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Unit 12: Nervous Control

Chapter 25. Unit 12: Nervous Control. The Role of the Nervous System. Which characteristic of life is an organism’s nervous system related to?. Nervous Response. 4 requirements before nervous response can occur: Detection of stimulus by sensory receptors

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Unit 12: Nervous Control

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  1. Chapter 25 Unit 12: Nervous Control

  2. The Role of the Nervous System • Which characteristic of life is an organism’s nervous system related to?

  3. Nervous Response • 4 requirements before nervous response can occur: • Detection of stimulus by sensory receptors • Transmission of impulse along neurons • Interpretation & analysis of impulses in coordination center • brain or spinal cord • Response by effectors • muscles or glands

  4. Nerve Tissue • Nerve • many neurons bundled together • Neurons • specialized cells that transmit nerve impulses through body • different types • sensory neurons • interneurons • motor neurons

  5. Different Types of Neurons • Sensory neurons • transmit impulses from receptors to coordination center • Interneurons • transfer impulses from sensory to motor neurons • in brain & spinal cord • Motor neurons • transmit outgoing impulses to effectors

  6. Neuron Structure • dendrites • conduct impulses toward cell body • cell body • resembles other types of cells • contains nucleus & cytoplasm • axon • carries impulses away from cell body • often covered with myelin sheath end branch

  7. Neuron Structure dendrites terminal buttons (end branch) nucleus cytoplasm cell body (soma) nodes of Ranvier axon myelin sheath

  8. Transmitting Impulses Along a Neuron • nerve impulse or “action potential” • results from changes in ion concentration inside/outside neuron plasma membrane

  9. Transmitting Impulses from Neuron to Neuron • between each neuron is a synapse • small fluid-filled space • neurotransmitters (chemicals) help impulse across synapse

  10. Nervous Systems • In bilaterally symmetrical animals the nervous system is divided into 2 parts • central nervous system (CNS) • peripheral nervous system (PNS)

  11. Coordination between the PNS & the CNS • receptors in PNS gather info about animal’s environment • impulses along the PNS’s sensory neurons travel to CNS • in CNS(brain & spinal cord) impulses are interpreted & analyzed • impulses leaving CNS by motor neurons of PNS are carried to effectors • which carryout response

  12. 3 Major Parts of the Brain • cerebrum • speech, reasoning, emotions • cerebellum • controls balance, posture, muscle tone • medulla (oblongata) • controls involuntary actions of internal organs • heart rate, breathing rate, peristalsis, etc.

  13. What are reflexes? • reflexes = involuntary/automatic responses to stimuli • Involve CNS, but require no conscious control or decision making b/c determined by fixed pathways • some through brain (ex. blinking) • others through spinal cord (ex. touch hot iron & respond)

  14. Reflexes: Initial Response & Reflex Arc Reflex Arc Animation Reflex Arc Animation 2 • Reflex arc • Receptors activated • Sensory neuron transmits impulse towards spinal cord • Impulse crosses synapse to interneuron in spinal cord • Impulse crosses synapse to motor neuron & leaves spinal cord • Impulse activates effectors which respond appropriately • Does NOT involve brain

  15. 1. Sensory receptor activated (receives stimulus) 2. Sensory neuron transmits impulse towards spinal cord 4. motor neuron transmits impulse away from spinal cord 3. Impulse crosses synapse into interneuron where interpreted & analyzed 5. Impulse received by effector (which responds appropriately)

  16. Reflex Arc Interneuron = association nerve

  17. Reflexes: Secondary Response • Since reflex actions (arcs) don’t involve the brain, how does your brain become aware? • Some spinal cord interneurons that receive sensory impulses connect w/ other neuron pathways leading to the brain • Brain becomes aware of what has happened • Secondary response occurs • You yell, “Ouch!”

  18. Comparison of Nervous Systems

  19. Nervous Systems in Unicellular Organisms • Euglena • Light-sensitive structure under the “eye-spot” • Allows Euglena to swim in direction of light • Paramecium • Can respond to obstacles in path • Turns 30 & moves forward again… • Continues to do this until passes object • Seems to be mainly under chemical control

  20. Nervous Systems in Invertebrates • Radially symmetrical organisms have no center for nervous control • Many short neurons form nerve net • No definite nerve pathways • Ex. Hydra • Bilaterally symmetric animals have a primitive control center(s) (ganglia) & specific nerve pathways • Ex. Planaria

  21. Nervous Systems in Invertebrates • Other bilaterally symmetric animals also have brains • Ex. earthworm • cerebral ganglia (slightly larger ganglia) • Ex. grasshopper • Brain divided into specialized areas • protocerebrum • deutocerebrum

  22. Nervous System in Fish • Lateral line system • can sense the slightest movements (vibrations) in water • Electrical sense • Ampullae of Lorenzini • sense changes in electrical fields

  23. Questions to Ponder& Extras • How do we see unity within diversity in relation to nervous control??? • How does form follow function??? • Kid’s Health website • http://kidshealth.org/PageManager.jsp?lic=1&article_set=59295&cat_id=20607

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