Comprehensive Human Sensory and Skin Anatomy: Receptors, Layers, and Functions

Thermoreceptors

Change in temp-

Heat- 45 degrees c

Cold-27 Celsius

Nociceptors

Detect pain, temp, pressure and chemicals /can vary

Spinal reflex

Allows rapid withdrawal before conscious perception.

Sensation

Detecting the stimulus.

Perception

Interpreting the stimulus. happens when the sensory stimulus is processed and organized into a meaningful pattern. To consciously interpret the stimuli, they have to reach their ultimate destination in the brain (central level).

Transduction

Converts stimulus energy into a nerve signal.

Photoreceptors

Light

Rods and cones in the retina that perform transduction in vision.

Phasic receptors

Adapt rapidly, so sensory input diminishes over time.

• does not provide information on the duration of the stimulus

• some convey information on rapid changes in stimulus intensity and rate

• Ex: smell

Tonic receptors

Maintain activity as long as the stimulus is present.

adapts slowly to a stimulus and continues to produce action potentials over the duration of the stimulus.

• it conveys information about the duration of the stimulus. 

• some are permanently active and indicate a background level

• Ex: pain receptors, tactile discs, muscle spindles, joint capsules, and Ruffini corpuscles.

Receptive fields

Small fields with high receptor density allow for better discrimination of stimuli.

Pacinian corpuscles

Detect deep pressure and vibration.

Meissner corpuscles

Detect light touch.

Muscle spindle

Proprioceptor.

Free nerve ending

Exteroceptor.

Taste bud

Special sense (exteroceptor).

Rods

Photoreceptors.

Mechanoreceptors

Touch/pressure receptors.

Chemoreceptors

Chemical detection receptors.

General senses

Touch, pressure, pain, temperature.

Special senses

Vision, hearing, smell, taste, equilibrium.

Olfactory receptors

Phasic receptors that adapt quickly.

Merkel discs

Detect continuous pressure.

Ruffini corpuscles

Detect skin stretch.

Epidermis

stratified squamous epithelium

Dermis

connective tissue (papillary: areolar, reticular: dense irregular)

Hypodermis

adipose + areolar tissue

Components of the integumentary system

Skin, hair, nails, sebaceous glands, sweat glands, sensory receptors.

Stratum Corneum

The most superficial layer of the epidermis; provides protection and a waterproof surface.

Stratum Lucidum

Found only in thick skin (palms and soles); provides protection and a waterproof surface.

Stratum Granulosum

A protective, water-sealant layer that helps prevent fluid loss.

Stratum Spinosum

A protective, water-sealant layer that contains dendritic cells (macrophages) for immune defense.

Stratum Basale

The deepest layer; forms new keratinocytes, contains Merkel discs (touch receptors), and melanocytes, which produce melanin and transfer it to keratinocytes for UV protection.

Functions lost after epidermis burn

Barrier protection, water retention, pigmentation (melanocytes), tactile discrimination (Merkel cells).

Thin vs Thick skin differences

Thick skin: palms/soles, 5 layers, no hair, more keratin → protection and friction. Thin skin: most of body, 4 layers, hair, sebaceous glands.

Keratinocytes

mechanical barrier

Melanocytes

UV protection

Langerhans

immune defense

Merkel

touch

Extracellular lipids

water barrier

Pale skin after sun exposure

Melanin production low or uneven; hemoglobin level may also influence color.

Dermis functions

Support, flexibility, houses blood vessels, sensory receptors, glands.

Hypodermis functions

Cushioning, insulation, fat storage, thermoregulation.

Structure/function of hair

Hair follicle produces hair shaft, protects, senses light touch, reduces heat loss.

Scalp vs Forearm hair sensitivity

Scalp has more hair follicles with active hair root plexuses; forearm has fewer.

Structure/function of nails

Protect fingertips, enhance sensation, growth from nail matrix.

Sebaceous and sweat glands

Sebaceous → sebum, lubricates hair/skin, absent in thick skin. Eccrine sweat → thermoregulation; Apocrine sweat → scent.

Palms dry but sensitive to touch

Thick skin lacks sebaceous glands but contains many Meissner corpuscles for fine touch.

Patient cannot sweat after exercise

Eccrine sweat glands, affecting thermoregulation.

Hair growth cycle

Anagen (growth), Catagen (regression), Telogen (resting/falling).

Cold pool response

Cold thermoreceptors detect decrease, hypothalamus triggers vasoconstriction & shivering → negative feedback to maintain temperature.

Sweating after running

Warm thermoreceptors detect heat, hypothalamus triggers eccrine sweat glands and vasodilation → cooling.

Older adults feeling colder

Fewer/sensitive thermoreceptors, thinner hypodermis fat layer, slower vasomotor response.

Below the head

carried from the periphery of the body by 31 pairs of mixed nerves, then through tracts within the spinal cord and finally reaching the postcentral gyrus of the brain

From the head

carried by 12 pairs of cranial nerves: some are sensory, some are motor, some are mixed. Special senses reach different parts of the brain.

Any sensory neuron detects stimuli within an area called

Receptive field