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Activating Strategy
• Label the following on the action potential graph:
– Hyperpolarization, Maximum Action Potential, Repolarization, Depolarization, Resting Potential, Threshold
AP Lesson #85
EQ: How are neurons able to
communicate with each other?
How does the nervous system allow a
baseball player to catch a ball?
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How is the nervous system organized?• Central nervous system (CNS)
– where integration takes place
– brain and a nerve cord
• Peripheral nervous system (PNS)
– which brings information into and out of the CNS
– Somatic (skeletal muscles) & Autonomic (involuntary muscles)
How do nervous systems process information?
•• Sensory NeuronsSensory Neurons
– Detect changes in internal and external stimuli
– Information is sent to processing center
•• InterneuronsInterneurons
– Analyze and interpret sensory input
•• Motor NeuronsMotor Neurons
– Transmit response signals to muscle cells
– Muscles respond
Sensory NeuronSensory Neuron
Motor NeuronMotor Neuron
InterneuronInterneuron
How are reflexes different from reactions?
• Reflex arc
– Rapid involuntary response to a stimulus
– Brain is not required to integrate the stimulus
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What allows neurons to send signals so quickly?
signaldirection
• Myelin sheath
• Axon coated with Schwann cells
– insulates axon
– speeds signal
• saltatory conduction
• signal hops from node to node
– 150 m/sec vs. 5 m/sec(330 mph vs. 11 mph)
myelin sheath
myelin
axon
Na+
Na+
++ + + +
––
action potential
saltatoryconduction
Multiple Sclerosis� immune system (T cells)
attack myelin sheath � loss of signal
Multiple Sclerosis� immune system (T cells)
attack myelin sheath � loss of signal
Synapse
• Impulse has to jump the synapse!
What happens to the signal once it reaches
the end of the axon?
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axon terminal
synaptic vesicles
muscle cell (fiber)
neurotransmitteracetylcholine (ACh)receptor protein
Ca++
synapse
action potential
How does the message cross the synapse?
1. action potential depolarizes membrane
2. opens Ca++ channels
3. neurotransmitter vesiclesfuse with membrane
4. release neurotransmitter to
synapse → diffusion
5. neurotransmitter binds with protein receptor
– Excited = channels open
– Inhibited = channels closed
6. neurotransmitter degraded or reabsorbed
Electrical Signal Electrical Signal �������� Chemical Signal (neurotransmitter)Chemical Signal (neurotransmitter)
How does the nerve impulse move into the next neuron?
• Post-synaptic neuron– Neurotransmitter signal opens ion-gated channels
– Signal is passed on
– + + + + + + ++ + + + + + +
– + + + + + + ++ + + + + + +
+ – – – – – – –– – – – – – –
+ – – – – – – –– – – – – – –
Na+
K+K+
Na+ Na+
Na+
ion channel
binding site ACh
snake toxin blocking
cholinesterase active site
How do neurons prevent over firing?
cholinesterase
active site in red
neurotoxin in green
• Enzymes that break down neurotransmitters
• Cholinesterase – breaks down acetylcholine
– Makes sure neurons don’t continue to fire
• Cholinesterase inhibitors – neurotoxins
• snake venom, insecticides
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What are the different types of neurotransmitters?
• Acetylcholine (ACh)
– Signals skeletal muscle to contract
•• Epinephrine (adrenaline) & norepinephrineEpinephrine (adrenaline) & norepinephrine
– fight-or-flight response
• Dopamine & Serotonin
– affects sleep, mood, attention & learning
Why are neurotransmitters the weak point of nervous system?
• any substance that affects neurotransmitters or mimics them affects nerve function
Summarizing Strategy• Describe the pathway of impulse that occurs
when you are driving a car and see a deer about to cross the road.
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Assessment
• HW: Chapter 48 & 49 Wkst
Activating Strategy
• Label the following on the action potential graph:
– Hyperpolarization, Maximum Action Potential, Reploarization, Depolarization, Resting Potential, Threshold
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