Week of Notes (Chapter 2)
Week of Notes (Chapter 2) PSYCH 3240
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This 7 page Class Notes was uploaded by Lucy Stevens on Thursday January 21, 2016. The Class Notes belongs to PSYCH 3240 at Clemson University taught by Dr. Claudio Cantalupo in Spring 2016. Since its upload, it has received 42 views. For similar materials see PSYCH 3240 in Psychlogy at Clemson University.
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Date Created: 01/21/16
Chapter 2 Structure and Function of the Nervous System (1-19-16) Microscopic Level Neurons: -Specialized cells that receive information and send it to other cells -Carry information within in the brain and throughout the rest of the body. -about 100 million neurons in the brain Glial Cells: -cells that provide structural and functional support for neurons Neuron Basic Structure Nucleus: control center Dendrite: receive signals Soma: surrounds the nucleus Axon: transmits signals Myelin Sheath: cover axons and is made of a special kind of glial cells Types of Neurons 1. Motor Neurons (output neurons): a. Receive information from the other neurons b. Carries information to muscle or gland cells 2. Sensory Neurons (input neurons): a. Receives a particular type of sensory information b. Carries information to other neurons 3. Interneuron a. Connects one neuron to another in a particular part of the central nervous system (CNS) *Can you connect motor and sensory neurons? What would the outcome be? -Yes! Reflexes work in this way. -Lots of animal behaviors work by the connection of sensory to motor neurons. *Adaptive Trait: any trait that carries for the individual and sends the trait to the next generation. It has nothing to do with good or bad behavior. *Is the wiring that you were born with adaptive? You can get adaptive behavior by attaching motor and sensory neurons. *What is the problem? You cannot change the hard wiring. Experiences and the environment will have no effect on the wiring. The environment is not constant. The middle “black box” allows you to change the output based on changes in the environment. Glial Cells 1. Oligodendrocytes: build myelin around axons in the brain and spinal chord (CNS) ( The membranes of most cells are made of fat) 2. Schwann Cells: build myelin around axons in the peripheral nervous system (PNS) Neural Membrane -critical for the neurons ability to carry information -consists of a phospholipid bilayer where protein molecules are sometimes embedded. -Head: Hydrophilic (attracted to water) -Tail: Hydrophobic (repelled by water) -Proteins are made of a sequence of amino acids Protein Molecules 1. Channels: molecules move down a gradient 2. Pumps: molecules are pushed against the gradient Polarization: difference in electrical charge (voltage) between the inside and outside of the cell. Potential: difference between inside and outside of the neuron *There is a small difference in potential between the inside and the outside of a neuron at resting point. -70 mV is the difference Resting Potential: difference in electrical charge between the inside and outside of the membrane of a neuron at rest *There is an unequal distribution of ions on the two sides of the membrane. *Ions are molecules or atoms with positive or negative charges (lost or acquired electrons) Organic anions (A-) Chloride Anions (Cl-) Sodium Cations (Na+) Potassium Cations (K+) *At resting potential: -more potassium inside the neuron -more sodium outside the neuron Resting Potential *Membrane of the neuron is selectively permeable- some chemicals can pass through it more freely than others. Protein molecules embedded n the membrane Na+ channels (closed at rest), K+ channels (slightly open at rest) If the membrane was permeable, some of the sodium would go in, and there would be more of a uniform concentration of sodium inside and outside because of diffusion. Inside of neuron is more negative than outside. Sodium Potassium Pump(Na+/K+) Pump: repeatedly moves 3 Na+ out of the neuron and 2 K+ inside the neuron at rest. *There are two forces (gradients) acting on the ions at any moment in time: Electrical Gradient and Concentration Gradient K+ Ions: attracted inside by Electrical Gradient , and attracted outside by the Concentration Gradient. Concentration Gradient is slightly stronger than the Electrical Gradient, but they are basically in balance with each other. These two forces are independent of each other, but they act at the same time. Na+ Ions: attracted inside by BOTH Electrical Gradient and Concentration Gradient. Electrical gradient is slightly stronger than the Concentration Gradient, but they are basically in balance with each other. Na+ would rush inside if Na+ channels were open. *Na+ and K+ channels are VOLTAGE-ACTIVATED. Their permeability depends on the voltage (potential) across the membrane *Hyperpolarization: reserved for any increase in polarization (going away from 0) *Depolarization: reserved for any decrease in polarization (going towards 0) *What happens if you double the intensity of the Stimulus? You would expect to see an even bigger and longer hyperpolarization or depolarization. *Difference between depolarization and hyperpolarization: With hyperpolarization you can keep going and see bigger and longer lasting hyperpolarization. This is not so for depolarization because there is a threshold limit, which is known as the threshold of excitation. *Threshold of Excitement: seen in depolarization at -60 mV *What happens?? 1. Massive influx of sodium into the neuron 2. Most of the potassium channels start opening (not as rapidly as the sodium channels) and potassium moves outside 3. Sodium Channels shut close and no more sodium can enter the neuron. (by now, the potassium channels are fully open) 4. Now lots of potassium leaving the neuron. Sodium channels are still closed. 5. Then there is some hyperpolarization caused by potassium channels starting to close slowly which causes excess leaking outside of potassium. Neuron is loosing even more positive charge and becoming more negative. 6. Pumps open and the normal distribution is acquired. *Absolute Refractory Period: The neuron does not react to any stimulus because the sodium channels will not open. Lays down a “speed limit” for the neuron in terms of how many times that neuron is able to fire over time. *Relative Refractory Period: Won’t produce an action potential unless the stimulus is stronger than normal. *Rate Law of Action Potentials: Intensity of a stimulus is encoded by the rate of action potentials. *As the stimulus gets stronger, the neuron goes faster. Ex: Hearing a louder sound or seeing a brighter light the neurons will fire faster in your brain. *Spontaneous Activity: firing of a neuron in absence of environmental stimulation *Action Potential: you need a passive (graded) potential that will end up changing the electrical difference within the membrane *The All or None Law: the height of the action potential curve is constant. Graded potential and action potential can occur anywhere on the neuron .
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