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Do Now: 3 Types of Nerve Cells Glue in your notebook on the next blank page! Do Now: 3 Types of Nerve Cells Levels of Organization Whiteboard Activity Opinion Question What is an ELECTROLYTE? You have 3 minutes to talk to your lab group and then be ready to share out. What is an ELECTROLYTE? DO NOT WRITE…DISCUSSION ONLY 1. All salts are electrolytes! 2. Substances that conduct an electrical current in a solution 3. A salt is an organic compound found in the body in the form of minerals – Calcium and phosphorus, found in teeth and bones – Dissolved minerals found in urine – Sodium and potassium ions used for nerve impulses in the brain – Iron, found in hemoglobin, in the blood cells (this is what makes it red in color) Notes: How Neurons Communicate Glue this picture on the next blank page Transmission of a Nerve Signal • Neuron communicate similar to dominoes – protein channels set up – Once the 1st channel is opened, the rest open up in succession (one after the other…) • all or nothing response – a “wave” action travels along neuron – have to re-set channels so neuron can react again Important Chemistry Vocabulary – anions (negative) • more concentrated IN THE CELL – cations (positive) • more concentrated in the extracellular fluid (OUTSIDE THE CELLS) K+ aa- K+ aaCl- Na+ ClK+ Na+ aa- Na+ K+ aa- K+ Na+ ClCl- Na+ aa- Na+ Na+ Na+ Claa- Cl- – Na+ Na+ Na+ + K+ channel leaks K+ Why is this impulse called an ACTION POTENTIAL? unstimulated neuron = resting potential of -70mV How does a nerve impulse travel? STEP 1 and 2 Step 1 - Stimulus: nerve is stimulated (ACTIVATED) • Open channels in cell membrane STEP 2 - Na+ ions diffuse into cell – charges reverse at that point The 1st domino goes down! • positive inside; negative outside – + + + + + + + + + + + + + + + – – – – – – – – – – – – – – Na+ + – – – – – – – – – – – – – – – + + + + + + + + + + + + + + How does a nerve impulse travel? STEP 3 STEP 3 - Wave: nerve impulse travels down neuron – change in charge opens next Na+ gates down the line – Na+ ions continue to diffuse into cell – “wave” moves down neuron = The rest of the dominoes fall! action potential Gate + + – channel closed + channel open – – – + + + + + + + + + + + + + + + – – – – – – – – – – – – Na+ + + + – – – – – – – – – – – – – – – + + + + + + + + + + + + wave How does a nerve impulse travel? STEP 4 STEP 4 - Re-set: 2nd wave travels down neuron – K+ channels open – K+ ions diffuse out of cell – charges reverse back at that point • negative inside; positive outside Set dominoes back up quickly! K+ + – – – – + + + + + + + + + + – + + + + – – – – – – – – – – Na+ – + + + + – – – – – – – – – – + – – – – + + + + + + + + + + wave Checking For Understanding 1. What are the 4 steps of nerve impulse travel? Write a paragraph or bullet points or draw a flow chart. Myelin sheath Axon coated with Schwann cells signal direction insulates axon speeds signal signal hops from node to node myelin sheath action potential saltatory conduction Na+ myelin axon + + + + + – – Na+ Multiple Sclerosis immune system (T cells) attack myelin sheath loss of signal What happens at the end of the axon? Impulse has to jump the synapse! – junction between neurons – has to jump quickly from one cell to next How does the wave jump the gap? Synapse Chemical synapse axon terminal Events at synapse action potential synaptic vesicles synapse Ca++ receptor protein neurotransmitter acetylcholine (ACh) muscle cell (fiber) We switched… from an electrical signal to a chemical signal 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 Nerve impulse in next neuron K+ • Post-synaptic neuron – triggers nerve impulse in next nerve cell • chemical signal opens ion-gated channels Na+ + binding site • Na diffuses into cell • K+ diffuses out of cell Here we go again! – switch back to voltage-gated channel ACh Na+ ion channel K+ K+ – + + + + + + + + + + + + + + + – – – – – – – – – – – – – – Na+ + – – – – – – – – – – – – – – – + + + + + + + + + + + + + + Na+ Neurotransmitters • Acetylcholine – transmit signal to skeletal muscle • Epinephrine (adrenaline) & norepinephrine – fight-or-flight response • Dopamine – widespread in brain – affects sleep, mood, attention & learning – lack of dopamine in brain associated with Parkinson’s disease – excessive dopamine linked to schizophrenia • Serotonin – widespread in brain – affects sleep, mood, attention & learning Checking For Understanding 2. How does the transmission of an action potential from neuron to neuron represent a set of dominoes falling down? Write a paragraph or bullet points or draw a flow chart. Human Action Potential 1. 2. 3. Everyone in your group should have at least 1 poster. (everyone participates) Objective: Stand up and stand on the line (tape on the floor) to assemble a human neuron. The order of the posters should demonstrate the change in electrical charges and movement of ions (charged particles) down the neuron. Exit Slip 1. Work on your own. 2. Open note. 3. When you finish your paragraph… • Peer grade - choose a lab group member to read your paragraph and provide feedback. 4. Turn in your exit slip into the exit slip tray