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CNS consists of:
brain, spinal cord
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PNS consists of:
- Afferent signals (input)
- Efferent signals (output)
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From PNS to CNS
Afferent neurons
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From CNS to PNS
Efferent neurons
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Neurons w/in CNS (most cells)
Interneurons
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2 types of nerve cells
- Neurons (Excitable cells) ~10%
- Glial cells (Support cells) ~90%
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Part of neuron which contains nucleus & most organelles
Cell body (soma)
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Part of neuron which receives incoming info
Dendrite
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Part of neuron which transmits elec impulses called action potentials
Axon
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Part of neuron where axon originates and action potentials are initiated
Axon hillock
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Part of neuron that releases neurotransmitter
Axon terminal
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Where 2 neurons or a neuron and an effector organ meet and communicate
Synapse
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3 types neuron ion channels
- Leak channels
- Ligand-gated channels
- Voltage-gated channels
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Type of neuron ion channel which is always open, located throughout the neuron, responsible for resting membrane potential
Leak channels
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Type neuron ion channel which open & close in response to ligand binding & which are often located on dendrites
Ligand-gated channels
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Type of neuron ion channel which open & close in response to chg in mem potential & which are mostly located on axons
Voltage-gated channels
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Difference in charge inside the cell relative to outside
Membrane potential
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The voltage across the mem of a cell that is not transmitting a signal
Resting membrane potential
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2 factors which determine resting mem pot
- Ion concentration gradients
- Membrane permeability to these ions (ion channels)
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RMP is caused by ___ ___ in neuron membranes & is approx ____ mV
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An ion is at _______ when the electrochemical force is 0
equilibrium
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Na+, K+ concentrations
Na+ high conc outside, K+ high conc inside
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Somatic vs autonomic PNS
- somatic: can control via muscles
- autonomic: cannot control (consists of para & symp nervous systems)
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What is the usually the charge of RMP and why? Is the cell at equilibrium at this time?
- negative b/c more neg chrgs inside cell than out;
- no
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What two factors determine resting membrane potential?
- Ion concentration gradients
- Membrane permeability to these ions (ion channels)
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At RMP:
chemical force drives K+ ___ and Na+ ____
electrical force drives K+ ___ and Na+ ____
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There are ___ leak channels for K+ and ___ leak channels for Ca+ in neurons
(so neurons are more permeable to __)
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Membrane potential where chemical force and elec force are equal (electrochemical force=0)
Equilibrium Potential (E)
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Net electrochemical force of K+ is ___ and Na+ is ____
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At rest:
small K+ leak (__ force, ___ permeability)
small Na+ leak (___ force, ___ permeability)
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To maintain rmp of -70 mV, 3__ go out and 2__ go in so have a net of __ out
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When membrane potential veers from RMP it's due to ___
ions passing thru gated channels
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What is diff b/w the way voltage-gated channels and ligand-gated channels open/close?
- VG: open/close based on membrane potential
- LG: open/close b/c ligand binds or doesn't bind to channel
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Shift from RMP to a more positive Vm
Depolarization
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Shift from RMP to a more negative Vm
Hyperpolarization
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Return to RMP
Repolarization
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Diff b/w graded potentials and action potentials
- Graded: small, travel short distances
- Action: large, travel long distances
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Something that opens a gated channel (can be ligand or voltage gated) and causes a small chg in Vm, and which has variations in magnitude
Graded potential stimulus
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How are graded potentials spread?
By conduction (magnitude decays as potential spreads)
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Diff b/w inhibitory vs excitatory graded potentials
- Prevent action potential (hyperpolarize)
- Cause action potential (depolarize)
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What causes an action potential?
If graded potential sums to reach threshold
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Large depolarization caused by opening of voltage-gated sodium channels which is a mechanism for cells to communicate
Action potential
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Type of summation which consists of the same stimulus repeated over & over close together in time, causing a sum & response
Temporal summation
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Type of summation which consists of diff stimuli and happen at the same time, causing a sum & response
Spatial summation (like knocking on all walls at once)
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What type of cells generate action potentials?
Excitable cells only
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Why does Na+ rush into cell so much faster than K+ after threshold is reached?
Force is much higher on Na+
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What happens to Na+ and K+ channels after reaching threshold?
- Sodium channels open rapidly then slowly close
- Potassium channels slowly open
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Type of threshold which doesn't cause action potential
Subthreshold depolarization
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Type of threshold which causes action potential & is above threshold
Suprathreshold stimulus
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Concept that action potential from threshold & suprathreshold stimulus are same magnitude & therefore generate same response
All-or-None Principle
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Explain how voltage-gated Na+ channels are opened
Activation gate at top of channel is opened by a more positive mem potential (above threshold)
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Explain how voltage-gated Na+ channels are closed
Inactivation gate at bottom of channel is already open at start of depolarization then closes during depolarization; remain closed until return to resting state (voltage and time dependent)
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Describe voltage-gated K+ channels
Only one gate which is open or closed & which allows K+ ions to leave; opened slowly by depolarization
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Period of time following an action potential of decreased excitability & during which time an action potential cannot be produced
Refractory period
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Diff b/w absolute & relative refractory period
- Absolute: no stimulus can generate second action potential no matter how strong
- Relative: occurs toward end of repolarization and which can allow a second action potential if stimulus is strong enough (as time goes on, a weaker stimulus can cause action potential)
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A means by which the central nervous system analyzes the content of a receptor; changes in stimulus intensity cause a change in the frequency of the impulses
Frequency coding
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Site of axon where depolarization is taking place & when it is more pos inside cell, and neg outside cell, & which moves along to next site via conduction
Region of depolarization (at the Nodes of Ranvier)
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Myelin nerve cells wrap themselves around ____
axons
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Type of myelin-forming cell which is part of CNS and the cells of which form several myelin sheaths & myelinates sections of several axons
Oligodendrocytes
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Type of myelin-forming cells which is part of PNS and the cells of which forms one myelin sheath and myelinates one section of an axon
Schwann cell
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Purpose of myelinated fibers when signals are conducted down an axon
Keeps that part of axon "neutral" so that action potential "jumps" from one Node of Ranvier to next, w/out itself being affected. Allows for speed of signal
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What 2 factors increase the speed of conduction velocity?
If myelin is present & the diameter of the myelin fiber
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2 types of glial cells which are support cells of nervous system and form myelin
Oligodendrocytes, Schwann cells
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