Chapter 2:

Neuroscience

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The Nervous System• System which relays messages throughout the

body

• Cells are called neurons. Over 100 billion in NS

• Two major divisions of the nervous system:

Central Nervous System

Peripheral Nervous System.

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• History of our understanding

• Heart was considered seat of consciousness

• Late 1800s, brain became the central focus

• Franz Gall - brain a muscle

• Bumps on head revealed one’s traits (phrenology).

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• Later 1800s, physicians treating wounded soldier during Franco-Prussian War

• Best word to describe how the brain functions?

• Electrochemically

• Three major functions of the nervous system and individual neurons.

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Input - receives messages. (sensory neurons)Internal processing - interneurons or

association neurons.Output - sends messages. (motor neurons)

• Each individual neuron - same three functions.

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• Dendrites - receive messages (input).

• Cell body - processing (cell metabolism).

• Axon - sends messages (output).6

• Nature of the message?

• A chemical message

• Chemicals called neurotransmitters passed from one neuron to another

• Dozens of different neurotransmitters - dopamine, serotonin, acetylcholine (Ach), endorphins; p. 58.

• How neurotransmitters are passed.

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• Neurotransmitters - excitatory or inhibitory

• Excitatory chemicals make it more likely that receiving neuron will release its electrical (action) potential

• The message is fire, fire, fire

• Inhibitory transmitters make it less likely that receiving neuron will fire

• The message is don’t fire, don’t fire.

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• Note the synaptic gap that these chemicals must cross as they send messages

• How does the neuron know when to fire?

• Threshold.

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Synaptic Gap

• Threshold - the level of stimulation required to trigger a neural impulse

• If this dividing point is passed, the receiving neuron releases its electrical potential (action potential)

• Positive ions outside the cell are sucked into the cell itself.

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• Refractory period - absolute and relative

• Absolute - neuron cannot fire

• Relative - neuron can fire, but takes more excitatory chemicals

• All-or-none process - neuron releases all of its electrical potential or none of it.

• Example: pulling trigger on a gun.

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• Let’s Review . . .

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An Exception: A Simple Reflex

Because the simple pain reflex pathway runs through the spinal cord and out, your hand jerks from the candle’s flame before your brain receives and responds to the information that causes you to feel pain. (page 63)

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Brain Structures Lower Brain Structures • the brainstem - responsible for

automatic survival functions. Crossover. Also no conscious effort.

• the medulla - the base of the brainstem; controls heartbeat and breathing;

• the reticular formation - plays an important role in arousal and attention.

• Thalamus – switchboard.• the cerebellum - coordinates

voluntary movement and balance.

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Brain Structures Mid-brain Structures The Limbic System

• hippocampus - linked to memory.

• amygdala - linked to emotion; aggressiom / fear; case of Julia.

• hypothalamus - eating, drinking, sexual behavior, and reward centers.

• Research of James Olds with rats and reward centers.

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Olds’ Experiment

• Do humans have limbic pleasure centers?

• Stimulated patients report mild pleasure, however, unlike rats, they are not driven to a frenzy

• Some have suggested that addictive disorders (alcoholism, drug abuse) may be related to pleasure centers.

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Brain Structures Higher Brain Structures

• cerebral cortex - an intricate covering of interconnected neurons, like bark on a tree, which forms a thin surface layer on the cerebral hemisphere.

• Our body’s ultimate control and information processing center.

• Makes us distinctly human.

Cerebral Cortex

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Brain StructuresLobes of Cortex

• Frontal lobe - Self-awareness, planning, goal-directed behavior; provides inhibitions, motor behavior.

• Phineas Gage.

• Motor cortex.

• Sensory cortex -Sense of touch.

• Auditory cortex

• Visual cortex.

Cerebral Cortex

• Electrical stimulation of motor cortex• Electrical stimulation of sensory cortex.

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Brain StructuresLobes of Cortex

• Occipital lobe - Visual cortex.

• Temporal lobe - Auditory cortex.

• Most of brain area is silent to the electrical probe.

• This may have lead to a myth that perhaps you have heard about the brain.

• Myth: We use only 10% of our brain.

Cerebral Cortex

Visual Cortex

Auditory Cortex

The Split Brain• The corpus callosum - large

band of nerve fibers connecting the left and right hemispheres.

• Carries messages between them.

• Some people have had this band severed (split brain). Why?

• To prevent continued seizures.

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Corpus Callosum

• Split brain research with animals

• Split brain research with humans

• The intact split brain and vision.

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Split Brain Subject Experiment

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Spoon is projected to right hemisphere only in split brain patient.

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HE projected to right hemisphere. ART projected to left hemisphere.

Split Brain Subject Experiment

Hemispheric Differences in the Intact Brain

• Activity increases in the left hemisphere when a person speaks or calculates

• A person recognizes a word faster and more accurately when flashed to the left hemisphere

• Activity increases in the right hemisphere when a person performs a perceptual task

• A person recognizes a picture faster and more accurately when flashed to the right hemisphere.

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