Nerve pathways


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Nerve pathways

  1. 1. Nerve Pathways Chapter 9: Nervous System Unit 3: Integration and Coordination
  2. 2. Nerve Pathways <ul><li>Nerve Pathways are the routes nerve impulses follow as they travel through the nervous system. </li></ul><ul><ul><li>Nerve pathways that require only a few neurons are called Reflex Arcs . </li></ul></ul><ul><ul><ul><li>Reflex arcs are the structural and functional basis for involuntary actions called Reflexes . </li></ul></ul></ul>
  3. 3. Parts of the Reflex Arc <ul><li>The reflex arc consists of the following structural components: </li></ul><ul><ul><li>Receptor </li></ul></ul><ul><ul><li>Sensory neuron </li></ul></ul><ul><ul><li>Interneuron </li></ul></ul><ul><ul><li>Motor neuron </li></ul></ul><ul><ul><li>Effector </li></ul></ul>
  4. 4. Reflex Arcs in General <ul><li>Receptors sense specific types of internal or external change. </li></ul><ul><ul><li>Sensory Fibers send this information to Interneurons found within the CNS </li></ul></ul><ul><ul><ul><li>Interneurons communicate with Motor Neurons whose fibers pass outward from the CNS. </li></ul></ul></ul><ul><ul><ul><ul><li>Effectors respond to stimulation by motor neurons and produces reflex or behavioral action. </li></ul></ul></ul></ul>
  5. 5. Reflex Behavior <ul><li>Reflexes are automatic subconscious responses to changes within or outside the body. </li></ul><ul><ul><li>Maintain homeostasis by controlling involuntary processes: </li></ul></ul><ul><ul><ul><li>Heart rate, breathing rate, blood pressure, and digestion. </li></ul></ul></ul><ul><ul><li>Also carry out automatic processes: </li></ul></ul><ul><ul><ul><li>Swallowing, sneezing, coughing, and vomiting </li></ul></ul></ul>
  6. 6. Patella Tendon Reflex <ul><li>This reflex employs only two neurons </li></ul><ul><ul><li>A sensory neuron communicating directly with a motor neuron. </li></ul></ul><ul><ul><ul><li>The knee-jerk reflex helps to maintain upright posture. </li></ul></ul></ul><ul><ul><ul><ul><li>If the knee begins to bend (force of gravity) while the person is standing still: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>The quadriceps femoris group is stretched </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>The reflex is triggered </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>The leg straightens out again </li></ul></ul></ul></ul></ul>
  7. 7. Events of the Knee-Jerk Reflex <ul><li>Strike the patella ligament </li></ul><ul><li>Quadriceps femoris grouping (attached to the patella by a tendon) is pulled slightly </li></ul><ul><li>Stretch stimulates stretch receptors within the muscles </li></ul><ul><li>Impulse travels along sensory neuron into the spinal cord </li></ul>
  8. 8. Events Continued <ul><li>Sensory neuron forms a synapse with a motor neuron in the spinal cord </li></ul><ul><li>Impulse continues along the motor neuron </li></ul><ul><li>Impulse reaches the quadriceps femoris group </li></ul><ul><li>Muscle group contracts in response, and the leg extends </li></ul>
  9. 10. Withdrawal Reflex <ul><li>The Withdrawal Reflex occurs when a person unexpectedly touches a body part to something painful. </li></ul><ul><ul><li>A protective measure because it limits tissue damage caused by touching something harmful. </li></ul></ul><ul><ul><ul><li>This reflex employs three types of neurons: </li></ul></ul></ul><ul><ul><ul><ul><li>Sensory Neuron </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Interneuron (within the reflex center) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Motor Neuron </li></ul></ul></ul></ul>
  10. 11. Withdrawal Reflex <ul><li>Skin receptors are activated </li></ul><ul><li>Skin receptors send information to sensory neuron </li></ul><ul><li>Sensory impulses are sent to the spinal cord </li></ul><ul><li>Impulse passes to an interneuron in the reflex center </li></ul>
  11. 12. Withdrawal Reflex Continued <ul><li>The interneuron directs the impulse to the motor neurons </li></ul><ul><li>Motor neurons transmit signals to flexor muscles in the injured part, and the muscle contracts in response </li></ul><ul><li>Antagonist extensor muscles are inhibited </li></ul>