Comprehensive Guide to Human Sensory Receptors and Senses

Special Senses

Senses that have specialized sense organs that gather sensory information and change it into nerve impulses.

General Senses

Senses associated with the sense of touch that lack special sense organs and gather sensory information through the skin and other body tissues.

Sensory Receptor

A specialized nerve cell that responds to a stimulus in the internal or external environment by generating a nerve impulse.

Mechanoreceptors

Sensory receptors that respond to mechanical forces such as pressure, roughness, vibration, and stretching.

Thermoreceptors

Sensory receptors that respond to variations in temperature, primarily found in the skin.

Pain Receptors (Nociceptors)

Sensory receptors that respond to potentially damaging stimuli, generally perceived as pain.

Photoreceptors

Sensory receptors that detect and respond to light, primarily found in the eyes.

Chemoreceptors

Sensory receptors that respond to certain chemicals, found mainly in taste buds on the tongue and in nasal passages.

Somatic Senses

Sensations all over the body received from the skin, muscles, limbs, and joints, also known as tactile sense.

Tactile Sense

The ability to sense pressure, vibration, temperature, pain, and other tactile stimuli.

Free Nerve Endings

A type of tactile receptor that generally responds to pain and temperature variations.

Merkel Cells

Tactile receptors associated with the sense of light touch and the discrimination of shapes and textures.

Meissner's Corpuscles

Tactile receptors that respond to light touch.

Pacinian Corpuscles

Tactile receptors that respond to deep pressure and vibration.

Root Hair Plexuses

Tactile receptors that respond to the movement of hair.

Ruffini Corpuscles

Tactile receptors that respond to skin stretch and sustained pressure.

Balance

The sense that allows the body to maintain its position and orientation in space, primarily facilitated by the inner ear.

Vision

The sense that allows for the detection of light and interpretation of visual information, primarily facilitated by the eyes.

Hearing

The sense that allows for the detection of sound, primarily facilitated by the ears.

Taste

The sense that allows for the detection of flavors, primarily facilitated by the taste buds on the tongue.

Smell

The sense that allows for the detection of odors, primarily facilitated by the nasal passages.

Encapsulated mechanoreceptors

Mechanoreceptors that are surrounded by a capsule.

Unencapsulated mechanoreceptors

Mechanoreceptors that are not surrounded by a capsule, including free nerve endings.

Merkel's disks

Slow-adapting, encapsulated nerve endings found in the upper layers of skin that respond to light touch.

Light touch

Also known as discriminative touch, it is a light pressure that allows the location of a stimulus to be pinpointed.

Receptive fields of Merkel's disks

Small with well-defined borders, making them finely sensitive to edges.

Ruffini endings

Slow-adapting, encapsulated mechanoreceptors that detect skin stretch, deformations within joints, and warmth.

Tactile corpuscles

Another name for Meissner's corpuscles.

Proprioception

The sense of body position and movement.

Kinesthesia

The sense of movement and position of the body.

Warmth detectors

Mechanoreceptors that detect warmth, situated deeper in the skin than cold detectors.

Cold detectors

Mechanoreceptors that detect cold stimuli.

Deep transient pressure

Pressure that is sensed by Pacinian corpuscles, which is not prolonged.

High-frequency vibration

Vibration that is detected by Pacinian corpuscles.

Skin stretch

A sensation detected by Ruffini endings.

Deformation within joints

A sensation detected by Ruffini endings.

Epidermis

The outer layer of skin where mechanoreceptors like Merkel's disks are found.

Dermis

The layer of skin beneath the epidermis where Meissner's corpuscles and Pacinian corpuscles are located.

Glabrous skin

Hairless skin where many mechanoreceptors are concentrated, such as on the fingertips.

Hairy skin

Skin that contains hair follicles, where some mechanoreceptors like Ruffini endings are also found.

Capsule

A structure that surrounds encapsulated mechanoreceptors.

Muscle spindles

Stretch receptors that detect the amount of stretch or lengthening of muscles.

Proprioceptive signals

Unconscious signals that run from the spinal cord to the cerebellum.

Kinesthetic signals

Signals that come from limbs regarding their position and movement.

Hair receptors

Rapidly adapting receptors found on nerve endings that wrap around hair follicles.

Nociceptive receptors

Receptors that detect pain and are located near the surface of the skin.

Two-point discrimination test

An experimental method to estimate the density of pressure receptors by determining if two points are felt as one or two.

Receptive field

The area in which a sensory receptor can detect stimuli.

Density of mechanoreceptors

The distribution of touch receptors varies across the body, being denser in hairless skin.

Skin thickness comparison

Hairless skin is typically thicker (4 to 5 mm) than hairy skin (2 to 3 mm).

Cranial nerves

Nerves that carry warmth and cold information from the face to the brain.

Adaptation of thermoreceptors

Thermoreceptors adapt quickly to changes in temperature.

Pain perception

Any stimulus that is too intense can be perceived as pain, as temperature sensations share pathways with pain sensations.

Integration of signals

The complex processing of stimuli from mechanoreceptors occurs in the primary somatosensory cortex and secondary cortical areas.

Refined sense of touch

The configuration of different types of receptors in human skin results in a very refined sense of touch.

Rapidly adapting receptors

Receptors that respond quickly to changes in stimuli.

Slowly adapting receptors

Receptors that respond more slowly to sustained stimuli.

Sensory information pathways

Most sensory information runs from the spinal cord to the thalamus, except for proprioceptive signals which go to the cerebellum.

Pain

Pain is the name given to nociception, which is the neural processing of injurious stimuli in response to tissue damage.

Nociception

Nociception starts at the sensory receptors, but pain does not start until it is communicated to the brain.

Capsaicin

Capsaicin is a compound that causes peppers to taste hot and is used in self-defense pepper sprays and certain topical medications.

Sensory receptors

Sensory receptors are specialized cells that detect specific types of stimuli.

Mechanoreceptor

A mechanoreceptor is a type of sensory receptor that responds to mechanical pressure or distortion.

Pacinian corpuscle

Pacinian corpuscles are mechanoreceptors that detect deep pressure and vibration.

Tactile mechanoreceptors

The four primary tactile mechanoreceptors in human skin include free nerve endings, Ruffini endings, Pacinian corpuscles, and hair receptors.

Taste bud

A taste bud is a cluster of gustatory receptors (taste cells) located within the bumps on the tongue called papillae.

Papillae

Papillae are the bumps on the tongue that contain taste buds.

Microvilli

Microvilli are hair-like processes at the tips of taste cells that extend into the taste bud pore.

Taste cell replacement

Each taste bud's taste cells are replaced every 10 to 14 days.

Aging and senses

Both tasting abilities and sense of smell change with age, declining dramatically by age 50.

Survival value of taste

Different tasting foods have attributes that can be helpful or harmful, such as sweetness indicating high caloric content.

Bitterness

Bitterness is often associated with toxicity.

Sourness

Sourness is often associated with spoiled food.

Saltiness

Saltiness is valuable in maintaining homeostasis by helping the body retain water and providing necessary ions.

Tastants

Food molecules that are dissolved in saliva and bind with receptors on microvilli.

Taste receptor cells

Cells that make contact with chemicals in food through tiny openings called taste pores.

Taste pores

Tiny openings through which taste receptor cells make contact with chemicals in food.

CNS

Central Nervous System, which receives nerve impulses generated by taste receptor cells.

Primary tastes

Five fundamental tastes: sweet, salty, sour, bitter, and umami.

Umami

The meaty or savory taste, identified as a fundamental taste in 1908 by Kikunae Ikeda.

L-glutamate

An amino acid responsible for the taste of umami.

Monosodium glutamate (MSG)

A substance often used in cooking to enhance the savory taste of certain foods.

Adaptive value of umami

The ability to distinguish umami is beneficial as savory substances tend to be high in protein.

Olfactory receptors

Millions of receptors in humans that work in various combinations to sense about 10,000 different odors.

Odorants

Molecules that enter the nose and dissolve in the olfactory epithelium.

Olfactory epithelium

A collection of specialized olfactory receptors in the back of the nasal cavity.

Olfactory bulb

The part of the brain that receives impulses from olfactory receptors.

Bipolar neurons

Neurons with two processes from the cell body, such as olfactory neurons.

Cilia

Hair-like structures extending from the dendrite of olfactory neurons that trap odorant molecules.

Cerebral cortex

The part of the brain that olfactory stimulation directly reaches, unlike other sensations which are relayed through the thalamus.

Flavor perception

The combined sensory experience of taste and smell.

Congested nasal passages

A condition that reduces a person's perception of flavor by interfering with the ability to smell.

Taste receptors

Specific receptors on the tongue that correspond to each of the five primary tastes.

Savory substances

Foods that are high in protein and are associated with the umami taste.

Kikunae Ikeda

The Japanese scientist who identified umami as a fundamental taste.

Taste receptor specificity

Each receptor is specific to its stimulus (tastant).

Olfactory nerve

A nerve with many endings located at the roof of the nasal cavity that senses chemicals in the air.

Brain portion for smell

The part of the brain that receives signals for the sense of smell.

Auditory stimuli

Sound waves that are mechanical pressure waves moving through a medium.

Speed of sound

At sea level and a temperature of 20° C (68° F), sound waves travel in air at about 343 meters per second.