PSB3004C Physiological Psychology Quiz 2 Key Concepts 1 There are 3 main factors in producing the resting potential a Negatively charged proteins in the cell b Selective permeability of K channels K is attracted into the cell because of the negative proteins but not enough K ions can enter to cancel out the negative charge because of the concentration gradient which tends to push K back out No other positive ions can easily leak into the cell so they cannot help to cancel the negative charge c The sodium potassium Na K pump which pumps 3 Na ions out for every 2 K ions it pumps in 2 The neuron exerts a great deal of energy during the resting potential in order that the passive ions flows of the action potential can occur quickly 3 Synaptic influences that hyperpolarize the cell making it more negative reduce the probability that a nerve impulse will be produced Depolarizations increase the probability that a nerve impulse will be produced Such perturbations spread passively from the site of stimulation decreasing with time and distance 4 Depolarizations that exceed an individual neuron s threshold will produce a nerve impulse or action potential in the axon The action potential is generated in an all or none fashion its size is independent of stimulus magnitude 5 During the peak of the action potential the membrane potential approaches 40mV due to sodium Na permeability that results from the opening of voltage gates Na channels These channels close rapidly K exits because of the increased charges inside the cell thereby restoring the resting potential 6 After the peak of the action potential the membrane becomes completely insensitive to further stimuli this is called the absolute refractory phase It is immediately followed by a brief period of reduced sensitivity called the relative refractory phase 7 Many cell bodies and dendrites contain few voltage gated ion channels and thus cannot propagate action potentials although some can 8 Action potentials arise in the axon hillock and spread down the axon through a regenerative process at speeds ranging from 5 to 120 m s Conduction velocity is increased in axons with large diameters and particularly in axons that are myelinated In the latter case the action potential jumps between nodes of Ranvier this is called salutatory conduction 9 The arrival of an action potential at the axon terminals of a presynaptic neuron and the subsequent release of neurotransmitter results in a small graded depolarization excitatory postsynaptic potential EPSP or graded 1 PSB3004C Physiological Psychology Quiz 2 hyperpolarization inhibitory postsynaptic potential IPSP of the membrane of the postsynaptic cell depending on whether the postsynaptic receptor is excitatory or inhibitory respectively If enough EPSPs are received the postsynaptic cell s threshold is reached and an action potential is produced Whether a synapse is excitatory or inhibitory depends on the type of neurotransmitter that it uses and the subtype of postsynaptic receptor for example nicotinic vs muscarinic acetylcholine receptors 10 The IPSPs and EPSPs produced in a postsynaptic neuron sum temporally and spatially If relatively more and or greater EPSPs occur the cell s threshold is exceeded at the axon hillock and an action potential is generated This integration is the basis of information processing by the neuron 11 At chemical synapses the arrival of an action potential causes voltage gated calcium Ca channels to open in the membrane of the axon terminal Calcium influx induces vesicles to fuse to the synaptic membrane and release transmitter the amount released is proportional to the size of the calcium current 12 Transmitter diffuses across the synaptic cleft binds to receptors and opens ion channels in postsynaptic membrane resulting in a change in the membrane potential Alternatively it activated a G protein coupled receptor which activates enzymes in the postsynaptic cell that produces long term changes The action of the transmitter is stopped rapidly either by chemical inactivation or reuptake Neuromodulators and hormones may alter the responsiveness of the postsynaptic membrane 13 Transmitter receptors operate like a lock and key particular transmitter key may open several different types of receptor locks receptor subtypes 14 Ionotropic receptors are ligand gated ion channels Metabotropic receptors involve the liberation of chemical second messengers which may have numerous effects within the cell 15 Some synapses are electrical rather than chemical and provide a direct electrical coupling between neurons 16 Neurons accomplish complex information processing by acting together in circuits such as neural chains feedback circuits and oscillator circuits 17 The electrical activity of populations of neurons can be measured using scalp electrodes EEG measures spontaneous electrical activity whereas ERPs reflect the reaction of populations of neurons to discrete stimuli Both techniques have important diagnostic applications such as in epilepsy EEG and auditory testing ERP as well as applications in basic research such as sleep research EEG and studies of cognitive processing ERP 2 PSB3004C Physiological Psychology Quiz 2 18 Under some circumstances the electrical activity of large populations of neurons may become synchronized resulting in seizures The behavioral characteristics of the seizures depend on the site at which the seizures originate and the degree to which the seizure activity spreads to other regions of the brain Objectives 1 What are the 3 main factors that result in the resting potential a Negatively charged b Selective permeability of K channels K is attracted into the cell proteins in the cell because of the negative proteins but not enough K ions can enter to cancel out the negative charge because of the concentration gradient which tends to push K back out No other positive ions can easily leak into the cell so they cannot help to cancel the negative charge c The sodium potassium Na K pump which pumps 3 Na ions out for every 2 K ions it pumps in 2 What attacks K ions into the neuron a The resting potential of the neuron reflects a balancing act between two opposing forces that drive K ions in and out of the neuron i Neuron shows selective permeability to K it can enter or leave ii Diffusion freely is the force that causes ions molecules to flow from areas of high to low concentration along their concentration gradient variation of the concentration of a