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Neuroglia & AP

Exam 5 - Lecture 2

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