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Chapter 4

Psych 101 Detailed Textbook Notes: Chapter 4

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Wilfrid Laurier University
Kathy Foxall

Psych Chapter 4 THE NERVOUS SYSTEM Central Nervous System  Defn: the portion of the nervous system consisting of the brain and spinal cord  Receives, processes, interprets, and stores incoming sensory information (taste, sounds, etc.)  Sends out messages for muscles, glands, and organs  Made up of two components: o The brain o The spinal cord  Extension of the brain  Defn: a collection of neurons and supporting tissue running from the base of the brain down the centre of the back, protected by a column of bones  Acts as a bridge between the brain and the parts of the body below the neck  Produces spinal reflexes (touching a hot iron and quickly removing hand)  Nerve impulses bring a message to the spinal cord, which then sends out a command for your muscles to retract your hand away from it  Reflexes above the neck involve the lower part of the brain  Can be influenced by thoughts and emotions (ex. Erection, controlling ejaculation, not moving your leg when it’s tapped) Peripheral Nervous System  Defn: all portions of the nervous system outside the brain and spinal cord; includes sensory and motor nerves  Handles the CNS’s input and output  Consists of 43 pairs of nerves that transmit information to and from the CNS o 12 pairs of cranial nerves in the head enter the brain directly o 31 pairs of spinal nerves enter the spinal cord at the spaces between the vertebrae  Kinds of nerves: o Sensory nerves – carry messages from receptors in the skin, muscles, and other internal and external sense organs and sends them to the brain o Motor nerves – carry orders from the CNS to the muscles, glands, and organs.  They enable us to move  Cause glands to contract and to secrete substances like hormones  Divided into two parts: o Somatic (bodily) nervous system  Sometimes called the skeletal nervous system  Consists of nerves that are connected to sensory receptors and to the skeletal muscles that permit voluntary action  Ex. When you feel a bug on your arm, when you write your name, when you turn off a light o Autonomic (self-governing) nervous system  Regulates the functioning of blood vessels, glands, and internal organs like the bladder, stomach, and heart  Ex. Seeing a crush and your heart pounds, hands get sweaty, cheeks feel hot  Divided into two parts:  Sympathetic nervous system o Defn: subdivision of the autonomic nervous system that mobilizes bodily resources and increases the output of energy during emotion and stress o Ex. Increases heart rate, dilates pupils, stimulates sweat glands o Fight or flight situations  Parasympathetic nervous system o Defn: subdivision of the autonomic nervous system that operates during relaxed states and that conserves energy o Ex. Slows heartbeat, constricts pupils o If you have to jump out of the way of a speeding motorcyclist, the parasympathetic nerves will slow things down again COMMUNICATION IN THE NERVOUS SYSTEM Neurons  Also called nerve cells  Defn: a cell that conducts electrochemical signals; the basic unit of the nervous system  Held in place by glia or glial cells o Defn: cells that support, nurture, and insulate neurons, remove debris when neurons die, enhance the formation and maintenance of neural connections, and modify neuronal functioning o Make up 90% of the brain`s cells o Also protect the brain from toxic agents o Without them, neurons could not function effectively o Help determine which neural connections get stronger or weaker o Vital role in learning and memory  Considered the building blocks of the nervous system  Structured like snow-flakes  Estimate of 100 billion neurons in the human brain The Structure of the Neuron  Three main parts: 1. Dendrites  Defn: a neuron’s branches that receive information from other neurons and transmit it toward the cell body  Look like branches of a tree  Comes from Greek word meaning “little tree”  Act as antennas 2. Cell body  Defn: the part of the neuron that keeps it alive and determines whether or not it will fire  Shaped like a sphere or pyramid  Contains the biochemistry machinery needed to keep the neuron alive 3. Axon  Defn: a neuron’s extending fibre that conducts impulses away from the cell body and transmits them to other neurons  Greek for “axle”  Divide at the end into branches called axon terminals  Vary in size from a few microns to more than a meter in length  Insulated by a surrounding layer of fatty material called the myelin sheath  Nodes divide it into segments  Prevents signals in adjacent cells from interfering with each other  Speeds up the conduction of neural impulses  In the peripheral nervous system the fibres of individual neurons (axons and sometimes dendrites) are collected together in bundles called nerves NEURONS IN THE NEWS  Severed axons in the spinal cord can regrow if you treat them with certain nervous system chemicals, from research on animals  Canadian neuroscientist, working with mice, immersed immature cells from the animal’s brains into a growth promoting protein and showed that these cells could give birth to new neurons in a process called neurogenesis o Defn: the production of new neurons from immature stem cells  Human brain and other body organs have the same cells, stem cells o Defn: immature cells that renew themselves and have the potential to develop into mature cells o Stem cells involved in learning and memory seem to divide and mature throughout adulthood o Physical activity, effortful mental activity, and a good environment promote production and survival of new cells o Aging, stress, and nicotine can inhibit their survival or kill them o Embryonic stem cells:  Preferred by scientists  Can differentiate into any type of cell o Success in animals – rats with spinal cord injuries regained ability to walk  Most of the cells turned into neurons or glial cell HOW NEURONS COMMUNICATE  Neurons do not touch each other, they are separated by a minuscule space called the synaptic cleft – where the axon terminal of one neuron nearly touches a dendrite or cell body of another  Entire site is called a synapse o Defn: the site where transmission of a nerve impulse from one nerve cellto another occurs; it includes the axon terminal, the synaptic cleft, and receptor sites in the membrane of the receiving cell o Number of synapses is in trillions +  Neurons speak to one another in an electrical and chemical language  Action potential o Defn: a brief change in electrical voltage that occurs between the inside and the outside of an axon when an neuron is stimulated; serves to produce an electrical impulse o Related to myelin sheath  Nerve impulses travel slower in babies because the myelin sheaths on their axons are not yet fully developed  When a neural impulse reaches the axon terminal’s tip, synaptic vesicles open and release neurotransmitters o Defn: a chemical substance that is released by a transmitting neuron at the synapse and that alters the activity of a receiving neuron  When they reach the other side, they bind briefly with receptor sites  Effect is either: o Excitatory – voltage shift in a positive direction  Will most likely fire o Inhibitory – voltage shift in a negative direction  Probably won’t fire  Inhibition is very important in the nervous system, without it we couldn’t sleep  Thousands of messages are sent to the cell, factors depending on which ones are successful: o The rate at which neurons are firing o How many are firing o What types of neurons are firing o Where they are located o The degree of synchrony among different neurons  Does NOT depend on the strength of the firing neurons THE PLASTIC BRAIN  As a child unused synaptic connections diminish, could explain why there are certain learning stages emphasized early in life  Another developmental phase that continues from adolescence for the rest of your life  Brain retains flexibility in adapting to new experiences, called plasticity o Defn: the brain’s ability to change and adapt in response to experience – for example, by reorganizing or growing new neural connections o Brains can rewire themselves to adapt to change, i.e. cannot move arm after brain injury regain use after physical therapy  Studies on people blind from birth or early childhood, when trying to determine where a sound is coming from, what happens in the occipital cortex?  The brain is capable of processing non-visual information, but only when needed, ex. Blind CHEMICAL MESSENGERS IN THE NERVOUS SYSTEM Neurotransmitters: versatile couriers  Can effect mood, memory, and well-being  The nature of the effect depends on o The level o Its location o Type of receptor it binds with  Some neurotransmitters and their effects: o Serotonin – sleep, appetite, sensory perception, temperature regulation, pain suppression, and mood o Dopamine – voluntary movement, learning, memory, emotion, pleasure or reward, response to novelty o Acetylcholine – muscle action, cognitive functioning, memory, emotion o Norepinephrine – increased heart rate and slowing of intestinal activity during stress, learning, memory, dreaming, waking from sleep, and emotion o GABA – major inhibitory neurotransmitter in the brain o Glutamate – major excitatory neurotransmitter; released by about 90% of neurons  Foods and their effects, ex. High-carb and no protein will make you calm or sluggish whereas a high-protein no carb meal will promote alertness Endorphins: The Brain’s Natural Opiates  Defn: chemical substances in the nervous system that are similar in structure and action to opiates; they are involved in pain reduction, pleasure, and memory  AKA endogenous opioid peptides  Some function as neurotransmitters, but most act by altering the effects of them, ex. By limiting or prolonging effects  Endorphin levels shoot up when scared or stressed, makes pain bearable  Connection with mother stimulates flow of endorphins, similar to falling in love Hormones: Long Distance Messengers  Defn: chemical substances secreted by organs called glands, that affect the functioning of other organs  Produced primarily in endocrine glands o Defn: internal organs that produce hormones and release them in the bloodstream  Jobs include promoting bodily growth to aiding digestion and regulating metabolism  Popular hormones: 1. Melatonin  Secreted by the pineal gland deep in the brain  Regulates daily biological rhythms and promotes sleep 2. Oxytocin  Secreted by the pituitary gland  Enhances uterine contractions during childbirth and facilitates breastfeeding  Contributes to relationships by promoting attachment and trust 3. Adrenal Hormones  Produced by the adrenal glands  Involved in emotion and stress  Also responds to heat, cold, injury, pain, burns, and some drugs  Two parts: o Outer – produces cortisol, increases sugar levels and boosts energy o Inner – produces epinephrine, or adrenaline, and norepinephrine
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