2. The Nervous System Anatomy and Physiology

3. Nervous System Functions 1. Sensory-receptors gather information and pass it on toward the CNS 2. Integrative-in the spinal cord or brain, we put information together and make sense of it 3. Motor-carry impulses to effectors such as muscles and glands

4. Basic Structures Central nervous system (CNS) consists of brain and spinal cord only Peripheral nervous system (PNS) are nerves outside the CNS

5. Basic Structures Neurons are the nerve cells that can transmit the electrical impulse Neurons are surrounded by support cells called neuroglial cells There are 5 types of neuroglial cells

6. Neuron Structure Cell body with nucleus Dendrites: branching fibers that RECEIVE impulses Axon: long fiber that SENDS the impulse on

7. Neuron Structure Axon is often wrapped in cells called Schwann cells A Schwann cell has its own nucleus and is made of myelin Nodes of Ranvier are the spaces between Schwann cells

8. Types of Neurons Sensory neurons carry information from sensory receptors to the CNS (AFFERANT) Interneurons relay impulses within the CNS Motor neurons carry impulses from CNS to effectors ( EFFERENT)

9. Types of Neurons Bipolar: only two fibers—one dendrite and one axon Unipolar: single fiber from the cell body which splits into dendrite and axon Multipolar: many dendrites; one axon

10. Identify which neuron is unipolar, bipolar, and multipolar. Identify which is the sensory neuron, the interneuron, and the motor neuron

11. The Nerve Impulse The membrane of a resting neuron is POLARIZED This means that there is a different electrical charge on the outside of the membrane as compared to the inside

12. Resting Potential

13. More positive ions outside than inside Result of actively pumping out sodium ions (Na+) Potassium ions are also involved (K+) Three Na+ ions are pumped out for every two K+ ions pumped in.

14. Becoming Polarized

15. Sodium Potassium Pump

16. Resting Potential More positive outside the membrane than inside (POLARIZED) This charge difference is called a potential difference Holds potential energy which can be released in the form of an electrical impulse

17. Action Potential When stimulated, the membrane of the neuron opens the channels and lets the Na+ rush inside This is DEPOLARIZATION This releases the potential energy in the form of a current down the neuron membrane

18. Like a Wave Depolarization of one section stimulates the next section of membrane

19. Action Potential

20. Back to Resting Potential After the wave, or current, of depolarization has passed, ions are restored to resting potential This means Na+ are again pumped out, setting up a more positive charge outside the neuron

21. Odds and Ends Threshold must be reached to trigger depolarization Each nerve fiber has an ALL OR NONE RESPONSE

22. Reflex Arc Minimum of three neurons Sensory to inter to motor neuron Fastest responses go only to the spinal cord, not all the way to the brain

23. Reflex Arc

25. Reaction Time Is the time between stimulation and the beginning of the response Sensory neuron to interneurons in brain, then motor neuron

26. Reaction Time Can get shorter, as we practice Use the same pathway over and over Learned behavior

27. Bell Ringer Which nerve would be faster at transmitting an impulse: 2 mm in diameter, or 4.5 mm in diameter Which neuron would be faster at transmitting an impulse: one with Schwann Cells, or a bare axon with no Schwann cells How is multiple sclerosis related to Schwann cells?