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Neuroscience and Behavior

Chapter 2

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“The brain is wider than the sky.”

Emily Dickinson, 1830-1886

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Neuroscience and BehaviorNeural Communication Neurons How Neurons Communicate How Neurotransmitters Influence Us

The Nervous System The Peripheral Nervous System The Central Nervous System

The Endocrine System

The Brain Older Brain Structures The Cerebral Cortex Our Divided Brain Studying Hemispheric Differences in the Intact Brain

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Neural Communication

The body’s information system is built from billions of interconnected cells called neurons.

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Neuron

A nerve cell, or a neuron, consists of many different parts.

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Parts of a Neuron

Cell Body: Life support center of the neuron.

Dendrites: Branching extensions at the cell body. Receive messages from other neurons.

Axon: Long single extension of a neuron, covered with myelin [MY-uh-lin] sheath to insulate and speed up messages through neurons.

Terminal Branches of axon: Branched endings of an axon that transmit messages to other neurons.

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Neurons: Communication

• Membrane: a skin that separates the inside from the outside of the neuron

• Ions: Molecules that are positively or negatively charged

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Neurons: Communication

• Resting Neuron:– When a neuron is

polarized, more negative ions are inside.

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Neurons: Communication

– When stimulated the positively charged ions flow in and negative ones flow out

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Neuron: Communication

• Action Potential– When neurons depolarized– When soma receives

enough stimulation, the gates open and lets some negative ions out and some positive ones in.

– Then the whole cell fires, more gates open and more positive ions rush in

– The electric charge of the neuron suddenly changes from negative to positive

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Action Potential

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Threshold

Threshold: Each neuron receives excitatory and inhibitory signals from many neurons. When the excitatory signals minus the inhibitory signals

exceed a minimum intensity (threshold) the neuron fires an action

potential.

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Action Potential Properties

All-or-None Response: A strong stimulus can trigger more neurons to fire, and to fire more often, but it does not affect the

action potentials strength or speed.

Intensity of an action potential remains the same throughout the length of the

axon.

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Synapse

Synapse [SIN-aps] a junction between the axon tip of the sending neuron and the

dendrite or cell body of the receiving neuron. This tiny gap is called the synaptic gap or

cleft.

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Neurotransmitters

Neurotransmitters (chemicals) released

from the sending neuron travel across the synapse and bind to receptor sites on

the receiving neuron, thereby influencing it to generate an action

potential.

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Reuptake

Neurotransmitters in the synapse are

reabsorbed into the sending neurons

through the process of reuptake. This

process applies the brakes on

neurotransmitter action.

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• Excitatory Neurotransmitters

• Inhibitory Neurotransmitters

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• Location

Brain, spinal cord, peripheral nervous system, especially some organs of the parasympathetic nervous system

• Effect

Excitatory in brain and autonomic nervous system; inhibitory elsewhere

• Function

Muscle movement; cognitive functioning

• Related to Drug Curare

poisonous darts that paralyze skeletal muscles

• Deficiency in ACh production in patients suffering from Alzheimer’s disease

Acetylcholine (ACh)

Neurotransmitters

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How Neurotransmitters Influence Us

Serotonin

From Mapping the Mind, Rita Carter, © 1989 University of California Press

LocationBrain, spinal cord

EffectInhibitory

FunctionSleeping, eating,

mood, pain, depression, alcoholism, suicide, impulsivity, aggression, and coping with stress

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Dopamine Pathways

LocationBrain

•EffectInhibitory or excitatory

•FunctionMuscle disorders, mental disorders, Parkinson’s From Mapping the Mind, Rita Carter, © 1989

University of California Press

22Endorphins

• LocationBrain, spinal cord

• EffectPrimarily inhibitory, except in hippocampus

• FunctionPain suppression, pleasurable feelings, appetites, placebos

– “runners high”

Neurotransmitters

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Lock & Key Mechanism

Neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism.

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Agonists

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Antagonists

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Nervous System

CentralNervousSystem(CNS)

PeripheralNervousSystem(PNS)

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The Nervous System

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Peripheral Nervous System

Somatic Nervous System: The division of the peripheral nervous system that controls the body’s skeletal muscles.

Autonomic Nervous System: Part of the PNS that controls the glands and other muscles.

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Autonomic Nervous System (ANS)

Sympathetic NS “Arouses”

(fight-or-flight)

Parasympathetic NS “Calms”

(rest and digest)

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Central Nervous System

• Receives, processes, interprets, and stores incoming sensory information– The brain is the control center– The spinal cord is an extension of the brain

• Has some autonomy• Produces spinal reflexes requiring no conscious

efforts

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Spinal Reflex

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Read the list

• Blue• Green• Red• Yellow• Red• Orange• Green• Brown• Yellow• Purple• Red

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Name the color

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Name the color

BrownBlueRedPurpleOrangeBlackBlueGreenBrown

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The Brain

Brain Stem

Cerebellum (little brain)

Limbic System

Cerebral Cortex

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The Brain: Older Brain Structures

The Brainstem is the oldest part of the brain, beginning where the spinal cord swells and enters the skull. It is responsible for automatic survival

functions.

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Brainstem

The Medulla [muh-DUL-uh] is the base

of the brainstem that controls heartbeat

and breathing.

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Brainstem

The Thalamus [THAL-uh-muss] is the brain’s sensory switchboard, located on top of the brainstem. It directs

messages to the sensory areas in the cortex and transmits

replies to the cerebellum and

medulla.

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Brainstem

Reticular Formation is a nerve network in the brainstem that plays an important role in controlling

arousal.

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The “little brain” attached to the rear of the brainstem. It

helps coordinate voluntary movements

and balance.

Cerebellum

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The Brain

Techniques to Study the Brain

A brain lesion experimentally

destroys brain tissue to study animal behaviors after such destruction.

Hubel (1990)

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Clinical ObservationClinical observations have shed light on a

number of brain disorders. Alterations in brain morphology due to neurological and

psychiatric diseases are now being catalogued.

Tom

Landers/ B

oston Globe

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Electroencephalogram (EEG)An amplified recording of the electrical waves

sweeping across the brain’s surface, measured by electrodes placed on the scalp.

AJ P

hoto/ Photo R

esearchers, Inc.

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PET Scan

PET (positron emission tomography)

Scan is a visual display of brain

activity that detects a radioactive form of glucose while the

brain performs a given task.

Courtesy of N

ational Brookhaven N

ational Laboratories

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MRI ScanMRI (magnetic

resonance imaging) uses magnetic fields and radio waves to produce computer-

generated images that distinguish among

different types of brain tissue. Top images show ventricular enlargement in a

schizophrenic patient. Bottom image shows brain regions when a

participants lies.

Both photos from Daniel Weinberger, M.D., CBDB, NIMH

James Salzano/ Salzano Photo Lucy Reading/ Lucy Illustrations

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The Limbic System is a doughnut-shaped system of neural

structures at the border of the brainstem and cerebrum, associated with emotions such as fear, aggression and

drives for food and sex. It includes the hippocampus, amygdala, and hypothalamus.

The Limbic System

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Amygdala

The Amygdala [ah-MIG-dah-la] consists of two lima bean-sized neural clusters linked to the emotions of fear and

anger.

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Hypothalamus

The Hypothalamus lies below (hypo) the thalamus. It directs several maintenance activities like eating,

drinking, body temperature, and

control of emotions. It helps govern the

endocrine system via the pituitary gland.

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Rats cross an electrified grid for self-

stimulation when electrodes are placed

in the reward (hypothalamus) center (top picture). When the

limbic system is manipulated, a rat will navigate fields or climb

up a tree (bottom picture).

Reward CenterS

anjiv Talw

ar, SU

NY

Dow

nstate

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Brain: Structures

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Structure of the Cortex

Each brain hemisphere is divided into four

lobes that are separated by

prominent fissures. These lobes are the

frontal lobe (forehead), parietal lobe (top to rear head), occipital lobe (back head) and temporal lobe (side of

head).

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BrainFrontal LobeEmotion, planning, creative thinking and motor cortex.

Left lobe, Broca’s area.

Parietal lobe receives information from pressure, pain, touch and temperature, from overall body.

Temporal lobe regulates hearing, balance, and equilibrium. It is important in face recognition, and contains auditory cortex.

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Visual Function

The functional MRI scan shows the visual cortex is active as the subject looks at faces.

Courtesy of V

.P. Clark, K

. Keill, J. M

a. M

aisog, S. Courtney, L

.G.

Ungerleider, and J.V

. Haxby,

National Institute of M

ental Health

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Auditory Function

The functional MRI scan shows the

auditory cortex is active in patients who

hallucinate.

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More intelligent animals have increased “uncommitted” or association areas of the

cortex.

Association Areas

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LanguageAphasia is an impairment of language,

usually caused by left hemisphere damage either to Broca’s area (impaired speaking)

or to Wernicke’s area (impaired understanding).

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Specialization & Integration

Brain activity when hearing, seeing, and speaking words

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Our Divided Brain

Our brain is divided into two hemispheres. The left hemisphere processes reading,

writing, speaking, mathematics, and comprehension skills. In the 1960s, it was

termed as the dominant brain.

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Non-Split Brains

People with intact brains also show left-right hemispheric differences in mental

abilities.

A number of brain scan studies show normal individuals engage their right

brain when completing a perceptual task and their left brain when carrying out a

linguistic task.

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Splitting the BrainA procedure in which the two hemispheres of the brain are isolated by cutting the connecting fibers

(mainly those of the corpus callosum) between them.

Corpus Callosum

Ma

rtin M

. Ro

the

r

Courtesy of T

erence William

s, University of Iow

a

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Split Brain Patients

With the corpus callosum severed, objects (apple) presented in the right visual field can be named.

Objects (pencil) in the left visual field cannot.

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Divided Consciousness

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Try This!

Try drawing one shape with your left hand and one with your right hand,

simultaneously.B

BC