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Nervous Systems of Animals from Simple to Complex Three trends in evolution of the nervous system • Centralization: – Are nerves concentrated or centralized? • Cephalization: – Is there a head region? • Specialization: – Are its sense organs complex? Sponges • Only multi-cellular organism with no nervous system. QuickTime™ and a decompressor are needed to see this picture. Cnidarians Nerve net: • A nerve net is a collection of separate, but "connected" neurons. • No ganglia, no centralization. • Some jellyfish have structure that detect – – – – light (called ocelli) balance (called statocysts) chemical detection (olfaction), touch (called sensory lappets) Quick Time™ and a decompressor are needed to s ee this pic ture. Platyhelminthes Flatworms • Nerve net connected by nerve cords connected to ganglia. • Contain some receptors to find food and to find light so that they can avoid it. • More cephalization than Cnidarians Quick Time™a nd a dec ompr esso r ar e nee ded to see this pictur e. Nematodes Roundworms • A roundworm, the nerve cells are even more centralized. A roundworm has two nerve cords that transmit impulses in the roundworm. Annelida Segmented worms • A earthworm has a nervous system with a simple brain and nerve cord. • The "brain" is located above the pharynx and is connected to the first ventral ganglion. • Each segment has its own ganglia, gets info from its own segment and controls, muscles in its own region • Earthworms have touch, light, vibration and chemical receptors all along the entire body surface. Echinoderms Simple nerve ring surrounds mouth and radial nerves into the arms • Eyespots on each arm that have light sensitive pigments. • Think back: What type of protist had an eyespot? Mollusks: Nervous System • Ganglia are organized into a brain • centralized brain and a multitude of sense organs Example: 1. Snails: 6 ganglia. 2. Bivalves: 3 pairs of ganglia Specialization: controls esophagus, muscles close to the shell, and foot. Arthropods Insecta • Example-Grasshopper • centralized brain and many sense organs • Receptors for for taste and smell and on antennae and legs • Antennae can detect odors or touch objects. • Insects have – simple eyes – compound eyes. Fish • Well developed nervous systems, highly developed sense organs (olfactory bulbs), and a lateral line system that detects water movement (That is why we do not pound on the glass of an aquarium) QuickTime™ and a decompressor are needed to see this picture. Amphibians • Well developed nervous and sensory systems, keen vision for spotting insects, hear through their tymphanic membranes, lateral line system in water Quic kTime™ and a dec ompres sor are needed to see this pic ture. Reptiles • Similar pattern of brain as amphibians • Cerebrum and cerebellum in reptile is much bigger than amphibians • Many snakes-good sense of smell • Simple external ear drum and single bone conducting sound to inner ear QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this pict ure. Birds • Well-developed sense organs needed for flight – Birds see well – Birds hear well Bird’s brain is large for its body size. Possess cerebrum, cerebellum and medulla oblongata Birds, cont. • Poor sense of smell but highly developed eyes. • Lens is highly flexible in water birds • Ear lacks external pinna and sound still conducted by a single bone (columella). • Cochlea is present though not spiralled as in mammals Primates • Binocular vision, welldeveloped cerebrum, fingers and toes, and arms that rotate around their shoulder joint. QuickTime™ and a decompressor are needed to see this picture. Chordates • Nonvertebrate chordates: simple nervous system with a mass of nerve cells that form a brain • Vertebrates: More complex brains with distinct regions each with a different functions. Sources • http://faculty.washington.edu/chudler/inv ert.html from Neuroscience for Kids • Miller and Levine Biology Textbook • Google images Nervous System Biologically speaking, all thought and action results from your nervous systems. Question of the Day We will go around the room and have each student name one disease of the nervous system. Some examples Alzheimers Parkinson’s Disease Multiple Sclerosis Tourette’s Syndrome Amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s Epilepsy Stroke Brain tumors Meningitis Muscular Dystrophy Tension headaches Concussions Migraines How do you receive signals? The cell body contains the nucleus and receives signals from other neurons on branches called dendrites or directly on the cell body. QuickTime™ and a decompressor are needed to see this picture. The axon conducts signals away from the cell body and divides into many branches at the nerve terminal. What are the parts of a nerve cell? Cell body Dendrite Axon What do neurons (nerve cells) do? receive, conduct, and transmit signals. http://www.youtube.com/watch?v=FZ3401XVY ww&feature=related http://www.youtube.com/watch?v=AjxJabpjDG o&feature=related How are signals transmitted? Impulses travel the nerve highway The nervous system uses chemicals called neurotransmitters and synapses. How do you interpret signals? Sense organs Central Nervous System How are you respond to the signals? 9-12.IV.G.2 The student will describe how the functions of individual organ systems are integrated to maintain a homeostatic balance in the body. Content Limit: Items are limited to those which require both hormonal and nervous regulation. Items will be placed in scenarios that refer to body temperature, breathing, and pulse rate as homeostatic disruptions of the human body, or any scenario that addresses symptoms or disruptions of homeostasis. Items will provide opportunities for students to describe examples they supply. Items will NOT address positive feedback. Neurotransmission ISAT 351, Spring, 2004 College of Integrated Science and Technology James Madison University Neuron Structure Neurons Signal next Reception (chemical) Signal Propagation (electrical) Relay to cell Electrical & Chemical Signal Propagation • Electrical Signal – Signal propagation within neuron – Branched axon terminus amplifies signal – Terminus makes synapses with target cells • Chemical Signal – Propagation between cells – Neurotransmitters – Relay electrical signal via exo- & endocytosis – Targets: • Another neuron • Dendrite • Muscle cell Types of Neurons Sensory neurons receive and convert stimuli from the environment into electrical signals Interneurons receive signals from neurons and transmits signals to neurons Motor neurons receive signals from interneurons and stimulate muscle or glands Structures are Similar Neuron Signals Electric signals transmit information within a cell from the cell body to the axon terminus by an electric impulse called an action potential Chemical signals transmit information from sensory cells, between neurons (synapses), and to specialized cells such as muscle or glands Neurons Form Circuits Electrical Signal Nerve signals are changes in the electrical potential across the neuron’s plasma membrane (membrane potential) The action potential or nerve impulse can carry a message without signal attenuation Action potentials actively propagate signal via voltage-gated Na+ channels Explosion of activity propagated & amplified along membrane Electrical Signal • Myelin sheath insulates nerve – Prevents signal attenuation – Promotes signal propagation and amplification – Multiple sclerosis involves demyelination Electrical Signal = Action Potential • Intra- & extracellular [ion] different – [K+] high internally – [Na+, Cl-] high externally • Consequences: – Unequal distribution of cations and anions – Baseline membrane potential changes when ion distribution changes Propagation of Action Potential Resting + + + + + + + + + Baseline Membrane Potential -60mV V1 + + + + + + + + - Action Potential -40mV V2 + + + + + + + + + - Recovery Propagation : Depolarization Wave So, Depolarizing membrane by about 20 mV triggers action potential Voltage-Gated Channels Mediate Action Potential •Depolarization causes channels to open and an influx of anions (Na+) causes further depolarization resulting in the action potential. •How is the membrane repolarized? Three Conformational States Channel inactivated until K+ ions repolarize membrane; speeds recovery The Action Potential Voltage-Gated Channel Measurement of Potential Propagation Measurement • 1 electrode inside, other outside • Stimulate & measure as a function of time • V1, V2, V3 have identical amplitudes – Shape & intensity of potential maintained – Zero attenuation as signal propagated Consequences • All-or-none; neurons are resting or conducting • Amplitude constant, so size of action potential not important • THE FREQUENCY OF ACTION POTENTIAL FIRINGS CARRY INFORMATION • RATE OF PROPAGATION FACILITATED BY MYELIN INSULATION Synapses Communicate Between Neurons • 10-100 BILLION neurons in human brain • 10-100 TRILLION synapses • Human forebrain: ratio of synapses:neurons about 40,000:1 • Elastic: improve connectivity by using neurons • Neurons communicate via neurotransmitters: – Electrical-to-chemical-to electrical signal conversion Electrical to Chemical Signal Conversion at Synapse Synapses The action potential opens voltage-gated Ca+ channels at the nerve terminal The increase in Ca+ triggers the release of neurotransmitters into the synaptic cleft The neurotransmitter diffuses across the synaptic cleft, binds to the target cell, and triggers an action potential Conversion Back to Electrical Signal Neurotransmitter Tidbits • Certain psychotic drugs (cocaine, morphine) & venoms mimic NT • Feel good with dopamine and serotonin – Natural reward system appeared early in evolution; reinforce behaviors favorable to survival – Prozac et al Dopamine Malfunctions • Parkinson’s disease • Insufficient dopamine due to destruction of cells that synthesize dopamine • Motor malfunctions appear after about 70% of neurons destroyed • Schizophrenia hallucinations: excessive dopamine • Tourette’s syndrome: supersensitive receptors Dopamine and Addictions • Stimulate feel good effects of dopamine using alcohol, nicotine, marijuana, and amphetamines – Amphetamines stimulate secretion – Cocaine keeps [dopamine] high • Dopamine may be common end-point of addictions; different mechanisms • Addicts’ feedback mechanisms impaired • Consequence: dopamine deficit Use it or lose it! Mental activity over lifetime reinforces synaptic junctions Learning and Memory Thousands of nerve terminals synapse on a neuron Combination of synapses determines if action potential is initiated Synaptic pathways provide a mechanism to store, analyze, and recall inputs Multiple Multiplesclerosis sclerosis (MS) (MS) is isaa disease disease that thatdestroys destroysmyelin, myelin,an aninsulating insulating material material that thatcoats coatsnerve nerve fibers fibers and andis is necessary necessaryfor for normal normalelectrical electrical conduction conduction in in the the nervous nervous system. system. This This breakdown breakdown of of the the myelin, myelin,called called demyelination, demyelination,results resultsin inimpairment impairmentof of the the function functionof of the the nerve. nerve. In InMS, MS,repeated repeated incidents incidentsof of inflammation inflammationcause cause scarring scarring (sclerosis) (sclerosis) and and permanent permanent abnormal abnormal function. function. The The name name is is derived derived from from this this process process -- multiple multiple (many) (many) since since it itoccurs occurs in in aa number number of of places places within withinthe the nervous nervoussystem systemand and sclerosis sclerosis (scars) (scars) which which means means the the hardened hardened tissue tissue that thatreplaces replaces damaged damaged myelin. myelin. During Duringan an MS MSattack, attack,myelin myelin becomes becomes inflamed, inflamed, causing causingsymptoms symptoms such suchas aslack lack of of coordination, coordination, weakness, weakness, tingling, tingling, impaired impaired sensation, sensation, double double vision visionor orbladder bladder problems. problems. If If the the inflammation inflammationis is severe, severe, the the myelin myelin may may actually actuallybe be damaged, damaged,however, however, regrowth regrowthof of myelin myelinmay may occur occur naturally naturallyduring during periods periods of of remission. remission. MS MSaffects affectsabout about 250,000 250,000 Americans Americans and andis is about abouttwice twice as as common common in in women womenas as in inmen. men. Multiple Multiple sclerosis sclerosis is isan an autoimmune autoimmune disease. disease. Something Something causes causesthe the body body to tobecome become allergic allergic to toits its own ownmyelin. myelin. There There may may be beaa genetic genetic component--a component--a predisposition-predisposition-to to susceptibility susceptibilityto to MS. MS. People People with withparticular particular types types of of histocompatibility histocompatibility antigens antigens (HLA (HLAantigens) antigens) develop develop MS MS more more often oftenthan than those those who whohave have other other HLA HLA antigens. antigens. HLA HLA antigens antigensoften often associated associated with withMS MS are areA3, A3, B7, B7,and and DW2. DW2. Common Common symptoms symptoms include: include: ·Loss ·Loss of of vision visionin inone one eye eyeor ordouble doublevision. vision. ·Loss ·Loss of of coordination coordination and and trembling trembling of of aa hand. hand. ·Instability ·Instabilityin inwalking walkingand and spasticity. spasticity. ·Loss ·Loss of of bladder bladdercontrol. control. ·Peculiar, ·Peculiar,spontaneous, spontaneous,nerve nerve sensations sensations such such as as aa pins-and-needles pins-and-needles feeling feelingover over part partof of the the body body(paresthesias). (paresthesias). MS is notoriously hard to diagnose. Current diagnostic tests include: using evoked potentials (EP) to measure the rate of nerve conduction in various parts of the central nervous system. Computer-assisted tomography (CT) may be used to scan the central nervous system using an x-ray technique which can detect areas of demyelination. Magnetic resonance imaging (MRI) may also be used to detect areas of demylenation, but without the use of x-rays.