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Unit 17: Nervous Control

Chapter 15 Nervous & Chemical Control (sec. 1 & 2). Unit 17: Nervous Control. The Role of the Nervous System. What is the nervous system? a system that lets an animal detect changes & respond to them nerve cells, sense organs, & brain

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Unit 17: Nervous Control

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  1. Chapter 15 Nervous & Chemical Control (sec. 1 & 2) Unit 17: Nervous Control

  2. The Role of the Nervous System • What is the nervous system? • a system that lets an animal detect changes & respond to them • nerve cells, sense organs, & brain • Which characteristic of life is an organism’s nervous system related to? • response to stimuli

  3. The Human Nervous System • How many parts is the human nervous system divided into? • two • 1. central nervous system (CNS) • brain • spinal cord • 2. peripheral nervous system (PNS) • body nerves

  4. 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. cerebrum cerebellum medulla (brain stem) spinal cord

  5. How do the PNS & CNS Work Together in Nervous Response? • Detectionof stimulus by sensory receptors • Transmission of impulse along nerve (PNS) • Interpretation & analysisof impulses in control center (CNS) • Transmission of impulse along nerve (PNS) • Responseby effector • muscle, gland, organ

  6. Nerves • What is a nerve? • many neurons bundled together • can be compared to a cable bundle of neurons

  7. Neurons • What is a neuron? • specialized cell that transmits nerve impulses (carries messages) through the body • can compare to electrical wires

  8. Neurons • What are the main parts of a neuron? • dendrites • receive impulses & move them toward cell body • cell body (soma) • nucleus & cytoplasm • axon • carries impulses awayfrom cell body towards end branch • terminal buttons/end branch of axon • help send impulses to next neuron or effector (muscle, organ, gland) Terminal buttons/ end branch of axon

  9. Neurons • What are the other parts of a neuron? • myelin sheath • fatty layer surrounding axon that protects it & allows impulses to move quickly • Schwann cells • make myelin • Nodes of Ranvier • sections of axon between Schwann cells not covered in myelin sheath • help transport impulses quickly

  10. Neurons Direction of impulse cell body (soma) Dendrites terminal buttons/ end branch of axon

  11. The Pathway of Impulses • How do messages move along a neuron? • an electrical charge moves along the axon • in one direction from dendrites to the end branch of the axon • So, there are 2 different pathways… • sensory receptor to control center • control center to effector (muscle, gland, organ)

  12. The Pathway of Impulses • Do neurons touch each other? • No, they are separated by a synapse. • small, fluid-filled space • between end branch of axon (of one neuron) and dendrites of next neuron • So, how do messages get from one neuron to the next? • neurotransmitters • chemical messengers that help impulse cross synapse

  13. The Pathway of Impulses Stimulus Sensory neuron • What are the types of neurons involved in the pathway of impulses? • sensory neurons • transmit incoming impulses (stimuli) • from receptors to control center • interneurons • transfer impulses within control centers (brain & spinal cord) • from sensory to motor neurons • motor neurons • transmit outgoing impulses • from control center to effectors • muscles, glands, organs interpretation interneuron response Motor neuron

  14. Reflexes • What is a reflex? • involuntary/automatic response to stimuli • Involve CNS, but does NOT require conscious control or decision making b/c determined by fixed pathways • some through brain (ex. blinking) • others through spinal cord (ex. touch cactus & respond) • known as reflex arc interneuron

  15. 5 Steps of the Reflex Arc & the Initial Response Reflex Arc Animation Reflex Arc Animation 2 • Reflex arc • Receptors detect stimulus & are activated • Sensory neuron transmits impulse towards spinal cord • Impulse crosses synapse to interneuron in spinal cord • From spinal cord impulse crosses synapse to motor neuron & leaves spinal cord • Impulse activates effectors (muscle, gland, organ) which responds appropriately • Does NOT involve brain

  16. 5 Steps of the Reflex Arc & the Initial Response 2. Sensory neuron transmits impulse towards spinal cord 1. Sensory receptor receives stimulus & is activated. interneuron 3. Impulse crosses synapse into interneuron in spinal cord where interpreted & analyzed 5. Impulse received by effector (which responds appropriately) • 4. impulse crosses synapse from spinal cord motor neuron & leaves spinal cord

  17. Reflex Arc Interneuron = association nerve

  18. The Secondary Response: After the Reflex Arc • 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/ the brain • This path is slower than the reflex arc • So, brain becomes aware of what has happened after your body has already responded. • secondary response… You yell, “Ouch!”

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