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NOTES: CH 48 Neurons, Synapses, and Signaling

NOTES: CH 48 Neurons, Synapses, and Signaling.  A nervous system has three overlapping functions:. 1) SENSORY INPUT : signals from sensory receptors to integration centers 2) INTEGRATION : information from sensory receptors is interpreted and associated with appropriate responses

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NOTES: CH 48 Neurons, Synapses, and Signaling

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  1. NOTES: CH 48Neurons, Synapses, and Signaling

  2.  A nervous system has three overlapping functions: 1) SENSORY INPUT: signals from sensory receptors to integration centers 2) INTEGRATION: information from sensory receptors is interpreted and associated with appropriate responses 3) MOTOR OUTPUT: conduction of signals from the integration center to effector cells (muscle cells or gland cells)

  3. *CENTRAL NERVOUS SYSTEM (CNS) integration center brain and spinal cord

  4. *PERIPHERAL NERVOUS SYSTEM (PNS) made up of nerves (ropelike bundles of neurons)  nerves communicate motor and sensory signals to and from CNS and rest of body

  5. Two Main Classes of Cells: 1) NEURONS:  functional unit of the nervous system  transmits signals from one location to another  made up of: cell body, dendrites, axon  many axons are enclosed by an insulating layer called the MYELIN SHEATH  include: sensory neurons, interneurons, motor neurons

  6. 2) GLIAL CELLS (“GLIA”) - SUPPORTING CELLS  10 to 50 times more numerous than neurons  provide structure; protect, insulate, assist neurons  example: Schwann cells and oligodendrocytes form myelin sheaths in the PNS and CNS, respectively

  7. MYELIN SHEATH:  produced by Schwann cells in the peripheral nervous system;  gaps between successive Schwann cells are called NODES OF RANVIER…. ***the #10 term!!! 

  8. NODES OF RANVIER! ***word #10 on my list!!! 1) Okazaki fragments 2) plasmodesmata 3) ??????? 4) ??????? 5) ??????? 6) rubisco 7) oxaloacetate 8) islets of Langerhans 9) Batesian mimicry 10) nodes of Ranvier

  9. 2) GLIA (SUPPORTING CELLS)  example:astrocytes: responsible for blood-brain barrier

  10. Astrocyte Nerve cells

  11. ACTION POTENTIALS & NERVE IMPULSES • all cells have an electrical charge difference across their plasma membranes; that is, they are POLARIZED.  this voltage is called the MEMBRANE POTENTIAL (usually –50 to –100 mV)  inside of cell is negative relative to outside  arises from differences in ionic concentrations inside and outside cell

  12. **A- = group of anions including proteins, amino acids, sulfate, phosphate, etc.; large molecules that cannot cross the membrane and therefore provide a pool of neg. charge that remains in the cell

  13. How is this potential maintained?  the sodium-potassium pump uses ATP to maintain the ionic gradients across the membrane (3 Na+ out; 2 K+ in)

  14.  the “resting potential” of a nerve cell is approx. –70 mV  neurons have special ion channels (GATED ION CHANNELS) that allow the cell to change its membrane potential (a.k.a. “excitable” cells)

  15.  when a stimulus reaches a neuron, it causes the opening of gated ion channels (e.g.: light  photoreceptors in the eye; sound waves/vibrations  hair cells in inner ear)

  16. HYPERPOLARIZATION: membrane potential becomes more negative (K+ channel opens; increased outflow of K+) DEPOLARIZATION: membrane potential becomes less negative (Na+ channel opens; increased inflow of Na+) **If the level of depolarization reaches the THRESHOLD POTENTIAL, an ACTION POTENTIAL is triggered.

  17. ACTION POTENTIALS (APs):  the nerve impulse all-or-none event; magnitude is independent of the strength of the stimulus

  18. 5 Phases of an A.P.: 1) Resting state 2) Depolarizing phase 3) Rising phase of A.P. 4) Falling phase of AP (repolarizing phase) 5) Undershoot

  19. Phase of A.P. State of Voltage-Gated Sodium (Na+) Channel State of Voltage-Gated Potassium (K+) channel Activation gate Inact. Gate Entire channel 1) Resting closed open closed closed 2 & 3) Depolari-zation open open open closed 4) Repolar-ization open closed closed open 5) Undershoot closed closed closed open

  20. **during the undershoot, both Na+ channel gates are closed; if a second depolarizing stimulus arrives during this time, the neuron will NOT respond (REFRACTORY PERIOD)  strong stimuli result in greater frequency of action potentials than weaker stimuli

  21. How do action potentials “travel” along an axon?  the strong depolarization of one action potential assures that the neighboring region of the neuron will be depolarized above threshold, triggering a new action potential, and so on…

  22. “Saltatory Conduction”

  23. SYNAPSE: junction between a neuron and another cell; found between: -2 neurons -sensory receptor & sensory neuron -motor neuron & muscle cell -neuron & gland cell

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