Somatosensation Revision Flashcards
Define ‘somatosensation’
Somatosensation is a mixed sensory category and includes all sensation received from the skin and mucous membranes, as well from as the limbs and joints. Somatosensation is also known as tactile sense, or more familiarly, as the sense of touch.
What is the outermost layer of skin in mammals?
Epidermis
Describe the blood supply of the epidermis
No blood supply
Physical function of epidermis?
The epidermis serves as a barrier to water and to invasion by pathogens.
What type of cells is the epidermis composed of?
Keratinised stratified epithelial cells
is a keratinocyte a type of epithelial cell?
Keratinocytes are epithelial cells that form the superficial layer of the skin.
What is found below the epidermis? What features does this contain?
Below this, the much thicker dermis contains blood vessels, sweat glands, hair follicles, lymph vessels, and lipid-secreting sebaceous glands
What is found below the dermis? What does this layer contain?
The subcutaneous tissue/hypodermis; fatty layer that contains blood vessels, connective tissue, and the axons of sensory neurons
Sensory receptors are classified into what 5 categories?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
- Proprioceptors
- Chemoreceptors
What is commonly referred to as “touch” involves more than one kind of stimulus and more than one kind of receptor.
Mechanoreceptors can be of what 2 types?
- Encapsulated
- Unencapsulated (free nerve endings)
What is a ‘free’ nerve ending?
An unencapsulated dendrite of a sensory neuron
What is the most common nerve ending in the skin?
Free nerve endings
Where do free nerve endings extend into?
Into the middle of the epidermis
What are free nerve endings sensitive to?
- Painful stimul (nociceptor) - most common
- Hot and cold (thermoreceptor)
- Light touch (mechanoreceptor)
Are free nerve endings slow or fast adapting? What does this mean?
Slow - are less sensitive to abrupt changes in stimulation
There are 3 classes of mechanoreceptors. What are these?
- Tactile
- Proprioceptors
- Baroreceptors
How do mechanoreceptors sense stimuli?
Mechanoreceptors sense stimuli due to physical deformation of their plasma membranes. They contain mechanically gated ion channels whose gates open or close in response to pressure, touch, stretching, and sound.
There are four primary tactile mechanoreceptors in human skin. What are these?
- Merkel’s disks
- Meissner’s corpuscles
- Ruffini endings
- Pacinian corpuscle
Two are located toward the surface of the skin and two are located deeper.
Two of the four primary tactile mechanoreceptors in human skin are located toward the surface of the skin and two are located deeper. Which are located where?
Upper - Merkel’s disks, Meissner’s corpuscles
Lower - Ruffini endings, Pacinian corpuscles (deepest)