AP Psychology Unit 1

Nature vs. Nurture 🌿

The age-old debate of nature versus nurture explores the impact on human behavior and mental processes.

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

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

Psychological perspectives differ on the weight they give to nature versus nurture.

• Evolutionary Approach: Leans towards nature, based on Darwin's theory of evolution.

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

  • Eugenics: An application of evolutionary approach principles that supports discriminatory practices.

    The belief in improving the genetic quality of the human population by selectively breeding for desirable traits and discouraging reproduction among those with traits considered undesirable.

• Epigenetics: Explores the relationship between heredity and the environment.

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

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

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

  • Explains differences in identical twins.

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

  • Includes family and adoption studies.

    • Colorado Adoption Project: Longitudinal study examining genetics and environmental influences on cognitive abilities, personalities, and mental processes.

• Plasticity: Brain's ability to change and adapt due to experiences by strengthening or weakening neural connections.

🧠 The Nervous System

Central vs. Peripheral Nervous System

• Central Nervous System (CNS): Made up of the brain and spinal cord.

• Peripheral Nervous System (PNS): Nerves that branch off from the brain and spine, connecting the CNS to the body's organs and muscles.

Types of Nerves

• Afferent Neurons (Sensory Neurons): Send signals from sensory receptors to the CNS.

  Afferent approaches the brain.

• Efferent Neurons (Motor Neurons): Send signals from the CNS to the PNS.

  Efferent exits the brain.

Peripheral Nervous System Divisions

• Sympathetic and parasympathetic systems work together in emergencies.

  Think of parasympathetic as a parachute that slows you down.

🧫 Neural Cells

Types of Neural Cells

• Glial Cells: Provide structure, insulation, communication, and waste transportation.

  The most abundant cells in the nervous system that support neurons.

  • Do not process information.

• Neurons: Basic functional unit of the nervous system.

  Communicate using electrical impulses and chemical signals.

Neurons in the Spinal Cord

• Sensory Neurons: Detect the Heat and send a signal through a sensory neuron to the spinal cord.

• Motor Neurons: Connect to Sensory Neurons within the CNS.

• Interneurons: Neurons within the brain and spinal cord that communicate internally.

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

🧠 Neural Communication and the Reflex Arc

Sensory vs. Motor Neurons

• Sensory neurons: Also known as afferent neurons, carry signals towards the central nervous system.

• Motor neurons: Also known as efferent neurons, transmit signals from the central nervous system to muscles and glands.

The Reflex Arc

The reflex arc allows for rapid responses to stimuli, protecting the body before the brain fully processes what is happening. For example, quickly pulling your hand away from a hot surface.

Neural Transmission Process

1. Stimulation: A neuron needs sufficient stimulation to initiate an action potential.

2. Action Potential:

   • A neuron "fires", sending an impulse down the axon.

   • Relies on the separation of positively and negatively charged ions by the cell membrane, creating a potential.

   • Permeability affects how easily ions cross the membrane.

3. Resting Potential: When a neuron is not sending a signal, it maintains a state where there are more negative ions inside compared to the outside.

4. Depolarization:

   A stimulus must be strong enough to meet the threshold to cause depolarization, leading the neuron to fire an action potential. If the threshold isn't met, the neuron returns to its resting state. (All-or-nothing principle).

5. Repolarization: The neuron returns to its resting potential, during which time:

   • Channels open to rebalance charges.

6. Refractory Period:

   The period during repolarization when the neuron cannot respond to another stimulus until it returns to its resting potential.

7. Synapse:

   The signal reaches the axon terminal, where it is converted and sent to another neuron across a small gap called the synapse.

⚡ Types of Synapses

• Chemical Synapses: Use neurotransmitters to transmit messages.

• Electrical Synapses: Facilitate rapid and immediate transmission of messages.

Neurotransmitters and Synaptic Transmission

1. Neurotransmitter Release: Neurotransmitters are released and diffuse across the synaptic gap.

   Synaptic Gap: The narrow space between the presynaptic terminal (axon terminal of the sending neuron) and the postsynaptic terminal (dendrite of the receiving neuron).

2. Message Transmission: Neurotransmitters deliver their messages.

3. Unbinding and Reuptake: After passing the message, neurotransmitters unbind from receptors. Some are destroyed, while others undergo reuptake.

   Reuptake: The process where the sending neuron reabsorbs excess neurotransmitters from the synaptic gap.

🚦 Excitatory vs. Inhibitory Neurotransmitters

• Excitatory Neurotransmitters: Increase the likelihood of an action potential in the postsynaptic neuron through depolarization.

• Inhibitory Neurotransmitters: Decrease the likelihood of an action potential through hyperpolarization (making the inside of the neuron more negative).

Neural Transmission Steps

1. Action potential travels down the axon to the presynaptic terminal.

2. Channels open, releasing neurotransmitters into the synaptic gap.

3. Neurotransmitters diffuse across the gap and bind to receptors on the postsynaptic terminal.

4. Neurotransmitters unbind; some are destroyed, and others undergo reuptake.

Neurological Disorders

Disruptions in neural transmission can lead to neurological disorders.

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

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

🧠 Types and Functions of Neurotransmitters and Hormones

Neurotransmitters

Hormones

Endocrine System vs. Nervous System

• Endocrine System: Slower; uses hormones sent through the bloodstream to target larger areas, regulating biological processes.

• Nervous System: Faster; uses neurons to quickly send messages to localized areas.

💊 Psychoactive Drugs: Agonists vs. Antagonists

Agonist Drugs

• Example: Anti-anxiety medications like Xanax, which increase GABA, decreasing neural activity and calming people down. Another example is Prozac.

Antagonist Drugs

Psychoactive Drugs 🧠

• Agonist substances: delay the reuptake of neurotransmitters, making them more available.

  • Example: Medication for depression that delays the reuptake of serotonin.

  • Example: Opioids.

• Antagonist substances: block receptors or the release of neurotransmitters.

  • Example: Medication for schizophrenia, which blocks dopamine receptors.

  • Example: Alcohol, which blocks the release of glutamate, acting as a depressant.

• Psychoactive drugs: alter an individual's perceptions, consciousness, or mood.

Categories of Psychoactive Drugs

Tolerance, Addiction, and Withdrawal ⚠

• Using psychoactive drugs can lead to a higher tolerance, requiring more of the drug to achieve the same effect.

• This can result in addiction and withdrawal symptoms.

Brain Structures and Regions 🧠

• Three major regions of the brain:

  • Hindbrain: Located at the bottom of the brain.

  • Midbrain: Located in the center, above the base of the brain.

  • Forebrain: Located at the top of the brain.

Hindbrain Structures

• Spinal Cord: Connects the brain to the rest of the body, allowing nerves to send information to the brain and vice versa.

• Brainstem: Located at the base of the brain on top of the spinal cord. Includes the medulla, the pons, and the midbrain. Severe damage can result in death due to its control of autonomic functions.

• Medulla Oblongata: Located above the spinal cord and below the pons. Helps regulate cardiovascular and respiratory systems and takes care of autonomic functions.

• Pons: A bridge between different areas of the nervous system, connecting the medulla with the cerebellum and helping coordinate movement. 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 brainstem. Involved in the regulation of arousal, alertness, and sleep-wake cycles. Stimulates other brain structures when something important happens.

• Cerebellum: Located in the back of the brain just below the occipital lobes and behind the pons. Helps with coordinating voluntary movements, maintaining posture and balance, refining motor skills, and plays a role in cognitive functions. Sometimes referred to as the "little brain".

Midbrain

• Helps with processing visual and auditory information, motor control, and integrating sensory and motor pathways.

Forebrain Structures

• Cerebrum: The largest part of the brain, dealing with complex thoughts. Divided into two hemispheres (left and right), each further subdivided into four lobes.

  • Made up of gray matter called the cerebral cortex and 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.

Lobes of the Brain

• Frontal Lobe: Located just behind the forehead, deals with higher-level thinking.

  • 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 the body, and the right motor cortex controls movement on the left side of the body.

    • Contralateral Hemispheric Organization: The way in which the brain's hemispheres control opposite sides of the body and processes sensory information.

    • Motor Homunculus: Visual representation of the amount of brain area that is dedicated towards a specific body part in the motor cortex.

  • 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.

    • Damage to this area results in Broca's Aphasia: Loss in ability to produce language, though individuals can still understand language and speech.

• Parietal Lobe: Located in the upper part of the brain, right behind the frontal lobe. Receives sensory information, allowing understanding of touch, pain, temperature, spatial orientation, and 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 the body, and the right sensory cortex controls sensations for the left side of the body.

    • Sensory Homunculus: Visualizes the amount of brain area that is dedicated towards specific body parts in the somatosensory cortex.

• Temporal Lobe: Located right above the ears, involved in processing auditory and linguistic information, recognizing faces, and assists with memory.

  • Hippocampus: Helps with learning and forming memories (but memories are not stored here).

  • Amygdala: Responsible for emotional reactions, such as fear, anxiety, and aggression.

  • Auditory Cortex: Located in the superior temporal gyrus of the temporal lobe, processes different sounds and allows recognition of things like music and speech.

  • Wernicke's Area: Typically located in the left temporal lobe, responsible for creating meaningful speech.

    • Damage to this area results in Wernicke's Aphasia: Loss of the ability to create meaningful speech.

• 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 such as recognizing objects, understanding spatial relationships, and perceiving depth and movement.

  • Works with the parietal and temporal lobes, showing that vision is not confined 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.

• The parietal lobe helps understand spatial orientation.

• The thalamus, located deep within the brain above the brain stem, receives sensory information from sensory organs (except smell).

  • It relays this information to the appropriate areas of the cerebral cortex for processing.

  • It is often called a relay station.

  • Visual information from the eye is sent to the thalamus, then relayed to the occipital lobe for visual processing.

• The limbic system is located on both sides of the thalamus.

  • It is responsible for emotions, learning, memory, and some basic drives.

  • Structures include the amygdala, hippocampus, thalamus, and hypothalamus.

• The hypothalamus helps maintain homeostasis, controls drives (thirst, hunger, temperature, sex), and works with the pituitary gland to regulate hormones.

• The pituitary gland is known as the "master gland".

  • It produces and releases hormones that regulate many bodily functions and controls other endocrine glands throughout the body.

Brain Lateralization 🧠

• Brain lateralization: differing functions of the left and right hemispheres

  • Each hemisphere has different areas it is more efficient in.

  • Both hemispheres are used to accomplish different tasks.

  • No one is simply just right-brained or left-brained.

• The left hemisphere is better at recognizing words, letters, and interpreting language.

• The right hemisphere is better at spatial concepts, facial recognition, and discerning direction.

Examining the Brain 🔬

Phineas Gage

• Phineas Gage was a railroad worker who had a tamping rod go through his head.

• He survived but had a personality change due to the rod severing his limbic system.

  • The limbic system is important for judgment and emotional regulation.

• His accident allowed researchers to better understand different brain structures.

Split-Brain Research

• Split-brain patients undergo a procedure where the corpus callosum is cut to treat severe epilepsy.

  • The corpus callosum connects the left and right hemispheres of the brain.

• Cutting the corpus callosum prevents the right and left hemispheres from communicating.

• Researchers test split-brain patients for cortex specialization.

  • This helps researchers understand how different areas of the cerebral cortex are specialized for specific functions.

• When patients are shown a word in their right visual field, they can say the word.

• When shown a word in the left visual field, they say they do not see anything, but they can draw the word with their left hand.

  • Once they draw the word, they can identify it because their right visual field sees the picture.

  • The left hemisphere contains language (Broca's area and Wernicke's area).

• This research helped in understanding the different functions of each hemisphere and the tasks each hemisphere is more efficient in.

Other Research Methods

• Lesion studies: Researchers destroy specific parts of the brain to gain insight into different functions, sometimes used to treat specific disorders.

• Autopsies: Examination of a deceased individual's body to discover the cause of death.

  • Allows for a better understanding of the extent of a disease.

  • Helps determine the exact cause of death.

  • Provides important information for the next of kin.

Neuroplasticity 🧠

• Learning new skills and information leads to neuroplasticity.

• Brain damage can result from infections, neurotoxins, genetic factors, head injuries, tumors, or stroke.

• The brain may or may not recover from damage, which can have life-altering impacts.

• When learning new information or practicing old skills, the brain creates neural pathways.

• The more a skill is practiced or information is studied, the more developed the pathways become.

Neuroimaging Techniques 🧠

• EEG (electroencephalogram): Uses electrodes placed on the scalp to record electrical signals from neurons firing.

  • Helps with sleep and seizure research.

• fMRI (functional magnetic resonance imaging): Similar to MRI but shows metabolic functions.

  • Provides a more detailed picture of brain activity compared to other scans like PET scans.

Sleep and Consciousness 😴

• Two types:

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

  • Sleep: 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 to gain insight into our consciousness.

Circadian Rhythm

• Impacts when we feel alert/awake and when we feel sleepy/ready for bed.

• Adjusts over time with age and life experiences.

• Can be disrupted by working the night shift or traveling across time zones.

Brain Waves During Sleep

• An EEG can be used to visualize different brain waves to understand which stage of sleep an individual is in.

• An EEG measures the frequency of a wave (number of waves per second) and the amplitude (size of the wave).

😴 Stages of Sleep

Here's a breakdown of the stages of sleep:

REM Deprivation and Rebound

• REM Deprivation: Occurs when sleep is interrupted, preventing sufficient REM sleep.

• REM Rebound: After REM deprivation, the body compensates by:

  • Entering REM sleep more quickly.

  • Spending more time in REM sleep.

🤔 Theories About Dreams

Activation-Synthesis Theory

• During REM sleep, brain activity occurs, and the brain attempts to create a narrative or dream from this activity.

Consolidation Theory

• During sleep, especially REM sleep, the brain organizes and strengthens connections between neurons related to recent experiences and information.

Restoration Theory

• Memory consolidation and restoration are considered two primary current theories about why sleep occurs.

🛏 The Importance of Sleep

• Physical and Mental Restoration: Sleep is crucial for the body's physical and mental recovery.

• Protection: Sleep can be seen as a protective mechanism, with animals sleeping according to their activity patterns and threats.

• Memory Consolidation: Sleep strengthens neural pathways, improving recall.

• Growth and Energy Conservation: The pituitary gland releases growth hormones during sleep, aiding muscle development. Sleep allows us to conserve energy.

• Creativity: Sleep and dreams can spark creativity.

😴 Sleep Disorders

• Insomnia: Difficulty falling asleep or staying asleep, often due to stress, pain, medication, or irregular sleep schedule.

• Sleep Apnea: Breathing difficulties during sleep, preventing proper rest and REM sleep.

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

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

• Sleep Terrors (Night Terrors): Experiencing intense fear during sleep.

• Narcolepsy: Uncontrollably falling asleep during the day, often with difficulties sleeping at night.

🧠 Sensation

• When an outside stimulus is taken through one of your senses, you activate your sensory neurons, which create a sensation for you. This is sensory transduction.

• Absolute Threshold: The smallest amount of stimulation needed for you to notice a sensation at least 50% of the time.

• Sensory Adaptation: When a stimulus is continuous and doesn't change, you eventually stop noticing it.

• Habituation: Repeated exposure to a stimulus leads to a reduced response.

Difference between Sensory Adaptation and Habituation

Here's a table showing the difference:

• Difference Threshold: The minimum change between two stimuli needed for an individual to detect the change.

Sensory Perception 👂

Difference Threshold and Weber's Law

To notice a difference between two stimuli, they must differ by a constant percent, not a constant amount. This concept is described by Weber's Law.

Example:

• Dropping one drop of water into an empty glass is noticeable.

• Adding one drop to a half-full glass is not.

Sensory Interaction 🤝

Sensory interaction refers to the collaboration of our senses (sight, hearing, taste, touch, and smell) to help us understand and respond to the world. Our senses do not operate in isolation; they constantly influence each other.

Example:

• Eating Skittles with and without smell. When your nose is plugged, each color of Skittle tastes the same, but when you smell them, you experience different flavors for each color.

Synesthesia 🧠

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

Examples:

• Seeing colors when hearing music.

• Tasting flavors when reading words.

Visual Sensory System 👁

The Eye and Light Processing

When light enters the eye through the cornea, it passes through the pupil. The lens then focuses the light onto the retina at the back of the eye. The retina is made up of layers of light-sensitive cells known as photoreceptors, which convert the light into neural impulses. This conversion process is called transduction, where light is converted into electrical signals.

1. Light enters through the cornea.

2. Passes through the pupil.

3. The lens focuses light onto the retina.

4. Photoreceptors convert light into neural impulses.

5. Neural impulses travel through the optic nerve.

6. Briefly stop at the thalamus.

7. Travel to the primary visual cortex in the occipital lobe for processing.

Blind Spot

The blind spot is a small area on the retina where the optic nerve is located, and there are no photoreceptors. As a result, there are no light-detecting cells in this area, creating a gap in our visual field. We don't usually notice this because our brain fills in the missing information from the other eye and surrounding areas.

Rods and Cones

Rods and cones are two types of photoreceptors in the eye:

Color Vision Theories

Trichromatic Theory

Individuals are able to see color because different wavelengths of light stimulate combinations of three color receptor photoreceptors that work in teams of three: red, green, and blue.

Opponent Processing Theory

Information received from the cones is sent to ganglion cells. Some neurons become excited, and others are inhibited. Color vision is based on three color pairings:

• Red and green

• Blue and yellow

• Black and white

This theory also explains afterimages, which occur when staring at an image for an extended period. The active ganglion cells responding to certain colors become fatigued. When looking at a neutral background, the fatigued cells do not respond as strongly, while the opposing cells become more active, creating an afterimage in complementary colors.

Wavelength and Amplitude

• Wavelength: Cooler colors have a shorter wavelength, while warmer colors have a longer wavelength.

• Amplitude: Determines the brightness of the color. Greater amplitude means brighter colors, while smaller amplitude means duller colors.

Color Blindness

• Achromatism: Only seeing black, white, and gray due to the absence of retinal cones.

• Dichromatism: Only possessing two of the three types of retinal cones, which may lead to confusion between certain colors. The most common type is red-green color blindness.

• Monochromatism: Being able to see everything in shades of one color due to the absence or malfunction of cone cells in the retina.

• Trichromatism: The ability 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): The lens focuses light in front of the retina, making distant objects appear blurry.

• Hyperopia (Farsightedness): The lens focuses light behind the retina, making close objects appear blurry.

Visual Disorders

Prosopagnosia (Face Blindness)

Results from damage to the occipital and temporal lobes. Individuals lose the ability to recognize faces.

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 Waves

Sound travels through the air as waves through the movement of air molecules. The wavelength of a sound wave is the distance between two identical parts of a wave (e.g., the distance between two peaks).

Frequency and Pitch

Frequency is the number of waves that pass a given point per second and determines the pitch of the sound (highness or lowness).

• High-frequency sound waves have short wavelengths and are perceived as high-pitched sounds.

• Low-frequency sound waves have long wavelengths and are perceived as low-pitched sounds.

Amplitude and Loudness

The amplitude of a sound wave refers to the height of the wave and determines the loudness of the sound.

• Greater amplitude means more energy and louder sounds.

• Smaller amplitude means less energy and quieter sounds.## 👂 Sound Localization and Theories of Pitch

Sound localization is the process by which the brain determines the origin of sounds in our environment, allowing us to identify the direction and distance of sounds.

When trying to understand pitch and sound, there are three different theories to consider:

Place Theory

The place theory states that certain hair cells respond to certain frequencies.

• Most effective at explaining the perception of higher pitch sounds

• Struggles with lower pitch sounds

Frequency Theory

The frequency theory states that the frequency of the auditory nerve impulses corresponds directly to the frequency of the sound wave.

• Best at explaining low pitch sounds

• Limited by the fact that individual neurons cannot fire faster than about a thousand times per second, while we can hear frequencies up to around 20,000 Hz

Volley Theory

The volley theory seeks to address the limitation of the frequency theory.

🤕 Hearing Loss

If an individual sees a decline in the clarity, loudness, and range of sounds, they may be experiencing hearing loss.

Types of Hearing Loss

• Sensory neural deafness: Damage to the cochlea or the auditory nerve.

• Conductive deafness: A blockage or damage that prevents sound from traveling efficiently from the outer ear to the middle ear and inner ear.

Treatments for Hearing Loss

• Cochlear implant: A device that converts sounds into electrical signals, which stimulate the auditory nerve and allow for signals to be sent to the brain.

• Hearing aid: A device that amplifies sounds to allow an individual to hear different sounds around them.

👃 The Chemical Sensory System: Smell

The process of smelling begins in the nose, where the olfactory receptors are located.

• Transduction occurs as chemical signals of odor molecules are converted into electrical signals that the brain can interpret.

• Smell is unique because it does not pass through the thalamus.

• Electrical signals generated by the olfactory receptors are sent directly to the olfactory bulb, then sent to various regions in the brain, including the olfactory cortex and the limbic system.

Pheromones

Pheromones are chemical signals released by an individual that affect the behavior or physiology of other individuals.

👅 Gustation (Taste)

Gustation is the term for the sense of taste, which consists of six different tastes:

• Sweet

• Sour

• Bitter

• Salty

• Umami

• Oleogustus

Taste Buds and Papillae

In order to experience these different tastes, we have to talk about the tongue, and more specifically, the papillae, which are small structures located on the tongue that house our taste buds.

There are four different types of papillae which allow you to experience the different types of taste.

The neurotransmitters stimulate sensory neurons, which transmit electrical signals to the brain. The signals go to the thalamus, which are sent to various parts of the brain such as the limbic system and the gustatory cortex, which is the area responsible for the perception of taste.

Types of Tasters

• Super tasters: Individuals that have a higher than average number of taste receptors, allowing them to experience tastes more intensely.

• Medium tasters: Individuals with an average number of taste receptors who have a more balanced sensitivity to different tastes.

• Non-tasters: Individuals that have fewer taste receptors, making them less sensitive to certain tastes.

Interaction of Taste and Smell

Taste and smell interact closely to create the full sensation of flavor. Taste buds detect the basic tastes, while the olfactory receptors identify the aromas released from the food. Together, these inputs are processed by the brain to produce the different flavors that we experience.

🖐 The Touch and Pain Sensory System

The skin is one of the largest organs of the body.

Layers of the Skin

• Epidermis: The outside layer of your skin that creates a barrier to protect a person from foreign pathogens and gives an individual their skin color.

• Dermis: Below the epidermis, this consists of two different layers of connective tissue where your blood vessels and nerve endings are located.

• Hypodermis: Underneath the dermis is a layer of fat that helps insulate an individual's tissues and absorbs shocks.

Skin Senses

When talking about touch, there are four skin senses:

• Pressure

• Warmth

• Cold

• Pain

These give us our sense of touch. Mechanical receptors are sensory receptors located in the skin that respond to pressure, while thermal receptors are sensory receptors that are located in the skin and respond to temperature changes.

🌡 Thermoceptors & Sensory Perception

Our bodies are equipped with thermoceptors, sensory receptors that detect temperature changes. Thermoceptors are activated when we encounter extreme heat, with both warm and cold receptors becoming active simultaneously. The brain interprets this mixed signal as a sensation of "hot," which commonly occurs when skin is exposed to high temperatures that excite both types of thermoceptors.

Depending on the amount of pressure, warmth, or cold of an object, we experience different sensations. When touch stimuli is detected by our receptors, it is converted from physical stimuli into electrical signals. These signals are transmitted through the peripheral nervous system to the spinal cord and brain, where they 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 & Pain Perception

We also have nociceptors, located in the dermis, which are pain receptors. They are sensory receptors that detect harmful stimuli such as:

• Extreme temperatures

• Damage

• Chemical irritants

Gate Control Theory

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

This gate is influenced by the relative activity of different types of nerve fibers.

• Open Gate: Pain signals can pass through and will be sent to the brain.

• Closed Gate: Pain signals are restricted from traveling to the brain.

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

• Distraction might reduce pain perception by closing the gate.

• Focusing on the pain would open the gate and cause the individual to experience more pain.

Phantom Limb Sensation

Phantom limb sensation may occur in individuals who have lost a body part. It is defined as:

Factors that could 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 Mapping: 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 & Movement

Vestibular Sense

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, this allows you to maintain your balance, resulting in nerve impulses being sent to the brain. This allows your brain to understand the direction and speed of rotation.

Kinesthesis

When you think of body movement, think of kinesthesis. This is the sense that:

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.

Proprioceptors

The brain understands what is happening with our body by using information from our proprioceptors. These are sensory receptors that are located in various muscles and tendons that allow for the brain to gain a better sense of position and movement of our limbs.

Cerebellum

The cerebellum plays a major role in:

• Coordinating voluntary movements

• Balance

• Processing information on precise movements