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AP Biology Nervous Systems Part 5 Slide 2 Important concepts from previous units: Conformational shape change triggers a transduction pathway leading to response. Actin and myosin microfilaments are part of the cytoskeleton. Calcium ions, calmodulin, is a secondary messenger within muscle cells. Slide 3 Actin and Myosin Microfilaments Slide 4 CYTOSOL Ca 2+ Endoplasmic reticulum (ER) IP 3 -gated calcium channel IP 3 (second messenger) DAG PIP 2 G-protein-linked receptor Phospholipase C G protein Signal molecule (first messenger) EXTRACELLULAR FLUID GTP Ca 2+ (second messenger) Various proteins activated Cellular re- sponses Slide 5 I. Sensation of Sight (The eyes are a collection of photoreceptors.) A. Structures in animals for detecting light energy. 1. Ocelli As seen in Cnidarians (Jellyfish) and Bi- valves (Clams and oysters). 2. Eye cup As seen in Platyhelminthes (Flatworms). 3. Eyes with a lens as seen in most other animals. Slide 6 Eye Cups Slide 7 Oscilli Slide 8 a. Compound Eye Found in invertebrates, such as insects. i. This produces multiple pictures of the same object.ii. This type of eye is great for detecting movement. b. Single Eye Found mollusks and vertebrates. These are good for detecting definition. Slide 9 Compound eye up close The cornea and crystalline cone of each ommatidium function as a lens that guide light to the photoreceptors. This creates a mosaic image because light strikes each at a different angle. Slide 10 Compound eyes of insect Slide 11 Single Eye Slide 12 B. Retina This layer of the eye is the site of the photoreceptors. 1. Rods - These photoreceptor cells are for seeing black, white, and shades of grey. a. They are the most abundant in all animals having these structures.. b. They possess Rhodopsin Pigment (It is a combination of retinal and opsin proteins.) i. A shape change allows for depolarization to occur in neuron. Slide 13 Location of the Retina in your eye Slide 14 2. Cones - These photoreceptor cells are used for seeing color. a. They are outnumbered 20 :1 by the rods. b. They are found in vertebrates: but not all. c. They possess Photopsin Pigments (red, blue, green) Slide 15 Rods vs. Cones (Look at the shape) Slide 16 Rods and Cones in the Retina Cone Photoreceptors Retina Rod Neurons Pigmented epithelium Bipolar cell Amacrine cell Horizontal cell Optic nerve fibers Ganglion cell Slide 17 II. Locomotion (A.K.A movement) This term refers to active movement of an organism or object. A. This process is the second largest consumer of ATP energy within an organism because: 1. Organism has to overcoming the force of gravity AND 2. Overcoming the force of friction (resistance). Slide 18 B. Types of environments dealing with locomotion: 1. Water (Organisms are swimming or floating.) a. Little gravity to overcome because of buoyancy; but much friction (water resistance). Having a fusiform (means torpedo shaped) body lessens friction Slide 19 2. Land (Organisms are standing/walking/running.) a. Much gravity to overcome; but little friction (air resistance). i. Organisms have strong muscular limbs to overcome gravity. Slide 20 Air (Organisms are flying or gliding.) a. Much gravity to overcome and much friction to overcome (air resistance). i. These require massive amounts of energy be consumed to overcome. Slide 21 III. Muscle function and structure: A. The main function of muscle is to provide movement using a pulling force. B. Motor unit This term refers to a muscle and corresponding motor nerve. 1. Muscle contraction process: (How a muscle contraction is accomplished.) Slide 22 Slide 23 Step 1: The neurotransmitter Acetylcholine attaches to receptor proteins on the muscle cell membrane. Step 2: Depolarization, Na+ flooding in, of the membrane occurs to generate an action potential. (This is electrical energy.) Step 3: The action potential travels along the membrane to a T tubule. Step 4: The action potential travels down the T tubule into the cell. Step 5; The action potential hits the Sarcoplasmic Reticulum causing release Calcium ions, Ca++into the cytoplasm of muscle cell. Step 6: The calcium ions, secondary messengers, bind with the Troponin complex. Slide 24 . Ca 2+ CYTOSOL Ca 2+ SR PLASMA MEMBRANE T TUBULE Synaptic cleft Synaptic terminal of motor neuron ACh Slide 25 . Myosin-binding sites blocked. Myosin-binding sites exposed. Tropomyosin Ca 2+ -binding sites Actin Troponin complex Myosin- binding site Ca 2+ Slide 26 Step 7: The calcium binding causes Tropomysin thread to roll off the Myosin binding sites holes on the Actin myofibril. Step 8: ATP is used to phophorylate the myosin heads Hands. Step 9: The Myosin heads hands grab the holes and pull slide the actin over. This is referred to as the Sliding Filament Theory. 2. Muscle relaxation process: (How a muscle relaxes is accomplished.) Step 1: Acetylcholine esterase destroys the Acetylcholine molecules on the membrane. Step 2: The Phosphorus is taken off the hands and actin slides back to its original position. Step 3: The Sarcoplasmic Reticulum reasbsorbs all the Calcium ions. Slide 27 . Thin filaments Thick filament Thin filament Thick filament Myosin head (low-energy configuration) Cross-bridge binding site Myosin head (high- energy configuration) Actin Cross-bridge Myosin head (low- energy configuration) Thin filament moves toward center of sacomere.