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AP Biology 2007-2008 Nervous System. AP Biology Essential Knowledge: Animals have nervous systems that detect external and internal signals, transmit.

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Presentation on theme: "AP Biology 2007-2008 Nervous System. AP Biology Essential Knowledge: Animals have nervous systems that detect external and internal signals, transmit."— Presentation transcript:

1 AP Biology 2007-2008 Nervous System

2 AP Biology Essential Knowledge: Animals have nervous systems that detect external and internal signals, transmit and integrate information and produce responses.

3 AP Biology Nervous system cells dendrites cell body axon synaptic terminal  Neuron  a nerve cell  Structure fits function  many entry points for signal  one path out  transmits signal signal direction signal direction dendrite  cell body  axon synapse myelin sheath

4 AP Biology Myelin sheath signal direction  Axon coated with Schwann cells  Insulation material (lipid)  speeds up signal  saltatory conduction  150 m/sec vs. 5 m/sec (330 mph vs. 11 mph) myelin sheath

5 AP Biology myelin axon Na + + + +++ – – action potential saltatory conduction Multiple Sclerosis  immune system (T cells) attack myelin sheath  loss of signal Multiple Sclerosis  immune system (T cells) attack myelin sheath  loss of signal

6 AP Biology Neuron Functional Differences Integrates and coordinates info from afferent, sends out response to efferent

7 AP Biology Information Processing  Describe the basic pathway of information flow through neurons that cause you to turn your head when someone calls your name (big picture).

8 AP Biology Neuron at Resting Potential  Opposite charges on opposite sides of cell membrane  membrane is polarized  negative inside; positive outside  charge gradient (-70m v )  stored energy (like a battery) +++++++++++++++ +++++++++++++++ –––––––––––––– ––––––––––––––

9 AP Biology What makes it polarized?  Cells live in a sea of charged ions  anions (negative)  more concentrated within the cell  Cl -, charged amino acids (aa - )  cations (positive)  Na + more concentrated in the extracellular fluid Na + K+K+ Cl - K+K+ K+K+ aa - K+K+ Cl - aa - K+K+ K+K+ channel leaks K + + –

10 AP Biology How does a nerve impulse travel?  Stimulus: nerve is stimulated  reaches threshold potential  open Na + channels in cell membrane  Na + ions diffuse into cell  charges reverse at that point on neuron  positive inside; negative outside  cell becomes depolarized –++++++++++++++ –++++++++++++++ +–––––––––––––– +–––––––––––––– Na + The 1st domino goes down!

11 AP Biology Gate +– + + channe l closed channe l open Depolarization  Wave: nerve impulse travels down neuron  change in charge opens next Na + gates down the line  “voltage-gated” channels  Na + continues to diffuse down neuron  “wave” moves down neuron = action potential ––++++++–++++++ ––++++++–++++++ ++––––––+–––––– ++––––––+–––––– Na + wave  The rest of the dominoes fall!

12 AP Biology Voltage-gated channels  Ion channels open & close in response to changes in charge across membrane Structure & function!

13 AP Biology Repolarization  Re-set: 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 +––+++++––+++++ +––+++++––+++++ –++–––––++––––– –++–––––++––––– Na + K+K+ wave  Set dominoes back up quickly!

14 AP Biology How does a nerve impulse travel?  wave of opening ion channels moves down neuron  flow of K + out of cell stops activation of Na + channels in wrong direction  Action Potential Propagation Action Potential Propagation ++––+++++––++++ ++––+++++––++++ ––++–––––++–––– ––++–––––++–––– Na + wave  K+K+ Ready for next time!

15 AP Biology How does the nerve re-set itself?  Sodium-Potassium pump  active transport protein in membrane  requires ATP  3 Na + pumped out  2 K + pumped in  re-sets charge across membrane ATP That’s a lot of ATP ! Feed me some sugar quick!

16 AP Biology 1. Resting potential 2. Stimulus reaches threshold potential 3. Depolarization Na + channels open; K + channels closed 4. Na + channels close; K + channels open 5. Repolarization reset charge gradient 6. Undershoot K + channels close slowly Action potential graph –70 mV –60 mV –80 mV –50 mV –40 mV –30 mV –20 mV –10 mV 0 mV 10 mV Depolarization Na + flows in 20 mV 30 mV 40 mV Repolarization K + flows out Threshold Hyperpolarization (undershoot) Resting potential Resting 1 2 3 4 5 6 Membrane potential

17 AP Biology All or nothing response  Once first one is opened, the rest open in succession  a “wave” action travels along neuron  have to re-set channels so neuron can react again How is a nerve impulse similar to playing with dominoes?

18 AP Biology Synapse Impulse has to jump the synapse!  junction between neurons  has to jump quickly from one cell to next  Synaptic Signaling Synaptic Signaling What happens at the end of the axon? How does the wave jump the gap?

19 AP Biology axon terminal synaptic vesicles muscle cell (fiber) neurotransmitter acetylcholine (ACh) receptor protein Ca ++ synapse action potential The Synapse  Action potential depolarizes membrane  Opens Ca ++ channels  Neurotransmitter vesicles fuse with membrane  Release neurotransmitter to synapse  diffusion  Neurotransmitter binds with protein receptor  ion-gated channels open  Neurotransmitter degraded or reabsorbed We switched… from an electrical signal to a chemical signal

20 AP Biology Neurotransmitters  Acetylcholine  transmit signal to skeletal muscle  Epinephrine (adrenaline) & norepinephrine  fight-or-flight response  Dopamine  affects sleep, mood, attention & learning  lack of dopamine in brain associated with Parkinson’s disease  excessive dopamine linked to schizophrenia  Serotonin  affects sleep, mood, attention & learning

21 AP Biology Weak point of nervous system  Any substance that affects neurotransmitters or mimics them affects nerve function  Ex: Gases, drugs, poisons  Acetylcholinesterase inhibitors = neurotoxins!  Ex: snake venom, insecticides, cone snail toxinscone snail toxins Snake toxin blocking acetylcholinesterase active site

22 AP Biology Vertebrate Brains  Evolutionary trends towards “Cephalization”  Central region for integrating and coordinating information.  Different regions have different functions:

23 AP Biology How are they similar? How are they different? More mass, more neurons, more connections….

24 AP Biology 2007-2008 Ponder this… Any Questions?? Action Potential Brain U Action Potential Propagation Synaptic Signaling cone snail toxins

25 AP Biology 2007-2008

26 AP Biology 2007-2008

27 AP Biology 2007-2008

28 AP Biology 2007-2008

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