1. Essential knowledge 3.E.2
Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses

2. The neuron is the basic structure of the nervous system that reflects function.

3. Hear about the neuron and how it functions from MIT Professor, Eric Lander, famous for heading up the Human Genome Project! (Homework: 50 minute lecture, but well worth the time.)
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4. 1. A typical neuron has a cell body, axon and dendrites
1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator. 2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. 3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

5. Action potentials propagate impulses along neurons.
1. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes.
2. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized.
3. Na+/K+ pumps, powered by ATP, work to maintain membrane potential.

6. Conduction of Action Potentials
An action potential can travel long distances by regenerating itself along the axon
At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane

7. Action potentials travel in only one direction: toward the synaptic terminals
Which direction does the action potential travel??

8. Figure 48.11 Conduction of an action potential
Axon
Plasma
membrane
Action
potential
Na+
Cytosol
Figure Conduction of an action potential

9. Figure 48.11 Conduction of an action potential
Axon
Plasma
membrane
Action
potential
Na+
Cytosol
Action
potential K+
Na+
Figure Conduction of an action potential K+

10. Figure 48.11 Conduction of an action potential
Axon
Plasma
membrane
Action
potential
Na+
Cytosol
Action
potential K+
Na+
Figure Conduction of an action potential K+
Action
potential K+
Na+ K+

11. Conduction Speed
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
Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS

12. Node of Ranvier Layers of myelin Schwann cell Nodes of Nucleus of
Fig a
Axon
Myelin sheath
Schwann
cell
Nodes of
Ranvier
Nucleus of
Schwann cell
Node of Ranvier
Layers of myelin
Figure Schwann cells and the myelin sheath

13. Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found
Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction
Axon
Myelin sheath
Schwann
cell
Nodes of
Ranvier
Nucleus of
Schwann cell
Node of Ranvier
Layers of myelin

14. Transmission of information between neurons occurs across synapses.
In most animals, transmission across synapses involves chemical messengers called neurotransmitters.
• Acetylcholine
• Epinephrine
• Norepinephrine
• Dopamine
• Serotonin
• GABA
2. Transmission of information along neurons and synapses results in a response.
3. The response can be stimulatory or inhibitory.
The location and functions of each of these neurotransmitters will not be on the AP Exam!

15. Concept 48.4: Neurons communicate with other cells at synapses
At electrical synapses, the electrical current flows from one neuron to another
At chemical synapses, a chemical neurotransmitter carries information across the gap junction
Most synapses are chemical synapses

16. Postsynaptic neuron Synaptic terminals of pre- synaptic neurons 5 µm
Fig
Postsynaptic
neuron
Synaptic
terminals
of pre-
synaptic
neurons
Figure Synaptic terminals on the cell body of a postsynaptic neuron (colorized SEM)
5 µm

17. The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal
The action potential causes the release of the neurotransmitter
The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell

18. Synaptic vesicles containing Presynaptic neurotransmitter membrane
Fig 5
Na+ K+
Synaptic vesicles
containing
neurotransmitter
Presynaptic
membrane
Voltage-gated
Ca2+ channel
Postsynaptic
membrane 1
Ca2+ 4 2 6
Figure A chemical synapse
Synaptic
cleft 3
Ligand-gated
ion channels

19. Fun Fact
Curare is a drug that causes paralysis. As an acetylcholine antagonist, it binds to acetylcholine receptors at nerve-muscle junctions, preventing communication between nerves and muscles.
Doctors sometimes use curare to immobilize patients during extremely delicate surgery.
South American tribes have long used curare as an arrow poison.

20. Generation of Postsynaptic Potentials
Direct synaptic transmission involves binding of neurotransmitters to ligand- gated ion channels in the postsynaptic cell
Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential

21. Postsynaptic potentials fall into two categories:
Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold
Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold

22. Different regions of the vertebrate brain have different functions.
Examples include:
• Vision
• Hearing
• Muscle movement
• Abstract thought and emotions
• Neuro-hormone productio
• Forebrain (cerebrum), midbrain (brainstem) and hindbrain
(cerebellum)
• Right and left cerebral hemispheres in humans

23. ✘✘ The types of nervous systems, development of the human nervous system, details of the various structures and features of the brain parts, and details of specific neurologic processes are beyond the scope of the course and the AP Exam.