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Chapter 3

Chapter 3

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University of Toronto Scarborough
Steve Joordens

Chapter 3: (pgs. 78-119) Psychology: The Evolution of a Science 1) Neurons: The Origin of Behavior (pgs 78 – 82)  All thoughts, feelings, and behaviors spring from cells in the brain called neurons that take in information and produce some kind of output  Discovery of How Neurons Function (pg 78)  Santiago Ramón y Cajal (1852 – 1934) learned of a new technique for staining neurons in the brain, called Golgi-Stained Neurons.  Provided important information about the nature and structure of the nervous system. o Learned that each neuron was composed of a body with many threads extending outward toward other neurons, but that the threads of each neuron did not actually touch other neurons. o Realized that neurons are information-processing units of the brain and even though there was a gap between neurons, they communicated in some way.  Components of the Neuron (pgs 79 – 80)  Cajal discovered that neurons are composed of three basic parts: the cell body, the dendrites, and the axon.  Cell body is the largest component of the neuron and coordinates functions such as protein synthesis, energy production, and metabolism to occur within it. Also contains a nucleus that houses chromosomes contain DNA. Cell body is surrounded by a porous cell membrane allowing molecules to flow in and out of the cell.  Neurons have two types of specialized extensions of the cell membrane allowing communication: dendrites and axon. o Dendrites receive information from other neurons  cell body. Look like tree branches; can be many of them. o Axon transmits information to other neurons, muscles, or glands  cell body. Each neuron has a single axon.  Axon is covered by a myelin sheath; composed of glial cells.  Myelin sheath insulates axon for more efficient transmission of information.  Example: Demyelinating diseases like Multiple Sclerosis, myelin sheath deteriorates  slows transmission of information  loss of feeling in limbs, partial blindness, and difficulties in coordinated movement and cognition.  Glial cells perform variety of functions like digesting parts of dead neurons, providing physical and nutritional support for neurons, and form myelin.  Small gap between axon of one neuron and, dendrites or cell body of another is called the synapse. Provides communication of information between neurons, allowing thinking, feeling, and behaving.  Major Types of Neurons (pg 81)  There are three major types of neurons, each with a distinct function: sensory neurons, motor neurons, and interneurons.  Sensory neurons receive information from external world  spinal cord  brain. Receive signals for five senses.  Motor neurons carry signals to produce movement from spinal cord  muscles How do the three types of neurons work together to transmit information?  Most of nervous system composed of interneurons: connect sensory neurons, motor neurons, or other interneurons.  Neurons Specialized by Location (pg 82)  Neurons are also specialized depending on their location; structure changes.  Purkinje cells carry information from cerebellum  rest of the brain/spinal cord. Have dense and multiple dendrites.  Pyramidal cells found in cerebral cortex have a triangular cell body and a single, long dendrite with multiple smaller dendrites.  Bipolar cells have a single axon and single dendrite, and are found in the retinas of the eye. Summary:  Neurons are the building blocks of the nervous system. They process information received from the outside world, they communicate with one another, and they send messages to the body’s muscles and organs.  Neurons are composed of three major parts: the cell body, dendrites, and the axon.  The cell body contains the nucleus, which houses the organism’s genetic material.  Dendrites receive sensory signals from other neurons and transmit this information to the cell body.  Each neuron has only one axon, which carries signals from the cell body to other neurons or to muscles and organs in the body.  Neurons don’t actually touch: They are separated by a small gap, which is part of the synapse across which signals are transmitted from one neuron to another.  Glial cells provide support for neurons, usually in the form of the myelin sheath, which coats the axon to facilitate the transmission of information. In demyelinating diseases, the myelin sheath deteriorates.  Neurons are differentiated according to the functions they perform. The three major types of neurons include sensory neurons, motor neurons, and interneurons. Examples of sensory neurons and interneurons are, respectively, bipolar neurons and Purkinje and pyramidal cells. 2) The Electrochemical Actions of Neurons: Information Processing (pgs 83 – 91)  Communication of information between neurons occurs in two stages: conduction and transmission. Referred to the electrochemical action of neurons.  During the first stage, conduction, an electrical signal is passed along from neurons  dendrites  cell body  axon  During the second stage, transmission, the electrical signal is passed between neurons over the synapse.  Electric Signaling: Conducting Information with a Neuron (pgs 83 – 86)  Neuron’s cell membrane is porous, allowing ions to flow in and out of cell.  The Resting Potential: The Origin of the Neuron’s Electrical Properties  Neurons have a natural negative electric charge of about – 70 millivolts called the resting potential; the difference in charge due to difference in concentration of ions inside and outside of the neuron. o In the resting state, there is a high concentration of positively charged ions, potassium + + (K ) inside the neuron; and a high concentration of positively charged ions, sodium (Na ) and negatively charged ions, chlorine (Cl ) outside the neuron. + +  During the resting state, K molecules flow freely across the cell membrane, while Na molecules are kept out of the neuron.  The Action Potential: Sending Signals Across the Neuron  Action potential only occurs when an electrical signal, reaching a threshold (about 40 millivolts), is sent to the neuron. The K channel is shut down and the Na channel opens, which allows increasing the positive charge within the neuron.  After the action potential reaches its maximum, the membrane channels return to original state. o At this point, refractory period occurs when the ions are imbalanced, and cannot initiate another action potential. o The imbalance of ions is reversed by an active chemical “pump”, moving Na outside the + axon, and moving K , inside the axon. This is how the transmission of information is passed along the axon.  The action potential is spread, initiating an action potential at another nearby location, and so on, thus transmitting the charge down the axon.  Myelin does cover the entire axon, it clumps around with little break points called the nodes of Ranvier o Discovered by Louis- Antoine Ranvier o Saltatory conduction: Charge seems to “jump” from node to node, helping speed the flow of information  Chemical Signaling: Transmission between Neurons (pg 86)  Electric charge of the action potential takes form that can cross the synaptic gap. How does a neuron communicate with another neuron?  Synaptic transmission: Axons sending the action potential end in terminal buttons that contain neurotransmitters. Dendrites receiving the action potential contain receptors. + +  As K and Na flow across, they move the sending neuron (presynaptic neuron), from a resting potential to an action potential o Action potential  Presynaptic neuron  Axon’s terminal button  Release of neurotransmitters from vesicles  Synapse  Moving the presynaptic neuron to the nearby dendrite’s receptor site of the receiving neuron (postsynaptic neuron) o Synapse  Binds to dendrite’s receptor site  Postsynaptic neuron  Action potential o Neurotransmitters and receptor sites act like a lock-and-key system What happens to the neurotransmitters left in the synapse after synaptic transmission?  Neurotransmitters leave the synapse through three processes: 1) Reuptake: Neurotransmitters are reabsorbed by the terminal buttons of the presynaptic neuron’s axon. 2) Enzyme deactivation: Neurotransmitters are destroyed by enzymes in the synapse. 3) Autoreceptors: Neurotransmitters can bind to the autoreceptors on presynaptic neurons. They detect how much of a neurotransmitter has been released into a synapse and signal the neuron to stop releasing the neurotransmitter when an excess is present.  Types and Functions of Neurotransmitters (pgs 86 – 87)  Acetylcholine (ACh): Involved in voluntary motor control. Found in neurons when axons connect to muscle and body organs, like the heart. Also contributes to regulation of attention, learning, sleeping, dreaming, and memory. Alzheimer’s disease involving severe memory impairments is associated with deterioration of Ach-producing neurons.  Dopamine: Regulates motor behavior, motivation, pleasure, and emotional arousal. Plays a role in drug addiction, linked to schizophrenia (high levels), and linked to Parkinson’s disease (low levels).  Glutamate: A major excitatory neurotransmitter; enhances transmission of information. High levels can overstimulate and cause seizures.  GABA (gamma-amniobutyric acid): A primary inhibitory neurotransmitter; stops the firing of neurons. Low levels can overstimulate and cause seizures.  Norepinephrine: Influences mood and arousal. Involved in states of vigilance and heightened awareness of danger. Low levels implicate mood disorders.  Serotonin: Regulates sleep and wakefulness, eating, and aggressive behavior. Low levels implicate mood disorders.  Endorphins: Act within pain pathways and emotion centers of brain. Dulls the experience of pain and elevates moods. For example, the “runner’s high” when athletes push their bodies to painful limits of endurance.  Imbalance of neurotransmitters can sometimes occur naturally or being actively caused by a person. o Naturally caused: Brain not producing enough serotonin  depressed or anxious moods o Actively caused: Smoking, drinking alcohol, and taking drugs  How Drugs Mimic Neurotransmitters (pgs 88 – 90)  Drugs affect nervous system by increasing, interfering with, or mimicking the manufacture or function of neurotransmitters; agonists and antagonists.  Examples: o L-dopa: Acts as an agonists by enhancing production of dopamine o MPTP: Acts as an antagonists by destroying dopamine-producing neurons o Methamphetamine: Combination of agonist and antagonist effects alters function of neurotransmitters that help perceive and interpret visual images (hallucinations) o Amphetamine: Agonist action of preventing reuptake of floods synapse with nor- epinephrine and dopamine. o Prozac: A selective serotonin reuptake inhibitor (SSRI): agonist action of blocking reuptake of serotonin. By blocking reuptake, serotonin remains in the synapse longer and produces greater activation of serotonin receptors  helps to relieve depression. o Beta-blockers: Obstructs receptor site for nor-epinephrine in heart  heart rate slows  regulates fast and irregular heartbeats. Summary:  The conduction of an electric signal within a neuron happens when the resting potential is changed by an electric impulse called an action potential. +  The neuron’s resting potential is due to differences in the K concentrations inside and outside the cell membrane, resulting from open potassium channels that allow K to flow outside the + membrane together with closed channels for Na and other ions.  If electric signals reach a threshold, this initiates an action potential, an all-or-none signal that moves down the entire length of the axon. The action potential occurs when sodium channels in the axon membrane open and potassium channels close, allowing the Na ions to flow inside the axon. After the action potential has reached its maximum, the sodium channels close and the potassium channels open, allowing K to flow out of the axon, returning the neuron to its resting potential. For a brief refractory period, the action potential cannot be re-initiated. Once it is initiated, the action potential spreads down the axon, jumping across the nodes of Ranvier to the synapse.  Communication between neurons takes place through synaptic transmission, where an action potential triggers release of neurotransmitters from the terminal buttons of the sending neuron’s axon, which travel across the synapse to bind with receptors in the receiving neuron’s dendrite.  Neurotransmitters bind to dendrites based on existing pathways in the brain and specific receptor sites for neurotransmitters. Neurotransmitters leave the synapse through reuptake through enzyme deactivation, and by binding to autoreceptors.  Some of the major neurotransmitters are acetylcholine (ACh), dopamine, glutamate, GABA, norepinephrine, serotonin, and endorphins.  Drugs can affect behavior by acting as agonists, that is, by facilitating or increasing the actions of neurotransmitters, or as antagonists by blocking the action of neurotransmitters. Recreational drug use can have an effect on brain function. 3) The Organization of the Nervous System (pgs 91 -95)  Network of neurons refers to the nervous system. The nervous system has major divisions and components.  Divisions of the Nervous System (pgs 91 -93)  Two major divisions of the nervous system: central nervous system and peripheral nervous system. o Central Nervous System (CNS) is composed of the brain and spinal cord. Receives information from external world, processes, and coordinates this information, and sends commands to skeletal and muscular systems. o Peripheral Nervous System (PNS) connects the CNS to the body’s organs and muscles. It has two major subdivisions: somatic nervous system and autonomic nervous system.  Somatic Nervous System used to convey information into and out of the CNS. Humans use it to perceive, think, and coordinate their behaviors.  Autonomic Nervous System used to control blood vessels, body organs, and glands to regulate bodily systems. It has two major subdivisions: sympathetic nervous system and parasympathetic nervous system.  Sympathetic nervous system is used for action in threatening situations.  Parasympathetic nervous system is used to return the body to a normal resting state.  Components of the Central Nervous System (pgs 93 – 95)  Central nervous system has only two elements: the brain and the spinal cord.  Spinal cord doesn’t always need input from the brain for some very basic behaviors. Connections between the sensory inputs and motor neurons in the spinal cord mediate spinal reflexes. o Example: Placing hand near a hot stove (input sensory neuron)  pull hand away (output motor neuron) Summary:  Neurons make up nerves, which in turn form the human nervous system.  The nervous system is divided into the peripheral and the central nervous systems.  The peripheral nervous system connects the central nervous system with the rest of the body, and it is itself divided into the somatic nervous system and the autonomic nervous system.  The somatic nervous system, which conveys information into and out of the central nervous system, controls voluntary muscles, whereas the autonomic nervous system automatically controls the body’s organs.  The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems, which complement each other in their effects on the body. The sympathetic nervous system prepares the body for action in threatening situations, and the parasympathetic nervous system returns it to its normal state.  The central nervous system is composed of the spinal cord and the brain. The spinal cord can mediate some basic behaviors such as spinal reflexes without input from the brain. 4) Structure of the Brain (pgs 95 – 104)  Each side of the brain is basically analogous, but one half of the brain specializes in some tasks that the other half doesn’t. Yet they are all part of one big, interacting, interdependent whole.  There are three major divisions of the brain: the forebrain, the midbrain, and the hindbrain  The Hindbrain (pg 96)  Responsible for information coming into and out of the spinal cord; controls the most basic functions of life like respiration, alertness, and motor skills.  There are three anatomical structures that make up the hindbrain: the medulla, the cerebellum, and the pons.  The medulla coordinates heart rate, circulation, and respiration. Inside the medulla is a small cluster of neurons, the reticular formation. o Reticular formation regulates sleep, wakefulness, and levels of arousal; what most general anesthetics tend to reduce activity in.  The cerebellum controls fine motor skills like riding a bike, playing the piano, or maintaining balance while walking and running to be graceful.  The pons act as a bridge between the cerebellum and other structures in the brain.  The Midbrain (pgs 96 – 97)  Important for orientation and movement.  The central location of neurotransmitters. Made up of two main structures: the tectum and the tegmentum.  The tectum is involved in motivation; receives stimulus input from eyes, ears, and skin and moves the organism in a coordinated way towards the stimulus.  The tegmentum is involved in movement and arousal.  The Forebrain (pg 96)  The forebrain is the highest level of the brain; it controls complex cognitive, emotional, sensory, and motor functions.  It is divided into two main sections: the cerebral cortex and the subcortical structures.  The cerebral cortex is the outmost layer which is divided into two hemispheres.  The subcortical structures are housed underneath the cerebral cortex.  Subcortical Structures  Thalamus, Hypothalamus, and Pituitary Gland  All located in the center of the brain  The thalamus receives inputs from all the major senses except smell and acts like a computer serve taking in multiple inputs and relaying them to a variety of locations. Also, closes input pathways during sleep.  The hypothalamus regulates body temperature, hunger, thirst, and sexual behavior.  The pituitary gland is the body’s hormone-producing system.  The Limbic System  Involved in motivation, emotion, learning, and memory. Three structures are part of the limbic system: the hypothalamus, the amygdala, and the h
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