1. The Human Body in Health and Illness, 4th edition
Barbara Herlihy
Chapter 10:
Nervous System: Nervous Tissue and Brain

2. Lesson 10-1 Objectives Define the two divisions of the nervous system.
List three functions of the nervous system.
Compare the neuroglia and neuron.
Explain the function of the myelin sheath.
Explain how a neuron transmits information.
Describe the structure and function of a synapse.
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3. Divisions of the Nervous System
Central nervous system (CNS): brain and spinal cord
Peripheral nervous system
The nervous system coordinates and directs the various organ systems of the body.
The central nervous system includes the brain and the spinal cord.
The peripheral nervous system consists of the nerves that connect the CNS with the rest of the body. It is located outside the CNS.
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4. Functions of the Nervous System
The sensory nerves gather information and carry it to the CNS.
The integrative function serves to process or interpret the information brought to the CNS by the sensory nerves.
The motor nerves convey information from the CNS to the muscles and glands to carry out the plans made by the CNS.
Ask students to give some example of what an integrative function could be.
Possible answers include interpreting sensory information and making a decision about what should be done.
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5. Types of Nervous Tissue
Neuroglia or glial cells
Most located in the CNS
Most abundant type
Support, protect, insulate, nourish, and generally care for neurons
Neurons
Do the communicating for the nervous system
Long shape makes them delicate
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6. Neuroglia Astrocytes Ependymal cells Microglia Schwann cells
Oligodendrocytes
These undergo mitosis, most primary CNS tumors are from these cells
Only two of the five types of glial cells are shown on the slide.
The astrocytes form the blood-brain barrier and will be discussed as part of that topic.
Ependymal cells help form cerebrospinal fluid (CSF).
Insert functions of each type of cell.
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7. Astrocytes Star shaped Most abundant of the glial cells Functions:
Support the neurons structurally
Secrete nerve growth factors that promote neuron growths and enhance synaptic development
phagocytes
Cover the entire surface of the brain as protective layer
Called the blood-brain barrier
Protects against toxic substances in the blood
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8. Anchors blood vessels to nerves for support
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9. Ependymal Cells Line the inside cavities of the brain
Assist in the formation of cerebrospinal fluid
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10. Microglia First and main form of active immune defense in the CNS
Macrophages – engulf and digest cellular debris, damaged tissue, and foreign objects
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11. Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc
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12. Schwann Cells In the PNS Myelinating Nonmyelinating
Cells wrap around the the axon of a neuron
Layers of membrane around the axon with the nuclei and cytoplasm on the outermost layer called the neurilemma
The gaps between the schwann cells are called nodes of Ranvier, help electrical impulse to move faster
Nonmyelinating
Maintenance of axons
Assists in regeneration of damaged fibers
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13. Schwann Cells
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14. Oligodendrocytes Produce myelin sheath for neurons in the CNS
Myelinated looks white
Unmyelinated looks gray
No neurilemma
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15. Parts of a Neuron Cell body Dendrites Axon Myelin sheath
Nodes of Ranvier
Neurilemma
Axon terminal
Neurotransmitters stored
The neuron is the second type of nerve cell and is the most important in the transmission of information.
Neurons have many shapes and sizes. They are also nonmitotic and therefore do not replicate or replace themselves when injured.
Ask students to identify the parts of the neuron on the slide.
The electrical signal travels from the cell body down toward the axon terminal, as the arrow illustrates.
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16. The Axon Myelin sheath Neurilemma Nodes of Ranvier
Formed by Schwann cells
The myelin protects and insults the axon
Myelination begins during the fourth month of fetal life and continues into the teenage years.
Infants need fat in the diet to lay down myelin
Neurilemma
Nodes of Ranvier
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17. Types of Neurons Sensory (afferent) neurons Motor (efferent) neurons
Carry information from periphery toward the CNS
Motor (efferent) neurons
Carry information from CNS toward periphery
Interneurons
Found only in CNS; connect sensory and motor nerves
Sensory neurons are also called afferent neurons. They carry information from the periphery toward the CNS.
Motor neurons, also called efferent neurons, carry information from the CNS toward the periphery.
Both sensory neurons and motor neurons are found in the CNS and in the peripheral nervous system.
Interneurons are found only in the CNS. They form connections between sensory and motor neurons.
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18. Clusters Nuclei – clusters of cell bodies in the CNS
Basal nuclei – patches of gray located in the brain
Ganglia – small clusters of cell bodies in the PNS
Singular – ganglion
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19. Nerve Impulses or Signals
Electrical signals convey information along a neuron
Also called action potential
Move along sensory or motor neurons
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20. The Action Potential Polarization: Resting state
Depolarization: Stimulated state
Repolarization: Return to resting
Polarization: The inside of the neuron is more negative than the outside when it is polarized.
Depolarization: This is the change inside the cell from negative to positive when the neuron is stimulated.
Repolarization: The inside of the cell becomes negative again.
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21. Ionic Basis of the Action Potential
Polarization
K+ leaks from neuron.
Determines resting membrane potential
Depolarization
Na+ rushes in.
Repolarization
K+ rushes out.
The movement of specific ions across the cell membrane of the neuron is responsible for the action potential, or nerve impulse.
During the resting state, the potassium ions tend to leak out of the cell, taking the positive charge with them. This leakage is responsible for the resting membrane potential.
The inward diffusion of sodium ions causes depolarization.
The outward diffusion of potassium causes repolarization, returning the cell to a resting state.
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22. Why Action Potential “Moves”
Forms at axon’s beginning
Regenerates along axon’s length
Enters axon terminal
Releases ACh from vesicles
Impulse is all-or-nothing
The terms nerve impulse and action potential mean the same thing.
A nerve impulse (or action potential) must move the length of the neuron.
As illustrated in Figure 10-7, each nerve impulse (or action potential) has the ability to depolarize the adjacent membrane. This causes the nerve impulse to move toward the axon like a wave.
The height of each nerve impulse is the same along the entire length of the axon. This ensures that the nerve impulse does not weaken as it travels the length of a long axon.
The action potential is responsible for the release of neurotransmitter.
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23. Increasing Action Potential’s Speed
Myelin insulates axon.
Myelin exposes some axonal membrane—nodes of Ranvier.
Action potentials jump quickly from node to node, like a kangaroo.
Called saltatory conduction
The action potential jumps from node to node to the axon terminal.
The jumping kangaroo effect increases the speed of the action potential.
The jumping of the action potential is also called saltatory conduction.
Myelinated fibers are therefore fast conducting fibers.
Why is the image of the kangaroo jumping appropriate when talking about myelinated fiber, but inappropriate when discussing nonmyelinated fibers?
The action potential cannot form on a nonmyelinated area, so it has to jump from node to node.
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24. Synapse Across Neurons
Synapse: the interaction between two nerves where chemical transmission of the electrical signal occurs
Synaptic cleft: the space between an axon terminal and a dendrite of another neuron
Neurotransmitters such as ACh, norepinephrine, glutamate, dopamine, gamma-aminobutyric acid, and endorphins
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25. Synapse Across Neurons
Inactivators are substances that stop the activity of the neurotransmitters.
ACh is inactivated by acetylcholinesterase, an enzyme that breaks down ACh
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26. Communication across the Synapse
ACh is
– Secreted from neuron A
– Diffused across synaptic cleft
– Bound to receptors on neuron B
Neuron B is activated.
Steps pp
Nerves must communicate with one another; they do so at the synapse.
In the upper panel, the boxed area shows the communication at the synapse. The lower panel shows the steps
How does communication across the synapse resemble communication at the neuromuscular junction (Chapter 9)?
Both have the same steps, but the neurotransmitters may vary.
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27. Lesson 10-2 Objectives Describe the four major areas of the brain.
Describe the functions of the four lobes of the cerebrum.
Describe how the skull, meninges, cerebrospinal fluid, and blood-brain barrier protect the central nervous system.
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28. Four Major Areas of the Brain
Cerebrum
Diencephalon
Brain stem
Cerebellum
The brain is located in the cranial cavity and is pinkish-gray, is delicate, has a soft consistency, and is divided into four major areas.
The primary source of energy for the brain is glucose.
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29. Cerebrum: Four Lobes Frontal lobe Parietal lobe Temporal lobe
Occipital lobe
The cerebrum is the largest part of the brain and is divided into the right and left cerebral hemispheres.
The corpus callosum, bands of white matter that form a large fiber tract, joins the two hemispheres and allows them to communicate with each other.
Each cerebral hemisphere has four major lobes that are named for the overlying cranial bones.
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30. Cerebrum: Markings Gyrus (convolution) Fissures (sulci) Central
Lateral
Longitudinal
The gyri (singular, gyrus), or convolutions, looks like speed bumps on the surface of the brain. By increasing surface area, they increase the amount of tissue available for thinking.
Fissures or sulci are grooves that separate the gyri. Of particular interest is the central sulcus, which separates the frontal lobe from the parietal lobe; it is an important landmark.
Ask students to examine Figure 10-11A. In what cerebral lobe is the precentral gyrus found? In what cerebral lobe is the postcentral gyrus found?
The precentral gyrus is found in the frontal lobe and the postcentral gyrus in found in the parietal lobe.
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31. Frontal Lobe “ The executive” – intellectual functions Behavior
Personality
Motor control
Memory storage
Emotional expression
Most frontal lobe functions are associated with higher order intellectual functioning and motor activity.
What do you think might happen to a person who has sustained a severe injury to the frontal lobe?
Answers will include difficulty with memory, changes in personality and behavior, and impairment of intellectual and motor functioning. For example, a person might need to relearn reading.
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32. Frontal Lobe: Motor Activity
Primary motor area
Precentral gyrus
Frontal eye field
Voluntary movements of the eyes and eyelids
Motor speech area
Broca’s area
If a person suffers a stroke involving Broca’s area, why may she understand what you are saying but be unable to respond verbally?
The motor speech area (Broca’s area) deals with the physical aspects of producing speech, not cognitive issues such as understanding the meanings of words.
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33. Frontal Lobe: Motor Homunculus
Shows percentages of frontal lobe devoted to body’s motor activities
The homunculus represents the amount of brain tissue that corresponds to a motor function of a particular body part.
Each part of the body is controlled by a specific area of the primary motor cortex of the precentral gyrus. Complicated movements require large amounts of brain tissue.
Ask students to compare the size of the homunculus’s hands and feet. Why are the hands bigger than the feet?
The hand performs more complex movements that require more brain tissue.
One could also draw a similar homunculus on the postcentral gyrus to illustrate sensory function.
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34. Other Cerebral Lobes Parietal Somatosensory area Sense of taste
Interprets temp, pain, pressure, light touch, and proprioception(where your body is)
Sense of taste
The parietal lobe contains the somatosensory area. This area interprets temperature, pain, pressure, light touch, and proprioception.
The temporal lobe contains the auditory cortex and the olfactory area. Information from the taste buds is interpreted in both the temporal and parietal lobes.
The occipital lobe contains the visual cortex.
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35. Other Cerebral Lobes Temportal Lobe Occipital Lobe Auditory cortex
Sense of taste
Olfactory area
Wernicke’s area – translation of thought into words
Located in parietal and temporal lobes
Occipital Lobe
Visual cortex
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36. Functions Spanning Cerebral Lobes
Speech areas
Span temporal, parietal and occipital lobes
Usually in left hemisphere
Wernicke’s area (helps translate thought into speech)
Association areas
Helps to interpret sensory information
Examples: Visual, auditory, somatosensory
Wernicke’s area is located in both the temporal and parietal lobes and is responsible for translating thought into words.
Explain why injury to the left hemisphere is much more likely to result in speech impairment than injury to the right hemisphere?
In most people, the speech centers are concentrated in the left hemisphere.
The primary visual cortex allows you to see an imagefor example, a tree. What additional information does the visual association area provide?
The visual association area allows you to interpret or apply meaning to the image, perhaps that it is an oak tree or that it needs water.
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37. Diencephalon
Thalamus – relay station for most of the sensory fibers traveling from the lower brain and spinal cord
Hypothalamus
There are two parts of the diencephalon, the thalamus and the hypothalamus.
The thalamus acts as a sensory pathway for information coming from the lower brain and the spinal cord to the sensory areas of the cerebrum. It is especially important with regard to pain sensation.
The hypothalamus sits above the pituitary gland and controls endocrine function. It is also the body’s thermostat and helps regulate autonomic functions.
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38. Diencephalon Continued
Hypothalamus
Helps regulate body temperature, water balance, and metabolism
It helps regulate the function of the autonomic(involuntary) nerves, so it has an effect on heart rate, blood pressure, and respiration.
Controls pituitary function
The pituitary directly or indirectly affects almost every hormone in the body
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39. Brain Stem Midbrain Medulla oblongata Relays sensory and motor info
Reflex centers of vision and hearing
Medulla oblongata
Vital center
Emetic center(vomiting)
Reflex center
Pons
plays an important role in the regulation of breathing rate and rhythm
Acts a bridge for information traveling
The midbrain contains nuclei that serve as reflex centers for vision and hearing.
The pons plays an important role in regulating breathing rate and rhythm.
The medulla oblongata descends through the foramen magnum as the spinal cord. It is called the vital center because it controls heart rate, blood pressure, and respiration. Its emetic center stimulates vomiting, either as a result of direct stimulation (e.g., fear, spinning, or distressing odors) or from indirect stimulation from the chemoreceptor trigger zone (CTZ), as in cancer chemotherapy.
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40. Cerebellum Mediates reflexes Coordinates motor activity
Evaluates sensory input
The primary responsibility of the cerebellum is the coordination of voluntary muscle activity. It produces a smooth, coordinated muscle response after integrating all the incoming information from many areas throughout the body.
It is also a major reflex center.
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41. Structures Spanning Brain Divisions
Limbic system
Emotional brain
Reticular formation: Reticular activating system; sleep-wake cycle, consciousness, gaze center
Memory areas
Immediate memory
Short-term memory
Long-term memory
These three important structures are not confined to any one division of the brain. They overlap several areas.
The limbic system is a wishbone-shaped group formed by parts of the cerebrum and diencephalon.
The reticular formation is responsible for maintaining consciousness and activating the sleep-wake cycle. It also contains the gaze center.
The memory areas allow the recollection of thoughts and images. Many areas of the brain are responsible for memory.
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42. Protecting the CNS: Four Layers
Bone
Meninges
Cerebrospinal fluid
Blood-brain barrier
The cranium and the vertebral column help protect the central nervous system.
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43. Protecting the CNS: Meninges
Dura mater
Outer most layer
Thick, tough, connective tissuse
Arachnoid mater
Subarachnoid space
weblike
Pia mater
Inner most layer
Soft, many blood vessels
The pia mater, the innermost layer, is a very thin membrane containing many blood vessels.
The arachnoid layer is a spider web–like membrane between the pia mater and dura mater. The subarachnoid space surrounds the entire CNS and is filled with cerebrospinal fluid (CSF) to cushion the CNS.
The dura mater is a thick, tough, connective tissue that splits into sinuses filled with blood. The subdural space is located beneath the dura mater; it contains blood.
Clinical application: A person sustains a sharp blow to the head and develops a subdural hematoma. Predict some possible symptoms.
Because the cranium cannot expand, a subdural hematoma causes pressure on the brain. The precise symptoms depend on the location of the pressure but might include a dragging foot, blurred vision, slurred speech, or decreased level of consciousness.
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44. Protecting the CNS: Cerebrospinal Fluid (CSF)
Formed in ventricles by choroid plexus
Circulates through subarachnoid space
From central canal of spinal cord
From foramina
Identify these structures on the slide: two lateral ventricles, one third ventricle, one fourth ventricle, and cerebral aqueduct.
Cerebrospinal fluid (CSF) is formed within the ventricles of the brain by the choroid plexus (the ependymal cells). CSF is a clear fluid and is similar in consistency to plasma.
Some of the CSF flows through the central canal, which is a hole in the center of the spinal cord. It eventually drains into the subarachnoid space at the base of the spinal cord. A second drainage path is through foramina near the brain.
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45. Drainage of CSF Drainage of CSF must equal its production.
Arachnoid villi project into dural sinuses filled with blood.
CSF drains into blood and leaves the brain.
The amount of CSF drained must equal the amount produced.
What if the canal between the third and fourth ventricles is blocked, perhaps by a congenital malformation?
The CSF would accumulate in the ventricles, increasing intracranial pressure and pressing on brain tissue. Treatment could include shunting the CSF around the blockage.
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46. Protecting the CNS: The Blood-Brain Barrier
Made of special cells (astrocytes) within cerebral capillaries.
Prevents some toxins from entering CNS from blood
Glial astrocytes are parts of the cerebral blood vessel (capillary) wall that supplies the brain and spinal cord. The astrocytes select the substances allowed to enter the CNS from the blood.
Some antibiotics cannot cross the blood-brain barrier. How, then, could an infection of the CNS be treated?
The infection could be treated either by selecting an antibiotic that does cross the blood-brain barrier or injecting the antibiotic into the subarachnoid space.
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