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Psych 1000 - Chapter 3 Notes.docx

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Psychology 1000
Terry Biggs

Biological Foundations of Human Behavior The organism as a machine - The reflex concept o Descartes was first to propose that humans should be studied as a machine o His views are still with us today as we employ metaphorical comparisons between the human mind and computers o To Descartes all action was a response to some external event o Chain of events:  Stimulation of a sense – relay to a brain – interpretation via the soul – relayed to muscles for action  Thus energy is taken in and REFLECTED back out  Note: use of the soul provides a means to account for inconsistency of responses - Basic Nervous Functions o We agree with Descartes that the bulk of human behavior is reflective o This necessitates the Tripartite system  Reception – via the senses  Reaction – via muscles and glands  Integration- mediator between reception and reaction via conduction (signals being moved through nerves) o The external event is called the stimulus as it stimulates the Receptors (Transducing nerves) o The receptors convert the energy and channel it to bundles of nerves called AFFERENT nerves (sensory) o Afferent nerves may lead to the spinal chord and travel to the brain to INTERNEURONS that connect to EFFERENT nerves (motor) which carry signals to muscles and glands or they may in some minority of instances, connect directly to Efferent nerves (straight reflex) – reflex directly from input to output for example when the doctor hits your patella and your leg automatically swings out) - Basic Building Blocks o The Neuron  Dendrites pick up information from incoming sources then a decision is made by the cell body with the information from the dendrites. It then sends a signal through the axon. The myelin sheath insulates the axon (which is of indeterminate length) to prevent short circuiting in nerves and results in faster transmission (cells that don’t have the sheath have slower transmission)  If the immune system attacks the sheath you get multiple sclerosis (degradation of the myelin sheath)  The terminal endings terminate in a bunch of dendrites of other nerve cells or in EFFECTOR cells (which are connected to muscles)  Not all nerve cells look the same (motor neurons and pyramidal cells look different but they all have many dendrites but one axon) o Dendrites  Receives messages form other neurons and send them onto the cell body where the incoming information is combined and processed o Cell body  Contains the biochemical structures needed to keep the neuron alive and its nucleus carries the genetic information that determines how the cell develops and functions o Axon  Conducts electrical impulses to other cells (muscles, nerves, etc.) - Glial cells o Surround neurons and hold them in place o They bring nutrients to the brain and get rid of waste (which is the residue of burned glucose) o Manufacture nutrient chemicals neurons need o They form the myelin sheath around some axons and absorb toxins and waste materials that might damage neurons - Many foreign substances can pass from the circulation into different organs but not into the brain because of the blood-brain barrier which prevents many substances (including toxins) from entering - Nerve Conduction o Neurons generate electricity that creates nerve impulses and they also release chemicals that allow them to communicate with other neurons o Neurons have a resting potential of -70 minivolts, creating a state of polarization o Neurons are surrounded by a salty liquid environment which has a high concentration of sodium ions (Na+) o The inside of the neuron has some positively charged potassium ions (K+) and many other negatively charged ions o The combination creates the resting potential o In resting state, the neuron’s ion channels are closed and the concentration of Na+ ions is 10 times higher outside the neuron than inside o The action potential:  Dendrites are stimulated by axons of other neurons  Na+ ions flow into the neuron by action of ion channels, making the membrane voltage more positive (depolarization)  If the partial depolarization reaches -65 minivolts (action potential threshold), the neuron fires according to the all-or- none law (if it doesn’t reach -65 nothing happens) o After the action potential is reached it goes to the refractory period (which is lower than -70) and then returns to resting membrane potential (during this period the cell can’t fire) o After the depolarization occurs, in order to restore the resting potential the cell closes its sodium channels and positively charged potassium ions flow out through their channels, restoring the negative resting potential; o Eventually the excess sodium ions flow out of the neuron and the escaped potassium ions are recovered o The charge runs down the axon o The peaks travel down the axon o Stimulus intensity  Given the action potential is all or none how do we distinguish between different sensations? (eg. The buzz of a mosquito vs. the roar of a jet engine)  This is the realm of stimulus intensity  Two mechanisms allow for the determination of stimulus intensity 1. The number of neurons firing – neurons differ in their threshold. Thus the mosquito will cause X number of neurons to fire while the jet will cause X+ neurons to fire 2. Frequency of Impulse – The duration of a signal will also affect the nerves firing as a prolonged signal will result n a 2,3,4….action potentials. The stronger the stimulus (intensity and duration) the more OFTEN the nerve will fire. The maximum rate is 1000 impulses per second (but some things go beyond that so there has to be more) o The myelin sheath and conduction  Insulation layer coves axon in the brain and spinal chord  Allows for high speed condition o Effects of neurotransmitters  Excitatory neurotransmitters depolarize the postsynaptic (cell that hasn’t been fired yet/cell the signal is supposed to reach) cell membrane by stimulating the inflow of sodium ions. This stimulation of the cell may exceed the action potential threshold and cause the postsynaptic cell to fire and action potential  Other neurotransmitters hyperpolarize the membrane by stimulating ion channels to allow K+ ions to flow out, thus inhibiting neuron firing o The Synapse  Inference of the synapse – that their has to be a gap, their can’t be continuous firing  Prior to the work of Sherrington trans mission of nerve signals was not well understood  Sherrington’s aim was to study the Simple Reflex  He employed dogs whose spinal chords were severed just below the neck  This insured that any responses to stimulation Afferent to Efferent only and did not involve the brain and interneurons  He found that 1 sub(below) threshold stimulation didn’t cause any response but several threshold stimulations in a row at 05 seconds intervals did cause a response  This is important s it revealed the nervous system was capable of temporal summation and the half second delay was too great to allow for this in 1 neuron (the process could work sub threshold if the time interval wasn’t too large)  Repeated sub threshold stimulations finally executed the movement  Temporal summation must occur outside the axon  Sherrington proposed that this occurred via chemical production and buildup between an axon and dendrite  Sherrington reported that the same summation effect could be found if several sub threshold stimuli were given to the same area  This is important as it demonstrates spatial summation of nerve signals  This suggests that several nerves axons may converge on the dendrites of one other nerve cell  Since each stimulation alone produced no response he argued this supported the chemical production and pooling outside the axon – The are is the Synapse and the gap is the SYNAPTIC CLEFT  The chemicals that are produced are called neurotransmitters they are produced at the terminal endings of the axon and are released into the synaptic cleft  They are taken up at the receptor sites along the dendrites o Deactivation of neurotransmitters (Fain, 1999)  Breakdown – Other chemicals in the synapse break down neurotransmitters into their chemical components  OR Reuptake – neurotransmitters are taken back into the presynaptic axon terminal o Specialized Transmitter Systems  Glutamate and gamma-aminobutyric acid(GABA) are neurotransmitters found in the central nervous system. Glutamate is excitatory and is important for learning and memory while GABA is inhibitory and used for motor control and control of anxiety  Acetylcholine (Ach) – Involved in memory and muscle activities. It’s an excitatory transmitter at the sunapses where neurons activate muscle cells  Dopamine – An excitatory transmitter (makes the brain work faster). It mediates a wide range of functions including motivation, reward, feelings of pleasure, voluntary motor control and control of though processes  Serotonin – Enhances mood, eating, sleep, and sexual behavior  Endorphins – Reduce pain and increase feeling of well- being  Most neurotransmitters have their excitatory or inhibitory effects only on specific neurons that have receptors for them  Neuromodulators have a more widespread and general influence on synaptic transmission and can circulate through the brain and increase or decrease the sensitivity of many neurons to their specific transmitters. They play an important role in eating, sleeping, and stress - Sometimes when molecules have the right shape to fit into the receiving molecule but the wrong function/purpose the molecule can’t be absorbed so there is no activity and then the molecule gets lodged or stuck in the receptor and transmission gets stopped there and they could become lethal (some poisons operate on this basis) - The Nervous System o There are three types of neurons:  Sensory (afferent): Carry input messages from the sense organs to the spinal chord and brain  Motor (Efferent): Transmit output impulses from the brain and the spinal chord to the muscles and organs  Interneurons: Perform connective or associative functions in the nervous system (which will mostly be in the central nervous system of your brain). They link the output and input functions o Organization of the nervous system  Central nervous system – brain and spinal cord (protected by bones and such) (CNS nerves don’t seem to regenerate the way peripheral nerves do)  Peripheral nervous system - connects the CNS with the muscles, glands, and sensory receptors o The Central Nervous System contains the brain and the spinal cord which connects most of the peripheral nervous system with the brain  The spinal cord  Where most nerves enter and leave the CNS  It’s neurons are protected by the vertebrae  It consists largely of grey-coloured neuron cell bodies and their interconnections. The grey matter is surrounded by white-colo
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