4 27 2014 CHAPTER 46 Animal Nervous Systems PPT Notes neurons nerve cells that conduct electrical signals makes connections w other neurons flows of ions across plasma membranes are basis for complex processes all animals have neurons muscles except for sponges neuron transmits signal muscle responds o o o o o o sensory cells cells that respond to stimuli monitor conditions important to homeostasis i e blood pH oxygen levels sensory receptors transmit streams of data about external environment sensory neuron nerve cell that receives data transmitted by sensory receptors transmit information to brain spinal cord composed of the same 3 parts information flows from dendrites to axon dendrite receives electrical signals from axons of adjacent cells cell body soma includes nucleus integrates the incoming signals generates an outgoing signal axon send signal to dendrites of other neurons large diameter neurons transmit action potentials faster than small axons can large axons have few Na channels per unit of membrane surface less current leaks back out of large axon than small axon charge spreads nerve myelination rapid transmission of electrical signals possible in small diameter axons Schwann cells PNS oligodendrocytes CNS specialized accessory cells membranes wrapped around axons glia accessory cells collectively glia wrap around an axon to form a myelin sheath that acts as electrical insulation preventing ions from leaking out as it spreads down axon node of Ranvier unmyleated section of axon impedes charge resulting from action potential dense concentration of voltage gated Na channels so action potentials can occur electrical signals jump down myelinated axon faster than unmyelinated o o o multiple sclerosis MS damage to myelin increases electrical signaling impaired muscles weaken coordination lessen occurs bc of myelin degeneration o synapse interface btwn 2 neurons synaptic cleft space btwn dendrite axon synaptic vesicles store neurotransmitters present inside synapse neurotransmitters chemical messengers that deliver signals from nerve to muscle presynaptic neuron sending cell postsynaptic neuron receiving cell postsynaptic potential synapses may be modulatory may modify neuron s response to EPSPs IPSPs 2 types excitatory postsynaptic potentials EPSPs membrane depolarizes likelihood of action potential inhibitory postsynaptic potentials IPSPs cause membrane to be hyperpolarized likelihood of action potential lead to depolarization or hyperpolarization depolarization occurs by taking in of Na ions hyperpolarization occurs by removal of K ions synaptic transmission o o o o o o o 1 action potential arrives end of axon 2 calcium ions triggered to enter presynaptic cell 3 synaptic vesicles fuse w presynaptic membrane release neurotransmitter 4 neurotransmitters bind to receptors on postsynaptic membrane initiate action potential if threshold potential is reached 5 response ends as neurotransmitter broken down taken back up by presynaptic cell 4 27 2014 nervous systems two types o o nerve net diffuse arrangement of cells found in cnidarians ctenophores vertebrate nervous system composed of 2 parts CNS PNS comprised of central nervous system CNS peripheral nervous system PNS central nervous system CNS large of neurons aggregated into ganglia clusters integrates information from sensory neurons most animals with a CNS have a large ganglia brain nerves receive information from vertebrate sensory neurons long tough stands of nervous tissue containing thousands of neurons interneurons cells that make connections btwn sensory neurons motor neurons motor neurons nerve cells that send signals to effector response cells in glands muscles spinal cord many nerves serves as information conduit brain processes information that travels to from spinal cord exception reflex action size varies greatly among vertebrates in mammals cerebrum focuses on reasoning memory reflex action sensory neurons stimulate interneurons in spinal cord stimulate motor neurons cerebrum composes bulk of brain divided into left right hemispheres is involved in conscious thought memory o o o o center for functions of right left side of body include sight hearing language memory corpus callosum thick band of axons that connects hemispheres 4 lobes of each hemisphere frontal parietal occipital and temporal lobes functions localized to specific brain areas developed by Broca mapped diseased damaged brains Penfield mapped brain function by electrically stimulating portions of the cerebrum of conscious patients during brain surgery cerebellum coordinates complex motor patterns diencephalon relays sensory information to cerebellum controls homeostasis brain stem connects brain to spinal cord autonomic center for regulating heart lungs digestive system o peripheral nervous system PNS all the components of the nervous system outside CNS sensory information from receptors in PNS sent to CNS where it is processed response transmitted back to appropriate body parts via motor neurons composed of 2 systems with distinct functions afferent division transmits sensory information to CNS o neurons monitor conditions inside outside CNS efferent division carries commands from CNS to body neurons carry signals that allow for a response divided into 2 systems o o somatic system controls movement carries out voluntary responses skeletal muscles serve as effectors autonomic system controls internal processes carries out involuntary responses smooth muscle cardiac muscle several glands are effectors responds to internal stimuli controls activity of internal organs glands parasymphathetic nervous system promotes relaxation digestion conserves restores energy sympathetic nervous system prepares organs for stressful situations membrane potential separation of charges that exists when an electrical potential exists on either side of a plasma membrane o membrane potentials are measured in millivolts mV o generally more negative ions on inside of plasma membrane than outside membrane potential has negative sign in neurons membrane potentials typically 70 80 mV o ions on both sides of membrane have potential energy 4 27 2014 electrical current flow of charge created if membrane is removed ions spontaneously move from area of like charge to unlike charge ions move across membranes in response to concentration gradients charge gradients electrochemical gradient combination of an electrical gradient concentration gradient resting potential voltage of
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