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Chapter 3

Chapter 3.docx

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Janelle Leboutillier

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Chapter 3 | Cells of the Nervous System Neurons and Glia - neurons: specialized to carry out functions of info processing and communication - glia: serve variety of support functions for neurons about 10-50 glia per neuron The Structure of Neurons - all animals have organelles: small structure w/in a cell that carries out specific function - cell body/soma: main mass of a neuron, containing nucleus and many organelles - differ from other cells because neurons have specialized branches extending from cell body axons: branch of neuron usually responsible for carrying signals to other neurons dendrites: branch of a neuron that generally receives info from other neurons Neuron Membranes - separates intracellular fluid from extracellular fluid - figure 3.2, p. 62 - made up of phospholipids fatty molecules that contain phosphate doesnt dissolve in water able to restrain water-based fluids on either side maintain structural integrity of cell only two phospholipids wide - important proteins suspended w/in this membrane tat control its permeability: movement of substances across the cell membrane two primary important to neural function 1) ion channels: allow ions to pass w/out additional energy 2) ion pumps: uses energy to move ions across - ion: electrically charged particle in solution - both pumps = ion selectivity amino acids (protein building blocks) make up ion channel or pump = determine ions allowed to pass - have ability to open and close in response to stimuli in immediate vicinity voltage-dependent channels: opens or closes in response to local electrical environment ligand-gated channels: open when come in contact w/ specific chemicals - two most important pumps 1) sodium-potassium pumps: help maintain differences in chemical composition between intracellular and extracellular fluids prisoner exchange sends three sodium ions out of cell while collecting two potassium ions from extracellular environment about 20-40% of brain energy used 2) calcium pumps: performs similar function as Na-K pumps, but just moves calcium ions out of cell w/out taking anything in The Neural Cytoskeleton - cytoskeleton: network of filaments that provide internal structure of a neuron - figure 3.3, p. 63 three fiber types compose cytoskeleton of neurons largest (25nm) microtubules: responsible for transport of neurotransmitters and other products to and from cell body anterograde transport: movement from cell body to axon terminal retrograde transport: movement from axon terminal back to cell body microtubules been implicated in development of alzheimers disease figure 3.4, p. 64 protein called tau holds microtubules together disconnected tau in alzheimers (due to molecules of phosphate) = neurofibrillary tangles eventually cell collapses and dies neurofilaments (10nm) run parallel to length of the axon similar structure of a hair smallest (3-5nm) microfilaments most located in branches of neuron may participate in changing shape and length of these structures during development; and to learning The Neural Cell Body - specialized to participate in communication function - figure 3.5, p.66 neural cell body nucleus: contains cells DNA nucleolus: w/in cell nucleus where ribosomes are produced ribosome: involved w/ protein synthesis endoplasmic reticulum smooth after proteins constructed by ribosome on rough, moves it to golgi apparatus rough have ribosomes attached to it golgi apparatus: packages proteins into vesicles mitochondria: provide energy to cell by transforming pyruvic acid and oxygen into molecules of adenosine triphosphate (ATP) Dendrites - location at which info from other neurons are received greater surface area of dendritic membrane = larger # of connections or synapses it can form w/ other neurons - synaptic gap: tiny fluid-filled space between neurons forming a synapse - @each synapse on dendrite ion channels serve as receptor sites on neural membrane interact w/ molecules of neurotransmitter from other neurons float across synaptic gap - dendritic spines: knob on dendrite that provides additional membrane area for formation of synapses w/ other neurons figure 3.6, p.66 allow additional locations for synapse to occur appear to change shape based on amount of activity occurring at synapse contributes to process of learning and memory figure 3.7, p.67 dendritic spine of ppl w/ retardation similar to human fetuses The Axon - responsible for carrying neural messages to other neurons - axon hillock: cone-shaped segment of axon located at junction of axon and cell body that is specialized for generation of action potentials - vary in diameter vertebrates 1micrometre to about 25micrometres invertebrates (like squid) 1mm size is crucial to speed of signaling myelin: fatty insulating material covering some axons that boosts speed and efficiency of electrical signaling - vary in length local circuit neurons: neuron that communicates w/ neurons in its immediate vicinity projection neuron: neuron w/ very long axon that communicates w/ neurons in distant areas of nervous system - collateral: one of branches near end of axon closest to its targets - axon terminal: swelling at tip of axon collateral specialized for release of neurotransmitter substances contains large # of mitochondria and synaptic vesicles: small structure in axon terminal that contains neurotransmitters - many axons in vertebrate nervous systems are covered by myelin vast majority of CNS neurons and peripheral motor neurons are myelinated formed by types of glia that wrap themselves or branches around segments of
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