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BU BIOL 118 - Nervous system
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Biol 118 1st Edition Lecture 28 Outline of Last Lecture I. IntroductionII. Principles of Electrical SignalingIII. How Does Action Potential Work?Outline of Current Lecture I. SynapsesII. Vertebrate Nervous SystemCurrent LectureSynapses- 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 & axono Synaptic vesicles: store neurotransmitters- Presynaptic neuron: sending cell- Postsynaptic neuron: receiving cell- Synaptic transmission:o Action potential arrives at the end of the axono Triggers the entry of calcium ions into the presynaptic cello Synaptic vesicles fuse with the presynaptic membrane, then release the neurotransmittero Neurotransmitters bind to receptors on the postsynaptic membrane, initiating anaction potential if the threshold potential is reachedo The response ends as the neurotransmitter is broken down and taken back up by the presynaptic cell- What do neurotransmitters doo Many functions as ligands (bind to specific site on receptor molecule) that bind to receptors called ligand-gated ion channelso Ligand-gated ion channel in the postsynaptic membrane opens and admits a flowof ions along an electrochemical gradientThese 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 neurotransmitterso 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 potentialso Synapses can be one of 2 general types leading to either depolarization or hyperpolarization of the membraneo Excitatory postsynaptic potentials (EPSPs): cause membrane to depolarize, increasing the likelihood of an action potentialo Inhibitory postsynaptic potentials (IPSPs): cause membrane to be hyperpolarized, decreasing the likelihood of an action potentialo Are not all or none events, but are graded in sizeo Size depends on the amount of neurotransmitter that is released at the synapseo Both types of signal are short lived because neurotransmitters do not bind irreversibly to channels in postsynaptic cell- Summation & Thresholdo If IPSP & EPSP occur close together, changes in membrane potential cancel each other outo If several EPSPs occur close together, they sum & make the neuron likely to fire an action potential Additive nature is called summationo Sodium channels that trigger action potentials in the postsynaptic cell are locatedat the axon hillocko Charges spread to axon hillock & if membrane here depolarizes past the threshold potential, an action potential begins & is propagated down axon to next synapseo Summation is critical because it determines whether action potential begins in postsynaptic cellVertebrate 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 hemisphereso 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 bodyo 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 aspecific experience in an individual’s lifeo Memory: retention of learned


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BU BIOL 118 - Nervous system

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