Chapter 23: Nervous and Motor Systems

1. Chapter 23: Nervous and Motor Systems Actions, reactions, sensations, and addictions: meet your nervous system Lecture by Danielle DuCharme, Waubonsee Community College

2. Learning Objectives • By the end of this chapter, you should be able to: • Define what the nervous system is • Describe how neurons work • Show how our senses detect and transmit stimuli

3. Learning Objectives • By the end of this chapter, you should be able to: • Understand how the muscular and skeletal systems generate movement. • Diagram brain structure and associated function. • Comprehend the effects of drugs on the body.

5. Heritable Sensory Autonomic Neuropathy • Gabby Gringas feels no pain. • Instead of being a benefit, this condition fails to alert Gabby of a dangerous situation. • Feeling pain is a necessary part of being a living animal.

6. The Nervous System The nervous system is a network of cells that collects information about the organism’s internal and external environments, processes that information, and sends signals to effectors, muscles, and glands that are capable of responding to the information.

7. The Nervous System Has Three Critical Features • Receives input from the surrounding world. 2. Processes that information. 3. Initiates responses to the environment when necessary.

8. Take-home message 23.1 • Present in all multicellular animals other than sponges, the nervous system is a network of cells that collects information about the organism’s internal and external environments, processes that information, and sends signals to muscles and glands in response to the information.

9. 23.2 Neurons are the building blocks of all nervous systems. • In all vertebrates, the nervous system is divided into two components: • The peripheral nervous system • The central nervous system

10. Peripheral Nervous System • Network of sensory cells that receive information from the environment and… • the cells that transmit signals to effectors, the organism’s muscles and glands.

11. Central Nervous System • Made of the spinal cord and the brain. • The central nervous system processes information that it receives from sensory cells about the organism’s surroundings and sends out instructions to other nervous tissue to act in response.

12. The Neuron • The type of cell specialized for carrying electrical signals • The building block of all nervous systems

13. Nerves • Nerves are comprised of neurons bundled together with connective tissue. • These structures connect us to our world by enabling us to sense light, sound, touch, tastes, and smells.

14. Parts of a Neuron • The cell body contains all of the typical machinery of a eukaryotic cell. • Neurons have two specialized structures: • the dendrite • the axon

15. The Dendrite The dendrite senses and responds to stimulation from outside the cell and sends that information toward the cell body of the neuron.

16. The Axon The axon is a tube-like extension of the main cell body that transmits the signals picked up by the dendrite to the rest of the organism’s body.

17. Glial Cells These non-neuronal cells function like a support staff to protect, insulate, and nourish the neurons.

18. Neurons Come in Three Types • Sensory Neurons • Motor Neurons • Interneurons

19. Overview of the Nervous System

20. Reflexes Some signals bypass the central nervous system and travel directly from sensory neurons to the spinal cord, where they connect directly with motor neurons. This is called a reflex.

21. Take-home message 23.2 • In all vertebrates, the nervous system is divided into the peripheral nervous system and the central nervous system. • The neuron is a type of cell specialized for carrying electrical signals and is the building block of all nervous systems.

22. Take-home message 23.2 • Each neuron is very small, but groups of neurons bundled together enable us to sense light, sound, touch, tastes, and smells and to respond to them.

24. 23.3 Dendrites receive external stimuli. • This occurs in two ways: • Motor neurons and interneurons generally connect with and receive signals from other neurons. • Sensory neuron dendrites, on the other hand, are modified to respond to a specific external stimulus such as a touch or sound, light, or a chemical.

25. Dendrite Action

26. Action Potential • At the cell body, signals from all of the dendrites of the neuron converge. • The cell body then integrates them. • If the sum total of signals coming in is positive, then the neuron initiates an action potential, an electrical signal that travels down its axon.

27. Gradations of Sensation The intensity of the sensation an individual feels is modulated by the number of neurons that fire as a result of the stimulation.

28. Take-home message 23.3 • Dendrites receive external stimuli in one of two ways.

29. Take-home message 23.3 • Dendrites on motor neurons and interneurons generally connect with and receive signals from other neurons. • Sensory neuron dendrites are modified to respond to a specific external stimulus such as a touch or sound, light, or a chemical.

30. 23.4 The action potential propagates a signal down the axon. In response to an action potential, axon terminals release the contents of vesicles into the extracellular matrix, potentially influencing adjacent cells.

31. The Axon

32. Myelin Sheaths Axons are insulated, by a fatty coating called the myelin sheath, preventing the action potential from weakening as it travels down the axon.

33. The Lack of Myelin • The lack of myelin on an axon can be seen in babies when they first start trying to walk. • At that time, myelin hasn’t completely formed around all of their axons and their gross motor control isn’t very good.

34. Take-home message 23.4 • Each neuron has one axon, a projection that leaves the cell body and can extend several feet or more. • At its end, an axon branches into numerous axon terminals (terminal buttons), positioned close to a muscle cell or gland or the dendrites of another neuron.

35. Take-home message 23.4 • In response to an action potential, the axon terminals release chemicals into the extracellular matrix, potentially influencing adjacent cells.

36. At the Synapse, Neurons Interact with Other Cells • The end of an axon—the axon terminal or terminal button—is always right next to another neuron or a muscle cell or a gland. • The point where they meet is called a synapse.

37. At the Synapse, Several Things Occur… • Sacs called vesicles release neurotransmitters into the synaptic cleft. 2. The neurotransmitter diffuses to nearby receptor sites.

38. At the Synapse, Several Things Occur… 3.The neurotransmitter attaches to postsynaptic receptors. 4. Gates open in the postsynaptic cell membrane.

39. At the Synapse, Several Things Occur… 5.Open gates enable the signal to pass to the postsynaptic cell. 6. Neurotransmitter is released from the postsynaptic cell receptors. 7. Neurotransmitter is recycled or broken down.

40. The Synapse

41. Like Call Screening for Your Brain Why would it be useful to inhibit activity and effectively block information from being passed along? • This option is not just useful, but essential to the nervous system’s capacity to control which signals get through.

42. Continual Stimulation • With continuous stimulation, too, most neurons gradually reduce the amount of neurotransmitter they release, and thus reduce the strength of the signal.

43. Take-home message 23.5 • At the synapse, a neuron interacts with other cells.

44. Take-home message 23.5 • In response to an action potential, neurotransmitters are released into the synaptic cleft, diffuse, and may bind to receptors on an adjacent neuron, muscle cell, or gland, potentially stimulating an action potential, muscle contraction, or secretion.

45. Take-home message 23.5 • Neurotransmitters may then be taken back in by the axon terminal or enzymatically broken down in the synaptic cleft.

46. 23.6 There are many types of neurotransmitters. About 25 neurotransmitters have been identified, each of which has a sort of personality based on its specific actions.

47. Neurotransmitters Four neurotransmitters are particularly important: 1.Acetylcholine 2. Glutamate 3. Dopamine 4. Serotonin

48. Acetylcholine • Acetylcholine is the neurotransmitter released by motor neurons at the point where they synapse with muscle cells. • When enough acetylcholine binds to a muscle cell, the muscle contracts.

49. Curare Curare works by blocking the receptor sites where acetylcholine binds to muscle cells. • Once it gets into an animal’s system, curare causes death from asphyxiation, because it makes it impossible for the skeletal muscles to contract.

50. Glutamate • This is an excitatory neurotransmitter. • It appears to be involved with learning and memory.