Chapter 3: The Biological Bases of Behavior

Types of Neurons  Afferent neurons (Sensory),  relay information from the senses to the brain and spinal cord. ▪ Eyes, ears, nose, mouth, and skin  Efferent neurons (motor),  send information from the central nervous system to the glands and muscles, ▪ enables the body to move.  Interneurons  carry information between neurons ▪ in the brain ▪ in the spinal cord WWBCopyright © Allyn & Bacon 2006

Structures of a neuron

The cell body ◦Round, centrally located structure ◦Contains DNA ◦Controls protein manufacturing ◦Directs metabolism ◦No role in neural signaling zContains the cell’s Nucleus

Dendrites  Information collectors  Receive inputs from neighboring neurons  Inputs may number in thousands  If enough inputs the cell’s AXON may generate an output

Dendritic Growth  Mature neurons generally can’t divide  But new dendrites can grow  Provides room for more connections to other neurons  New connections are basis for learning

Axon The cell’s output structure One axon per cell, 2 distinct parts ◦tubelike structure branches at end that connect to dendrites of other cells

Myelin sheath  White fatty casing on axon  Acts as an electrical insulator  Not present on all cells  When present increases the speed of neural signals down the axon. Myelin Sheath

The Neuron at Rest  Hodgkin & Huxley (1952) - giant squid  Fluids inside and outside neuron  Electrically charged particles (ions)  Neuron at rest – negative charge on inside compared to outside  -70 millivolts – resting potential

How neurons communicate Neurons communicate by means of an electrical signal called the Action Potential Action Potentials are based on movements of ions between the outside and inside of the cell When an Action Potential occurs a molecular message is sent to neighboring neurons

The Action Potential  Stimulation causes cell membrane to open briefly  Positively charged sodium ions flow in  Shift in electrical charge travels along neuron  The Action Potential  All – or – none law

Figure 3.2 The neural impulse

Neuron to Neuron  Axons branch out and end near dendrites of neighboring cells  Axon terminals are the tips of the axon’s branches  A gap separates the axon terminals from dendrites  Gap is the Synapse Cell Body Dendrite Axon

Synapse  axon terminals contain small storage sacs called synaptic vesicles yvesicles contain neurotransmitter molecules Sending Neuron Synapse Axon Terminal

Neurotransmitter Release Action Potential causes vesicle to open zNeurotransmitter released into synapse zLocks onto receptor molecule in postsynaptic membrane

Figure 3.3 The synapse

Figure 3.4 Overview of synaptic transmission

Locks and Keys Neurotransmitter molecules have specific shapes positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize zWhen NT binds to receptor, ions enter zReceptor molecules have binding sites

Some Drugs work on receptors  Some drugs are shaped like neurotransmitters  Antagonists : fit the receptor but poorly and block the NT  e.g. beta blockers zAgonists : fit receptor well and act like the NT ye.g. nicotine.

When a Neurotransmitter Binds: The Postsynaptic Potential Voltage change at receptor site – postsynaptic potential (PSP) ◦Not all-or-none ◦Changes the probability of the postsynaptic neuron firing Positive voltage shift – excitatory PSP Negative voltage shift – inhibitory PSP

Neurotransmitters and Behavior  Specific neurotransmitters work at specific synapses  Lock and key mechanism  Agonist – mimics neurotransmitter action  Antagonist – opposes action of a neurotransmitter  More than 40 neurotransmitters known at present  Interactions between neurotransmitter circuits

Types of Neurotransmitters Acetylcholine Serotonin Norepinephrine Dopamine Endorphins GABA Glutamate

Table 3.1 Common Neurotransmitters and Some of their Functions

Acetylcholine Found in neuromuscular junction Involved in muscle movements

Alzheimer’s Disease Deterioration of memory, reasoning and language skills Symptoms may be due to loss of ACh neurons

Serotonin Involved in sleep Involved in depression ◦Prozac works by keeping serotonin in the synapse longer, giving it more time to exert an effect

Norepinephrine Arousal “Fight or flight” response

Dopamine Involved in movement, attention and learning Dopamine imbalance also involved in schizophrenia Loss of dopamine- producing neurons is cause of Parkinson’s Disease

Endorphins  Control pain and pleasure  Released in response to pain  Morphine and codeine work on endorphin receptors Involved in healing effects of acupuncture

Gamma-Aminobutyric Acid (GABA) Main inhibitory neurotransmitter Benzodiazepines (which include tranquilizers such as Valium) and alcohol work on GABA receptor complexes

Glutamate Major excitatory neurotransmitter Too much glutamate (and too little GABA) associated with epileptic seizures

Integrating Signals  One neuron, signals from thousands of other neurons  Neural networks  Patterns of neural activity  Interconnected neurons that fire together or sequentially  Synaptic connections  Elimination and creation  Synaptic pruning

Communication in the Nervous System Glia – structural support and insulation Neurons – communication ◦Soma – cell body ◦Dendrites – receive ◦Axon – transmit away ◦Myelin sheath – speeds up transmission ◦Terminal Button – end of axon; secretes neurotransmitters ◦Neurotransmitters – chemical messengers

Central Nervous System  Brain and Spinal Cord Spinal Cord Brain

Central nervous system Peripheral nervous system

Figure 3.5 Organization of the human nervous system

Sympathetic “ Fight or flight” response Release adrenaline and noradrenaline Increases heart rate and blood pressure Increases blood flow to skeletal muscles Inhibits digestive functions CENTRAL NERVOUS SYSTEM Brain Spinal cord SYMPATHETIC Dilates pupil Stimulates salivation Relaxes bronchi Accelerates heartbeat Inhibits activity Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Stimulates ejaculation in male Sympathetic ganglia Salivary glands Lungs Heart Stomach Pancreas Liver Adrenal gland Kidney

Parasympathetic “ Rest and digest ” system Calms body to conserve and maintain energy Lowers heartbeat, breathing rate, blood pressure CENTRAL NERVOUS SYSTEM Brain PARASYMPATHETIC Spinal cord Stimulates salivation Constricts bronchi Slows heartbeat Stimulates activity Contracts bladder Stimulates erection of sex organs Stimulates gallbladder Gallbladder Contracts pupil

Summary of autonomic differences Autonomic nervous system controls physiological arousal Sympathetic division (arousing) Parasympathetic division (calming) Pupils dilate EYES Pupils contract Decreases SALVATION Increases Perspires SKIN Dries Increases RESPERATION Decreases Accelerates HEART Slows Inhibits DIGESTION Activates Secrete stress hormones ADRENAL GLANDS Decrease secretion of stress hormones

Studying the Brain: Research Methods  Damage studies/lesioning  Electrical stimulation (ESB)  Brain imaging –  computerized tomography  positron emission tomography  magnetic resonance imaging  Transcranial magnetic stimulation (TMS)

Brain has 2 Hemispheres Left & Right sides are separate Corpus Callosum : major pathway between hemispheres Some functions are ‘lateralized’ ◦language on left ◦math, music on right Lateralization is never 100% Left Hemisphere Corpus Callosum Right Hemisphere

Figure 3.14 The cerebral hemispheres and the corpus callosum

Right Brain/Left Brain: Cerebral Specialization Cerebral Hemispheres – two specialized halves connected by the corpus collosum ◦Left hemisphere – verbal processing: language, speech, reading, writing ◦Right hemisphere – nonverbal processing: spatial, musical, visual recognition

Brain Regions and Functions  Hindbrain – vital functions – medulla, pons, and cerebellum  Midbrain – sensory functions – dopaminergic projections, reticular activating system  Forebrain – emotion, complex thought – thalamus, hypothalamus, limbic system, cerebrum, cerebral cortex

Figure 3.12 Structures and areas in the human brain

WWB Copyright © Allyn & Bacon 2006 Cerebrum Continued Cerebral Cortex Higher mental processes of language, memory, and thinking. Left Cerebral Cortex Frontal lobe Motor cortex Broca’s Area Parietal lobe Somatosensory cortex Occipital lobe Visual cortex Temporal lobe Auditory Cortex Wernicke’s area

Figure 3.16 Language processing in the brain

Each hemisphere is divided into 4 lobes Frontal Parietal Occipital Temporal

The Cerebrum: The Seat of Complex Thought  Four Lobes:  Occipital – vision  Parietal - somatosensory  Temporal - auditory  Frontal – movement, executive control systems

The Limbic System Hypothalamus Amygdala Hippocampus

Hypothalamus Contains nuclei involved in a variety of behaviors ◦ sexual behavior ◦hunger, thirst ◦sleep ◦water and salt balance ◦body temperature regulation ◦circadian rhythms ◦role in hormone secretion

Hypothalamus and Hormones Hypothalamus releases hormones or releasing factors which in turn cause pituitary gland to release its hormones

Amygdala Inputs come from all senses Amygdala ‘reads’ emotional significance of inputs Output influences such functions as heart rate, adrenaline release

Hippocampus Important in forming new memories

Thalamus Relay station in brain Processes most information to and from higher brain centers

Reticular Formation Network of neurons in the brainstem (and thalamus) Sleep and arousal Attention

Hindbrain Structures Cerebellum Brainstem ◦medulla ◦reticular formation ◦pons

Cerebellum Coordinated, rapid voluntary movements ◦e.g., playing the piano, kicking, throwing, etc. Lesions to cerebellum ◦jerky, exaggerated movements ◦difficulty walking ◦ loss of balance ◦ shaking hands

Medulla Breathing Heart rate Digestion Other vital reflexes ◦swallowing ◦coughing ◦vomiting ◦sneezing

The Endocrine System: Another Way to Communicate  Hormones – chemical messengers in the bloodstream  Endocrine glands  Pituitary – “master gland,” growth hormone  Thyroid – metabolic rate  Adrenal – salt and carbohydrate metabolism  Pancreas – sugar metabolism  Gonads – sex hormones

Endocrine System Pituitary gland—attached to the base of the brain, hormones affect the function of other glands Adrenal glands—hormones involved in human stress response Gonads—hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females

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Genes and Behavioral Genetics Genes: – segments of DNA on chromosomes transmit heredity traits Chromosomes – rod shaped and contain all genes that carry genetic information to make a human being. Dominant-recessive pattern – a set of inheritance rules for genes ◦One dominant gene or two recessive genes required for a trait to be expressed. Multifactorial inheritance – an inheritance pattern in which a trait is influenced by both genes and environmental factors. Polygenic inheritance – many genes influence a particular characteristic like skin color. Sex linked inheritance – involves genes on the X and Y chromosomes ◦E.g. male or female body type and red-green color blindness Behavioral Genetics – a field of research that uses twin and adoption studies to investigate the relative effects of heredity and environment on behavior. WWBCopyright © Allyn & Bacon 2006

Basic Principles of Genetics  Chromosomes – strands of DNA carrying genetic information  Human cells contain 46 chromosomes in pairs (sex-cells – 23 single)  Each chromosome – thousands of genes, also in pairs  Polygenic traits

Research Methods in Behavioral Genetics  Family studies – does it run in the family?  Twin studies – compare resemblance of identical (monozygotic) and fraternal (dizygotic) twins on a trait  Adoption studies – examine resemblance between adopted children and their biological and adoptive parents

Figure 3.19 Genetic relatedness

Figure 3.20 Twin studies of intelligence and personality

The Evolutionary Bases of Behavior  Based on Darwin’s ideas of natural selection  Reproductive success key  Adaptations – behavioral as well as physical  Fight-or-flight response  Taste preferences  Parental investment and mating