Cutaneous Sensation Flashcards
different classes of somatic sense
Touch/tactile Sensation: Perception of touch, pressure, vibration, and texture on the skin’s surface or within the body.
Thermal Sensation: Detection of temperature changes, including hot and cold sensations.
Pain Sensation: Perception of discomfort or injury, signaling potential tissue damage or inflammation.
Proprioception: Awareness of the body’s position, movement, and orientation in space, derived from sensory feedback from muscles, tendons, and joints.
Kinesthesia: Perception of the body’s movement, including the rate and direction of motion, aiding in coordination and motor control.
Itch : the uncomfortable sensation that prompts a desire to scratch the affected area
somatic vs visceral stimuli
Somatic stimuli:
* from the external environment or the body’s surface, such as touch, pressure, temperature, and pain.
* detected by sensory receptors located in the skin, muscles, joints, and other superficial tissues
* consciously perceived, allowing individuals to interact with their environment and respond to external stimuli.
Visceral stimuli:
* from internal organs or viscera, such as the heart, lungs, gastrointestinal tract, and bladder.
* distension, stretching, pressure, and pain within the internal organs.
* unconsciously perceived = autonomic reflex responses or visceral reflexes that regulate physiological functions, such as digestion, respiration, and cardiovascular activity.
what are Receptive Fields
- regions of sensory surfaces, such as the skin or retina, where the presence of a stimulus influences the activity of sensory neurons.
- represent the area in which sensory receptors are sensitive to external stimuli.
- can vary in size and shape depending on the type and location of sensory receptors.
how convergence influences the size of receptive fields
When lots of sensors send their signals to one neuron, that neuron’s receptive field gets bigger.
So, when many sensors converge onto one neuron, that neuron’s receptive field expands to cover a larger area.
Convergence helps the brain make sense of all the sensory information it receives.
But bigger receptive fields mean less precise information about where a stimulus is coming from.
fewer neurons converge, secondary receptive fields are smaller
2 stimuli activate separate pathwats to the brain
two points are perceived as distinct stimui and there is two-point discrimination
what is convergence
Convergence is when lots of inputs come together to influence one thing. In our case, it’s when signals from many sensors all come together to affect one neuron in the brain.
So, if you have a bunch of sensors detecting touch in one area of your skin, all those signals might get combined into one nerve cell in your brain.
e.g. the receptive fields of three different primary sensory neurones overlap to form one large secondary receptive field
convergence of primary neurones allows simulaneous subthreshold stimuli to sum at the secondary sensory neuron to initiate action potential
2 stimuli that fall within the same secondary receptive field are perceived as one single point because only one signal goes to the brain = no two-point discrimination
two point discrimination
two-point discrimination measures how accurately your skin can detect two separate points of touch. The better your two-point discrimination, the more sensitive your skin is to small differences in touch
Imagine someone gently touches your skin with two small objects, like the tips of two pencils. If you can tell that there are two separate points touching your skin, your skin has good two-point discrimination.
when two stimuli fall within same secondary receptive field = only perceived as a single point and no two-point discrimination
classes of sensory receptors
chemoreceptors
stimuli:
* oxygen
* pH
* organic molecules like glucose
mechanoreceptors
stimuli:
* pressure (baroreceptors)
* cell stretch (osmoreceptors)
* vibration
* acceleration
* sound
photoreceptors
stimuli:
* photons of light
thermoreceptors
stimuli:
* varying degrees of heat
the different types of mechanoreceptors in the skin
Mechanoreceptors are sensory receptors in the skin that respond to mechanical stimuli, such as touch, pressure, vibration, and stretch
- Meissner’s Corpuscles
* superifical layers of skin = Located in the dermal papillae (just below the epidermis)
* sensitive to light touch and vibration.
* abundant in areas like the fingertips and lips. - Pacinian Corpuscles
* deep layers of skin
* are sensitive to deep pressure and high-frequency vibration
* detect things like the firm pressure of a handshake. - Ruffini Endings/corpuscles
* deep layers of skin
* sensitive to skin stretch and continuous pressure
* detecting changes in joint position and skin stretching. - Merkel Cells/Receptors
* superficial layers of skin = found in the epidermis (the outer layer of the skin)
* are sensitive to light touch and pressure - free nerve endings
* around hair roots and under surface of skin
* temperature, noxious (harmful) stimuli, hair movement
whats Piezo2
Piezo2 is a protein found in the membranes of some mechanoreceptor cells.
an excitatory ion channel that responds to mechanical forces by opening and allowing ions to flow across the cell membrane.
It plays a crucial role in converting mechanical stimuli, like pressure or stretching, into electrical signals that the nervous system can understand.
This process is called mechanotransduction.
the role of Piezo2 in mechanotransduction
an excitatory ion channel that responds to mechanical forces by opening and allowing ions to flow across the cell membrane.
When the cell membrane is stretched or deformed by mechanical stimuli, like touch or pressure == Piezo2 responds by opening up and allowing ions to flow through the cells (Merkel cells)
–> generates an electrical signal that is transmitted along nerve fibers to the spinal cord and then to the brain, where it is interpreted as touch or pressure sensation.
different types of thermoreceptor
Cold Receptors:
* respond to decreases in temperature.
* particularly sensitive to temperatures < 37°C
–> (normal body temp is 37°C so it is sensitive to temperatures below that)
Warm Receptors:
* respond to increases in temperature.
* sensitive to (37 - 45°C).
–> (normal body temp is 37 so it is sensitive to temperatures above it)
There are far more cold receptors than warm receptors
rely on TRP (transient receptor potential) channels
Temperatures >45°C activate pain receptors
influence of adaptation on sensing temperature
Adaptation by which sensory receptors become less responsive to a constant stimulus over time
–> occurs between 20°C - 40°C
When exposed to a cold/warm environment for an extended period, cold/warm receptors gradually become less responsive to cold/warm temperatures, less sensitive to heat/cold stimulus = sensation of coldness/heat diminishes as the cold/warm receptors adapt to the stimulus
thermoreceptors gradually adapt to the constant stimulus. This means that they become less responsive to the unchanging temperature, allowing the body to focus its attention on detecting new temperature changes instead.
TRP channes
TRPV1: heat activated ion channel
–> activated in response to change in termperature
–> ligand gated ion channel
(also known as capsicin receptor) = activates your sensation of heat
TRPM8: cold activated channel through menthol receptor
–> ligand gated
TRPA1 : chemoreceptor for irritants found in environment and inflammatory agents
–> wasabi receptor
= itch and irritiation
Mechanism of nociceptors
nociceptors sense noxious stimuli –> deliver information to CNS
also separate synapses within periphery that can release substrates
=> can act on themselves/auto-acting molecules to increase sensitivity
=> when injured, the area will feel sensitive to touch
* hypersensitivity of the pain receptors within that area
-> positive feedback on themselves
4 properties of stimuluis
- modality : what you’re detecing
- location : where you’re detecting
- intensity : how severe the stumulus is
- duration : how long stimulus lasts
