Psychobiology Chapter 1 Notes
Psychobiology Chapter 1 Notes PSYC2070
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This 3 page Class Notes was uploaded by Karly Lord on Tuesday January 19, 2016. The Class Notes belongs to PSYC2070 at University of Cincinnati taught by Dr. Kenneth King in Fall 2016. Since its upload, it has received 97 views. For similar materials see Psychobiology in Psychlogy at University of Cincinnati.
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Date Created: 01/19/16
Chapter 1 - Lecture Neuron Monday, January 11, 2016 11:30 AM • Dendrites work like antennae Glial cells Axon terminals • Myelin is grown by glial cells ○ Myelin acts as an insulator ○ Sheath is not continuous, gaps are known as nodes Gaps let in water (ECF) to the membrane underneath the myelin sheath • Membrane surrounds the nerve cell Nodes • Fluid inside cell - intracellular fluid (ICF) • Fluid outside cell - extracellular fluid (ECF) • Membrane ○ Bimolecular leaflet - membrane is 2 molecules thick Membrane Phospho ○ Fluid mosaic ○ Made of phospholipid molecules Lipid Lipid part of the molecule is hydrophobic • Resting Membrane Potential (RMP) ○ Membrane impermeable to Sodium Organic ions ○ Permeable to Cl Potassium depolarization Potassium flows out ○ RMP = -70 MV = -1/14 volt +40 • Graded Potential ○ Voltage gets to -60, the graded potential changes and is set off drastically - action potential At -60 voltage-gated channels open Action Potential hyperpolarization Sodium rushes in Voltage goes from -60 to +40 and goes back down again At the top point, potassium channels open and potassium flows out making the -60 voltage go back down again □ Inside of the cell is turned positive, potassium is positive - so they flow out of -70 the cell Refractory period Sodium channels open first letting sodium flow in at -60. At +40, potassium channels -80 Sodium rushes in open letting potassium flow out Refractory period after action potential is at -80 and is hard for it to fire again □ Pump protein that pushes sodium back out and pulls potassium back in so it can RMB Graded Potential fire again □ Gets back up to -70 and process begins again ○ Depolarization - up into the positive ○ Hyperpolarization - down into the negative • Action Potential ○ Begins at axon hillock (-60 threshold) ○ Propagation - action potential fires the next one, which fires the next one, etc. Works at 1 mph Works fine in nerve cells in the brain and small insects but not in larger animals or to parts of the body since it works so slow ○ If blocked by the myelin sheath it becomes a passive current and shoots through the sheath Action potentials in nodes between myelin sheath Works a lot faster - 100 or 200 mph Psychobiology Page 1 Chapter 1 - Book Wednesday, January 20, 2016 12:16 PM The Structure of a Neuron • Neuron shapes varies enormously from one neuron to another • Larger neurons have dendrites, a soma, an axon, and presynaptic terminals ○ The tiniest neurons lack axons and some lack well-defined dendrites • A motor neuron receives excitation through its dendrites and conducts impulses along its axon to a muscle • A sensory neuron is specialized at one end to be highly sensitive to a particular type of stimulation, such as light, sound or touch. Dendrites • Branching fibers that get narrower near their ends • Surface is line with specialized synaptic receptors- receives information from other neurons ○ The greater the surface area, the more info it can receive • Many contain dendritic spines - short outgrowths that increase the surface area available for synapses Cell body, or soma • Contains the nucleus, ribosomes, and mitochondria • Most metabolic work occurs here • Range in diameter from .005 mm to .1 mm in mammals and up to a millimeter in certain invertebrates Axon • Thin fiber of constant diameter • Conveys an impulse toward other neurons, an organ, or a muscle • Range up to more than a meter in length ○ Axons from your spinal cord to your feet • Covered with myelin sheath with interruptions called nodes of Ranvier ○ Invertebrate axons do not have myelin sheath • Axon branches and swells at its tip forming presynaptic terminals (aka end bulb or bouton) ○ Releases chemicals that cross through the junction between one neuron and the next • Afferent axon - brings info into a structure ○ Every sensory neuron is an afferent to the rest of the nervous system • Efferent axon - carries info away from a structure ○ Every motor neuron is an efferent from the nervous system • Interneuron or intrinsic neuron - a cell's dendrites and axons are entirely contained within a single structure Variations among Neurons • The shape of a neuron determines its connections with other cells and determines its function ○ Widely branching dendrites can enable a cell to receive input from thousands of other neurons ○ Short branches lead cells to only receive input from very few other cells (as few as two other cells) Glia • Glia - Greek word meaning "glue" • Several types of glia in the brain ○ Star shaped astrocytes - wrap around the presynaptic terminals of a group of functionally related axons Shields it from chemicals circulating in the surround Taking up ions released by axons and then releasing them back- helps synchronize the activity of the axons Remove waste material created when neurons die and control amount of blood flow to each brain area Dilate blood vessels to bring in more nutrients during periods of heightened activity in some brain area ○ Microglia - act as part of the immune system Remove waste material, viruses, and fungi from the brain Necessary for the survival of certain neurons early in life ○ Oligodendrocytes and Schwann cells - glia cells that build myelin sheaths Supply an axon with nutrients necessary for its functioning ○ Radial glia - guide the migration of neurons and their axons and dendrites during embryonic development The Blood-Brain Barrier • Mechanisms that excludes most chemicals from the brain • Why we need it: ○ The brain does not replace damaged neurons for the most part ○ To minimize the risk of irreparable brain damage, the body builds a wall along the sides of the brain's blood vessels ○ The wall keeps out most viruses, bacteria, and harmful chemicals • How it works: ○ Depends on the endothelial cells that form the walls of the capillaries Outside the brain, these cells have small gaps but in the brain, they are joined tightly together to block viruses, bacteria, and other harmful chemicals • Vertebrate neurons depend almost entirely on glucose ○ Need a steady flow of oxygen because the pathways that use glucose requires oxygen ○ Brain constitutes only 2% of the body's weight, yet it uses 20% of its oxygen ○ Glucose is the only nutrient that crosses the blood-brain barrier in large quantities Resting Potential of the Neuron • The structure of the membrane and its proteins controls the flow of chemicals between the inside and outside of the cell Psychobiology Page 2 the cell • The membrane maintains an electrical gradient (difference in electrical charges between the inside and outside of the cell), also known as polarization ○ Neurons inside have slight negative electrical potential with respect to the outside ○ Difference results in a resting potential - condition of a neuron's membrane when it has not been stimulated or inhibited ○ A typical level in neurons is -70 mV Forces Acting on Sodium and Potassium Ions • The membrane is selectively permeable ○ Selectively permeable - ability of some chemicals to pass more freely than others through a membrane ○ Oxygen, carbon dioxide, urea, and water cross freely through channels that are always open. ○ When the membrane is at rest, sodium and potassium channels are closed, but sometimes they are open • Sodium-potassium pump - mechanism that actively transports sodium ions out of the cell while drawing in two potassium ions ○ Sodium ions are more than 10 times more concentrated outside the membrane than inside and potassium ions are similarly more concentrated inside than outside ○ Because the membrane is selectively permeable, the sodium ions that are pumped out cannot leak back in again ○ Some potassium ions slowly leak out, carrying a positive charge with them and causing an increase in the electrical gradient across the membrane • Concentration gradient - difference in distribution of ions across the neuron's membrane • The resting potential prepares the neuron to respond rapidly Action Potential • Voltage-gated channels - membrane channels whose permeability to sodium (or some other ion) depend on the voltage difference across the membrane • All-or-none law - the size and shape of the action potential are independent of the intensity of the stimulus that initiated it ○ Every depolarization beyond the threshold of excitation produces an action potential of about the same amplitude and velocity for a given axon ○ Once the voltage gets to a certain level it shoots off to the action potential - reaching a higher voltage does not make the action potential larger Analogy - to flush a toilet you have to make a press of at least a certain strength, but pressing harder does not make the toilet flush faster or more vigorously Refractory Period • Time when the cell resists the production of further action potentials • Absolute refractory period - a time when the membrane is unable to produce an action potential • Relative refractory period - time after the absolute refractory period that requires a stronger stimulus to initiate an action potential • The refractory period depends on two factors - the sodium channels are closed and potassium is flowing out of the cell at a faster than usual rate Propagation of the Action Potential • Describes the transmission of an action potential down an axon Action potential ○ To increase the speed of an action potential it uses the myelin sheath as an insulator making it move down the axon faster ○ Action potentials are set off in the nodes of the myelin sheath Distance between nodes are generally at least 100 times as long as a node • The jumping of action potentials from node to node is called saltatory conduction Local Neurons • Local neurons - neurons without an axon myelin node • When a local neuron receives info from other neurons, it has graded potential ○ Graded potential - a membrane potential that varies in magnitude in proportion to the intensity of the stimulus ○ The change in membrane potential is conducted to adjacent areas of the cell, in all directions, gradually decaying as it travels Psychobiology Page 3
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