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Psych- Neuroscience 1.pdf

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Joe Kim

o Establishes a good reputation for oneself o People are more generous and more law-abiding when observed by others Neuroscience I René Descartes th - 17 century scientist and philosopher - Saw the mind as a separate entity existing outside our biology, yet in control of our actions and thoughts - The physical brain was thought to serve as a connection between mind and body The Neuron - Specialized for communication - Communicate via synaptic transmissions - Contains two distinct zones: - [1] Receptive Zone - Designed to receive signals from other neurons - Composed of the dendrites branching out from the cell body - Dendrites reach out to other neurons and receive signals to be relayed through the dendritic branch to the cell body - Some signals will go on to be conveyed down the axon - [2] Transmission Zone - Designed to pass on signals to other cells - Composed of the axon and terminal ends - Signals are passed down the axon - Axons can vary in length - At the end of the axon are the terminal ends - Terminal ends reach out and make connections with the receptive zone of nearby neurons to transmit the signal further Ions In The Brain - Neuron’s cell membrane separates the intracellular fluid and the extracellular fluid - Ions in the intracellular and extracellular fluid contain positive/negative charges - Membrane is selectively permeable - Membrane contains protein channels (ex. Potassium channel, sodium channel), which act as passageways for ions to pass through - The Resting Potential [Of A Neuron]:When a neuron isn’t sending a signal and there’s a baseline imbalance between concentrations of ions in the intracellular and extracellular fluid of a neuron. o Controlled by two forces: o [1] Diffusion: The tendency for molecules to distribute themselves evenly in a medium. ƒ Ex. Pouring cream into a cup of coffee o [2] Electrostatic Force: The repulsion between ions with the same charge. - Differing concentrations of ions produces anelectrical imbalance between the outside and inside of the neuron - Typical neuron starts off at -70mV (millivolt) relative to the outside of the cell - Net result of the diffusion and electrostatic forces lead to an overall resting potential of -70mv inside the cell compared to the outside - Negatively charged large protein molecules within the neuron are too large to pass through the cell membrane - Electrostatic force of the negatively charged protein molecules keep the negatively charged chloride ions on the outside of the cell - Potassium, sodium, and chloride ions are mobile - Two types of potassium channels: - [1] Leaky Potassium Channel - Resembles a faucet that’s always open - Allows positively charged potassium to pass through the cell membrane out of the neuron - Not all potassium ions pass through and much remains inside at rest - Major contributor to maintaining the resting potential of the neuron - [2] Voltage-gated Channel - Important for the action potential - Voltage-gated sodium channels are closed in the resting state of the neuron - Positively charged sodium ions flow only in very low concentrations into the cell - Flow of sodium is less important to the resting state of the neuron than potassium - The Action Potential [Of A Neuron]: Occurs when a neuron sends information down an axon, away from the cell body, and an explosion of electrical activity is created by a depolarizing current. o Means that a stimulus caused the resting potential to move toward 0mV o The threshold is when the depolarization reaches about -50mV and a neuron fires an action potential - Sodium channels being to open (up to thispoint, most Na+ have piled up outside) - Force of diffusion causes the positively charged sodium ions to rush inside - Causes charge on the inside of the cell to become more positive relative to the outside - Electrostatic force pushes some positively charged K+ out of the cell through the leaky potassium channels - Positivity builds up inside the cell until the voltage-gated potassium channels open and allow more positively charged potassium ions to rush out the cell - After reaching a peak charge of ~+40mV inside the cell, the sodium channels close - Sodium stops entering the cell, but potassium continues to rush out the voltage-gated potassium channel - Inside of cell begins losing positive charge and drops below -70mV - Voltage-gated potassium channels completely close - Cell returns to -70mV - Short refractory period occurs and the neuron cannot fire another action potential until it settles/recovers - Sodium-Potassium Pump:Removing sodium from the cell and replacing potassium. o Expels three Na+ from the intracellular fluid and replaces them with two K+ o Moves slowly and utilizes extensive energy, therefore playing little role in the action potential o Important part of maintaining the ion balance of the neuron and recovering from action potential cascades - Glial Cells: Provides structural support, nourishment, and insulation to neurons. o Coat axons with a type of fatty, insulating tissue called myelin o These special cells are the Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system o Insulating layer of myelin allows the action potential to travel down the axon faster o When an action potential reaches a myelin sheath, it jumps across it through a process called saltatory conduction o Between segments of myelin are open regions on the axon called nodes of Ranvier o As electrical signals jump through the myelin sheath, it weakens o At the nodes, the signal can be strengthened again through ion channel cascades before jumping through the next myelin sheath o Process allows a signal to travel through a long axon rapidly without strength loss Sending A Signal - All-Or-None Principle:The amplitude of an action potential is independent of the amount of current that produced it. o Large currents don’t create large action potentials o Action potentials either fully occur or not at all o Action potentials produced by a neuron are roughly identical in strength and duration o Frequency of action potentials is what encodes for the intensity of a stimulus (ex. Strong signal will lead to many sequential action potentials) The Synapse:The area of connection between the terminal end of neuron A and the receptive zone of neuron B. - Not a direct physical connection - Within the terminal end of the presynaptic neuron are neurotransmitters - Neurotransmitters are found within vesicles - As the action potential reaches the terminal ends, some vesicles move toward the cell membrane - Vesicles fuse with the membrane ofthe presynaptic neuron and opens - Neurotransmitter molecule
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