Introduction to Psychology

Chapter 3: The Biological Basis

of Behavior

Nervous System

CNS: Brain and Spinal Cord

Peripheral Nervous System: network of nerves that carries information to and from the nervous system

Nervous SystemNervous System

CNS Peripheral NS

Somatic Autonomic Sympathetic Parasympathetic

Peripheral Nervous System

Somatic System: carries messages to and from sense organs and skeletal muscles

Controls voluntary behavior

Peripheral Nervous System Somatic system:

Afferent nerve fibers carry info from the body to the nervous system

Efferent nerve fibers carry info from the nervous system to the body

Peripheral Nervous System

Autonomic Nervous System: glands and organs; “automatic functions”

Heartbeat, digestion

Peripheral Nervous System

Sympathetic: fight or flight; prepares for action

Parasympathetic: quiets the body; lowers arousal

Neurons

Nerve cells in the brain

Carry messages; activate muscles and glands

100 billion neurons in the brain

The Neuron

Fig. 3.8

Parts of the Neuron

Dendrites: receives messages from other neurons

Soma: receives messages; sends nerve impulse down the axon

Parts of the Neuron

Axon: thin fiber leading to the terminal buttons; nerve impulses travel down the axon; carries messages

Myelin sheath: fatty layer covering the axon that helps nerve impulses move faster

Parts of the Neuron

Synapse: the microscopic space between the neurons over which messages pass

Neurotransmitters travel across the axon

Ions: electrically charged molecules found inside and outside the neuron, with + or - charges

Resting Potential

Electrical charge of an inactive neuron

-70 mv

Messages from other neurons raise or lower the resting potential

Threshold

If the charge raises to -50 mv, the neuron reaches its threshold

Threshold=trigger point for firing

Ready to fire

Neural Firing An action potential (nerve impulse)

sweeps down the axon

Ion channels open and sodium ions rush in

After the action potential....

Positive ions flow back out; the neuron becomes negatively charged again

Resting state is restored

After firing, the neuron dips below resting level and is less willing to fire

Firing...

Firing is an all or nothing event The neuron either fires, or doesn’t

fire

It take 1/1000 of a second for a neuron to fire; on average, they fire between 1-400 times per second

Neurotransmitters

Chemicals that alter activity in the neurons

Travel from terminal buttons across synapse connect to special receptors sites

dendrites/soma of next neuron

Neurotransmitters

Neurotransmitters can excite or inhibit firing

Types of Neurotransmitters Dopamine: too little=Parkinson’s, too

much=schizophrenia Acetylcholine: activates muscles Serotonin: deficiency associated with

depression/anxiety Neuropeptides: influence memory,

pain, emotion, and mood Endorphins: released by the pituitary

glad; lessens pain

The Brain

Right and Left hemispheres

Lateralization

Divided by the corpus callosum

Left Hemisphere Detail oriented

Speech and language

Calculating

Understands one word at a time, not the big picture

Right Hemisphere Non-verbal

Face recognition

Express/detect emotion

Understanding speech context/nuances of language

The Brain’s Four Lobes

Fig. 3.7

Functions of Lobes of the Cortex

Frontal lobes

Occipital lobes

Temporal lobes

Involved in voluntary movement, thinking, personality, and intentionality or purpose

Function in vision

Active role in hearing, language processing, and memory

Parietal lobesRoles in registering spatial location, attention, and motor control

The Brain

Recent research:

Both heredity and environment shape the brain

The role of experience and brain plasticity

Dendritic Spreading

Fig. 3.11

Experience and the Brain Exposure to trauma:

PTSD: reduced size of the hippocampus

Depression: Parts of the brain atrophy over time

Addiction: Changes in neurotransmitters

Experience and the Brain

Children reared in deprived environments have depressed brain activity (i.e. Romanian orphans)

Can be reversed; brain plasticity/resilience

DNA, Chromosomes, and Genes Chromosomes: in the nucleus;

threadlike structures that contain DNA

DNA: contains genetic instructions

Genes: unit of hereditary information; each has its own function and location

Nucleus (center of cell) contains

chromosomes and genes

Chromosomes are threadlike structures

composed of DNA molecules

Gene: a segment of DNA (spiraled double chain)

containing the hereditary code

Fig. 2.3

Polygenetic Inheritance

Polygenetic Inheritance: when many genes interact to influence a characteristic

Behavioral traits are caused by several genes (and the environment)

Genes Human Genome Project:

Humans have 20,000-25,000 genes

All humans: genes are 99.9% the same

Humans and apes share 96-98% of their genes

Nature vs. Nurture

Nature: the role of genes

Nurture: the role of the environment and external conditions

**Interactionist Perspective: Both nature and nurture shape development

Behavioral Genetics

A field that looks at the influence of heredity and environment Twin studies: comparing identical

and fraternal twins

Adoption studies: are children more similar to the biological or adoptive parent?

Twin Studies

Identical Twins share 100% of their genes

Fraternal/non-twin siblings share 50% of their genes

Twin Studies

We compare identical and fraternal twins

If identical twins are more similar than fraternal twins, we can make the case for heredity

Adoption Studies

If adopted children are more similar to biological parents, we can make the case for heredity

More similar to adoptive parents: case for environment