Bioe 20B Nervous System Lecture Notes (10/17/24) PDF

REMINDERS ANNOUNCEMENTS 1. Today: Nervous System Thursday, 10/17/24 2. Due Sunday: HW 3, Quiz 3 3. Midterm 1 is on Thursday, October 24th Week 3, Day 2 Midterm content: Form and Function, Energetics and Nervous System Metabolism,...

REMINDERS ANNOUNCEMENTS 1. Today: Nervous System Thursday, 10/17/24 2. Due Sunday: HW 3, Quiz 3 3. Midterm 1 is on Thursday, October 24th Week 3, Day 2 Midterm content: Form and Function, Energetics and Nervous System Metabolism, Nutrition and Digestion, Osmoregulation, Circulation, Respiration, Nervous System Format: Individual, similar to practice exam Extra credit for being caught up with content videos by Sunday (with 24 hour grace) TODAY’S AGENDA (8-9:35AM) Basic Nervous System Overview Neuron – basic structure Resting Membrane Potentials Action Potentials 5 min break Synapses and Drugs Kahoot: Action Potentials The nervous system  Key Key Concepts Concepts forfor Today Today 1. Basic Nervous System overview 2. Neuron – basic structure 3. Resting Membrane Potentials 4. Action potentials 5. Synapses & Drugs REVIEW: Nervous System What makes up our nervous system? 2 communication systems: Wired System = Nervous system Wireless System = Endocrine system  Key Key Concepts Concepts forfor Today Today 1. Basic Nervous System overview 2. Neuron – basic structure 3. Resting Membrane Potentials 4. Action potentials 5. Synapses & Drugs REVIEW: Nervous System Label the Neuron: Where does information come in? Dendrite Where does information go out? Axon Cell body Where do you find neurotransmitters? Synaptic terminal What is “information” in the context of the nervous system? Myelin Sheath Draw the direction of information flow. Axon hillock REVIEW: Nervous System Dendrites Axon terminals Receives incoming signals Neuron Synapse/site of (one-way) communication with a target cell Myelin sheath (insulation layer) Node of Ranvier Cell body (un-insulated layer) Neutrotransmitters (contains nucleus found on axon and organelles) terminals Axon Axon hillock (transmits information by (generates action conducting action potential potential) away from cell body ) REVIEW: Nervous System  Key Key Concepts Concepts forfor Today Today 1. Basic Nervous System overview 2. Neuron – basic structure 3. Resting Membrane Potentials 4. Action potentials 5. Synapses & Drugs How is the chemical gradient established? Inside Outside More K+ More Na+ 3Na+ ATP 1 K+ Na/K ATPase K+ Na+ K+ 2K+ Na+ Na+ K+ K+ Na+ K+ Na+ Na+ K+ Na+ K+ Na+ K+ K+ K+ Na+ Na+ Na+ Cell is using energy to pump 3 Na+ out of the cell for 2K+ into the cell What about the electrical part of the gradient? Inside Outside More K+ More Na+ 3Na+ ATP 1 K+ Na/K ATPase K+ Na+ K+ Na+ Na+ 2K+ K+ K+ K+ Na+ K+ Na+ K+ Na+ K+ K+ K+ K+ K+ Na+ Na+ Na+ K+ leak channels allow K+ to leave the cell to go down its concentration gradient…  What about the electrical part of the gradient? Inside Outside More K+ More Na+ 3Na+ Negative ions (like Cl-) get left behind. 1 ATP K+ Na/K ATPase K+ Na+ Proteins- Na+ K+ 2K+ Na+ - + - -60 mV Proteins- - + K+ K+ K+ Na+ - + K+ Na+ Cl- K+ Cl- - + Na+ K+ Proteins- Cl- - + K+ K+ K+ Cl- - K+ Na+ + Na+ Na+ The difference in charge comes from K+ leaving the cell and Cl- as well as negatively charged proteins left behind  If membrane were suddenly permeable to sodium? Inside Outside More K+ More Na+ Na+ Proteins- 3Na+ ATP K+ Cl- Cl- Na/K ATPase K+ Na+ K+ Na+ Na+ 2K+ -60 mVà-50 mV (threshold) Proteins- K+ K+ Cl- Cl- Na+ K+ Na+ Na+ K+ Na+ Cl- K+ K+ K+ K+ Na+ Na+ Na+ Proteins- Cl- Na+ We change the membrane potential from negative 60 mV to -50 mV stimulating an action potential REVIEW: Resting Membrane Potentials What is the the resting membrane potential? A difference in charge between the inside and outside of the cell. It is usually around -60 mV. How is the chemical part of the electrochemical gradient is established? The “chemical part” is established by ATP pumps that pump 3Na+ out and 2K+ in the cell. It is always on! How is the electrical part of the electrochemical gradient is established? The “electrical part” is established by open channels for K+ which allows K+ to flow down its concentration gradient. K+ is pulled out of cell by the concentration gradient but pulled back into cell by the negative charge. REVIEW: Action Potentials The Big Picture: 1) Action potentials result from a sudden change in the resting membrane potential. 2) That change is propagated down the neuron in a fast, self-propagating way. 3) When action potential arrives at the other end of neuron, it will result in release or inhibition of neurotransmitters  Key Key Concepts Concepts forfor Today Today 1. Basic Nervous System overview 2. Neuron – basic structure 3. Resting Membrane Potentials 4. Action potentials 5. Synapses & Drugs REVIEW: Action Potentials If enough Na+ get to axon hillock…AP gets Na+ generated Na+ + Na+ Na Na+ Na+ Na+ Na+ Na+ Na+ Na+ Process of touching a table… 1. Na+ is let into dendrites 2. Na+ moves to axon hillock Stretch gates or 3. An action potential is generated and a wave of positive charge gets sent down axon to axon terminal Ligand gates 4. Synaptic terminal releases neurotransmitters open and let Na 5. Signal transmits to other neurons up your hand, up your arm, to spinal + cord, and then to your brain to sense the table in... REVIEW: Action Potentials Describe what the gates are doing at each letter. REVIEW: Action Potentials 1. K+ leak channel is always open to maintain electro-chemical gradient and establish resting membrane potential (-60 mV) Key Steps 2. Na+ voltage gated channel opens to let Na+ into the cell ATPase = 3. More Na+ voltage gates open to 3Na out lead to rapid change in membrane for 2K+ in Positive potential (depolarization) and pass feedback! threshold to achieve an action potential (all or nothing) Threshold = -50mV 4. Na+ inactivation gates close and K+ voltage gates open to bring membrane potential back down (repolarize/hyperpolarize) 5. All gated channels close, Na+ inactivation gates reopen, and resting membrane potential is reestablished (-60 mV) REVIEW: Action Potentials On your boards… When an action potential fires A. The whole neuron gets more positive B. The whole axon gets more positive C. A small wave of positive charge rolls down the axon REVIEW: Action Potentials Refractory Period Propels action potentials in one direction! Similar to a toilet where after you flush you must wait for the water to refill the tank before flushing again, an action potential must proceed in one direction. This is because in the region where the action potential just fired, the Na+ channels are inactivated and the voltage-gated K+ channels are still open. REVIEW: Action Potentials Node of Ranvier Saltatory Conduction Leaping conduction AP’s jump from node Speeds up the action to node potential Myelin sheath physically separates opposite charges to reduce attraction to each other that would otherwise slow action potential (similar to separating magnets) REVIEW: Action Potentials Speed of Action Potentials Neuron Size: larger neurons will conduct the AP faster; less resistance to ion movement Myelin sheaths: increase the speed of action potentials in Vertebrates  Key Key Concepts Concepts forfor Today Today 1. Basic Nervous System overview 2. Neuron – basic structure 3. Resting Membrane Potentials 4. Action potentials 5. Synapses & Drugs  5-min Break! Attendance Time Scan the QR code or go to https://tinyurl.com/W3D2Oct17 to answer the following question: 1) What establishes the resting membrane potential in a neuron? (This will be used for taking attendance today.) REVIEW: Synapses Neurotransmitters are released from vesicles via exocytosis into the synaptic cleft. They then bind to receptors on the postsynaptic cell. Botox inhibits the binding of vesicles with neurotransmitters to the cell membrane. What does the action potential graph look like? REVIEW: Synapses With your neighbor If you were to take a drug that that had an inhibitory effect on the postsynaptic neuron, what would happen to the resting membrane potential of the postsynaptic neuron? Would it be easier for this neuron to fire an action potential or more What about an difficult as a result? excitatory drug? Membrane Threshold potential Excitatory drug = more likey to fire potential Resting potential action potential (mV) Inhibitory drug = less likely to fire action potential Time (ms) REVIEW: Synapses What would happen to the action potential graph if: Delay in repolarization/ Delay in depolarization/ No action potential generation; returning to resting membrane reaching threshold (B) Threshold not reached (B) potential (D) the voltage gated sodium the voltage gated the voltage gated channel activation gate sodium channel potassium channel opened more slowly were blocked? opened more slowly compared to normal? than normal?  Key Concepts for: Nervous System What did we learn? Diagram basic neuron anatomy Understand the blood brain barrier and its role in nervous system Know the role of myelin and how it is formed Understand the purpose of an action potential Explain what the electrochemical gradient means and how it is established Accurately describe the five components of the action potential Describe why an action potential travels in one direction and why it is an example of positive feedback Accurately graph an action potential and understand the spatial aspect of an action potential Understand what neurotransmitters are and how they work generally Explain the mechanism of action of treatment with particular drugs that cause paralysis and/or numbness on an action potential Draw graphs of action potentials under the influence of different drugs (that we discussed or hypothetical drugs)  Kahoot Review Time! Action Potentials Extra Credit awarded to 1st, 2nd, and 3rd place!