Biological Basis of Behavior - BISD Front Door · Psychology: An Introduction Charles A. Morris &...

Psychology: An Introduction

Charles A. Morris & Albert A. Maisto

© 2005 Prentice Hall

The Biological Basis

of Behavior




Neurons: The Messengers

About 100 billion neurons (nerve cells) in the human brain

Neurons have many of the same features as other cells

Nucleus

Cytoplasm

Cell membrane

What makes neurons unique is their shape and function




Structure of Neurons

Dendrites

Carry information to the cell

body from other neurons

Cell Body (Soma)

Contains nucleus

Axon

Carries information to the

next cell

Myelin Sheath

Insulates the axon and

speeds up the neural

impulse




Types of Neurons

Sensory neurons

Carry information from sensory systems to the brain

Also referred to as afferent

Motor neurons

Carry information from the brain to muscles and

glands

Also referred to as efferent

Interneurons

Carry information between other neurons




Glial Cells

Cells that insulate and support neurons

Create the myelin sheath

Remove waste products

Provide nourishment

Prevent harmful substances from entering

the brain




The Neural Impulse




The Neural Impulse

Ions

Charged molecules

Resting Potential

When more negative

ions are inside the

neuron than outside

Charge is

approximately -70mV

Neuron is not

transmitting

information




The Neural Impulse

Polarization

When the electrical charge of a cell moves

away from zero

Depolarization

When the electrical charge of a cell moves

toward zero




The Neural Impulse

Action Potential

Sudden, massive

change in charge in

the neuron

Occurs when

depolarization reaches

the threshold of

excitation

Ions flow across cell

membrane




The Neural Impulse

Graded Potentials

Subthreshold depolarization

Many subthreshold depolarizations are added

together to produce an action potential (a

process known as summation)




The Neural Impulse

All-or-None Law

A neuron either fires or it does not

When it does fire, it will always produce an

impulse of the same strength

Intensity of a stimulus is coded by the

frequency of action potentials




The Neural Impulse

Absolute refractory period

Period immediately after an

action potential when

another action potential

cannot occur

Relative refractory period

Period following absolute

refractory period when a

neuron will only respond to

a stronger than normal

impulse




The Synapse

Synaptic space (synaptic cleft)

Tiny gap between neurons

Terminal button

Enlarged area at the end of an axon

The synapse

Composed of the terminal button of one

neuron, the synaptic space, and the dendrites

or cell body of the receiving neuron




Transmission Between Neurons

Synaptic vesicles Sacs in terminal button

that release chemicals into synaptic space

Neurotransmitters Chemicals released by

synaptic vesicles

Receptor sites Location on receptor

neuron for specific neurotransmitter




Some Well-Known

Neurotransmitters Acetylcholine (ACh)

Released at the neuromuscular junction

Plays an important role in arousal and attention

Loss of ACh producing cells is linked to Alzheimer’s

Disease

Dopamine

Affects neurons associated with voluntary movement

Plays a role in learning, memory, and emotions

Loss of dopamine-producing cells causes symptoms

of Parkinson’s Disease




Some Well-Known

Neurotransmitters

Serotonin

Found throughout the brain

Appears to sets an “emotional tone”

Low serotonin levels are implicated in

depression

Endorphins

Reduce pain by inhibiting or “turning down”

neurons that transmit pain information




Psychopharmacology

Most psychoactive drugs (and toxins) work

by blocking or enhancing synaptic

transmission

Botulism

Blocks release of ACh at the neuromuscular

junction, causing paralysis

“Botox” is botulism toxin used to prevent facial

muscles from making wrinkles




Psychopharmacology

Curare

Can stun or kill prey quickly

Blocks ACh receptors causing paralysis

Antipsychotic medications

Block dopamine receptors

Reduces schizophrenic hallucinations

Caffeine

Increases the release of excitatory neurotransmitters

by blocking the inhibitory neurotransmitter adenosine




Psychopharmacology

Cocaine

Prevents reabsorption of dopamine

Leads to heightened arousal of entire nervous

system




Neural Plasticity

The brain can be changed, both

structurally and chemically, by experience

Rat studies show that an “enriched”

environment leads to larger neurons with

more connections

Has also been shown in humans

Recent research has uncovered evidence

of neurogenesis, or the production of new

brain cells, in human brains




Nervous System Organization

Central nervous system (CNS) Consists of the brain

and spinal cord

Peripheral nervous system Connects the CNS to

the rest of the body Somatic nervous

system

Autonomic nervous system




Central Nervous System

Central Nervous System

Brain Spinal Cord




The Brain – The Central Core

Medulla

Controls breathing,

heart rate, and blood

pressure

Pons

Maintains the sleep-

wake cycle

Cerebellum

Coordinates body’s

movements





Thalamus

Relays information from

sensory receptors to the

brain

Hypothalamus

Influences motivated

behavior

Regulates hunger, thirst,

body temperature, and

sexual drive.

Directly involved in

emotional behavior





Reticular formation

Network of neurons found throughout the

brain

Serves to alert and arouse higher brain in

response to incoming information




The Brain – The Limbic System

Ring of structures located

between the central core

and the cerebral

hemispheres

Important to learning and

emotional behavior

Hippocampus essential in

formation of new memories

Amygdala, together with

the hippocampus, is

important for regulating

emotions




The Cerebral Cortex

Occipital lobe

Receives and processes

visual information

Temporal lobe

Complex visual tasks such

as face recognition

Receives and processed

auditory information

Involved in balance, some

emotions and motivations

Some language processing




The Cerebral Cortex

Parietal lobe

Receives sensory

information from body

Involved in spatial abilities

Frontal lobe

Coordinated information

from other lobes

Controls voluntary

movement, attention,

setting goals, and

expression of appropriate

emotions




Hemispheric Specialization

Corpus Callosum

Fibers that connect the

two hemispheres

Allow close

communication

between left and right

hemishphere

Each hemisphere

appears to specialize

in certain functions




Split-Brain Research

Much information about functions of each

hemisphere has come from studying split-

brain patients




Tools for Studying the

Nervous System




Microelectrode Techniques

Very small electrodes inserted into

individual neurons

Used to study activity of a single neuron




Macroelectrode Techniques

Used to get a picture of overall activity in

the brain

An example is an EEG, which uses

electrodes placed on a person’s scalp to

measure brain activity




Structural Imaging

Computerized Axial Tomography (CT-

scan)

Uses X-rays to create a 3-dimensional image

of the brain

Magnetic Resonance Imaging (MRI)

Uses a magnetic field and radio waves to

produce images




Functional Imaging

EEG imaging

electrical activity on the scalp from millions of

neurons is used to produce a continuous

picture of activity in the brain

Magentoencephalography (MEG) and

Magnetic source imaging (MSI)

Can localize activity more precisely than EEG




Functional Imaging

Positron Emission Tomography (PET) and

Single Photon Emission Computed

Tomography (SPECT)

Use radioactive glucose to determine location

of greatest brain activity

Functional Magnetic Resonance Imaging

(fMRI)

Shows function and structure by measuring

movement of blood molecules within the brain




The Spinal Cord




The Spinal Cord

Complex cable of nerves that connects

brain to rest of the body

Carries motor impulses from the brain to

internal organs and muscles

Carries sensory information from

extremities and internal organs to the brain




The Spinal Cord

The spinal cord controls some protective

reflex movements without any input from

the brain




The Peripheral Nervous System

Peripheral Nervous System

Somatic Nervous System Autonomic Nervous System

Sympathetic Division Parasympathetic Division




The Somatic Nervous System

Consists of neurons that communicate

between the body and the brain

Afferent neurons

Neurons that carry messages from sense

organs to spinal cord

Efferent neurons

Neurons that carry messages from the spinal

cord or brain to muscles and glands




The Autonomic Nervous System

Sympathetic division

Most active when you

are angry, afraid, or

aroused

Fight-or-flight

response

Increases heart rate

and breathing

Stops digestion




The Autonomic Nervous System

Parasympathetic

division

Calms body

Produces effects

opposite to those of

the sympathetic

division

Reduces heart rate

and breathing

Restores digestion




The Endocrine System





Helps coordinate and integrate complex

psychological reactions

Endocrine glands secrete hormones into

the bloodstream

Hormones serve to organize the nervous

system and body

Hormones also activate behavior, such as

sexual behavior





Thyroid gland Secretes hormones

(primarily thyroxin) that control metabolism

Parathyroid glands Control levels of

calcium and phosphate which in turn controls levels of excitability





Pineal gland Secretes melatonin

which regulates the sleep-wake cycle

Pancreas Regulates blood-sugar

levels

Secretes insulin and glucagon





Pituitary gland

Referred to as the

“master gland”

because it regulates

many other glands

Gonads

Ovaries and testes

secrete estrogens and

androgens

Adrenal glands

Secretes hormones in

reaction to stress




Genes, Evolution, and

Behavior




Genetics

Heredity - transmission of trait from one

generation to next

Chromosomes

Pairs of thread like bodies that contain genes

Deoxyribonucleic acid (DNA)

Organic molecule arranged in a double-helix

Contains the “code of life”




Behavior Genetics

Study of behavior from a genetic

perspective

Animal behavior genetic studies include:

Strain studies

Selection studies




Human Behavior Genetics

Family studies

Assume that close family members share

more of a trait than non-relatives

Used to assess the heritability of

psychological disorders or traits

Twin studies

Used to determine how heritable a trait or

disorder may be

Identical twins would have highest heritability




Human Behavior Genetics

Adoption studies

Used to assess the influence of environment

Molecular genetics

Direct study of the genetic code




Evolutionary Psychology

Natural selection

“Survival of the fittest”

Evolutionary psychology looks at the

adaptive or survival value of behaviors




Social Implications

Study of biological origins of behavior

could lead to genocide and eugenics

aimed at eliminating certain types of

people

Could also be used to create new

categories of people, such as people bred

to be good soldiers or manual laborers

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