Exam 5 - Lecture 2
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| Neurons | Functional cells of nervous system; communicate to muscles, glands, other neurons, or adipocytes; NO DIVISION
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| Neuroglia | ”Support” cells; Repair, regulate, protect, support; MAY DIVIDE
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| Neuroglia Outnumber Neurons __:1 | 20:1
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| CNS Glial Cells | Astrocytes, Microglia, Ependymal Cell, Oligodendrocytes
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| PNS Glial Cells | Schwann Cells, Satellite Cells
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| Astrocytes | Largest and most numerous CNS neuroglia
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| Most abundant glial cell in the nervous system: | Astrocytes
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| Functions of Astrocytes | 1. Enhance or suppress synaptics communication 2. Maintain extracellular environment 3. Component of the blood-brain barrier 4. Stabilize damaged neural tissue 5. Structural framework/support for CNS 6. Contribute to neuronal development in utero
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| How astrocytes enhance or suppress synaptic communication | Absorb and recycle neurotransmitters (especially glutamate and GABA)
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| How astrocytes maintain extracellular environment | Regulate osmolarity of K+, Na+, and CO2; conduit for nutrients, ions and dissolved gas from blood vessels to/from neurons
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| How astrocytes function as a component of the blood-brain barrier | Feet of astrocytes cover the capillaries and limit the movement in/out and blood flow/volume
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| How astrocytes stabilize damaged neural tissue | Migrate into damaged area, wall off injured tissue and stabilize the area
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| How astrocytes function for framework/support for CNS | Very abundant, extensive cytoskeleton
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| Which glial cells contribute to neuronal development in utero? | Astrocytes
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| Microglia | Smallest and least numerous; Wandering police force and janitors; Monocyte/Macrophage lineage
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| Function of Microglia | Phagocytose debris and pathogens
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| When do you get microglia? | They migrate into developing nervous system during gestation (the do NOT migrate into an adult brain!) They have a limited ability to divide following traumatic brain injury or during acute infections
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| Ependymal Cells | Line the brain ventricles and central canal of spinal cord (bathe and cushion the brain)
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| Functions of Ependymal Cells | 1. Aid in production/circulation of and monitor the composition of cerebrospinal fluid 2. Transport dissolved nutrients, gasses, and waste 3. Some have cilia that beat and circulate the CSF and help monitor/adjust the composition of it
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| Oligodendrocytes | Produce myelin for CNS nerurons by wrapping their cell membrane around axons
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| Functions of Oligodendrocytes | 1. Produce myelin for CNS neuron 2. Concentric layers of oligodendrocyte cell membrane wrap around the axon
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| One oligodendrocyte can wrap around ____ axons | Several
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| ___ Oligodendrocytes contribute to myelination of one axon | Many
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| Myelin | Fatty cell membrane that allows current down the cell axon (layers like a jelly roll)
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| Internode | Single myelinated region
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| Node (of Ranvier) | Unmyelinated region
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| White Matter | Regions of CNS and PNS that contain numerous myelinated axons
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| Functions of Myelin | 1. Acts as insulation 2. Limits leakage of ions out of /into the axon which therefore increases conduction of electrical signals
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| Myelin is usually found: | Where speed is vital (Cortex of spinal cord and peripheral nerves)
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| What gives myelin the white color? | Lipids
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| White matter is located where in the brain? | Center
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| White matter is located where in the spinal cord? | Outside
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| Gray Matter | Contains neuron cell bodies, dendrites, and unmyelinated axons; Nissl bodies give it its gray color
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| Nissl Bodies | Clusters of rough endoplasmic reticulum and ribosomes (gives Gray matter its gray color)
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| PNS | All neural tissue outside of the brain and spinal cord; Delivers sensory information to CNS; Carries out motor commands
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| Nerve is composed of: | Nerve fibers, blood vessels, and connective tissue
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| CNS is protected by: | Blood-brain barrier, blood-CSF barrier, and cranium
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| PNS is not protected like CNS and is therefore more readily exposed to: | toxins and mechanical trauma
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| What part of neurons in the PNS are protected/ covered by neuroglia? | Entire neuron
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| Satellite Cells | Protects neuronal cell bodies of ganglia and regulate gases nutrients and neurotransmitters surrounding ganglia
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| Ganglia | Clusters of cell bodies in the PNS
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| Satellite Cells are analogous to what CNS cell? | Astrocytes
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| Schwann Cells | Produce myelin for PNS axons; Wraps around axon once to multiple times; Protects axons from extracellular fluid
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| One Schwann Cell coats one region of ____ axon(s) | One
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| Schwann Cell covering the axon in its own cell membrane in a jelly roll fashion, then the axon is: | Myelinated
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| Schwann Cell covering the axon in its own cell membrane with only one layer, then the axon is: | Unmyelinated, just being protected from the outside, not helping save the electrical conduction
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| Schwann Cells are analogous to what CNS cell? | Oligodendrocytes
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| Demyelination Disorders First Degree Damage | Damage to myelin and/or myelinating glia
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| Demyelination Disorders Second Degree Damage | Damage to axon which leads to cognitive, sensory, and/or motor problems
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| Diptheria Toxin | Bacterial infection of skin or respiratory tract; toxin damages Schwann cells which leads to sensory and motor problems
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| Guillain-Barre Syndrome | Immune-mediated loss of PNS myelin, usually follows a bacterial infection; 70% usually recover
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| Multiple Sclerosis | Immune-mediated loss of CNS myelin, caused by viral mimicry, sunlight, diet, genetics, hormones(?)
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| MS Treatments | Glucocorticoids, Interferon-Beta, Muscle Relaxants
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| Heavy Metal Poisoning | Exposure to lead or mercury is toxic to myelinating glia in CNS and PNS; causes cognitive, sensory, and motor problems
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| Ion concentration inside the cell Equals/Does Not Equal the ion concentration outside of the cell | Does Not Equal
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| Membrane Potential | The potential difference across a cell membrane; the ability to do work
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| The inside of a cell is more _________ than the outside | Negative
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| Cell is much more permeable to K+ or Na+? | K+
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| Why is cell interior more negative? | 1. Permeability of K+ is much higher than Na+ 2. Na+/K+ pump sends 2 K+ inside per 3 Na+ outside 3. Fixed negatively charged proteins (A- stuck inside of cell)
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| Resting Membrane Potential | Membrane potential of an undisturbed cell (at rest); pretty consistent, but there are always ions moving across the membrane
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| Electrochemical Gradient | Chemical (ionic) Gradient + Electrical Gradient
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| Primary factors affecting membrane potential | Electrochemical Gradients for K+ and Na+
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| ECG can either ______ or _______ the chemical gradient for each ion | Reinforce or Oppose
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| K+ will want to go ______ the cell by the chemical gradient (lots does) | out of
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| K+ will want to go ______ the cell by the electrical gradient (little does) | into
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| Overall Electrochemical Gradient wants K+ to go ______ the cell | out of
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| Na+ will want to go ______ the cell by the chemical gradient (lots does) | into
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| Na+ will want to go ______ the cell by the electrical gradient (little does) | out of
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| Overall Electrochemical Gradient wants Na+ to go ______ the cell | into
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| Resting Membrane Potential of a Neuron | -70 mV
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| If the neuron had free permeability of K+ across the membrane until chemical = electrical gradient, the inside of the cell would be ___ mV | -90 mV
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| If the neuron had free permeability of Na+ across the membrane until chemical = electrical gradient, the inside of the cell would be ___ mV | +66 mV
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| The greatest contributing factor of the RMP being -70 mV in a neuron is ___ | K+ (-90 mV is closer to -70 mV than +66 mV)
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| Equilibrium Potential | If the membrane were freely permeable to an ion, it would move until its equilibrium potential was reached, meaning no net movement of that ion across the membrane
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| At rest, the permeability to Na+ is _____ and the permeability to K+ is _____ | Na+ is low, K+ is high (more K+ leaves the cell)
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| Ligand Gated Channels are found in | Dendrite and soma
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| Ligand Gated Channels are responsible for | Graded Potentials
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| Voltage Gated Channels are found in | Axons
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| Voltage Gated Channels are responsible for | Action Potentials
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| Voltage Gated Na+ Channels have activation and inactivation gates that function ________ | Independently
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| Depolarization | Charge across the membrane is “less polar;” A shift in the RMP toward a more positive potential (moves toward zero); Positive ions (Na+) rush into cell
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| Repolarization | Restores normal RMP following depolarization; Positive ions (K+) leave cell (Na+/K+ Pump)
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| Does depolarization always make an action potential? | No
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| Hyperpolarization | Membrane potential moves away from zero; Cell interior becomes more negative [than RMP]; Negative ions (Cl-) rush in OR positive ions (K+) rush out
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| Hyperpolarization _________ the chance of generating an action potential | Decreases (will take much more Na+ to get to threshold and action potential)
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| Threshold | The membrane potential at which voltage gated Na+ channels open up to initiate an action potential (-60 mV)
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| Action Potential | Self-regenerating wave of electrochemical activity due to opening of voltage gated Na+ channels on the axon
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| Threshold is ____ mV | -60 mV
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| Action Potential occurs at ____ mV | +30 mV
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| How do neurons communicate at the synapse? | Synaptic activity (neurotransmitter release)
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| What causes neurotransmitter release on the postsynaptic neuron? | Action potentials
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| What causes action potentials? | Graded potentials
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| Local change in membrane potential occurs where? | Dendrites, Soma, Axon Hillock
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| Local change in membrane potential causes: | depolarization or hyperpolarization depending upon what channel is opened
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| Axon Hillock has _______ channels | Ligand Gated Channels
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| Axon has ______ channels | Voltage Gated Channels
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| An action potential can be: | Depolarizing only
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| Graded potentials can be: | Hyperpolarizing or Depolarizing
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| Local Current | Passive movement of positive charge inside of the membrane (parallel to inner/outer surface of membrane) that propagates the opening of other channels to cause depolarization or hyperpolarization of local, adjacent areas of a membrane
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| Properties of Graded Potentials | Decays as it moves, Short-distance signal; Non-regenerating (smaller changes in mV than action potentials)
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| Magnitude of depolarization depends on | The amount of stimulus (larger, longer stimulus = larger, longer graded potential)
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| At threshold, the cell membrane is _____ permeable to Na+ | More
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| A resting membrane is _____ permeable to K+ | More
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| Propagation is a _______ feedback mechanism | Positive (more Na+ channels open as the threshold propagates)
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| Action potentials only occur in ______ membranes | Excitable (neurons and muscle fibers)
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| Action potentials regenerate at _______ regions of axons | unmyelinated regions (nodes)
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| Properties of Action Potentials | Always depolarizing, all or none response, can’t be summer, magnitude of stimulus is negligible, does not decay
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| What happens if threshold is reached at the axon hillock? | Voltage gated Na+ channels (activation gates) open at initial segment; Na+ floods into neuron even faster; Neuron goes from -60 mV toward +30 mV; Triggers voltage gated Na+ channels to open all along axon [propagation]
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| When neuron membrane potential = +30 mV: | Voltage gated Na+ channels close (via inactivation gates) and no more Na+ enters the cell; Voltage gated K+ channels open and K+ rushes out of the cell and neuron begins repolarizing
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| When neuron membrane potential = -70 mV: | Voltage gated K+ channels slowly shut; membrane potential reaches -90 mV
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| A neuron can generate _____ AP/second | 1,000
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| Absolute Refractory Period | Neuron can absolutely NOT generate another action potential; Voltage gated Na+ channels need to fully recover
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| Relative Refractory Period | Neuron can generate another action potential but a stronger stimulus is needed to reach threshold
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| Propagation | An action potential at one site causes depolarization at ‘downstream’ adjacent sites, bringing those adjacent sites to threshold
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| Why does the action potential only propagate ‘downstream’? | Because the Na+ is moving that direction and it’s too positive ‘upstream’
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| Final Outcome of Propagation | Depolarization of axon terminal causes neurotransmitter release via opening of voltage gated Ca++ channels
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| Continuous Propagation | Unmyelinated axon; action potentials generated repeatedly along the axon; voltage gated opening of Na+ channels takes time; the increase in energy is used to restore the ion gradients
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| Saltatory Propagation | myelinated axon; action potential regenerated only at the nodes; myelin increases membrane resistance and decrease leakage of ions which increases the sped of propagation and saves energy
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| Myelin _____ the speed of propagation | Increases
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