Name ____________________________________ Date ____________ Period _____
NEURONS AND THE NERVOUS SYSTEM
Raven Ch. 45
Big Idea 2: BIOLOGICAL SYSTEMS UTILIZE FREE ENERGY AND MOLECULAR BUILDING
BLOCKS TO GROW, TO REPRODUCE AND TO MAINTAIN HOMEOSTASIS.
Essential Knowledge:
 Cell membranes are selectively permeable due to their structure.
 Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.
 Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.


All biological systems from cells and organisms to populations, communities and ecosystems are
affected by complex biotic and abiotic interactions involving exchange of matter and free energy.
Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different
environments.
Why do animals need a nervous system?
_______________________________________
What characteristics do animals need in a nervous system? _______________________________________
Neuron= __________________________
Structure fits function:
__________________________
__________________________
__________________________
Transmission of a nerve signal:
 Think dominoes!
 __________________________
 knock down line of dominoes by tipping 1st one
 __________________________
 dominoes pass a wave down the line
 __________________________
 before you can do it again, have to set up dominoes again
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
Neuron has similar system
 _________________________ in membrane are set up
 once first one is opened, the rest open in succession
 _________________________________
 a “_______________” action travels along neuron
 have to ________________ channels so neuron can react again
Cells: surrounded by charged ions
 Cells live in a sea of charged ions
 _________________________
 more concentrated within the cell
 Cl-, charged amino acids (aa-)
 _________________________
 more concentrated outside in the extracellular fluid
 Mostly Na+ (some K+ leaks out)
Cells have voltage!
 Opposite charges on opposite sides of cell membrane
 membrane is ________________________________
 negative inside; positive outside
 This is a ________________________________
 stored energy (like a battery)
Unstimulated neuron = resting potential=_________________
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How does a nerve impulse travel?

________________: nerve is stimulated (sensory, chemical, etc)
 If cell reaches a ________________:
 open Na+ channels in cell membrane
 Na+ ions diffuse into cell (outside becomes more negative)
 ________________: at that point on neuron
 positive inside; negative outside
 cell becomes depolarized

________________: nerve impulse travels down neuron
 change in charge opens next Na+ gates down the line
 “voltage-gated” channels
 Na+ ions continue to diffuse into cell
 “wave” moves down neuron = ___________________

_______________: 2nd wave travels down neuron
 K+ channels open
 K+ channels open up more slowly than Na+ channels
 K+ ions diffuse out of cell
 charges reverse back at that point
 negative inside; positive outside

Combined waves travel down neuron
 wave of opening Na+ ion channels moves down neuron
 signal moves in one direction     
 flow of K+ out of cell stops activation of Na+ channels in wrong direction

Action potential propagates
 wave = nerve impulse, or action potential
 brain  finger tips in milliseconds!
Ion channels: Na+: _____________________________
K+: _____________________________
After firing a neuron has to re-set itself: Na+: _____________________________
K+: _____________________________

Both need to move ____________ concentration gradients… need a ______________!!
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How does the nerve re-set itself?
 ________________________________
 active transport protein in membrane
 requires _________
 3 Na+ pumped out
 2 K+ pumped in
 re-sets charge across membrane
1. ____________________________________
2. ____________________________________
3. ____________________________________
4. ____________________________________
5. ____________________________________
6. ____________________________________
Myelin sheath
 Most axons coated with Schwann cells
 insulates axon
 speeds signal
 signal hops from node to node
 saltatory conduction
 150 m/sec vs. 5 m/sec
(330 mph vs. 11 mph)
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What happens at the end of the axon?
Impulse has to jump the ___________________________!
 junction between neurons
 has to jump quickly from one cell to next
Chemical synapse
 Events at synapse
 action potential depolarizes membrane
 opens Ca++ channels
 _____________________ vesicles fuse with membrane
 release neurotransmitter to synapse  diffusion
 neurotransmitter binds with protein receptor
 ion-gated channels open
 neurotransmitter degraded or reabsorbed
Neurotransmitters
 ________________________
 transmit signal to skeletal muscle
 ____________________________________
 fight-or-flight response
 ________________________
 widespread in brain
 affects sleep, mood, attention & learning
 lack of dopamine in brain associated with Parkinson’s disease
 excessive dopamine linked to schizophrenia
 ________________________
 widespread in brain
 affects sleep, mood, attention & learning
Weak point of nervous system
 any substance that affects neurotransmitters or mimics them affects nerve function
 gases: nitrous oxide, carbon monoxide
 mood altering drugs:
 stimulants
 amphetamines, caffeine, nicotine
 depressants
 quaaludes, barbiturates
 hallucinogenic drugs: LSD, peyote
 SSRIs: Prozac, Zoloft, Paxil
 poisons
Acetylcholinesterase: _____________________________________________________________________
Acetylcholinesterase inhibitors: ____________________________________________________________
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