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TRANSCRIPT
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The Nervous System
Chapter 38.1-38.5
Anatomy of a Neuron
I. Dendrites
II. Cell Body
III. Axon
Synaptic terminal
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Neuron Connections
cell body
axon axon terminal cell body
axon
cell body
axon axon terminals dendrites
dendrites
sensory neuron
interneuron motor neuron
detect stimuli and signal interneurons
process information from sensory neurons and send signals to motor neurons
control muscles and glands
Action Potentials
• Potential = difference in electrical charge between inside and outside of cell
• An electrical signal which carries information within the neuron
– When stimulus in the neuron’s trigger zone reaches threshold gated sodium channels open
– Voltage difference between inside and outside the cell decreases and starts the action potential
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5
3
4
1 2
time
(milliseconds)
resting
potential
action potential
threshold
less negative more
negative
Electrical Events During an Action Potential
Fig. 38-2
Neuron at Rest
Resting K channel maintains negative charge in resting cell
resting K+ channel (always open)
voltage-gated Na+ channel (closed)
voltage-gated K+ channel (closed)
Cl Cl Cl
Cl
K K
K
K
K
K
Na
Na Na
Na
(a) The resting potential
neuron cytoplasm (- charge, high K+ concentration)
extracellular fluid (+ charge, high Na concentration)
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Neuron is Stimulated
Na+ influx creates positive charge in cell
+ + – – – – –
Cl
Cl
Cl
Cl
K
K
K
K
K
Na
Na Na
Na
Na
Na
(b) The action potential
A voltage-gated Na+ channel opens
action potential
Na
First influx of Na+ causes chain reaction
• Opens nearby K+ gates
– K+ rushes out of cell
– Negative charge inside cell restored, causing Na+ gate to close
• Opens nearby Na+ gates
– AP moves down axon + + – – – – –
Cl
Cl
Cl
K
K
K K
K
K
Na
Na
Na
Na
K
(c) The resting potential is restored
The voltage-gated Na+ channel closes
The voltage- gated K+ channel opens
Na
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A Myelinated Axon
Fig. 38-3
node
An action potential jumps
from node to node, greatly
speeding up conduction
down the axon
axon
myelin myelin
sheath
axon
Schwann cell
Copyright © 2011 Pearson Education, Inc.
Action Potential Releases Neurotransmitters
Neurotransmitters bind to receptors on the postsynaptic neuron
dendrite of postsynaptic neuron
receptor
neurotransmitter
ions
4
synaptic vesicle
synaptic cleft
The positive charge of the action potential causes the synaptic vesicles to release neurotransmitters
An action potential is initiated
The action potential reaches the synaptic terminal of the presynaptic neuron
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2
3
Neurotransmitters are taken back into the synaptic terminal, are degraded, or diffuse out of the synaptic cleft
6
synaptic terminal of presynaptic neuron
neurotransmitters
Neurotransmitter binding causes ion channels to open, and ions flow in or out
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Neurotransmitters
Neurons use chemicals called neurotransmitters to communicate with other neurons, muscles, or glands.
Acetylcholine (Ach)
• Controls motor function
• Stimulates digestion
• Maintains heart activity
• Regulates REM and short-term memory formation
• Anger control – Alzheimer’s patients show up to a 90% decrease of
Ach activity in the brain
– Botox inhibits Ach release from neurons connecting to muscles
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Norepinephrine
• “Fight or Flight” response
– Increases heart rate, blood pressure and alertness
– Triggers release of glucose from energy stores
– Increases blood flow to brain and muscles
– Halts digestive processes
• Associated with ADHD
– Adderall and Ritalin increase norepi and dopamine production
Serotonin
• Controls overall sense of well-being
• Controls hunger – THC decreases serotonin sensitivity
• Helps regulate sleep patterns
• Intimately tied to sensory perception
• Controls cognitive functions such as memory and learning abilities – Linked to OCD, learning disabilities, and depression
– Prozac blocks the clearing of serotonin out of synapse
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GABA
• Inhibitory effects of other neurotransmitters in the brain-Quiets brain activity
• Binds to neurotransmitter receptors to block action
• Associated with anxiety disorders
• Valium enhances effects
• Like Dopamine, cannot pass the blood-brain barrier
Glutamate
• Excitatory relative of GABA
• Is actually toxic to nerve cells and can destroy them in excess
• Lou Gehrig's’ Disease (ALS) is the excessive production of Glutamate
• Brain damage and stroke often lead to overproduction
Endorphins • Blocks pain receptors
• Create sense of well-being, involved in arousal
• Produced in the pituitary during periods of stress, while exercising, in pain, and during sex
• Triggers hibernation in bears: slows metabolism, heart rate and respiration
• Very similar in structure and function to opiates such as morphine and heroin
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Dopamine
• Produced in the pleasure center of the brain whenever you do something you like – Major player in drug addiction
• Inhibitory Neurotransmitter – Blocks response neuron from firing
• Too much = Schizophrenia
• Too little = Parkinson’s Disease – Can’t inhibit Ach, which leads to incontrollable
tremors
ring of ganglia
diffuse network
of neurons
(a) Hydra
Nervous System Organization
Fig. 38-6a
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Nervous System Organization
Fig. 38-6b, c
nerve cords cerebral
ganglia
(brain)
brain
(b) Flatworm (c) Octopus
Organization and Functions of the Vertebrate Nervous System
Fig. 38-7
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stimulus
sensory
neuron spinal
cord
motor
neuron
dorsal root
interneuron
ventral
root
The motor neuron stimulates the effector muscle
The effector muscle causes a withdrawal response
A painful stimulus activates a pain sensory neuron
The signal is transmitted by the pain sensory neuron to the spinal cord
The signal is transmitted to an interneuron and then to a motor neuron
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3
2
1
5
The Pain-withdrawal Reflex
Fig. 38-10
hypothalamus
olfactory
bulb
thalamus
hippocampus amygdala
cerebral cortex limbic region
of cortex
corpus callosum
The Limbic System Emotions
Fig. 38-13