BIOL 1040 notes, Chapter 35
BIOL 1040 notes, Chapter 35 BIOL 1040
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This 6 page Class Notes was uploaded by Sarah Stewart on Thursday January 14, 2016. The Class Notes belongs to BIOL 1040 at Clemson University taught by Dr. William Surver in Fall 2016. Since its upload, it has received 36 views. For similar materials see General Biology II in Biology at Clemson University.
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Date Created: 01/14/16
Chapter 35: Neurons and the Nervous System Lecture given 1/19/16 *Review membrane of a cell, diffusion, active transport Neuron – functional cell in a nervous system • Cell body (soma) • Dendrites • Axon • Myelin sheath • Synapse Glial cells – accessory cells that maintain the environment of nervous system Nervous System consists of 2 sections 1. Central nervous system (CNS) – consists of the brain and the spinal cord 2. Peripheral nervous system (PNS) – consists of nerves (bundles of neurons wrapped in connective tissue) and ganglia clusters of cell bodies The nervous system must • Obtain sensory information, sensory input • Process sensory information, integration • Send commands to effector cells (muscles/glands) that carry out responses, motor output • All of these performed by neurons, anatomically the same but carry out different tasks • Discriminates between important info and unimportant info Sensory neurons – convey signals from sensory receptors to the CNS Interneurons – located exclusively in CNS, integrate info and send to motor neurons Motor neurons - convey signals to effector cells Simple reflex arc – demonstrates the relationship between neurons and nervous system structure/function, brain excluded; how “quick reflexes” function Neuron Function • Resting potential • Action potential i) Threshold ii) Depolarization iii) Repolarization iv) Hyperpolarization Propagation – movement of action potential down a neuron; one-way chain • Propagation speeds up when a myelin sheath is present, areas not covered by sheath called nodes of ranvier Synapse – relay points between synaptic terminals of a sending neuron and a receiving neuron; receiving cell can be another neuron or an effector cell i.e. a muscle cell Resting Potential of Neurons • Concentration gradient of K+ goes from inside to outside cell membrane; outside contains more Na+ (sodium-potassium pump) • More K+ channels than Na+ channels, allows K+ to diffuse to outside membrane • Na+/K+ ions move against gradient w/ a 3:2 ratio; moves more Na+ which maintains equilibrium • Neuron must be at resting potential to be stimulated Acting Potential of Neurons • Action potential is the change of membrane voltage from resting potential, to its max level, back to its resting potential • When stimulus applied, Na+ channels open up, allows those ions to move inside cell membrane • Cell interior gains a more positive charge; this is depolarization • If stimulus great enough, will generate action potential; if not great enough, will go back to resting potential • Makes action potential a “All or Nothing” phenomenon • If it reaches action potential, K+ gates open and ions stream out of cell membrane so cell interior has a negative charge; this is hyperpolarization Ch. 35 continued… Lecture given 1/21/16 **Read last section of chapter for reference Threshold-discrimination – when the energy threshold is not reached in a neuron • If action potential is reached, the charge travels down the axon in a chain reaction • Neurons do not touch each other, there is a space the charge has to cross Chemical Synapses • The ending cell (presynaptic cell) secretes a chemical signal called a neurotransmitter, crosses the synaptic cleft, which is the space between the neurons • Vesicles are membranous sacs that contain the neurotransmitters • Begin to fuse together, move to end of axons and release the neurotransmitters into the synaptic cleft • The receiving cell (postsynaptic cell) has receptors that absorb Na+ once a neurotransmitter bind to them; causes depolarization and continuation of the action potential • Neurotransmitters can also bind to K+ channels; causes hyperpolarization and the lowering of the energy threshold Neurotransmitters E.P.S.P. – excite a receiving cell I.P.S.P. – inhibit a receiving cell • Receiving neuron’s membrane may receive these signals from different sending neurons • Summation of excitation and inhibition determines if a neuron will transmit a nerve signal or not Overview of Nervous System • Flow of info within nervous system relies on synaptic integration, or how many neurons are organized within the body • Thousands of neurons in brain, arranged in blocks that either receive excitatory or inhibitory signals • Divergent circuit neurons form connections with other blocks • Convergent circuit signals from a many blocks are relayed to a few Trends to look for (simple to complex): 1. Whole body response to more local response 2. Cephalization – the formation of a head 3. Specialized functions of sensory, integrating, and responding Most bilaterally symmetrical animals evolved: • Concentration of nervous system in head area (cephalization) • Centralization – central nervous system distinct from peripheral nervous system • Presence of ganglia • Radially symmetrical organisms have a nerve system arranged in a web of nerves called a nerve net Human Nervous System Central nervous system (CNS) • Contains the brain and the spinal cord Peripheral nervous system (PNS) • Divided into 2 components: the motor system (voluntary) and the automatic nervous system (involuntary) Motor nervous system – carries signals to and from skeletal muscles, respond mostly to external stimuli Automatic nervous system – regulates internal environment, controls smooth and cardiac muscle, organs, and glands Chapter 37: Hormones and the Endocrine System • Consists of all hormone-secreting cells, works w/ nervous system in regulating body activity • Response slower than compared to nervous system, but it lasts longer Chemical messengers: • Hormones – released by endocrine glands/some neurons into the blood stream; acts on target tissues and cells, not entire body • Neurotransmitters – end of axon • Local signaling molecules – released by assorted cells • Pheromones – secretions of exocrine glands
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