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Biology (Sci)
BIOL 111

Bio 111 Alanna Houston October 25, 2007 - nervous tissue does not first appear in flatworms but in invertebrates Neuron: - Dendrites – receive impulses - Cell body – contains most organelles - Axons – conduct impulses away from the cell body - Axon terminals – synapse with other cells - Vertebrate Nervous System: - - Afferent neurons: bring sensory info to CNS - Interneurons: in CNS store, integrate, and relay info - Efferent Neurons: Bring motor info from CNS Spinal Reflex Arc: - Example: knee jerk reflex - Involved: spinal cord (CNS) and 2 neurons (PNS) Bio 111 Alanna Houston - - There is a stimulus (rubber mallet on tendon) that hits a sensory neuron (stretches dendrites) sending impulse up the sensory neuron to the spinal cord. Impulse is transferred to motor neuron and travels from spinal cord. This impulse triggers response in effector and the lower leg extends. - ** A ganglion is a cluster of nerve cells - Dendrites bring information to the cell body and axon brings it away from the cell body How do neurons work? - Electrochemically - Difference in charge across the cell (neuron) membrane and a charge due to ions (Na+, K+, Cl-) and negatively charged proteins. - Look at the neurons at rest slide: o Na+ outside o K+ inside and outside and Cl- and negatively charged proteins inside o Electrochemical gradient across the membrane o Voltage difference = membrane potential o Voltage difference when neuron is at rest…FINISH - measuring membrane potentials: o electrodes inserted into axon o can chart electrical potential across membrane over course of an impulse o use squid neurons (1 mm) - Nerve impulse = action potential o Rapid voltage change (1 to 2 milliseconds) o 3 major processes:  depolarization (2,3)  depolarization (4)  Na+/k+ pump (all) Bio 111 Alanna Houston  Involve movement of Na+ and K+ FINISH What controls ion movement? - Ion channels and ion pumps (membrane proteins) - Ion Channels: o May be gated (voltage or chemically) o Ions flow with gradient o No energy used (diffusion) - Ion Pumps: o Sodium – potassium pump o Ions move against gradient o Use energy (active transport) - These proteins are selective: Na+, K+ etc only - - Bio 111 Alanna Houston - - Why is there hyperpolarization??? FIGURE THIS OUT WITH TEXT ETC. - Refractory period due to: neuron hyperpolarization, membrane potential is positive, and Na+ and K+ on wrong sides of cell membrane Action Potential Summary: 1) Depolarization: inside becomes less negative a. Stimulus causes Na+ voltage gates to open b. Na+ -> in c. If threshold reached (-50 mV) ETC FINISH - Look at transmission of action potential along axon slide (2 diagrams) - Why is action potential unidirectional? Bio 111 Alanna Houston - Speed of Transmission: - depends upon axon diameter - cephalopod axons = 1 mm diameter – impulse travels at 25 m/s - vertebrate axons
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