Psych 1000 chapter 3 textbook notes - Chapter 3 Biological Foundations of Behaviour Neurons Basic building blocks of the nervous system 100 billion at

Psych 1000 chapter 3 textbook notes - Chapter 3 Biological...

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Chapter 3 – Biological Foundations of Behaviour Neurons Basic building blocks of the nervous system 100 billion at birth, lose 10,000 every day Three main parts: o Cell body or Soma Contains biochemical structures needed to keep the neuron alive Nucleus carries genetic information that determines how the cell develops and functions o Dendrites Branch-like fibres that emerge from the cell body Collect messages from neighbouring neurons and send them to cell body o Axon Extends from cell body, conducting electrical impulses to other neurons, muscles, or glands Branches out to form axon terminals Connect with dendritic branches from numerous neurons Glial cells surround neurons and hold them in place o Also manufacture nutrients, form myelin sheath, absorb toxins and waste o Guide newly divided neurons to place in brain during development Blood-brain barrier prevents substances from entering brain Nerve Conduction Neurons surrounded by salty liquid environment o High concentration of sodium (Na+) o Inside of neuron is more negative, causing it to be more electrically negative o Resting potential across the membrane: -70 mV Action potential (nerve impulse) is a sudden reversal in neuron’s membrane voltage o Depolarization - changes from –70 mV to +40 mV o Graded potentials – changes proportional to the amount of incoming stimulation If potentials aren’t very strong, the neuron will be partially depolarized, but not enough for action potential If strong enough, graded potential reaches action potential threshold – about –55 mV (obeys all-or- none law) o Graded potentials changes membrane potential by acting on tiny protein structures in the cell membrane called ion channels Open channels allow rushing in of Na+, making neuron less negative Creates state of partial depolarization that may reach action potential o When membrane reaches action potential threshold, Na+ rushes in due to attraction to negative force in cell Ion channels close quickly, K+ channels open and K+ leaves cell Restores neuron to resting potential Na+ and K+ flow back to respective positions to restore distribution o Refractory period – time period during which the membrane is not excitable and cannot discharge another action potential Occurs immediately after impulse passes Limits rate at which action potentials can be triggered (300 impulses per second in human) o Rate of firing or number of neurons fired help differentiate between strength of stimuli Myelin sheath is a fatty, whitish insulation layer derived from glial cells that covers axons o Thins out at regular intervals, by nodes of Ranvier o Allow for high conduction speeds along axon (still slower than speed of electricity in electrical wire)
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Synaptic Transmission Otto Loewi discovered that neurons release chemicals to pass over to next neuron Researchers found synaptic cleft between axon terminals of one neuron and dendrite of the next
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