The Biological Basis of Behavior Chapter 2

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 Cell Body (Soma) Axon Myelin Sheath 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 Nodes of Ranvier

Types of Neurons Sensory neurons Motor neurons Interneurons 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 Types of 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 Intraneural transmission – within on neuron This is an ELECTRICAL process Occurs as a result of the exchange of charged particles called ions

The Neural Impulse Resting Potential When more negative ions are inside the neuron than outside Neuron is not transmitting information Similar to a compressed spring The neuron is POLARIZED – meaning it has a charge System WANTS to reach equilibrium and balance charges, but is closed when at rest.

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 Na+ in, K+ out Neuron fires and DEPOLARIZES – no charge

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

SO… Impulse has traveled down the length of the axon Signal end up at terminal buttons, very end points of the axon terminals Then what? Signal must get to other neurons, but how?

The Synapse The synapse Synaptic space (synaptic cleft) Composed of the terminal button of one neuron, the synaptic space, and the dendrites or cell body of the receiving neuron Synaptic space (synaptic cleft) Tiny gap between neurons Messages must travel across the space to get from one neuron to the next

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 Lock and key Reuptake “Recycling” neurotransmitters

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 – found in vines in S. America; used as poison 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/Neuroplasticity 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

The Brain – The Central Core Medulla Controls breathing, heart rate, and blood pressure Pons Maintains the sleep-wake cycle Cerebellum Coordinates body’s movements

The Brain – The Central Core Thalamus Relays information from sensory receptors to the brain – except smell Hypothalamus Influences motivated behavior Regulates hunger, thirst, body temperature, and sexual drive. Directly involved in emotional behavior

The Brain – The Central Core 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 Temporal 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 Frontal 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

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

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

The Endocrine System Thyroid gland Parathyroid glands Secretes hormones (primarily thyroxin) that control metabolism Parathyroid glands Control levels of calcium and phosphate which in turn controls levels of excitability

The Endocrine System Pineal gland Pancreas Secretes melatonin which regulates the sleep-wake cycle Pancreas Regulates blood-sugar levels Secretes insulin and glucagon

The Endocrine System Pituitary gland Gonads Adrenal glands 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