Exam 3 BIOL 1361H Neurons and Synapses Neurons nerve cells that transfer info w i the body Electrical signals long distance Chemical Signals short distance Ganglia simple cluster of neurons Dendrites receive signals from other neurons Cell body location of neurons organelles Axon transmits signals to other neurons Axon hillock where signals potentials are generated Synaptic cleft junction in which signals are transmitted Neurotransmitters chemical messengers that pass info Glial cells supporting cells of neurons glia neurons Functions a surround and hold neurons in place b supply nutrients and O2 c insulate d destroy pathogens e remove dead neurons 3 Stages of Processing Info 1 Sensory Input 2 Integration 3 Motor Output Sensory neurons transmit info from sensors that detect external stimuli or internal conditions Interneurons info from the sensory neuron is sent her and integrated Motor Neurons extend out of the processing center to trigger muscle gland activity Membrane potential charge difference voltage bc of the attraction of opposite charges across membr Inside is negative due to potential energy of inside vs outside Resting Potential 60 to 80 mV memb potential of a neuron not sending signals Concentration of K is higher inside Na is higher outside Kept by Na K pump 3 Na out 2 K in Ion Channels allow ions to diffuse back and forth opening converts chemical potential energy to electrical potential energy Leak Channels K channels that are always open even in a resting neuron to establish resting potential Equilibrium potential magnitude of the membr Voltage at equilibrium for a particular ion Hyperpolarization increase in magnitude of a membrane potential K channels open K out neg Depolarization reduction in magnitude of membrane potential Na channels open Na in pos Graded Potential shift in memb potentials where magnitude of change varies with stimulus strength Action Potential if depolarization shits memb potential significantly and results is positive change in mV Voltage gated Ion Channels opening closing depends on if memb pot passes a certain level Threshold action potential occurs when depolarization incr memb potential to this value 55 mV 1 most Na ch closed most K closed 2 some Na open Na in 3 Threshold crossed More Na open 4 Na closes K opens K out 5 undershoot more K open than resting potential Refractory period time btwn 1st action pot and 2nd action pot where the 2nd can t be carried out b c of the temporary inactivation of Na channels 1 2 msec Travel from axon hillock to synapse can t travel backward bc of the inactive Na channels behind the zone of depolarization Axon diameter incr action potential incr Channels Ligand Gated Ion Channels nt bind to this they open and create a postsynaptic potential Saltatory conduction increases action pot in myelinated axons by making it jump btwn nodes of Ranvier Oligodendrocytes CNS Schwann Cells PNS Glia that make up myelin sheath which insulates axon to get a faster conduction of action potentials Nodes of Ranvier Where action potentials are formed Na Neurotransmitters are packaged into synaptic vessels action potential opens voltage gated Ca 2 channels Ca 2 in synaptic vessels fuse with terminal membrane and release nt nt diffuse across synapse nt binds to receptor receptor causes postsynaptic potential Receptors can be metabotropic depends on 1 metab steps binding of nt causes signal transduction pathway involving second messenger slow but last longer ex norepinephrine metab receptor G protein activated adenylyl cyclase activated cAMP activates protein kinase A protein kinase A phosphorylates ion channel proteins Nt examples a Acetylcholine muscle stimulation memory learning toxins disrupt sarin nerve gas and toxin that causes botulism b Glutamate long term memory in CNS Neurotransmitters in synaptic cleft are either a recaptured b fuel for glia c removed by hydrolysis Postsynaptic Potential 1 Excitatory EPSP depolarization synaptic LGIC is permeable to K and Na 2 Inhibitory IPSP Hyperpolarization synaptic LGIC is permeable to K and Cl Cell Signaling Autocrine signals act on the same cell that secretes them and amplify response ex Cytokines Paracrine Signals diffuse locally and act of neighboring cells ex Growth factor signals Endocrine signals hormones carried btwn cells by blood Neural Signals diffuse a short distance btwn neurons Neuroendocrine signals release from the neurons but act on distant cells Pheromones released into the environment and act on a different individual 3 Processes of Cell Signaling 1 Reception 2 Transduction 3 Response Receptors a G Protein Coupled Receptor signaling mcl binds to receptor which makes GDP GTP GTP activates G protein active G protein activated another enzyme b Ligand Gated Ion Channels signaling mlcl binds to and opens gate ions come inside and bind to other enzyme hydrophobic messengers cross memb freely ex steroid thyroid hormone NO nitrogen oxide hormone signaling vs neuron signaling hormone signaling travels everywhere but only cells with specific receptors generate a response neuron signals travel to a specific location Hypothalamus integrates nervous and endocrine systems signals travel to pituitary Ex Epinephrine raises blood glucose increases blood flow to muscles decreases blood flow to digestive has alpha and beta receptors Ex Gonadotropin releasing hormone GnRH secreted by hypothalamus and directs FSH follicle stim hormone and LH leutenzing hormone Ex Oxytocin positive feedback stretching of cervix stimulates oxytocin release oxytocin causes uterine muscle to contract which is more pressure on cervix Hormonal contraceptives places the body in a pseudo pregnancy state by affecting estrogen and progestin levels Endocrine Disrupting Compounds mimic block modulate synthesis of hormone ex EE2 TB Asexual reproduction offspring w o fusion of egg and sperm ex budding fission fragmentation parthenogenesis Immaculate Conception Sexual Reproduction Offspring by fusion of male gamete and female gamete Asexual vs Sexual Reproduction Asexual 2n 2n Sexual 2n n 2n diploid n haploid Hermaphroditism switching sexual roles to mate freely or to self fertilize Digestion Nutrient Absorption Essential Nutrients amino acids fatty acids vitamins minerals 1 Amino acids about half can be synth from diet remaining are essential and must come preassembled 2 Fatty Acids converted to membrane phospholipids signaling mlcl storage 3 Vitamins organic mlcl required in small amts fat or water soluble 13