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Psychology (9,695)
PSYA01H3 (1,206)
Steve Joordens (1,058)
Chapter 3-4

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Steve Joordens

-A neuron is made up of three parts: a cell body that houses the chromosomes with the organisms DNA and maintains the health of the cell; dendrites that receive information from other neurons; and an axon that transmits information to other neurons, muscles, and glands. Dendrites- Receive info from other neuron and relay to cell body Axon- transmits info from other neurons muscles or glands. Myelin Sheath- insulating layer of fatty material (glial cells) around axon. The Myelin helps the axon work more efficiently. in diseases like multiple sclerosis the sheath breaks down slowing the transfer of info Cajal found that dendrites and axons do not touch each other. There is a small gap between called the Synapse. The Synapse is the junction between axon of one neuron the dendrite or cell body of another. (Neurons dont touch synaptic gap) between axon dendrite. Three major types of Neurons- 1) Sensory Neurons receive info from external world and convey it to brain via spinal cord. ie. Signals for light, south, taste, touch, smell. 2) Motor Neurons carry signal from spinal cord to muscles to produce movement. ie. Neurons with long axons to stretch out to muscles. 3) Interneruons- connect sensory, motor or other neurons together. ie. Brings info from nervous system to sensory, nervous to motor, etc. Neuron Location 1) Purkinje Cells- a type of interneuron that carries info from cerebellum to rest of brain and spinal cord 2) Pyramidal Cells- found in cerebral cortex (brain) 3) Bipolar Cells- type of sensory neuron found in eye. Communiciation between two neurons has 2 stages, conduction and transmission. First stage is the conduction of an electric signal within neurons from dentrites to cell body then through axon. Second stage is transmission of electric signal between neurons over the synapse. + + K is closed during resting potential, for action potential K channels briefly shut down, and other channels that allow the flow of a positively charged ion, Na , are opened. Na is typically much more concentrated outside the axon than inside. When the + Na channels open, those positively charged ions flow inside, increasing the positive charge inside the axon relative to that outside. This flow of Na into the axon triggers the action potential After the action potential comes, the membrane channels return to their original state, and + K flows out until the axon returns to its resting potential. + + This leaves a lot of extra Na ions inside the axon and a lot of extra K ions outside the axon. During this period where the ions are imbalanced, the neuron cannot initiate another action potential, so it is said to be in a refractory period, the time following an action potential during which a new action potential cannot be initiated. The imbalance in ions eventually is reversed by an active chemical pump in the cell membrane that + + moves Na outside the axon and moves K inside the axon (the pump does not operate during the action potential) (action potential- an electric signal conducted along length of neurons axon to synapse) Nodes of Ranvier- breaks in the myelin sheath How does action potential (electric signal) travel along axon? When an electric signal passes down length of a myelinated axon the charge jumps from each node to node rather than through the entire axon. This process is called Saltatory Conduction which helps speed the flow of information down the axon. Axons end in terminal buttons (top part of left figure). They are filled with tiny vesicles (bags) that contain neurotransmitters (chemicals that transmit information from synapse to dendrite) The dendrites of the other neuron contain receptors that receive neurotransmitters. As K+ and Na+ flow across cell membrane they trigger a change from resting to action potential which travels down the length of axon to the terminal button. This will release neurotransmitters from vesicles into synapse. They will bind onto receptor sites on a nearby dendrite of receiving neuron which starts a new process (called synaptic transmission) The neurotransmittors will be either 4) 5) or 6) happen to them.
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