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Psychology (9,546)
PSYB65H3 (479)
Ted Petit (185)
Chapter 2

Chapter 2 - Neuroanatomy

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University of Toronto Scarborough
Ted Petit

Function of the cerebral hemispheres brain vascular supply2 14 cerebral ventricles cerebral coverings Chapter 2NeuroanatomyModule 21 Cells of the NSNeurons and Glia Neurons and glia are specialized cells of the NS and the are specialized in both structure and function y Gross Anatomy of the Neuron The neuron consists of 3 main components 1 the dendrite which receive incoming information from other neurons 2 the somacell body which contains the genetic machinerywhich sends and most of the metabolic machinery needed for common cell functions and 3 the axonneural information to other neurons Information is passed form the axon to the dendrite across a gap 2050 nm called the synapseBased on the positions relative to synapse events that occur in the axon referred to as presynaptic and events that happen in the dendrite referred to as postsynapticDendrites increase in surface area available for the reception from the axons of other neuronsThe extent of branching of the dendrites gives indication of the number of connectionssynapses it makes with incoming axonsDendrites are often covered with tiny spines which grow and retract in response to experience The spines can form synapses with other neuronsThe axon is thought of as the information sender Its a long fiber or wire that can pass its message along to many different cells Myelin is insulation in the mammalian NSthey help to speed the rate of information transfer ad to ensure that the message gets to the end of the axon The end of the axon is the terminal buttonInformation that passes from the axon across the synapse is in the form of the neurochemical messageby substances called the neurotransmitters which may be transformed into an electrical message within the dendrite y Internal Anatomy of the Neuron The plasma membrane consists of a bilayer of continuous sheets of phospholipids that separate 2 fluid HO environments1 inside the cell cytoplasm and the other outside the cell 2 Inside the main cell body small components of the cell called organelles form a complex environment where organelles perform various genetic nucleus synthetic ribosomes endoplasmic reticulum and metabolic mitochondria process that keep the neuron functioningThe nucleus packages and controls the genetic information containing DNA The nucleus processes the information needed to complete a series of events that form a path form the recipe that the genetic information provide to form proteins that the neuron needs The nucleus also contains all the info Needed to code proteins y Structure and Function of Neurons Structurally the most common neurons are unipolar bipolar or multipolar Unipolar neurons have only 1 process emanating from the body cell body bipolar neurons has 2 processes and multipolar have numerous processes extending from the cell body Neurons with no axons or only very short axons are called interneurons and tend to integrate information Neurons can be classified by the type of signals they give Neurons can be classed as being afferent bringing information to the CNS or structure or efferent sending information from the brain or away from a structureGlia perform support functions different types of glia providing different types of support Support cells outside of the brain and spinal cord are called satellite cells There are at least 3 types of glia 1 Astrocytes are the largest glia and are called that way because they are starshaped Astrocytes fill the space between neurons resulting in close contact between neurons and astrocytes Astrocytes are also essential for regulation of chemical content of extracellular space They are also important in the storage of neurotransmitters have a clear functionto make myelin They wrap their processes around most axons 2 Oligodendrocytesin the brain and spinal cord These processes are made of myelin which is a fatty substance that acts to insulate the axon Axons outside of the brain and spinal cord are also frequently myelinated with the myelin form Schwann cells3Microglia are named with reference to their sizethey are smallest of glia They are phagocytesthat remove debris from the NS Debris can accumulate in the brain as a result of injury disease infection or aging They are made on the outside of the brain and spinal cord by macrophages Excessive activation of microglia has been implicated in neurodegenerative disease such as MDS and Alzheimersy Communication within the Neuron The Action PotentialThe resting potentialis the initial site of the neuron it maintains an electrical charge of 70 mV the electrical charge on the inside of neuron is 70 mV less than the charge on the outsideThe resting potential of the neuron depends on the difference between the concentration of ions across the neuron membrane st The neuron has 2 properties that promote the uneven distribution of ions The 1 property relates to permeability of the cell membrane that covers the neuron membrane is not permeable to all ionsIons cross the membrane through proteins embedded in the membrane which are called ion channelsNeurons actively import Kand actively export Nathrough a transport mechanism known as a sodiumpotassium pump The NaK pump requires the neuron to use energyThe opening of Na channels allows Na to rapidly enter the neuron which makes the in intracellular space moreWhen the change in membrane potential moves form resting 70 to 50 this change in membrane potential is called depolarization an action potential occurs When this happens neurotransmitters are released from the terminal buttonsAs the neuron becomes depolarized K channels open and K ions rapidly leave the neuron The efflux of K triggers the closing of Na channels and the neuron return to resting state repolarization Bc the K channels take longer to close some K leaks out which results in temporary change in the membrane beyond 70 mV hyperpolarizationThere are several features of an action potential that must be considered There are times when an action potential cant be triggeredModule 22 The NS Communication Within the Neuron The Action Potential When a neurotransmitter diffuses across the synapse to interact w postsynaptic site a series of electrical events can occur some send information and some inhibit informationThe electrical events that make the transmissioninhibition of information relies on the balance of ions between the inside of the neuron intracellular and the outside of the neuron extracellularWhen the neuron is at rest it maintains an electrical charge 70 mV which means that the electrical charge on the inside of the neurons is 70 mV lessthan the charge on the outsidethis is calledresting potentialThe RP of the neuron depends on the difference between the concentrations of ions across the neuron membraneneurons contain variety of ions most important are Na ions and K ionsAt rest extracellular fluid contains high concentration of Na and intracellular fluid contains high concentration of KIn the brain ions are concentrated in either extracellularintracellular fluidThe neuron has 2 properties that promote the uneven distribution of ions 1 Related to permeability of the cell membrane that covers the neuronmembrane is not permeable to all
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