Sensation and Perception Neurons and NeurophysiologyNeurons There are two kinds of brain cells o Neurons Nerve cell Specialized cell transmitting nerve impulses o Glia Non neural cells Most abundant cell types in the centralnervous system Neurons are like any other cell in the body in manyways o They do have all the organelles that other cellshave as well as a plasma membrane like othercells Neurons are different from other cells in some veryimportant ways o They differ from other cells in theirmorphology shape and in that they aregenerally postmitotic Postmitotic Does not cannot under gomitosis o They also differ sort of from other cells inthat they communicate over long distanceswith each other Neurons have different parts each with specificfunctions o Neurons form synapses with each other Synapses Where two cells meet o Neurotransmitters A chemical released by thecommunicating neuron to receiving neuron Chemicals released from one neuron thataffect a second neuron Are relayed from one neuron to another atthe synapse The neurotransmitter either excites orinhibits the receiving neuron o An electrical charge called an action potentialtravels down the neuron causing the release ofthe neurotransmitter Action Potential The movement of theions into and out of the axon The brief electrical impulses thatprovide the basis of conduction ofinformation along an axon The Neuron Cell Membrane of Neurons Phospholipid Bilayer Two layers of fat molecules thatare free to float around one another Semipermeable Water oxygen and carbon dioxidemove freely o Na Ca2 K Cl move through ion channels protein channels o Most chemicals cannot cross the cell membrane Axons and Myelin Mylein Increases speed and energy efficiency ofaction potentials o Made by glial cells o Oligodendrocytes in the CNS schwann cells inthe PNS Axons Where impulses are conducted from the cellbody to other cells o Can be short or long thin or thick and can havevarying amounts of myelination o Axon width and degree of myelination determineconduction velocity Conduction Velocity How fast an actionpotential travels o The wider the axon plus more myelin equalsfaster conduction Terminal Axon Terminal o At the end of the axon o Vesicles contain neurotransmitters for chemicaltransmission between neurons Neurotransmittesr are synthesized by neuronsand packaged in vesicles Neurotransmitters are released from thepresynaptic cell and bind to proteins called receptors on the postsynaptic cell Synapse Where the two cells meet The Main Types of Neurons Top to bottom multipolar typical bipolar unipolar DRG The Main Types of Neurons The cell body can be in different places with respect tothe rest of the neuron o Multipolar neuron is usually in the brain o Unipolar neuron exemplifies the type of neuronfound in the dorsal root ganglia where the cellbody is in the DRG unipolar and the sensoryendings are somewhere peripheral The soma makes most of the macromolecules for theneurons o There is a protein synthetic machinerythroughout the neuron o Transcription DNA RNA in nucleus RNA leaves the nucleus for translation toprotein in cytoplasm Neurons can connect with other neurons with bloodvessels or with muscle Different Types of Neurons Differences in size of soma length of axon presence of spines size of dendritic tree Classification based on connections receptor cells o Sensory Directly sensitive or connected to o Motor End in muscles glands or neurons in o Interneurons Local all processes in small area o Projection Neurons Long axons connecting PNS ganglia of CNS different areas to spinal cord Like upper motor neuron going from cortex A lot of cell bodies together nucleus or ganglion A lot of axons nerve PNS tract CNS fasciculus peduncle etc Many neurons are multipolar Bipolar Two processes off of soma o Some just keeps neuron alive o Mainly in most sensory systems Unipolar One process off of soma o Found mainly in skin senses Like for touch pain and temperature Connect Neurons 1 1 relay Many 1 gain complexity 1 Many arousal Neurotransmitters If the neuron has an action potential it will release a The neurotransmitter can be excitatory inhibitory or neurotransmitter modulatory o Excitatory Excites the postsynaptic cell Example Gultamate o Inhibitory Inhibits the postsynaptic cell o Modulatory Excites or inhibits the postsynaptic Example GABA cell depends on receptor Example Dopamine Neurons Action Potential There are a lot of synapses on a neuron Whether a cell fires an action potential depends on the balance of excitatory and inhibitory inputs Action Potential Electrical activity that travels down the axon of a neuron o Due to movement in ions o Ion An atom having fewer more electrons than protons atom Ions have electrical charge They are subject to entropy like any other That is they will move from areas of high concentration to areas of low concentration o This requires that they be in a solution example water A lot of sodium and chloride are outside of the cell and just a little inside a lot of potassium inside the cell and just a little outside Other negatively charged organic compounds inside the cell A contribute to its resting potential which is 70 mV o Resting Potential The membrane potential of a neuron when it is not being altered by Action Potential excitatory or inhibitory postsynaptic potential Neurons contain and are surrounded by potassium sodium chloride and calcium Depolarization When the neuron becomes less negative o Reduction towards zero of the membrane potential of a cell from its normal resting potential Hyperpolarization When the neuron becomes more o An increase in the membrane potential of a cell negative relative to the normal resting potential Ions flow through voltage gated channels in the membrane of the axon o Voltage Gated Channels A protein channel that can be opened or closed in response to changes in the electric potential across a cell membrane and an electrical gradient Ions flow in and out along a concentration gradient o Concentration Gradient Ions flow from high o Electrical Gradient Ions flow to areas of concentration to low concentration opposite charge When threshold 50 mV is reached at the axon hillock voltage gated sodium channels open up sodium rushes into the cell the cell becomes depolarized Voltage gated potassium channels open up and voltage gated sodium channels close potassium rushes out of the cell the cell becomes hyperpolarized Action Potential Saltatory Voltage gated potassium channels close
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