Unit 1 Summary: Biological Basis of Behavior 🧠 Nature vs. Nurture 🌿 The age-old question of whether nature (heredity) or nurture (environmental fact

Unit 1 Summary: Biological Basis of Behavior 🧠

Nature vs. Nurture 🌿

• The age-old question of whether nature (heredity) or nurture (environmental factors) has a greater impact on human behavior.

• The current understanding is that it's nature and nurture working together, not one or the other.

  • Nature: Heredity, the passing on of physical and mental traits from one generation to another.

  • Nurture: Environmental factors like family life, social groups, education, and societal influences.

Psychological Perspectives: Heredity and Environment 🧐

• Different psychological perspectives view the roles of heredity and environment differently.

Evolutionary Approach 🐒

• Based on Darwin's theory of evolution, leaning towards the nature side of the debate.

• Charles Darwin focused on how heredity and environment impact individuals.

  • Theory of Evolution: Evolution happens through natural selection, where beneficial traits survive and are passed on, while undesirable traits die off.

• Eugenics: Improving genetic quality by selectively breeding desirable traits and discouraging reproduction of undesirable traits.

Epigenetics 🧬

• Focuses on how the environment and behavior affect a person's genes and how they work.

• Examines how an individual's body reads a DNA sequence.

• Genes are turned on or off due to sustained environmental pressures.

• Explains why identical twins (with nearly 100% shared genes) can develop different characteristics.

  • Minnesota Study of Twins Reared Apart: Examines similarities and differences in identical twins raised in different environments.

• Family Studies and Adoption Studies: Used to understand the impact of heredity and environment.

  • Colorado Adoption Project: A longitudinal study that began in 1975, following biological and adoptive families to understand the influences of genetics and environment on cognitive abilities, personalities, and mental processes.

Plasticity 🧠

• Brain's ability to change and adapt as a result of experiences.

• Involves strengthening or weakening neural connections.

Nervous System 🌟

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

Types of Nerves

Peripheral Nervous System Breakdown

Autonomic Nervous System Divisions

Neurons 💡

Types of Neural Cells

Reflex Arc ⚡

• Nerve pathway that allows the body to respond to a stimulus without thinking.

• Involves sensory neurons, motor neurons, and interneurons.

  • Sensory Neurons: Detect stimuli (e.g., heat) and send signals to the spinal cord.

  • Interneurons: Neurons within the brain and spinal cord that connect sensory neurons to motor neurons within the CNS.

  • Motor Neurons: Carry signals from the CNS to muscles to initiate a response.

🧠 Neural Transmission and Communication

🏃 The Reflex Arc

Sensory neurons (also known as afferent neurons) send signals to the central nervous system, while motor neurons (also known as efferent neurons) carry signals from the central nervous system to the muscles. When a signal reaches the motor neurons, it prompts the muscles to move, such as pulling a hand away from a hot surface. This entire process is part of the body's autonomic response, which is involuntary and does not require conscious thought.

The reflex arc is a protective mechanism that allows the body to respond to threats quickly, before the brain fully processes what is happening.

🔥 Action Potential

For neurons to send messages, they must receive enough stimulation to cause an action potential.

This process requires positively and negatively charged ions. The cell membrane separates these ions, creating a positive or negative environment on either side of the barrier. This separation gives neurons their potential. Permeability refers to how easily ions can cross the membrane.

When a neuron is not sending a signal, it has more negative ions inside than outside, which is known as the resting potential. To trigger an action potential, a neuron must depolarize.

If the stimulus does not meet the threshold, the neuron will not fire and will return to its resting state. This is an "all or nothing" phenomenon.

After an action potential occurs, the neuron goes through repolarization, which returns it to its resting potential. During repolarization, channels open to rebalance the charges by letting more positive ions back outside the cell membrane.

During the refractory period, the neuron cannot respond to any other stimulus until repolarization occurs and the cell returns to its resting potential.

🌉 The Synapse

Once a signal reaches the axon terminal, it is converted and sent to another neuron through the synapse.

There are two types of synapses:

• Chemical synapses: Use neurotransmitters (chemical messengers) to send messages.

• Electrical synapses: Transmit messages quickly and immediately.

When neurotransmitters are sent, they diffuse through the synaptic gap to deliver their messages.

• Presynaptic terminal: The axon terminal of the neuron, which converts the electrical signal to a chemical one and sends neurotransmitters into the synaptic gap.

• Postsynaptic terminal: Where neurotransmitters are accepted in the dendrite of the receiving neuron.

After neurotransmitters pass their message to the postsynaptic neuron, they unbind with the receptors. Some are destroyed, while others are reabsorbed through a process called reuptake.

Neurotransmitters can either excite or inhibit the receiving neuron, depending on the receptors they bind to:

• Excitatory neurotransmitters: Increase the likelihood that a neuron will fire an action potential through depolarization.

• Inhibitory neurotransmitters: Decrease the likelihood that a neuron will fire an action potential, leading to hyperpolarization.

  Hyperpolarization is when the inside of the neuron becomes more negative, moving it farther away from its threshold.

Here is the chain of events:

1. An action potential sends a signal down the axon of the neuron to the presynaptic terminal.

2. Channels in the axon terminal open, and neurotransmitters are released into the synaptic gap.

3. Neurotransmitters diffuse through the synaptic gap and bind to receptor sites in the postsynaptic terminal.

4. Neurotransmitters unbind with the receptors; some are destroyed, and others go through reuptake.

🤕 Neurological Disorders

Disruptions in neural transmission can lead to neurological disorders:

• Multiple Sclerosis (MS): Damage to the myelin sheath disrupts the transmission of electrical signals, leading to muscle weakness, coordination problems, and fatigue.

• Myasthenia Gravis: An autoimmune disorder affecting communication between nerves and muscles, where antibodies block or destroy acetylcholine receptors, preventing muscle contraction and causing muscle weakness and fatigue.

🧪 Neurotransmitters and Hormones

Each neurotransmitter has a specific function that connects to different behaviors and mental processes:

Hormones also perform different functions similar to neurotransmitters:

The endocrine system uses hormones to regulate biological processes throughout the body, while the nervous system uses neurons to quickly send messages to localized areas.

💊 Psychoactive Drugs: Agonists vs. Antagonists

Agonist drugs increase the effectiveness of a neurotransmitter, while antagonist drugs decrease the effectiveness of a neurotransmitter.

Agonists:

• Bind to receptors in the synapse, mimicking neurotransmitters

• Increase neurotransmitter production

• Block reuptake, making more neurotransmitters available in the synapse

Antagonists:

• Block neurotransmitters from being released from the presynaptic axon terminal

• Connect to postsynaptic receptors and block the intended neurotransmitters from binding

Examples:

• Agonists:

  • Xanax: Increases GABA, decreasing neural activity and calming people down.

  • Prozac: (The transcript ends abruptly here)## Psychoactive Drugs 🧠 Psychoactive drugs can have different psychological and physiological effects on the body. These substances purposely alter an individual's perception, consciousness, or mood.

• Stimulants: Excite and promote neural activity.

  • Give an individual energy.

  • Reduce a person's appetite.

  • Can cause irritability.

  • Examples: caffeine, nicotine, or cocaine.

• Depressants: Reduce neural activity.

  • Cause drowsiness.

  • Muscle relaxation.

  • Lowered breathing.

  • If abused, possibly death.

  • Examples: alcohol or sleeping pills.

• Hallucinogens: Cause an individual to sense things that are not actually there.

  • Can reduce an individual's motivation.

  • Can lead to an individual to panic.

  • Examples: marijuana, peyote, or LSD.

• Opioids: Function as a depressant but have their own category due to their addictive nature.

  • Give an individual pain relief.

  • Examples: morphine, heroin, or oxycontin.

  Using different psychoactive drugs can lead a person to develop a higher tolerance, which would require more of the drug to be consumed to achieve the same effect. This could result in addiction and withdrawal symptoms.

Brain Structures and Regions 🧠

The brain can be seen as having three major regions: the hindbrain, midbrain, and forebrain.

Hindbrain

The hindbrain is located at the bottom of the brain.

• Spinal Cord: Connects your brain to the rest of your body; the information highway that allows nerves to send information to your brain and vice versa.

• Brain Stem: Located at the base of your brain on top of the spinal cord. Includes the medulla, the pons, and the midbrain. If severely damaged, it will most likely result in death since it controls autonomic functions.

  • Medulla Oblongata: Right above the spinal cord and below the pons.

    Helps with the regulation of a person's cardiovascular and respiratory systems and takes care of autonomic functions.

  • Pons: The bridge between different areas of the nervous system. Connects the medulla with the cerebellum and helps with coordinating movement. It also helps with sleep and dreams.

• Reticular Activating System (RAS): Part of the reticular formation.

  A network of nerve cell bodies and fibers within the brain stem involved in the regulation of arousal, alertness, and sleep-wake cycles. It also helps stimulate other brain structures when something important happens that needs immediate attention.

• Cerebellum: Located in the back of the brain, just below the occipital lobes and behind the pons. Sometimes referenced as the "little brain".

  Helps with coordinating voluntary movements, maintaining posture and balance, refining motor skills, and plays a role in cognitive functions.

Midbrain

The midbrain is located in the center, sitting above the base of the brain. It helps with processing visual and auditory information, motor control, and integrating sensory and motor pathways.

Forebrain

The forebrain is the top of the brain.

• Cerebrum: The largest part of the brain that deals with complex thoughts. It can be divided into two hemispheres (left and right), and each hemisphere can be further subdivided into four different lobes. The cerebrum is made up of gray matter called the cerebral cortex and also white matter.

  • Cerebral Cortex: A thin outer layer of billions of nerve cells that cover the whole brain.

  • Corpus Callosum: A thick band of nerve fibers that connects the two cerebral hemispheres, allowing them to communicate with each other.

• Frontal Lobe: Located just behind your forehead.

  Deals with higher-level thinking and is separated into two important areas: the prefrontal cortex and the motor cortex.

  • Prefrontal Cortex: Deals with foresight, judgment, speech, and complex thought.

  • Motor Cortex: Deals with voluntary movement and is located in the back of the frontal lobe. The left motor cortex controls movement on the right side of your body, and the right motor cortex controls movement on the left side of your body.

    Example of the brain's contralateral hemispheric organization, which refers to the way in which the brain's hemispheres control opposite sides of the body and processes sensory information.

    The functions of the motor cortex can be represented by the motor homunculus, which shows a visual representation of the amount of brain area that is dedicated to a specific body part.

  • Broca's Area: Found only in the left hemisphere in front of the motor cortex.

    Crucial for language production, particularly in controlling the movements of the muscles involved in speech. If this part of the brain is damaged, an individual will experience Broca's aphasia, which is the loss in the ability to produce language. Individuals with Broca's aphasia can still understand language and speech but will struggle to speak fluently.

• Parietal Lobe: Located in the upper part of the brain, right behind the frontal lobe.

  Receives sensory information and lets you understand things such as touch, pain, temperature, and spatial orientation. It also helps with processing and organizing information.

  • Somatosensory Cortex: Situated parallel to and directly behind the motor cortex.

    Responsible for processing touch, pressure, temperature, and body position. The left sensory cortex controls sensations for the right side of your body, and the right sensory cortex controls sensations for the left side of your body.

    The amount of brain area dedicated to specific body parts can be visualized when looking at the sensory homunculus.

• Temporal Lobe: Located just below the parietal lobe, right above your ears.

  Involved in processing auditory and linguistic information, recognizing faces, and assists with memory.

  • Hippocampus: Located within the temporal lobe.

    Helps us learn and form memories, but it is not where memories are stored.

  • Amygdala: Located at the end of each arm of the hippocampus; these two round clusters are where you get your emotional reactions from.

    Responsible for fear, anxiety, and aggression.

  • Auditory Cortex: Located in the superior temporal gyrus of the temporal lobe.

    Processes the different sounds that you hear and allows you to recognize things like music and speech.

  • Wernicke's Area: Typically located in the left temporal lobe.

    Responsible for creating meaningful speech. If this part of the brain is ever damaged, a person will lose the ability to create meaningful speech, which is known as Wernicke's aphasia.

• Occipital Lobe: Located at the back of the brain, just above the cerebellum.

  Responsible for processing visual information.

  • Primary Visual Cortex: Receives visual input from the eyes.

    Processes basic information and more complex visual tasks as well, such as recognizing objects, understanding spatial relationships, and perceiving depth and movement. It works with the parietal lobe and temporal lobe, which shows that vision does not confine itself to just one area of the brain.

🧠 Brain Structures and Functions

The occipital lobe detects an object's color and shape. The temporal lobe helps with identifying the object, and the parietal lobe helps understand spatial orientation.

Thalamus: The Relay Station

The thalamus, located deep within the brain above the brainstem, receives sensory information from sensory organs (except smell). It relays this information to the appropriate areas of the cerebral cortex for processing. It's often called a relay station.

The Limbic System: Emotions, Learning, and Memory

Located on both sides of the thalamus, the limbic system is involved in emotions, learning, memory, and basic drives. Structures include:

• Amygdala

• Hippocampus

• Thalamus

• Hypothalamus

Hypothalamus and Homeostasis

The hypothalamus maintains body balance and homeostasis. It controls drives like:

• Thirst

• Hunger

• Temperature

• Sex

The hypothalamus works with the pituitary gland to regulate and control hormones.

Brain Lateralization: Division of Labor

Brain lateralization refers to the differing functions of the left and right hemispheres. It's a division of labor, where each hemisphere excels in different areas. Everyone uses both hemispheres to accomplish tasks. The brain has hemispheric specialization.

🔬 Examining the Brain

Phineas Gage: A Case Study

Phineas Gage was a railroad worker who survived a tamping rod shooting through his head. While he lived and retained cognitive functions, he experienced a significant personality change due to the rod severing his limbic system, which is crucial for judgment and emotional regulation.

Split-Brain Research

Split-brain patients undergo a procedure where the corpus callosum, which connects the left and right hemispheres, is cut to treat severe epilepsy. This prevents communication between the hemispheres. Researchers study these patients to understand cortex specialization.

In one experiment, when a word was shown in the right visual field, the patient could say the word. However, when shown in the left visual field, the patient claimed to see nothing but could draw the word with their left hand. Once drawn, they could identify it, as the right visual field then perceived the picture.

Lesion Studies and Autopsies

• Lesion studies: Researchers destroy specific parts of the brain to understand their functions, sometimes to treat disorders.

• Autopsies: Examination of a deceased individual's body to determine the cause of death, understand diseases, and provide information to relatives.

Neuroplasticity: The Brain's Adaptability

Neuroplasticity is the brain's ability to change, modify, and repair itself. It occurs when learning new skills or information. When learning, the brain creates neural pathways. The more a skill is practiced, the more developed these pathways become. Brain damage can result from:

• Infections

• Neurotoxins

• Genetic factors

• Head injuries

• Tumors

• Stroke

🧠 Neuroimaging Techniques

EEG (Electroencephalogram)

Uses electrodes on the scalp to record electrical signals from neurons firing. Useful for sleep and seizure research.

fMRI (Functional Magnetic Resonance Imaging)

Similar to an MRI but shows metabolic functions, providing a detailed picture of brain activity.

😴 Sleep and Consciousness

Consciousness is our awareness of ourselves and our environment.

• Wakefulness: Being awake, aware of surroundings, and able to think, feel, and react.

• Sleep: A lower level of awareness, not fully aware of surroundings, but the brain is still active.

Cognitive neuroscience studies how brain activity is linked with cognition.

Circadian Rhythm: The Biological Clock

The circadian rhythm is a 24-hour biological clock that regulates:

• Blood pressure

• Internal temperature

• Hormones

• Sleep-wake cycle

It impacts when we feel alert and sleepy and adjusts with age and life experiences. Disruptions can occur due to night shifts or traveling across time zones, leading to jet lag.

Brain Waves and Sleep Stages

An EEG measures brain waves to understand sleep stages.

• Frequency: Number of waves per second.

• Amplitude: Size of the wave.

😴 Stages of Sleep

The slowest frequency of brain waves occurs when you are most relaxed, often during the deepest levels of sleep.

• Non-REM Stage 1: A very light sleep that lasts about 5-10 minutes.

  • Body starts to relax, and the mind slows.

  • Common waves: Alpha waves.

• Non-REM Stage 2: A transitional stage lasting around 10-20 minutes.

  • Experience K complexes and sleep spindles (bursts of neural activity).

  • Common waves: Theta waves.

• Non-REM Stage 3: One of the deepest states of sleep, lasting around 30 minutes.

  • Growth hormones are produced.

  • May experience sleepwalking or sleeptalking.

  • Common waves: Delta waves.

• REM (Rapid Eye Movement): The last stage.

  • External muscles are paralyzed while internal muscles become active.

  • Brain emits beta waves (similar to wakefulness).

  • Generally lasts about 10 minutes.

  • Dreams or nightmares may occur.

  • Considered paradoxical sleep because brain waves resemble wakefulness, but the body is most relaxed.

  • Periods of REM sleep become longer and more frequent as the sleep cycle progresses.

If an individual is deprived of REM sleep, they may experience:

• REM Deprivation: Occurs when someone is frequently interrupted during sleep.

• REM Rebound: The next time they sleep, they enter REM sleep more quickly and spend more time in REM to compensate for the lost sleep.

💭 Dreams

Hypnogogic Sensations

• Occur during non-REM stage 1.

• Sensations feel real but are imagined.

• Example: Feeling like you are falling and waking up suddenly.

Theories About the Purpose of Dreams

• Activation Synthesis Theory:

  Dreams are the brain's way of making sense of random neural activity during sleep. When we enter REM sleep, the brain tries to create a story to interpret this activity.

• Consolidation Theory:

  Dreams help process and strengthen memories and experiences, especially during REM sleep. The brain organizes and strengthens connections between neurons related to recent experiences and information. Focuses on the role of sleep in memory consolidation and learning.

• Restoration Theory:

  We sleep to restore our energy and resources after daily activities.

• Current Main Theories: Memory consolidation theory and the restoration theory.

Sleep's Crucial Functions

• Physical and mental restoration.

• Protection: Different animals sleep at different times and for different durations based on their activity and threats.

• Memory Consolidation: Strengthens neural pathways for better recall.

• Growth Support: Pituitary gland releases growth hormones during sleep, aiding muscle development.

• Energy Conservation.

• Creativity: Thinking about problems before sleep or using dreams as inspiration.

🩺 Sleep Disorders

• Insomnia: Difficulty falling asleep or staying asleep, caused by stress, pain, medication, or irregular sleep schedule.

• Sleep Apnea: Difficulty falling or staying asleep due to breathing problems, preventing restful sleep and REM sleep.

• REM Sleep Behavior Disorder (RBD): Acting out dreams during REM sleep due to absent or incomplete paralysis.

• Somnambulism (Sleepwalking): Getting up and walking around while still sleeping, most common during stage 3 sleep.

• Sleep Terrors (Night Terrors): Experiencing intense fear while sleeping, leading to sleep deprivation and disrupted sleep.

• Narcolepsy: Struggling to sleep at night and uncontrollably falling asleep during the day.

👁 Sensation

Sensation vs. Perception

• Sensation: Detecting information from the environment.

• Perception: Will be discussed further in unit 2.

Sensory Transduction

Absolute Threshold

Sensory Adaptation vs. Habituation

Difference Threshold

Difference Threshold and Weber-Fechner Law ⚖

To notice a difference between two stimuli, they must differ by a constant percentage, not a constant amount. This concept is formalized by the Weber-Fechner Law.

For example, one drop of water added to an empty glass is noticeable, but one drop added to a half-full glass is not.

Sensory Interaction 🤝

Sensory interaction is when our senses (sight, hearing, taste, touch, and smell) work together and influence each other.

Consider the Skittles experiment: if you plug your nose while eating Skittles, all the colors taste the same.

Synesthesia 🧠

Synesthesia is a neurological condition where one sense is experienced through another.

Visual Sensory System and the Eye 👁

When light enters the eye through the cornea, it passes through the pupil, where the lens focuses it onto the retina at the back of the eye.

The retina contains light-sensitive cells called photoreceptors that convert light into neural impulses.

This process is called transduction.

The neural impulses travel through the optic nerve, briefly stop at the thalamus, and then travel to the primary visual cortex in the occipital lobe for processing.

Blind Spot

There is a small area on the retina where the optic nerve is located that has no photoreceptors. This creates a blind spot because no light can be detected in this area. Our brain fills in the missing information from the other eye and surrounding area, so we normally do not notice it.

Rods and Cones

Rods and cones are two types of photoreceptors that convert light into neural impulses.

Color Vision Theories 🌈

Two theories explain our color vision:

1. Trichromatic Theory: Different wavelengths of light stimulate combinations of three color receptors (red, green, and blue).

2. Opponent Processing Theory: Information from cones is sent to ganglion cells, causing some neurons to become excited and others inhibited. Color vision is based on three color pairings: red-green, blue-yellow, and black-white.

The opponent processing theory explains afterimages, which occur when you stare at an image for a long period of time, fatiguing the active ganglion cells. When you look at a neutral background, the fatigued cells don't respond as strongly, while the opposing cells become more active, creating an afterimage in complementary colors.

Wavelength and Amplitude 📏

• Cooler colors have shorter wavelengths.

• Warmer colors have longer wavelengths.

• Amplitude determines brightness.

• Short wavelength = high frequency = cooler colors

• Long wavelength = low frequency = warmer colors

• Greater amplitude = brighter colors

• Smaller amplitude = duller colors

Color Blindness 🎨

• Achromatism: Only see black, white, and gray due to lack of retinal cones.

• Dichromatism: Only possess two of the three types of retinal cones, leading to confusion between certain colors (e.g., red-green color blindness).

• Monochromatism: Absence or malfunction of cone cells, resulting in seeing everything in shades of one color.

• Trichromatism: Able to see all colors.

Accommodation 👓

Accommodation refers to the eye's ability to change shape to focus light onto the retina, allowing us to see objects clearly at different distances.

• Myopia (nearsightedness): Lens focuses light in front of the retina; distant objects appear blurry.

• Hyperopia (farsightedness): Lens focuses light behind the retina; close objects appear blurry.

Brain Disorders Related to Vision 🧠

Prosopagnosia (Face Blindness)

Prosopagnosia results from damage to the occipital and temporal lobes. Individuals lose the ability to recognize faces, even those of close friends and family.

Blindsight

Blindsight occurs when there is damage to the primary visual cortex in the occipital lobe. Individuals appear blind in part of their visual field but can still respond to certain visual stimuli without conscious awareness.

Auditory Sensory System 👂

Sound travels through the air as waves through the movement of air molecules.

• Wavelength: The distance between two identical parts of a wave.

• Frequency: The number of waves that pass a given point per second (determines pitch).

• Amplitude: The height of the wave (determines loudness).

• High frequency = short wavelengths = high-pitched sounds

• Low frequency = long wavelengths = low-pitched sounds

• Greater amplitude = louder sounds

• Smaller amplitude = quieter sounds

👂 Sound Localization and Pitch Theories

Sound localization is how the brain determines the origin of sounds, identifying direction and distance using the auditory system and various auditory cues.

Pitch Perception Theories

Place Theory

• States that specific hair cells respond to specific frequencies.

• Hair cells at the base of the cochlea detect high-pitch sounds.

• Hair cells at the top of the cochlea detect low-pitch sounds.

• The brain identifies pitch based on the location of activated hair cells on the cochlea.

  Place Theory: The brain determines the pitch of a sound based on the specific location along the cochlea where hair cells are activated.

  • Most effective at explaining the perception of higher-pitch sounds but struggles with lower-pitch sounds.

Frequency Theory

• The frequency of auditory nerve impulses directly corresponds to the frequency of the sound wave.

• A sound wave at 100 Hz causes the auditory nerve to fire 100 times per second.

  Frequency Theory: The frequency of auditory nerve impulses corresponds directly to the frequency of the sound wave.

  • Best at explaining low-pitch sounds.

  • Limited because individual neurons cannot fire faster than about 1,000 times per second, while humans can hear frequencies up to 20,000 Hz.

Volley Theory

• Addresses the limitations of the frequency theory.

• Groups of neurons work together to fire in a staggered manner, collectively matching the frequency of higher-pitch sounds.

  Volley Theory: Groups of neurons work together, firing in a staggered manner, to match the frequency of higher-pitch sounds.

Hearing Loss

A decline in the clarity, loudness, and range of sounds could indicate damage to the cilia in the auditory nerve.

Types of Hearing Loss

• Sensory Neural Deafness:

  Damage to the cilia or the auditory nerve

• Conductive Deafness:

  Blockage or damage prevents sound from traveling efficiently from the outer ear to the middle and inner ear.

Interventions

• Cochlear Implant: Converts sounds into electrical signals, stimulating the auditory nerve to send signals to the brain.

• Hearing Aid: Amplifies sounds to improve hearing.

👃 Chemical Sensory System: Smell (Olfaction)

Olfactory Process

1. Olfactory Receptors:

   • Located in the olfactory epithelium inside the nasal cavity.

   • Odor molecules bind to these receptors.

2. Transduction:

   • Chemical signals are converted into electrical signals.

3. Neural Pathways:

   • Signals bypass the thalamus and are sent directly to the olfactory bulb.

   • From the olfactory bulb, signals are sent to the olfactory cortex and the limbic system for identifying, processing odors, and associating them with emotions and memories.

     Unlike other senses, smell does not pass through the thalamus, the brain's relay station for sensory information.

Pheromones

Pheromones are chemical signals released by an individual that affect the behavior or physiology of others within the same species. They are detected by the olfactory system and play a role in attraction, social interaction, and communication.

👅 Chemical Sensory System: Taste (Gustation)

Gustation, or the sense of taste, involves six primary tastes:

• Sweet

• Sour

• Bitter

• Salty

• Umami (savory)

• Olestra (fat)

Taste Perception

1. Papillae:

   • Small structures on the tongue that house taste buds.

   • Four types of papillae allow you to experience different types of tastes.

2. Taste Buds:

   • Each taste bud contains various taste receptor cells.

3. Process:

   • Food molecules dissolve in saliva and bind to receptors on the taste receptor cells.

   • This triggers a chemical reaction, releasing neurotransmitters.

   • Neurotransmitters stimulate sensory neurons, which transmit electrical signals to the thalamus and then to various brain areas like the limbic system and gustatory cortex.

     Gustatory Cortex: the area responsible for the perception of taste

Tasters

Sensitivity to taste varies among individuals and can be categorized as:

Interaction of Taste and Smell

Taste and smell interact closely to create the full sensation of flavor. Taste buds detect basic tastes, while olfactory receptors identify aromas. Without smell, taste sensations are muted because specific flavors and aromas are absent.

👋 Touch and Pain Sensory System

The skin is the largest organ, comprising three main layers:

• Epidermis:

  • The outer layer of skin.

  • Creates a barrier to protect from pathogens.

  • Provides skin color.

• Dermis:

  • Located below the epidermis, consisting of two layers.

  • Contains connective tissue, blood vessels, and nerve endings.

  • Responsible for the sense of touch and pain.

• Hypodermis:

  • A layer of fat beneath the dermis that helps insulate tissues and absorb shocks.

  • Not technically skin.

Skin Senses

The four skin senses that give us our sense of touch:

• Pressure

• Warmth

• Cold

• Pain

Receptors

• Mechanical Receptors:

  Sensory receptors in the skin that respond to pressure.

• Thermal Receptors:

  Sensory receptors in the skin that respond to temperature changes.

  • Warm Receptors: Activated by an increase in temperature.

  • Cold Receptors: Activated by a decrease in temperature.

🌡 Thermo Receptors

Our warm and cold receptors become activated when we encounter extreme heat. The simultaneous activation of both warm and cold receptors is interpreted by the brain as a sensation of hot. This commonly happens when the skin is exposed to high temperatures that stimulate both types of thermo receptors.

🖐 Touch Stimuli

When touch stimuli is detected by our receptors, it is converted from physical stimuli into electrical signals. These signals are then transmitted through the peripheral nervous system to the spinal cord and brain. The signals are sent to the thalamus and then to appropriate regions of the brain, such as the somatosensory cortex, which processes and interprets incoming sensory information to help us perceive touch.

🤕 Nociceptors

Nociceptors are located in the dermis and are also known as pain receptors.

🚪 Gate Control Theory of Pain

The gate control theory seeks to provide insight into how the body processes pain. It suggests that:

• If the gate is open, pain signals can pass through and will be sent to the brain.

• If the gate is closed, pain signals will be restricted from traveling to the brain.

An individual's psychological state, attention, and other sensory inputs can influence the gate's activity. For instance:

• If an individual is distracted, it might reduce the pain perception by closing the gate.

• When the person becomes more focused on the pain, the gate would open and cause the individual to experience more pain.

👻 Phantom Limb Sensation

Phantom limb sensation may occur with an individual who has lost a body part. It is when:

Different factors can cause this sensation:

• Neurological: After amputation, the brain and spinal cord may still receive signals from the nerves that once served the missing limb. These nerves can become hyperactive or misinterpret other signals as coming from the missing limb.

• Brain: The brain has a map of the body, and even after a limb is lost, the corresponding area in the brain's map may remain active and produce sensations as if the limb was still there.

⚖ Balance and Movement

When you think of balance, think of the vestibular sense. When you move your head, the fluid inside the semicircular canals moves, causing the hair cells in the canals to bend, ultimately allowing you to maintain your balance. This results in nerve impulses being sent to the brain, allowing your brain to understand the direction and speed of rotation.

When you think of body movement, think of kinesthesis.

This sensory system allows you to know where your limbs are in space and how they are moving without you having to constantly look at them. The brain understands what is happening with our bodies by using information from our proprioceptors.

The cerebellum plays a major role in coordinating voluntary movements, balance, and processing information on precise movements.