Essential knowledge 3.E.2
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Essential knowledge 3.E.2 Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses
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Essential knowledge 3.E.2. Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. The neuron is the basic structure of the nervous system that reflects function. - PowerPoint PPT Presentation
Transcript of Essential knowledge 3.E.2
Essential knowledge 3.E.2
Animals have nervous systems that detect external
and internal signals, transmit and integrate
information, and produce responses
The neuron is the basic structure of the nervous system that
reflects function.
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.)
https://www.youtube.com/watch?v=BAldLXDPWZM
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.
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.
Conduction of Action PotentialsAn 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
Action potentials travel in only one direction: toward the synaptic terminals
Which direction does the action potential travel??
Fig. 48-11-1
Axon
Plasmamembrane
Cytosol
Actionpotential
Na+
Fig. 48-11-2
Axon
Plasmamembrane
Cytosol
Actionpotential
Na+
Actionpotential
Na+
K+
K+
Fig. 48-11-3
Axon
Plasmamembrane
Cytosol
Actionpotential
Na+
Actionpotential
Na+
K+
K+
ActionpotentialK+
K+
Na+
Conduction SpeedThe speed of an action potential
increases with the axon’s diameterIn 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
Fig. 48-12a
Axon Myelin sheath
Schwanncell
Nodes ofRanvier
SchwanncellNucleus ofSchwann cell
Node of Ranvier
Layers of myelinAxon
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
Schwanncell
Nodes ofRanvier
SchwanncellNucleus ofSchwann cell
Node of RanvierLayers of myelin
Axon
Transmission of information between neurons occurs across synapses.
1. 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!
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
Fig. 48-14
Postsynapticneuron
Synapticterminalsof pre-synapticneurons
5 µm
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
Fig. 48-15
Voltage-gatedCa2+ channel
Ca2+12
3
4
Synapticcleft
Ligand-gatedion channels
Postsynapticmembrane
Presynapticmembrane
Synaptic vesiclescontainingneurotransmitter
5
6
K+Na+
Fun FactCurare 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.
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
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
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
✘✘ 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.
