* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download video slide
Neural engineering wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Membrane potential wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Action potential wikipedia , lookup
Node of Ranvier wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neuroregeneration wikipedia , lookup
Resting potential wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Electrophysiology wikipedia , lookup
Synaptic gating wikipedia , lookup
Biological neuron model wikipedia , lookup
Single-unit recording wikipedia , lookup
Neurotransmitter wikipedia , lookup
End-plate potential wikipedia , lookup
Synaptogenesis wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Nervous system network models wikipedia , lookup
Neuroanatomy wikipedia , lookup
Chapter 48 Neurons, Synapses, and Signaling PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings What you need to know… • The components of a reflex arc and how they work. • The organization and function of the major parts of the nervous system. • One function of each major brain region. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Lines of Communication • The cone snail kills prey with venom that disables neurons • Neurons are nerve cells that transfer information within the body • Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-1 48.1: Nervous Systems consist of Neuron Circuits • All animals except sponges may have some type of nervous system • What distinguishes the nervous systems of different animal groups – Is how the neurons are organized into circuits Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Quick Evolution of Nervous System Overview • Nerve Net – cnidarians • Cephalization – trend toward clustering sensory neurons and interneurons at anterior end – Flatworms – small brain and longitudinal nerve cord; simplest clearly defined nervous system – Annelids (earthworms, arthropods) – have a ventral nerve cord – Vertebrates – have a hollow dorsal nerve cord Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Nervous Systems Most Simplest CNS Nerve Nets Ventral Nerve Cord Vertebrates – hollow dorsal nerve cord Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Information Processing • Nervous Systems process information in three stages – Sensory input, integration, and motor output Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Information Processing • Sensory neurons – Transmit information from sensors that detect external stimuli and internal conditions • Sensory information – Sent to the CNS where interneurons integrate the information • Motor output leaves the CNS via motor neurons – Which communicate with effector cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Information Processing Example • Reflex – simple autonomic nerve circuit in response to a stimulus – Ex: Jerking finger off a flame – stimulus is detected by a receptor in the skin, conveyed via a sensory neuron to an interneuron in the spinal cord, which synapses with a motor neuron, which will causes the effector, a muscle cell, to contract Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Information Processing Example • The 3 stages of information processing are illustrated in the knee-jerk reflex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Definitions to know! • Cerebrospinal fluid – circulates through central canal in spinal cord and ventricles of brain – bathes cells with nutrients, carries away wastes • Grey Matter – consists of mainly neuron cell bodies and unmyelinated axons • White matter – white because of the myelin sheaths around the axons Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neuron Structure and Function • Most of a neuron’s organelles are in the cell body • Most neurons have dendrites, highly branched extensions that receive signals from other neurons • The axon is typically a much longer extension that transmits signals to other cells at synapses • An axon joins the cell body at the axon hillock Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-4 Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic cell Axon Synapse Synaptic terminals Postsynaptic cell Neurotransmitter • A synapse is a junction between an axon and another cell • The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell) • Most neurons are nourished or insulated by cells called glia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-5 Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons Cell bodies of overlapping neurons 80 µm Motor neuron CNS vs PNS • Central Nervous System (CNS) – Brain and spinal cord • Peripheral Nervous System (PNS) – Consists of paired cranial and spinal nerves associated with ganglia – Divided into • Motor (somatic) nervous system • Autonomic nervous system Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Motor (somatic) and Autonomic Nervous System • Motor (somatic) Nervous System – Carries signals to skeletal muscles – Voluntary • Autonomic Nervous System – Regulates the primarily automatic, visceral functions of smooth and cardiac muscles – Involuntary – 2 Divisions: Sympathetic Division and Parasympathetic Division Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sympathetic and Parasympathetic Divisions • Autonomic Nervous System – transmits signals that regulate the internal environment by controlling smooth and cardiac muscle – Sympathetic – when activated causes heart to beat faster and adrenaline to be secreted (with all its effects) – Parasympathetic – has the opposite effect when activated – slowing heartbeat and digestions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nervous System Flow Chart Nervous System Central Nervous System (CNS) Brain Spinal Cord: Nerve bundle that communicates with body Peripheral Nervous System (PNS) Somatic Nervous System: Voluntary control over muscles Sympathetic Division: Fight or flight Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Automatic Nervous System: Involuntary Control over Organs Parasympathetic Division: Rest and Digest • Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) – Are glia that form from the myelin sheaths around the axons of many vertebrate neurons Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 48.2: Vertebrate Brain is Regionally Specialized • Brain – Provides the integrative power that underlies the complex behavior of vertebrates • Spinal Cord – Integrates simple responses to certain kinds of stimuli and conveys information to and from the brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brain Parts • Brainstem – – Made up of the medulla oblongata, pons, and midbrain – Controls homeostatic functions such as breathing rate – Conducts sensory and motor signals between the spinal cord and higher brain centers – Regulates arousal and sleep Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brain Parts (cont) • Cerebellum – Helps coordinate motor, perceptual, and cognitive functions • Thalamus – Main center through which sensory and motor information passes to and from the cerebellum • Hypothalamus – Regulates homeostasis – basic survival features such as feeding, fighting, fleeing, and reproducing; thermostat, appestat, thirst center, and circadian rhythms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brain Parts (cont) • Cerebrum – 2 hemispheres – each with a covering of grey matter over white matter – Information processing is centered here, and this region is extensive in mammals • Cerebral cortex – – Controls voluntary movement and cognitive functions • Corpus callosum – Thick band of axons that enables communication between right and left cortices Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brain Parts (cont) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Membrane Potential: Formation of the Resting Potential • In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell • Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane • These concentration gradients represent chemical potential energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential • A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell • Anions trapped inside the cell contribute to the negative charge within the neuron Animation: Resting Potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-6 Key Na+ K+ OUTSIDE CELL OUTSIDE [K+] CELL 5 mM INSIDE [K+] CELL 140 mM [Na+] [Cl–] 150 mM 120 mM [Na+] 15 mM [Cl–] 10 mM [A–] 100 mM INSIDE CELL (a) (b) Sodiumpotassium pump Potassium channel Sodium channel Fig. 48-6a OUTSIDE [K+] CELL 5 mM INSIDE [K+] CELL 140 mM (a) [Na+] [Cl–] 150 mM 120 mM [Na+] 15 mM [Cl–] 10 mM [A–] 100 mM Fig. 48-6b Key Na+ K+ OUTSIDE CELL INSIDE CELL (b) Sodiumpotassium pump Potassium channel Sodium channel Modeling of the Resting Potential • Resting potential can be modeled by an artificial membrane that separates two chambers – The concentration of KCl is higher in the inner chamber and lower in the outer chamber – K+ diffuses down its gradient to the outer chamber – Negative charge builds up in the inner chamber • At equilibrium, both the electrical and chemical gradients are balanced Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-7 –90 mV Inner chamber +62 mV Outer chamber 140 mM KCI 150 mM 15 mM NaCI 5 mM KCI NaCI Cl– K+ Cl– Potassium channel (a) Membrane selectively permeable to K+ ( EK = 62 mV log 5 mM 140 mM ) = –90 mV Na+ Sodium channel (b) Membrane selectively permeable to Na+ ( ENa = 62 mV log 150 mM 15 mM ) = +62 mV Fig. 48-7a Inner chamber –90 mV Outer chamber 140 mM KCI 5 mM KCI K+ Cl– Potassium channel (a) Membrane selectively permeable to K+ ( 5 mM EK = 62 mV log 140 mM ) = –90 mV • In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-7b +62 mV 150 mM NaCI 15 mM NaCI Cl– Na+ Sodium channel (b) Membrane selectively permeable to Na+ ( ENa = 62 mV log ) = +62 mV 150 mM 15 mM Neurons communicate with other cells at synapses • At electrical synapses, the electrical current flows from one neuron to another • At chemical synapses, a chemical neurotransmitter carries information across the gap junction • Most synapses are chemical synapses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-14 Synaptic terminals of presynaptic neurons 5 µm Postsynaptic neuron • The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal • The action potential causes the release of the neurotransmitter • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell Animation: Synapse Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-15 5 Synaptic vesicles containing neurotransmitter Voltage-gated Ca2+ channel Postsynaptic membrane 1 Ca2+ 4 2 Synaptic cleft Presynaptic membrane 3 Ligand-gated ion channels 6 K+ Na+ Generation of Postsynaptic Potentials • Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell • Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-16 Terminal branch of presynaptic neuron E2 E1 E2 Membrane potential (mV) Postsynaptic neuron E1 E1 E1 E2 E2 I I Axon hillock I I 0 Action potential Threshold of axon of postsynaptic neuron Action potential Resting potential –70 E1 E1 (a) Subthreshold, no summation E1 E1 (b) Temporal summation E1 + E2 (c) Spatial summation E1 I E1 + I (d) Spatial summation of EPSP and IPSP Acetylcholine • Acetylcholine is a common neurotransmitter in vertebrates and invertebrates • In vertebrates it is usually an excitatory transmitter Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Biogenic Amines • Biogenic amines include epinephrine, norepinephrine, dopamine, and serotonin • They are active in the CNS and PNS Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Amino Acids • Two amino acids are known to function as major neurotransmitters in the CNS: gammaaminobutyric acid (GABA) and glutamate Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1. Distinguish among the following sets of terms: sensory neurons, interneurons, and motor neurons; membrane potential and resting potential; ungated and gated ion channels; electrical synapse and chemical synapse; EPSP and IPSP; temporal and spatial summation 2. Explain the role of the sodium-potassium pump in maintaining the resting potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3. Describe the stages of an action potential; explain the role of voltage-gated ion channels in this process 4. Explain why the action potential cannot travel back toward the cell body 5. Describe saltatory conduction 6. Describe the events that lead to the release of neurotransmitters into the synaptic cleft Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 7. Explain the statement: “Unlike action potentials, which are all-or-none events, postsynaptic potentials are graded” 8. Name and describe five categories of neurotransmitters Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings