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Chapter 4

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Todd Ferretti

Chapter 4: The Brain the mind and self The Nervous System Two main parts  Central nervous system: receives, processes, interprets and stores incoming sensory information -sends out messages to muscles, glands, organs, etc  Peripheral nervous system: handles input and output from CNS -all portions of the nervous system outside the brain and spinal cord CNS  Two components: brain and 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 PNS  Contains two subdivisions (messages carried through sensory and motor nerves) 1. Somatic nervous system: nerves connected to sensory receptors and skeletal muscle 2. Autonomic nervous system: regulates functioning of blood vessels, glands, internal organs -Sympathetic: engaged when something shocks or frightens you, fight or flight -Parasympathetic division: engage in calming you down (conserve) Communication in the Nervous System  Nervous system made up of: 1. Neurons: cells that conduct electrochemical signals; basis of the nervous system 2. Glia: cells that support, nurture, and insulate neurons, remove debris when neurons die, enhance the formation and maintenance of neural connections, and modify neural functioning Structure of the Neuron  Approximately 100 billion neurons in the brain  Neurons vary in size and shape  Dendrites -branch like fibres that receive information from other neurons and transmit towards cell body  Cell body -keeps neuron alive and plays key role in determining whether neurons will fire  Axon -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 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 -constrictions in converging (Nodes) divide myelin into segments -purpose to speed conduction of neural impulses and prevent interference from neighbouring signals Neurons in the News  Neurogenesis: Production of new neurons from immature stem cells  Stem Cells -immature cells that renew themselves and have the potential to develop into mature cells -stem cells from early embryos can develop into any cell type 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 -Canadian researchers have had some success with adult stem cells developing to brain cells 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  Communication occurs through electrical and chemical signals -Stimulation causes change in charge between inside and outside of cell -inflow of sodium ions cause an action potential -Synaptic vesicles release chemicals called neurotransmitters  Neurotransmitters bind to receptor sites on receiving neuron and causes changes in the cell membrane -Excitatory changes--a voltage shift in a positive direction -increases probability of receiving neuron firing -Inhibitory changes--a voltage shift in the negative direction -decreases probability of receiving neuron firing Brain Plasticity  Plasticity -the brains 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 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, norepineephrine, GABA, glutamate  Each neurotransmitter has different effects: -Serotonin: sleep, appetite, sensory perception, temp regulation, pain suppression, mood -Dopamine: voluntary movement, learning, memory, emotion, pleasure or reward, response to novelty -Acetylcholine: muscle action, cognitive functioning -Norepinephrine: increased heart rate, slowed intestinal activity during stress, learning, memory, dreaming, waking, emotion -GABA: major inhibitory neurotransmitter -Glutamate: major excitatory neurotransmitter in brain  Endorphins -chemical substances in the nervous system that are similar in structure and action to opiates -involved in pain reduction, pleasure and memory  Hormones -Chemical substances, secreted by organs called endocrine glands, that affect the functioning of other organs -regulates growth, metabolism, sexual development and behaviour, and other functions -Major hormones: -Melatonin: regulates daily biological rhythms, sleep -Oxytocin: childbirth contractions, milk ejection -Adrenal Hormones: emotion, stress, epinephrine -Sex Hormones: androgens and estrogens Mapping the Brain
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