1. AP Bio
The Nervous System,

2. The Nervous System
Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses.
This is the essential knowledge statement from the curriculum framework. Detect---process---response
Image: Hillis, Principles of Life

3. What trends do you notice?
What trends do you notice? Students should see an increased presence in the nervous system as you move up the evolutionary ladder from hydra to jelly fish. They will also notice the increased presence of ganglia and increased presence of brain tissue. Carefully note that the sea star is evolutionarily misplaced in this trend-revealing graphic. (exception to the evolutionary trend)

4. Noteworthy Trends In Development
Increase in ganglia
Increase in sensory reception
Increase in cephalization
Cephalization is the concentration of nervous tissue in the anterior region of the organism.
Students may have prior knowledge of these terms. Ask them to define each term.
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies.
In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism.
Cephalization is defined on the slide.

5. Human Nervous System
Note the cephalization of the human nervous system. Our nervous system is divided into two main categories; the central (composed of brain and spine) and then the Peripheral system composed of the nerves and ganglia out side the brain and spine. Which system do you think would be more involved in detection, CNS or PNS? (PNS) Point out that nerves are composed of bundles of neuron (cell) projections called axons.

6. Consider this image. Ask students the following questions:
Which portion indicates where detection of a stimulus is occurring? Processing? Responding?
Our body continually detects stimuli from inside and outside our body. What are you detecting right now? (accept answers like the amount of light, hot/cold, pressure, etc)
What receptors are you using? Try to lead them to the 5 senses

7. Describe the flow of communication through the reflex arc showing that this pathway includes sensory input, integration/process and response. A reflex pathway includes the central nervous system and the peripheral nervous system in the pathway.

8. Neuron = nerve cells
The neuron is the basic structure of the nervous system that reflects function.
Neuron structure allows for the detection, generation, transmission, and integration of signal information.
Image from Hillis, Principles of Life

9. Take a moment to analyze the similarities and differences between each type of neuron. (next slide)

10. Neuron Anatomy A typical neuron has a cell body, axon and dendrites.
Describe the features of the neuron. Dendrites receive incoming stimuli. Notice there are several dendrites on the single neuron. The cell body contains organelles including the nucleus. The triangular axon hillock is the location in which the action potential will be generated. Once the action potential is generated, the signal will travel down the axon toward the synapse. The cell prior to the synapse is called the presynaptic neuron, the one occurring after the synapse is called the post synaptic neuron. Neuron transmitters will be released in the space or synaptic cleft.

11. Myelin Sheath Axon coated with Schwann cells insulates axon
speeds signal
signal hops from node to node
saltatory conduction
Some neurons have myelin sheaths produced by Schwann cells surrounding the axon.

12. Multiple Sclerosis action potential saltatory conduction Na+ myelin +–
axon + + + + –
Na+
Multiple Sclerosis
immune system (T cells) attack myelin sheath
loss of signal

13. dendrite  cell body  axon
signal
direction
Structure fits function
many entry points for signal
one path out
transmits signal
dendrites
cell body
axon
signal direction
synaptic terminal
myelin sheath
synapse

14. Evolutionary Adaptations of Axon Structure
The speed of an action potential increases with the axon’s diameter
In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase
Emphasize that students need to be able to write about these evolutionary adaptations when answering free-response quesitons.

15. Nucleus of Schwann cell Axon Myelin sheath
Node of Ranvier
Layers of myelin
Axon
Schwann cell
Schwann cell
Nodes of Ranvier
Nucleus of Schwann cell
Axon
Myelin sheath
Schwann cells and the myelin sheath. Notice the location of the Schwann cell on the exterior of the axon. What cellular process must occur at high levels in order for the Schwann cell to perform its function of myelin production? (protein synthesis)
0.1 m 15

16. Saltatory Conduction
Saltatory conduction. Notice that the conduction along a myelinated axon can occur quickly as large spaces can be skipped and impulse propagation occurs only at the nodes of Ranvier.
Cell body
Schwann cell
Depolarized region (node of Ranvier)
Myelin sheath
Axon
Notice that the conduction along a myelinated axon can occur quickly because large spaces can be skipped and occurs only at the node of Ranvier. Saltare is Latin for “to leap” and that is why conduction on a myelinated sheath is called saltatory conduction. What would you expect would happen when a disease such as multiple sclerosis causes demyelination? 16

17. Describe a Resting Potential:
What is the charge inside the neuron at rest?
Membranes of neurons are polarized by the establishment of electrical potentials across the membranes
Have students write out a description of a resting potential on a note card or piece of paper. They will likely want you to show the video a couple of times. When they have their description, ask them to trade with someone. Play the video one last time asking the card holders to correct any misinformation that is written. Return the card to the owner.
Resting potential = -70 mV Negatively charged proteins inside the cell are too large to move through resulting in an overall negative charge. Potassium moves out through the channels resulting in more positive external environment. Na/K pumps move sodium out and potassium out.

18. Source of Charge Differences:

19. Action Potential Action potentials propagate impulses along neurons.
In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized.
Na+/K+ pumps, powered by ATP, work to maintain membrane potential.
So, what is “polarized” anyway? Magnets have two poles & opposites attract while likes repel. Water has two polar H—O bonds due to the electronegativity differences between the elements H & O. Water is a polar molecule since it is 3-D with a slightly negative end (where the unshared electron pairs are located) and a slightly positive end (where the H’s are located). Polarity just means a “separation” of charge. One side of the neuronal membrane is more negative than the other side.

20. Membrane potential (mV)
Figure 48.11a
Action potential
Threshold
Resting potential
Time
Membrane potential (mV)
50
100
50 1 2 3 4 5 20

21. Action potential graph
Resting potential
Stimulus reaches threshold potential
Depolarization Na+ channels open; K+ channels closed
Na+ channels close; K+ channels open
Repolarization reset charge gradient
Undershoot K+ channels close slowly
40 mV 4
30 mV
20 mV
Depolarization
Na+ flows in
Repolarization
K+ flows out
10 mV
0 mV
–10 mV 3 5
Membrane potential
–20 mV
–30 mV
–40 mV
Hyperpolarization
(undershoot)
–50 mV
Threshold
–60 mV 2
–70 mV 1
Resting potential 6
Resting
–80 mV

22. Membrane potential (mV)
OUTSIDE OF CELL
INSIDE OF CELL
Inactivation loop
Sodium channel
Potassium channel
Threshold
Resting potential
Time
Membrane potential (mV)
50
100
50
Na K
Key 1
Resting state
At resting potential
Most voltage-gated sodium (Na+) channels are closed; most of the voltage-gated potassium (K+) channels are also closed
 Threshold & Resting State: The role of voltage-gated ion channels in the generation of an action potential. Ask students to read the graph and estimate the resting potential (-70 mV). 22

23. Membrane potential (mV)
When an action potential is generated
Voltage-gated Na+ channels open first and Na+ flows into the cell
50 2
Depolarization
OUTSIDE OF CELL
Sodium channel
Potassium channel
Membrane potential (mV)
Threshold 2
50
INSIDE OF CELL 1
Resting potential 1
Resting state
100
Inactivation loop
Time 23

24. Rising phase of the action potential Membrane potential (mV)
Key
Na K
Action potential
50 3
Rising phase of the action potential 3
During the rising phase, the threshold is crossed, and the membrane potential increases to and past zero
Membrane potential (mV) 2
50 1 2
Depolarization
100
Time
OUTSIDE OF CELL
Sodium channel
Potassium channel
INSIDE OF CELL
Inactivation loop 1
Resting state 24

25. Key
Na K
4. During the falling phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell 4
Falling phase of the action potential 3
Rising phase of the action potential
50
Action potential 3
Membrane potential (mV)
Threshold 4 2
50 1 2
Depolarization
Resting potential
100
At the peak of the action potential, when enough Na+ has entered the neuron and the membrane's potential has become high enough, the Na+ channels inactivate themselves by closing their inactivation gates. Closure of the inactivation gate causes Na+ flow through the channel to stop, which in turn causes the membrane potential to stop rising.
With its inactivation gate closed, the channel is said to be inactivated. With the Na+ channel no longer contributing to the membrane potential, the potential decreases back to its resting potential as the neuron depolarizes and subsequently hyperpolarizes itself. This decrease in voltage constitutes the falling phase of the action potential.
Time
OUTSIDE OF CELL
Sodium channel
Potassium channel
INSIDE OF CELL
Inactivation loop 1
Resting state 25

26. 5. During the undershoot, membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close and resting potential is restored
***Action potentials travel in only one direction: toward the synaptic terminals

27. Falling phase of the action potential 3
Key
Na K 4
Falling phase of the action potential 3
Rising phase of the action potential
50
Action potential 3
Membrane potential (mV)
Threshold 4 2
50 1 1 5 2
Depolarization
Resting potential
100
The raised voltage opened many more potassium channels than usual, and some of these do not close right away when the membrane returns to its normal resting voltage. Hence, there is an undershoot or hyperpolarization that persists until the membrane potassium permeability returns to its usual value.
Time
OUTSIDE OF CELL
Sodium channel
Potassium channel
INSIDE OF CELL
Inactivation loop 1
Resting state 5
Undershoot 27

28. Sequence the following in order of occurrence
Depolarization
Resting state
Repolarization
Hyperpolarization
Ask them to sequence these events (in their head or on paper)

29. Sequenced in order of occurrence
Resting state
Depolarization
Hyperpolarization
Repolarization
Once you show the sequence then ask students to describe the events using the graphic on the next slide/

30. Membrane potential (mV)?
Time
Membrane potential (mV)
50
100
50 1 2 3 4 5
Resting state
Depolarization
Hyperpolarization
Repolarization
What is represented by each question mark? Describe what is occurring at 1,2,3,4,5 using the words: Resting state, depolarization, repolarization, and hyperpolarization

31. a. the resting membrane potential to drop to 0 mV.
Adding a poison that specifically disables the Na+/K+ pumps to a culture of neurons will cause
a. the resting membrane potential to drop to 0 mV.
b. the inside of the neuron to become more negative relative to the outside.
c. the inside of the neuron to become positively charged relative to the outside.
d. sodium to diffuse out of the cell and potassium to diffuse into the cell.
Answer: a

32. How does the nerve re-set itself?
Sodium-Potassium pump
active transport protein in membrane
requires ATP
3 Na+ pumped out
2 K+ pumped in
re-sets charge across membrane
ATP
Dominoes set back up again.
Na/K pumps are one of the main drains on ATP production in your body. Your brain is a very expensive organ to run!

33. Name three specific adaptions of the neuron membrane that allow it to specialize in conduction
Responses should include voltage-gated K+ channels, sodium/potassium pumps, voltage-gated Na+ channels.

34. What happens when the impulse reaches the end of the axon?

35. Synapses
Transmission of information between neurons occurs across synapses.
A chemical synapse is a junction between two nerve cells consisting of a narrow gap across which impulses pass by means of a neurotransmitter
3.E.2.c begins here. Emphasize that there is much more to the story!

36. Cell To Cell Communication Events
Action potential depolarized the membrane of synaptic terminal, this triggers an influx of Ca2+.
That causes synaptic vesicles to fuse with the membrane of the pre-synaptic neuron.
Vesicles release neurotransmitter molecules into the synaptic cleft.
Neurotransmitters bind to the receptors of ion channels embedded in the postsynaptic membrane.

37. Calcium gated channels in the synaptic knob
Note the structural features that allow the cell to cell communication to occur in the synaptic region:
Calcium gated channels in the synaptic knob
Sodium channels in the post-synaptic membrane
Fluidity of the lipid bi-layer allows for exocytosis of the neurotransmitter
The transfer of information that occurs at the synapse is a classic example of cell to cell communication. The membrane is specifically adapted for this task. The synaptic knob membrane contains voltage gated Ca2+ channels, the post synaptic membrane contains receptor-bearing sodium, Na+ channels, and the fluidity of the membrane allows for the fusion of vesicles.

38. Action potential depolarized the membrane of synaptic terminal, this triggers an influx of Ca2+.
That causes synaptic vesicles to fuse with the membrane of the presynaptic neuron.
Vesicles release neurotransmitter molecules into the synaptic cleft.
Neurotransmitters bind to the receptors of ion channels embedded in the postsynaptic membrane.

39. Exocytosis Neurotransmitter release is a form of exocytosis.
In exocytosis, internal vesicles fuse with the plasma membrane to secrete macromolecules out of the cell.

40. Neuron Transmitter Binds With A Receptor On The Postsynaptic Membrane
The released neurotransmitter binds with the receptor on the postsynaptic membrane causing the channel to open allowing sodium ions to rush in. This influx of sodium can contribute to the development of an action potential in the receiving cell.

41. The neurotransmitter will then be released from the postsynaptic membrane and degraded.

42. Response
Transmission of information along neurons and synapses results in a response.
The response can be stimulatory or inhibitory.
3.E.2.c.2

43. Some synapses are excitatory others inhibitory
Some synapses are excitatory others inhibitory. Think of them as “on” and “off” switches.

44. ***There are more than 100 neurotransmitters
1 neurotransmitter may have more than a dozen different receptors
Acetylcholine
transmit signal to skeletal muscle
Epinephrine (adrenaline) & norepinephrine
fight-or-flight response
Dopamine
widespread in brain
affects sleep, mood, attention & learning
lack of dopamine in brain associated with Parkinson’s disease
excessive dopamine linked to schizophrenia
Serotonin
Nerves communicate with one another and with muscle cells by using neurotransmitters. These are small molecules that are released from the nerve cell and rapidly diffuse to neighboring cells, stimulating a response once they arrive. Many different neurotransmitters are used for different jobs:
glutamate excites nerves into action;
GABA inhibits the passing of information;
dopamine and serotonin are involved in the subtle messages of thought and cognition.
The main job of the neurotransmitter acetylcholine is to carry the signal from nerve cells to muscle cells. When a motor nerve cell gets the proper signal from the nervous system, it releases acetylcholine into its synapses with muscle cells. There, acetylcholine opens receptors on the muscle cells, triggering the process of contraction. Of course, once the message is passed, the neurotransmitter must be destroyed, otherwise later signals would get mixed up in a jumble of obsolete neurotransmitter molecules. The cleanup of old acetylcholine is the job of the enzyme acetylcholinesterase.

45. Neurotransmitters Weak point of nervous system
any substance that affects neurotransmitters or mimics them affects nerve function
gases: nitrous oxide, carbon monoxide
mood altering drugs:
stimulants
amphetamines, caffeine, nicotine
depressants
quaaludes, barbiturates
hallucinogenic drugs: LSD, peyote
SSRIs: Prozac, Zoloft, Paxil
poisons
Selective serotonin reuptake inhibitor

46. Injecting ethylene glycol tetraacetic acid (EGTA), a chelating agent that prevents calcium ions from moving across membranes, to a synaptic region would likely
a. increase the release of neurotransmitters by the presynaptic neuron.
b. decrease the release of neurotransmitters by the presynaptic neuron.
c. result in neurotransmitters being released, but could not bind to its receptors on the post synaptic neuron.
d. result in the lack of calcium ions keeping the ligand-gated ion channels open on the post synaptic neurons.
Answer: b

47. Ex - Nervous and muscular
The contraction of a muscle is a typical response generated by the nervous system.
Muscle contraction demonstrates the interdependence of the nervous and muscle systems.
Today we will consider a very specific mechanism for a RESPONSE generated by the nervous system: Muscle contraction. We will learn how a muscle contracts when stimulated by a chemical signal.

48. Motor cortex (control of skeletal muscles)
Somatosensory cortex (sense of touch)
Frontal lobe
Parietal lobe
Prefrontal cortex (decision making, planning)
Sensory association cortex (integration of sensory information)
Visual association cortex (combining images and object recognition)
Broca’s area (forming speech)
What parts of your cerebrum help you see and understand what you are seeing? (occipital lobe & parietal lobe)
What parts of your brain help you hear and make sense of what you are hearing? (temporal lobe)
Today we will look at the structural features that allow eyes and ears to function as receptors of stimuli.
Temporal lobe
Occipital lobe
Auditory cortex (hearing)
Visual cortex (processing visual stimuli and pattern recognition)
Cerebellum
Wernicke’s area (comprehending language)