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2. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep

3. Chapter 49 Nervous System and Sense Organs Table of Contents Section 1 Neurons and Nerve Impulses Section 2 Structure of the Nervous System Section 3 Sensory Systems Section 4 Drugs and the Nervous System

4. Section 1 Neurons and Nerve Impulses Chapter 49 Objectives • Describethe structure of a neuron. • Summarizethe electrical and chemical conditions that characterize a resting potential. • Outlinethe electrical and chemical changes that occur during an action potential. • Explainthe role of neurotransmitters in transmitting a signal across a synapse.

5. Section 1 Neurons and Nerve Impulses Chapter 49 Neuron Structure • A neuron, or nerve cell, is made up of a cell body, dendrites, and axons. • A cell body is the nucleus of a neuron and most of its organelles. • Dendrites extend from the cell body and are covered by a membrane. • The axon is a long membrane-bound projection that transmits information away from the cell body in the form of electrical signals.

6. Section 1 Neurons and Nerve Impulses Chapter 49 Structure of a Neuron

7. Section 1 Neurons and Nerve Impulses Chapter 49 Parts of a Neuron Click below to watch the Visual Concept. Visual Concept

8. Section 1 Neurons and Nerve Impulses Chapter 49 Neuron Structure, continued • The electrical signals that transmit information away from the cell body are called action potentials. • The end of an axon is called an axon terminal. • Axons are covered by a lipid layer called a myelin sheath. • The myelin sheath insulates the neuron which speeds up the transmission of action potentials along the axon.

9. Section 1 Neurons and Nerve Impulses Chapter 49 Neuron Structure, continued • The signaling activity of the nervous system is made up of electrical activity within neurons and chemical flow between neurons. • Neurons communicate with each other at special junctions called synapses. • These synapses do not communicate by touch, but by releasing chemicals, or neurotransmitters, into a gap between the synapses called the synaptic cleft. • The synaptic cleft is a small gap between the axon terminal and the receiving cell.

10. Section 1 Neurons and Nerve Impulses Chapter 49 Nerve Impulses • A neuron, like all other cells, has a membrane potential. • A membrane potential is a difference in the electrical charge across a cell membrane. • A membrane potential can change with an addition or removal of ions within the cell. • Ions move in and out of the cell by passing through proteins that act as ion channels. Whether the ion channels are open or closed affects the membrane potential.

11. Section 1 Neurons and Nerve Impulses Chapter 49 Nerve Impulses, continued • Resting Potential • A neuron is at rest when it is not sending or receiving a signal. • When at rest, the neuron is more negatively charged on the inside than on the outside of the cell body. • The electric potential across the cell membrane when the neuron is at rest is called the resting potential.

12. Section 1 Neurons and Nerve Impulses Chapter 49 Nerve Impulses, continued • Action Potential • When a dendrite or cell body is stimulated, the permeability of the neuron’s membrane changes suddenly. • The membrane potential reverses and the neuron’s cell body becomes more positively charged than the exterior of a cell. • This reverse in polarity begins an action potential.

13. Section 1 Neurons and Nerve Impulses Chapter 49 Nerve Impulses, continued • Action Potential, continued • After the first segment of the neuron is stimulated the segment next to the first will become stimulated. • The action potential will continue away from the cell body. • Soon after being stimulated, the interior of the neuron begins to become more and more negative. • This signals the end of the action potential.

14. Section 1 Neurons and Nerve Impulses Chapter 49 Nerve Impulses, continued • Action Potential, continued • A neuron cannot generate another action potential until it has returned to its resting potential. • The period in which a neuron cannot send a signal is called the refractory period. • Returning the neuron to its resting potential requires energy.

15. Section 1 Neurons and Nerve Impulses Chapter 49 Conduction of a Nerve Impulse

16. Section 1 Neurons and Nerve Impulses Chapter 49 Action Potential Click below to watch the Visual Concept. Visual Concept

17. Section 1 Neurons and Nerve Impulses Chapter 49 Communication Between Neurons • Once an action potential reaches the axon terminal, it releases neurotransmitters into the synaptic cleft. These neurotransmitters bind to receptors proteins and open the ion channels of the new neuron cell. • If enough ion channels are opened, the action potential will continue through the new neuron. If not, the nervous signal will be terminated. • After the neurotransmitters have opened the ion channels, they will be cleared out of the synaptic cleft by being reabsorbed by the neuron that released them or broken down by enzymes.

18. Section 1 Neurons and Nerve Impulses Chapter 49 Synaptic Transmission

19. Section 1 Neurons and Nerve Impulses Chapter 49 Release of Neurotransmitter Click below to watch the Visual Concept. Visual Concept

20. Section 2 Structure of the Nervous Systems Chapter 49 Objectives • Identifythe two main parts of the central nervous system. • Summarizethe functions of the major parts of the brain. • Describethe roles of the sensory and motor divisions of the peripheral nervous system. • Distinguishbetween the somatic and autonomic nervous systems.

21. Section 2 Structure of the Nervous Systems Chapter 49 Organization of the Nervous System • The nervous system includes two major divisions. • The first division is the central nervous system and is made up of the brain and the spinal cord. • The brain is the control center of the nervous system. • The spinal cord carries nerve signals between the body and the brain.

22. Section 2 Structure of the Nervous Systems Chapter 49 Structure of the Human Brain

23. Section 2 Structure of the Nervous Systems Chapter 49 Parts of a Human Brain Click below to watch the Visual Concept. Visual Concept

24. Section 2 Structure of the Nervous Systems Chapter 49 Organization of the Nervous System, continued • The second division is the peripheral nervous system and consists of neurons that have cell bodies and that are not included in the brain and spinal cord. • Peripheral neurons send information to and from the central nervous system.

25. Section 2 Structure of the Nervous Systems Chapter 49 Brain • Cerebrum • The cerebrum is the upper part of the brain that receives sensation and controls movement. • Thecerebrum is made of two hemispheres, called the cerebral hemispheres. • Each hemisphere is made up of four lobes, called the frontal, parietal, temporal, and occipital.

26. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Cerebrum, continued • The folded outer layer of the cerebrum is called the cerebral cortex. • The cerebral cortex is the portion of the cerebrum that controls higher mental functions, general movement, organ function, perception, and behavioral reactions. • The many folds of the cerebral cortex allow the brain to have a large surface area and still fit into the skull.

27. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Cerebrum, continued • The cerebral cortex is called gray matter. Beneath the gray matter is white matter. • White matter is made up of myelinated axons, which link specific regions of the cortex with each other and with other neural centers.

28. Section 2 Structure of the Nervous Systems Chapter 49 Cerebrum Click below to watch the Visual Concept. Visual Concept

29. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Diencephalon • This section of the brain is made up of two parts, the thalamus and hypothalamus. • The thalamus directs most incoming sensory signals to the proper region of the cerebral cortex. • The hypothalamus helps maintain homeostasis and directly controls most of the body’s hormone production.

30. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Brian Stem • This section of the brain is made up of three parts: the midbrain, pons, and medulla oblongata. • The midbrain relays visual and auditory information. • The pons relays communications between the cerebral hemispheres and the cerebellum.

31. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Brian Stem, continued • The last section of the brain stem is the medulla oblongata. The medulla oblongata serves as both a relay center and a control center for heart rate, respiration rate, and other homeostatic activities. • The brain stem also has a network of neurons called the reticular formation. This section of the brain stem helps control respiration and circulation and helps separate signals that are important from those that are not.

32. Section 2 Structure of the Nervous Systems Chapter 49 Brain Stem Click below to watch the Visual Concept. Visual Concept

33. Section 2 Structure of the Nervous Systems Chapter 49 Brain, continued • Cerebellum • The cerebellum lies below and behind the cerebral hemispheres and helps to coordinate muscle action. • The cerebellum receives sensory impulses from muscles, tendons, joints, eyes, and ears and other brain centers.

34. Section 2 Structure of the Nervous Systems Chapter 49 Cerebellum Click below to watch the Visual Concept. Visual Concept

35. Section 2 Structure of the Nervous Systems Chapter 49 Spinal Cord • The spinal cord is a column of nervous tissue that starts at the medulla oblongata and runs throughout the vertebral column. • The spinal cord is composed of white and gray matter.

36. Section 2 Structure of the Nervous Systems Chapter 49 Parts of a Human Spinal Cord Click below to watch the Visual Concept. Visual Concept

37. Section 2 Structure of the Nervous Systems Chapter 49 Peripheral Nervous System • The central nervous system interacts with the peripheral nervous system through nerves. • Nerves are bundled axons and dendrites of many neurons. Spinal nerves are made up of both a dorsal and ventral root. • The dorsal roots carry signals into the central nervous system from sensory receptors. • The sensory receptors are neurons that are specialized to detect stimuli such as light, pressure, and heat.

38. Section 2 Structure of the Nervous Systems Chapter 49 Peripheral Nervous System, continued • The peripheral nervous system also contains ventral roots. Ventral roots contain the axons of motor neurons. • Motor neurons are neurons that carry information from the central nervous system to muscles and glands. • Interneurons can also be found in both sections of the nervous system. Interneurons can relay information between other neurons.

39. Section 2 Structure of the Nervous Systems Chapter 49 Peripheral Nervous System

40. Section 2 Structure of the Nervous Systems Chapter 49 Sensory Division • The sensory division of the peripheral nervous system contains sensory receptors and the interneurons that connect them to the central nervous system. • Sensory receptors receive information from the body’s external and internal environments.

41. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division • The motor division of the peripheral nervous system allows the body to react to sensory information. • The motor division of the peripheral nervous system is made up of the somatic nervous system and the autonomic nervous system.

42. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division, continued • Somatic Nervous System • The somatic nervous system contains motor neurons that control the movement of skeletal muscles. • The somatic system is considered voluntary, but can operate without conscious control.

43. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division, continued • Somatic Nervous System, continued • Somatic system also relays the signals in reflexes. • Reflexes are involuntary and often self-protective movements. An example is the patellar, or knee-jerk, reflex. • The patellar reflex is an example of a spinal reflex, which involves only neurons in the body and bypasses the brain.

44. Section 2 Structure of the Nervous Systems Chapter 49 Knee-Jerk Response

45. Section 2 Structure of the Nervous Systems Chapter 49 Reflex Click below to watch the Visual Concept. Visual Concept

46. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division, continued • Autonomic Nervous System • The autonomic nervous system controls internal body conditions by regulating smooth muscles in blood vessels and organs. • The autonomic system is considered involuntary, and can be broken up into two subdivisions.

47. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division, continued • Autonomic Nervous System, continued • The first subdivision of the autonomic nervous system is the sympathetic division. • The sympathetic division prepares the body when activated by physical or emotional stress. • For example, pupils dilate and heart rate increases.

48. Section 2 Structure of the Nervous Systems Chapter 49 Motor Division, continued • Autonomic Nervous System, continued • The second subdivision of the autonomic nervous system is the parasympathetic division. • The parasympathetic division controls the internal environment during routine conditions. • For example, pupils constrict and heart rate decreases.

49. Section 2 Structure of the Nervous Systems Chapter 49 Physiological Effects of the Autonomic Nervous System

50. Section 2 Structure of the Nervous Systems Chapter 49 Comparing the Somatic and Autonomic Nervous Systems Click below to watch the Visual Concept. Visual Concept