Somatosensory Pathways Flashcards
What is a sensory modality?
A type of stimulus (e.g. hot, cold, touch). They have specialised receptors
Give examples of some receptors and what they do
Touch, pressure, vibration -> mechanoreceptors
Proprioception (joint position, muscle length/tension) -> mechanoreceptor
Temperature -> thermoreceptor
Nociception (pain) -> nociceptors
How are sensory fibres classified? (3 types)
Mechanoreceptors of the skin (Aβ) – very fast (large, myelinated) transmit mechanical stimulation
Pain, temperature (Aδ) – slightly fast (myelinated) transmit fast pain and temperature signals
Temperature, pain, itch (C) – slow transducing (no myelination) transmit slower, achy pain
Within a peripheral nerve, there are different types of sensory fibres
How do nerves differ for different modalities?
Individual axons within the sensory fibres have modified terminals which are specific to different modalities. E.g. C fibres are unmyelinated and have free nerve endings specific for heat and the endings are close to the skin.
What is a transducer?
They convert energy from one form to another e.g. sensory receptors convert energy from the environment into action potentials.
What is the absolute threshold?
Is the level of stimulus (stimulus strength) required to produce a positive response of detection 50% of the time.
What happens if the generator potential is larger and longer?
Action potentials that are faster, and more NT released at the end.
Describe the properties and structure of thermoreceptors
Free nerve endings with high thermal sensitivity
What are happens when a change in temperature is detected by thermoreceptors?
Change in temperature activates a family of transient receptor potential (TRP) ion channels
What are the types of TRP ion channels?
4 heat-activated TRP channels: TRPV 1–4 – ranging from noxious heat to tepid heat
2 cold activated TRP channels: TRPM8 and TRPA1
Nerve endings have a combination.
What is a dermatome?
An area of the skin supplied by nerves from a single spinal nerve.
What is a receptive field?
Is the region on the skin that causes activation of a single sensory neuron when activated. Different parts of the body have different sizes of receptive fields. Small receptive field=precise perception vice versa
What is 2 point discrimination?
The minimum distance at which two points are perceived as separate. This is related to the size of the receptive field. The smaller the field, the more densely packed the neurones are. So you are more likely to recognise that there are two points of touch.
What do Aδ fibres do? What is their speed and therefore are they myelinated?
What are the two types and what do they do?
Aδ fibres mediate sharp, intense or first pain
Myelinated – quite fast
Type 1: Aδ-mechano-heat receptors (noxious mechanical and thermal stimuli)
Type 2: Aδ-mechanoreceptors (purely noxious mechanical stimuli)
What do C-fibres do? Are they fast or slow and therefore are they myelinated?
C-fibres mediate dull, persistent or second pain
- Unmyelinated so slow
- Respond to thermal, mechanical and chemical stimuli (polymodal)
- Chemical stimuli include inflammatory mediators
- Polymodal: respond to all the modalities (all kinds of pain) as only one C fibre
