Cells Cellular Physiology part 1 Flashcards Preview

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Flashcards in Cells Cellular Physiology part 1 Deck (80):
1

two types of cells in the nervous systems

Neurons and Neuroglia cells (glia)

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Neurons

generate and transmit information for the control of body function

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Neuroglia Cells

(glia)
surround and support neurons including providing the ability for neurons to conduct information at high speeds

4

Neurons (shapes and sizes)

~comes in many configurations & sizes, but most have the same basic structure
~central cell body
~multiple short highly branching dendrites
~single long terminally branching axon

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Neuron (cell body)

(SOMA)
~trophic center of the neuron
~contain the nucleus with chromatin material
~contains cell organelles(rough endoplasmic reticulum with attached ribosomes, Golgi apparatus, mitochondria)

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Neurons (dendrites)

~major source of input connections into the neurons
~extensive, highly branched
~dendritic spines
~slowly conducting

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Neurons (dendritic spines)

~increases surface area
~increases connections
~> 100,000 per neuron
~associated with learning and memory

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Neurons (axons)

~single output from the neuron
~rapidly conducting
~may be myelinated or unmyelinated
~highly branched near termination- axon collaterals
~each has an axon or synaptic terminal (synaptic knob or bouton)

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Neuron (axoplasmic transport)

~can transport intracellular material along the lengthen of the axon utilizing microtubules (or neurotubules) which extend along the length of axons
~anterograde transport moves vesicles and proteins and lipids to axon terminal

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Neuron (retrograde transport)

moves membrane fragments and neurotrophic agents back to cell soma

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Neuron (cell membrane)

~Lipid bilayer with imbedded protein
~proteins function in variety of ways similar to other cells but have five important functions (ionic pores, transmitter receptors, transmitter reuptakes pumps, ionic pumps, & specialized communication elements

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Neuroglia

comes form the word "glue:, but serves many more functions than just holding the nervous system together

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Types of Glial cells (4)

~Astrocytes
~Oligodendroglia
~Microglia
~Ependymal cells

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Astrocyte (what is it)

large cell with starburst ("astro") of processes from central cell body

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Astrocyte (function)

~structural support (physical framework supporting neurons- fibroblasts of the brain)
~metabolic support (providing a storage area in the brain of free glucose and other micronutrients to maintain a consistent supply for neurons)
~enhanced blood brain barrier (astrocytic end-feet encircling endothelial cells of blood capillaries forming part of the blood-brain barrier by assisting the tight junction between capillary endothelial cells)
~regulate transmitter level thru uptakes and release (astrocytes take up a variety of transmitters regulating the extracellular concentration of these transmitters)

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Astrocytes (more functions)

~regulate extracellular ionic concentrations (rapidly clear excess accumulation of K+ in the extracellular space and can regulate neuronal excitability)
~vasomodulation (astroglia may serve as intermediaries in neuronal regulation of cerebral blood flow)
~repair of damaged neural tissue (but in this role may block reconnection of severed axons through glial o astrocytic scarring)
~enhance or inhibit the activity of other glial cells (release of substance that stimulate or inhibit the activities of both oligodendroglia and microglia)

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Oligodendroglia

~large cells with central cells body and multiple processes
~provides myelination of CNS axons (wraps processes around axons)

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Microglia

~small, mobile immune cells of the CNS
~phagocytic action to attack infectious organisms and remove damaged tissue
~seen in large numbers around dying cells as in neurodegenerative diseases (like Alzheimer's disease)

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Ependymal cells

~epithelial like cells that line the ventricular surfaces
~play important roles in regulating amount and ionic concentration of extracellular fluids
~regulate exchanges of substances between CSF and extracellular space

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There are two types of neuroglia in the PNS

Schwann cells and Satellite cells

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Schwann cells

~abundant in PNS
~form myelin sheaths of PNS axons
~whole cell wraps around the axon
~similar to the oligodendrocytes of the CNS

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Satellite cells

~surround cell bodies located in PNS ganglia
~support the function of ganglion cells
~role in metabolism of ganglion cells
~functions somewhat like an astrocyte

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Cell membrane

~lipid bilayer with imbedded proteins
~semipermeable
~permeable to gasses and lipid soluble substances
~blocks water and water soluble substances (ions)

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Ionic movement in the cell membrane

Ions move through pores or "ionic channels"
~move by diffusion down concentrations gradient
~repelled or attached by the charge gradient across the membrane
~ions reach electo-chemical equilibrium
~rate of movement governed by permeability of the membrane to that ion
~permeability governed by the number and how open channels are

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Ions move by ___ ___ the concentration gradient

diffusion
down

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The rate of movement of ions is governed by __________ to the ion

permeability

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Permeability is governed by ____ and ______

number and how open channels are

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A higher concentration of K+ is (inside or outside) the cell

inside

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A higher concentration of Na+ is (inside or outside) the cell

outside

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When the channel opens (Na+ or K+) enters and (Na+ or K+) leaves the cell

Na+ enters and K+ leaves because there is a higher concentration of Na+ outside and needs to migrate inside; K+ has a higher concentration inside and needs to migrate outside

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The charge is more ____ on the inside that outside the cell

more negative

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Why is the charge more ___ on the inside that outside the cell?

(negative)
~more K+ with its positive charge leaving (higher K+ permeability) than Na+ entering (low Na+ permeability)
~negatively charged proteins on inside
~Cl- current also across cell membrane down its concentration gradient from outside to inside carrying its negative charge

33

The potential difference across the neural membrane is called the

"resting membrane potential"

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The resting membrane potential (definition and how)

~produced by the leakage of ions
~maintained by an active pump that restores the intracellular-extracellular balance of Na+ and K+; this is the active Na+ K+ ATPase pump which transports ions up their concentration gradient

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Na+ and K+ ATPase Pump

~breaks down ATP into ADP and inorganic phosphate (ATP enzymes) to generate the energy to pump the ions (Na+ and K+) up their concentration gradients

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Resting membrane potential (details)

~varies from neuron to neuron but stable in each
~dependent upon the relative movement of ions ~use -70 mv as standard

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for resting membrane potential, greater movement of K+ (more or less) negative

more negative

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for resting membrane potential, greater movement of Na+ (more or less) negative

less negative

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what is the standard for resting membrane potential?

70 mv

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Depolarization

lessening of charge difference across the membrane

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Hyperpolarization

increase of the charge difference across the membrane

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Two main types of channels in the membrane

Leak channels and gated channels

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leak channels

constantly open all the time and ions just leak across down concentration gradients

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gated channels

open by specific stimulus

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types of gated channels

modality-gated, ligand-gated, voltage-gated

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modality-gated channels

~open to environmental stimulus (modality) applied to the neuron or a receptor cell
~can include mechanical, temperature, sound, or electromagnetic radiation
~the basis of sensory receptors and "receptor potential"

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Ligand-gated channels

~open to binding of chemical (ligand) to its receptor which is linked to the channel
~the basis of synaptic potentials and transmission of impulses from one neuron to another

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Voltage-gated channels

~opens when there is a change in polarity (charge) across the membrane
~generally occurs when the membrane polarity is lessened- membrane depolarized
~mechanism involves a "voltage sensor element to the channel
~activation of this voltage sensor element opens the channel

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Modality-gated local potentials

~are produced by the application of the stimulus to the cell membrane
~in most cases, activation of the modality gate channel increases Na+ permeability across membrane- so mere Na+ with + charge enters the neuron and the axonal membrane depolarizes
~occurs at the location of sensory receptors
~ these potentials are nor propagated along the axonal membrane so they occurs only in the local area of h membrane where the sensory receptor is and for a short period of time and space away from the application of the stimulus

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Voltage-gated channel produced action potentials

~axonal membranes (and some dendritic membranes) have voltage-gated ionic channels
~can produce regenerative potentials (called action potentials)

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Voltage-gated channel produced action potentials (details)

~channel must be exposed to a depolarization that is sufficient to open the channel
~the depolarization changes the positions of specific proteins of the channel (voltage sensors) which allow the proteins which form the channel to move and ion the channel wide open to allow ions to flood into the cell

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Massive change in membrane polarity

~inrush of Na+ produces a massive change in membrane polarity
~there is a massive depolarization (membrane area becomes less negative) which followed by a local reversal of polarity with the inside becoming more positive than outside
~ the membrane potential can go from -70 to greater than 0 mv

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Initial depolarization requires that

the depolarization is sufficient to open the channel

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Initial Depolarization

~must reach threshold to depolarize
~if the depolarization is below the threshold, the voltage-gated channels do not open and no massive depolarization occurs
~if reach threshold, get a full response
~there is a all or none response to get the action potential

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the amount of depolarization needed to open the channel

the threshold

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When threshold is met:

~voltage-gated Na+ channels fully open with massive inrush of Na+
~voltage gated K+ open but has a slower movement of K+

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Voltage-gated Na+ response (why)

~high concentration gradient for Na+
~initially the inside of the cell is negatively charges and the Na+ attached electrically inward

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Voltage-gated K+ response (why)

~less concentration gradient
~initially with the outside more positive, there is an opposing charge gradient for the movement

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K+ Voltage-gated channels

*after the massive opening of the Na+ channels, these quickly close completely
~efflux of K+ increase because the K+ channels remain open with the inside of the membrane now more positive than the outside; there is an increase in driving voltage gradient for K+
~combination of open K+ channels and increase efflux of K+ with the closed Na+ channels produce the first return to resting to resting membrane potential (after slightly hyperpolarization)

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The efflux of K+ is due to

high K+ conductance (permeability) and charge gradient
~(and the Na+ channels closing, which causes a low Na+ permeability)

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Return to resting membrane potential:

~Na+ channels are back to there very low permeability (very low Na+ conductance)
~K+ conductance (permeability) returns to its resting levels (much higher than Na+ permeability)
~membrane potential returns to resting levels

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Refractory periods

~periods during the action potential where there is less excitability

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two types of refractory periods

absolute and relative

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Absolute refractory period

when there is an inability to produce a 2nd action potential
~occurs during an action potential spike
~Na+ channels either all the way open or closed tight
~if they are closed, the membrane cannot generate another action potential

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Relative refractory period

when there is the need for more stimulation to reach threshold and produce an action potential
~occurs after a spike hyperpolarization
~K+ continues to leave at higher rates and the membrane falls below resting membrane potential
~the membrane potential is farther from threshold so more depolarization is need to reach threshold
~it is possible to create another action potential, it is just more difficult because more stimulation is needed

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the great thing about action potential compared to local potential is

action potential is regenerative and can be conducted along the axon

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During action potential, there is a build up of _________ at the point of action potential (and details)

intracellular Na+

~this Na+ will diffuse away from this site though the cytoplasm of the axon with its positive charge
~this migration of Na+ with its positive charge will produce depolarization to threshold at that new point along the membrane a dew microns away from the initial site of stimulation
~one this new area of membrane reaches threshold, an action potential will generate at that new location along the membrane

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The newly generated action potential will then excite the __________ producing an action potential at the next point along the membrane

(next area of membrane)

~this will repeat itself as the action potential move away from the point of initial stimulation

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Action potential will move (up/down) the axon and not reverse direction because....

(down)
~because the area of membrane behind the action potential is refractory
~so when the axon behind the action potential is exposed to elevated intracellular Na+, it cannot reach threshold because it is refractory

70

Conduction velocity can be (increased/decreased) by increasing the diameter of the axon (details)

(increased)
~in peripheral nerves, the diameters range from .2-20 um
~conduction velocities range from .5-120 meters per second
~although some of this difference is contributed by the increase in axon diameter, much of increase in conduction velocity is due to saltatory conduction

71

Saltatory conduction

results from the fact that many axons are myelinated
*myelin blocks movement of ions across the axonal membrane

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Saltatory conduction (how to get around it)

~since the myelin block the movement of ions across the axonal membrane, Na+ must diffuse farther along the axon to gap in the myelin coat to reach the voltage-gated pores that can allow ionic movement across the membrane

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The gaps in myelin is called _______ (details)

(nodes of Ranvier)
~formed by gaps between adjacent Schwann cells in PNS
~formed by aps between adjacent processes of oligodendrocytes in CNS

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Saltatory (where does the name come from and why is it misleading)

~salutatory comes from the Latin meaning" to jump"- as the action potential appears to jump from node to node
~However, this is quite misleading due to the fact that it is produced by the continuous diffusion of Na+ ions along axon to the next node (so not really a jump at all)

75

Size for myelination versus unmyelination

~1 um diameter unmyelinated "c" fibers in peripheral nerve conduct at 1 m/s, which is a similar size to myelinated "A-delta" axons that conduct 3 meters per second
~combined increased diameter and myelination allow "a-delta" axons to conduct at 120 meters per second

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In PNS, there are ______ types of nerves (myelinated, unmyelinated, poorly myelinated, etc)

Large number of myelinated and poorly or non-myelianted axons

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In CNS, there are ______ types of nerves (myelinated, unmyelinated, poorly myelinated, etc)

few examples of unmyelinated axons or tracts

78

Demylinated diseases

~Guillain-Barre Syndrome
~Multiple sclerosis

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Guillain-Barre Syndrome

an autoimmune disease of the PNS

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Multiple sclerosis

an autoimmune disease of the CNS