Biol 118 1st Edition Lecture 28 Outline of Last Lecture I Introduction II Principles of Electrical Signaling III How Does Action Potential Work Outline of Current Lecture I II Synapses Vertebrate Nervous System Current Lecture Synapses When action potential arrives at the interface between cells molecules transmit information from 1 neuron to another or from a neuron to a target cell muscle or gland Signal from nerve to muscle is delivered by a chemical neurotransmitters Synapse interface between two neurons o Synaptic cleft space between the dendrite axon o Synaptic vesicles store neurotransmitters Presynaptic neuron sending cell Postsynaptic neuron receiving cell Synaptic transmission o Action potential arrives at the end of the axon o Triggers the entry of calcium ions into the presynaptic cell o Synaptic vesicles fuse with the presynaptic membrane then release the neurotransmitter o Neurotransmitters bind to receptors on the postsynaptic membrane initiating an action potential if the threshold potential is reached o The response ends as the neurotransmitter is broken down and taken back up by the presynaptic cell What do neurotransmitters do o Many functions as ligands bind to specific site on receptor molecule that bind to receptors called ligand gated ion channels o Ligand gated ion channel in the postsynaptic membrane opens and admits a flow of ions along an electrochemical gradient These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Neurotransmitter s chemical signal is transduced to an electrical signal changing the membrane potential of the postsynaptic cell Nonbinding neurotransmitters o Some bind to receptors that activate enzymes for production of a second messenger Chemical signals produced inside the cell when a chemical signal arrives at the cell surface May trigger changes in gene expression enzyme activity or membrane potential Postsynaptic potentials o Synapses can be one of 2 general types leading to either depolarization or hyperpolarization of the membrane o Excitatory postsynaptic potentials EPSPs cause membrane to depolarize increasing the likelihood of an action potential o Inhibitory postsynaptic potentials IPSPs cause membrane to be hyperpolarized decreasing the likelihood of an action potential o Are not all or none events but are graded in size o Size depends on the amount of neurotransmitter that is released at the synapse o Both types of signal are short lived because neurotransmitters do not bind irreversibly to channels in postsynaptic cell Summation Threshold o If IPSP EPSP occur close together changes in membrane potential cancel each other out o If several EPSPs occur close together they sum make the neuron likely to fire an action potential Additive nature is called summation o Sodium channels that trigger action potentials in the postsynaptic cell are located at the axon hillock o Charges spread to axon hillock if membrane here depolarizes past the threshold potential an action potential begins is propagated down axon to next synapse o Summation is critical because it determines whether action potential begins in postsynaptic cell Vertebrate Nervous System Central Nervous System CNS o Spinal cord made up of many nerves serves as an information conduit o Brain consists of 4 structures Cerebrum Makes up the bulk of the brain Divided into left right hemispheres o Connected by thick band of axons called corpus callosum Involved in conscious thought memory Four lobes in each hemispheres frontal parietal occipital temporal Cerebellum coordinates complex motor patterns Diencephalon relates sensory information to the cerebellum controls homeostasis Brain stem Connects the brain to the spinal cord Autonomic center for regulating heart lungs digestive system Peripheral Nervous System PNS o Afferent division transmits sensory information to the CNS Monitor conditions inside outside body o Efferent division carries commands from the CNS to the body Carry signals that allow for a response Somatic system controls movement Carries out voluntary responses skeletal muscles serve as the effectors Autonomic system controls internal processes Carries out involuntary responses smooth muscles cardiac muscle several glands serve as the effectors Parasympathetic nervous system promotes relaxation digestion functions to conserve restore energy Sympathetic nervous system Prepares organs for stressful situations fight or flight How Does Memory Work o Learning often enduring usually adaptive change in behavior that results from a specific experience in an individual s life o Memory retention of learned information
View Full Document
Unlocking...