Chapter 3 Biological Psychology neurons nerve cells exquisitely specialized for communication which each other cell body soma is the central region of the neuron Contains the nucleus where proteins are manufactured dendrites branchlike extensions for receiving information from other neurons axons are long tail like extensions protruding from the cell body send messages to other neu rons Their narrowness creates an area called the trigger zone that s easily activated axon terminal is a knoblike structure at the far end of the axon They contain synaptic vesicles tiny spheres that contain neurotransmitters neurotransmitters chemical messengers that neurons use to communicate with each other synaptic vesicles are manufactured in the cell body and travel down the length of the axon when synaptic vesicles reach the end of the axon terminal it bursts releasing neuro transmitters then neurotransmitters enter the synapse synapse a miniscule fluid filled space between neurons through which neurotransmitters travel consists of synaptic cleft synaptic cleft a gap into which neurotransmitters are released from the axon terminal surrounded by small patches of membrane on each side one on the sending axon of the first neuron and the other on the receiving dendrite of the second neuron Sir Charles Sherrington was one of the first to hypothesize about the existence of synapses 1906 argued that neurons were separate cells from muscle cells Santiago Ramon y Cajal showed that Sherrington was right through a staining tech nique then it was proven even more through the existence of the electron microscope Glial cells bit part actors in the nervous system that surround the synapse and provide protective scaffolding for neurons they hold in place astrocytes are the most abundant of glial cells Can find a lot of them in the blood brain barrier a fatty coating that wraps around tiny blood vessels oligodendrocytes promotes new connections among nerve cells and releases chemicals to aid in healing produces a myelin sheath myelin sheath glial cells that are an insulating wrapper around axons the myelin sheath contains nodes gaps all the way along the axon nodes help the neuron conduct electricity more efficiently When the membrane is at resting potential there are no neurotransmitters acting on the neuron There are more negative particles inside than outside the neuron Threshold membrane potential necessary to trigger action potential threshold occurs when the electrical charge reaches a high enough level relative to the outside The Action Potential electrical impulse that travels down the axon triggering the release of neurotransmitters Action potential is when a neuron is at rest there are positive and negative ions on both sides of the membrane During an action potential positive ions rush in and then out of the axon This process recurs along the axon until the axon terminal releases neurotrans mitters Action potentials are triggered by a change in charge inside the axon Neurons either fire or they don t all or none During an action potential positively charged particles flow rapidly into the axon and then just as rapidly flow out causing a spike in positive charge followed by a sudden de crease in charge with the inside charge ending up at a slightly more negative level than its original resting value These sudden shifts in charge produce a release of electricity Each action potential is followed by an absolute refractory period Absolute Refractory Period cur It limits the maximal firing rate a brief interval during which another action potential can t oc maximal firing rate is the rate at which a neuron can fire Electrical events transmit information within neurons chemical events transmit infor mation among neurons chemical communication neurotransmission after neurotransmitters are released they bind to the receptor sites of dendrites of other neurons lock and key model neurotransmission can be halted by reuptake reuptake a process by which the synaptic vesicles reabsorbs the neurotransmitter recycling of neurotransmitters nature s recycling mechanism Neurtransmitters glumate and GABA are the most common neurotransmitters in the central nervous sys tem Glumate main excitatory neurotransmitter in the nervous system In charge of en hanced learning and memory participates in relay of sensory information learning High levels of this can cause schizophrenia Alcohol and memory enhancers interact with glumate receptors like NMDA GABA inhibits neurons decreasing neural activity plays critical roles in learning memory and sleep Most antianxiety drugs bind to GABA receptors Acetylcholine in charge of muscle contraction PNS cortical arousal CNS plays a role in arousal selective attention sleep and memory Monoamines dopamine norepinephrine and serotin called monamines b c they contain only one amino acid Norepinephrine brain arousal and other functions like mood hunger and sleep Dopamine motor function and reward rewarding experiences that occur when we seek out or accomplish goals Serotonin mood and temperature reg ulation aggression and sleep cycles Norepinephrine and Serotonin activate or deactivate various parts of the brain influencing arousal and our readiness to respond to stimuli Neuropeptides short strings of amino acids in the nervous system Have special ized roles Endorphins play a specialized role in pain reduction discovered by Candance Pert and Solomon Snyder Anandamide pain reduction increase in appetite motivation and sleep psychoactive drugs drugs that interact with neurotransmitter systems meaning they affect mood arousal or behavior agonists such as morphine codeine reduce our emotional response to painful stimuli by binding with opioid receptors and by mimicking endorphins antagonists they decrease receptor site activity plasticity the nervous system s ability to change the nervous system is constantly changing BUT does not change enough following in juries Neural Plasticity Over Development the network of neurons in the brain changes over the course of development in four primary ways 1 2 3 4 growth of dendrites and axons synaptogenesis the formation of new synapses pruning consisting of the death of certain neurons and retraction of axons myelination the insulation of axons with a myelin sheath B c of pruning our brains can process information more efficiently with fewer neurons potentiation when synapses perform better show stronger and more prolonged excitatory re sponses When its
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