6 - Somatosensory Pathways Flashcards
Where do the sensory nerve fibres enter?
The dorsal roots
How many layers are there in the dorsal horn?
6
Where do the touch afferents synapse?
Lamina III and IV
Where do the proprioceptors synapse?
Lamina V and VI
Where do the nociceptors synapse?
Lamina I and II
What are the two compartments of the spinothalamic tract?
Paleo - lateral - older - crude touch - localises the pain stimulus to a part of the body
Neo - medial - new - pain and temperature - produces a sensation of pain
What does the spinothalamic tract do?
Transmits modalities of cutaneous sensation
- Heavy Pressure
- Crude Touch
- Temperature
- Pain
What fibres send a branch to the dorsal funiculi?
Touch and proprioceptive fibres (Aa & Ab)
What is the dorsal funiculi also known as?
Posterior or Dorsal columns
What are the two divisions of the dorsal columns?
Fasciculus gracilis and fasciculus cuneatus
What afferents do the two divisions of the dorsal columns contain?
Fasciculus gracilis - afferents from the lower limb and genitalia
Fasciculus cuneatus - afferents from the upper limb
What are the dorsal column nuclei?
Where the dorsal fasciculi project into - cuneate and gracile nuclei in the medulla
Where is the VPL nucleus?
In the contralateral thalamus
Which pathway is crossed - spinothalamic or dorsal column pathway?
Spinothalamic - crossed
Dorsal column pathway - uncrossed
What is the difference between VPL and VPM?
VPL is thalamic relay sensation from the body
VPM is thalamic relay sensation from face
Where is the somatosensory cortex?
Medio-lateral just posterior to the central sulcus
Where is the face represented in the homunculus of the somatosensory cortex?
Lateral
What does the somatosensory cortex tell you?
Where something is on your body and its touch and texture
Not temperature and whether it is painful
Which areas on the body have the highest density of touch receptors?
Fingertips, lips and tongue
Why do we have two pathways to the somatosensory cortex? What are they?
Both the spinothalamic and dorsal column medial lemniscus go to the somatosensory cortex
However they convey different kinds of somatosensory information
Spinothalamic tract = sense of pressure and heavy touch
Dorsal columns = discriminative touch and recognising objects by handling them
What is Romberg’s test?
Assesses proprioception (ability to sense the position of our limbs)
Patient stands upright with eyes closed, instability is positive
a. What are 3 other tests for dorsal column function?
- Two-point discrimination
- Vibration Sense
- Joint position sense
- Graphesthesia (recognise shapes of objects drawn on the skin)
Where does the DCML cross over?
Closed Medulla
What are tissue damage receptors called?
Nociceptors
What is the difference between Ad and C nerve fibres?
Ad - small myelinated - fast pain
C - unmyelinated - slow pain
