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The Nervous System & Neurons

The Nervous System & Neurons. Unit 8 Chapter 35-2. Overview of the Nervous System. STRUCTURES: brain , spinal cord , & peripheral nerves FUNCTION: Recognizes and coordinates the body ’ s response to changes in its internal and external environments. Overview of the Nervous System.

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The Nervous System & Neurons

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  1. The Nervous System & Neurons Unit 8 Chapter 35-2

  2. Overview of the Nervous System • STRUCTURES: brain, spinal cord, & peripheral nerves • FUNCTION: Recognizes and coordinates the body’s response to changes in its internal and external environments

  3. Overview of the Nervous System • The ultimate control of all the organ systems is done by the nervous system.

  4. A. Neurons • Neurons are nerve cells that carry electrical impulses through the body • Impulse = message • Neurons are classified according to the direction an impulse travels.

  5. 3 Types of Neurons • 1. Sensory: carry impulses from sense organs to the brain • 2. Motor: carry impulses from the brain to muscles & glands • 3. Interneurons: connect sensory and motor neurons and process impulses

  6. Interneuron Sensory Neuron Motor Neuron

  7. Reflex Arc Sensory Neuron Interneuron Motor Neuron

  8. Nucleus Dendrites Axon terminals Cell body Myelin sheath Axon Nodes • Structure of a Neuron

  9. 1. Dendrites: receive impulses

  10. 2. Cell body: contains nucleus & cytoplasm, largest part of cell

  11. 3. Axon: transmit impulses away from cell body

  12. 4. Myelin Sheath: covering that insulates the axon, sending the impulse faster and gives axon a whitish appearance • Neurons with axons that have myelin make up “white matter” in the brain, while neurons without myelin are called “gray matter”

  13. 5. Nodes: gaps in the myelin sheath where membrane is exposed • Impulses jump from one node to the next

  14. 6. Axon terminals: transmits impulse (message) to next cell

  15. II. Transmission of an Impulse • A nerve impulse is an electrical message. • At rest, no impulse is being sent. • The neuron must be stimulated (receive input) to send a impulse.

  16. + + - - - - + + A. Resting Neuron • STEP 1: At rest, the neuron is not transmitting an impulse • inside of cell has a net negative charge – • outside of cell has a net positive charge + • The cell membrane has Membrane Potential, the potential to carry an electrical current because there is a difference in charge • The ions sodium (Na+) and potassium (K +) cause the potential

  17. (K+)

  18. Sodium-potassium pumps in the nerve cell membrane pumps sodium (Na+)ions out of the cell and potassium (K+)ions into the cell by means of active transport. • As a result, the inside of the cell contains more K+ ions and fewer Na+ ions than the outside.

  19. B. Stimulated Neuron • STEP 2: An impulse begins when a neuron is stimulated by another neuron or the environment • The stimulated impulse must reach threshold, the minimum impulse strength needed to create a new impulse (all or none)

  20. STEP 3: At the leading edge of the impulse, gates in the sodium channels open allowing positively charged sodium (Na+) ions to flow into the cell membane.

  21. This reversal of charges is called is called the nerve impulse or an ACTION POTENTIAL (AP)

  22. As the action potential passes, gates in the potassium channels open, allowing potassium (K+) ions to flow OUT of the cell • This restores the negative potential inside the axon.

  23. STEP 4: The AP jumps from node to node along the axon

  24. 1. 3. At Rest - - - - - - - - - - - - - - - - - + + - - - - - 4. 2. Action Potential + + - - - - - - - - - - - - - - - - - - - + + - STEP 5: The AP continues along the axon in one direction to the axon terminals.

  25. Action Potential

  26. C. Synapse • Synapse: the space where the axon terminal of one neuron can transfer an impulse to another neuron (or cell) • The small space between cells is the synaptic cleft • Axon terminals contain vesicles filled with neurotransmitter

  27. Neurotransmitters (NTs) are chemical signals of neurons that transmit an impulse across the synapse to another cell • NTs fit like a lock and key with receptors

  28. Steps of Transmission • STEP 6: Action Potential reaches axon terminal • STEP 7: Neurotransmitter is released from vesicles into synaptic cleft • STEP 8: Neurotransmitter binds to receptors on next neuron. • STEP 9: Channels open, which creates a new action potential in next neuron http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter45/animations.html#

  29. Re-uptake of NTs • Re-uptake: After the NT has done its job, it is taken back into the axon terminal so it can be used again or broken down.

  30. Types & Effects of Neurotransmitters • There are dozens of different NTs, but a few do most of the work. • Each NT fits with its own specific receptor. • It won’t cause a response without the right receptor Acetylcholine Serotonin dopamine EPI GABA Endorphins

  31. NTs can be excitatory or inhibitory • Excitatory NTs cause impulses in the next neurons • Inhibitory NTs stop an impulse from being sent in the next neuron • http://learn.genetics.utah.edu/content/addiction/reward/neurontalk.html

  32. Major NTs • 1) GABA – Inhibitory • Effects: Relaxation, calming, anti-anxiety, and sleep • Depressant drugs like heroin, marijuana, and alcohol intensify effects of GABA

  33. 2) Glutamate – Excitatory • Effects: Stimulates learning and memory formation • Some drugs can interfere with glutamate, causing short-term memories not to be formed

  34. 3) Dopamine – Excitatory • Effects: Pleasure, Euphoria, Reward-centers, addiction, positive reinforcement, movement and posture • Most addictive drugs (cocaine, PCP, heroin, opiates, marijuana, and amphetamines) work by flooding the synapse with dopamine

  35. 4) Serotonin – Excitatory • Effects: Sleep, mood, appetite, pain, body temperature • Low serotonin linked to depression, suicide, impulsive behavior, and aggression • Alcohol, stimulants, marijuana and hallucinogens alter serotonin levels

  36. 5) Endorphins – Excitatory & Inhibitory • Effects: alertness, blocks pain, happy (runner’s high), sexual arousal • Often released after physical activity • 6) Norepinephrine – Excitatory • Effects: alertness, energy, stress, sexual arousal

  37. 7) Acetylcholine – Excitatory • Effects: alertness, memory, muscle contraction, appetite, sexual arousal

  38. Effects of Drugs • Many prescription and illegal drugs can alter the brain’s chemistry. • Many drugs are agonists (enhancers) of certain NTs that cause many of the pleasurable sensations of drugs and lead to addiction. • Addiction: chemical dependency on a substance as a result of it altering the brain’s chemistry after repeated use.

  39. Ways Drugs interfere with Neurotransmission • 1) Increase number of impulses • 2) Release NT from vesicles with or without an impulse • 3) Block reuptake or block receptors • 4) Produce more or less NT • 5) Prevent vesicles from releasing NT

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