Tuesday, April 1, 2014
GOALS
Learn about homeostasis from the webquest
Learn how action potentials are propagated along a
neuron
Review action potentials using the webquest
HOMEWORK:
Work on Target Packet
Read 48.2 and 48.3—take notes, etc.
Remember—Quiz on Thursday
1
Neurons
• Functional unit of nervous system
• Bundles of neurons called nerves
• Know parts & functions:
– Cell body
-Axon
– Dendrite
-Axon hillock
– Synaptic terminal
(figure 48.4)
-Myelin sheath
-Node of Ranvier
-Schwann cell
(glial)
• Types of neurons:
– Motor neurons
– Sensory neurons
– Interneuron
2
Neurons (figure 48.4)
3
Glial Cells (figure 48.12)
• CNS has glial cells called astrocytes
• Oligodendrocytes (of CNS) & Schwann cells
(PNS) make myelin
4
Saltatory Conduction (figure 48.13)
Glial cells allow electrical messages to travel
faster along axon of neuron.
5
Human Nervous System Components
• Central Nervous System
 Brain and spinal cord
 Process, associate, integrate
 Composed of interneurons
 With myelin = white matter
 Without myelin = grey matter
• Peripheral Nervous System
• Sense stimuli (receptors - dendrite of neuron)
• Motor responses using effectors (muscles, organs,
glands)
• Transmit information to and from CNS
• Sensory and motor neurons
• Groups of cell bodies of PNS called ganglia
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Summary of Information Processing
(figure 48.3)
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How Neurons Work: REVIEW
• ION CHANNELS
– Integral plasma membrane proteins
– Neurons have K+ and Na+ channels
– Allow specific ions to diffuse down chemical and
electrical gradient
– Can be gated or ungated ion channels:
• UNGATED = open all the time, no gradient
established across membrane
• GATED = open (or close) in response to chemical or
electrical stimulus
*Chemically gated = channels open in response to
binding of ligand, ion, hormone
*Voltage gated = open in response to change in
electrical charge across plasma membrane
8
Na+ and K + are voltage-gated ions channels
How Neurons Work: Resting Potential
• Lots of Na+ outside neuron
• Lots of K+, anions, & proteins INSIDE neuron
• Inside of neuron is less positive (negative)
compared to outside of neuron (figure 48.6a,b)
• Energy is required to maintain resting potential
• Na+/K+ pump works (use ATP) to maintain
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gradient of Na+ out and K+ inside (fig 8.15, 48.7b)
How Neurons Work: Toilet Analogy
• Little flush…
subthreshhold stimulus
• Normal flush…
threshhold stimulus
• BIG flush…
threshhold stimulus, same
threshhold regardless of stimulus strength
All or NONE responses
• Push down flusher when water is emptying or
filling…
refractory period
• Push up on flusher (rather than down)…
hyperpolarization
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How Neurons Work: Changing
Membrane Potential (figure 48.9)
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How Neurons Work: Action Potential
1. Stimulus causes change in membrane voltage,
Na+ channels open, and Na+ rushes into
neuron
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How Neurons Work: Action Potential
2. Nearby Na+ channels open along axon,
causing more Na+ to rush into neuron
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How Neurons Work: Action Potential
3. Voltage gated Na+ channels close, and K+
channels open, causing more negative change
inside of neuron
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How Neurons Work: Action Potential
4. Hyperpolarization occurs before the sodium /
potassium pump restores resting potential
15
Neuron Circuits
Presynaptic Neuron
Postsynaptic Neuron
a.
b.
c.
Reflex Arc
16
Neuron Circuit: Reflex Arc (2) (3)
• Involve two or all three types of neurons
• Are automatic & innate; cannot be learned
• Protect body from harmful stimuli
*Name other
examples of
reflexes
*Do other
animals have
reflexes?
Provide an
example...
*What’s the
selective
advantage of
reflexes?
17
Use graph to answer questions:
1. Neuron membrane is
unable to respond to
any further stimulation,
regardless of intensity.
2. The Na+ gates (are)
open.
3. Threshhold potential is
achieved.
4. Repolarization occurs,
Na+ gates close, K+
gates (are) open.
5. Hyperpolarization
6. Action potential 18(max.
depolarization)
A multiple guess for your CNS!
7. The threshhold potential of a membrane:
A. Equals 70mV
B. Opens voltage-gated channels that result in
rapid outflow of Na+ ions
C. Is the depolarization that is need to generate
an action potential
D. Is a graded potential that is proportional to
the strength of a stimulus
19
Another multiple guess for your CNS!
8. A toxin that binds specifically to the voltagegated sodium channels of axons would:
A. Block all sodium movement into or out of a
neuron
B. Block repolarization
C. Prevent the axon from reaching the
threshhold potential
D. Ultimately block sodium and potassium
movement
20
Another multiple guess for your CNS!
9. Action potentials are usually propagated in only
one direction along an axon because:
A. The node of Ranvier conducts in one direction
B. The brief refractory period prevents opening of
voltage gated Na+ channels
C. The axon hillock has a higher membrane
potential than the tips of the axon
D. Ions can flow along a neuron in only one
direction
E. Both Na+ and K+ voltage-gated channels open
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in one direction
Saltatory Conduction (figure 48.13)
Glial cells allow electrical messages to travel
faster along axon of neuron.
22
Synaptic Transmission
depolarization or hyperpolarization
1. If neurotransmitter causes Na+ channels to open,
what will happen to postsynaptic neuron? Why?
2. If neurotransmitter causes K+ channels to open, what
happens to postsynaptic neuron? Why?
3. If neurotransmitter causes Cl- channels to open, what
happens to postsynaptic neuron? Why?
Which situation(s) is (are) examples of excitatory
postsynaptic potentials (EPSP)? Explain.
Which situation(s) is(are) examples of inhibitory
postsynaptic potentials (IPSP)? Explain.
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Neural Integration
What determines whether or not a postsynaptic neuron
continues the action potential (message)?
Amount of neurotransmitter binding to receptors
Amount of neurons releasing neurotransmitters into
synapse
Distance of synapse, distance of receptor from axon hillock
Frequency of neurotransmitter discharge (Summation)
ALL OF THE ABOVE RELATE TO STRENGTH OF A
STIMULUS! (and intensity of brain perception of stimulus)
WARM VS. HOT
PRESSURE VS. PAIN
LIGHT VS. BLINDING
SOUND VS. LOUD
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Neural Integration - SUMMATION
TWO TYPES OF SUMMATION:
TEMPORAL: lots of chemical transmissions in small
amount of time
Spatial: lots of different pre-synaptic neurons stimulate
post-synaptic cell (in a particular space)
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Neural Integration - SUMMATION
Figure
48.16a,b
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Neural Integration - SUMMATION
Figure
48.16c,d
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Neuron Circuit: Reflex Arc (2) (3)
• Involve two or all three types of neurons
• Are automatic & innate; cannot be learned
• Protect body from harmful stimuli
Figure 49.3
*Name other
examples of
reflexes
*Do other
animals have
reflexes?
Provide an
example...
*What’s the
selective
advantage of
reflexes?
28
Reflex Concept Generalization
patellar reflex, stimulus
(hammer), effector (upper
quadriceps), sensory receptor,
sensory neuron, motor neuron,
spinal cord, brain, interneuron,
inhibition, synapse(s)
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