Chapter 2Biological Foundations of

Behavior

Lecture Overview

• The Nervous System

• Neurons

• Neural Impulses

• The Brain

• The Spinal Cord

• The Endocrine System

• Genetics

The Nervous System

Central Nervous System

• The CNS is composed of the brain and spinal cord

• Spinal cord connects the brain with the PNS– Spinal cord is comprised of cell bodies and

axons that carry messages• Afferent: toward the brain (sensory function)• Efferent: away from the brain (motor function)

Peripheral Nervous System

• The Peripheral Nervous System (PNS) includes all nerves outside the brain and spinal cord– Somatic NS carries sensory messages to

brain and motor commands to the muscles– Autonomic NS regulates automatic body

functions (such as heart rate, breathing)• Sympathetic: “Fight or Flight”• Parasympathetic: dominant when relaxed

The Autonomic Nervous System

Neurons

• Neurons are cells that transmit information

• Neurons are composed of:– Dendrites: receive neural impulses and

pass it to cell body; information receiver– Cell Body: summarizes information– Axon: extends from cell body; sends

message to adjacent neurons; information sender

Neuron Structure

Neural Impulses:Neural Communication

• Within a neuron, communication occurs through an action potential (neural impulse that carries information along the axon of a neuron).

Resting Potential

Sodium ions are concentrated on the outside of the axon membrane.

Potassium ions are concentrated on the inside of the axon membrane.

Ion channels are closed.

The inside of the axon membrane is more negative that is the outside.

Action Potential

Action potential occurs when the membrane potential rapidly shifts from -70 to +40 mV– Ion channels open in the membrane, allowing sodium ions

to enter the axon– Sodium entry shifts the membrane potential toward a

positive value– Potential is restored when other channels open, allowing

potassium ions to exit the axon

The Action Potential

Action Potential Details

• Action potentials vary in frequency (a few pulses per second to a max of 1000 pulses per second)

• APs have a refractory period (about 1 msec)

• AP is “all or none” in nature

Myelin

• Myelin is a fatty, waxy substance coating the axon of some neurons.

• Functions:– Speeds neurotransmission– Insulates neurons from each other– Makes neurotransmission more efficient

Synapse

• The synapse is the junction between an axon terminal and an adjacent dendrite or cell body.

• Neurotransmitter (NT) molecules are released from the axon terminal into the synapse when the action potential arrives at the axon terminal.

The Synapse

1. Synthesis of neurotransmitter (NT)

2. Storage and transport of NT within vesicles

3. NT Release4. Activation of

postsynaptic receptors5. Termination of

transmitter effect (e.g. reuptake)

Common Neurotransmitters and some of their functions

Acetylcholine (ACh)

• Activates motor neurons controlling skeletal muscles.

• Contributes to the regulation of attention, arousal, and memory.

• Some ACh receptors stimulated by nicotine

Dopamine (DA)• Contributes to control of voluntary movement,

pleasurable emotions.• Decreased levels associated with Parkinson’s

disease• Over activity at DA synapses associated with

schizophrenia • Cocaine and amphetamines elevate activity at

DA synapses

Norepinephrine (NE)

• Contributes to modulation of mood and arousal

• Cocaine and amphetamines elevate activity at NE synapses

Serotonin• Involved in regulation of sleep and

wakefulness, eating, aggression• Abnormal levels may contribute to

depression and obsessive compulsive disorder

• Prozac and similar antidepressant drug affect serotonin circuits

Endorphins

• Resemble opiate drugs in structure and effects

• Contribute to pain relief and perhaps to some pleasurable emotions

• “Runner’s high” may be associated with high endorphin levels

GABA (gamma-aminobutyric acid).

• Destruction of GABA – producing neurons in Huntington’s disease produces tremors and loss of motor control as well as personality changes.

Psychoactive Drugs

• Psychoactive drugs affect the nervous system to alter mood, emotion, and thought

• Psychoactive drugs act by:– Increasing or decreasing release

of neurotransmitters – Stimulating or blocking receptor

sites

Psychoactive Drugs

• Agonists enhance neurotransmitter function

• Antagonists block neurotransmitter function

Midline Brain View

Brainstem

• Brainstem is a primitive portion of brain– Pons: involved in respiration, sleep

regulation, dreaming– Medulla: involved in life support functions

such as respiration and heart rate– Reticular activating system is an arousal

system within the brainstem

Subcortical Brain Areas

• Corpus callosum: band of axons that interconnects the hemispheres

• Thalamus: sensory relay area

• Limbic system: involved in emotionality

• Hypothalamus: feeding, fleeing, mating, fighting, homeostasis

• Cerebellum: involved in motor control

Limbic System

Cerebral Cortex• Cortex refers to the outer covering of the brain

– Consists of left and right hemispheres

– Cortex is divided into lobes• Frontal: Self-awareness, planning, voluntary movement,

emotional control, speech, working memory• Parietal: Body sensations• Occipital: Vision• Temporal: Hearing, language comprehension

Cortical Lobes

Motor and Somatosensory Cortex

Summary of Hemispheric Specializations

Split-Brain Research

• When a split-brain patient is asked to stare straight ahead while a photo of a fork is flashed to his left visual field, he cannot name it.

Split-Brain Research

• CASE STUDY

• Phineas Gage was a railway worker in 19 th century Vermont who survived a bizarre accident: A metre-long iron rod shot through his head, changing him and the study of ...

• www.bbc.co.uk/radio4/science/case_study_20080521.shtml

The Spinal Cord

The Endocrine System

• Hormones are secreted into the blood by the endocrine system

• Hypothalamus controls hormone release

The Endocrine System

Functions of the endocrine system:

1. Maintain homeostasis

2. Regulate reproductive system

Behavioral Genetics• Behavioral genetics examines the influence of

genes (versus environment) on behavior• Research strategies:

– Twin studies: compare the concordance (agreement) rates between identical and fraternal twins

– Adoption studies: compare the similarity between adopted children and their biological/adopted parents

– Mutations: examine behaviors in genetically abnormal subjects or in animals in which a specific gene has been “knocked out”

Messinger

Chromosomes

In vitro Ordered by karotyping

Principles of Heredity Transmission

The Genetic Code

Conception is the moment of fertilization, when a sperm penetrates an ovum, forming a zygote.

• The zygote contains 46 chromosomes, consisting of thousands of chemical segments, or genes.

• Genes are hereditary blueprints for development that are passed on unchanged from generation to generation.

• Chromosomes come in matching pairs. (23 chromosomes from each parent.)

The 23rd pair of chromosomes• The sex of the zygote is determined by the 23rd pair of

chromosomes.• For a female sex, both of these sex chromosomes are an X

chromosome.• For a male sex, the 23rd pair consists of one X chromosome and one

Y chromosome.

The purpose of our genes…..• Our genes are responsible for the construction of our enzymes and

other proteins.• These genes are essential in order to form new cells and their

specific functions.• Other genes are accountable for regulating the pace of

development.

Normal human cells contain 23 pairs of chromosomes

During cell division we can identify chromosomes

• Haploid: set of 23 chromosomes• Diploid: normal number of 46 chromosomes• Aneuploidy: less than an even multiple of 23

usually is 45 or 47 and rarely 48,49• Triploidy: 69 chromosomes• Mosaicism• Abnormal in deletion and translocation

Chromosomal and Genetic Abnormalities

• DOWN SYNDROME (TRISOMY 21)

Down Syndrome

• Incidence 1/700• 2/3 of down fetus spontaneously abort• Trisomy 21 in 94% of cases with extra

chromosome from mother mostly(95%)• Risk correlate with maternal age

– <25 y/o 1/1600– >40 y/0 1/80

• 2% are mosaic

Chromosomal and Genetic Abnormalities

EDWARD’S SYNDROME (TRISOMY 18)

Chromosomal and Genetic Abnormalities

PATAU SYNDROME (TRISOMY 13)

Chromosomal and Genetic Abnormalities

TURNER SYNDROME (XO)

Chromosomal and Genetic Abnormalities

KLINEFELTER SYNDROME (XXY)

Chromosomal and Genetic Abnormalities

FRAGILE X SYNDROME

Chromosomal and Genetic Abnormalities

ANGELMAN SYNDROME

Chromosomal and Genetic Abnormalities

PRADER - WILLI SYNDROME

Evolutionary Psychology

• Darwin argued that natural forces select traits that are adaptive for survival– Natural selection: certain traits are passed on

because these traits gave an advantage for survival

• Organisms with these traits are able to reproduce and pass on the trait to their offspring

– Genetic mutations can be beneficial or disastrous

• Evolutionary psychology examines how evolutionary processes impact behavior