Somatic Sensory System Flashcards
How can nerve endings be classified?
Encapsulated and unencapsulated
Give 3 examples of encapsulated nerve endings
- Meissner(tactile) corpuscles
- Pacinian (lamellate) corpuscles
- Ruffini corpuscles
What are Pacinian corpuscles involved in?
Deep pressure, stretch, tickle, vibration
What are Meissner corpuscles involved in?
Light touch/texture
What are Ruffini corpuscles involved in?
Heavy touch, joint movement
Give 2 examples of unencapsulated nerves
- Merkel(tactile) discs
- Free nerve endings
What are free nerve endings involved in?
In epithelia; pain, heat cold
What are Merkel discs involved in?
Light touch, texture, edges, shapes
How are primary axons classified?
By conduction velocity
What is sensory information organised into and where?
Into layers in the spinal cord dorsal horn
What happens in the spinal cord dorsal horn?
Sensory information is organised into layers
2 tracts that information gets delivered to the brain
- Medial lemniscal tracts
- Spinothalamic tracts
What kind of info do medial lemniscal tracts carry?
Mechanoreceptive and proprioceptive information to the thalamus
What kind of info do spinothalamic tracts carry?
Pain and temperature signals to the thalamus
What do first order neurones do?
Detect stimulus and transmit to spinal cord
What do second order neurones do?
Relay signals to the thalamus
What do third order neurones do?
Carry the signal from the thalamus to the cortex
Which order neurones are commissural?
2nd order
How are axons organised in the medial lemniscal system?
Topographically
In the medial lemniscal system, what are the two pathways?
Lateral and medial pathways
Medial lemniscal system: upper body
- Follow the lateral pathway
- Synapse on 2nd order neurones in cuneate nucleus
Medial lemniscal system: lower body
- Follow the medial pathway
- Synapse on neurons in gracile nucleus
Medial lemniscal system: What are the lateral and medial pathways together known as?
Dorsal column nuclei
What happens when 2nd order neurones cross the midline and ascend in the medial lemniscus? Which order neurones reverse topology?
The topology is revered so that the lower body axons are more lateral
3rd order axons reverse it
What is a dermatome?
A region of skin innovated by a specific sensory ganglipn
Why do dermatomes arise?
Due to dermis of each region deriving from a specific somite
What is the area of cortex dedicated to each dermatome proportional to?
Density of innervation in that area, not the physical size of the area
All sensory fibre tracts cross the midline in the brainstem: true or false?
False, olfactory system
