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Gnarly Nervous Physiology Chapter 48-49 Notes I. Nerve Structure Review II. Nerve Signals Membrane Potential • Electrical charge difference across the plasma membrane • Anions (-): Concentrated inside the cell • Cations (+): Concentrated in extracellular matrix II. Nerve Signals • Resting potential: Membrane potential of an unstimulated neuron • Action potential: A nerve impulse that can be transmitted to another nerve Nerve Signals Details 1. Resting: Na+ and K+ gates closed (resting potential) 2. Threshold: Na+ gates open 3. Depolarization: Na+ rushes into the cell (interior more +) 4. If signal is strong enough – generates an ACTION POTENTIAL 5. Repolarization: Na+ gates close, K+ channels open. K+ leaves cell (interior more -) Nerve Signal Details (cont) 6. Undershoot: Inside gets extra – 7. Refractory Period: Na+ / K+ pump gets things back to normal. III. Neuron communication at the Synapses • A. The Process • *Cytoplasm at end of axon contains synaptic vesicles • The vesicles contain neurotransmitters • These are chemical messengers Neuron Communication at the Synapses 1. Ca+ gates open. Ca+ enters the cell 2. Synaptic vesicles merge with presynaptic nerve’s membrane 3. Releases neurotransmitter into synapse. Neurotransmitter binds with receptors on next neuron (postsynaptic) 4. Neurotransmitter bound to ion channel, opens it which allows ions to rush in (depolarize) Nerve Communication at the Synapses • If Na+ gates open, membrane becomes depolarized (more +) and results in excitatory postsynaptic potential. It may generate an action potential if strong enough. • If K+ gates open, membrane becomes polarized and results in inhibitory postsynaptic potential (more - because K+ goes out). No action potential. IV. Common Neurotransmitters A. Acetylcholine *Found at neuromuscular junctions. Stimulates muscle contraction. B. Epinephrine, Nor epinephrine, Dopamine, & Serotonin *Secreted between neurons in CNS *Dopamine and serotonin affect sleep, mood, attention and learning *Excessive dopamine is linked to schizophrenia *Some hallucinogenic drugs bind to serotonin and dopamine receptors Mighty Muscular Physiology • I. Mighty Muscular • *Muscles only shorten or contract Mighty Muscular • • • • • A. Muscle Structure *Muscle Cell= muscle fiber *Cell Membrane= sarcolemma *Cytoplasm= sarcoplasm *Endoplasmic Reticulum= Sarcoplasmic Reticulum Mighty Muscular 1. Muscle fibers are made up of myofilaments 2. Myofilaments are made of actin (thin) and myosin (thick) microfilaments. 3. Repeating units along a muscle fiber are called sarcomeres--they are the contractile unit of the muscle. 4. Note on diagram: Z line, H zone, I band, A band, M line Muscle contractions • *Length of sarcomere is reduced (distance between Z lines gets smaller) • *I band shortens, A band stays the same, H zone disappears Sliding Filament Model 1. 2. 3. 4. ATP binds to myosin head ATP----- ADP + Pi Myosin head binds to actin forming cross-bridge ADP + Pi are released. Myosin head changes shape. This slides the actin toward the center of the sarcomere (Z lines get closer) Whoo Hoo! Contraction! 5. ATP binds, releases myosin head. We start again. (Corpse is “stiff ” because there is not ATP to undo the contraction) It Can’t Be That Simple • *When muscles are at rest, the myosin binding sites on the actin are blocked by a protein called tropomyosin. The proteins in the troponin complex control the position of tropomyosin on the actin. • For contraction to occur, the binding sites need to be uncovered. • Ca+ to the rescue!! Calcium binds to troponin, it alters the shape and exposes the myosin binding sites on the actin. • So drink lots of milk!! No Ca+ ---no contraction!!