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University of Guelph
PSYC 1000
Benjamin Giguere

NEURAL AND HORMONAL SYSTEMS Biology, Behaviour and the Mind  Phrenology (study bumps on skull) focused attention to the localization of function- the idea that various brain regions have particular functions.  Biological perspective  studying links between biological activity and psychological events  Announcing discoveries about the interplay of our biology and behaviour and mind  By understanding the biology of the mind researchers have discovered the body is composed of cells; among these are nerve cells that conduct electricity and talk to one another by sending chemical messages across a tiny gap that separates them; specific brain systems serve specific functions; we integrate information processed in these different brain systems to construct our experience of sights and sounds, meanings and memories, pain and passion; our adaptive brain is wired by our experience; each system is compose of subsystems-tiny cells organize to form body organs-these organs form larger system- the individual is part of family, culture, community = biopscychosocial systems What do phrenology and psychology’s biological perspective have in common? They share a focus on the links between biology and behaviour. Phrenology faded because it had no scientific basis-skull bumps don’t reveal mental traits and abilities. Neural Communication Neurons  Neural information system is complexity built from simplicity  Building blocks are neurons, or nerve cells  Each consists of a cell body and its branching fibers that receive messages and conduct impulses toward to cell body (dendrites)  The cells lengthy axon fiber passes the message through its terminal branches to other neurons or to muscles or glands.  Dendrites listen, axons speak  Axons are encased in a myelin sheath – a layer of fatty tissue that insulates them and speeds their impulses  If myelin sheath degenerates, multiple sclerosis results: communication to muscles slow, with eventual loss of muscle control  Neurons transmit messages when stimulated by signals from our senses or when triggered by chemical signals from neighbouring neurons  In response, a neuron fires an impulse called the action potential-a brief electrical charge that travels down its axon NEURAL AND HORMONAL SYSTEMS A motor neuron  Depending on fibre, a neural impulse travels at a range of speed  Neurons generate electricity from chemical events-ions (electrically charged atoms) are exchanged  The fluid outside an axons membrane has mostly positively charged ions; a resting axons fluid interior has negatively charged ions. This positive-outside/negative-inside state is called the resting potential.  The axons surface is selectively permeable-surface is selective what is allows through the gate  When a neuron fires the security parameters change: the first section of the axon opens its gates, and positively charged sodium ions flood through cell membrane. This depolarizes that axon section, causing another axon channel to open and another (domino effect)  During a resting pause (the refractory period, rather like a web pausing to refresh), the neuron pumps the positively charged sodium ions back outside. Then it can fire again. Action Potential NEURAL AND HORMONAL SYSTEMS  Most signals are excitatory, somewhat like pushing a neuron’s accelerator. Some are inhibitory, more like pushing on the break  If excitatory signals minus inhibitory signals exceed a minimum intensity, or threshold (level of stimulation required to trigger a neural impulse), the combined signals trigger an action impulse. The action potential then travels down the axon, which branches into junctions with hundreds or 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 impulses intensity. The neuron’s reaction is an all-or-none response  A strong stimulus can trigger more neurons to fire and fire more often but cannot affect the action potential’s strength or speed. When a neuron fires an action potential, the information travels through the axon, the dendrites, and the axon’s terminal branches, but not in that order. Place in order. Dendrites, axon, axons terminal branches How does our nervous system allow us to experience the difference between a slap and a tap on the back? Stronger stimuli (the slap) cause more neurons to fire and to fire more frequently than happens with weaker stimuli (the tap). How Neurons Communicate  Sir Charles Sherrington noticed that neural impulses were taking an unexpectedly long time to travel a neural pathway. Inferring that there must be a brief interruption in the transmission, Sherrington called the meeting point between neurons a synapse  The axon terminal of one neuron is in fact separated from the receiving neuron by a synaptic gap  When an action potential reaches the knob-like terminals at an axons 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- as a key fits a lock  The neurotransmitter unlocks tiny channels at the receiving site, and electrically charged atoms flow in, exciting or inhabiting the receiving neurons readiness to fire. Then, in a process called reuptake the sending neuron reabsorbs the excess neurotransmitters. What happens in the synaptic gap? What is reuptake? Neurons send neurotransmitters (chemical messengers) to one another across this tiny space between one neurons terminal branch and the next neurons dendrite. In reuptake, a sending neuron reabsorbs the extra neurotransmitters. NEURAL AND HORMONAL SYSTEMS How neurons communicate How Neurotransmitters Influence Us Neurotransmitter pathways- each of the brain’s differing chemical messengers has designated pathways where it operates, as shown here for serotonin and dopamine NEURAL AND HORMONAL SYSTEMS  A brain pathway may use only one or two neurotransmitters and particular neurotransmitters may affect specific behaviours and emotions. But neurotransmitters systems don’t operate in isolation; they interact, and their effects vary with the receptors they stimulate  Researchers soon confirmed that the brain does produce its own naturally occurring opiates  Our body releases several types of neurotransmitter molecules similar to morphine in response to pain and vigorous exercise- these endorphins (natural morphine) help explain good feelings, the painkilling effects of acupuncture, and the indifference to pain in some severely injured people Some Neurotransmitters and their functions Neurotransmitter Function Examples of Malfunctions Acetylcholine (Ach) Enables muscle action, learning, and With Alzheimer’s disease, Ach- memory producing neurons deteriorate Dopamine Influences movement, learning, Oversupply linked to schizophrenia. attention, and emotion Undersupply linked to tremors and decreased mobility in Parkinson’s diseases Serotonin Affects mood, hunger, sleep and Undersupply linked to depression. arousal Some anti-depressant drugs raise serotonin levels Norepinephrine Helps control alertness and arousal Undersupply can depress mood GABA (gamma aminobutyric acid) A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia Glutamate
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