BIOL110s05-38 - BIOL 110: Principles of Biology Spring 2005...

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Unformatted text preview: BIOL 110: Principles of Biology Spring 2005 Lecture 38, W 5/4/05 • EXTRA CREDIT: Stanford U. Community Lecture Series – Wed, 5/4/05, 7pm: “50 Years of Computational Biology” Biology” • Clark Center Auditorium: • 1 page summary. 15 points, + 5 if you ask a question (include in in summmary) summmary) • Week 14 Lab assignments due THIS week, for In-Lab InDiscussion (Environmental Issues)!! (SIGN UP!!!) (SIGN • Week 15 Field Trip: Edgewood Park (@ 280 & Edgewood Road) Edgewood – Grade for participation & Worksheet!!! (Replace 1 quiz!!!) – Bring: Good shoes/boots, light-colored clothing/pants, notepad light& worksheet, binoculars?, hat, sunblock, water, snack? worksheet • Next: 25, 23, 29 & 30, (31, 32). REVIEW: • Ch. 18 (19): Plant Structure & Function – Vascular cylinder: • Phloem = Sugar transport; – Reproductive physiology • Ch. 25: Nervous System [& Senses] – Neurons: sensory (receive), interneurons (process), motor (command; response) TODAY: • Ch. 25: Nervous System [& Senses] – Neuron Structure – Sensory conduction 1 Neuroglia • Make up more than half the volume of the vertebrate nervous system • = Type of cells that metabolically assist, structurally support, and protect the neurons Structure of a Neuron dendrites cell body INPUT ZONE axon OUPUT ZONE axon endings TRIGGER ZONE CONDUCTING ZONE 2 A. Resting Potential • = Charge difference (Voltage/ electrical potential) across the plasma membrane of a neuron • Fluid just outside cell is more POSITIVELY outside POSITIVELY charged than fluid inside – Cytoplasm is more negatively-charged than outside. negatively- • Potential is measured in millivolts • Resting potential is usually about -70mV Maintaining Resting Potential K+ and Na+ can’t diffuse across bilayer Na+ pumped out K+ leaks out Na+ leaks in K+ pumped in K+ leaks in 3 Ion Concentrations at Resting Potential • Potassium (K+ ) – higher inside cell – Concentration inside the neuron is higher inside higher than the concentration outside • Sodium (Na+ ) – higher outside cell – Concentration inside the neuron is lower inside lower than the concentration outside B. Action Potential • A transitory reversal in membrane potential • Voltage change causes voltage-gated voltage channels in the membrane to open channels – VG Sodium Channels open – Sodium rushes in (more positive inside!!) • As a result of ion flow through these channels, the inside of neuron briefly becomes more inside positive than outside – “Depolarization” Depolarization” 4 STIMULUS Action Potential trigger zone interstitial fluid 1. Resting K+ K+ K+ cytoplasm Na+ Na+ Na+ K+ K+ 2. Action Potential K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ 3. Reversal Na+ 4. Recovery of resting Action Potential Click to view animation. animation 5 Positive Feedback more Na+ ions flow into the neuron more gated channels for Na+ open neuron becomes more positive inside “All or Nothing” Response 1. All action potentials are the same size 2. If stimulation is below threshold level, no no action potential occurs 3. If it is above threshold level, cell is cell always depolarized to the same level 6 C. Repolarization 1. 2. 3. 4. Once peak depolarization is reached, Na+ gates close and K+ gates open close Movement of K+ out of cell repolarizes the cell The inside of the cell once again becomes more negative than the outside Na+/K+ active transport pumps restore the resting potential (ion balance). Recording of Action Potential +40 Membrane potential (milliseconds) +20 0 -20 -40 threshold action potential -70 resting membrane potential 1 2 3 4 5 6 0 (Time milliseconds) 7 D. Propagation of Action Potentials • An action potential in one part of an axon brings a neighboring region to threshold • Action potential occurs in one patch of membrane after another II. Chemical Synapse • Gap between the terminal ending of an axon and the input zone of another cell neurotransmitter molecule in synaptic cleft receptor for the neurotransmitter on gated channel protein in plasma membrane of postsynapic cell ions that affect membrane excitability plasma membrane of axon ending of presynapic cell synaptic vesicle plasma membrane of postsynapic cell synaptic cleft membrane receptor 8 Postsynaptic Membrane: Ion Gates Open neurotransmitter ions receptor for neurotransmitter gated channel protein slice from spinal chord stimulus (input) receptors sensory neurons integrators interneurons of brain, spinal cord motor neurons effectors muscles, glands response (output) motor neuron axons in a nerve leading from spinal chord muscle neuromuscular junction 9 ...
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