Somatosensory system 2

Question 1

What does the dorsal column medial lemniscus pathway control?

Answer 1

Discrimminatory touch, pressure, vibration, conscious proprioception, stereognosis (ability to recognise an object by feeling it)

Question 2

What does the spinothalamic tract control?

Answer 2

Pain, thermosensation, itch, tickle, crude touch

Question 3

What do the dorsal columns consist of?

Answer 3

Medial fasciculus gracilis and lateral fasciculus cuneatus

Question 4

What does the fasciculus gracilis provide sensory input to?

Answer 4

T6 and below including legs and lower trunk

Question 5

What does the fasciculus cuneatus provide sensory input to ?

Answer 5

T6 and above including the arms and upper trunk

Question 6

From lateral to medial, which areas of the dorsal column provide innervation to which spinal segments?

Answer 6

Lateral to medial: cervical -> thoracic -> lumbar -> sacral

Question 7

What do the dorsal and ventral spinocerebellar tracts do?

Answer 7

Convey unconscious proprioceptive information to the cerebellum which is important in motor coordination

Question 8

What is contrast enhancement?

Answer 8

As information is conveyed from one neuron to the next in a sensory pathway, differences in the activity of adjacent neurons are amplified, producing contrast enhancement

Question 9

What is lateral inhibition?

Answer 9

When one neuron is active, it inhibits the activity of its neighbours via inhibitory interneurons, a process known as lateral inhibition. Lateral inhibition sharpens stimulus perception and is one mechanism by which information is transformed at the synapses of the DCML pathway

Question 10

Name the 3 divisions of the trigeminal nerve

Answer 10

1 - ophthalmic, 2 - maxillary, 3 - mandibular

Question 11

Where are the soma of sensory neurons located (within the trigeminal system) ?

Answer 11

In the trigeminal sensory ganglion

Question 12

Central terminals of the trigeminal nerve synapse upon 2nd order neurons in the chief sensory nucleus (general tactile stimuli) or spinal nucleus (pain, temperature information) which then decussate and project via?

Answer 12

The trigeminal lemniscus to the ventroposteriomedial nucleus of the thalamus

Question 13

How do third order neurons relay information to the cortex in the trigeminal system?

Answer 13

Via thalamocortical neurons

Question 14

Where is the somatosensory cortex located?

Answer 14

Post-central gyrus of the parietal cortex immediately posterior to the central sulcus and adjacent to the posterior parietal cortex

Question 15

What does the central sulcus (SI) consist of?

Answer 15

Brodmann areas 1, 2, 3a and 3b

Question 16

How many layers of cells are present in the somatosensory cortex?

Answer 16

6 cell layers - thalamic inputs to the central sulcus terminate mainly on neurons within layer IV (4)

Question 17

If a finger e.g. D3 is lost in an accident, or amputated what happens to the area of SI representing the finger?

Answer 17

The area formerly representing D3, after several months now responds to stuimulation of the adjacent digits (D2 and D4 - their cortical representation expands into the territory formerly representing D3)

Question 18

What happens if the sensory input from a finger increases?

Answer 18

The cortical representation of that digit, over months, increases, relative that of inputs generating less activity - imaging of SI of violinists who ‘finger’ with their left hand shows that the area of right cortex devoted to the left fingers is enlarged compared to that of the left hemisphere representing the right hand

Question 19

What does the posterior parietal cortex do?

Answer 19

Receives and integrates information from SI and other cortical (visual, auditory) and sub-cortical (thalamus) areas. It is important in deciphering deeper meaning of the information from SI

Question 20

What can happen as a result of damage to the posterior parietal cortex?

Answer 20

Bizarre neurological disorders e.g. agnostic, astereognosia and hemispatial neglect syndrome but simple sensory skills remain intact