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Lecture 3

PSYB64 Lecture 3.docx

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Elizabeth Page- Gould

Lecture 3 Cells of the nervous system NEURONS AND GLIA  The Structure of neurons ◦ Neuron membranes separate intracellular fluid from extracellular fluid ◦ The neural cytoskeleton provides structural support that maintains the shape of the neuron NEURAL MEMBRANE Membrane is a bi-layer composed largely of phospholipids and other lipids studded with proteins and other large molecules Ion Channels • Allow ions to diffuse down concentration gradient • Selective permeability to certain ions • Don’t require additional energy Ion Pumps • Actively move ions against concentration gradient • Create ion concentration gradients • Require Energy 3 FIBER TYPES COMPOSE THE CYTOSKELETON OF NEURONS Neurons and Glia  Structural Features of Neurons ◦ Cell body (soma) contains nucleus and other organelles ◦ Dendrites – branches that serve as locations at which information from other neurons is received  spines ◦ Axons are responsible for carrying neural messages to other neurons  Vary in diameter and length  Many covered by myelin Axons and dendrites STRUCTURAL VARIATIONS IN NEURONS o Unipolar  Bipolar  Multipolar 1. Unipolar Single branch extending from the cell body 2. Bipolar Two branches extending from the neural cell body: one axon and one dendrite 3. Multipolar Many branches extending from the cell body; usually one axon and many dendrites FUNCTIONAL VARIATION IN NEURONS  Sensory Neurons ◦ Specialized to receive information from the outside world  Motor Neurons ◦ Transmit commands from the CNS directly to muscles and glands  Interneurons ◦ Act as bridges between the sensory and motor systems TYPES OF GLIA THE GENERATION OF THE ACTION POTENTIAL  Ionic Composition of the Intracellular and Extracellular Fluids ◦ The difference between these fluids provides the neuron with a source of energy for electrical signaling ◦ Differ from each other in the relative concentrations of ions they contain THE COMPOSITION OF INTRACELLULAR AND EXTRACELLULAR FLUIDS MEASURING THE RESTING POTENTIAL OF NEURONS THE GENERATION OF THE ACTION POTENTIAL  The Movement of Ions ◦ Diffusion is the tendency for molecules to distribute themselves equally within a medium ◦ Electrical force is an important cause of movement  Like electrical charges repel  Opposite electrical charges attract DIFFUSION AND ELECTRICAL FORCE  The Resting Potential ◦ Membrane allows potassium to cross freely ◦ Measures about -70mV ◦ If potassium levels in extracellular fluid increase, resting potential is wiped out THE ACTION POTENTIAL  Threshold ◦ When recording reaches about - 65mV  Channels open & close during action potential
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