Transcript 2014 nervous system ppt

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
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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
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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.
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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
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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
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Neuron Circuits
Presynaptic Neuron
Postsynaptic Neuron
a.
b.
c.
Reflex Arc
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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
*Name other
examples of
reflexes
*Do other
animals have
reflexes?
Provide an
example...
*What’s the
selective
advantage of
reflexes?
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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
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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
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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.
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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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