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Nervous System

Nervous System. Nervous system. Coordinates and regulates the function of all other body systems 2 major division Central Nervous System (CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Nerves carry sensory info to the CNS Motor commands from CNS to muscles.

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Nervous System

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  1. Nervous System

  2. Nervous system • Coordinates and regulates the function of all other body systems • 2 major division • Central Nervous System (CNS) • Brain • Spinal Cord • Peripheral Nervous System (PNS) • Nerves • carry sensory info to the CNS • Motor commands from CNS to muscles

  3. Basic Divisions of the Nervous System

  4. Nervous system • 2 types of cells • Neurons • transmit nerve impulses between parts of the nervous system • Neuroglia • Support and nourish neurons • Maintain homeostasis • Form myelin • Help in signal transmission

  5. Neurons • 3 types of neurons • Sensory neurons • Take messages to the CNS • Sensory receptors detect changes in the environment • Interneuron • Receive input from the sensory neurons before communicate to motor neuron • Motor neuron • Takes message away from CNS to rest of body (organ, muscle or gland)

  6. Fig. 17.1b brain sensory neurons sensory receptors motor neurons skeletal muscles other motor neurons smooth muscle cardiac muscle glands Central nervous system Peripheral nervous system

  7. Neurons • Anatomy of a neuron • Cell body • Dendrites • Receive signals from other neurons and send them to cell body • Axon • Conducts nerve impulses away from the cell body and send them toward other neurons

  8. Neurons • Myelin Sheath • Formed by Schwann Cells around the axon • Gaps between Schwan Cells are called nodes of Ranvier • Myelin Sheath gives nerves white colour • Helps protect and insulate the nerve • Helps conduct nerve impulse

  9. Neurons

  10. axon node of Ranvier myelin sheath

  11. Sensory neuron cell body direction of conduction node of Ranvier sensory receptor (in skin) axon dendrites

  12. axon cell body Interneuron dendrites axon terminal

  13. cell body dendrites Motor neuron node of Ranvier direction of conduction axon nucleus of Schwann cell (neuroglial cell) effector (muscle)

  14. cell body dendrites Motor neuron node of Ranvier direction of conduction axon cell body Interneuron effector (muscle) dendrites axonterminal cell body sensory receptor (in skin) direction of conduction node of Ranvier axon Sensory neuron dendrites

  15. Nerve impulse • Nervous system uses a nerve impulse to send information • When an axon is not conducting a nerve impulse we call it at resting potential • More negative inside the axon • Positive outside the axon

  16. Nerve impulse • Difference in polarity is due to ion concentration • More Na+ ions outside the axon • More K+ ions inside the axon • Sodium-potassium pumps • Actively transport Na+ out of axon and K+ into axon • 3 Na+ for every 2 K+

  17. reference electrode outside axon recording electrode Inside axon + + + + + + + + + +           axonal membrane +          + + + + + + + + inside axon K+ Na+ gated K+ channel gated Na+ channel outside axon a. Resting potential: more Na+ outside the axon and more K+ inside the axon causes polarization.

  18. Nerve Impulse • Action potential • Rapid change in polarity across the axon • Nerve impulse • During an action potential • DEPOLARIZATION • Sodium channels open up • Sodium enters the axon • Axon becomes more positive • REPOLARIZATION • Potassium gates open • K+ moves outside of axon • Axon returns to original negative charge

  19.  + + + + + + + + + +         direction of impulse + +           + + + + + + + + open Na+ channel b. Action potential be gins: depolarization occurs when Na+ gates open and Na+ moves inside the axon.

  20. + +           + + + + + + + + direction of impulse   + + + + + + + + + +         open K+ channel c. Action potential ends: repolarization occurs when K+ gates open and K+ moves outside the axon.

  21. Nerve Impulse • Refractory period • Returns K+ to the inside of cell and Na+ outside through pump • returning the neuron to its normal polarized state

  22. +60 +40 Na+ moves to inside axon K+ moves to outside axon action potential +20 repolarization depolarization 0 Voltage (mV) –20 threshold –40 resting potential –60 0 1 2 3 4 5 6 Time (milliseconds) d. An action potential can be visualized if voltage changes are graphed over time.

  23. Nerve impulse • https://www.youtube.com/watch?v=7EyhsOewnH4

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