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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

1

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

5

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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

4

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