Skin lecture 1

Somatosensory System Overview

  • Understanding sensation: Origin of "somato"

    • "Soma" refers to the body.

    • Somatosensation encompasses sensations related specifically to the body.

Types of Sensations

  • Sensations that arise from the body, emphasizing the need for nuanced definitions:

    • Vision: This has multiple aspects such as color and depth which are complex.

    • Pain: Types to distinguish:

    • Sharp pain: E.g., pain from a paper cut.

    • Aching pain: E.g., chronic conditions like arthritis, which consist of non-sharp, constant pain.

    • Temperature: Sensation of heat or cold.

    • Pressure: Pressure sensation on the skin.

    • Movement: Related to stimuli like wind or brushing against a surface.

Kinesthesia

  • Definition: The sense of movement and position of body parts.

    • Importance of this sensation in everyday activities such as walking and balancing on uneven surfaces.

Somatosensation Composition

  • Somatosensation involves multiple categories:

    • Temperature

    • Pain

    • Touch

    • Movement (Kinaesthesia)

Legal Structure of Skin

  • Layers of Skin:

    • Epidermis: Outermost layer comprised primarily of dead skin cells.

    • Two layers of dead cells.

    • Develops calluses in response to repetitive pressure for protection.

    • Dermis: The living layer rich in receptors where sensation occurs.

    • Subcutaneous Fat: Layer beneath the dermis, consisting of fat tissue.

Receptors in the Skin

  • Major mechanoreceptors responsible for different types of touch sensations:

    • Merkel Receptors:

    • Location: Junction between dermis and epidermis.

    • Function: Slow adapting, responding continuously to sustained pressure.

    • Meissner Corpuscles:

    • Location: At the same junction.

    • Function: Rapid adapting, responsive to changes such as light touch or flutter.

    • Pacinian Corpuscles:

    • Location: In subcutaneous fat.

    • Function: Rapid adapting, particularly sensitive to high-frequency vibrations and changes in pressure.

    • Ruffini Endings:

    • Location: Within the dermis.

    • Function: Slow adapting, sensitive to skin stretch and sustained pressure.

Receptive Fields

  • Definition: The area of skin a specific neuron responds to.

  • Size differences:

    • Smaller receptive fields found closer to the surface of the skin (e.g., Merkel and Meissner).

    • Larger receptive fields deeper in the skin (e.g., Ruffini and Pacinian).

Properties of Receptors

  • Adaptive Speed:

    • Slow Adapting: Continuous firing in response to persistent stimulation (Merkel and Ruffini).

    • Rapid Adapting: Firing only when there is a change in stimulation (Meissner and Pacinian).

  • Frequency Response:

    • Reactive to different stimulus intensities (low vs high frequencies).

    • Examples: Tapping vs constant pressure, electric toothbrush motion.

  • Location: Structure of the receptor helps delineate which types of stimulus reach them due to skin layers.

Perception Elements

  • Mechanosensory functions:

    • Merkel Cells: Perception of fine details due to small receptive fields.

    • Meissner Cells: Detect fluctuations and grip control, responding to slight vibrations.

    • Ruffini Endings: Sense stretch and help recognize overall positioning of limbs.

    • Pacinian Corpuscles: Detect texture and higher frequency vibrations.

Acuity Thresholds Across Body

  • Mapping tactile acuity:

    • High acuity in fingertips, face; low acuity on calf, thigh, and belly.

    • Importance of tactile acuity in facial expressions and eating, allowing for feedback on texture and safety of foods.