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The Brain: Source of Mind and Self Chapter 4 Copyright © 2010 Pearson Education Canada 4-1 Chapter Outline • The Nervous System: A Basic Blueprint • Communication in the Nervous System • Mapping the Brain • A Tour Through the Brain • The Two Hemispheres of the Brain • Two Stubborn Issues in Brain Research • Using Our Brains about Brain Research Copyright © 2010 Pearson Education Canada 4-2 The Nervous System • Two main parts: – Central nervous system (CNS): receives, processes, interprets, & stores incoming sensory information; sends out messages to muscles, glands, organs – Peripheral nervous system (PNS): handles input & output from the CNS; all portions of the nervous system outside the brain & spinal cord Copyright © 2010 Pearson Education Canada 4-3 Central Nervous System • Two components: brain & spinal cord • Spinal cord is a bridge between the brain and parts of the body below the neck • Spinal nerves protected by the spinal column • Enables spinal reflexes Copyright © 2010 Pearson Education Canada 4-4 Peripheral Nervous System • Contains two subdivisions (messages carried through sensory & motor nerves): 1. Somatic nervous system: nerves connected to sensory receptors and skeletal muscles 2. Autonomic nervous system: regulates functioning of blood vessels, glands, & internal organs • Contains the sympathetic & parasympathetic nervous systems Copyright © 2010 Pearson Education Canada 4-5 Autonomic Nervous System Copyright © 2010 Pearson Education Canada 4-6 Communication in the Nervous System • Nervous system made up of: – Neurons: cells that conduct electrochemical signals; basic unit of the nervous system – Glia: cells that support, nurture, and insulate neurons, remove debris when neurons die, enhance the formation & maintenance of neural connections, and modify neural functioning Copyright © 2010 Pearson Education Canada 4-7 Structure of the Neuron • Dendrites • Axon – Branch-like fibres that receive information from other neurons & transmit towards cell body • Cell body – Keeps neuron alive & plays key role in determining whether neuron will “fire” – Extending fibre that conducts impulse away from cell body and transmits to other cells – Branches at end called axon terminals – May be collected together in bundles called nerves Copyright © 2010 Pearson Education Canada 4-8 Structure of the Neuron Copyright © 2010 Pearson Education Canada 4-9 The Myelin Sheath • Many axons are insulated by surrounding layer of fatty material called myelin sheath – In the CNS, this is made up of glial cells – Divided into segments due to constrictions in covering (nodes) – Purpose to speed conduction of neural impulses & prevent interference from neighbouring signals Copyright © 2010 Pearson Education Canada 4-10 Neurons in the News • Neurogenesis – Production of new neurons from immature stem cells • Stem cells – Immature cells that renew themselves & have the potential to develop into mature cells – Stem cells from early embryos can develop into any cell type Copyright © 2010 Pearson Education Canada 4-11 Stem-Cell Research • Embryonic stem cells can differentiate into any type of cell; adult stem cells limited • Use is controversial and surrounded by ethical debates regarding extraction* • Most promising in developing treatments for cancer, blood, organ, and brain disorders (e.g., Parkinson’s) • Canadian researchers have had some success with adult stem cells transforming to brain cells Copyright © 2010 Pearson Education Canada 4-12 Brain Plasticity • Plasticity – The brain’s ability to change and adapt in response to experience (e.g., reorganizing or growing new neural connections) – Behavioural deficits that occur as a result of brain damage may be lessened by enriching environments people live in (e.g., Kolb et al., 1991) Copyright © 2010 Pearson Education Canada 4-13 How Neurons Communicate • No direct contact between neurons • Communicate through the synapse – Includes the axon terminal, synaptic cleft, and receptor sites in the membrane of the receiving cell Copyright © 2010 Pearson Education Canada 4-14 How Neurons Communicate • When nerve is stimulated, produces an electrical potential between the inside & outside of a cell • If enough stimulation, produces an action potential that sends an impulse down the axon (speed depends on myelination) • Axon terminals release neurotransmitters from synaptic vesicles into synaptic cleft • Neurotransmitters bind to post-synaptic receptor sites that they fit (causing excitatory or inhibitory inputs) Copyright © 2010 Pearson Education Canada 4-15 Chemical Messengers • Neurotransmitters – A chemical substance that is released by a transmitting neuron at the synapse and that alters the activity of a receiving neuron • Major neurotransmitters: – Serotonin, dopamine, acetylcholine, norepinephrine, GABA, glutamate Copyright © 2010 Pearson Education Canada 4-16 Chemical Messengers • Endorphins – Chemical substances in the nervous system that are similar in structure and action to opiates – Involved in pain reduction, pleasure, and memory – Technically known as endogenous opioid peptides Copyright © 2010 Pearson Education Canada 4-17 Chemical Messengers • Hormones – Chemical substances, secreted by organs called endocrine glands, that affect the functioning of other organs • Regulate growth, metabolism, sexual development & behaviour, and other functions – Major hormones: • Melatonin, oxytocin, adrenal hormones, sex hormones (androgens & estrogens) Copyright © 2010 Pearson Education Canada 4-18 Mapping the Brain • Many ways scientists can study the brain: – Patients with brain damage – Lesion method • Involves damaging or removing section of brain in animals and then observing the effects – Electrical & magnetic detection – Brain scans Copyright © 2010 Pearson Education Canada 4-19 Electrical & Magnetic Detection • Electroencephalography (EEG) – Recording neural activity detected by electrodes – Limited precision as recording multiple cells – Recent techniques include needle & micro-electrodes • Transcranial magnetic stimulation (TMS) – Uses a powerful magnetic field produced by a wire coil placed on person’s head to stimulate cells – Can cause neurons to fire & inactivate others Copyright © 2010 Pearson Education Canada 4-20 Brain Scans • PET scan (positron-emission tomography) – Method for analyzing biochemical activity in the brain, using injections of a glucose-like substance containing a radioactive element • MRI (magnetic resonance imaging) – Method for studying body and brain tissue, using magnetic fields and special radio receivers • Performance assessed by functional MRI or fMRI Copyright © 2010 Pearson Education Canada 4-21 Brain Scans Copyright © 2010 Pearson Education Canada 4-22 Touring the Brain • Localization of function – Specialization of particular brain areas for particular function • Major areas/structures: – Brain stem, cerebellum, thalamus, hypothalamus & pituitary gland, amygdala, hippocampus, cerebrum & cerebral cortex Copyright © 2010 Pearson Education Canada 4-23 The Brain Stem • Medulla – Responsible for automatic functions such as breathing & heart rate • Pons – Involved in sleeping, waking, & dreaming • Reticular activating system (RAS) – Extends from brain stem; arouses cortex & screens incoming information Copyright © 2010 Pearson Education Canada 4-24 The Cerebellum • Cerebellum – Regulates movement & balance – Involved in learning of certain kinds of simple skills & acquired reflexes – Role in complex cognitive tasks (e.g., problem solving) Copyright © 2010 Pearson Education Canada 4-25 The Thalamus • Thalamus – Brain structure that relays sensory messages to the cerebral cortex • Includes all sensory messages except those from olfactory bulb Copyright © 2010 Pearson Education Canada 4-26 Hypothalamus & Pituitary Gland • Hypothalamus – Involved in emotions & drives vital to survival, such as fear, hunger, thirst & reproduction; regulates autonomic nervous system • Pituitary gland – Endocrine gland at base of brain that releases many hormones & regulates other endocrine glands Copyright © 2010 Pearson Education Canada 4-27 The Limbic System • Hippocampus – Involved in the storage of new information in memory • Amygdala – Involved in arousal and regulation of emotion; initial emotional response to sensory information Copyright © 2010 Pearson Education Canada 4-28 The Cerebrum • Cerebrum – Largest brain structure – Divided into two cerebral hemispheres, connected by corpus callosum – Hemispheres specialized for certain tasks (lateralization) – Contains layers of densely packed cells called cerebral cortex (divided into lobes) Copyright © 2010 Pearson Education Canada 4-29 Lobes of the Cortex Copyright © 2010 Pearson Education Canada 4-30 Lobes of the Cortex • Occipital lobes – Includes visual cortex • Parietal lobes – Includes somatosensory cortex (pressure, pain, touch, temperature) – Homunculus – Attention & mental operations • Temporal lobes – Includes the auditory cortex & Wernicke’s area (left) – Memory, perception, emotion • Frontal lobes – Includes the motor cortex & Broca’s area (left) – Emotion, planning, creative thinking Copyright © 2010 Pearson Education Canada 4-31 The Case of Phineas Gage • 1848: Explosion at railroad construction site forced steel tamping rod through Gage’s head • Survived accident but some said he was “no longer Gage” • Problems with emotional processing & rational decision making Copyright © 2010 Pearson Education Canada 4-32 Two Hemispheres of the Brain • Hemispheres have different areas of specialization & control opposite sides of the body – Communicate through corpus callosum – If severed through split-brain surgery, perception & memory disturbed, although most other processing intact • E.g., facial identification tasks by Sperry & colleagues Copyright © 2010 Pearson Education Canada 4-33 Split Brain Experiments Copyright © 2010 Pearson Education Canada 4-34 Hemispheric Allies or Opposites? • Studies of split-brain patients have demonstrated: – Most right-handed & the majority of left-handed people process language mainly in the left hemisphere – Many researchers believe in left hemisphere dominance – Right hemisphere important for problems involving spatial-visual ability, facial recognition, music processing, & some language abilities Copyright © 2010 Pearson Education Canada 4-35 Where is the Self? • Brain scientists consider the mind a physical product of cerebral cortex – Many actions & choices occur without conscious awareness – Brain structures create sense of reality, interacting mental modules – Frontal lobes may be critical in “self” experience – Some still question relationship between subjective experience & physical processes Copyright © 2010 Pearson Education Canada 4-36 “His” and “Hers” Brains? • Are there sex differences in the brain? – Some evidence to suggest anatomical differences – Differences in lateralization of language: • Males show left hemisphere activation only whereas females show activation in both hemispheres Copyright © 2010 Pearson Education Canada 4-37 Gender & Language Laterality Copyright © 2010 Pearson Education Canada 4-38 Problems with Gendered Brains? • What these sex differences mean with respect to behaviour or personality should be interpreted with caution: a) Supposed gender differences (e.g., intuition, abilities) are stereotypes b) A brain difference does not necessarily explain behaviour or performance c) Sex differences in the brain could be the result rather than the cause of behavioural differences Copyright © 2010 Pearson Education Canada 4-39 Using Our Brains about Brain Research • Study of the brain illuminates many aspects of functioning, but also raises many questions about future research – Neuroethics: interdisciplinary specialty addressing the legal, ethical, and scientific implications of brain research Copyright © 2010 Pearson Education Canada 4-40 End of Chapter 4 Copyright © 2010 Pearson Education Canada 4-41