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PSYCH 261 (91)


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University of Waterloo
Deltcho Valtchanov

Structure and Function of Neurons Chapter 2 Cells of the Nervous System *Neurons *Soma – cell body (contains the nucleus). *Dendrite – branched, treelike structure attached to soma; receives information from other neurons. *Synapse – junction between neurons. *Axon – long, cylindrical structure conveys information from soma to terminal buttons. *Terminal Buttons – bud at the end of an axon branch. Cells of the Nervous System *Multipolar Neuron – one axon, many dendrites attached to soma. *Bipolar Neuron – one axon and one dendrite attached to soma. *Unipolar Neuron – one axon attached to soma; *axon divides, one branch receiving sensory information and the other sending information to central nervous system. *Electrochemical Communication *Electrical signal within the neuron *Chemical signal between neurons *Internal Structure *Nucleus *Contains the nucleolus and chromosomes involved in protein synthesis and contain the cell’s DNA. *Mitochondria *Considered the power house of the cell because of their ability to extract energy. *Golgi Apparatus *Acts as a packaging plant, where other molecules (e.g., neurotransmitters) are packaged in small containers *Glia = “glue”: supporting cells that provide structural/nutritional support for the nervous system. *Astrocytes *Provide structural support to neurons and clean up debris. *Oligodendrocytes *Support axons and produce the myelin sheath. *Microglia *Act as phagocytes and protect the brain from microorganisms. Astrocytes *“Star” cells *Connect with multiple neurons and provide structural support *Maintain the blood brain barrier *Neurons receive nutrients from astrocytes *(and some from capilliaries) *Break down glucose into lactate *(is metabolised faster than glucose) *Phagocytic processes Oligodendrocytes *Produce myelin sheath for CNS *Fatty covering of axons *Aids efficient transmission of electrical signal along the axon *Segmented – gaps in myelin sheath referred to as Nodes of Ranvier Oligodendrocytes and Schwann cells *Oligodendrocytes – CNS *Myelinate multiple axons *Schwann cell – PNS *Myelinate a single axon Blood-brain Barrier *A semipermeable barrier between the CNS and circulatory system, which helps to regulate the flow of nutrient rich fluid into the brain. *Area Postrema *A region of the medulla where the blood-brain barrier is weak. Toxins in the blood stimulate this area, initiating vomiting Communication Within a Neuron *Components of a Simple Withdrawal Reflex *Sensory Neuron *Motor Neuron *Interneuron Communication Within a Neuron *Inhibition in the Withdrawal Reflex *Brain input prevents the withdrawal reflex by decreasing activity of the motor neuron. Measuring ‘Action’ Potentials *Membrane Potential – electrical charge across a cell membrane; difference in electrical potential inside and outside the cell. *Resting Potential – membrane potential of a neuron when not being excited or inhibited (~ -70 mV). Measuring ‘Action’ Potentials *Depolarization – reduction (toward zero) of membrane potential. *Hyperpolarized – increase in the membrane potential of a cell. *Action Potential – brief electrical impulse that provides the basis for conduction of information along an axon. *Threshold of Excitation – value of the membrane potential that must be reached to produce an action potential. Membrane Potential *Intracellular Fluid Has Higher
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