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Ted Petit (185)
Chapter 2

Chapter 2 Notes

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University of Toronto Scarborough
Ted Petit

Chapter 2 Neuroatanomy Cells of the nervous system 2 cells of the nervous system: neurons & glia specialized in both structure and function Glia provide support functions Neurons communicators; react and respond to stimuli - basis of behaviour - also learn & store info about their external behaviour Neurons and Glia: Structure and Function GrossAnatomy of the Neuron Neuron's shape linked to its function: to receive, conduct, and transmit signals to collect info and send it on (or not) 3 main components: dendrites, soma, axon Dendrites receive incoming information from other neurons Its extensive branches allow for inputs of up to 100, 000 for a single neuron! Receives info and then sends it to the rest of the neuron in the form of an electric charge (action potential) Dendrites are covered with spines can also form synapses Soma contains the genetic machinery and most of the metabolic machinery needed for common cellular functions Axon which sends neural information to other neurons (passes it through dendrites) 1 axon per neuron it is the information sender long thin, fiber/wire covered with myelin (insulation) helps to speed up transfer of info Terminal button at the end of the axon this releases neurotransmitter into synapse Synapse Presynaptic events that occur in the axon Postsynaptic events that occur in the dendrites (of other neurons) InternalAnatomy of the Neuron Neuron is covered with a membrane plasma membrane Consists of a bilayer of continuous sheets of phospholipids that separate 2 fluid environments one inside the cell (cytoplasm) and the other outside the cell Within the membrane there are protein channels that allow the passage of materials into and out of the neuron Enclosed within is the cell nucleus packages and controls the genetic info contained in DNA, and also contains genetic info needed to code proteins (eye or hair colour) Structure and Function of Neurons Structurally classified as being either: unipolar, bipolar, multipolar (the most common) Unipolar have only 1 process emanating from the cell body Bipolar have 2 processes Multipolar have numerous processes extending from the cell body Interneurons neurons with no axons or very short axons integrate info within structure rather than mingling with other structures (can make connections btwn cells) Functionally classified by the types of signals the process Sensory neurons process info elicited from sensory-type stimuli Motor neurons e.g. Signal for muscle contraction Also can be classified as.... Afferent bringing info to the CNS (approach) Efferent output; sending info from the brain or a structure (exit) SO....neurons vary in size, shape, and function, and can also change as a result of experience Glia Support functions Different types of glia Astrocytes Largest glia filling the space between neurons (close contact w/ neurons which affects growth of neurons) Also involved in blood-brain barrier Perform nutritive & metabolic functions for neurons Also essential for the regulation of the chemical content of the extracellular space May even play a role in the transmission of info in the nervous system Affect neurotransmitters Regulate how far neuroatransmitters and other substances released, can spread Storage of neurotransmitters Oligodendrocytes Make myelin wrap their processes around most axons in the brain & spinal cord Axons outside the brain myelin is provided by Schwann cells (whereas Schwann cells can only provide 1 segment of myelin to an axon, oligodendrocytes can contribute many segments to many axons more efficient) Microglia Smallest of the glia - micro Microglia are phagocytes that remove debris from nervous system ( due to injury, disease, infection, aging) Different from the other cells made outside of the CNS by machrophages Excessive activation of these cells involved inAlzheimer's & MS (hence, auto-immune disease where cells attack themselves) Communication within the Neuron: The Action Potential Neuron's resting potential = -70 mV electrical charge on the inside is 70 mV less than the outside (Na+), (K+) outside is more positive due to high concentrations of (Na+), and inside contains more (K+) What causes the uneven distribution (resting potential)? 1) Permeability ability of some ions to cross through while others dont At rest, K+ readily crosses the membrane but Na+ cannot easily enter. 2) Sodium-potassium pump Neurons actively import K+ and export Na+ through a transport mechanism requires the neuron to use energy which ensures uneven distribution. Pump exchanged 3 Na+ ions inside the cell for two K+ ions that are outside the cell so pumps out 3 sodium ions for 2 potassium ions, hence the high concentration of na+ on the outside. Action potential Opening of sodium channels Na+ flows in making inside more positive goes from -70 mV to + 50 mV = depolarization = action potential =
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