Unit 4

Skin

The body's largest organ that protects against injury, heat, and light radiation, helps regulate temperature, and acts as a barrier.

Hairy Skin

Skin that covers most of the body.

Glabrous Skin

Hairless skin that is thicker and found on palms and soles of feet.

Epidermis

The outermost layer of skin, composed mostly of dead skin cells.

Dermis

The thick connective membrane layer of skin beneath the epidermis.

Hypodermis

Connective tissue layer beneath the dermis.

Mechanoreceptors

Receptors that respond to sensations on the skin, including touch and texture.

Rapidly Adapting Receptors (RA)

Mechanoreceptors that fire upon application or removal of a stimulus, responding to fast vibrations and changes in texture.

Slowly Adapting Receptors (SA)

Mechanoreceptors that fire as long as the stimulus is applied, responding to skin stretching and fine details.

Thermoreceptors

Receptors that respond to temperature changes, including warm and cold fibers.

Nociceptors

Receptors that respond to harmful stimuli such as intense pressure, high heat, or burning chemicals.

Two-point Threshold

A measure of skin acuity, referring to the smallest separation between two points on the skin that is perceived as two distinct points.

Homonculus

A representation of the body in the somatosensory cortex, showing areas of high and low acuity.

Phantom Limb Pain

The perception of pain in a limb that has been amputated, often occurring in 70% of cases.

Placebo Effects

The phenomenon where a patient believes that a treatment will reduce pain and does so, even if the treatment is inert.

Gate Control Theory

A theory of pain perception that suggests a 'gate' mechanism in the spinal cord controls the flow of pain signals to the brain.

Large Diameter Fibers

Highly myelinated fibers that send rapid signals to the spine, potentially mediating initial pain responses.

Small Diameter Fibers

Less myelinated fibers responsible for slower transmission of pain signals, associated with nociceptive responses.

Central Control System

A top-down mechanism from the brain influencing pain perception through cognitive functions such as expectation and attention.

Taste Primaries

The four basic tastes: sweet, sour, salty, and bitter, detected by taste receptors on the tongue.

Taste Buds

Structures containing taste receptors, located in the mouth and throat.

Olfactory Process

The process by which molecules of odorants are absorbed into the olfactory mucosa and attach to receptors.

Endorphins

Neuropeptides that help relieve pain and induce feelings of pleasure.

Substantia Gelatinosa

A region in the spinal cord involved in the gate control system; it processes incoming pain signals and plays a key role in opening or closing the gate.

Large Diameter Fibers

Highly myelinated nerve fibers that send rapid signals to the spinal cord. These fibers tend to close the gate and reduce pain, especially through physical stimuli like rubbing, applying heat, or cold packs.

Small Diameter Fibers

Less myelinated, slower nerve fibers associated with nociceptors. These fibers tend to open the gate, increasing pain by sending signals related to tissue damage.

Central Control

Efferent signals from the brain that influence the gate mechanism. Cognitive processes like expectation, attention, and distraction activate central control and generally close the gate, reducing pain perception.

Transmission Cells (T-cells)

Cells in the spinal cord that integrate input from large fibers, small fibers, and central control. Their level of activity determines how much pain signal is transmitted to the brain.