3.2—how the nervous system works: cells and neurotransmitters Flashcards Preview

🚫 PSY100H1: Introduction to Psychology (Winter 2016) with J. Vervaeke > 3.2—how the nervous system works: cells and neurotransmitters > Flashcards

Flashcards in 3.2—how the nervous system works: cells and neurotransmitters Deck (33):
1

3.2 Learning Objectives

  • know the key terminology associated with nerve cells, hormones, and their functioning.
  • understand how nerve cells communicate.
  • understand the ways that drugs and other substances affect the brain.
  • understand the roles that hormones play in our behaviour.
  • apply your knowledge of neurotransmitters to form hypotheses about drug actions.
  • analyze the claim that we are born with all the nerve cells we will ever have.

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3.2 Focus Questions

  • which normal processes of nerve cells are disrupted by a substance like snake venom?
  • what roles do chemicals play in normal nerve cell functioning?

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Neurons

  • neurons: one of the major types of cells found in the nervous system, that are responsible for sending and receiving messages throughout the body.
  • genes in the cell body synthesize proteins that form the chemicals and structures that allow the neuron to function.
  • the activity of these genes can be influenced by the input coming from other cells, received by dendrites.
  • at any given point in time, a neuron will receive input from several other (sometimes over 1000) other neurons.
  • the impulses from other cells travel across the neuron to the base of the cell body, known as the axon hillock.
  • if the axon hillock receives enough stimulation from other neurons, it initiates a chemical reaction that flows down the rest of the neuron.
  • the activity travels from the axon hillock to the axon, until it reaches the end of the axon, known as the axon terminal, bulb-like extensions filled with vesicles containing neurotransmitters.
  • the impulse travelling down the axon will stimulate the release of neurotransmitters, allowing neural communication to take place.
  • sensory neurons: receive information from the bodily senses and bring it toward the brain.
  • motor neurons: carry messages away from the brain and spinal cord toward muscles in order to control their flexion and extension. (figure 3.13)
  • some cells have few or no dendrites, while some have very many branches; the physical structure of a neuron is related to the function it performs.
  • neurogenesis: the formation of new neurons.
    • stem cells: a type of cell that doesn’t have a predestined function; the deciding factor seems to be the stem cell’s chemical environment.
    • for a long time, scientists thought that nerves couldn’t regenerate, but recently they have observed neurogenesis in a number of brain regions, particularly in a region critical for learning and memory.

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Cell Body | Neurons

(soma) the part of a neuron that contains the nucleus that houses the cell’s genetic material. (figure 3.12)

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Dendrites | Neurons

small branches radiating from the cell body that receive messages from other cells and transmit those messages toward the rest of the cell.

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Axons | Neurons

transports information in the form of electrochemical reactions from the cell bod to the end of the neuron.

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Neurotransmitters | Neurons

the chemicals that function as messengers allowing neurons to communicate with each other.

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Glial Cells | Neurons

specialized cells of the nervous system that are involved in mounting immune responses in the brain, removing waste, and synchronizing the activity of the billions of neurons that constitute the nervous system.

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Myelin | Neurons

  • myelin: a fatty sheath, formed by glial cells, that insulates axons from one another, resulting in increased speed and efficiency of neural communication.
  • multiple sclerosis: a disease in which the immune system doesn’t recognize myelin and attacks it—a process that can devastate the structural functional integrity of the nervous system.
  • when myelin breaks down, it impairs the ability of the affected neurons to transmit information along their axons.
  • as a result, groups of brain structures that normally fire together to produce a behaviour can no longer work as a functional network.

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The Neuron's Electrical System

  • the network of cells that make up the neuron allows messages to be transmitted within the brain and the rest of the body; this activity involves the most important function a neuron can perform: to fire.
  • neural activity is based on changes in the concentrations of charged atoms called ions.
  • when a neuron is not transmitting information, the outside has a high concentration of positively charged ions (Na and K), while the interior has a high concentration of negatively charged ions (Cl).
  • electrostatic gradient: the inside and outside of the cell have difference charges.
  • concentration gradient: different types of ions are more densely packed on one side of the membrane than on the other.
  • ion channels: small pores in a cell membrane.
  • most substances have a tendency to move from areas of high concentration to areas of low concentration.
  • if ion channels opened up in the neuron’s cell membrane, there would be a natural tendency for positively charged sodium ions to rush into the cell.
  • when a neuron is stimulated, the surge of positive ions into the cell changes the potential of the neuron.
  • if enough positively charged ions reach the axon hillock to push its charge past that cell’s firing threshold, the neuron will initiate an action potential.
  • when an action potential occurs, the charge of that part of the axon changes from -70mV to +35mV (from negatively to positively charged). (figure 3.15)
  • once an axon becomes depolarized, it forces open the ion channels ahead of it, causing the action potential to move down the length of the axon as positively charged ions rush into the ion channels.
  • at each point of the axon, ion channels shut as soon as the action potential occurs; the K- ions that came into the cell are pumped back out.
  • hyperpolarized: the cell is more negative than its normal resting potential.
    • when the K- leave the cell, it causes the neuron to become hyperpolarized, making the cell less likely to fire.

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Resting Potential | The Neuron's Electrical System

approximately -70mV; the relatively stable state during which the cell is not transmitting messages.

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Action Potential | The Neuron's Electrical System

a wave of electrical activity that originates at the base of the axon and rapidly travels down its length. (figure 3.14)

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Refractory Period | The Neuron's Electrical System

the brief period (2-3 milliseconds) in which a neuron can’t fire.

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Synapses | The Neuron's Electrical System

  • synapses: the microscopically small spaces that separate individual nerve cells.
  • presynaptic cell: the cell that releases chemicals (neurotransmitters) into the synapse.
  • postsynaptic cell: the cell that contain receptors to receive the chemical input.
  • the dendrites of the postsynaptic cell contain specialized receptors that are designed to hold specific molecules, including neurotransmitters.
  • excitatory: when a neurotransmitter causes the neuron’s membrane potential to become less negative; it has increased the probability that an action potential will occur in a given period of time.
  • inhibitory: when a neurotransmitter causes the membrane potential to become more negative; it decreases the likelihood of an action potential occurring.

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All-Or-None Principle | The Neuron's Electrical System

  • all-or-none principle: individual nerve cells fire at the same strength every time an action potential occurs.
  • when stimulated, a given neuron always fires at the same intensity and speed.
  • the strength of a sensation is determined by the rate at which nerve cells fire as well as by the number of nerve cells stimulated.

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Neurotransmitters

  • each neurotransmitter has its own unique molecular shape; like a lock and key. (table 3.1)
  • after neurotransmitters have bound to postsynaptic receptors of a neighbouring cell, they’re released back into the synaptic cleft.
  • prolonged stimulation of the receptors makes it more difficult for the cell to return to its resting potential.
  • if a neurotransmitter attaches onto a receptor for long periods of time, it decreases the number of times that the neurons could fire (i.e. making your brain less powerful).

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Synaptic Cleft | Neurotransmitters

the minute space between the axon terminal (terminal button) and the dendrite.

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Reuptake | Neurotransmitters

a process whereby neurotransmitter molecules that have been released into the synapse are reabsorbed into the axon terminals of the presynaptic neuron. (figure 3.17)

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Glutamate | Neurotransmitters

  • glutamate: the most common excitatory neurotransmitter in the brains of vertebrates.
  • it’s involved in a number of processes, including our ability to form new memories.
  • abnormal functioning of glutamate-releasing neurons has been implicated in a number of brain disorders, including the triggering of seizures in epilepsy.

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GABA | Neurotransmitters

  • GABA: (gamma-amino butyric acid) the primary inhibitory neurotransmitter of the nervous system, meaning that it prevents neurons from generating action potentials.
  • it reduces the negative charge of neighbouring neurons further than their resting state of -70mV by causing an influx of Cl- to enter the cell.
  • it facilitates sleep and reduces arousal of the nervous system.
  • low levels of GABA have been linked to epilepsy, likely because there’s an imbalance between GABA and glutamate.

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Acetylcholine | Neurotransmitters

  • acetylcholine: one of the most widespread neurotransmitters within the body, found at the junctions between nerve cells and skeletal muscles; it is very important for voluntary movement.
  • released from neurons connected to the spinal cord; binds to receptors on muscles.
  • the change in electrical properties of the muscle fibres leads to a contraction of that muscle.
  • neuromuscular junction: the link between the nervous system and muscles.
  • activity is also associated with attention and memory.
  • drugs have been used to reduce the progression of Alzheimer’s disease by removing acetylcholine from the synapse, thus allowing it to have a larger effect on the postsynaptic cells

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Dopamine | Neurotransmitters

  • dopamine: a monoamine neurotransmitter involved in such varied functions as mood, control of voluntary movement, and processing of rewarding experiences.
  • is released by neurons in (at least) three pathways extending to different parts of the brain, including areas in the center related to movement and reward responses, and areas in the front third involved with controlling attention.

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Norepinephrine | Neurotransmitters

  • norepinephrine: (also known as noradrenaline) a monoamine synthesized from dopamine molecules that is involved in regulating stress responses, including increasing arousal, attention, and heart rate.
  • is formed in a specialized nuclei in the bottom of the brain (known as the brain stem) and projects throughout the cortex, influencing the activity of a number of different systems ranging from wakefulness to attention.
  • serves as a part of the “fight-or-flight” response.
  • works alongside epinephrine: (also known as adrenaline) a hormone and neurotransmitter created in the adrenal gland on the kidneys.

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Serotonin | Neurotransmitters

  • serotonin: a monoamine involved in regulating mood, sleep, aggression, and appetite.
  • formed in the brain stem and projects throughout the brain and spinal cord.
  • many antidepressants block the reuptake of serotonin, elevating mood and decreasing symptoms of depression and anxiety.
  • is also related to pain; e.g. individuals prone to migraines are more likely to have lower levels of serotonin.

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Substance P | Neurotransmitters

  • Substance P: a neurotransmitter involved in the experience of pain.
  • first discovered in 1931 when a paste made from the brain and intestine of a hose was found to cause muscles to contract.
  • found in the dorsal root of the spinal cord, an area that transmits pain information to the brain, as well as different areas of the brain related to pain response.
  • from an evolutionary standpoint, pain is an important messenger telling you to stop doing something that’s harming your body.
  • periaqueductal grey: the middle of the brain region; receives pain and temperature-related input from the spinal cord and sends it to the different areas of the cerebral cortex.
  • cerebral cortex: the wrinkled outer surface of the brain involved with many sophisticated processes.
  • Substance P is found in the amygdala (which responds to fear and arousal) and the hypothalamus (which is related to fight-or-flight responses and the release of different hormones).
  • congenital insensitivity to pain: a rare condition in which individuals lack the ability to perceive pain.
  • by better understanding the physiological basis of pain, researchers may be able to develop more effective drugs and other techniques to help alleviate pain.

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Agonists

  • agonists: drugs that enhance or mimic the effects of a neurotransmitter’s actions.
  • nicotine is an acetylcholine agonist, i.e. it stimulates the receptor sites for this neurotransmitter.
  • Xanax (alprazolam) is a GABA agonist, i.e. causes relaxation by increasing the activity of this inhibitory neurotransmitter.
  • direct agonist: physically binds to that neurotransmitter’s receptors at the postsynaptic cells.
  • indirect agonist: facilitates the effects of a neurotransmitter, but does not physically bind to the same part of the receptor as the neurotransmitter.

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Antagonists

  • antagonists: inhibit neurotransmitter activity by blocking receptors or preventing synthesis of a neurotransmitter. (figure 3.18)
  • Botox, which is derived from nerve-paralyzing bacterium that cause botulism, blocks the action of acetylcholine by binding to its postsynaptic receptor sites.
  • since Botox directly binds with acetylcholine receptors, it’s considered a direct antagonist.
  • if a chemical reduces the influence of a neurotransmitter without physically blocking the receptor, it would be classified as an indirect antagonist.

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Hormones | Endocrine System

  • hormones: chemicals secreted by the glands of the endocrine system.
  • neurotransmitters work almost immediately within the microscopic space of the synapse, whereas hormones are secreted in the bloodstream and travel throughout the body.
  • the endocrine system contributes to homeostasis: the balance of energy, metabolism, body temperature, and other basic functions that keeps the body working properly.

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Hypothalamus | Endocrine System

a brain structure that regulates basic biological needs and motivational systems.

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Pituitary Glands | Endocrine System

  • pituitary gland: the master gland of the endocrine system that produces hormones and sends commands about hormone production to the other glands of the endocrine system.
  • stress is loosely defined as an imbalance between perceived demands and the perceived resources available to meet those demands.
  • the hypothalamus signals the pituitary gland to release a hormone into the bloodstream that in turn stimulates the adrenal glands.

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Adrenal Gland | Endocrine System

  • adrenal glands: a pair of endocrine glands located adjacent to the kidneys that release stress hormones, such as cortisol and epinephrine.
  • cortisol and epinephrine help mobilize the body during stress, providing enough energy for you to deal with 

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Endorphin | Endocrine System

  • endorphin: a hormone produced by the pituitary gland and the hypothalamus that functions to reduce pain and induce feelings of pleasure.
  • released into the bloodstream during strenuous exercise, sexual activity, or injury.
  • morphine is a drug that binds to endorphin receptors, producing painkilling and euphoric effects.

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Endocrine System

  • testosterone is a hormone that drives physical and sexual development over the long term, and surges during sexual activity and in response to threats.
    • is correlated with aggressive thoughts and feelings.
  • in the last few years, a number of genes related to different neurotransmitters have been identified.
    • this affects neurotransmitter levels, and consequently how neurons communicate with each other.

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