Perception Chapter 3 expanded

Somatosensation

The collection of body senses—including touch, temperature, pain, proprioception, and balance—that provide continuous information about the state of the body and its interaction with the environment.

Somesthesis

Skin-based sensory experiences such as light touch, deep pressure, heat, cold, and pain; comes from receptors embedded in the skin.

Chemoreceptors

Skin receptors that respond to chemical irritation (e.g., capsaicin, menthol, acids) and trigger sensations such as burning or tingling.

Thermoreceptors

Receptors sensitive to temperature changes; separate warm and cold receptors help detect thermal increases or decreases on the skin.

Mechanoreceptors

Receptors that respond to physical deformation of the skin like pressure, vibration, or stretching; basis of touch perception.

The Skin

The body’s largest organ, composed of multiple layers (epidermis, dermis, subcutaneous tissue) that protect the body and contain sensory receptors.

Epidermis

The thin, outermost layer of skin designed for protection; where some free nerve endings are located.

Dermis

The thicker middle layer beneath the epidermis containing most specialized touch receptors, blood vessels, and hair follicles.

Subcutaneous

The deepest skin layer made of fat and connective tissue that cushions the body and insulates temperature.

Physiological Zero

The temperature range (~85–90°F) where the skin perceives no warmth or cold because thermoreceptors adapt to this “neutral” point.

Skin Displacement

Physical movement or indentation of the skin surface that activates mechanoreceptors responsible for touch and pressure.

Nociceptors

Pain receptors that respond to harmful or potentially damaging stimuli such as extreme heat, extreme cold, pressure, or chemicals.

Merkel’s Disc

Slow-adapting receptors that detect steady, sustained pressure and fine details (e.g., reading Braille).

Free Nerve Endings

Bare nerve endings distributed throughout the skin that detect pain, temperature changes, touch, and skin stretch.

Meissner’s Corpuscle

Fast-adapting receptors located near the surface of glabrous skin that detect light touch, flutter, and subtle texture changes.

Hair Follicle Receptors

Receptors wrapped around hair follicles that detect hair movement and help sense very light touch.

Pacinian Corpuscle

Onion-like deep receptors that respond to fast vibrations and deep pressure, useful for detecting tool use or object manipulation.

Ruffini’s End Organ

Slow-adapting receptors sensitive to skin stretch and sustained pressure; important for perceiving hand position during grasping.

Paradoxical Cold

A cold sensation produced when intense heat activates cold receptors due to their unusual response at extreme temperatures.

A-delta fibers

Thin, myelinated nerve fibers that transmit sharp, immediate, localized pain and some temperature sensations quickly.

C fibers

Slow, unmyelinated fibers that carry dull, aching, diffuse pain, and signals related to heat, cold, and chemical irritation.

Congenital Insensitivity to Pain w/ Anhidrosis

Rare genetic disorder in which individuals lack functional pain and temperature receptors and are unable to sweat, making accidental self-injury and overheating common.

Specific Receptive Field

The exact patch of skin where a single receptor responds to stimulation; determines how precisely sensations can be localized.

Two-point Threshold Procedure

A method used to measure tactile acuity by determining the smallest distance at which a person can distinguish two separate points of touch.

Primary Receptors

The specific receptor types (e.g., mechanoreceptors, thermoreceptors) that identify what kind of physical energy is being detected.

Intensity

The strength of a sensation, determined by how many neurons fire and how quickly they fire action potentials.

Location

Where a stimulus is on the body, determined by which receptors and which receptive fields are activated.

Duration

How long a stimulus lasts, determined by the beginning and end of receptor firing; some receptors adapt quickly while others do not.

Touch (directionally-sensitive)

Touch receptors that respond differently depending on the direction the skin is moved, allowing detection of movement across the skin.

Gate Control Theory of Pain

A theory stating that pain signals must pass through a “gate” in the spinal cord, which can be closed by touch signals or influenced by the brain’s expectations, emotions, and attention.

Spinal Cord Gate

The substantia gelatinosa region of the spinal cord that modulates whether pain signals are allowed to continue to the brain.

Top-down control

Brain-driven modulation of perception, where expectations, attention, mood, and context influence how painful a stimulus feels.

Ventrobasal Complex

Thalamic region receiving inputs from A-beta fibers that carry fine touch and pressure information.

Ventrobasal Nucleus

Specific nucleus of the thalamus that relays detailed touch and pressure signals to the somatosensory cortex.

Somatosensory Cortex

Brain region in the parietal lobe that receives and interprets incoming signals from the skin, muscles, and joints.

Sensory Homunculus

A distorted cortical map showing body parts sized according to receptor density rather than physical size.

Phantom Limb

The sensation or pain perceived in a limb that has been amputated, caused by cortical reorganization in the brain.

Psychophysiological Pain

Pain influenced strongly by emotional, cognitive, and physiological factors rather than purely physical causes.

Pharmacological Interventions

Medications such as NSAIDs, acetaminophen, opioids, and cannabinoids used to alter pain signaling or reduce inflammation.

Transcutaneous Electrical Nerve Stimulation

Device that uses mild electrical currents to stimulate touch fibers and reduce pain by closing the spinal gate.

Opiate Drugs

Pain-relieving drugs that activate endorphin and enkephalin pathways, reducing the transmission of pain at the spinal gate.

SG Gate

The substantia gelatinosa “gate” where pain signals are inhibited or amplified before traveling to the brain.

Acupuncture

Traditional technique involving needle insertion that may relieve pain by triggering endorphin release, modulating brain activity, or producing placebo effects.

Biofeedback

Training method where physiological signals (heart rate, muscle tension) are monitored and intentionally controlled to reduce stress and pain.

Proprioception

The internal sense of body position, posture, and movement derived from signals in muscles, joints, and tendons.

Kinesthesis

Subcomponent of proprioception that provides information about limb movement, muscle stretch, and the positioning of body parts in space.

Vestibular

Balance system in the inner ear that detects head rotation, tilt, and acceleration through semicircular canals and otolith organs.

Golgi Organ

Receptor at the muscle–tendon junction that monitors muscle tension and protects against excessive force by inhibiting contraction.

Muscle Spindle

Receptor within muscles that senses stretching and triggers reflexes to maintain muscle length and posture.

Reflexive Contractions

Fast, involuntary muscle responses initiated by muscle spindles when a muscle is unexpectedly stretched.

Pulmonary Stretch Receptors

Receptors in lung tissue that monitor airway expansion, contributing to breathing regulation and protective reflexes.

Muscle Memory

Learned improvement in skilled movements through repeated practice, leading to automaticity and precision.

Body Awareness

Ability to sense the relative positions, movements, and posture of one’s body without visual input.

Hand-eye Coordination

Integration of visual information with motor commands to guide precise and accurate movements.

Fine & Gross Muscle Movement Control

Fine movements involve precision (e.g., writing), while gross movements involve larger muscle groups (e.g., running, jumping).

Postural Control & Adjustments

Continuous corrections made by proprioceptive and vestibular systems to maintain balance and stability.

Semicircular Canal

Three fluid-filled structures in the inner ear that detect rotational movements of the head.

Hair Cell Receptors (vestibular)

Sensory cells that bend when inner ear fluid moves, transducing rotational or linear acceleration.

Otolith Organs

Utricle and saccule; detect linear acceleration and head tilt using calcium carbonate “ear stones.”

Vertigo

Disturbance of the vestibular system producing the false sensation of spinning or rotation.

Dizziness

General sensation of unsteadiness or spatial disorientation, often involving lightheadedness or imbalance.

Motion Sickness

Nausea and discomfort caused by mismatched signals between the visual system and the vestibular system.

Percival Lowell

19th-century astronomer who mistakenly believed he saw artificial canals on planets like Mars and Venus.

Venus Canals

Imagined linear structures early astronomers thought existed on Venus or Mars; later shown to be optical illusions.

Electromagnetic Radiation

Energy that travels as waves and particles; includes visible light and moves at extremely high speed.

Infrared

Electromagnetic wavelength just beyond visible red; sensed as heat rather than visible light.

Light Energy Waves

Waves characterized by wavelength, amplitude, and complexity, which determine color, brightness, and saturation.

Amplitude

Height of a light wave, determining the perceived brightness of light.

Wavelength

Distance between successive wave peaks, which determines the color of light.

Complexity

The variety of wavelengths in a light source, determining how pure or saturated the color appears.

Eyeball

Almost spherical sensory organ housing the cornea, lens, retina, and structures needed for vision.

Fibrous Tunic

The eye’s tough outer layer including the sclera and transparent cornea.

Sclera

White, protective outer layer of the eyeball.

Cornea

Transparent curved structure that begins focusing incoming light.

Middle Vascular Tunic

Layer containing the choroid, iris, and ciliary body, which nourish the eye and regulate light entry.

Choroid

Vascular layer supplying nutrients and oxygen to the retina and other eye structures.

Ciliary Body

Controls the shape of the lens for focusing and produces aqueous humor.

Iris

Pigmented muscle tissue that controls pupil size and regulates light entering the eye.

Pupil

Adjustable opening in the iris controlling the amount of light reaching the retina.

Lens

Transparent, flexible structure that focuses light on the retina through accommodation.

Vitreous Chamber

Gel-filled interior cavity of the eye that maintains shape and supports the retina.

Myopia

Nearsightedness where the eye is too long or lens too strong, causing images to focus in front of the retina.

Hyperopia

Farsightedness where the eye is too short or lens too weak, causing images to focus behind the retina.

Presbyopia

Age-related stiffening of the lens causing difficulty focusing on close objects.

Cataracts

Clouding of the lens that scatters light and reduces vision clarity.

Retina

Light-sensitive neural tissue containing photoreceptors and multiple cell layers that convert light into neural signals.

Blind Spot

Region where the optic nerve exits the eye; contains no photoreceptors.

Retinal Image

The inverted, two-dimensional, imperfect image projected onto the retina before the brain reconstructs it.

Rods

Highly sensitive photoreceptors used for low-light (night) vision, with poor detail and no color detection.

Cones

Photoreceptors responsible for bright-light (daytime) vision, color perception, and fine visual detail.

Photoreceptors

Rods and cones; cells that convert light into electrical neural signals.

Fovea

Small region in the retina densely packed with cones, producing the sharpest vision.

Parallel Processing

Visual system’s ability to process multiple aspects of a scene (color, motion, depth, shape) at the same time through separate neural pathways.

Photopigment

Light-sensitive chemical in photoreceptors made of opsin + retinal; initiates the visual transduction process.

Opsins

Proteins in rods and cones that determine each photoreceptor’s spectral sensitivity.

Rhodopsin

The photopigment in rods specialized for low-light detection.

Color Blindness

Condition caused by absence or malfunction of one or more cone types, reducing color discrimination.

Trichromats

Individuals with functioning red, green, and blue cones (normal color vision).

Dichromats

Individuals missing one type of cone, leading to partial color blindness.

Protanopia

Red cone deficiency causing difficulty perceiving red–green distinctions.