual behavior Tunes into your blood chemistry and any incoming orders from other brain parts Helps govern the endocrine system via the pituitary Linked to emotion and reward This all allows the hypothalamus to help to maintain a steady (homeostatic) internal state’ o The hippocampus Processes conscious memories The Cerebral Cortex: a thin surface layer of interconnected neural cells (covers the cerebral hemispheres)—your body’s ultimate control and information-processing center - Subdivided into four lobes, separated by prominent fissures - Frontal lobes (behind your forehead) o Motor cortex: an area at the rear of the frontal lobes that controls voluntary movements - Parietal lobes (at the top and to the rear of your head) o Sensory cortex: area at the front of the parietal lobes that registers and processes body touch and movement sensations - Occipital lobes (at the back of your head) - Temporal lobes (just above your ears) - Association areas: areas of the cerebral cortex that are not involved in primary motor or sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking, and speaking Plasticity: the brain’s ability to change (especially during childhood) by reorganizing/modifying itself after damage or by building new pathways based on experience - Brain is constantly changing, building new pathways as it adjusts to little mishaps and new experiences - May occur after serious damage - Blindness or deafness makes unused brain areas available for other uses - Sometimes attempts to mend itself by producing the brain cells— neurogenesis Splitting the brain: Corpus callosum: the wide band of axon fibers connecting the two hemispheres and carrying messages between them Split brain: a condition resulting from surgery that isolates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them—the patients with split brains are surprisingly normal Right and left differences in the brain: Right o When a person performs a perceptual task there is increased activity in the right hemisphere o Helps us modulate our speech to make meaning clear o Helps orchestrate our self-awareness Left o When a person speaks or calculates activity increases in the left hemisphere o Just as hearing people use the left hemisphere to process spoken language, deaf people use the left hemisphere to process sign language—language is language to the brain This increased activity is show by brain waves, bloodflow, and glucose consumption Behavior Genetics: study of the relative power and limits of genetic and environmental influences on behavior - Our shared brain architecture predisposes some common behavioral tendencies—we sense the world, develop language, and feel hunger through identical mechanisms Environment: every nongenetic influence, from prenatal nutrition to the people and things around us Chromosome: threadlike structures made of DNA molecules that contain the genes Genes: small segments of the giant DNA molecules Identical twins: develop from a single (monozygotic) fertilized egg that splits in two Fraternal twins: develop from separate (dizygotic) fertilized eggs Biological versus adoptive relatives: - People who grow up together, whether biologically related or not, do not much resemble one another in personality - The environment shard by a family’s children has virtually no discernible impact on their personalities - Parents do influence their children’s attitudes, values, manners, faith, and politics
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