1. Intro to The Nervous System

2. Functions of the Human N.S.
The nervous system consists of:
brain
spinal cord
sensory organs
all of the nerves that connect these organs with the rest of the body.
These parts are responsible for the control of the body and communication among its parts.

3. Two Divisions of the Nervous System
Central nervous system (CNS)—brain and spinal cord
2. Peripheral nervous system (PNS)—all nerves
What are the two principal divisions of the nervous system? The central nervous system and the peripheral nervous system

4. Divisions of the nervous system.

5. Cells of the Nervous System
Neurons
Consist of three parts
Cell body of neuron—main part
Dendrites—branching projections that conduct impulses to cell body of neuron
Axon—elongated projection that conducts impulses away from cell body of neuron
What are the two types of cells found in the nervous system? Neurons, or nerve cells, and glia, specialized connective tissue cells
What is the direction of neural transmission from sensory neurons and motor neurons? Sensory neurons transmit impulses TO the spinal cord and brain; motor neurons transmit impulses AWAY from the brain and spinal cord.
What are interneurons? Interneurons conduct impulses from sensory neurons to motor neurons. Also called central or connecting neurons.

6. Structure of a neuron. A, Diagram of a typical neuron showing dendrites, a cell body, and an axon. B, Segment of a myelinated axon cut to show detail of the concentric layers of the Schwann cell filled with myelin. C, Photomicrograph of neuron. (C, Dennis Strete.)

7. Types of Neurons Neurons
Neurons classified according to function or direction of impulse
1. Sensory neurons: conduct impulses to the spinal cord and brain; also called afferent neurons
2. Motor neurons: conduct impulses away from brain and spinal cord to muscles and glands; also called efferent neurons
3. Interneurons: conduct impulses from sensory neurons to motor neurons; also called central or connecting neurons

8. Cells of the Nervous System
Glia (neuroglia)
Support cells, bringing the cells of nervous tissue together structurally and functionally
Three main types of connective tissue cells of the CNS
Astrocytes—star-shaped cells that anchor small blood vessels to neurons
Microglia—small cells that move in inflamed brain tissue carrying on phagocytosis
Oligodendrocytes—form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only)
What is the function of glia cells? Glia cells (Greek for glue) hold the functioning neurons together, protect them, and regulate neuron function.
How are the three types of glia different? (1) Astrocytes are relatively large, star-shaped cells that attach to neurons and small blood vessels to hold these structures close to each other. (2) Microglia usually remain stationary but in inflammation or degeneration of the brain, they enlarge, move about, and act as microbe-eating scavengers. (3) Oligodendrocytes help hold nerve fibers together and also produce the fatty myelin sheath.
What is myelin? Myelin is a white, fatty substance.

9. Glia. A, Astrocytes have extensions attached to blood vessels in the brain. B, Microglia within the central nervous system can enlarge and consume microbes by phagocytosis. C, Oligodendrocytes have extensions that form myelin sheaths around axons in the central nervous system.

10. Cells of the Nervous System
Disorders of nervous tissue
Multiple sclerosis—characterized by myelin loss in central nerve fibers and resulting conduction impairments
Tumors
General name for nervous system tumors is neuroma
Most neuromas are gliomas, glial tumors
Multiple neurofibromatosis—characterized by numerous benign tumors
Where is myelin produced in the central nervous system? In oligodendrocytes.
Where is myelin produced in the peripheral nervous system? In Schwann cells.
How might symptoms differ according to where myelin production is being impaired? Symptoms will depend on the nerve affected as well as the area of the nerve affected.

11. Effects of multiple sclerosis (MS)
Effects of multiple sclerosis (MS). A, A normal myelin sheath allows rapid conduction. B, In those with MS, the myelin sheath is damaged, disrupting normal nerve conduction.

12. Multiple neurofibromatosis
Multiple neurofibromatosis. This photo shows multiple tumors of Schwann cells in the nerves of the skin that are characteristic of this inherited condition. (From Feldman M, Friedman L, Brandt L: Sleisenger & Fordtran’s gastrointestinal and liver disease, ed 8, Philadelphia, 2006, Saunders.)

13. Nerves Nerve—bundle of peripheral axons Tract—bundle of central axons
White matter—brain or cord tissue composed primarily of myelinated axons (tracts)
Gray matter—brain or cord tissue composed primarily of cell bodies and unmyelinated fibers
What is white matter composed of ? Nerve fibers usually have a myelin sheath and myelin is white.
What is gray matter composed of ? Tissue composed of cell bodies and unmyelinated axons and dendrites is called gray matter because of its characteristic gray appearance.

14. The nerve. Each nerve contains axons bundled into fascicles
The nerve. Each nerve contains axons bundled into fascicles. A connective tissue epineurium wraps the entire nerve. Perineurium surrounds each fascicle. Inset shows a scanning electron micrograph of a cross section of a nerve. (Micrograph: Courtesy Dr. Richard Kessel, Professor of Biological Sciences, University of Iowa, Iowa City.)

15. Nerves Nerve coverings—fibrous connective tissue
Endoneurium—surrounds individual fibers within a nerve
Perineurium—surrounds a group (fascicle) of nerve fibers
Epineurium—surrounds the entire nerve
Ask students to describe the coverings that surround an axon.

16. Reflex Arcs
Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs; conduction by a reflex arc results in a reflex (i.e., contraction by a muscle or secretion by a gland)
The simplest reflex arcs are two-neuron arcs—consisting of sensory neurons synapsing in the spinal cord with motor neurons; three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons
What is the difference between a neuron pathway and a reflex arc? A reflex arc is the simplest type of neuron pathway.
What is a two-neuron arc? The simplest type of reflex arc consisting of only two types of neurons: sensory neurons and motor neurons.
What is a three-neuron arc? It consists of three different types of neurons: sensory neurons, motor neurons, and interneurons.
What is an effector, and how does it relate to the reflex arc?

17. Patellar reflex. The neural pathway involved in the patellar (“knee-jerk”) reflex.

18. Nerve Impulses
Definition—self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane; sometimes called action potentials
Where does impulse conduction originate? It normally starts in receptors, the beginnings of dendrites of sensory neurons.
The end of the sensory neuron’s axon synapses first with an interneuron before chemical signals are sent across a second synapse, resulting in conduction through the motor neuron. For example, application of an irritating stimulus to the skin of the thigh initiates a three-neuron reflex response that causes contraction of muscles to pull the leg away from the irritant.
What are some types of stimuli that initiate nerve impulses? Pressure, temperature, chemical changes

19. Conduction of nerve impulses
Conduction of nerve impulses. A, In an unmyelinated fiber, a nerve impulse (action potential) is aself-propagating wave of electrical disturbance. B, In a myelinated fiber, the action potential “jumps” around the insulating myelin in a rapid type of conduction called saltatory conduction.

20. Nerve Impulses Mechanism
At rest, the neuron’s membrane is slightly positive on the outside—polarized—from a slight excess of Na+ on the outside
A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron

21. Nerve Impulses Mechanism
Inward movement of Na+ depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential)
The stimulated section of membrane immediately repolarizes, but by that time the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane

22. The Synapse
Definition—the place where impulses are transmitted from one neuron to another (the postsynaptic neuron)
Synapse made of three structures—synaptic knob, synaptic cleft, and plasma membrane
Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane
What are the three structures that make up a synapse? A synaptic knob, a neurotransmitter, and a synaptic cleft
How does a nerve impulse travel from one neuron to another? Through a synapse via a neurotransmitter
Ask students to draw a schematic diagram correctly charting the following structures and chemicals: axon terminal, synaptic knob, presynaptic neuron, postsynaptic neuron, neurotransmitter, synaptic cleft, plasma membrane, receptor molecules.

23. Components of a synapse
Components of a synapse. Diagram shows synaptic knob or axon terminal of presynaptic neuron, the plasma membrane of a postsynaptic neuron, and a synaptic cleft. On the arrival of an action potential at a synaptic knob, neurotransmitter molecules are released from vesicles in the knob into the synaptic cleft. The combining of neurotransmitter and receptor molecules in the plasma membrane of the postsynaptic neuron opens ion channels and thereby initiates impulse conduction in the postsynaptic neuron.

24. The Synapse
Names of neurotransmitters—acetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), endorphins, enkephalins, nitric oxide (NO), and other compounds
Parkinson disease (PD)—characterized by abnormally low levels of dopamine in motor control areas of the brain; patients usually exhibit involuntary trembling and muscle rigidity
What is a neurotransmitter and how many are there? Neurotransmitters are chemicals by which neurons communicate. At least 30 different compounds have been identified as neurotransmitters.
Name some of the neurotransmitters. Acetylcholine, norepinephrine, dopamine, serotonin, catecholamines
Acetylcholine is released at some of the synapses in the spinal cord and at neuromuscular junctions.
Norepinephrine, dopamine, and serotonin belong to a group of compounds called catecholamines, which may play a role in sleep, motor function, mood, and pleasure recognition.
Two morphine-like neurotransmitters called endorphins and enkephalins are natural painkillers.

25. Parkinsonism. Parkinsonism is a syndrome typically found in individuals with Parkinson disease (PD). The signs include (but are not limited to) rigidity and trembling of the head and extremities, a forward tilt of the trunk, and a shuffling gait with short steps and reduced arm swinging. (Rolin Graphics.)

26. Central Nervous System
Divisions of the brain
Brainstem
Consists of three parts, named in ascending order: medulla oblongata, pons, and midbrain
Structure—white matter with bits of gray matter scattered through it
What are the three main parts of the brainstem? The medulla oblongata, pons, and midbrain
Structure—white matter with bits of gray matter scattered through it.
What is the function of the brainstem? It functions as a two-way conduction pathway. Many important reflex centers (cardiac, respiratory, and vasomotor centers – “vital centers”) are located in the brainstem.

27. The nervous system. The brain and spinal cord (highlighted green) constitute the central nervous system (CNS), and the nerves (yellow) make up the peripheral nervous system (PNS).

28. Central Nervous System
Divisions of the brain
Brainstem
Functions
All three parts of brainstem are two-way conduction paths
Sensory tracts in the brainstem conduct impulses to the higher parts of the brain
Motor tracts conduct from the higher parts of the brain to the spinal cord
Many important reflex centers lie in the brainstem

29. Central Nervous System
Diencephalon
Structure and function of the hypothalamus
Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter
Acts as the major center for controlling the ANS; therefore, helps control the functioning of most internal organs
Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands
Contains centers for controlling appetite, wakefulness, pleasure, etc.
What is the structure of the hypothalamus? One of the most important brain structures. Lies below thalamus.
What is the function of the hypothalamus? Manufactures hormones, part of the mechanism for maintaining body temperature, involved in regulation of water balance, involved in sleep cycle, involved in control of appetite and many emotions of pleasure, fear, anger, sexual arousal, and pain.

30. Central Nervous System
Structure and function of the thalamus
Dumbbell-shaped mass of gray matter extending into each cerebral hemisphere
Relays sensory impulses to cerebral cortex sensory areas
In some way produces the emotions of pleasantness or unpleasantness associated with sensations
What is the structure of the thalamus? Dumbbell-shaped section of gray matter above the hypothalamus.
What is the function of the thalamus? (1) Helps produce sensations – relays impulses to the cerebral cortex from sense organs; (2) associates sensations with emotions; (3) plays a part in the arousal or alerting mechanism

31. Central Nervous System
Cerebellum
Second largest part of the human brain
Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures
Recent evidence shows the coordinating effects of the cerebellum may be more extensive, also assisting the cerebrum and other regions of the brain

32. Central Nervous System
Cerebrum
Largest part of the human brain
Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons
Interior of the cerebrum composed mainly of white matter (i.e., nerve fibers arranged in bundles called tracts)
Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements

33. Major regions of the central nervous system
Major regions of the central nervous system. A, Sagittal sections of the brain and spinal cord. B, Section of preserved brain. (B, Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

34. Central Nervous System
Brain disorders
Destruction of brain tissue
Cerebrovascular accident (CVA)—hemorrhage from or cessation of blood flow through cerebral blood vessels; a “stroke”
Cerebral palsy (CP)—condition in which damage to motor control areas of the brain before, during, or shortly after birth causes paralysis (usually spastic) of one or more limbs
What is the lay term for CVA? Stroke
How would you describe hemiplegia, paraplegia, triplegia, quadriplegia, and spastic paralysis? Hemiplegia – spastic paralysis of one side of the body; paraplegia – paralysis of both legs; triplegia – paralysis of both legs and one arm; quadriplegia – paralysis of all four extremities; paralysis – inability to initiate voluntary contractions, may be accompanied by involuntary contractions of affected muscles.
What is an EEG? An electroencephalogram is a graphic representation of brain activity.

35. Cerebral palsy (CP). This patient requires crutches to walk because abnormal tension (spasticity) in muscles prevents normal walking movements. (From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 5, Philadelphia, 2007.)

36. Central Nervous System
Brain disorders
Dementia—progressive loss of memory, shortened attention span, personality changes, reduced intellectual capacity, motor control deficit
Alzheimer disease (AD)—brain disorder of the middle and late adult years characterized by dementia
Huntington disease (HD)—inherited disorder characterized by chorea (purposeless movement) progressing to severe dementia
HIV (also causes AIDS) can infect neurons and thus cause dementia

37. Alzheimer disease (AD)
Alzheimer disease (AD). The CT scan on the left shows a horizontal section of a normal brain. In the CT scan on the right, however, you can see the dark patches in the cerebral cortex that show damage to brain tissue typical of AD. (James King-Holmes and Science Photo Library.)

38. Central Nervous System
Brain disorders
Seizure disorders
Seizure—sudden burst of abnormal neuron activity that results in temporary changes in brain function
Epilepsy—many forms, all characterized by recurring seizures
Electroencephalogram—graphic representation of voltage changes in the brain used to evaluate brain activity

39. Electroencephalography
Electroencephalography. A, Photograph of a person with voltage-sensitive electrodes attached to her skull. Information from these electrodes is used to produce a graphic recording of brain activity—an electroencephalogram (EEG). B, An EEG tracing showing activity in four different places in the brain (obtained from four sets of electrodes). Compare the moderate chaotic activity identified as normal with the explosive activity that occurs during a seizure.

40. Central Nervous System
Spinal cord
Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts
Interior composed of gray matter made up mainly of neuron dendrites and cell bodies (Figure 9-18)
Spinal cord tracts provide two-way conduction paths—ascending and descending
Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain
Typically, how long is the spinal cord? About 17 to 18 inches long.
Distinguish between the spinal cord and the spinal column. The spinal cord lies inside the spinal column in the spinal cavity.
Tracts are functional organizations: all axons composing one tract serve a general function.
Other ascending tracts transmit sensations of touch and pressure to the brain.

41. Spinal cord and spinal nerves
Spinal cord and spinal nerves. Inset is a dissection of the cervical segment of the spinal cord showing emerging cervical nerves. The spinal cord is viewed from behind (posterior aspect).

42. Spinal cord cross section
Spinal cord cross section. Cross section of the spinal cord showing the gray matter in the center, surrounded by white matter pathways (nerve tracts), and spinal nerve roots.

43. Central Nervous System
Coverings and fluid spaces of the brain and spinal cord
Coverings
Cranial bones and vertebrae
Cerebral and spinal meninges—the dura mater, arachnoid mater, and the pia mater
Fluid spaces
Subarachnoid spaces of meninges
Central canal inside cord
Ventricles in brain
Nerve tissue needs to be protected, so the brain and spinal cord are surrounded by a tough, fluid-containing membrane called the meninges.
The meninges are surrounded by bone. The spinal meninges form a tubelike covering around the spinal cord and line the bony vertebral foramen of the vertebrae that surround the cord.
What are the three layers of the spinal meninges? Dura mater – tough outer layer that lines the vertebral canal; arachnoid mater – membrane between the dura and pia mater; pia mater – innermost membrane covering the spinal cord.

44. Spinal cord and its coverings
Spinal cord and its coverings. The meninges, spinal nerves, and sympathetic trunk are all depicted in this drawing.

45. Fluid spaces in the brain
Fluid spaces in the brain. A, The ventricles are highlighted within the brain in a left lateral view. B, The ventricles shown from above.

46. Flow of the cerebrospinal fluid
Flow of the cerebrospinal fluid. The fluid produced by filtration of blood by the choroid plexus of each ventricle flows inferiorly through the lateral ventricles, interventricular foramen, third ventricle, cerebral aqueduct, fourth ventricle, and subarachnoid space and then to the blood.

47. Peripheral Nervous System
Cranial nerves
12 pairs—attached to undersurface of the brain
Connect brain with the neck and structures in the thorax and abdomen
Spinal nerves
31 pairs—contain dendrites of sensory neurons and axons of motor neurons
Conduct impulses necessary for sensations and voluntary movements
Skin surface area supplied by a single nerve is called a dermatome
What are some of the structures included in the peripheral nervous system? Includes cranial and spinal nerves that connect the brain and spinal cord, respectively, to peripheral structures such as the skin surface and the skeletal muscles.
Other structures in the autonomic nervous system are considered part of the peripheral nervous system; they connect the brain and spinal cord to various glands in the body and to the cardiac and smooth muscles in the thorax and abdomen.

48. Cranial nerves. View of the undersurface of the brain shows attachments of the cranial nerves.

49. Dermatomes. Segmental dermatome distribution of spinal nerves to the front, back, and side of the body. C, Cervical segments; T, thoracic segments; L, lumbar segments; S, sacral segments; CX, coccygeal segment.

50. Peripheral Nervous System
Peripheral nerve disorders
Neuritis—general term referring to nerve inflammation
Sciatica is inflammation of the sciatic nerve that innervates the legs
Neuralgia, or muscle pain, often accompanies neuritis

51. Peripheral Nervous System
Peripheral nerve disorders
Trigeminal neuralgia—recurring episodes of stabbing pain along one or more branches of the trigeminal (fifth cranial) nerve in the head
Bell palsy—paralysis of facial features resulting from damage to the facial (seventh cranial) nerve

52. Peripheral Nervous System
Peripheral nerve disorders
Herpes zoster or shingles
Viral infection caused by chickenpox virus that has invaded the dorsal root ganglion and remained dormant until an episode of shingles
Usually affects a single dermatome, producing characteristic painful plaques or vesicles
What is the causative agent for herpes zoster? Varicella zoster
What childhood disease has a patient contracted to be susceptible to herpes zoster? Chickenpox
What is a dermatome? Skin surface areas supplied by a single spinal nerve.

53. Herpes zoster (shingles)
Herpes zoster (shingles). Photograph of a 13-year-old boy with eruptions involving dermatome T4 (see Figure 9-24). (From Habif TP: Clinical dermatology, ed 2, St. Louis, 1990, Mosby.)

54. Autonomic Nervous System
Autonomic nervous system—motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates body’s automatic or involuntary functions
Autonomic neurons—preganglionic autonomic neurons conduct from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue
Motor nerves that control the voluntary actions of skeletal muscles are sometimes called the somatic nervous system.
What are the two divisions of the autonomic nervous system (ANS)? Sympathetic nervous system, parasympathetic nervous system
Spinal nerves conduct impulses between the spinal cord and parts of the body not supplied by cranial nerves.
Spinal nerves function to make possible sensations and movements.

55. Innervation of the major target organs by the autonomic nervous system
Innervation of the major target organs by the autonomic nervous system. The sympathetic pathways are highlighted with orange, and the parasympathetic pathways are highlighted with green.

56. Autonomic Nervous System
Autonomic or visceral effectors—tissues to which autonomic neurons conduct impulses (i.e., cardiac and smooth muscle and glandular epithelial tissue)
What are autonomic effectors? Tissues to which autonomic neurons conduct impulses—cardiac and smooth muscle and glandular epithelial tissue.
Autonomic paths to visceral effectors consist of two-neuron relays. Impulses travel over preganglionic neurons from the spinal cord or brainstem to autonomic ganglia. There they are relayed across synapses to postganglionic neurons, which then conduct the impulses from the ganglia to visceral effectors.
In contrast, somatic motor neurons conduct all the way from the spinal cord or brainstem to somatic effectors with no intervening synapses.

57. Autonomic Nervous System
Composed of two divisions: the sympathetic system and the parasympathetic system
Autonomic conduction paths
Consist of two-neuron relays (i.e., preganglionic neurons from the CNS to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors)
In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses

58. Autonomic conduction paths
Autonomic conduction paths. A, One somatic motor neuron conducts impulses all the way from the spinal cord to a somatic effector. Conduction from the spinal cord to any visceral effector, however, requires a relay of at least two autonomic motor neurons—a preganglionic and a postganglionic neuron (B).

59. Autonomic Nervous System
Sympathetic nervous system
Dendrites and cell bodies of sympathetic preganglionic neurons located in gray matter of thoracic and upper lumbar segments of spinal cord
Axons leave spinal cord in the anterior roots of spinal nerves, extend to sympathetic or collateral ganglia, and synapse with several postganglionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors
A chain of sympathetic ganglia is in front of and at each side of the spinal column
What are the two divisions of the autonomic nervous system (ANS)? Sympathetic and parasympathetic; see Figure 9-26.
What is the structure of the sympathetic nervous system? Also referred to as the “thoracolumbar system,” it leaves the spinal cord in the anterior (ventral) root of a spinal nerve, enters the spinal nerve, but soon leaves it to extend to and through a sympathetic ganglion and terminate in a collateral ganglion where it synapses with several postganglionic neurons whose axons extend to terminate in visceral effectors.

60. Autonomic Nervous System
Functions of the sympathetic nervous system
Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are elicited
Group of changes induced by sympathetic control is called the fight-or-flight response
What are the functions of the sympathetic nervous system? It functions as an emergency system. It takes control of many internal organs when we exercise strenuously and when strong emotions are elicited. It other words, it functions during stress. See Table 9-3.
What physiological changes are associated with the fight-or-flight response? Heart beats faster, blood vessels constrict causing blood pressure to increase, blood vessels in muscle dilate delivering more blood to the muscles, sweat glands and adrenal glands secrete more abundantly, salivary and other digestive glands secrete more sparingly, peristalsis becomes sluggish, and we are ready for “flight or flight.”
The sympathetic nervous system controls visceral effectors during strenuous exercise and strong emotions (such as anger, fear, hate, or anxiety).

61. Autonomic Nervous System
Parasympathetic nervous system
Structure
Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of spinal cord
Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors
Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector
Where are the dendrite and cell bodies of the sympathetic preganglionic neurons located? In the parasympathetic nervous system in the spinal cord and brainstem.

62. Autonomic Nervous System
Parasympathetic nervous system
Function—dominates control of many visceral effectors under normal, everyday conditions
What are the functions of the parasympathetic nervous system, and how do they differ from the functions of the sympathetic nervous system? It dominates control of many visceral effectors during normal, everyday conditions. Impulses tend to slow heartbeat, increase peristalsis, and increase secretion of digestive juices and insulin. See Table 9-3.

63. Autonomic Nervous System
Autonomic neurotransmitters
Cholinergic fibers—preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine
Adrenergic fibers—axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline)
What are neurotransmitters? Chemicals that continue a nervous impulse through a synapse.
Ask students to offer examples of neurotransmitters associated with the ANS, including the division of the ANS associated with each neurotransmitter.
Three axons—the sympathetic preganglionic axon, the parasympathetic preganglionic axon, and the parasympathetic postganglionic axon—release acetylcholine. These axons are classified as cholinergic fibers.
Only one type of autonomic axon releases the neurotransmitter norepinephrine; this is the axon of a sympathetic postganglionic neuron, and such neurons are classified as adrenergic fibers.
What determines the nature of an organ’s response to stimulation by the autonomic nervous system? Cholinergic and adrenergic fibers

64. Autonomic neurotransmitters
Autonomic neurotransmitters. Three of the four fiber types are cholinergic, secreting the neurotransmitter acetylcholine (Ach) into a synapse. Only the sympathetic 4. What problems in the body arise from ANS malfunctions? Postganglionic fiber is adrenergic, secreting norepinephrine (NE) into a synapse.

65. Autonomic Nervous System
Autonomic nervous system as a whole
Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis
Many visceral effectors are doubly innervated (i.e., they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions)

66. Autonomic Nervous System
Disorders of the autonomic nervous system
Stress-induced disease
Prolonged or excessive response to stress can disrupt normal functioning throughout the body
Examples of stress-induced conditions include heart disease, digestive problems, and reduced resistance to disease

67. Autonomic Nervous System
Disorders of the autonomic nervous system
Neuroblastoma—highly malignant tumor of the sympathetic nervous system, primarily affecting young children
What are examples of stress-induced diseases? Heart disease, ulcers, colitis, autoimmune disorders, and a depressed immune system resulting in infections, colds, etc.
Stress can oversecrete gastric hydrochloric acid.