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Neuroglia & AP
Exam 5 - Lecture 2
| Question | Answer |
|---|---|
| Neurons | Functional cells of nervous system; communicate to muscles, glands, other neurons, or adipocytes; NO DIVISION |
| Neuroglia | ”Support” cells; Repair, regulate, protect, support; MAY DIVIDE |
| Neuroglia Outnumber Neurons __:1 | 20:1 |
| CNS Glial Cells | Astrocytes, Microglia, Ependymal Cell, Oligodendrocytes |
| PNS Glial Cells | Schwann Cells, Satellite Cells |
| Astrocytes | Largest and most numerous CNS neuroglia |
| Most abundant glial cell in the nervous system: | Astrocytes |
| 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 |
| How astrocytes enhance or suppress synaptic communication | Absorb and recycle neurotransmitters (especially glutamate and GABA) |
| 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 |
| 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 |
| How astrocytes stabilize damaged neural tissue | Migrate into damaged area, wall off injured tissue and stabilize the area |
| How astrocytes function for framework/support for CNS | Very abundant, extensive cytoskeleton |
| Which glial cells contribute to neuronal development in utero? | Astrocytes |
| Microglia | Smallest and least numerous; Wandering police force and janitors; Monocyte/Macrophage lineage |
| Function of Microglia | Phagocytose debris and pathogens |
| 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 |
| Ependymal Cells | Line the brain ventricles and central canal of spinal cord (bathe and cushion the brain) |
| 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 |
| Oligodendrocytes | Produce myelin for CNS nerurons by wrapping their cell membrane around axons |
| Functions of Oligodendrocytes | 1. Produce myelin for CNS neuron 2. Concentric layers of oligodendrocyte cell membrane wrap around the axon |
| One oligodendrocyte can wrap around ____ axons | Several |
| ___ Oligodendrocytes contribute to myelination of one axon | Many |
| Myelin | Fatty cell membrane that allows current down the cell axon (layers like a jelly roll) |
| Internode | Single myelinated region |
| Node (of Ranvier) | Unmyelinated region |
| White Matter | Regions of CNS and PNS that contain numerous myelinated axons |
| Functions of Myelin | 1. Acts as insulation 2. Limits leakage of ions out of /into the axon which therefore increases conduction of electrical signals |
| Myelin is usually found: | Where speed is vital (Cortex of spinal cord and peripheral nerves) |
| What gives myelin the white color? | Lipids |
| White matter is located where in the brain? | Center |
| White matter is located where in the spinal cord? | Outside |
| Gray Matter | Contains neuron cell bodies, dendrites, and unmyelinated axons; Nissl bodies give it its gray color |
| Nissl Bodies | Clusters of rough endoplasmic reticulum and ribosomes (gives Gray matter its gray color) |
| PNS | All neural tissue outside of the brain and spinal cord; Delivers sensory information to CNS; Carries out motor commands |
| Nerve is composed of: | Nerve fibers, blood vessels, and connective tissue |
| CNS is protected by: | Blood-brain barrier, blood-CSF barrier, and cranium |
| PNS is not protected like CNS and is therefore more readily exposed to: | toxins and mechanical trauma |
| What part of neurons in the PNS are protected/ covered by neuroglia? | Entire neuron |
| Satellite Cells | Protects neuronal cell bodies of ganglia and regulate gases nutrients and neurotransmitters surrounding ganglia |
| Ganglia | Clusters of cell bodies in the PNS |
| Satellite Cells are analogous to what CNS cell? | Astrocytes |
| Schwann Cells | Produce myelin for PNS axons; Wraps around axon once to multiple times; Protects axons from extracellular fluid |
| One Schwann Cell coats one region of ____ axon(s) | One |
| Schwann Cell covering the axon in its own cell membrane in a jelly roll fashion, then the axon is: | Myelinated |
| 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 |
| Schwann Cells are analogous to what CNS cell? | Oligodendrocytes |
| Demyelination Disorders First Degree Damage | Damage to myelin and/or myelinating glia |
| Demyelination Disorders Second Degree Damage | Damage to axon which leads to cognitive, sensory, and/or motor problems |
| Diptheria Toxin | Bacterial infection of skin or respiratory tract; toxin damages Schwann cells which leads to sensory and motor problems |
| Guillain-Barre Syndrome | Immune-mediated loss of PNS myelin, usually follows a bacterial infection; 70% usually recover |
| Multiple Sclerosis | Immune-mediated loss of CNS myelin, caused by viral mimicry, sunlight, diet, genetics, hormones(?) |
| MS Treatments | Glucocorticoids, Interferon-Beta, Muscle Relaxants |
| Heavy Metal Poisoning | Exposure to lead or mercury is toxic to myelinating glia in CNS and PNS; causes cognitive, sensory, and motor problems |
| Ion concentration inside the cell Equals/Does Not Equal the ion concentration outside of the cell | Does Not Equal |
| Membrane Potential | The potential difference across a cell membrane; the ability to do work |
| The inside of a cell is more _________ than the outside | Negative |
| Cell is much more permeable to K+ or Na+? | K+ |
| 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) |
| Resting Membrane Potential | Membrane potential of an undisturbed cell (at rest); pretty consistent, but there are always ions moving across the membrane |
| Electrochemical Gradient | Chemical (ionic) Gradient + Electrical Gradient |
| Primary factors affecting membrane potential | Electrochemical Gradients for K+ and Na+ |
| ECG can either ______ or _______ the chemical gradient for each ion | Reinforce or Oppose |
| K+ will want to go ______ the cell by the chemical gradient (lots does) | out of |
| K+ will want to go ______ the cell by the electrical gradient (little does) | into |
| Overall Electrochemical Gradient wants K+ to go ______ the cell | out of |
| Na+ will want to go ______ the cell by the chemical gradient (lots does) | into |
| Na+ will want to go ______ the cell by the electrical gradient (little does) | out of |
| Overall Electrochemical Gradient wants Na+ to go ______ the cell | into |
| Resting Membrane Potential of a Neuron | -70 mV |
| 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 |
| 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 |
| 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) |
| 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 |
| At rest, the permeability to Na+ is _____ and the permeability to K+ is _____ | Na+ is low, K+ is high (more K+ leaves the cell) |
| Ligand Gated Channels are found in | Dendrite and soma |
| Ligand Gated Channels are responsible for | Graded Potentials |
| Voltage Gated Channels are found in | Axons |
| Voltage Gated Channels are responsible for | Action Potentials |
| Voltage Gated Na+ Channels have activation and inactivation gates that function ________ | Independently |
| 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 |
| Repolarization | Restores normal RMP following depolarization; Positive ions (K+) leave cell (Na+/K+ Pump) |
| Does depolarization always make an action potential? | No |
| 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 |
| Hyperpolarization _________ the chance of generating an action potential | Decreases (will take much more Na+ to get to threshold and action potential) |
| Threshold | The membrane potential at which voltage gated Na+ channels open up to initiate an action potential (-60 mV) |
| Action Potential | Self-regenerating wave of electrochemical activity due to opening of voltage gated Na+ channels on the axon |
| Threshold is ____ mV | -60 mV |
| Action Potential occurs at ____ mV | +30 mV |
| How do neurons communicate at the synapse? | Synaptic activity (neurotransmitter release) |
| What causes neurotransmitter release on the postsynaptic neuron? | Action potentials |
| What causes action potentials? | Graded potentials |
| Local change in membrane potential occurs where? | Dendrites, Soma, Axon Hillock |
| Local change in membrane potential causes: | depolarization or hyperpolarization depending upon what channel is opened |
| Axon Hillock has _______ channels | Ligand Gated Channels |
| Axon has ______ channels | Voltage Gated Channels |
| An action potential can be: | Depolarizing only |
| Graded potentials can be: | Hyperpolarizing or Depolarizing |
| 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 |
| Properties of Graded Potentials | Decays as it moves, Short-distance signal; Non-regenerating (smaller changes in mV than action potentials) |
| Magnitude of depolarization depends on | The amount of stimulus (larger, longer stimulus = larger, longer graded potential) |
| At threshold, the cell membrane is _____ permeable to Na+ | More |
| A resting membrane is _____ permeable to K+ | More |
| Propagation is a _______ feedback mechanism | Positive (more Na+ channels open as the threshold propagates) |
| Action potentials only occur in ______ membranes | Excitable (neurons and muscle fibers) |
| Action potentials regenerate at _______ regions of axons | unmyelinated regions (nodes) |
| Properties of Action Potentials | Always depolarizing, all or none response, can’t be summer, magnitude of stimulus is negligible, does not decay |
| 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] |
| 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 |
| When neuron membrane potential = -70 mV: | Voltage gated K+ channels slowly shut; membrane potential reaches -90 mV |
| A neuron can generate _____ AP/second | 1,000 |
| Absolute Refractory Period | Neuron can absolutely NOT generate another action potential; Voltage gated Na+ channels need to fully recover |
| Relative Refractory Period | Neuron can generate another action potential but a stronger stimulus is needed to reach threshold |
| Propagation | An action potential at one site causes depolarization at ‘downstream’ adjacent sites, bringing those adjacent sites to threshold |
| Why does the action potential only propagate ‘downstream’? | Because the Na+ is moving that direction and it’s too positive ‘upstream’ |
| Final Outcome of Propagation | Depolarization of axon terminal causes neurotransmitter release via opening of voltage gated Ca++ channels |
| 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 |
| 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 |
| Myelin _____ the speed of propagation | Increases |
Created by:
Cyndi1087
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