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)
Which primary tactile mechanoreceptor is located deepest in human skin?
Pacinian corpuscle
What type of skin are Merkel’s discs located in?
Hairy AND glabrous skin
What is glabrous skin?
the hairless skin found on the palms and fingers, the soles of the feet, and the lips
Merkel’s discs:
- Slow or fast adapting?
- Encapsulated or unencapsulated?
- What do they respond to?
- Slow-adapting
- Unencapsulated
- Light touch
What is ‘light touch’?
Light touch, also known as discriminative touch, is a light pressure that allows the location of a stimulus to be pinpointed.
The receptive fields of Merkel’s disks are small with well-defined borders. What does this mean?
makes them finely sensitive to edges
Which sensory receptor would come into use in tasks such as typing on a keyboard?
Merkel’s discs
Where are Merkel’s disks densely distributed?
In the fingertips and lips
What type of skin are Meissner’s corpuscles located in?
They are found primarily in the glabrous skin on the fingertips and eyelids.
What layer of skin are Meissner’s corpuscles located in?
found in the upper dermis, but they project into the epidermis
Meissner’s corpuscles:
- Slow or fast adapting?
- Encapsulated or unencapsulated?
- What do they respond to?
- Slow
- Capsulated
- Respond to fine touch and pressure, but they also respond to low-frequency vibration or flutter.
Are Merkel’s discs more plentiful in the palms or the fingertips?
Fingertips
Are Meissner’s corpuscles more plentiful in the palms or the fingertips?
Fingertips
What type of skin are Ruffini endings located in?
Both glabrous and hairy skin
Ruffini endings:
- Slow or fast adapting?
- Unencapsulated or encapsulated?
- What do they detect?
- Slow adapting
- Encapsulated
- detect skin stretch and deformations within joints; provide valuable feedback for gripping objects and controlling finger position and movement
What layer of skin are Pacinian corpuscles located in?
located deep in the dermis
What type of skin are Pacinian corpuscles located in?
Glabrous AND hairy skin
Pacinian corpuscles:
- Slow or fast adapting?
- Encapsulated or unencapsulated?
- What do they detect?
- Fast adapting
- Encapsulated
- Deep transient (not prolonged) pressure and high frequency vibration
What are the 2 most frequent mechanoreceptors in the skin?
Merkel’s disks and Meissner’s corpuscles.
What type of receptors are muscle spindles? What do they detect?
Stretch receptors that detect the amount of stretch, or lengthening of muscles.
What type of receptors are Golgi tendon organs? What do they detect?
Tension receptors that detect the force of muscle contraction
Unconscious proprioceptive signals run from the spinal cord to the ___?
Cerebellum; the brain region that coordinates muscle contraction, rather than to the thalamus, like most other sensory information.
What do baroreceptors detect?
detect pressure changes in an organ
Where are baroreceptors found? What do they detect here?
- Walls of carotid artery and aorta –> monitor blood pressure
- Lungs –> detect degree of lung expansion
What are hair receptors? How are they formed?
Found on nerve endings that wrap around the base of a hair follicles. There are a few types of hair receptors that detect slow and rapid hair movement, and they differ in their sensitivity to movement.
Small, finely calibrated mechanoreceptors;
- What 2 receptors are these?
- Where are they located in the skin?
- What do they detect?
- Merkel’s disks and Meissner’s corpuscles
- Located in the upper layers
- Can precisely localise even gentle touch
Large mechanoreceptors;
- What 2 receptors are these?
- Where are they located in the skin?
- What do they detect?
- Pacinian corpuscles and Ruffini endings
- Located in the lower layers
- Respond to deeper touch (the deep pressure that reaches those deeper receptors would not need to be finely localised)
What type of skin are touch receptors denser in?
Glabrous skin (the type found on human fingertips and lips, for example) which is typically more sensitive and is thicker than hairy skin
How can the relative density of pressure receptors in different locations on the body be demonstrated?
using a two-point discrimination test
What is the receptor found only in glabrous skin?
Meissner’s corpuscles
