Chapter 3: The Brain, Genetics, and Evolution

The Neuron • Neurons – cell that receives signals from other neurons or sense organs, processes these signals, and sends the signals to other neurons, muscles, or bodily organs © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Neuron • Three types: • Sensory neurons – a neuron that responds to input from sense organs • Motor neurons – a neuron that sends signals to muscles to control movement • Interneuron – a neuron that is connected to other neurons (found in the brain) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Neurons • Neurons are composed of: • Dendrites: receive information and pass it to cell body • Cell Body: summarizes information • Axon: extends from cell body, carries electrical potential, sends a chemical message to adjacent neurons © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Resting Potential Neurons are not always firing. When at rest they maintain a negative charge which is called the resting potential. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Resting Potential • During resting potential: Sodium ions are concentrated on the outside of the axon membrane. + Potassium ions are concentrated on the inside of the axon membrane. + Chloride and Anion ions are concentrated inside the cell. (Both are negatively charged) Ion channels are closed. The inside of the axon membrane is more negative than is the outside. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Action Potential – cell fires • Action potential occurs when the membrane potential becomes positive • Ion channels (holes, pores) open in the membrane, allowing sodium ions to enter the axon • Sodium entry shifts the membrane potential toward a positive value • Potassium channels open and potassium ions exit the cell; due to excess + charged sodium ion influx • Anion ions (-) remain in the neuron • Neurotransmitters are released down the axon © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Resting Potential • Resting Potential is restored when other channels open, allowing potassium ions to re-enter the axon and sodium ions to exit the axon © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Myelin • Myelin is a fatty, waxy substance coating the axon of some neurons. • Functions: • Speeds neurotransmission • Insulates neurons from each other • Makes neurotransmission more efficient © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Neurotransmitters • The synapse is the junction between an axon terminal and an adjacent dendrite or cell body. • Neurotransmitter (NT) molecules are released from the axon terminal into the synapse when the action potential arrives at the axon terminal. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Neurotransmitters • Synaptic Cleft – the gap between the axon of one neuron and the membrane of another, across which communication occurs • Receptor – a site on the dendrite or the cell body where the messenger molecule attaches itself © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Synapse • Synthesis of neurotransmitter (NT) • Storage and transport of NT within vesicles • NT Release • Activation of postsynaptic receptors • Termination of transmitter effect (e.g. reuptake) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Neurotransmitters – Chemical Messengers • Serotonin- affects mood, sleep, appetite • Acetylcholine – affects muscle action, cognitive functioning, memory • Dopamine – affects movement, attention, learning, emotion • Norepinephrine – affects learning, memory, dreaming, emotion • Epinephrine – affects emotional arousal and memory storage • GABA – inhibitory actions in the CNS • Endorphins – elevate mood, reduce pain, affect memory © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Psychoactive Drugs • Psychoactive drugs affect the nervous system to alter mood, emotion, and thought • Psychoactive drugs act by: • Increasing or decreasing release of neurotransmitters • Stimulating or blocking receptor sites © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Psychoactive Drugs • Agonists enhance neurotransmitter function • Antagonists block neurotransmitter function • SSRI – selective serotonin reuptake inhibitor © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Central Nervous System • The CNS is composed of the brain and spinal cord • Spinal cord connects the brain with the PNS • Spinal cord is comprised of cell bodies and axons that carry messages • Afferent: toward the brain (sensory function) • Efferent: away from the brain (motor function) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Peripheral Nervous System • The Peripheral Nervous System (PNS) includes all nerves outside the brain and spinal cord • Somatic NS carries sensory messages to brain and motor commands to the muscles • Autonomic NS regulates automatic body functions (such as heart rate, breathing) • Sympathetic: “Fight or Flight” (response to threat) • Parasympathetic: dominant when relaxed (acts to calm the body down) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Brain • Meninges – 3 protective layered membranes that cover the brain; first thing you would see under the skull • Cerebral Hemisphere – left or right half of the brain © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Brain • Corpus Callosum – band of nerve fibers that connect the 2 halves of the brain • Cerebral Cortex – the pinkish gray surface of the brain where most mental processes take place • Sulcus – a crease in the cerebral cortex © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Brain Cortex is divided into lobes • Frontal: Self-awareness, planning, voluntary movement, emotional control, speech, working memory • Parietal: Body sensations, motor control • Occipital: Vision • Temporal: Hearing, language comprehension © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Brain • Localization of function: do discrete circuits carry out different functions? Somatosensory Strip – registers sensation on the body and is organized by the body Motor Strip – controls fine movements and is organized by body part © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Brainstem-Hindbrain • Brainstem is a primitive portion of brain • Pons: involved in respiration, sleep regulation, dreaming • Medulla: involved in life support functions such as respiration and heart rate • Reticular activating system is an arousal system within the brainstem; plays a role in keeping a person awake and alert © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Subcortical Brain Areas • Corpus callosum: band of axons that interconnects the hemispheres • Thalamus: sensory relay area • Limbic system: involved in emotionality • Hypothalamus: feeding, fleeing, mating, fighting, homeostasis • Cerebellum: involved in motor control © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Endocrine System • Network of glands; Hormones are secreted into the blood by the endocrine system • Hypothalamus controls the pituitary gland (size of a pea), which is responsible for releasing hormones that flow throughout the body © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

The Endocrine System - Hormones • Testosterone – causes males to develop sex characteristics and build muscle volume • Estrogen – causes women to develop sex characteristics and is involved in the menstrual cycle • Cortisol – helps the body cope with extra energy demands of stress by breaking down and converting fat and protein into sugar © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Behavioral Genetics • Behavioral genetics examines the influence of genes (versus environment) on behavior • Research strategies: • Twin studies: compare the concordance (agreement) rates between identical and fraternal twins • Adoption studies: compare the similarity between adopted children and their biological/adopted parents • Mutations: examine behaviors in genetically abnormal subjects or in animals in which a specific gene has been “knocked out” (e.g., down syndrome, schizophrenia) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Evolutionary Psychology • Evolutionary psychology examines how evolutionary processes impact behavior • Darwin argued that natural forces select traits that are adaptive for survival • Natural selection: certain traits are passed on because these traits gave an advantage for survival • Organisms with these traits are able to reproduce and pass on the trait to their offspring • Genetic mutations can be beneficial or disastrous © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7E

Chapter 3: The Brain, Genetics, and Evolution