biological bases of behavior

2.1 Interaction of Heredity and Environment

  • Heredity: the passing on of physical and mental traits from one generation to another
    • Individuals like Charles Darwin investigated how heredity and environment impacted an individual (Darwin’s theory of evolution promoted natural selection: traits that are beneficial to a species’ survival would be passed on)
  • Heritability: a mathematical measure to estimate how much variation there is in a population related to genes (how much of a trait is genetics)
    • ex. if the heritability of a trait is 0.6, 60% of the variations for that trait are caused by genetics, 40% due to the environment
  • NATURE VS. NURTURE: whether genetics or the environment impact us more
    • From most nature to most nurture: biological → evolutionary → cognitive → humanistic → psychodynamic → behavioral → sociocultural
    • There is technically truth in both!
  • Epigenetics: how the environment/behavior affects a person’s genes
    • DNA does not change, but some genes are turned on/off due to sustained environmental pressure

2.2 The Endocrine System

  • Consists of all the body’s different glands which produce different hormones to regulate biological processes
  • Along with nervous system, helps our bodies function and send messages throughout it
  • SEPARATE FROM NERVOUS SYSTEM: nervous system uses neurons to send fast, short-lived, electrical messages to localized areas of the body; endocrine system uses glands to create hormones and send slower messages targeting large areas
  • Homeostasis: the regulation of the body’s interval environment (ex. body temp)
    • Leaving homeostasis → a desire/need to move back

PARTS OF THE ENDOCRINE SYSTEM

  • Hypothalamus: controls the pituitary gland (releases growth hormones oxytocin and vasopressin to direct other glands); directs different autonomic functions of the body
  • Pineal gland: helps regulate sleep cycles; produces melatonin to help fall asleep
  • Thyroid/parathyroid: (throat) help regulate an individual’s metabolism, growth, nervous system, and regulate calcium levels in your blood
  • Adrenal glands: (above the kidneys) secrete several hormones that regulate salt, blood pressure, oxygen intake, increase heart rate, and increase blood flow; produce epinephrine (adrenaline), norepinephrine (noradrenaline), and aldosterone
  • Pancreas: (near stomach) produces insulin and glucagon to regulate an individual’s blood sugar level
  • Gonads (ovaries/testes): main reproductive organs; produce sex hormones of testosterone, estrogen, and progesterone

2.3 Overview of the Nervous System and the Neuron

  • Nervous system is composed of CNS (central) and PNS (peripheral)
    • CNS: brain and spinal cord - sends out orders to the body
    • PNS: other nerves - allows nervous system to communicate throughout body (vessel for CNS, can bring messages back)
    • Sensory division (afferent division)
      • Focuses on conducting impulses from sensory stimuli to the CNS
    • Motor division (efferent division)
      • Has signals that come from the CNS and go out to the muscles and glands of your body through efferent neurons
      • includes somatic and autonomic nervous systems
      • Somatic: 5 senses and skeletal muscle movement - conscious and voluntary movements
      • Autonomic: involuntary activity - unconscious, necessary movements (ex. heartbeat, breathing, etc.)
      • sympathetic: mobilizes body to get it ready for action
      • parasympathetic: calms body down when stressor is over
  • Supported by glial cells - provide neurons with nutrition, and protect them by providing structural support
  • Neurons are the basic functional units of the nervous system
    • Communicate with each other using electrical and chemical signals
    • Composed of:
    • Dendrites - branching, threadlike extensions of the cell body that increase the receptive surface of the neuron
    • Soma (cell body) - control center of neuron; determines whether to fire or not
    • Nucleus - core of a cell body of a neuron, containing genes
    • Receptor sites - spots on the soma that can be stimulated by other neurons
    • Myelin sheath - the insulating layer around many axons that increases the speed of conduction of nerve impulses
    • Axon - long, tubular structure in a neuron that transmits action potentials
    • Nodes of Ranvier - successive regularly spaced gaps in the myelin sheath surrounding an axon; permitting the exchange of ions across the plasma membrane at those points, allowing the nerve impulse to leap from one node to the next in so-called saltatory conduction across the axon
    • Schwann cell - nonneural PNS cell (glia) that creates myelin sheaths
    • Terminal buttons - responsible for transmitting signals to other neurons through the synapse (located at the end of the neuron)

2.4 Neural Firing

  • In order for neurons to send a message, they need to receive enough stimulation to cause an action potential
    • When a neuron fires and sends an impulse down the axon
  • Permeability: the ability for certain ions to cross the cell membrane
  • For this to happen:
    • A neuron must depolarize, allowing positive ions in (when outside stimulus is strong enough to meet threshold that causes depolarization)
    • Action potential sent down axon
    • Neuron must repolarize and come back to resting potential
    • Channels open in the membrane to let more positive ions back out
  • Refractory period: a short time when no other action potentials can occur until the axon is back in its resting state
  • Once an action potential reaches the terminal buttons, it stimulates the release of neurotransmitters that are released into the synapse
    • Chemical synapse: junctions between two neurons that use neurotransmitters to send neural signals
    • Electrical synapse: used for messages that need to be sent quickly and immediately
  • Synaptic gap: small space between the presynaptic terminal of one neuron and the postsynaptic dendrite of another
  • Once the neurotransmitters have stimulated the next neuron, they unbind from the receptors and are either destroyed or reabsorbed through the process of reuptake
  • Some neurotransmitters excite another neuron into firing, others keep it from firing
    • Excitatory: increase the likelihood that a neuron will fire an action potential; done through the depolarization process in the postsynaptic neuron
    • Inhibitory: decrease the likelihood that a neuron will fire an action potential; leading to hyperpolarization (when the inside of the neuron becomes more negative, moving it farther away from reaching its threshold)

IN SUMMARY:

  • Action potential sends a signal down the axon of a neuron to the presynaptic terminal
  • Channels in the axon terminal are opened and the neurotransmitters are released into the synaptic gap (for chemical messages)
  • The neurotransmitters diffuse through the synaptic gap and bind to receptor sites in the postsynaptic terminal
  • Neurotransmitters unbind with the receptors; some are destroyed and others go through the process of reuptake

TYPES OF NEUROTRANSMITTERS

  • Acetylcholine: enables muscle action, learning, and memory
  • Dopamine: helps with movement, learning, attention, and emotions
  • Serotonin: impacts an individual’s hunger, sleep, arousal, and mood
  • Endorphins: help with pain control and impacts individual’s pain tolerance
  • Epinephrine (adrenaline): helps with the body’s response to high emotional situations and helps form memories
  • Norepinephrine (noradrenaline): increases blood pressure, heart rate, and alertness
  • Glutamate: involved with long term memory and learning
  • GABA: helps with sleep, movement, and slows down your nervous system

2.5 Influence of Drugs on Neural Firing

  • Some drugs are agonists, others are antagonists
    • Agonists increase the effectiveness of a neurotransmitter by binding to receptors for neurotransmitters in the synapse and mimicking them, increasing production, or blocking reuptake to absorb extras
    • ex. Xanax (anxiety meds) are agonists and increase GABA, Prozac treats depression by delaying the reuptake of serotonin, opioids
    • Antagonists decrease the effectiveness of a neurotransmitter by either blocking its release or blocking the neurotransmitters from entering the receptor sites
    • ex. schizophrenia meds block dopamine receptors, alcohol blocks release of glutamate

2.6 The Brain

  • Broca’s area - in charge of facial muscles used to help with speech, damage leads to Broca’s aphasia (loss of ability to produce language)
  • Wernicke’s area - area in the left temporal lobe that is associated with interpreting and creating meaningful language, damage leads to Wernicke’s aphasia
  • Medulla oblongata - above the spinal cord/below the pons, helps regulate autonomic functions like breathing, heart rate, and blood pressure
  • Pons - connects the medulla with the cerebellum, helps coordinate movement + with sleep and dreams
  • Cerebellum - at the base of the brain in the back, helps maintain balance + coordination
  • Brainstem - base of brain/top of spinal cord, includes medulla/pons/midbrain, damage leads to death (controls autonomic functions necessary for life)
  • Spinal cord - connects brain to the rest of the body, allowing nerves and brain to communicate
  • Midbrain - helps send visual and auditory info to the appropriate brain structures
  • Reticular formation - structure that tunnels down the brainstem, main function is arousal in the sleep cycle
  • Reticular activating system (RAS) - network of nerves that run through the brainstem and out to the thalamus
  • Cerebrum - parts of the brain that are not the brainstem and cerebellum, where brain processes that are not just for survival occur (complex thoughts)
  • Cerebral cortex - thin layer of billions of nerve cells covering the whole brain
  • Corpus callosum - nerve fibers connecting the two cerebral hemispheres and allowing communication between them
  • Frontal lobe - located behind the forehead, deals with higher level thinking, separated into two important areas
    • Prefrontal cortex - deals with foresight, judgment, speech, and complex thought
    • Motor cortex - deals with voluntary movement, located in back
  • Parietal lobe - sits on top of your head behind the frontal lobe, main function is to receive sensory info, lets you understand different senses (touch, pain, temperature, orientation)
    • Somatosensory cortex - touches motor cortex, allows you to register touch and movement sensations
  • Occipital lobe - located on the back of the head, contains visual cortex allowing sight
  • Temporal lobe - located right above the ears, helps recognize faces, smells, hear noise, balance, and assists with memory (contains Wernicke’s area and angular gyrus)
    • Angular gyrus - allows you to read words on paper and transfer it to auditory form
    • Auditory cortex - processes different sounds
  • Limbic system - group of structures between brainstem and cerebral cortex that control emotions, learning, memory, and basic drives
    • Hippocampus - allows creation of memories (not storage)
    • Amygdala - located at each arm of the hippocampus, origin of emotional reactions (ex. fear, anger, etc.)
    • Thalamus - takes all the different sensory info and sends it to the forebrain for interpretation (relay station)
    • Hypothalamus - maintains homeostasis, controls drives (thirst/hunger/temp/sex), works with pituitary gland to regulate and control hormones
  • Nucleus accumbens - located near limbic system, main function is pleasure, reward, and motivation (associated with drug dependency)
  • Basal ganglia - link the thalamus with the motor cortex, involved in intentional body movements (damage could lead to Parkinson’s, cerebral palsy, or Huntington’s)

3 MAJOR REGIONS

  • Hindbrain (at the bottom)
  • Midbrain (above the base, surrounded by forebrain)
  • Forebrain (on the top)

The brain uses lateralization (differing functions of left/right hemispheres - division of labor) to accomplish different tasks.

  • Left hemisphere: recognizing words/letters, interpreting/processing language, logic
  • Right hemisphere: spatial concepts, facial recognition, depth perception

2.7 Tools for Examining Brain Structure and Function

PHINEAS GAGE

  • Gage was a railroad worker injured when a rod shot through his head
  • He lived and technically functioned but suffered a severe personality change as the rod severed his limbic system + damaged his prefrontal cortex (important for judgment + emotional regulation)

SPLIT BRAIN RESEARCH

  • Sperry + Ganzaniga
  • Help treat people with severe epilepsy by severing corpus callosum to prevent hemispheric communication
  • Did not cause changes in personality or intelligence
  • When patients were shown a word in the right visual field they could say it with no problem, but when shown in the left field, the patient said they didn’t see anything but could draw the word with their left hand
    • Broca’s and Wernicke’s area both located in left hemisphere

LESIONS + AUTOPSIES

  • lesions: intentional destruction of certain parts of the brain to gain insight into different functions of the brain or treat disorders
  • autopsies: examination of a corpse to determine cause of death, allowing for further understanding of the extent of a disease

NEUROIMAGING TECHNIQUES

  • EEG (electroencephalogram): use electrodes placed on an individual’s scalp to record electrical signals from firing neurons (helps with sleep/seizure research)
  • CT (computerized tomography): series of advanced X-rays, can help locate brain damage or tumors
  • PET scans: inject small amount of radioactive glucose into an individual to track the usage of glucose in specific brain areas, allowing researchers to see activity in real time
  • MRI scans: provide detailed pictures of the brain by using a strong magnetic field to cause molecules to vibrate at different frequencies
  • fMRI scans: similar to MRIs but show metabolic functions to demonstrate brain activity

2.8 The Adaptable Brain

  • Neuroplasticity: the ability for the brain to change or modify itself
  • Various occurrences can lead to permanent alterations
  • When learning new info or practicing skills, the brain creates and develops neural pathways
  • Individuals like William James believed our consciousness was one interconnected stream while others like Freud believed it was made up of our conscious, subconscious, and unconscious mind
  • Different drugs have different impacts
    • Psychoactive substances alter an individual’s perception, consciousness, or mood
    • Depressants reduce neural activity; causing drowsiness, muscle relaxation, lowered breathing, possibly death (ex. alcohol)
    • Opioids are like more addictive depressants and provide pain relief (ex. morphine, heroin, oxycodone)
    • Stimulants excite and promote neural activity; giving energy, reducing appetite and causing irritability (ex. caffeine, nicotine, cocaine)
    • Hallucinogens (ex. marijuana, peyote, LSD) cause an individual to sense nonexistent things; can reduce motivation and lead to panic

2.9 Sleep and Dreaming

  • Circadian rhythm: biological clock involving changes in blood pressure, internal temperature, hormones, and sleep/wake cycle regulation
  • Restoration theory: we sleep because we get tired from daily activities and need to restore our energy and resources
  • Adaptive theory: we sleep because it allows us to conserve energy and save it for when we will need it the most; focuses on evolutionary aspects and how it protects us, allowing us to survive
  • Information-processing theory: sleep allows us to restore/build memories; sleep deprivation leads to struggling with info learned in a day
  • Different sleep stages show different brain waves on an EEG
    • Alpha waves: brain waves that occur when you are in an awake, relaxed state - not focusing on anything in particular (slow frequency, high amplitude)
    • Beta waves: low amplitude brain waves that occur when you are in an awake and alert state (fastest brain waves)
    • Theta waves: brain waves that occur when you are relaxed and focused, such as daydreaming (high amplitude, low frequency)
    • Delta waves: lowest frequency brain waves that occur in deep sleep - stage NREM-3 (greatest amplitude, lowest frequency)
  • Sleep stages
    • NREM-1: alpha waves, light sleep only lasting ~10 minutes, begin to relax
    • NREM-2: theta waves, 10-20 minutes with K-complexes and sleep spindles (bursts of neural activity)
    • NREM-3: delta waves, deepest sleep, lasts ~30 minutes, growth hormones produced, may experience sleepwalking/sleeptalking
    • REM: beta waves, rapid eye movement, external muscles paralyzed while internal structures become active, dreams/nightmares
  • Hypnagogic sensations: experiences that occur when an individual is getting drowsy that feel like they are happening in real life (NREM-1)
  • Dream theories
    • Activation-synthesis model: dreams are our brain trying to make sense of random neural activity that happens while we are asleep
    • Cognitive development theory: dreams are a reflection of our cognitive development, which is why they are more simple for children than adults
    • Activation theory: specific areas of the brain are activated and depending on which area of the brain is active, your dreams will have different context/content
    • Physiological function approach: looks at how dreams stimulate our neural pathways and allow them to grow and be preserved
  • Sleep disorders
    • Insomnia: struggle falling or staying asleep (can be due to stress, pain, meds, or irregular sleep schedule)
    • Sleep apnea: hard time falling/staying asleep because of struggle with breathing, cannot go into REM
    • Night terrors: intense fear while sleeping which can disrupt sleep
    • Narcolepsy: individuals struggle to sleep at night and uncontrollably fall asleep during the day