chapter 3 neuroscience the brain and...

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Copyright © Allyn & Bacon 2006

NeuroscienceBiology and Psychology

Chapter 3


Neuroscience: The Brain and BehaviorI. How is the Nervous System Organized?II. Methods of Studying the BrainIII. How Does the Brain Function?IV. What Effects Do Hormones Have on

Behavior?V. How Do Genetic Factors Affect

Behavior?


I. How is the Nervous System Organized?

A. Cellular Level1. The Neuron

• Building block of the nervous system• Single nerve cell = neuron• Bundle of neurons = nerve or tract

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A. Cellular Level1. The Neuron

a. Three types of neuron

ii. Efferent or Motor Neurons: Carry info from the brain & spinal cord to other structures in the body

iii. Interneurons: Connect sensory and motor neurons

i. Afferent or Sensory Neurons: Carry info to the brain & spinal cord


1. The Neuronb. Glial cells surround, nourish, and support

the neurons– Smaller than neurons– More prevalent than neurons– Form the myelin sheath that covers some

large motor neurons• Speeds up transmission of neural signals• Multiple sclerosis causes a loss of

myelination


1. The NeuronAlzheimer’s Disease• A progressive deterioration of cognitive

skills (memory loss).• Reduced branching of the dendrite trees.• No cure.• Etiology: genetic, defective gene on the

21st chromosome, environmental factors.

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1. The Neurond. The Synapse

– Small space between neurons


A. Cellular Level2. The Functioning of Neurons

– Communication is an electrochemical process• Within neurons it is electrical• Between neurons it is chemical• A thin membrane around the neuron

allows the process


•Partially permeable cell membrane

– Traps charged particles inside or outside the neuron

– At rest, the interior carries a negative electrical charge

– The exterior carries a positive electrical charge

– This difference in charges creates a state of polarization

2. The Function of Neurons

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•Each neuron has a threshold–Level of stimulation required for activation

•When the threshold is reached:– “Gates” open in cell

membrane– Positive ions rush into

cell– Neuron is depolarized

• Relative charge is reversed

– Action potential has formed



•Action potential– The “spike charge” is an

electrical current that travels down an axon

• All-or-none Principle– Either the neuron fires or it doesn’t– Action potential is always the same strength

• If the threshold is not reached, the neuron will not fire



•Neuron must recover between firings–Refractory period– No action potentials can occur until resting

state is re-established


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A. Cellular Level3. Neurotransmitters and Behavior

– Chemical signal• At the axon terminal, the action potential

causes the release of neurotransmitters

– Communication must cross the synapse between neurons



3. Neurotransmitters• After binding with an adjacent neuron, one

of two processes occurs– Breakdown by enzymes– Reuptake back into the releasing neuron

• Neurotransmitters have two effects– Excitatory: receiving neuron fires more

easily– Inhibitory: receiving neuron fires less

easily

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3. Neurotransmitters• There are at least 50 different

neurotransmitters• Examples:

– Acetylcholine (Ach)• Excitatory• Receptors in skeletal muscles• Involved in memory and learning• Alzheimer’s disease involves

insufficient production of acetylcholine


3. Neurotransmitters

– Serotonin• Inhibitory• Involved in sleep regulation, appetite,

anxiety, and depression• Antidepressants affect serotonin• A monoamine neurotransmitter


3. Neurotransmitters– Dopamine

• Inhibitory• Involved in movement, learning and

memory, emotions, pleasure• Also involved in Schizophrenia,

ADHD, Parkinson’s Disease

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3. Neurotransmitters– Norephinephrine

• Excitatory• Involved in arousal, hunger, learning,

memory, & mood disorders.


3. Neurotransmitters• Neuropeptides are chemicals similar to

neurotransmitters– Endorphins

Inhibitory, Painkillers. Occur naturally in the brain & bloodstream. Similar to morphine.


A. The Cellular Level4. Neurotransmitters, Drugs and Behavior

–Psychopharmacology•Study of how drugs affect behavior

–Types of effects:a. Alter amount of neurotransmitter

released• Ecstasy causes massive release of

serotonin• May also block release of

neurotransmitters

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A. The Cellular Level– Types of effects:

a. Increase production of neurotransmitters

b. L-dopa, used to treat Parkinson’s disease


4. Neurotransmitters, Drugs, and Behavior

c. Change the speed at which neurotransmitters are disabled after release• Prozac and Zoloft slow reuptake of

serotonind. Bind to neurotransmitter receptor sites


4. Neurotransmitters, Drugs, and Behavior– Medications to treat Schizophrenia are often

dopamine antagonists• Mimic effects of dopamine• Reduce symptoms of schizophrenia

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Divisions of the NS

Nervous System

Peripheral Nervous System

Central Nervous System

Brain Spinal Cord

SomaticNS

Autonomic NS

SympatheticNS

Parasympathetic NS


Central Nervous Systema. The Brain

– Lower structures are involved in more basic functions

– Higher structures are involved in more complex functions


Divisions of the Nervous System

b. Spinal Cord

–Controls spinal reflexes without input from the brain

• Knee-jerk reflex–Relays information to and from the brain

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Divisions of the Nervous System

2. Peripheral Nervous System (PNS)– Carries information to and from the CNS– Consists of neurons and nerves found

outside the CNS


1. Peripheral Nervous Systema. Somatic nervous system

– Responds to and acts on the external stimuli

– Under voluntary control– Both sensory and motor neurons

b. Autonomic nervous system– Controls automatic processes– Two subdivisions


1. Peripheral Nervous Systemb. Autonomic Nervous System (ANS)

i. Sympathetic nervous system• Produces physiological changes,

increases heart rate, blood pressure, & respiration to perceived emergencies.

• Activates fight-or-flight responseii. Parasympathetic nervous system

• Controls normal physiological operations and calms the body

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Central Nervous System

Brain

Midbrain ForebrainHindbrain


b. The Braini. The Hindbrain: Survival functions

a) Medulla• Controls involuntary reflexes, heartbeat

and breathing• Contains the reticular formation

– Involved in arousal, sleep, attentionb) Pons

• Links lower brain with the rest of the brain

• Also involved in sleep and arousal


i. The Hindbrainc) Cerebellum

•“Little brain”•Influences balance, coordination, and movement• Only 10% of brain volume, but has >50%

of neurons• Alcohol disrupts the cerebellum

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b. The Brainii. Midbrain

• Collections of cell bodies that receive signals from the spinal cord and other parts of the brain

• Involved in smooth movement, temperature, and some reflexes


b. The Brainiii. The Forebrain

a) Thalamus • Relay station for sensory information

b) Hypothalamus: Controls ANS & endocrine system, body temperature, motivation & emotion • Regulates hormone secretion, hunger, eating,

drinking, and sexual activity


b. The Brainc) The Limbic System: Hunger, sex,

aggression, emotion, & memoryHippocampus

MemoryAmygdala

Emotion

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iii. The Forebrain


iii. The Forebrainc) Limbic System

• Contains the pleasure center• Involved in addiction

d) Basal Ganglia• Link the thalamus and cortex• Control movement and posture• Degeneration is associated with

Parkinson’s Disease


iii. The Forebraine) Cerebrum

• Largest structure in the human brain• Two hemispheres

–Connected by the corpus callosum

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• Covered by the cortex– 2 to 3 mm thick. Wrinkled and convoluted– Controls cognitive functioning, voluntary

action• Left Hemisphere: Primarily speech,

language, analytical skills, calculation• Right Hemisphere: Primarily interpretation

of emotions, creativity, intuition• Neither hemisphere acts in isolation of

the other



• Four lobes

Frontal Lobe

Parietal Lobe

Temporal Lobe

Occipital Lobe


Methods of Studying the BrainA. Phrenology

B. Anatomical Studies• Brain lesions: Tissue damage• Electrical Stimulation of the Brain (ESB):

Technique used to relate activity in particular brain regions to behavior.

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II. Methods of Studying the Brain

C. Monitoring Neural Activity– Single-unit recording

• Measures activity in individual neurons– Electroencephalography (EEG)

• Measures electrical activity – Computerized Axial Tomography (CAT)

scans • Computer-enhanced X-rays


A. Monitoring Neural Activity• Magnetic Resonance Imaging (MRI)

– Uses magnetic fields to trace activity & make up of tissue

– Images are clearer and more detailed than CT scans

• Positron Emission Tomography (PET) – Tracks radioactive markers that have been

injected into the bloodstream


III.How Does the Brain Function?

• Information from damaged brains– Damage from strokes and accidents

• Learned that Broca’s area and Wernicke’s area are involved in language

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III. How Does the Brain Function?

B. Brain Specialization1. Splitting the brain

• Cerebral hemispheres are not identical• Left hemisphere more involved in

language• Information comes from study of split-

brain patients– Individuals whose corpus callosum has

been cut to treat severe epilepsy


1. Splitting the Brain• Left hemisphere controls the right side of the

body• Right hemisphere controls the left side of the

body• Split brain patients can not use left-brain

language abilities to describe right-brain activities


An image in the left visual field appears in the right (non-verbal) hemisphere when looking straight ahead

1. Splitting the Brain

????

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An image in the right visual field appears in the left (verbal) hemisphere when looking straight ahead

It’s a silly yellow and pink polka-dotted bug.

1. Splitting the Brain


B. Brain Specialization 2. Gender and the Brain

• There are NOT masculine and feminine sides of the brain

• However, there are some gender differences–Women may be less lateralized than men on

some tasks–Individual variation is larger than gender

differences


IV. What Effects Do Hormones Have on Behavior?

•Hormones are chemicals produced by endocrine glands

–Secreted directly into the bloodstream–Regulate activities of specific organs or cells–Slower action than that of neurotransmitters

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III. Hormones Brain

Target Organs

Endocrine Glands

Behavior


III. Hormones


III. HormonesB. Endocrine Glands

1. Pituitary Gland• “Master gland”• Regulates many other endocrine glands• Linked to the hypothalamus

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B. Endocrine Glands2. Gonads

• Ovaries and testes• Produce androgens and estrogens

3. Adrenal Glands• Located above kidneys• Produce adrenaline (epinephrine)


B. Endocrine Glands4. Pancreas

• Produces insulin• Regulates body’s sugar levels• Diabetes mellitus results when pancreas

doesn’t produce enough insulin• Hypoglycemia is caused by overproduction of

insulin


V. How Do Genetic Factors Affect Behavior?

A. The Issue of Nature versus Nurture– Nature refers to biology– Nurture refers to environment– Which is more influential?

• Neither can solely account for behavior• Relative importance is source of much

debate

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V. How Do Genetic Factors Affect Behavior?

B. The Basics of Genetics– Each human cell contains 23 pairs of

chromosomes• Strands of DNA• Carry genes

– Fundamental units of heredity– Genetically determined traits are

controlled by pairs of genes


B. The Basics of Genetics•Genotype

–A person’s genetic make-up–Fixed at birth

•Phenotype–A person’s observable characteristics– Will reflect recessive traits only if

both members of the gene pair are recessive


B. The Basics of Genetics•Mutation

–An unexpected change in gene replication–Important sources of diversity in the human gene pool–Not always undesirable

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IV. How Do Genetic Factors Affect Behavior?

C. How Genes Affect Behavior• Genes affect behavior indirectly• Behavioral genetics

– The study of the influence of genes on behavior

– Heritability• The degree to which genetics

influences traits


C. How Genes Affect Behavior•Twin Studies

–Fraternal Twins• Dizygotic twins• Two sperm and two eggs

• Monozygotic twins• One sperm and one

egg split• Identical genes

• No more genetically similar than non-twin siblings

– Identical Twins


C. How Genes Affect Behavior• Twin Studies

– Identical twins raised apart share genes, but not environment

– Fraternal twins raised together share environment, but not genes

– Allows study of effects of genes and environment

• Most behaviors are determined by an interaction between genes and environment

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