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Chapter 4: Neuroscience Chapter Outline 1. 2. 3. 4. 5. 6. 7. 8. How do scientists study the nervous system? How does the nervous system work? How do neurons work? How is the nervous system organized? Structures of the brain Evolutionary psychology Brain side and brain size Neurological diseases © John Wiley & Sons Canada, Ltd. How Do Scientists Study the Nervous System? Examining autopsy tissue Testing the behaviour of patients with brain damage. Electroencephalograms (EEG)—recording brain activity from the surface of the scalp Animal studies Neuroimaging techniques that show visual images in awake humans © John Wiley & Sons Canada, Ltd. The Brain at Work © John Wiley & Sons Canada, Ltd. How Does the Nervous System Work? Neurons (nerve cell)—Main building block of the brain Sensory—Gathers sensory information Motor—Communicates information to the muscles Interneuron—Carries information between neurons in the brain and the spinal cord Glia—Cells that help support neurons Astrocytes—Creates blood-brain barrier, influences communication between neurons, and helps heal brain damage One type of astrocytes is the stem cell, which creates new neurons Oligodendroglia—Provides myelin to speed up transmission of neurons Microglia—Cleans up dead cells and prevents infection in the brain © John Wiley & Sons Canada, Ltd. The Structure of Neurons Cell Body—contains nucleus, which provides energy for the neuron (C) Dendrites—receive messages from other neurons (B) Axon—carries information away from the cell body (D). Axon Terminals—transmit signals to the dendrites (E) Myelin Sheath—A substance that speeds up the firing of the neuron (F) Nodes of Ranvier—The small gaps on the neuron that have no myelin covering (A). © John Wiley & Sons Canada, Ltd. The Neuron © John Wiley & Sons Canada, Ltd. How Do Neurons Work? Resting potential—When a neuron is at rest It is negatively charged inside and positively charged outside. This resting charge is maintained through the actions of sodium-potassium pumps. Action potential—When a neuron fires Pores in the neuron (ion channels) open to let the positive charge come in and the negative charge go out. This shift in electrical charge triggers the axon terminals to release neurotransmitters. © John Wiley & Sons Canada, Ltd. The Action Potential © John Wiley & Sons Canada, Ltd. Communication Between Neurons An action potential triggers the release of neurotransmitters Neurotransmitters are chemicals that help neighbouring neurons talk to each other. These chemicals float from the synaptic vessel of one neuron and are taken up by the neurotransmitter receptors in a neighbouring neuron. Synapse—the small space between neurons Plasticity—Repeated release of neurotransmitters can cause permanent change to the neurons © John Wiley & Sons Canada, Ltd. All-or-None Principle Either a neuron is sufficiently stimulated to start an action potential (all) or it is not (nothing). Meaning you cannot have a neuron fire a lot or a little. It fires or it doesn’t. If you tap your finger, you cannot feel it as much as if you slam your finger in the door. Why? Refractory period—After firing, a neuron can’t fire for 1000th of a second. Absolute refractory period—a short time after an action potential, during which a neuron is completely unable to fire again Relative refractory period—just after the absolute refractory period, during which a neuron can only fire if it receives a stimulus stronger than its usual threshold level © John Wiley & Sons Canada, Ltd. Nodes of Ranvier The nodes of Ranvier are the regions of bare axon that are between areas wrapped in myelin. Action potentials travel down the axon by jumping from node to node. © John Wiley & Sons Canada, Ltd. Neurotransmitter Receptors Postsynaptic potentials are electrical events in postsynaptic neurons that occur when a neurotransmitter binds to one of its receptors. The electrical response of the postsynaptic cell is determined by the receptor. Depolarized regions of postsynaptic membranes have been stimulated by excitatory neurochemicals to open their ion channels and increase the likelihood that the neuron they are part of will initiate an action potential. Hyperpolarized areas of a cell have had their negative charge increased in an inhibitory fashion, making it less likely that the cell will generate an action potential. © John Wiley & Sons Canada, Ltd. Neural Networks Neural networks— clusters of neurons that communicate with each other © John Wiley & Sons Canada, Ltd. How Is the Nervous System Organized? 1. Central Nervous System—Neurons in the brain and spinal cord 2. Peripheral Nervous System—Neurons in the rest of the body a) Somatic Nervous System—All the neurons that take in sensory information (touch and pain) from all over the body and deliver it to the spinal cord and brain b) Autonomic Nervous System i. Sympathetic Nervous System—Controls fight-orflight function ii. Parasympathetic Nervous System—Controls digestive and other organ function © John Wiley & Sons Canada, Ltd. Organization of the Nervous System © John Wiley & Sons Canada, Ltd. Pain Reflex Circuit of the Spinal Cord Allows for rapid motor reactions to pain and controls pain reflexes without any communication with the brain Consists of three neurons: A sensory neuron, whose cell body is located in the periphery but whose axon travels into the spinal cord A connecting neuron, called an interneuron A motor neuron, whose cell body is located in the spinal cord and whose axon travels out to the body © John Wiley & Sons Canada, Ltd. Reflex Circuit of the Spinal Cord © John Wiley & Sons Canada, Ltd. Structures of the Brain Hindbrain Pons, reticular formation, cerebellum, medulla Midbrain Thalamus, hypothalamus, hippocampus, substantia nigra, pituitary gland Neocortex Visual, auditory, motor, sensory, cognitive © John Wiley & Sons Canada, Ltd. Hindbrain Function Regulates basic life functions Location Part of the brain closest to the spinal cord Parts of Hindbrain Reticular formation—regulates sleep/wake cycle Main source of the neurotransmitter serotonin, which is important for mood and activity levels Pons—sends signals to and from the forebrain and cerebellum Important for sleep, breathing, swallowing, eye movements, and facial sensation and expression Locus coeruleus uses neurotransmitter norepinephrine, which is important for arousal and attention. © John Wiley & Sons Canada, Ltd. Hindbrain Parts of Hindbrain (continued) Medulla—regulates heartbeat, breathing, sneezing, and coughing Cerebellum—important for motor coordination and certain types of learning that involve movement, such as learning to play the piano © John Wiley & Sons Canada, Ltd. The Cerebellum The cerebellum has many folds on its surface, shown here in this fluorescent image of a slice through this part of the brain. © John Wiley & Sons Canada, Ltd. Midbrain Function A large variety of functions (see below) Location Right on top of the brainstem (middle of the brain) Parts of Midbrain Thalamus—serves as a relay station for incoming sensory information Hypothalamus—important for motivation, basic drives, and control of the endocrine system Pituitary Gland—regulates hormones Hippocampus—important for certain types of learning and memory Amygdala—involved in processing information about emotions, particularly fear The thalamus, hypothalamus, amygdala, and hippocampus form the limbic system. © John Wiley & Sons Canada, Ltd. Midbrain Parts of Midbrain (continued) Straitum—produces fluid movements and helps with learning and memory that does not require conscious awareness Nucleus accumbens—important for motivation, reward, and addiction © John Wiley & Sons Canada, Ltd. The HPA Axis © John Wiley & Sons Canada, Ltd. Neocortex Location Top part of the brain, with many convolutions Four lobes Frontal lobe (front of brain)— higher intellectual thinking Broca’s area—speech production Prefrontal cortex—memory, morality, mood, planning Occipital lobe (back of brain)—vision Temporal lobe (sides of brain)— speech comprehension, recognizing complex visual stimuli (like faces) Wenicke’s area—language comprehension © John Wiley & Sons Canada, Ltd. Speech © John Wiley & Sons Canada, Ltd. Vision: Crossed Pathway © John Wiley & Sons Canada, Ltd. Parietal Lobe Located at the top of the brain—perception of touch and complex visual information, particularly about locations Somatosensory strip contains neurons that register the sensation of touch © John Wiley & Sons Canada, Ltd. The Brain’s Body Map © John Wiley & Sons Canada, Ltd. Localization of Function © John Wiley & Sons Canada, Ltd. Areas of the Neocortex Sensory Cortex—registers sensory neurons (touch) Motor Cortex—registers the motor neurons (muscles) Association Cortex—registers complex functions, including higher-order sensory processing, integrating information from different senses, thinking, planning © John Wiley & Sons Canada, Ltd. Parallel Processing Parallel processing—Air traffic controllers must react to an array of sensory stimuli and make quick decisions. Communication among the association cortex within and between the lobes of the brain allows us to perform such complex functions simultaneously. © John Wiley & Sons Canada, Ltd. Corpus Callosum Function Dense bundle of neural fibres (axons) that allow communication of information from one side of the brain to the other Location Connects the two brain hemispheres © John Wiley & Sons Canada, Ltd. Evolutionary Psychology Evolutionary psychology examines how the process of evolution has shaped the body and brain via the interaction of our genes and the environment to produce our thoughts and behaviours. Phylogeny—the development of unique species over time Mammals evolved from an offshoot of reptiles All life on earth is interrelated and derives from one common ancestor, LUCA (last universal common ancestor) Three super kingdoms—Eucharia (includes humans), Archea, and Bacteria © John Wiley & Sons Canada, Ltd. The Missing Link Tiktaalik—a fish in the Canadian Arctic that had a primitive wrist with fingerlike bones © John Wiley & Sons Canada, Ltd. Tree of Life © John Wiley & Sons Canada, Ltd. Evolution of Characteristics of Species Homologous traits—characteristics that are similar between species and can be traced back to a common ancestor Analogous traits—characteristics that have evolved independently in different species Convergent evolution—the development of similar physical characteristics or behaviours in different species that do not share a common ancestor (e.g., wings on birds and on bees) © John Wiley & Sons Canada, Ltd. Charles Darwin The father of evolution— Darwin’s extensive cataloguing of various life forms he encountered during his voyage on the HMS Beagle led to his famous book On the Origin of Species (1859) and to scientific acceptance of the theory of evolution. © John Wiley & Sons Canada, Ltd. Natural Selection Evolution by natural selection—animals with physical and behavioural attributes well suited to their environment are more likely to survive, reproduce, and pass on their traits to their offspring Fitnessan individual’s ability to successfully grow to maturity and have offspring © John Wiley & Sons Canada, Ltd. Natural Selection Evolution by natural selection—animals with physical and behavioural attributes well suited to their environment are more likely to survive, reproduce, and pass on their traits to their offspring Fitness—an individual’s ability to successfully grow to maturity and have offspring © John Wiley & Sons Canada, Ltd. Darwin’s Observations Darwin made four important observations: Animals were changing over time Aspects of species that seem different on the surface, such as a human hand, a bat’s wing, and a cat’s paw, had structural similarities underneath Selective breeding of captive animals leads to changes in the appearance of the animal Not all animals that are born will survive to maturity and be able to reproduce Survival of the fit enough—As the environment changes the organisms that successfully live in that environment will also change, and these changes will be passed on to their offspring © John Wiley & Sons Canada, Ltd. Different but Similar: Comparative Anatomy © John Wiley & Sons Canada, Ltd. Evolution of the Brain Encephalization factor (EF)—ratio of brain weight to body weight Humans: 7.4–7.8 Mice: 0.5 Elephant: 1.13–2.36 Size of neocortex is most important 80% of human brain is neocortex © John Wiley & Sons Canada, Ltd. Skull Size The Australopithecus skull on the left is about 1/3 the size of the present-day human skull on the right. It has a much smaller frontal area, which leads to the assumption that the frontal cortex in the Australopithecus was also smaller. © John Wiley & Sons Canada, Ltd. The Evolution of Behaviour Behaviours that influence the likelihood of reproductive success and survival Mate Choice Males prefer younger women who have a greater likelihood of being able to become pregnant and carry to term viable offspring Females prefer males with resources Parental Investment In order for human offspring to survive and eventually reproduce, parents spend an enormous amount of time caring for their young © John Wiley & Sons Canada, Ltd. Brain Side and Brain Size Both sides of the brain are involved in everything we do due to corpus callosum; the two hemispheres are more similar than they are different The left brain can accomplish what the right brain can do, it’s just less efficient at some tasks and more efficient at others Split-brain studies show hemispheric localization of some perceptual and cognitive functions, but these patients show very few problems in daily life There is no relationship between brain size and IQ for normal individuals Gender differences in brain structure are VERY small and do not predict much © John Wiley & Sons Canada, Ltd. Neurological Diseases Neurological diseases—structural, biochemical, or electrical circuit abnormalities of the brain, spinal cord, and nerves Multiple sclerosis—loss of myelin on the axons resulting in poor motor skills, poor sensory capabilities, and pain Amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease)— degeneration of motor neurons in the spinal cord, leading to loss of movement and eventual death Parkinson’s disease—dopaminergic neurons die, causing tremors and muscle rigidity Huntington’s disease—neurons in the striatum die, which causes awkward movements and symptoms of psychosis © John Wiley & Sons Canada, Ltd. Stem Cells Some of these disorders may respond to stem cell transplants Stem Cell—undifferentiated cell that can divide to replace itself and create new cells that have the potential to become all other cells of the body, including neurons © John Wiley & Sons Canada, Ltd. Copyright Copyright © 2012 John Wiley & Sons Canada, Ltd. All rights reserved. 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