1. Presentation title slide

2. UNIT B: Human Body Systems
Chapter 8: Human Organization
Chapter 9: Digestive System
Chapter 10: Circulatory System and Lymphatic System
Chapter 11: Respiratory System
Chapter 12: Nervous System:
Section 12.2
Chapter 13: Urinary System
Chapter 14: Reproductive System

3. Chapter 12: Nervous System
UNIT B
Chapter 12: Nervous System
Chapter 12: Nervous System
In this chapter, you will learn about the structure and function of the nervous system.
How might a researcher study the effects of frequent head trauma?
How might one determine which part of the brain has been affected by repeated blunt impacts?
Given the available information about CTE, what steps do you feel should be taken to prevent its occurrence (if any)?
Sport-Related Head Trauma and Brain Function. Neurosurgeon Dr. Robert Cantu has studied the brains of many deceased athletes, including hockey and football players. He has found that these players often suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated blunt impact to the head.
Chapter opener figure background:
Former NHL players Rick Rypien, Wade Belak, and Derek Boogaard had something in common; they were all “enforcers.” They were expected to
fight during hockey games.
There is another similarity among these men. They are all dead. Each died of causes that increasingly seem tied to their activities on the ice. Neurosurgeon Dr. Robert Cantu has studied the brains of many deceased athletes, including hockey and football players. He has found that these players often suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated blunt impact to the head. CTE seems to manifest itself in addiction, depression, and anxiety, conditions suffered by some or all of the deceased players.
Dr. David Goldbloom, senior medical adviser at Toronto’s Centre for Addiction and Mental Health, thinks it is important not to assume that the deaths of the players were all the result of the same thing. Each was an individual and each had his own mental health history. Rypien and Belak had battled depression, and Boogaard was still recovering from previous concussions. Goldbloom feels that attributing the deaths to CTE is an oversimplification, but he does think further study in this area is worth pursuing.
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4. 12.2 Transmission of Nerve Impulses
UNIT B
Chapter 12: Nervous System
Section 12.2
12.2 Transmission of Nerve Impulses
The nervous system uses the nerve impulse to convey information.
The nerve impulse can be studied using excised axons and a voltmeter called an oscilloscope.
Voltage: measured in millivolts (mV); a measure of the electrical potential difference between two points
In a neuron, the two points are in the inside (axoplasm) and the outside of the axons
On a voltmeter, voltage is displayed as a trace (pattern) over time
nerve impulse: a type of impulse used by the nervous system to convey information
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5. Resting Potential UNIT B
Chapter 12: Nervous System
Section 12.2
Resting Potential
In an axon that is not conducting an impulse, the voltmeter records a potential difference across an axon membrane equal to -70mV.
This reading, known as the resting potential, shows that the inside of the axon is negative compared to the outside (there is polarity across the axonal membrane)
The resting potential is the potential difference across the membrane in a resting neuron
resting potential: the membrane potential of an inactive neuron
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6. UNIT B
Chapter 12: Nervous System
Section 12.2
The polarity of the resting axonal membrane is due to a difference in ion distribution on each side.
The concentration of Na+ is greater outside the axon than inside
The concentration of K+ is greater inside the axon than outside
Figure Action Potential.
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7. UNIT B
Chapter 12: Nervous System
Section 12.2
This unequal distribution is maintained by carrier proteins called sodium-potassium pumps, which actively transport Na+ out of the axon and K+ into the axon
The pumps are always working because the membrane is permeable to Na+ and K+
The membrane is more permeable to K+, therefore there are always more positive ions outside the membrane than inside
Negatively charged organic ions on the inside of the axon also contribute to the polarity across a resting axonal membrane
sodium-potassium pump: a carrier protein that moves sodium ions to the outside of a cell and potassium ions to the inside; especially in nerve and muscle cells
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8. Action Potential UNIT B
Chapter 12: Nervous System
Section 12.2
Action Potential
An action potential is a rapid change in polarity across an axonal membrane as the nerve impulse occurs.
An all-or-none phenomenon: if a stimulus causes the membrane to depolarize to a certain level (threshold), an action potential occurs
The strength of an action potential does not change, but an intense stimulus can cause an axon to fire (start an action potential) more often
Requires two gated channel proteins in the membrane:
One channel protein allows Na+ to pass into the axon
One channel protein allows K+ to pass out of the axon
action potential: electrochemical changes that take place across the axon membrane; the nerve impulse
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9. UNIT B Chapter 12: Nervous System Section 12.2
Figure Action Potential. c. The changes in the transmembrane potential of the axon are a result of sodium ions flowing into the axon and potassium ions flowing out. An action potential lasts only a few seconds.
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10. Action Potential: Sequence of Events
UNIT B
Chapter 12: Nervous System
Section 12.2
Action Potential: Sequence of Events
Sodium Gates Open (Depolarization)
When an action potential begins, sodium channel gates open, and Na+ flows down its concentration gradient into the axon
As Na+ moves inside the axon, the membrane potential changes from -70 mV to +35 mV
This is called depolarization because the charge inside the axon changes from negative to positive
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11. UNIT B Chapter 12: Nervous System Section 12.2
Figure Action Potential. a. The action potential begins as the sodium gates (purple) open and Na+ ions move into the axon through facilitated diffusion. This is depolarization as the membrane potential jumps from −70 to +35 millivolts.
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12. Action Potential: Sequence of Events
UNIT B
Chapter 12: Nervous System
Section 12.2
Action Potential: Sequence of Events
Potassium Gates Open (Repolarization)
The potassium channel gates open, and K+ flows down its concentration gradient out of the axon
As K+ flows out of the axon, the action potential becomes more negative again (repolarization)
During this time, it briefly becomes slightly more negative that its original resting potential (hyperpolarization)
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13. UNIT B Chapter 12: Nervous System Section 12.2
Figure Action Potential. b. The repolarization of a neuron occurs as the potassium gates (orange) open and K+ ions move out of the axon through facilitated diffusion.
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14. Conduction of an Action Potential
UNIT B
Chapter 12: Nervous System
Section 12.2
Conduction of an Action Potential
Action potentials in nonmyelinated axons
The action potential travels down an axon one small section at a time
When an action potential has moved on, the previous section undergoes a refractory period, during which the sodium gates are unable to open
The action potential cannot move backward; it always moves down an axon
When the refractory period is over, the sodium-potassium pump has restored the ion distribution by pumping Na+ out of the axon and K+ into the axon
refractory period: in nonmyelinated axons, a period in which sodium gates are unable to open following an action potential
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15. Action potentials in myelinated axons
UNIT B
Chapter 12: Nervous System
Section 12.2
Action potentials in myelinated axons
The gated ion channels that produce an action potential are concentrated at the nodes of Ranvier
Ion exchange only occurs at these nodes, therefore the action potential travels faster than in nonmyelinated axons
The action potential “jumps” from node to node (saltatory conduction)
saltatory conduction: occurs in myelinated axons when the action potential “jumps” from node to node
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16. Transmission Across a Synapse
UNIT B
Chapter 12: Nervous System
Section 12.2
Transmission Across a Synapse
Every axon branches into endings that have a small swelling called an axon terminal
Each terminal lies close to the dendrite or cell body of another neuron or a muscle cell
This region of close proximity is called a synapse or chemical synapse
Membrane of the first neuron: presynaptic membrane
Membrane of the second neuron: postsynaptic membrane
Two neurons at a synapse do not physically touch each other; they are separated by a tiny gap called the synaptic cleft
synapse: the region of close proximity between an axon terminal and the dendrite or cell body of another neuron or muscle cell
synaptic cleft: a tiny gap separating two neurons at a synapse
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17. UNIT B An action potential cannot cross a synapse.
Chapter 12: Nervous System
Section 12.2
An action potential cannot cross a synapse.
Communication between two neurons at a chemical synapse is carried out by neurotransmitters (chemicals stored in the synaptic vesicles in axon terminals)
Figure 12.5 Structure and function of a synapse. Transmission across a synapse from one neuron to another occurs when an action potential causes a neurotransmitter to be released at the presynaptic membrane.
neurotransmitters: molecules that carry out communication between the two neurons at a chemical synapse
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18. UNIT B When an action potential arrives at an axon terminal:
Chapter 12: Nervous System
Section 12.2
When an action potential arrives at an axon terminal:
Gated channels for Ca2+ open, and Ca2+ enters the terminal
Ca2+ interacts with contractile proteins, which contract and pull the synaptic vesicles to the presynaptic membrane
Rise in Ca2+ stimulates synaptic vesicles to merge with the presynaptic membrane, resulting in exocytosis
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19. UNIT B
Chapter 12: Nervous System
Section 12.2
Neurotransmitter molecules are released into the synaptic cleft and diffuse across the synapse to the postsynaptic membrane, where they bind to specific receptors
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20. UNIT B
Chapter 12: Nervous System
Section 12.2
Depending on the neurotransmitter, the postsynaptic neuron can either be excited (causing an action potential) or inhibited (stopping an action potential)
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21. Synaptic Integration UNIT B
Chapter 12: Nervous System
Section 12.2
Synaptic Integration
A neuron may receive many excitatory and inhibitory signals since its dendrites and cell body can have synapses with many other neurons.
Excitatory signals: cause a depolarizing effect
Inhibitory signals: cause a hyperpolarizing effect
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Figure 12.6 Synaptic integration.

22. UNIT B
Chapter 12: Nervous System
Section 12.2
Synaptic integration is the summing up of the excitatory and inhibitory signals in a postsynaptic neuron.
If the combined signals cause the membrane potential to rise above threshold, an action potential will occur
Figure 12.6 Synaptic integration.
a. Inhibitory signals and excitatory signals are summed up in the dendrites and cell body of the postsynaptic neuron. Only if the combined signals cause the membrane potential to rise above threshold does an action potential occur. b. In this example, threshold was not reached.
integration: the summing up of excitatory and inhibitory signals by a neuron
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23. Neurotransmitters UNIT B
Chapter 12: Nervous System
Section 12.2
Neurotransmitters
Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft.
This prevents continuous stimulation (or inhibition) of postsynaptic membranes
In some synapses, the postsynaptic membrane contains enzymes that break down the neurotransmitter
In other synapses, the presynaptic membrane reabsorbs the neurotransmitter for repackaging in synaptic vesicles
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24. Neurotransmitters UNIT B
Chapter 12: Nervous System
Section 12.2
Neurotransmitters
Many drugs that affect the nervous system act by interfering or enhancing the action of neurotransmitters. Drugs can:
Enhance or block the release of neurotransmitter
Mimic the neurotransmitter
Block the receptor for the neurotransmitter
Interfere with the removal of the neurotransmitter
Example:
Sarin gas is a chemical weapon that inhibits acetylcholinesterase (AChE), an enzyme that is responsible for the breakdown of acetylcholine (ACh)
Leads to prolonged ACh activity (convulsive spasms)
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25. Check Your Progress UNIT B
Chapter 12: Nervous System
Section 12.2
Check Your Progress
Describe the activity of the sodium-potassium pump present in neurons.
Explain how the changes in Na+ and K+ ion concentrations that occur during an action potential are associated with depolarization and repolarization.
Define refractory period, saltatory conduction, and synaptic integration.
ANSWERS
1. The sodium-potassium pump in neurons are always transporting Na+ ions to the outside and K+ ions to the inside of the cell. This is active transport and requires an expenditure of ATP energy.
2. During an action potential, the sodium voltage-gated channel proteins open and Na+ ions enter the cell, causing a depolarization. The potential difference across the membrane rises from −70 mV to +35 mV. Then the sodium gates close, the potassium voltage-gated channel proteins open, and K+ ions enter the cell. This causes a repolarization and, briefly, a slight hyperpolarization.
3. refractory period—in nonmyelinated axons, a period in which sodium gates are unable to open following an action potential; saltatory conduction—a type of conduction in mylenated axons when the action potention “jumps” from node to node”; synaptic integration—the summation of all incoming excitatory and inhibitory messages at the cell body of a neuron.
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26. UNIT B
Chapter 12: Nervous System
Section 12.2
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27. UNIT B
Chapter 12: Nervous System
Section 12.2
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