Examples 1 2 3 4 5 6 Thinkables

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Thinkables: Complete sentences. 1. Obviously the way a cell looks is different depending on the function. Do you think a cell will have differences in organelles depending on the function of that cell? Explain your answer. What organelle(s) would muscle cells need a lot of? 2. All cells have a phospholipid bilayer as a cell membrane. Thinking about the variety of shapes and sizes of cells what can you conclude about the cell membrane? 3. True/False: The nucleus of a cell contains different types of DNA depending on the structure and function of the cell for that organism. Explain your answer. 4. How/Where do you get the different cells in your body?

Practice Questions 1. Muscle cells found in the heart contain many more mitochondria than cells that store fat in adult humans. Which explanation best explains why that is true? a. Heart muscle cells are larger than fat cells. b. Heart muscle cells require a lot of energy. c. Cells that compose fatty tissue are not living. d. Cells that compose fat tissue do not make proteins.

2. If most of an organism’s cells have the same DNA, why is it true that all cells do not make the same proteins? a. b. c. d. because of chromosome pairing because of DNA mutation because of differentiated ribosomes because of gene (DNA) regulation

3. Each body cell in a human contains the same DNA, but heart cells and liver cells have different functions. Why is this true? a. Heart tissue develops before liver tissue. b. Liver tissue develops before heart tissue. c. When heart cells divide, mutations occur. d. Heart cells express different genes than liver cells.

• #4 Stem Cell Video & Questions

• Are sperm and egg stem cells? Circle the cells that are undifferentiated stem cells.

• Part 2: Neurons • Drawing, Video and Questions

Figure 45 -3 Information flow through neurons Neurons form networks for information flow Nucleus Dendrites Cell body Collect electrical signals Integrates incoming signals and generates outgoing signal to axon Axon Passes electrical signals to dendrites of another cell or to an effector cell

Impulse Transmission • Chemical changes across the membranes of neurons transmit the impulse. • An unstimulated neuron is polarized. Pumps in the membrane maintain this gradient. • Overall, the inside of the cell is negative b/c of a large number of very negatively charged molecules and ions inside the cell. • RESTING POTENTIAL/REST PHASE

Figure 45 -4 Instrument records voltage across membrane Outside of cell Microelectrode 0 m. V K channel – 65 m. V Inside of cell

The Impulse • In response to a stimulus, gated ion channels open and allow Na+ to rush into the cell, meaning that the cell depolarizes. REQUIRES NO ENERGY!!! • If the impulse is strong enough more ion channels open. • Other channels open to allow K+ outside of the cell to repolarize the cell (turn off the signal). An impulse moves along the neuron by opening and closing channels.

Figure 45 -11 PROPAGATION OF ACTION POTENTIAL Axon Neuron Action potential spreads as a wave of depolarization. Electrode A 1. Na+ enters axon. Neuron Electrode B Electrode C A B 2. Charge spreads; membrane “downstream” depolarizes. Depolarization at next ion channel 3. Voltage-gated channel opens in response to depolarization. C

Figure 45 -12 b WHY ACTION POTENTIALS JUMP DOWN MYELINATED AXONS Schwann cell 1. As charge spreads down an axon, myelination (via Schwann cells) prevents ions from leaking out across the plasma membrane. Node of Ranvier 2. Charge spreads unimpeded until it reaches an unmyelinated section of the axon, called the node of Ranvier, which is packed with Na+ channels. 3. In this way, electrical signals continue to jump down the axon much faster than they can move down an unmyelinated cell.

Myelinzation • Some neurons are myelinized (covered with a sheath of Schwann cells), which insulate the nerve’s impulse • Breaks in this sheath are called nodes of Ranvier.

Refractory Period • The neuron cannot now respond to a new stimulus b/c K+ and Na+ are on the wrong sides of the membrane • Sodium/Potassium pumps must now reestablish resting potential so that the neuron can react to a new stimulus REQUIRES ATP!

Figure 45 -6 1. Depolarization phase 2. Repolarization phase Threshold potential Resting potential 3. Hyperpolarization phase

Figure 45 -15 At the Synapse (electrical changes to chemical): ACTION POTENTIAL TRIGGERS RELEASE OF NEUROTRANSMITTER Na+ and K+ channels Presynaptic neuron 1. Action potential arrives; Action potentials triggers entry of Ca 2+. 2. In response to Ca 2+, synaptic Presynaptic membrane (axon) vesicles fuse with presynaptic membrane, then release neurotransmitter. 3. Ion channels open when Postsynaptic neuron neurotransmitter binds; ion flows cause change in postsynaptic cell potential. Postsynaptic membrane (dendrite or cell body) 4. Ion channels will close as Synaptic cleft neurotransmitter is broken down or taken back up by presynaptic cell (not shown).