1. The Nervous System

2. Functions of the Nervous System
Sensory input—gathering information
To monitor changes occurring inside and outside the body
Changes = stimuli
Integration
To process and interpret sensory input and decide if action is needed

3. Functions of the Nervous System
Motor output
A response to integrated stimuli
The response activates muscles or glands

4. Functions of the Nervous System
Figure 7.1

5. Structural Classification of the Nervous System
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Nerves outside the brain and spinal cord
Spinal nerves
Cranial nerves

6. Functional Classification of the Peripheral Nervous System
Sensory (afferent) division
Nerve fibers that carry information to the central nervous system
Motor (efferent) division
Nerve fibers that carry impulses away from the central nervous system
They activate muscles and glands

7. Organization of the Nervous System
Figure 7.2

8. Functional Classification of the Peripheral Nervous System
Motor (efferent) division (continued)
Two subdivisions
Somatic nervous system = voluntary
Autonomic nervous system = involuntary
Can be divided into sympathetic and parasympathetic

9. Nervous Tissue: Support Cells
Support cells in the CNS are grouped together as “neuroglia”
Function: to support, insulate, and protect neurons
Cells are called glial cells
Have special functions
Can’t transport impulses

10. Nervous Tissue: Support Cells
Astrocytes
Abundant, star-shaped cells
Brace neurons
Form barrier between capillaries and neurons
Control the chemical environment of the brain

11. Nervous Tissue: Support Cells
Figure 7.3a

12. Nervous Tissue: Support Cells
Microglia
Spiderlike phagocytes
Dispose of debris

13. Nervous Tissue: Support Cells
Figure 7.3b

14. Nervous Tissue: Support Cells
Ependymal cells
Line cavities of the brain and spinal cord
Circulate cerebrospinal fluid

15. Nervous Tissue: Support Cells
Figure 7.3c

16. Nervous Tissue: Support Cells
Oligodendrocytes
Wrap around nerve fibers in the central nervous system
Produce myelin sheaths

17. Nervous Tissue: Support Cells
Figure 7.3d

18. Nervous Tissue: Support Cells
Satellite cells
Protect neuron cell bodies
Schwann cells
Form myelin sheath in the peripheral nervous system

19. Nervous Tissue: Support Cells
Figure 7.3e

20. Nervous Tissue: Neurons
Neurons = nerve cells
Cells specialized to transmit messages
Major regions of neurons
Cell body—nucleus and metabolic center of the cell
Processes—fibers that extend from the cell body

21. Nervous Tissue: Neurons
Cell body
Nissl substance
Specialized rough endoplasmic reticulum
Neurofibrils
Intermediate cytoskeleton
Maintains cell shape

22. Nervous Tissue: Neurons
Figure 7.4

23. Nervous Tissue: Neurons
Cell body
Nucleus
Large nucleolus
Processes outside the cell body
Dendrites—conduct impulses toward the cell body
Axons—conduct impulses away from the cell body

24. Nervous Tissue: Neurons
Figure 7.4

25. Nervous Tissue: Neurons
Axons end in axonal terminals
Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from the next neuron by a gap
Synaptic cleft—gap between adjacent neurons
Synapse—junction between nerves

26. Nervous Tissue: Neurons
Myelin sheath—whitish, fatty material covering axons
Schwann cells—produce myelin sheaths in jelly roll–like fashion
Nodes of Ranvier—gaps in myelin sheath along the axon

27. Nervous Tissue: Neurons
Figure 7.5

28. Neuron Cell Body Location
Most neuron cell bodies are found in the central nervous system
Gray matter—cell bodies and unmyelinated fibers
Nuclei—clusters of cell bodies within the white matter of the central nervous system
Ganglia—collections of cell bodies outside the central nervous system

29. Multiple Sclerosis
Myelin sheath around nerve fiber is gradually destroyed
Converted to hardened sheaths called scelroses
Is an autoimmune disorder

30. Functional Classification of Neurons
Sensory (afferent) neurons
Carry impulses from the sensory receptors to the CNS
Cutaneous sense organs
Proprioceptors—detect stretch or tension
Motor (efferent) neurons
Carry impulses from the central nervous system to viscera, muscles, or glands

31. Functional Classification of Neurons
Figure 7.7

32. Functional Classification of Neurons
Interneurons (association neurons)
Found in neural pathways in the central nervous system
Connect sensory and motor neurons

33. Neuron Classification
Figure 7.6

34. Structural Classification of Neurons
Multipolar neurons—many extensions from the cell body
Figure 7.8a

35. Structural Classification of Neurons
Bipolar neurons—one axon and one dendrite
Figure 7.8b

36. Structural Classification of Neurons
Unipolar neurons—have a short single process leaving the cell body
Figure 7.8c

37. Functional Properties of Neurons
Irritability
Ability to respond to stimuli
Conductivity
Ability to transmit an impulse

38. Nerve Impulses Resting neuron The plasma membrane at rest is polarized
Fewer positive ions are inside the cell than outside the cell
Depolarization
A stimulus depolarizes the neuron’s membrane
A depolarized membrane allows sodium (Na+) to flow inside the membrane
The exchange of ions initiates an action potential in the neuron

39. Nerve Impulses
Figure 7.9a–b

40. Nerve Impulses Action potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon
Impulses travel faster when fibers have a myelin sheath

41. Nerve Impulses
Figure 7.9c–d

42. Nerve Impulses Repolarization
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
The sodium-potassium pump, using ATP, restores the original configuration

43. Nerve Impulses
Figure 7.9e–f

44. Transmission of a Signal at Synapses
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerve’s axon terminal
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
An action potential is started in the dendrite

45. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Figure 7.10

46. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Figure 7.10, step 1

47. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Vesicle fuses with plasma membrane
Ion channels
Transmitting neuron
Figure 7.10, step 2

48. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Figure 7.10, step 3

49. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Figure 7.10, step 4

50. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Ion channel opens
Figure 7.10, step 5

51. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Figure 7.10, step 6

52. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Figure 7.10, step 7

53. Impairment of Electrical Impulses
Sedatives and anesthetics block nerve impulses by altering membrane permeability to sodium ions

54. The Reflex Arc
Reflex—rapid, predictable, and involuntary response to a stimulus
Occurs over pathways called reflex arcs
Reflex arc—direct route from a sensory neuron, to an interneuron, to an effector

55. The Reflex Arc Figure 7.11a Stimulus at distal end of neuron Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a

56. The Reflex Arc Figure 7.11a, step 1 Skin
Stimulus at distal end of neuron
Skin
Receptor
(a)
Figure 7.11a, step 1

57. The Reflex Arc Figure 7.11a, step 2 Skin
Stimulus at distal end of neuron
Skin
Receptor
Sensory neuron
(a)
Figure 7.11a, step 2

58. The Reflex Arc Figure 7.11a, step 3 Skin Spinal cord
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Integration center
(a)
Figure 7.11a, step 3

59. The Reflex Arc Figure 7.11a, step 4 Skin Spinal cord
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a, step 4

60. The Reflex Arc Figure 7.11a, step 5 Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a, step 5

61. Simple Reflex Arc Figure 7.11b–c
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Synapse in ventral horn gray matter
Inter- neuron
Motor (efferent) neuron
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
Effector (biceps brachii muscle)
(b)
(c)
Figure 7.11b–c

62. Simple Reflex Arc Figure 7.11b, step 1
Sensory receptors (stretch receptors in the quadriceps muscle)
Spinal cord
(b)
Figure 7.11b, step 1

63. Simple Reflex Arc Figure 7.11b, step 2
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
(b)
Figure 7.11b, step 2

64. Simple Reflex Arc Figure 7.11b, step 3
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
(b)
Figure 7.11b, step 3

65. Simple Reflex Arc Figure 7.11b, step 4
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
Motor (efferent) neuron
(b)
Figure 7.11b, step 4

66. Simple Reflex Arc Figure 7.11b, step 5
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
(b)
Figure 7.11b, step 5

67. Simple Reflex Arc Figure 7.11c, step 1
Sensory receptors (pain receptors in the skin)
Spinal cord
(c)
Figure 7.11c, step 1

68. Simple Reflex Arc Figure 7.11c, step 2
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
(c)
Figure 7.11c, step 2

69. Simple Reflex Arc Figure 7.11c, step 3
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
(c)
Figure 7.11c, step 3

70. Simple Reflex Arc Figure 7.11c, step 4a
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
Motor (efferent) neuron
(c)
Figure 7.11c, step 4a

71. Simple Reflex Arc Figure 7.11c, step 4b
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
Motor (efferent) neuron
Effector (biceps brachii muscle)
(c)
Figure 7.11c, step 4b

72. Simple Reflex Arc Figure 7.11b–c
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Synapse in ventral horn gray matter
Inter- neuron
Motor (efferent) neuron
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
Effector (biceps brachii muscle)
(b)
(c)
Figure 7.11b–c

73. Types of Reflexes and Regulation
Somatic reflexes
Activation of skeletal muscles
Example: When you move your hand away from a hot stove

74. Types of Reflexes and Regulation
Autonomic reflexes
Smooth muscle regulation
Heart and blood pressure regulation
Regulation of glands
Digestive system regulation

75. Types of Reflexes and Regulation
Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arc
Figure 7.11d