Term
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Definition
| since neurons are excitable cells, they communicate with one another by using electrical potential and currents |
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Term
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Definition
| the difference in concentration of charges particles on either side of membrane of neuron |
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Term
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Definition
| involves flow of charges particles from one point to another |
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Term
| what happens when a neuron is stimulated? |
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Definition
| electrical potential can chage suddenly to produce local potentials and/or action potentials |
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Term
| why do local potentials and action potential occur? |
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Definition
| due to ion flow through channels in membrane |
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Term
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Definition
| allow electrocytes to flow across membrane, which establishes a current |
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Term
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Definition
| are always open and allow Na+1, and K+1 to move |
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Term
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Definition
| open and close in response to stimuli |
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Term
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Definition
| open in response to change in electical potential |
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Term
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Definition
| open and close in respinse to specific chemical stimulus (acetylcholine) |
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Term
| mechanically gated channels |
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Definition
| open or close in response to vibration or pressure or tissue stretching |
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Term
| why is there difference in electrial charges between ECF and ICF of a neuron? |
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Definition
| because of unequal distribution of ions on either side of plasma membrane |
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Term
| the plasma membrane is most permeable to what ion? |
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Definition
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Term
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Definition
| is higher in ICF than in ECF, so K+1 diffuse out of neuron along their concentration gradient |
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Term
| where are the large organic anion and what do they do? |
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Definition
| trapped inside neuron and tend to draw K+1 back into neuron along electrial gradient |
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Term
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Definition
| is higher in ECF than in ICF, so Na+1 tend to diffuse into neuron along their concentration and electrial gradients |
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Term
| consequences of differences in K+ and Na+ |
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Definition
| inside of neuron is negative with respect to outside and neuron is polarized |
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Term
| Rest membrane potential (RMP) |
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Definition
| potential difference of -70mv is established with inside of neuron 70mv more negative than outside of neuron |
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Term
| what happens when there is diffusion of sodium ions into the neuron and diffusion of potassium ion out of neuron? |
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Definition
| this will eventually eliminate resting membrane potential (RMP) |
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Term
| what is the role of ATP-driven membrane pump? |
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Definition
| actively transports 3 Na+1 out of neuron and 2 K+1 into neuron per molecule of ATP spent to maintain electrochemical gradient nd keep RMP at -70mv |
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Term
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Definition
| small change in RMP caused by stimulus that opens ligand-regulate sodium gate in plasma membrane of a neuron |
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Term
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Definition
| Na+1 rush into neuron causing membrane to depolarize |
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Term
| what is the pathway of a local potential? |
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Definition
| local potential typocally beings al dendrite, spread through soma, then travels from axonal trigger zone to synaptic knob |
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Term
| what kind of communication is local potentials used for? |
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Definition
| only short distance communication |
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Term
| why are local potentials graded? |
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Definition
they vary is size according to stimulus strength
-strong stimulus causes grater change in membrane potential and gates open, which allows current to flow farther |
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Term
| where do local potential become weaker? |
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Definition
as they spread away from the point of stimulation
-plasma membrane is permeable to ions, so charge is lost and current dies out |
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Term
| when would local potential be reversed? |
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Definition
| RMP gets restored if stimulation ceases prematurely |
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Term
| local potential is excitatory if.. |
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Definition
| it depolarized plasma membrane of neuron to make potential defferences less negative |
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Term
| local potential in inhibitory if... |
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Definition
| it hyperpolarizes plasma membrane of neuron to make potential differences more negative |
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Term
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Definition
| a dramatic change in membrane potential resulting from opening and closing voltage-gates ion channels during interval of about 1msec |
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Term
| excitatory stimulus applied to neuron generates what? |
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Definition
| excitatory local potential that depolarizes membrane causing RMP to be less negative |
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Term
| what happens if excitatory local potential spreads to "trigger zone"? |
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Definition
| if it remains strong enough, it opens enough voltage-regualted gates to generate action potential |
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Term
| what is the threshold voltage? (#) |
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Definition
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Term
| what happens if membrane reaches critical threshold voltage? |
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Definition
| voltage-gated sodium channels open |
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Term
| at threshold voltage, what happens with sodium ions? |
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Definition
| they rush into neuron and establish positive feedback that depolarizes membrane from -55mv to 0mv to +35mv |
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Term
| what does depolarization trigger? |
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Definition
slow sodium inactivation gates to close, which prevents and more Na+1 from entering neuron
-membrane is now positive and negative outside |
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Term
| what happens at peak depolarization? |
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Definition
| slow volatage-gated potassium channels open and K+ rushes out of neuron to repolarize membrane from +30mv to 0mv to -70mv |
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Term
| what do voltage-regulated potassium channels do the restore RMP? |
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Definition
| remain oen longer that voltage-gated sodium channels, so loss of K+1 may cause after-hyperpoalization, making membrane potential more negative that RMP until voltage-gates potassium channels close to restore RMP |
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Term
| 3 characteristics of an action potential |
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Definition
-they follow all-or-nothing principle because any stimulus that depolarizes membrane to threshold will generate action potential
-they do not become weaker as the spread away from point of stimulation
-they are irreversible |
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Term
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Definition
| brief period of time during which meuron may not be able to generate another action potential |
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Term
| how long does absolute refractory period last? |
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Definition
| last from threshold until repolarization is complete |
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Term
| neuron restimulation during absolute refractory period? |
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Definition
| neuron can't be restimulated by stimulus of any strength because voltage-gated sodium channels open and then are inactivated |
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Term
| how long does relative refractatory period last? |
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Definition
| last until hyperpolarization ends |
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Term
| neuron restimulation in relative refractory period? |
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Definition
| neuron can be restimulated if stimulus is larger than threshold |
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Term
| how can a neuron communicate with another neuron? |
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Definition
| for communication a nerve signal mush travel length of the axon |
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Term
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Definition
| traveling wave of excitation produced by self-propagating chian of action potentials moving in only one direction (dominoes) |
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Term
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Definition
| produced in unmyelinated fibers where there is a step-by-step depolaritation of each adjacent area of plasma membrane |
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Term
| propagation in unmyelinated fibers? |
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Definition
| is slow but does not lose power because last action potential generated at synaptic knob has same voltage as first action potential generated at trigger zone |
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Term
| nerve signals in myelinated fibers |
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Definition
| seem to 'leap' along neuron from one node of ranvier to next node of ranvier by saltatory conduction |
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Term
| propagation in myelinated fibers |
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Definition
| much faster, but does lose power (is decremental) |
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Term
| why is propagtion in myelinated fibers decremantal? |
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Definition
| signal gets weaker, but reaches next node of ranvier just in time to open voltage-gated sodium channels to generat new action potential |
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Term
| how is propagation speed determined? |
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Definition
| is determined by presence or absence of myelin, diameter of fiber, temperater and not determined by strength of stimuli |
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Term
| propagation speed and large diameter fibers.. |
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Definition
conduct signals faster than small ones because:
-they tend to be myelinated and small fibers tend to be unmyelinated
-there is more surface area |
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Term
| propagation speed and temperature |
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Definition
| nerve fibers conduct signals faster in warm temperatures |
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