Are the dorsal columns grey matter or white matter?
What sort of information travels in the dorsal columns?
Ascending sensory information from the tactile receptors
How are the dorsal columns organised?
Segregated into topographic regions
How many neurons are involved in the tactile mechanoreceptive pathway?
Where does decussation occur in the tactile mechanoreceptive pathway?
Where does information from the tactile mechanoreceptive pathway travel to in the brain?
How far up does the first axon in the tactile mechanoreceptor pathway travel?
Then meets next neuron
What are the dorsal column nuclei called?
Gracile nucleus and Cuneate nucleus
What areas of the body do the gracile and cuneate nuclei transmit information about?
Gracile: lower limb
Cuneate: thoracic and cervical regions
What are the internal arcuate fibres?
Internal arcuate fibers are the axons of neurons within the gracile and cuneate nuclei of the medulla oblongata.
These fibres cross from one side of the medulla to the other to form the medial lemniscus.
Where are the gracile and cuneate nuclei located?
What happens to the axons in the tactile mechanoreceptor pathway once they leave the dorsal column nuclei?
Enter medial lemniscus
Twisting: dorsal goes to ventral
'Bundle of fibres that form a ribbon'
What happens to the axons in the tactile mechanoreceptor pathway when they leave the medial lemniscus?
More twisting > orgnaising topography for somatosensory cortex
Go to thalamus > terminate in ventral posterolateral nucleus
Where in the thalamus do axons in the tactile mechanoreceptor pathway terminate?
Ventral posterolateral nucleus
Where does the ventral posterolateral nucleus project to?
Cerebral cortex (somatosensory cortex)
Describe the tactile mechanoreceptive pathway?
Where in the brain do proprioceptive pathways project to?
Give a basic description of the tactile mechanoreceptor pathway?
Which part of the tactile mechanoreceptor pathway is ipsilateral?
Primary sensory neuron (first neuron in chain)
How many somatic sensory cortices are there? What are they called?
S1: Primary somatic sensory cortex
S2: Secondary somatic sensory cortex
How many subregions are there in S1? What are they called?
4: Areas 1, 2, 3a and 3b
Describe the locations of the subregions in S1?
Where does S2 receive most of its input from?
How do we know that there are two somatic sensory cortices (ie. S1 and S2)?
Body is represented twice in the cortex (repeated in miniature form in S2)
Describe the representation of the body surfaces within the somatic sensory cortices?
What determines the size of a body part's represenation on the somatic sensory cortex?
The amount of sensory information coming from that body part
How many maps of the body are represented in the somatic sensory cortices on each side of the brain?
6 on each side; 1 from each region of S1, and 2 from S2
Describe the arrangement of slowly adapting and rapidly adapting receptors in the somatic sensory cortex?
Why do four maps exist in S1?
May each receive information about different aspects of sense; segregation of information
eg. Area 1 receives information about texture
Which subregion of S1 receives the greatest amount of thalamic input?
Describe the concept of somatosensory plasticity?
Changes in somatosensory cortex can occur after changes in use
eg. after amputation
Describe how the somatosensory cortical representation of the digits changes after differential stimulation of digits 2 and 3?
Territories of digits 2 and 3 in the cortex expand
Where does somatosensory plasticity occur?
Describe the problem with nerve regeneration after injury in the PNS?
Nerves can regrow, but often regrow to the wrong place
Central plasticity doesn't change to match > perception in the wrong place