BIOL 200B 1st EditionExam # 3 Study Guide Lectures: 16 - 20Chapter 46 Animal Nervous SystemsNeurons – cells mainly responsible for the working of the brain and the rest of the nervous systemOrganized into two basic types of nervous systems1. the diffuse arrangement of cells called a nerve net2. a central nervous system including large numbers of neurons aggregated into clusters called gangliaTypes of Neurons- Sensory neurons – sensory cells, send information to the brain where it is integrated with information from other sources - Interneurons – pass signals from one neuron to another- Motor neurons – nerve cells that send signals to effector cells in glands or muscles Nerves – bundles of motor and sensory neurons in tough strands of nervous tissueAll neurons and other components of the nervous that are outside the central nervous system and part of the peripheral nervous system Neurons have three parts:1.cell body – contains the nucleus 2.dendrites – highly branched group of relatively short projections; receive signals 3.axons – one or more relatively long projections; send signals Electrical potential/voltage – different of electrical charge between any two points; standard unit is voltElectrochemical gradient – combination of electrical and concentration gradient Resting potential – the difference in charge across a neurons membrane - interior side of the membrane has low Na+ and Cl- concentration, high K+ concentration, and some organic anions- in the extracellular fluid, sodium and chloride ions predominateIons cross membranes in three ways:1. ion channel2. carried with another ion that diffuses along its electrochemical gradient 3. pumped against electrochemical gradient by membrane protein that hydrolyzes ATPK+ leak channelEquilibrium potential – no longer net movement of K+Na+/K+ -ATPaseAction potential – rapid, temporary change in a membrane potential; most important type of electrical signal in cells3 phases:1. Depolarization – membrane becomes less polarized; moves from highly negative toward zero and then is briefly positive 2. Repolarization – changes the membrane potential back to negative; rapid3. Hyperpolarization – membrane is slightly more negative that the resting potential “all-or-none” signal- No such thing as partial action potential - All action potentials for given neuron are identical in magnitude and duration- Action potentials are always propagated down the entire length of the axonVoltage-gated channels – membrane proteins open and close in response to change in membrane voltage Voltage-gated channels are either open or closedSodium channels open quickly after depolarizationPotassium channels open with a delay after depolarization Na+ channels become more likely to open as a membrane depolarizes – positive feedbackNeurotoxins – poisons that affect neuron function Figure 46.8Synapse – interface between neurons Presynaptic neuron – “sending cell”Postsynaptic neuron – “receiving cell”Neurotransmitters – chemical messengers that transmit information from one neuron to another, or from neuron to target cell- binds to a ligand-gated channel in postsynaptic membrane, channel opens and admits flow of ions along electrochemical gradient - chemical signal is transduced to electrical signal – change in membrane potential of postsynaptic cellSecond messengers – chemical signals produced inside a cell in response to chemical signal that arrives at the cell surface Excitatory postsynaptic potentials – changes in postsynaptic cell that bring membrane potential closer to threshold Inhibitory postsynaptic potentials – make the membrane potential more negative Table 46.2Somatic nervous system – controls voluntary movements Autonomic nervous system – controls internal processes such as digestion and heart rateParasympathetic nervous system – promotes “rest and digest”, conserve or restore energy Sympathetic nervous system – prepares organs for stressful “fight or flight” responses Brain: cerebrum, cerebellum, diencephalon, brain stem, lobes Learning and memory Chapter 49 Chemical Signals in AnimalsEndocrine system – collection of organs and cells that secrete chemical signals into the bloodstream Hormone – chemical signal that circulates through body fluids and affects distant target cells Animal chemical signals are present in extremely low concentrations but can have enormous effects on their target cells; have a relatively long-lasting effect Categories of chemical signals:- Autocrine – act on the same cell that secretes them; cytokines- Paracrine – act on neighboring cells; insulin, glucagon, somatostatin - Endocrine – hormones - Neural signals – neurotransmitters- Neuroendrocrine signals – act at a distance; neuroendocrine, neurohormones Before production of a hormonal signal, information about the external or internal conditions is gathered by sensory receptors and then integrated by neurons in the central nervous system 3 types of signaling pathways:1.direct from an endocrine cell2.direct from the CNS3.CNS to endocrine system Pathways are regulated by negative feedback, or feedback inhibition – reduces production or secretion of the hormone, or both Endocrine glands – secrete hormones into the bloodstream Exocrine glands – deliver their secretions through outlets called ducts into a space other than the circulatory system 3 classes of chemicals that act as hormones in animals:1.polypeptides 2.amino acid derivatives 3.steroids Hormone concentrations are low but their effects are large Only some hormones can cross cell membrane – only steroids are lipid soluble; to affect a targetcell most polypeptides and amino acid derivatives bind to a receptor on the cell surface Hormones coordinate activities of cells in 3 areas:1.development, growth, and reproduction - metamorphosis is amphibians and insects, depends on interactions of two hormones- sexual development and activity in vertebrates, testosterone and estradiol; puberty- photoperiod – change in day lengths affects sex hormone release; pineal gland, melatonin - some chemicals can disrupt hormone signaling – endocrine disruptor, xenoestrogens 2.response to environmental changes - short term responses to stress – fight-or-flight response; epinephrine, adrenaline; coordinates the activities of cells in many organs and systems in the body to prepare individual to cope with life threatening situation - long