Biological Psychology Thirteenth Edition Chapter 1 PDF

Biological Psychology Thirteenth Edition Chapter 1 Nerve Cells and Nerve Impulses © 2019 Cengage. All rights reserved.  1.1 The Cells of the Nervous System Your mental experiences depend on the activity of a huge number of separate but inte...

Biological Psychology Thirteenth Edition Chapter 1 Nerve Cells and Nerve Impulses © 2019 Cengage. All rights reserved.  1.1 The Cells of the Nervous System Your mental experiences depend on the activity of a huge number of separate but interconnected cells We can begin to understand how this works by looking at the cells of the nervous system The human nervous system comprises two kinds of cells – Neurons – Glia The human brain contains approximately 86 billion individual neurons © 2019 Cengage. All rights reserved. How Many Neurons Do We Have? © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Santiago Ramón y Cajal, a Pioneer of Neuroscience In the late 1800s, the Spanish investigator Santiago Ramón y Cajal (1852–1934) was the first to demonstrate that the individual cells comprising the nervous system remained separate – He showed that they did not merge into each other as previously believed © 2019 Cengage. All rights reserved.  The Structures of an Animal Cell (1 of 2) Like other cells in the body, neurons contain the following structures: – Membrane – Nucleus – Mitochondria – Ribosomes – Endoplasmic reticulum © 2019 Cengage. All rights reserved. An Electron Micrograph of the Parts of a Neuron © 2019 Cengage. All rights reserved.  The Structures of an Animal Cell (2 of 2) Membrane: separates the inside of the cell from the outside environment Nucleus: contains the chromosomes Mitochondrion: performs metabolic activities and provides energy that the cells requires Ribosomes: sites at which the cell synthesizes new protein molecules Endoplasmic reticulum: network of thin tubes that transports newly synthesized proteins to their location © 2019 Cengage. All rights reserved.  The Structure of a Neuron Neuron cells are similar to other cells of the body but have a distinctive shape © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Motor and Sensory Neurons A motor neuron – Has its soma in the spinal cord – Receives excitation from other neurons – Conducts impulses along its axon to a muscle or gland A sensory neuron – Is specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound, etc.) © 2019 Cengage. All rights reserved. A Vertebrate Motor Neuron © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved. A Vertebrate Sensory Neuron © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Components of All Neurons Dendrites Soma/cell body Axon Presynaptic terminals © 2019 Cengage. All rights reserved.  Dendrites Branching fibers with a surface lined with synaptic receptors responsible for bringing information into the neuron Some also contain dendritic spines that further branch out and increase the surface area of the dendrite The greater the surface area of the dendrite, the more information it can receive © 2019 Cengage. All rights reserved. Dendritic Spines © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Cell Body/Soma Contains the nucleus, mitochondria, and ribosomes Responsible for the metabolic work of the neuron Covered with synapses on its surface in many neurons © 2019 Cengage. All rights reserved.  Axons Thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles Maybe have a myelin sheath, an insulating material that contains interruptions in the sheath known as nodes of Ranvier Presynaptic terminals at the end points of an axon release chemicals to communicate with other neurons © 2019 Cengage. All rights reserved.  Afferent, Efferent, and Intrinsic Afferent axon: refers to bringing information into a structure Efferent axon: refers to carrying information away from a structure Interneurons or intrinsic neurons are those whose dendrites and axons are completely contained within a single structure © 2019 Cengage. All rights reserved. Cell Structures and Axons © 2019 Cengage. All rights reserved.  Variations Among Neurons Neurons vary in size, shape, and function The shape of a neuron determines it connection with other neurons and its contribution to the nervous system The function is closely related to the shape of a neuron – Example: Purkinje cells of the cerebellum branch extremely widely within a single plane © 2019 Cengage. All rights reserved. The Diverse Shape of Neurons © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Types of Glia Astrocytes – Help synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon – Responsible for dilating blood vessels to bring more nutrients into brain areas with heightened activity Microglia – Remove waste material, viruses, and fungi from the brain – Also remove dead, dying, or damaged neurons © 2019 Cengage. All rights reserved.  Neurons and Glia Oligodendrocytes (in the brain and spinal cord) and Schwann cells (in the periphery of the body) – Build the myelin sheath that surrounds and insulates certain vertebrate axons Radial glia – Guide the migration of neurons and the growth of their axons and dendrites during embryonic development – When embryonic development finishes, most radial glia differentiate into neurons and a smaller number differentiate into astrocytes and oligodendrocytes © 2019 Cengage. All rights reserved. Shapes of Various Glia Cells © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved. How An Astrocyte Synchronizes Associated Axons © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  The Blood-Brain Barrier A mechanism that surrounds the brain and blocks most chemicals from entering – The immune system destroys damaged or infected cells throughout the body – Because neurons in the brain generally do not regenerate, it is vitally important for the blood brain barrier to block incoming viruses, bacteria, or other harmful material from entering © 2019 Cengage. All rights reserved. How the Blood-Brain Barrier Works © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Active Transport The protein-mediated process that expends energy to pump chemicals from the blood into the brain – Glucose, certain hormones, amino acids, and a few vitamins are brought into the brain via active transport The blood-brain barrier is essential to health, but can pose a difficulty in allowing chemicals such as chemotherapy for brain cancer to pass the barrier © 2019 Cengage. All rights reserved.  Nourishment of Vertebrate Neurons Vertebrate neurons depend almost entirely on glucose – A sugar that is one of the few nutrients that can pass through the blood-brain barrier Neurons need a steady supply of oxygen – 20 percent of all oxygen consumed by the body is used by the brain The body needs a vitamin, thiamine, to use glucose Prolonged thiamine deficiency leads to death of neurons as seen in Korsakoff’s syndrome, a result of chronic alcoholism – Korsakoff’s syndrome is marked by severe memory impairment © 2019 Cengage. All rights reserved.  1.2 The Nerve Impulse The electrical message that is transmitted down the axon of a neuron – Does not travel directly down the axon, but is regenerated at points along the axon so that it is not weakened The speed of nerve impulses ranges from less than 1 meter/second to 100 meters/second – A touch on the shoulder reaches the brain more quickly than a touch on the foot The brain is not set up to register small differences in the time of arrival of touch messages However, in vision, movements must be detected as accurately as possible The properties of impulse control are well adapted to the exact needs for information transfer in the nervous system © 2019 Cengage. All rights reserved.  The Resting Potential of the Neuron Messages in a neuron develop from disturbances of the resting potential At rest, the membrane maintains an electrical gradient known as polarization – A difference in the electrical charge inside and outside of the cell The inside of the membrane is slightly negative with respect to the outside (approximately −70 millivolts) The resting potential of a neuron refers to the state of the neuron prior to the sending of a nerve impulse © 2019 Cengage. All rights reserved. The Membrane of a Neuron © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved. Methods for Recording Activity of a Neuron © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Forces Acting on Sodium and Potassium Ions The membrane is selectively permeable, allowing some chemicals to pass more freely than others Sodium, potassium, calcium, and chloride pass through channels in the membrane When the membrane is at rest: – Sodium channels are closed – Potassium channels are partially closed allowing the slow passage of potassium © 2019 Cengage. All rights reserved. Ion Channels in the Membrane of a Neuron © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Ion Channels The sodium-potassium pump is a protein complex – Continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell – Helps to maintain the electrical gradient – Uses active transport (requires ATP) © 2019 Cengage. All rights reserved.  Electrical and Concentration Gradients The electrical gradient and the concentration gradient— the difference in distributions of ions—work to pull sodium ions into the cell The electrical gradient tends to pull potassium ions into the cells – However, they slowly leak out, carrying a positive charge with them © 2019 Cengage. All rights reserved. Sodium and Potassium Gradients for a Resting Membrane © 2019 Cengage. All rights reserved.  The Action Potential (1 of 2) The resting potential remains stable until the neuron is stimulated – Hyperpolarization: increasing the polarization or the difference between the electrical charge of two places – Depolarization: decreasing the polarization toward zero – The threshold of excitation: a level above which any stimulation produces a massive depolarization © 2019 Cengage. All rights reserved.  The Action Potential (2 of 2) A rapid depolarization of the neuron The action potential threshold varies from one neuron to another, but is consistent for each neuron Stimulation of the neuron past the threshold of excitation triggers a nerve impulse or action potential © 2019 Cengage. All rights reserved.  Voltage-Activated Channels Membrane channels whose permeability depends upon the voltage difference across the membrane – Sodium and potassium channels When sodium channels are opened, positively charged sodium ions rush in and a subsequent nerve impulse occurs © 2019 Cengage. All rights reserved. The Movement of Sodium and Potassium Ions During an Action Potential © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved. The Movement of Sodium and Potassium After an action potential occurs, sodium channels are quickly closed The neuron is returned to its resting state by the opening of potassium channels – Potassium ions flow out due to the concentration gradient and take with them their positive charge The sodium-potassium pump later restores the original distribution of ions © 2019 Cengage. All rights reserved. Action Potential Animation © 2019 Cengage. All rights reserved.  Restoring the Sodium-Potassium Pump The process of restoring the sodium-potassium pump to its original distribution of ions takes time An unusually rapid series of action potentials can lead to a buildup of sodium within the axon – Can be toxic to a cell, but only in rare instances such as stroke and after the use of certain drugs © 2019 Cengage. All rights reserved.  Blocking Sodium Channels Local anesthetic drugs block sodium channels and therefore prevent action potentials from occurring – Example: Novocain and Xylocaine © 2019 Cengage. All rights reserved.  The All-or-None Law (1 of 2) Action potentials back-propagate into the cell body and dendrites – Dendrites become more susceptible to structural changes responsible for learning The all-or-none law – States that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it – Action potentials are equal in intensity and speed within a given neuron © 2019 Cengage. All rights reserved.  The All-or-None Law (2 of 2) Action potentials vary from one neuron to another in terms of amplitude, velocity, and shape Studies of mammalian axons show that there is much variation in the types of protein channels and therefore in the characteristics of the action potentials © 2019 Cengage. All rights reserved.  Refractory Periods After an action potential, a neuron has a refractory period during which time the neuron resists the production of another action potential – The absolute refractory period: the first part of the period in which the membrane cannot produce an action potential – The relative refractory period: the second part, in which it takes a stronger than usual stimulus to trigger an action potential © 2019 Cengage. All rights reserved. Propagation of an Action Potential (1 of 2) In a motor neuron, the action potential begins at the axon hillock (a swelling where the axon exits the soma) Propagation of the action potential: the transmission of the action potential down the axon – The action potential does not directly travel down the axon © 2019 Cengage. All rights reserved. Propagation of an Action Potential (2 of 2) © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  The Myelin Sheath The myelin sheath of axons are interrupted by short unmyelinated sections called nodes of Ranvier – Myelin is an insulating material composed of fats and proteins – At each node of Ranvier, the action potential is regenerated by a chain of positively charged ions pushed along by the previous segment © 2019 Cengage. All rights reserved. An Axon Surrounded by a Myelin Sheath © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Saltatory Conduction The “jumping” of the action potential from node to node – Provides rapid conduction of impulses – Conserves energy for the cell Multiple sclerosis: disease in which the myelin sheath is destroyed – Associated with poor muscle coordination and sometimes visual impairments © 2019 Cengage. All rights reserved. Saltatory Conduction in a Myelinated Axon © 2019 © 2019 Cengage. Cengage. All Allrights rightsreserved. reserved.  Local Neurons (1 of 2) Have short axons, exchange information with only close neighbors, and do not produce action potentials When stimulated, produce graded potentials— membrane potentials that vary in magnitude and do not follow the all-or-none law Depolarize or hyperpolarize in proportion to the stimulation © 2019 Cengage. All rights reserved.  Local Neurons (2 of 2) Difficult to study due to their small size Most of our knowledge has come from the study of large neurons Myth – Only 10 percent of neurons are active at any given moment Truth – You use all of your brain, even at times when you might not be using it very well © 2019 Cengage. All rights reserved.