Intro Neurons and Neurophysiology 1 20 1 22 two main types of cells in the brain neurons glial cells provide nutritional and structural support Neurons differ in do have all same organelles as other cells as well as plasma membrane more complex morphology shape postmitotic no longer dividing communicate electrically via action potential over very long distances and chemically with each other via neurotransmitters have different parts each with specific fxs form synapses with each other presynaptic cell releasing info postsynaptic cell receiving info neurotransmitters relayed from one neuron to another at the synapse action potential travels down neuron causing release of neurotransmitter A P movement of ions into Na and out K of axon Parts of a Neuron cell body soma contains nucleus and DNA two extensions from cell body 1 dendrites receive information contain proteins that NT can bind to to change the energy dendritic spines additional protrusions 2 axon send info out in the form of electrical currents 1 can be shirt or long thin or thick and have varying amounts of myelination width and degree of myelination determine conduction velocity how fast 1 20 1 22 an AP travels oligodendrocytes CNS myelin sheath fatty protein made by glial cells schwann cells PNS increases speed and energy efficiency of APs AP regenerated at Nodes of Ranvier terminals at the end of an axon vesicles store neurotransmitters that are released after action potential for transmission between neurons cell membrane another phospholipid bilayer 2 layers of fat molecules that are free to float around one semipermeable water oxygen carbon dioxide move freely Na Ca2 K Cl move through ion channels protein channels most chemicals cannot cross membrane Types of Neurons multipolar most common multiple processes bipolar two processes happening off cell body mainly in sensory systems retina olfactory auditory unipolar one process occurring from cell body contains sensory nerve endings that relay info via axon touch temperature pain differences in types of soma length of axon presence of spines size of dendritic tree classification based on connections sensory motor interneuron projection nucleus ganglion lots of cell bodies together neuron 2 lots of axons nerve PNS tract CNS fasciculus peduncle 1 20 1 22 Connections 1 1 relay many 1 gain complexity 1 many arousal neurotransmitter can be excitatory increases cell activity depolarization glutamate inhibitory decreases cell activity less likely to have an AP hyperpolarization GABA most common modulatory can either inhibit or excite cell depending on receptor dopamine whether a cell fires an AP depends on balance of inhibitory excitatory inputs Action Potential historical until 1800s scientists believed in vitalism force distinct from physical entities which travelled in nerve fibers Von Hemholtz measured speed of signal transmission in frog legs later estimated speed of signals in human sensory nerves Ramon y Cajal detailed neurons thru light microscopy realizing they were their own separate cells with tiny gaps between them Sherrington defined synapse signal transmission speed decreased at synapse concluded something different must happen there Loewi synapses must be chemical neurotransmitters Hodgkin and Huxley used giant squid axon to test how nerve impulses electrochemically traveled along axon discovered Na in K out at first membrane is polarized lots of Sodium and chloride outside of cell just a little inside lots of potassium inside a little outside 3 1 20 1 22 other negatively charged organic compounds inside the cell A contribute to resting potential of 70 mV depolarization neuron becomes less negative effect of Na or K entering cell hyperpolarization neuron becomes more negative effect of Cl entering cell or K leaving cell ions flow through voltage gated channels in the membrane of the axon flow in and out along concentration gradient diffusion naturally move from area of high concentration to area of low concentration electrical gradient electrostatic pressure negative ions attracted to positive environment and vice versa Process 1 threshold 50mV is reached at axon hillock based on E and I inputs i voltage gated Na channels open Na rushes in cell becomes 2 voltage gated K channels open Na channels close K rushes out cell deplolarized becomes hyperpolarized 3 K channels close that part of neuron returns to 70mV 4 K diffuses away Na in cell diffuses to next Node of Ranvier 5 AP reaches axon terminal voltage gated calcium channels open 6 calcium enters terminal synaptic vesicles full of NT bind to terminal membrane release NT to synaptic cleft threshold to peak 1 millisecond saltatory conduction propagation of an AP down a myelinated axon GNaC VGKC Na K pumps clustered at nodes Na K pumps located in the cell membrane helps maintain resting potential continually pushes 3 Na out of cell and brings 2 K in assists in recovery from AP 40 of a neuron s energy is used to run pumps AP is all or none happens only when at threshold 50mV size remains the same all the way down axon 4 speed calculated from delay between stimulus and AP rate law strength of stimulus represented by axon s rate of firing of APs fired per 1 20 1 22 second intense stimulus many APs weak stimulus few APs rate of firing limited by refractory period Synaptic Potential Synaptic activity EPSP IPSP on the dendrites and soma generally on the neuron causes threshold to be reached at axon hillock 1 NT released from presynaptic cell binds to receptor in membrane of postsynaptic cell 2 ion channel opens acetylcholine released receptor itself might be channel or maybe not receptor channel is called ligand gated as opposed to voltage gated ions go through slightly depolarizing hyperpolarizing postsynaptic cell Cl in or K out if inhibitory neurotransmitter Na or Ca2 or K in if excitatory neurotransmitter 3 Synaptic potential change in voltage is graded EPSP or IPSP as opposed to action EPSP excitatory postsynaptic potential depolarization in postsynaptic cell can be potentials which are all or none dependent on ion flow various sizes Receptors receptor protein in the membrane that a NT binds to ionotropic also channel NT binds channel opens ions pass though metabotropic do not have channels 2 NT binds 3 G protein activated on receptor inside the cell 4 alpha subunit breaks away opens ion channel 5 5 1 20 1 22 second messenger used to open ion channels and or move to nucleus other parts of cell 1 Generally
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