Unit 1: Biological Bases of Behaviour

1.1 Interaction of Heredity & Environment

Nature vs Nurture influences:

• personality characteristics & persona; preference

• intelligence & psychological health

• language acquisition

Nature vs Nurture

• genetic influences on behaviour and traits

• environmental factors shaping individual experiences

• the interplay between heredity and upbringing in development

• Noam Chomsky (nature side): believed that stuff like language acquisition is in our nature to learn and that’s why babies pick it up so easily.

• John B Watson (nurture side): said that he could train a dozen healthy infants to be anything he wanted to, because he believed that a person’s traits are influenced by their environment & condition

• This debate highlights the ongoing discussion in psychology regarding the extent to which genetics versus environment influences human behavior and development.

Epigenetics

• helps us understand how genetics & nurture influence us

• Rat licking studies: research that showed how environment can alter genetics

Twin Studies

• Identical Twins: same DNA, same sex, monozygotic (one egg).

• Fraternal Twins: different DNA, no more genetically similar than non-twin siblings, might be same/opposite sex, dizygotic (two eggs).

• Example - Minnesota Twin Study: separated identical twins at birth for 35 years; when brought back together, they had insane similarities — wives had the same name, had dogs of the same name, named their sons almost the same thing etc.

Heritability

• the amount of variation among individuals that we can attribute to genetics

• provides insight into nature vs nurture

• studied in twin studies, adoption studies, family studies, DNA studies.

1.2 The Nervous System

Neurons

• building blocks of nervous system

• general jobs: receive, carry, send message (all done within milliseconds, speed approx 30 mph).

• neuron cells fire in a particular patter for thoughts to occur.

Types of a Neuron

• Sensory Neurons: measures sensation.

  • respond to non-chemical stimulation.

  • receives raw materials from the body’s sense organs like free nerve endings in the epidermis.

  • carry messages from the senses to the brain (ARRIVE at the brain).

• Motor Neurons: measures reflexes.

  • are connected to muscle fibres and can make the muscles contract.

  • can react to voluntary and involuntary signals.

  • carry messages from the brain to the senses (EXIT the brain).

• Interneurons: connect neurons within the brain and spinal cord.

Structure of a Neuron

• Dendrites: Receive signals from other neurons.

• Cell Body (Soma): Contains the nucleus and processes signals.

• Axon: Transmits signals away from the cell body to other neurons.

• Myelin Sheath: Insulates the axon to speed up signal transmission.

• Axon Terminals: Release neurotransmitters to communicate with other neurons.

• Synapse: The junction where communication between neurons occurs via neurotransmitters.

Neural Firing

Basics of Neural Firing

• Resting Potential: Polarised (-70 millivolts).

• Firing Threshold: Reached if enough volts are there.

• All or None Law: Once at threshold, the neuron WILL fire, and it will fire at the same intensity every time.

• Action Potential: An electric impulse that travels down the axon. This change in electricity creates a positive electric charge (+30 millivolts) inside the neuron - this is called depolarisation.

• Refractory Period: A brief period when the neuron can’t fire again.

• Reuptake: The sending neuron recollects neurotransmitters.

Process of Neural Firing

• Neurons fire when there is a shift in electric energy - creating an action potential.

• When the action potential reaches the terminal buttons, neurotransmitters are released into the synapse.

• Neurotransmitters then lock into the next neuron.

Summary of Neural Firing

Neuron fires → Synaptic vesicles release neurotransmitters from axon terminals → Neurotransmitters travel across the synapse & fit into the post-synaptic receptors.

1.3 Neurotransmitters

• chemical messengers of the nervous system.

• excitatory - pushes neurons "accelerator" - encites response

• inhibitory - pushes neurons "brake" - blocks response

  • antagonist - binds to dendrites & prevents or blocks a response.

  • agonist - bind to receptor sites & mimic the affects of a specific neurotransmitter.

Types of Neurotransmitters

Agonists

Agonists enhance the actions of neurotransmitters.

Direct Agonists

Direct Agonists mimic the neurotransmitters and bind with the receptors of the next neurons.

Examples:

• Heroin

  • agonist for endorphins.

  • mimic → receptor sites can’t distinguish between an endorphin and the chemical structure of heroin.

• Nicotine

  • agonist for acetycholine.

  • stimulates skeletal muscles & causes increased heart rate.

• Black Widow Venom (a toxin, not a drug)

  • agonist for acetycholine.

  • causes ACh to be continuously released at neuromuscular junctions.

  • increase in heart rate, spasms → leads to death.

Indirect Agonists

Indirect Agonists block the reuptake of a neurotransmitter; thus are also known as reuptake inhibitors. (these are introduced at the synapse).

Examples:

• Prozac

  • inhibits the reuptake of serotonin → floods the synapse with serotonin.

  • decreases symptoms of depression & anxiety for some people.

• Cocaine

  • inhibits reuptake of dopamine.

  • also decreases symptoms of depression & anxiety, can slow down parkinson’s effects.

Antagonists

• inhibit the actions of neurotransmitters in many ways.

• often bind to a receptor but do not stimulate it.

• block a neurotransmitter from being released by the terminal or from binding to the receptor site.

• this inhibits the normal functions of an neurotransmitter.

Examples:

• Botox (a toxin)

  • an antagonist for ACh.

  • blocks ACh from reaching receptors.

  • effected muscles can’t move → freeze muscle from firing to prevent wrinkles.

• Thorazine

  • an antagonist for dopamine.

  • blocks dopamine receptors and starves the synapse of this neurotransmitter.

  • early drug for schizophrenia (as oversupply of dopamine is linked to schizophrenia and this slows down the supply of it).

Psychoactive drugs

What do all psychoactive drugs have in common?

• they alter mental states.

• activate dopamine-producing neurons in the brain’s reward system.

• this increase in dopamine is associated with greater reward, which can lead to a stronger desire to take the drug again.

• many drugs can create tolerance - needing increasing amounts of the drugs to create the original high/desired effect.

• many drugs lead to physical dependance - with repeated use, a person may need to administer the drug to prevent withdrawal symptoms (here, drug acts as a negative reinforcement to take these symptoms away).

• the effect of a drug is primarily dependant on which neurotransmitter is affected.

Blood-Brain Barrier: barrier that allows some chemicals to pass from the blood into the brain but prevents other chemical structures from entering.

Categories of Psychoactive drugs: Depressants, Opiates, Stimulants, Hallucinogens / Psychedelics.

Depressants

• show or inhibit CNS functions.

• create drowsiness, sedation or sleep → relieve anxiety or lower inhibitions.

• combining depressants can be deadly.

Examples:

• Alcohol

  • 2^nd most widely used depressant in the U.S.

  • agonist for GABA (gamma-aminobutyric acid).

  • lessens inhibitions by depressing brain centres for judgement and self-control.

Opiates/Opiods

• agonist for endorphins.

• incredibly addictive & creates powerful withdrawal symptoms.

Examples: heroin, oxytocin, fentanyl.

Stimulants

• active sympathetic nervous system.

• increase brain activity, arouse behaviour, & increase mental alertness.

Examples:

• Caffiene

  • most widely used drug in the U.S.

  • promotes wakefulness, mental alertness, & faster thought processes by stimulating release of dopamine.

  • antagonist for adenosine → blocks sleep-inducing effects.

  • is physically addictive and creates withdrawal symptoms.

• Cocaine

  • dopamine antagonist (reuptake inhibitor).

  • also elevates serotonin & norepinephrin.

  • creates intense euphoria, alertness, & heightened self-confidence.

  • highly addictive & causes a crash after the high dissipates.

Hallucinogens / Psychedelics

• create sensory & perceptual disorders, alter mood, and affect thinking.

• there is lots of current research on psychedelics in therapeutic settings (anxiety, depression & more) but it’s still in the experimental phase.

Examples:

• Tetrahydrocannabinol (THC or cannabis)

  • very mind hallucinogen.

  • produces sense of well-being, mild euphoria, dreamy state of relaxation.

  • interferes with muscle coordination, learning, memory, and overall cognitive function.

  • has various therapeutic uses.

1.4 The Brain

Structure of a Brain

• Structure of the brain divided into three main regions:

  • Hindbrain: Bottom of the brain.

  • Midbrain: Center region, connects upper and lower brain parts.

  • Forebrain: Top region containing central structures and outer layer.

Hindbrain

• Located at the base of the brain, near the brain stem.

Brain Stem

• Function: Responsible for essential life functions.

Medulla Oblongata

• Location: At the bottom of the brain stem, above the spinal cord.

• Function: Automatic functions (heart rate, breathing, blood pressure), reflex coordination (swallowing, coughing, sneezing).

• Description: Looks like a small ice cream cone shape.

Pons

• Note: Not an essential concept according to College Board.

• Description: Resembles an Adam's apple/curved letter P.

• Function: Unconscious processes (sleep/wake cycles).

Reticular Activating System (RAS)

• Description: A bundle of nerve fibers running through the brain stem.

• Function: Influences consciousness and alertness.

• Example: Electrical stimulation in a cat caused a coma, illustrating its role in consciousness.

Cerebellum

• Location: Underneath the backside of the brain, behind the brain stem.

• Description: About the size of a fist, referred to as the "little brain."

• Function: Coordinates voluntary movements, balance, posture, and fine-tuning motor activities.

• Role in learning motor skills and refining movements.

Midbrain

• nerve system connecting higher and lower portions of the brain.

• relays info between the brain & the eyes & the ears.

Forebrain

Thalamus

• Location: Egg-shaped structures deep within the brain, above the brain stem.

• Function: Relay system for sensory information directing it to appropriate brain areas for interpretation.

• Role in regulating alertness and consciousness.

Limbic System

• Location: Encircles the top of the brain stem, includes the hippocampus, amygdala, and hypothalamus.

• Function: Emotional and behavioral responses.

Hippocampus

• Location: The green arm-like structures in the limbic system.

• Function: Memory formation, especially in long-term memory consolidation.

Amygdala

• Location: Blue almond-shaped structures at the ends of the hippocampus.

• Function: Processes emotions (fear, aggression, pleasure), recognizes emotional experiences, influences emotional memory formation.

Hypothalamus

• Location: Center of the limbic system, maroon triangular shape.

• Function: Regulates basic drives (hunger, thirst, body temperature), connects nervous system to endocrine system via pituitary gland.

Cerebrum

• Location: Largest part covering the limbic system, thalamus, and brain stem.

• Function: Higher brain functions (thinking, reasoning, planning, problem-solving) and sensory processing.

• Cerebral Cortex: Outer layer responsible for complex functions.

Corpus Callosum

• Description: Thick band of nerve fibers connecting right and left hemispheres.

• Function: Facilitates communication between hemispheres for coordinated complex functions (movement, language, problem-solving).

Pituitary Gland

• Location: Small, pea-sized structure below hypothalamus.

• Function: "Master gland" of the endocrine system, regulates growth, metabolism, stress responses through hormone production; works closely with the hypothalamus.

Cerebral cortex structure

The cerebral cortex is the most evolutionarily advanced part of the brain, responsible for our most sophisticated mental capabilities. It consists of two hemispheres connected by the corpus callosum, with each hemisphere specialized for different types of processing.

The cortex is organized into distinct regions:

Right hemisphere:

• Processes spatial info

• Handles nonverbal communication

• Takes a big-picture approach Left hemisphere:

• Manages language processing

• Handles logical operations

• Processes analytical tasks Four main lobes plus the limbic system:

  • Frontal, parietal, temporal, and occipital lobes

  • Limbic system includes structures crucial for emotion and memory

Occipital lobe

The occipital lobe is dedicated to processing visual information. Located at the back of the brain, it contains multiple specialized areas for different aspects of vision. 👀 🖼

Main functions:

• Processes visual information from the eyes

• Interprets color, shape, depth, and motion

• Damage can cause visual deficits (blindness, agnosia, hallucinations)

Temporal lobe

The temporal lobe processes auditory information and plays a crucial role in memory and emotion. Located on the sides of the brain, it contains several important structures including the hippocampus and amygdala. 😭💬

This region is responsible for:

• Processing auditory information and language comprehension via Wernicke's area

• Memory formation and retrieval via the hippocampus

• Emotion, social perception, and memory via the amygdala

• Damage can affect hearing, language, or personality

Parietal lobe

The parietal lobe integrates sensory information and helps us understand our position in space. It serves as a hub for processing various types of sensory input and coordinating responses.

Critical functions include:

• Processing sensory information (touch, pressure, temperature, pain)

• Integrating sensory input with motor output

• Spatial processing and navigation

• Body awareness and attention

Frontal lobe

The frontal lobe is the seat of our highest cognitive abilities and personality. It's involved in planning, decision-making, and emotional regulation.

This region handles:

• Higher-order cognitive processes (planning, decision-making, problem-solving)

• Voluntary movements and fine motor skills via motor cortex

• Emotional responses and social behavior

• Language production via Broca's area

Split brain research

Split-brain studies have provided remarkable insights into how the two hemispheres of the brain function independently and together. This research began as a treatment for severe epilepsy but revealed fundamental principles about brain organization.

Key findings include:

• Demonstrates specialized functions of left and right hemispheres

• Shows how the brain processes information in isolation

• Reveals the brain's adaptive capabilities

Language areas in brain

Language processing involves multiple specialized regions working together. The two main areas are Broca's and Wernicke's areas, each serving distinct functions in language use. Most language functions are lateralized to the left hemisphere.

Broca's area (left frontal lobe)

• Controls speech production

• Damage leads to trouble producing speech Wernicke's area (left temporal lobe)

• Manages language comprehension

• Damage results in comprehension difficulties

Cortex specialization testing

Research on cortical specialization helps us understand how different brain regions process information. This is particularly evident in split-brain patients, where researchers can study each hemisphere in isolation.

Testing methods include:

• Presenting stimuli to specific visual fields

• Studying hemispheric differences in perception

• Examining contralateral organization of pathways These tests reveal:

• Hemispheric differences in perception

• Specialized cognitive processing

• Motor pathway organization

Brain plasticity concept

Brain plasticity refers to the brain's remarkable ability to change and adapt throughout life. This property allows for learning, memory formation, and recovery from injury.

Key aspects of plasticity:

• Formation of new neural connections

• Strengthening or weakening of existing connections

• Most pronounced during development but continues throughout life

• Enables compensation for damage

Brain research methods

Modern neuroscience employs various techniques to study brain structure and function. Each method provides unique insights into brain activity and organization.

Current research tools include:

• EEG for measuring electrical activity

• fMRI for tracking blood flow changes

• PET scans for visualizing metabolism and neurotransmitter activity

• Case studies of brain lesions

• Transcranial magnetic stimulation (TMS) for temporary disruption studies

• Optogenetics for precise neural control

1.5 Sleep

Sleep is a big deal for how we act and feel. Our sleep/wake cycle follows a circadian rhythm, which is like our body's internal clock, controlled by a part of the brain called the suprachiasmatic nucleus. When this rhythm gets messed up (like with jet lag or working night shifts), it can really throw us off.

Sleep has different stages, including non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. These stages are key for memory, brain restoration, and those wild dreams we have. Knowing about sleep disorders and keeping good sleep habits is crucial for staying on top of our physical and mental health game.

Sleep/wake cycle effects on behavior

Levels of consciousness

Consciousness = how aware we are of stuff going on inside and outside our bodies.

😳 During wakefulness, we experience:

• High levels of awareness and responsiveness

• Active engagement with our environment

• Clear perception of stimuli

😴 In contrast, sleep is characterized by:

• Reduced awareness of surroundings

• Decreased responsiveness to external stimuli

• Altered states of consciousness

Circadian rhythm and disruptions

Our body's internal clock runs on about a 24-hour cycle, controlled by the suprachiasmatic nucleus (SCN) in the brain. This biological timekeeper responds to environmental cues, especially light and dark.

Common disruptions include:

• Jet lag from crossing time zones

• Shift work schedules, especially if they keep changing

• Irregular sleep schedules

• Exposure to artificial light at night (aka doom scrolling)

These disruptions can lead to:

• Trouble falling asleep, staying asleep, or staying awake

• Feeling foggy-headed

• Changes in appetite (hangry) or mood

• Feel physically off (tired, queasy)

Stages of sleep

Sleep progresses through multiple stages throughout the night, each serving distinct biological purposes.

NREM sleep consists of three stages:

1. Stage 1: Light sleep transition

   • Brief duration

   • Easily awakened

   • Hypnagogic sensations

2. Stage 2: Intermediate sleep with some specific brain wave patterns

   • Sleep spindles appear

   • K-complexes present on EEG

   • Decreased body temperature

3. Stage 3: Deep sleep with slow brain waves

   • Slow-wave activity

   • Difficult to wake

   • Critical for physical restoration

These stages change throughout the night, with the deepest sleep happening earlier on.

REM sleep characteristics

REM sleep is a unique state that combines aspects of both sleep and wakefulness. During this phase, the brain becomes highly active while the body remains largely paralyzed.

Key features include:

• Rapid eye movements (even though they are closed)

• Muscle atonia (so you don't act out your dreams)

• Vivid dreaming

• Increased brain activity

The timing and duration of REM periods follow a predictable pattern:

• First REM period occurs about 90 minutes after falling asleep

• Later REM periods become progressively longer, with longest happening in the morning

• REM rebound occurs after REM deprivation

Theories of dream function

Dreams serve multiple potential functions in cognitive processing and emotional regulation. The two main scientific theories explain dreams through different mechanisms.

Activation-synthesis theory proposes that:

• Dreams result from the brain interpreting random neural firing

• The brain creates narratives to make sense of this activity

• Dream content reflects this synthesis process

Memory consolidation theory suggests that:

• Dreams help process daily experiences

• Emotional memories are integrated during dreaming

• Dream content often incorporates recent events

🚫 Exclusion Note: The psychoanalytic theory of dreams is not assessed on the AP Psych exam.

Sleep's role in memory

Sleep plays a vital role in learning and memory formation. During sleep, the brain processes and stabilizes new information while clearing away unnecessary data. aka you need to sleep before big tests!

Memory consolidation occurs through:

• Neural replay of daytime experiences

• Strengthening of important synaptic connections

• Transfer of information to long-term storage

The restoration process involves:

• Clearing metabolic waste from the brain

• Replenishing neurotransmitters

• Optimizing neural networks for new learning

Sleep disorders and effects

Sleep disorders can significantly impact daily functioning and overall health. Understanding these conditions is crucial for proper diagnosis and treatment.

Common sleep disorders include:

• Insomnia (difficulty falling or staying asleep)

• Narcolepsy (excessive daytime sleepiness or suddenly falling asleep)

• Sleep apnea (interrupted breathing during sleep)

• REM sleep behavior disorder (physically acting out dreams)

• Somnambulism (sleepwalking)

🚫 Exclusion Note: The AP Psych exam will only cover the sleep disorders listed above.

These conditions can lead to various effects:

1. Cognitive impacts:

   • Reduced attention span

   • Impaired decision-making

   • Memory problems

2. Physical effects:

   • Increased accident risk

   • Weakened immune system

   • Weight gain

   • Cardiovascular issues

3. Emotional consequences:

   • Mood swings

   • Irritability

   • Increased anxiety

   • Depression risk

1.6 Sensation

Sensation is how we detect and process environmental stimuli. Our sensory systems work together to pick up information from light, sound, taste, and touch.

Our brains take this sensory input and turn it into meaningful perceptions. This includes getting used to constant stimuli, noticing changes, and sometimes experiencing weird sensory combos like synesthesia. Understanding sensation helps explain how we interact with the world around us.

Sensation and behavior

Detection of sensory information

Sensation begins when environmental stimuli reach our sensory organs and are converted into neural signals. This process requires stimuli to meet certain thresholds before being detected and processed by the brain.

Key detection concepts:

• Absolute threshold: minimum stimulus intensity detected 50% of the time

• Just-noticeable difference: smallest detectable change in stimulus intensity

• Sensory adaptation: decreased sensitivity to constant stimulation Our senses rarely work alone. Instead, they team up through:

• Cross-modal processing combining multiple senses

• Sensory interaction enhancing overall perception

• Unique phenomena like synesthesia where senses overlap

Change detection and adaptation

Our sensory systems are particularly attuned to detecting changes in stimulation rather than constant levels of stimulation. This helps us notice important environmental changes while conserving energy by reducing responses to ongoing stimulation.

Weber's law governs how we detect differences:

• The just-noticeable difference (JND) is proportional to stimulus intensity

• Larger changes needed to detect differences in stronger stimuli

• Applies across different sensory modalities Adaptation helps us:

• Tune out constant background noise

• Stay sensitive to new or changing stimuli

• Adjust to different environments

• Optimize sensory processing for what's happening now

Sensory interaction and synesthesia

The brain integrates information from multiple senses to create coherent experiences. This integration happens automatically and continuously, enhancing our ability to understand and navigate our environment.

Common sensory interactions include:

• Taste enhanced by smell and visual cues

• Speech comprehension improved by watching lip movements

• Balance maintained through vision and inner ear input Synesthesia represents an unusual form of sensory interaction where:

• One sensory experience automatically triggers another

• Associations are consistent and automatic

• Experiences can involve any combination of senses and can boost memory and creativity

Visual system and behavior

Retina and image processing

The retina serves as the primary visual receptor, converting light into neural signals. This complex tissue contains multiple cell layers that begin processing visual information before it reaches the brain.

Initial processing includes:

• Detecting light intensity

• Basic edge and motion detection

• Color processing in cone-rich areas The brain makes up for retinal limitations by:

• Filling in the blind spot

• Maintaining perceptual stability

• Integrating information from both eyes

Lens accommodation and vision

The lens adjusts to focus images clearly on the retina. This process of accommodation involves:

• Lens shape changes for near and far vision

• Pupil size adjustments for light intensity

• Eye muscle coordination for binocular vision Vision problems can occur when:

• Myopia: images focus in front of the retina (nearsightedness)

• Hyperopia: images focus behind the retina (farsightedness)

• Astigmatism: irregular cornea shape causes distortion

Rod cells and light adaptation

Rod cells give us vision in low light and are crucial for detecting movement in our peripheral vision. These cells adapt significantly as lighting conditions change.

Light adaptation happens fast when entering bright areas:

• Rod sensitivity decreases

• Cone cells become more active

• Pupil constricts to reduce light entry Dark adaptation is slower and involves:

• Increased rod sensitivity

• Reduced cone activity

• Pupil dilation

• Rhodopsin regeneration

Theories of color vision

Color vision relies on multiple mechanisms working together. Two main theories explain how we perceive color:

Trichromatic Theory explains initial color processing:

• Three types of cone cells – 💙 short-wavelength (blue), 💚 medium-wavelength (green), and ❤ long-wavelength (red)

• Each responds to different wavelengths

• Combining signals creates color perception Opponent-Process Theory describes how the brain processes color information:

• Opposing pairs of colors (red-green, blue-yellow)

• Black-white opposition for brightness

• Explains afterimages and color contrast effects

Brain damage and vision disorders

Damage to visual processing areas can create unique disorders that reveal how the visual system works. The complexity of vision becomes apparent through various conditions:

Common disorders include:

• Prosopagnosia (face blindness)

• Blindsight

• Visual agnosia Impact varies based on:

• Location of damage

• Extent of injury

• Timing of damage during development

Auditory system and behavior

Sound perception and processing

Sound travels through air as pressure waves at various frequencies and amplitudes. Our auditory system converts these waves into neural signals that we interpret as meaningful sounds.

Key sound properties include:

• Pitch determined by wave frequency (measured in Hz)

• Loudness determined by wave amplitude (measured in dB)

• Timbre determined by sound wave complexity The ear processes sound through:

• Outer ear collecting and channeling sound waves

• Middle ear amplifying vibrations

• Inner ear converting mechanical energy to neural signals

Theories of pitch perception

Multiple theories work together to explain how we perceive pitch across different frequency ranges. Each theory addresses specific aspects of auditory processing.

Place theory explains high-frequency perception:

• Different frequencies stimulate different areas of the basilar membrane

• Higher frequencies activate the base of the cochlea

• Lower frequencies activate the apex of the cochlea Frequency theory works for lower pitches:

• Neurons fire at the same rate as sound wave frequency

• Works best below 1000 Hz

• Neural firing patterns match sound wave patterns Volley theory handles mid-range frequencies:

• Groups of neurons fire in alternating patterns

• Multiple neurons together can represent frequencies up to 4000 Hz

• Combines aspects of both place and frequency theories

Sound localization mechanisms

Our ability to locate sound sources in space relies on comparing input between our ears and integrating this with other sensory information.

Localization depends on:

• Interaural time differences (sound reaches one ear before the other)

• Interaural intensity differences (sound is louder in one ear)

• Head-related transfer functions (how the ear shape filters sound) The brain processes these cues in the:

• Superior olive (initial binaural processing)

• Inferior colliculus (integration of spatial information)

• Auditory cortex (conscious perception of sound location)

Hearing loss and disorders

Hearing impairment can result from various factors and affect different parts of the auditory system. Understanding these conditions reveals how our hearing system functions.

Conduction deafness involves:

• Problems in the outer or middle ear

• Difficulty transmitting sound waves to the cochlea

• Often temporary and treatable

• Caused by earwax buildup, ear infections, or ossicle damage Sensorineural deafness involves:

• Damage to the cochlea or auditory nerve

• Usually permanent hearing loss

• Common causes include aging (presbycusis), loud noise exposure, and certain medications

• Often treated with hearing aids or cochlear implants Other hearing conditions include:

• Tinnitus (phantom ringing or buzzing sounds)

• Auditory processing disorders (brain struggles to process sound)

• Hyperacusis (increased sensitivity to everyday sounds)

Chemical sensory systems and behavior

Olfactory (smell)

The olfactory system detects airborne chemicals and converts them into meaningful smell perceptions. It's the only sense not processed first in the thalamus.

Olfactory processing involves:

• Odorant molecules binding to receptors in nasal epithelium

• Signals traveling directly to the olfactory bulb

• Information bypassing the thalamus (unique among senses)

• Direct connections to the limbic system for emotional processing Pheromones represent specialized chemical signals that:

• Communicate between members of the same species

• May influence mood, attraction, and physiological states

• Are processed by the vomeronasal organ in many mammals

• May play subtle roles in human behavior

Basic taste qualities and perception

Gustation allows us to evaluate what we're about to consume. This chemical sense helps us identify nutritious foods and avoid potential toxins.

The primary taste qualities include:

• Sweet (sugars and some proteins)

• Sour (acids)

• Salty (sodium and essential minerals)

• Bitter (potentially toxic compounds)

• Umami (savory, protein-rich foods)

• Oleogustus (fatty acids) Taste receptor distribution creates:

• Supertasters with abundant taste buds and heightened sensitivity

• Medium tasters with average taste perception

• Nontasters with fewer taste buds and reduced sensitivity

Gustatory structures and taste sensitivity

Taste information follows specific neural pathways from the tongue to conscious perception. This processing helps us make rapid decisions about food consumption.

The taste system includes:

• Taste buds containing specialized receptor cells

• Cranial nerves carrying taste information

• Brainstem nuclei for initial processing

• Thalamic relay to the gustatory cortex

• Integration in the orbitofrontal cortex Taste preferences develop through:

• Innate preferences for sweet and umami

• Innate aversions to bitter

• Cultural and personal experience

• Conditioning and learning

Interaction between taste and smell

Flavor perception results from the integration of multiple sensory inputs. This multisensory experience enhances our ability to identify and remember foods.

Taste and smell interact through:

• Retronasal olfaction during chewing and swallowing

• Shared neural pathways in the orbitofrontal cortex

• Complementary information processing Without smell, taste perception is:

• Limited to basic taste qualities

• Significantly reduced in intensity

• Missing the complexity we call "flavor"

• Often described as "bland" or "flat" Other factors influencing flavor include:

• Texture (somatosensory input)

• Temperature

• Visual appearance

• Sound (crunchiness)

• Prior expectations

Touch sensory system and behavior

Somatosensory receptors and processing

The tactile system provides crucial information about objects we contact and our position in space. Various receptor types in the skin detect different aspects of touch.

Specialized mechanoreceptors include:

• Merkel cells for pressure and texture

• Meissner corpuscles for light touch and vibration

• Pacinian corpuscles for deep pressure and rapid vibration

• Ruffini endings for skin stretch and joint position Neural pathways for touch include:

• Sensory neurons carrying signals to the spinal cord

• Ascending pathways to the thalamus

• Projections to the somatosensory cortex

• Secondary processing in association areas

Temperature perception mechanisms

Temperature sensation helps us maintain homeostasis and avoid tissue damage. Our perception of hot and cold relies on specialized thermoreceptors.

Temperature processing involves:

• TRPM8 receptors activated by cold

• TRPV1 receptors activated by heat

• Paradoxical activation creating mixed sensations The sensation of "hot" results from:

• Simultaneous activation of warm and cold receptors

• Integration of these signals in the central nervous system

• Contextual interpretation based on baseline temperature

• Cross-activation of pain receptors at extreme temperatures

Vestibular and kinesthetic systems and behavior

Vestibular structures and balance

The vestibular system provides constant information about head position and movement. This system is essential for maintaining balance and coordinating movements.

Vestibular processing involves:

• Semicircular canals detecting rotational movements

• Otolith organs (utricle and saccule) sensing linear acceleration

• Hair cells converting mechanical movement to neural signals

• Vestibular nuclei in the brainstem integrating signals Balance maintenance relies on:

• Vestibular input about head position

• Visual information about the environment

• Proprioceptive feedback from joints and muscles

• Cerebellar integration of these sensory inputs

Kinesthetic sensing and movement

Kinesthesis gives us awareness of body position and movement without visual input. This proprioceptive sense allows for smooth, coordinated actions.

Key kinesthetic structures include:

• Muscle spindles detecting muscle stretch

• Golgi tendon organs monitoring tension

• Joint receptors sensing position

• Somatosensory cortex integrating body position information Kinesthesis enables:

• Coordinated movements without visual monitoring

• Automatic postural adjustments

• Spatial awareness of limb positions

• Skilled motor learning through body awareness

Unit Overview

What's This Unit All About?

• Explores the biological underpinnings of behavior and mental processes

• Focuses on the structure and function of the brain and nervous system

• Examines how neurons communicate with each other to transmit information

• Investigates the role of neurotransmitters in regulating behavior and mood

• Discusses the influence of hormones on behavior and psychological processes

• Covers the central and peripheral nervous systems and their respective functions

• Delves into various brain disorders and their effects on behavior and cognition

• Highlights real-life applications of understanding the biological bases of behavior (treating mental illnesses, developing medications, improving learning and memory)

Key Brain Parts and What They Do

• Cerebral cortex: responsible for higher-order cognitive functions (thinking, reasoning, decision-making)

  • Divided into four lobes: frontal, parietal, temporal, and occipital

  • Each lobe specializes in processing specific types of information (visual, auditory, sensory, motor)

• Limbic system: involved in emotional processing, memory formation, and motivation

  • Includes the amygdala, which plays a crucial role in fear and emotional responses

  • Hippocampus is essential for forming new memories and spatial navigation

• Hypothalamus: regulates basic biological needs and drives (hunger, thirst, sleep, sexual behavior)

  • Controls the release of hormones from the pituitary gland

• Brainstem: connects the brain to the spinal cord and regulates vital functions (breathing, heart rate, blood pressure)

• Cerebellum: coordinates fine motor movements, balance, and posture

• Basal ganglia: involved in motor control, learning, and decision-making

• Thalamus: relays sensory and motor information between the brain and body

Neurons: The Brain's Building Blocks

• Neurons are specialized cells that transmit electrical and chemical signals throughout the nervous system

• Consist of three main parts: dendrites, cell body (soma), and axon

  • Dendrites receive incoming signals from other neurons

  • Cell body contains the nucleus and other organelles necessary for cellular functions

  • Axon is a long, thin fiber that carries electrical signals away from the cell body

• Neurons are surrounded by a fatty substance called myelin, which insulates the axon and speeds up signal transmission

• There are three main types of neurons: sensory neurons, motor neurons, and interneurons

  • Sensory neurons detect stimuli from the environment and send signals to the central nervous system

  • Motor neurons carry signals from the central nervous system to muscles and glands

  • Interneurons connect sensory and motor neurons and process information within the central nervous system

• Neurons do not divide or regenerate once they are damaged or lost, making brain injuries and neurodegenerative diseases particularly devastating

How Neurons Talk to Each Other

• Neurons communicate with each other through electrical and chemical signals

• Electrical signals, called action potentials, travel along the axon of a neuron

  • Action potentials are generated when the neuron's membrane potential reaches a certain threshold

  • The action potential is an all-or-none response, meaning it either occurs at full strength or not at all

• Chemical signals, called neurotransmitters, are released from the axon terminals of one neuron and bind to receptors on the dendrites of another neuron

  • Neurotransmitters can have either excitatory or inhibitory effects on the receiving neuron

  • Common neurotransmitters include dopamine, serotonin, norepinephrine, and GABA

• The junction between two neurons where neurotransmitters are released is called a synapse

  • Synaptic transmission can be modulated by various factors (neurotransmitter availability, receptor sensitivity, reuptake mechanisms)

• Long-term potentiation (LTP) and long-term depression (LTD) are processes that strengthen or weaken synaptic connections, respectively, and are thought to underlie learning and memory

The Nervous System: Central vs. Peripheral

• The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS)

• The CNS consists of the brain and spinal cord and is responsible for processing information and generating responses

  • The brain is the control center of the nervous system and is involved in higher-order cognitive functions, emotion, and behavior

  • The spinal cord relays sensory and motor information between the brain and the rest of the body

• The PNS consists of all the nerves and ganglia outside the brain and spinal cord

  • Divided into the somatic nervous system and the autonomic nervous system

  • The somatic nervous system controls voluntary movements and receives sensory input from the environment

  • The autonomic nervous system regulates involuntary functions (heart rate, digestion, respiration) and is further divided into the sympathetic and parasympathetic nervous systems

    • The sympathetic nervous system activates the "fight or flight" response during stress or emergencies

    • The parasympathetic nervous system promotes "rest and digest" functions and helps maintain homeostasis

Hormones and Behavior

• Hormones are chemical messengers released by endocrine glands that travel through the bloodstream and affect target cells throughout the body

• Hormones play a crucial role in regulating behavior, mood, and various physiological processes

  • Examples include cortisol (stress response), testosterone (aggression, sexual behavior), and oxytocin (social bonding, maternal behavior)

• The hypothalamus-pituitary-adrenal (HPA) axis is a key system that regulates the body's response to stress

  • The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH)

  • ACTH then stimulates the adrenal glands to release cortisol, which helps the body cope with stress

• Hormonal imbalances can lead to various behavioral and psychological disorders (depression, anxiety, mood swings)

• Sex hormones, such as estrogen and testosterone, play a significant role in sexual differentiation and the development of gender-specific behaviors

• Hormones interact with neurotransmitters and other signaling molecules to modulate brain function and behavior

When Things Go Wrong: Brain Disorders

• Brain disorders can arise from a variety of factors, including genetic predisposition, environmental influences, and injury or illness

• Neurodegenerative diseases, such as Alzheimer's and Parkinson's, involve the progressive loss of neurons in specific brain regions

  • Alzheimer's disease is characterized by memory loss, cognitive decline, and changes in behavior and personality

  • Parkinson's disease affects motor function, causing tremors, rigidity, and difficulty with movement

• Mental illnesses, such as depression, anxiety disorders, and schizophrenia, are associated with imbalances in neurotransmitter systems and abnormalities in brain structure and function

  • Depression is linked to reduced levels of serotonin and norepinephrine in the brain

  • Schizophrenia involves disruptions in dopamine signaling and abnormal brain development

• Substance use disorders, such as addiction to drugs or alcohol, involve changes in the brain's reward system and can lead to compulsive drug-seeking behavior

• Traumatic brain injuries (TBIs) can result in a range of cognitive, emotional, and behavioral deficits, depending on the location and severity of the injury

• Understanding the biological basis of brain disorders is crucial for developing effective treatments and interventions

Real-Life Applications

• Knowledge of the biological bases of behavior has led to the development of various pharmacological treatments for mental illnesses (antidepressants, antipsychotics, anxiolytics)

  • These medications work by modulating neurotransmitter systems in the brain to alleviate symptoms and improve functioning

• Cognitive-behavioral therapy (CBT) is a psychotherapeutic approach that aims to modify maladaptive thoughts and behaviors by targeting the underlying neural circuits involved in emotional processing and decision-making

• Neurofeedback is a technique that uses real-time monitoring of brain activity to help individuals learn to regulate their own brain function and improve symptoms of various disorders (ADHD, anxiety, depression)

• Understanding the role of the brain in learning and memory has informed educational practices and the development of strategies to enhance academic performance (spaced repetition, retrieval practice, elaborative encoding)

• Research on the biological basis of addiction has led to the development of medications and behavioral interventions to help individuals overcome substance use disorders (methadone, buprenorphine, contingency management)

• Advances in neuroimaging techniques (fMRI, PET, EEG) have allowed researchers to study the living brain and gain insights into the neural basis of behavior, cognition, and mental disorders

• Knowledge of the biological factors underlying aggression and violence has informed the development of prevention and intervention strategies to reduce antisocial behavior and promote prosocial behavior