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45 Cards in this Set
- Front
- Back
Resting Membrane Potential
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A difference in electrical charge from the inside of the cell to the outside
-70mv Maintained by different concentration in ions: More K+ inside cell than outside More Na+ outside cell than inside Inside cell membrane is negative; outside of cell membrane is positive Cell uses energy to maintain the gradient |
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Ion channels
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-Leakage channels
-Voltage-gated channels -Chemically (ligand) gated channels -Mechanically gated channels Are Integral or transmembrane Channels are specific Sodium Ion channels only allow sodium through |
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Leakage channels
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Randomly alternate between open and closed positions. Typically more K+ leakage channels
Found in nearly all cells, including the dendrites, cell bodies and axons of all types of neurons |
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Voltage-gated channels
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Opens in response to a change in membrane potential (voltage)
Voltage-Gated channels participate in the generation and conduction of action potentials found in axons of all types of neurons |
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Chemically (ligand) - gated channels
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Opens or closes in response to a specific chemical stimulus like neurotransmitters
Dendrites of some sensory neurons such as pain receptors and dendrites and cell bodies of interneurons and motor neurons |
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Mechanically gated channels
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Opens or closes in response to mechanical stimulation in the form of vibration such as sound waves, touch, pressure, or tissue stretching.
Dendrites of some sensory neurons such as touch receptors, pressure receptors and some pain receptors |
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Graded (local) Potential
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Short distance transmission
Occurs in dendrites and cell body May be depolarizing or hyperpolarizing Signals decrease in strength with distance No Refractory period Involves summation fo impulses at axon hilock Involves voltage-gated Na+ channels |
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Action Potential
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Transfers impulses over longer distances
Occurs along axons Always depolarizes then Repolarizes All or Nothing Principle Signal does not lose strength over distance Involves voltage-gated Na+ channels and voltage-gated K+ channels |
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Dendrites
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Gather input and relay signals through cell body to axon hillock in graded potentials
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Cell body
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Summates input (adds up) input signals converge at axon hillock
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Axon hillock
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Trigger zone where cell reaches
-55mv in order to reach threshold to send action potential |
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Graded potential
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a small deviation from the membrane potential that makes the membrane either more or less polarized
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Depolarizing
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Making inside of cell more positive
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Hyperpolarizing
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making inside of cell more negative
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In action potentials
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When stimulated to threshold, the axon depolarizes, beginning the action potential
The action potential (nerve impulse) propagates along the axon The action potential is generated; it is ALWAYS exactly the same strength and duration Involves voltage-gated Na+ and K+ channels |
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Impulse conduction Process
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Begins with stimuli coming through dendrites
Types of ion channels involved are Mechanical-gated channels or chemical (ligand)-gated channels Summation occurs: -Depolarizing stimuli make inside of cell more positive -Hyperpolarizing stimuli make inside of cell more negative |
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Summation
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Adding up the exitatory and inhibitory impulses at the trigger zone (axon hillock) determines if an action potential is generated
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Spatial summation
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Impulses come from many synaptic end bulbs
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Temporal summation
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Impulses come repeatedly from the same synaptic end bulb
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Results of summation
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Action potential is generated- there are enough exitatory impulses to reach threshold -55mv
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Depolarization
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-55 to +30 is depalarization
All or nothing principle Requires stimulus strong enough to reach threshold of -55mv Action potential is always the same strength Voltage-gated Na+ channels upen Membrane potential becomes 30mv Inactivation gates close - no more Na+ enter |
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Repolarization
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Cell returns to -70mv
Voltage gated K+ channels open and K+ flows OUT of cell Na+ is being pumped out via pumps Anions remain in cell Membrane potential of -70mv is established once again May hyperpolarize to -90mv |
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Refractory Period
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Absolute- Cell CANNOT generate another action potential no matter how strong the stimulus is
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Relative Period
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While the K+ ions are moving back into cell; requires a larger than normal stimulus to generate an action potential
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Moving along Axon
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Propagation or Conduction
One way impulse transmittion -refractory period prevents impulse from moving backwards |
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Continuous conduction
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Slower, in unmyelinated axons
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Saltatory
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Faster, in myelinated axons, requires less energy: ion moves through extracellular fluid
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Factors affecting speed of impulse
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Myelination
Axon Diameter: Larger diameter has bigger surface area and impulse moves faster Temp affects speed: Warmer is faster |
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Intensity of Stimulus
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Action potential is All-or-Nothing
Difference in intensity of stimulus are determined by -Frequency of impulse -Number of sensory neurons stimulated |
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Electrical Synapses
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Electrical transfer of impulse occurs at gap junctions
Found in visceral smooth muscle, cardiac muscle, CNS, and embryo Advantages: Faster Synchronization of cell responses |
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Chemical Synapses
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Neurons and effector do not touch
Requires carrier molecules to cross the space, called a neurotrasmitter Chemical exchanges delays impulse by about 0.5 msec |
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Excitatory postsynaptic Potential
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Bring neuron closer to threshold; cell becomes more positive inside
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Inhibitory Postsynaptic Potential
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Takes cell farther away from threshold, same as hyperpolarizing cell becomes more negative inside
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Signal Transmission at Chemical Synapse
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More than 50 substances act as neurotransmitters
Cells usually can release more than one type Transmitters may be exitatory or inhibitory Classified by chemical structure |
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Small Molecule Neurotransmitters
Acetylcholine |
1st one identified
Activates all Motor neurons Deactivated by enzyme Acetylcholinesterase |
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Small Molecule Neurotransmitters
Glutamate and Aspartate |
Acive in CNS
Amino Acids Glutamate main Excitatory Glutamate is responsible for Ischemic Strokes Inactivated by reuptake |
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Small Molecule Neurotransmitters
GABA and Glycine |
Amino acids
GABA is only in CNS INHIBITORY Valium enhances GABA GABA-main inhibitory |
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Biogenic Amines Neurotransmitters
Catecholamines |
Hormones responsible for Fight or Flight:
Epinephrine, Norepinephrine and Dopamine Serotonin Can either be Excitatory or Inhibitory Depending on the receptors |
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Dopamine
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Emotional Response, Addictive behavior, Pleasure pathway,
Inactivated by reuptake and enzymatic action (MAO-MonAmine Oxidase) |
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Seratonin
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Sensory perception, mood, appetite, sleep induction
Inactivated by reuptake Prozac blocks reuptake Blocked by LSD Enhanced by Ecstasy |
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Neuropeptides
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Consists of 3-40 amino acids
Found in both CNS and PNS Excitatory and Inhibitory |
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Opiod Peptides
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BLOCK SUBSTANCE P
Enkephalins Endorphins Dynorphins |
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Substance P
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Enhances pain signal transmission
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Influencing Neurotransmitters
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Synthesis may be stimulated or Inhibited
Released is enhanced or blocked Receptors are activated or blocked Removal can be stimulated or Inhibited |
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Removal or Neurotransmitter
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Neurotransmitter MUST be removed after transmission to allow for cell recovery
Diffusion Enzyme degradation Reuptake by cells or uptake by neuroglia |